Recent Trends in Wave Mechanics and Vibrations

Flexible Robotic Systems, by and large, are prone to inherent vibration that recreates itself in several modal frequencies. This in-situ vibration in flexible robots or in any such complaint robotic units becomes tricky so far as the control system architecture is concerned. Thus, customization of the design and firmware of higher-order flexible robots is highly challenging due to its inherent parameters related to real-time vibration. Subsuming technological challenges, the field of Flexible Robotics has come out as a niche ensemble of harnessing non-linearity in dynamics of the robotic system(s).

This paper presents a computationally efficient finite element, based on Generalised Beam Theory (GBT), that enables assessing the vibration serviceability limit state (the calculation of undamped natural frequencies and vibration mode shapes) of steel-concrete composite beams, accounting for concrete cracking and cross-section in-plane and out-of-plane deformation. It is shown that the modal decomposition features of GBT enable an in-depth characterisation of the vibration modes. A numerical example is presented to illustrate the accuracy and efficiency of the proposed element, through comparison with refined shell finite element model results.

Natural vibrations of a homogeneous isotropic elastic solid of rotation are studied. A modification of the Petrov–Galerkin method is applied to find numerically the eigenfrequencies and eigenforms of the rod when its surface is free of loads. According to this approach, local stress-strain and momentum-velocity relations are replaced by an integral equality. Approximate solution to the eigeproblem is based on polynomial semi-discretization of displacements and stresses: a finite-dimensional expansion in powers of two lateral coordinates is used. The rod’s motions are decomposed into independent groups of eigenmodes due to axial symmetry. Four of these groups are considered, namely, torsional, longitudinal, and two type of bending vibrations. At the lowest approximation order, the governing equations are reduced to two differential systems of fourth order for bending and two systems of second order for longitudinal and torsional motions. Spectrum features related to the variability of the cross-sectional radius are discussed.

Analysis of the disproportionate collapses of buildings and structures that have occurred in recent decades, as well as the results of experimental studies on this problem, show dynamic effects in structures adjacent to the site of initial local destruction such as sudden column removal. In this case, the columns adjacent to the bay of the initial local destruction can be subjected to the simultaneous action of the axial shock impact. In this regard, the subject of this research is the dynamic response of reinforced concrete columns exposed to shock impact. The paper proposes an analytical solution to the problem based on Bessel function. It considers structural damping, physical nonlinearity and geometric nonlinearity of the first order (P - delta effect). To take into account the physical nonlinearity of the material and the P - delta effect, the solution is carried out step by step by dividing the time into separate steps, within which the load is considered as a linear function of time. The provided parametric analysis shows that the maximum dynamic deflection of a compressed reinforced concrete column, subjected to a shock impact, increases almost linearly with an increase in slenderness ratio at a load value in the range from 0.6 to 8 of ultimate bearing capacity. With an increase in the slenderness ratio of the column up to 20, dynamic deflections begin to grow more intensively with increasing of load.

In the current numerical study, axial quasi-static crashworthiness performance of circular crash-boxes having the same geometry but made up of various frequently used wrought aluminium alloys is investigated using ABAQUS/Explicit. All the considered crash-boxes showed a stable progressive axi-symmetric collapse. Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), one of the most widely used Multi-Criteria Decision-Making (MCDM) techniques, is then employed to determine the most suitable aluminium alloy for the application of a crash-box in an automobile. It is found that, out of the considered aluminium alloys AA 6060 T4 is the most suitable aluminium alloy to be used as a crash-box in an automobile.

The behavior of reinforced concrete (RC) structures under extreme demands, as in strong ground motions or impact loading, is quite intricate because of the joint operation of concrete and steel coupled with respective failure models. In addition to that, new advances are made in the field of dynamics engineering due to the complexity and importance for seismic and impact activities worldwide. However, numerical models based on finite element codes had occurrence on several developments because of their simplicity and cost effectiveness. Therefore, the manuscript focused on the estimation of accuracy of compressive and tensile damage parameters (dc and dt) of the Concrete Damage Plasticity (CDP) model based on continuum mechanics to simulate the concrete behavior in ABAQUS finite element software. Within the context, it has been summarized analytical equations describing behavior of concrete for stress-inelastic strain in uniaxial compression and stress-displacement in uniaxial tension and their respective damage variables in uniaxial compression and tension, presented by several researchers over the past decade. The methodology provides a basis for the evaluation of analytical models which will be applicable to CDP model. The accuracy and reliability are validated with the experimental results available for uniaxial tension and compression tests. The parameters associated with the biaxial and triaxial behavior of concrete for CDP model will be kept same as originally proposed in Lubliner/ Lee/ Fenves formulation and were given in ABAQUS manual. The numerical results thus obtained were compared with the experimental results and it was postulated that each model predicted static results very accurately. For impact problem, the model by Alfarah et al. [16] best predicted crack pattern and peak load with a 6% difference.

Masonry structures are sensibly vulnerable against low velocity out of plane impacts caused due to vehicular collision, rockfalls, debris impact. Sometimes, these impacts cause severe consequences hence methods are developed based upon experimental investigations to assess the response of wall systems. However, in experiments, physical limitations are present accompanied by the increased cost of the study hence computational analysis of masonry structural systems are being used widely. In this manuscript, an attempt has been made to exploit the constitutive models available in ABAQUS in-built library for the modelling of masonry walls. The response of walls subjected to multiple hits were studied experimentally and validated numerically using Drucker Prager (DP), Mohr-coulomb (MC) and concrete damage plasticity model (CDP). It was observed that among chosen models, MC model overpredicts the structural response of walls measured in terms of contact force whereas DP and CDP model predicts the contact force under 10% deviation from experimental results. Further, the CDP model was able to simulate the crack within brick units whereas DP and MC model were able to simulate joint failure only. It was concluded that DP and CDP models can be adopted for simulating the structural response of masonry walls subjected to multiple hits.

The expansion of either plane or spherical or cylindrical shock waves, in this analysis, is examined by the influence of either axial or azimuthal magnetic field; monochromatic radiation in a dust-pervade gas. Equilibrium circumstances are expected to be retained for the flow and the advancing piston provides the varying energy input constantly. With a view to getting the self-similar solutions, the density of the uninterrupted media is considered to remain unchanged. The flow framework of the parameters was calculated numerically. Detailed data is provided on the impacts of the parameter of gas non-idealness as well as existence of magnetic field. It’s noticeable that the pressure and density at the expansive region wear down in the presence of an azimuthal magnetic field, resulting in the creation of a vacuum at the symmetry’s centre, it is perfectly consistent with the settings in the lab that created the shock wave.

Unreinforced brick masonry (URM) in mud mortar is the most common building typology in Dhulikhel. Most of these buildings were constructed more than 100 years ago with traditional construction techniques and locally available materials. These old buildings are made up of thick walls and consist timber floors /roofs representing the main structural system of the typology. Dhulikhel is considered one of the oldest and historical cities in Nepal and buildings constructed here with old Newari architecture exhibit high historical and cultural value. These buildings experienced devastating earthquakes and most of them are still serviceable after traditional maintenance. However, due to the limited intrinsic capacity of unreinforced masonry against lateral load, construction without seismic provisions, and construction deficiencies such as inadequate wall-to-wall or wall-to-floor connections, these buildings are categorized as the most vulnerable constructions. Past earthquakes showed severe damage to URM buildings in Nepal with frequent out-of-plane failure. In the last decades, masonry structures have gained increasing attention after the realization of their historical and cultural importance and the great risk that they suffer in seismic areas. In this study, linear dynamic analysis is performed to develop fragility curves for a typical representative building. The building is selected based on a rapid visual screening survey carried out in the city. The result of this study highlights that the URM buildings in Dhulikhel are highly susceptible to out of plane failure because of the long unsupported length of a masonry wall and flexible floor.

For nonlinear time history analysis, employing a time integration method and some nonlinearity iterative method (for implicit analyses) is a broadly accepted practice. In 2015, the authors proposed a change in the analysis, according to which, when the nonlinearity iterations do not converge, the analysis proceeds to the next integration step. In this paper, this change, and no other change, is applied to seismic analysis according to the seismic code of New Zealand, NZS 1170.5:2004. The purpose is to clarify whether the change can increase the analysis efficiency. The possibility of improving the efficiency is shown via analysis of a tall building’s structural model. The observations are explained, discussed, and generalized. As a main result, the change proposed in 2015 may considerably improve the efficiency when the tolerance is sufficiently small and is ineffective when the nonlinearity tolerance is sufficiently large.

Structures made from concrete, metal or any other material, are designed to have a long service life. However, to ensure a durable structure, it must have constant and efficient maintenance. Structural Health Monitoring (SHM) can be described as the method of monitoring and evaluating the structural health through the collection and analysis of data extracted from sensors, which are connected or not to the structure in the matter. In this way, the difficulties are in how to collect that data, analyze it and have information about it to give a final response about the structure status. This research focus at the development of a low-cost bridge management system, which will allow remote monitoring of special structures and shows their real-time status. Subjects as Finite Element Method (FEM), dynamic test and Internet of Things (IoT) are studied to create a viable system. The first step is modelling a case-study bridge on SAP2000 to analyze the theoretical behavior of the bridge. The second step is using low-cost devices to extract data with low noise, process it and send a response about the structure status, involving Wireless Sensor Networks. Then, experimental results are analyzed.

This paper proposes analytical solutions of the mass-spring-damper systems described by conformable fractional differential transform method. Conformable fractional transform method is based on new relation between fractional calculus and calculus based on basic limit definition were used. The behaviors of the analytical solutions of the mass-spring-damper systems described by conformable fractional transform method were represented analytically and graphically. Then the effect of the orders of the fractional derivative on the system was analyzed. The results obtained by this approach provide new explanation on the importance of fractional calculus on mechanical systems and showed clearly the amplitude of steady state solution depends on time; with contrary to what is known.

In this paper the pushover analysis for pile-supported wharf structures (PSWSs) is carried out. This nonlinear static analysis is a common method to estimate the optimum displacement demand for seismic design of constructions. The main aspect of this study is to account for the dynamic magnification factors due to torsional effects. 2D and 3D models by finite element method (FEM) were computed considering the seismic loadings, modal analysis, and the lateral stiffnesses imposed to consider the soil-piles interactions. The seismic design of the piles consists in accounting for the formation of plastic hinges. The purpose is to determine, in a deterministic way, the performance points of the structure in terms of base shears and displacements, then, in a stochastic analysis, to estimate the probability of exceedance of horizontal displacements of a semi-flexible model with respect to a flexible model. The case study is a real pile-supported wharf in ports placed in a high seismicity area, in this sense, this paper should provide some useful technical data. The advantage of using the nonlinear pushover analysis in terms of displacements was estimated about 30%.

Fatigue behavior of a bridge is considered as a main concern for structural engineers especially for bridge construction due to the rapid growth of overloaded trucks. Truck traffic has increased significantly on bridge structures in Bangkok. Moving loads due to overloaded trucks on a steel girder bridge would cause fracture formation and propagation. The study is conducted to assess the safety of a steel girder bridge under actual truck traffic data. The study addresses the fatigue behavior of the bridge structure using FEM analysis. This will help to evaluate the remaining service life under the operational performance of several truck classes. The service life of this steel girder bridge can be evaluated by S-N curve application based on Miner’s damage rule which is recommended by AASHTO LRFD standard specifications. The bridge consists of 19 spans with 1.75 m transverse width of each five longitudinal steel girders including reinforced concrete slabs. The dynamic behavior of the steel girders was validated by field instrumentation. The fatigue truck model was constructed using data of 102,546 truck movements in 2020. The data included gross weight, axle weight, and axle spacing. The number of stress cycles can be measured by analytical investigation at the midspan of each girder. The result obtained from analytical investigation revealed that the steel girder bridge would be affected fatigue failure with the expected growth of truck traffic and the classified fatigue trucks based on the actual truck data.

Misalignment of an orthotic ankle joint with respect to the anatomical ankle joint leads to “pistoning motion” which is the relative sliding motion between a limb and its externally wearable orthosis. This pistoning motion and resulting pressure points are the cause of skin problems due to which an orthosis user experiences pain and discomfort. This work quantifies the effects of sagittal plane ankle joint misalignments in terms of relative motion between the limb and the orthosis. A 2D link segment model was developed using MATLAB software to simulate relative motion between the limb and the orthosis for a functional range of ankle motion. The orthotic ankle joint was methodically misaligned with respect to the anatomical ankle joint in the Anterior-Posterior (A-P), Proximal-Distal (P-D) directions, and their combinations to simulate orthosis sliding and locate pressure points on the limb. Simulation results showed that A-P misalignments caused a significantly greater pistoning motion than P-D misalignments, which agrees with previous studies. Combined misalignments (Anterior-Proximal, Anterior-Distal, Posterior-Proximal, and Posterior-Distal) were found to have a greater effect on overall relative motion between the limb and the orthosis as a result of the superposition of relative motions from the A-P and P-D directions. The 2D model also predicts pressure point locations due to joint misalignment, which supports the results from previous studies. Simple 2D simulations presented in this work can be used to interpret the consequences of orthotic ankle joint misalignments. It further emphasizes the importance of accurate alignment of orthotic and anatomical ankle joints and provides insights for modifications in orthosis for improved user comfort. Such a simulation-based model can be used to guide anatomical and external joint alignments in ankle-foot orthoses and lower-limb exoskeleton devices.

Boring shallow tunnels in urban areas generates ground-borne vibrations with energy distributed over a wide range of frequencies, up 100 Hz during excavation. As a multiple vibration source, the TBM emits waves until existing building foundations and the free surface. They do not depend only on the source and its surrounding environment but also on the propagation environment. Based on several dynamic in-situ campaigns with synchronized measurements inside the TBM and on the ground, a numerical modelling of the propagation of waves emitted by a tunnel boring machine is proposed with an original considering of the source term.

In this paper, we introduce an Extended Finite Element Method (XFEM) to simulate the wave propagation in an imperfect concrete structure. The XFEM allows simulating a small discontinuity in the structure and the change of this discontinuity without re-meshing the whole structure. Therefore, the meshed structure is kept consistent while the structural discontinuity changes. Simultaneously, we improve the model with XFEM mass lumping technique and viscous boundary conditions in order to simulate efficiently the damping of signals’ amplitudes. Furthermore, ultrasonic experiments were carried out in our lab to validate the numerical simulation. The simulations and experiments with and without cracks are presented. The effects of the crack on received signal, e.g., time-of-flight, wavelength, and spectrum are also discussed in the paper.

A numerical procedure for vibration analysis of pressurised and rotating cylindrical shells by the Rayleigh Ritz method is presented. Potential and kinetic energies are specified. Stiffness matrix, geometrical stiffness matrix and three mass matrices due to centrifugal forces, Coriolis forces and the inertia forces are derived. Three basic sets of boundary conditions are considered, i.e. free, clamped, and simply supported in all the three directions. Appropriate sets of orthogonal trigonometric functions are used for the approximation of the displacement fields. The accuracy of the results obtained is verified analytically, by the finite strip method (FSM), and by the Finite Element Method (FEM).

An analytical solution of the problem of free bending vibrations of rectangular plates with Levy boundary conditions lying on a continuous variable elastic foundation, which is described by the Winkler model, is given. An exact solution of the differential equation of free vibrations of plates when the bedding coefficient is an arbitrary continuous function of one variable is found. The quadratures for numerical realization of the found solutions are derived. The formulas for dynamic state parameters, which allow one to investigate free vibrations of the plates under any boundary conditions at two parallel edges, are obtained. The dependence of the frequency of free vibrations of the system under consideration on its other parameters is established in the analytical form. Computational formulas for determining the spectrum of frequencies of free vibrations of the plates are obtained. The general form of frequency equation and formulas for the main forms of vibrations corresponding to the three cases of boundary conditions are established. Frequency spectra of free vibrations of hinged plates resting on a variable elastic base for four different laws of bedding coefficient changes are determined. It is shown that in the case of constant bedding coefficient the frequencies calculated by the author’s method practically coincide with the frequencies calculated by the known exact formula.

The dynamic elasticity problem for rectangular domain is presented in this paper. The conditions of the second main elasticity problem are given at the lateral sides. It is necessary to find the wave field of the rectangular domain under steady state loading. The integral Fourier transform was applied to the formulated boundary value problem and reduced it to a one dimensional vector boundary problem. The last one was solved with the method based on matrix differential calculations which was successfully applied earlier to solve the analogous static problem [1, 2]. As a result, the non-homogeneous one-dimensional boundary problem was derived and solved with the help of Green’s matrix-function apparatus [3]. The wave field is constructed as a superposition of the homogeneous and non-homogeneous solutions and contains the unknown derivative of the displacements. To find this unknown displacement the singular integral equation is derived and solved with the help of the orthogonal polynomial method. Application of the inverse integral Fourier transform finalized the construction of the stated problem solution. The analysis of wave field of the rectangular domain depending on different loading types, frequency values and domain’s size was done.

The work is devoted to the mathematical modeling of a sandwich circular plate. Free flexural axisymmetric vibrations of generalized three-layer plate is studied. The mechanical properties of the plate’s core vary through its thickness. The mechanical properties of faces are constant. The individual nonlinear theory of deformation of the straight normal line to the middle plane of the plate is elaborated taking into account the shear effect. Two cases of the supported edge of the plate are considered: simply supported, and clamped. Based on the Hamilton's principle two differential equations of motion are obtained. This system of equations is approximately solved and the fundamental natural frequencies are obtained for two circular sandwich plates.

During operation, a steam turbine shaft is subjected to a wide range of thermomechanical and thermochemical loading. Despite significant reserve of static and dynamic strength, laid down at the stage of turbine design, fatigue cracks still appear in its structural elements, which lead to catastrophic failures. Potential reasons of damage in turbine shafts are all technological operations used in the process of manufacture (forging, turning, and milling, heat treatment), since they are accompanied with plastic deformation of material. Damage accumulates during long-term cyclic deformation and turns into local damage of a fatigue crack type. In addition, cracking in turbine shafts is caused by the presence of stress concentrators. The analytical model of high-pressure rotor of the K-200-130 steam turbine has been developed to study the transverse vibrations when rotor passes through the first critical speed. The growth of crack is predicted based on fracture mechanics approaches through the determined maximal stresses in the cracked section and on the experimental dependences of the crack growth rate on the stress intensity factor range for the rotor steel.

Driving a road vehicle on uneven roads causes its bodywork to vibrate. Vibration of the bodywork can result in fatigue damage of critical bodywork nodes. In the case of buses (trolleybuses, battery electric buses), the critical structural nodes are welds of thin-walled profiles, most often corners of openings for doors and windows. The fatigue properties of critical structural nodes are expressed by S-N lines. S-N lines can be determined in advance by performing laboratory fatigue tests. The time series data of stresses in the bodywork have the character of a random process. These stresses can only be determined with sufficient accuracy by strain gauge measurements, either while the vehicle is running on real tracks or on a proving ground. Fatigue damage can then be estimated using the appropriate fatigue damage accumulation hypothesis. The paper demonstrates a case study that use data from the authors’ practical cooperation with bus producers.

This study proposes a method to improve the feeding speed in an underactuated and flexible linear vibratory feeder through the simultaneous synthesis of the optimal excitation forces and the tuning of the mechanical design. The target is to increase the flow of the parts by ensuring uniform displacements along the tray with the prescribed throw angle, despite the relevant tray flexibility. First, a multi-DOF (degrees of freedom) analytical model of the underactuated feeder is formulated in term of actuated and unactuated coordinates. Hence, the subspace of allowable motion is computed, to highlight the relation between the achievable displacements and the physical parameters of the system (mass, stiffness and force distribution matrices and excitation frequency). Then, such subspace is optimized through dynamic structural modification where parametric sensitivities are adopted to select the structural modifications that enable to reduce the actuation effort. Once the mechanical design has been optimized, the optimal harmonic forces are computed through an ad-hoc inverse dynamics algorithm, defined “force shaping”. Finally, a multibody model developed in MSC Adams is used to evaluate the flow of the parts over the feeder. The improved mechanical design of the system together with the shaped forces evidence the improved system performances with reduced actuation forces.

Wind energy is one of the renewable sources in fast development and implementation around the world. The development of competitive renewable energies and the energy supply networks, e.g. wind turbine (WT), performance are essential to guarantee a sustainable power supply in cities and megacities. In these scenarios, a reliable energy supply is crucial. The WT selected is a National Renewable Energy Lab (NREL) monopile 5 MW baseline wind turbine. This WT is a conventional three-bladed variable-speed, pitch-to-pitch, upwind controlled turbine. In this paper, we explore the dynamic characteristic of the WT monopile 5 MW by mean of the spectral element method, which is a highly accurate method with low computational cost. A tapered spectral element couple to a lumped mass is formulated and used as the WT model. The results reveal a varied of modal properties and mode-coupling instability in the vibrations, which is essential information to the turbine’s monitoring and control.

Sports and physical activities cause different effects within the body systems. They may affect the equilibrium of the internal environment. The relationship between physical exercise and muscle fatigue has particularly attracted attention, by many researchers for more than a century. Such a relationship is very complex and still needs further research.Human locomotion analysis is used extensively by physicians for pre-treatment analysis. In general, human locomotion can be defined as sequences of cyclic and repeated gestures. Previous analyses have proved the cyclostationarity behavior of vertical ground reaction forces (VGRF) recorded during walking and running. In this article, the Random Slope Modulation (RSM) is introduced as a new model for characterizing cyclostationarity. This model presents the impact of random slope variation on the cyclic spectrum of the signal and, hence, it lends itself the ability to extract information about the cyclostationary properties and structure of the signals in question. The model is applied in the study of biomechanical signals where it considers the slope as a specific measure extracted from the VGRF. We show that the calculated slope is random and different for every passive peak which visualizes the random character of VGRF signals. This randomness introduces a cyclostationarity of order 2. Hence, the obtained signal presents a random phenomenon through a slope that varies randomly, but is repeated periodically. The results show that the slope and polynomial random coefficients of the passive component of the VGRF can provide interesting information concerning biomechanics running and concerning fatigue associated with long-distance running.

A combined - analytical, numerical and experimental study of forced undamped vibrations of 2DOF discrete system from seismic impact is presented in the paper. The study refers to a horizontal vibrating system, consisting of two translational moving bodies, connected by three springs. The seismic action is applied to the fixed point of the first of the three springs. With such an idealized scheme, the dynamic behavior of two-stories one-bay structures can be studied at an initial stage. The mathematical model of the vibrating system is presented in a matrix form. Numerical studies are conducted in two ways. Firstly, in the Simulink environment, a simulation model was composed, with a geometrically oriented approach in simulating the vibrating process. Then, in the MATLAB environment, an animation model was developed using the third animation method offered by the programming system. The experimental studies were conducted by Stand for study the vibrations of discrete planar systems. There were conducted numerical studies on vibrating systems with varied inertial and elastic characteristics and in varied seismic impact. For such systems an experimental verification of the results was also carried out. All models - the dynamic model and its corresponding mathematical, simulation, animation and experimental model are open to additional bodies to obtain discrete vibrating systems with a greater number of degrees of freedom. The models also allow a change of the point and nature of the impact.

We consider a vibrating system consisting of a thin rectilinear elastic rod actuated by external loads applied at the ends as well as by a normal force, which is distributed piecewise constantly in space. Such a force may be implemented by piezoelectric actuators. The intervals of constancy of this normal force are equal in length, and the force value on each of these sections is considered as an independent control input. We study the longitudinal motions of the rod and the means of control optimization. Based on the eigenmode decomposition, it is shown in the case of uniform rod that the original continuous system is split into several infinite vibrating subsystems each of which is controlled by a certain linearly independent combination of control inputs. It follows that if any of these combinations is taken equal to zero, then the corresponding subsystem becomes uncontrollable. Next, an optimal control problem on a finite time horizon is considered, where the terminal mechanical energy of the rod and energy losses in the control circuit are minimized with some weighting coefficients. We show that for a fixed number of actuators distributed along the rod, approximation of the problem is reduced to the design of linear-quadratic regulators. An example of a uniform rod is presented where finite expressions for the optimal control functions are obtained. Amplitudes of controlled and affected but not minimized modes are derived for approximated suboptimal control.

This work proposes a novel receptance-based robust structural modification method of the natural frequency assignment. Potential perturbation of the target natural frequency, which arises from uncertainties in physical parameter modifications, is quantified by utilizing analytical sensitivity formulae derived in this research. The proposed sensitivity formula is introduced to the natural frequency assignment optimization calculation as an extra term penalizing poor-robust solutions. Such an improvement can boost obtaining the nominal values of structural modifications with high robustness in preserving the model-free superiority of receptance-based techniques. The numerical validation of the proposed method on a five-degree-of-freedom system demonstrates its capability to compute high-robust modifications in meeting the prescribed requirements and satisfying all the constraints.

The Wave Based Method (WBM) uses weighted wave functions in order to model boundary value problems. These wave functions have to satisfy the underlying differential equations and usually violate the boundary conditions of a WBM element. A weighted residual formulation permits to minimize this error by determining the weighting factor for each wave function. By applying the WBM to a 2D saturated soil structure, the propagation of two longitudinal waves and one shear wave is modeled. In compliance with Biot’s theory, the field variables consist of displacement components in the solid phase and seepage field components, which influence the decay of the wave amplitude within the structure. In order to fulfill the Sommerfeld radiation condition, this model is extended by an absorbing boundary condition, which transmits incident waves. The model is tested for different excitation frequencies and hydraulic conductivities in order to observe the radiated power within one period.

Prediction of vibrations in buildings due to railway traffic is challenging due to several aspects, namely the huge dimensions of the domain, the interaction between different systems, and the uncertainties inherent to the complexity of the system. Therefore, experimental/numerical hybrid prediction techniques are of great interest since they take advantage of the combination between experimental data and numerical resources. In this context, the type of foundations of a building are preponderant in the dynamic soil-structure interaction effect and may have an influence on the accuracy of the hybrid prediction. The presence of the building foundations could significantly modify the response of the local sub-soil of the building. This fact makes that the prediction of vibrations in buildings becomes a complex wave propagation problem. As different types of foundations behave differently, they lead to different dynamic responses in the structure for a prescribed incident wave field. Therefore, dynamic soil-structure interaction coupling is also affected by the building’s foundation type. In order to investigate this phenomenon, this paper studies the influence that the consideration of three different foundation typologies, shallow, slab and deep foundations, have on the prediction of railway-induced vibrations on a building using an experimental/numerical hybrid methodology. A comparison is made between the results obtained through the hybrid method and the numerical results obtained through a numerical model based on the full system.

In this paper, a methodology is proposed in order to extract a relevant representation of a response spectrum considering numerous acquisitions from dynamic sensors located in different places and sollicitated under different sollicitations. This methodology, which is an extension of the Frequency Domain Decomposition method, is based on the intercorrelation of signals and the extraction of the singular values of the spectral density matrix. We illustrate it on the study of the impact of vibrations generated by the excavation of a tunnel by a tunnel boring machine (TBM), with measurements on the ground and inside a TBM under ambient noise then during the excavation.

The article compared the transmission of underground vibrations caused by mines to foundations of representative low-rise masonry buildings situated in two different seismically active mining areas in Poland: the Legnica-Glogow Copperfield (LGC) and the Upper Silesian Coalfield (USC). The soil-structure interaction (SSI) effect has been investigated on experimental measurements of free-field (near to the building) and building foundation vibration accelerations occurring at the same time. Long-term (several years, hundreds of strong shocks), full-scale monitoring with the application of so-called ‘an armed partition’ measuring equipment, was carried out. The focus has been on the horizontal vibrations in the directions of the transverse and longitudinal axis of the buildings. It has been stated that records of the ground and building foundation vibrations registered at the same time can vary considerably in the case of the LGC, as well as the USC mining regions. The differences between the ground and building foundation vibrations have been analysed using the comparisons of dimensional and dimensionless response spectra from the building foundation and free-field vibrations, respectively. Furthermore, the relationship between the foundation and ground response spectra, the so-called ratio of response spectra (RRS), has been taken into account. Influences of epicentre distance, the magnitude of mining tremor energy, peak ground value of vibrations related to mining tremors on the SSI in the case of the same type of building but situated in mining regions with some differences concerning, e.g., site conditions, have also been analysed and compared.

Modern societies demand for efficient mass transportation systems, becoming the rail transport competitive for short to medium distance travels. The increasing rail network gives rise to new engineering challenges since the surrounding infrastructures will experience discomfort problems. To developed realistic studies in the pursue of mitigation measures design precisely to solve the previous problem, robust numerical tools needs to be developed. Several numerical methods were proposed in the last years, such as 2.5D models, capable of dealing, assuming some simplifications, with ground-borne vibrations problems. However, the application of such efficient methods is restricted to longitudinal invariant structures, which can represent a rough approximation. Since a rail track is clearly a tri dimensional structure, in this paper is presented a tri dimensional FEM-PML capable of modelling periodic structures by adopting special boundaries conditions.

The attenuation of wave amplitudes is ruled by the planar, cylindrical or spherical geometry of the wave front (the geometric or power-law attenuation) but also by the damping of the soil (an exponential attenuation). Several low- and high-frequency filter effects are derived for the layering and the damping of the soil, for the moving static and the distributed train loads and for a homogeneous or randomly heterogeneous soil. Measurements of hammer- and train-induced vibrations at five sites have been analysed for these attenuation and filter effects. The measured attenuation with distance can be discribed by generalised power laws and some reasons will be discussed. The theoretical filter effects can well be found in the measurements.

Pipes carrying fluid may resonate at certain fluid velocities which is called the critical fluid speed/velocity. This resonance may lead to pipe buckling or fatigue failure of welded pipes. Usually, such velocity is high in value and difficult to measure experimentally as this type of test will cause a severe damage to the pipes system. However, in this paper a new laboratory experimental approach was developed to measure fundamental natural frequencies of the pipe at different fluid velocity for laminar and/or turbulent fluid systems. The test method was carried out in the laboratory on sample pipes and the test results were validated with the theoretical/analytical results to establish the test accuracy.

The pseudo-static case for a poroelastic axisymmetric cylinder is considered in the terms of Biot’s model. The cylinder is loaded by its boundary r = a, where the perfect drainage conditions are fulfilled, and the boundaries z = 0 and z = h are in slide contact and undrained conditions. The initial conditions are zero. The initial problem is reduced to the one-dimensional problem with the help of Laplace and Fourier integral transforms applied by t and z variables respectively. The one-dimensional problem in transform space is formulated in a vector form, which is solved with the help of matrix differential calculation apparatus. According to it the corresponding matrix equation is considered, and the system of fundamental matrix solutions is constructed by the contour integral calculation. So, the exact solution of the vector boundary problem in Laplace-Fourier transform space is derived. The Heaviside expansion theorem is used to invert Laplace transforms, and the stress and pore pressure values are investigated for different ratios between a and h, and for different poroelastic materials.

Due to the massive number of products transported every day, the use of lightweight pallets made of recyclable materials, easy to clean, resistant and cheap should be ideal. In this paper, new modular metal pallets that combine blocks and deck boards to produce different configurations for use in transportation/stationary conditions are proposed. Due to the lack of specific codes to design this structure, a more complete structural analysis (analytical and numerical) to evaluate stresses and deformations has been carried out. Then, laboratory experimental tests were performed to validate the model. A comparative life cycle analysis (LCA) was also carried out to identify the main environmental impacts with respect the wood/plastic/aluminium pallets. Numerical and experimental results provided new ultimate loadings between about 10.0–100.0 kN with a maximum deformation of about 35.0 mm. This indicates that steel pallets perform satisfactorily in terms of resistance and stiffness. Results from LCA suggested that steel pallets perform better than their wood, plastic, and aluminium pallets, mainly due to high recyclability and less need of repairing. Therefore, for a specific analysis of metal pallets, the values and procedures provided in the current codes should be updated. Because the different demands of dimensions and weight, the development of modular pallets could be a good choice to fulfil the functional requirements for several industries.

Model updating plays an important role in dynamics modeling with high accuracy, which is widely used in mechanical engineering. However, the uncertainty of the system will greatly increase the difficulty of updating the model. In this paper, an interval model updating method for uncertain vibration systems using the frequency response function is proposed. This method can realize simultaneous updating of multiple frequency bands. Firstly, the uncertain parameters of the model are replaced through the intervals where they should belong, and the frequency response function of the model is replaced through the interval accordingly. Then multiple frequency bands are selected to update the model simultaneously, and the optimal solution of the updated parameters is calculated by the NSGA-II algorithm. To verify the effectiveness of the proposed method, a simulated 3-DoFs system is utilized in this paper. The results prove that the experimental results are totally covered in the frequency response function interval of the updated model, which proves that the method proposed has great effectiveness.

The present work compares the numerical performance of parametric updating between a proprietary tool and the GA/Matlab toolbox, using a genetic algorithm. The precision and processing time of parameter identifications are evaluated for two structural systems: (a) a numerical cantilever beam; and (b) the experimental results of a free-free beam. Parametric updating uses classic metrics for cost functions, for example: natural frequency, modal form, and the linear weights of the above. This work is part of the Demonstration Platform on Structural Integrity, a project developed collaboratively between the PPG Integrity (FGA-FT/UnB) and Embraer.

The effect of different intentional mistuning (IM) patterns is investigated with respect to the forced response of an academic axial blisk. It could be shown in numerical analyses that a preliminary use of sensitivity algorithms helps to understand the feasibility and efficiency of introducing geometric changes of the blades. The implementation of IM patterns requires conducting intensive sensitivity studies based on FE simulations in order to identify the consequences of slight geometrical blade modifications on natural frequencies. Typical changes might be a modification of fillet radii or partial modifications of blade thickness, which are most suitable to adjust a target natural frequency without a severe loss of aerodynamic performance. A software tool developed at Irkutsk SAU is employed to evaluate the impact of mass and stiffness contributions, and with that, geometric deviations on blade natural frequencies.Intensive blade vibration due to aerodynamic excitation of blisks is known as major source of high cycle fatigue, which may cause severe failures of turbine and compressor wheels during operation. The problem is relevant for several sectors of industry such as power generation, aviation or vehicle manufacturing. In consequence, there is a broad request of preventing any inadmissible vibration at any time. The application of IM can be regarded as powerful tool to avoid both, large forced responses and self-excited vibration. However, there is a lack of knowledge about how to implement mistuning without strong distortions of the flow passage. The main objective of this work is to close this gap based on comprehensive numerical analyses with regard to the effects of intended geometric modifications of blades on modal quantities.Using FE models, the effectiveness of the proposed block models of mistuning is analyzed with and without taking into account the operational speed of the axial impeller. In conclusion, the consequences of different IM implementations on the forced response of an academic blisk are discussed. In particular, the most promising IM patterns are identified yielding the least forced response.

Piezoactuators are popularly employed in precise positioning applications at the micro- and nanometer scales. Their positioning performance, especially for low-frequency responses, is significantly impacted by creep - a phenomenon where the actuator deformation gradually changes in the presence of a persistently applied constant voltage. This change in deformation manifests itself in the gradual drifting of the end-effector position that the piezoactuator is driving. A significant research effort has therefore focussed on the accurate modelling of creep. This paper compares three popularly employed creep models against experimentally measured creep data obtained from a piezo-drive nanopositioner axis and quantifies their modelling accuracy. The quantification demonstrates that the fractional-order model (double logarithmic model) outperforms the other two integer-order models (Logarithmic and LTI models) along multiple, key performance indices.

Multi-stable systems can be found in many fields of engineering from vibro-impact energy harvesters to origami structures. They are mainly characterised by the presence of co-existing attractors in their dynamic response. This feature can be beneficial when the system is required to adapt to the environment or unfavourable as the system may diverge from the desired behaviour. Hence, these systems usually require actuation or control that can be activated to maintain the desired response or switch between configurations. Recently, the idea to use the time-delayed feedback method to switch between co-existent attractors was proposed focusing on the controlled system’s ability to exchange between attractors or maintain a specific type of behaviour. However, the control method is still required to have its gains set on a trial and error basis when dealing with stable solutions. Furthermore, it requires a deeper analysis of the system dynamics when dealing with unstable orbits. To address the beforementioned challenges and eliminate requirements of a priori knowledge of the system evolution function, this work uses the adaptive gain time-delayed feedback method to switch between co-existing attractors. Numerical results show that the proposed controller can be a viable low energy control option in multi-stable systems.

Often, the system nonlinearities adversely impact system behaviour/performance. A deeper understanding of these nonlinearities and the parametric dependencies thereof has the potential to enable the formulation of robust, energy-efficient control strategies. Moreover, input constraints and/or delays significantly impact the controlled system performance and overall system stability. In this work, we present a systematic investigation to test the performance of control methodology in the presence of delay and control input constraints. Impact oscillators have been proved to be suitable testbeds to implement nonlinear control methods considering the system’s dynamic rather than using high, control-effort-consuming gains. Therefore, a mass-excited impact oscillator is chosen as a candidate system to demonstrate the proposed control scheme’s effectiveness. As a case study, the coexistence of impacting and non-impacting behaviour of the system is considered. A time-delayed feedback (TDF) scheme is employed in closed loop with the impact oscillator to achieve a non-impacting solution. Subsequently, the closed-loop performance of the overall system with and without constraints and delay are simulated and contrasted. It has been observed that the controller successfully exchanges the chosen attractors. However, the controller fails to stabilise the system with higher delays and constraints, even with higher gains. Therefore a new approach would be required to deal with delays and constraints in such scenarios.

To study the feasibility of deploying a novel type of anchor with variable buoyancy for mooring floating offshore wind turbines, a set of detailed modelling studies was performed in the state-of-the-art, Marine Simulator at the National Decommissioning Centre (NDC). The aim of the multi-physics simulations is to fully assess the proposed deployment method using a small tugboat fitted with a simple winch, thereby simplifying the process and reducing installation costs. The anchor has a 10 m square base, 4.5 m height and weight of 163 tonnes. The anchor is subjected to irregular waves with a JONSWAP spectrum with a significant wave height up to 5 m and peak period of 10 s. The analysis is divided in three sections: characterisation of the anchor buoyancy, positioning the anchor under the stern of the vessel and the controlled descent of the anchor to the seabed. An ideal winch speed of 0.35 m/s is identified, at which working load range on the winch cable decreases from 80 kN at the lowest winch speeds to about 30 kN. The sinking trajectory is similar at all winch speeds, however, the slower the descent, the further the anchor drifts. At this winch velocity, the descent from the resting position under the stern to the seabed takes roughly 5 min. In addition, the anchor’s yaw range during the descent is below $$10^{\circ }$$ 10 ∘ at the optimal conditions.

A model including the cross-flow and in-line vibration of a top tensioned riser (TTR) under excitation from vortices and time-varying tension is proposed, where the Van der Pol wake oscillator is used to simulate the load caused by the vortex shedding. The governing partial differential equations describing the fluid-structure interactions are formulated and multi-mode approximations are obtained using the Galerkin projection method. The first-order approximation is analysed in this work. Dynamic responses of the in-line and cross-flow displacements are obtained by the numerical simulation for different parameter values. Results show that the large-amplitude vibration of the structure can be induced by the combined resonance. The results can be helpful to enhance design process of top tension risers.

Friction-induced vibration problems possess inherent randomness due to factors such as the roughness of the contact interface, nondeterministic external load, and stochastic driven velocities. The spatial randomness in friction caused by rough contact is only addressed in a few papers in the existing literature and can significantly impact the dynamics in practical engineering. In this paper, the spatial randomness in planar friction is considered by modelling the coefficient of friction (COF) as a random field. The statistical properties of the frictional forces and torque resulting from uneven distributed COF are analysed for a disc in the pure sliding planar motion. It is found that the coefficient of variation of the frictional forces and torque are strongly dependent on the ratio of correlation length of the COF random field to the geometrical characterised length of the disc. A numerical case is presented to illustrate the impact of COF random field modelling on the stick-slip effects. New three-variable stick-slip transition criteria are proposed to accomplish the analysis.

An enhanced inverse dynamics approach is presented for feedforward control of a nonlinear underactuated multibody system. Its theoretical formulation is carefully explained and subsequently assessed through a numerical test case. In particular, the internal dynamics model is achieved and a stability analysis is performed in order to find the condition that makes the system a non-minimum phase one, obtaining an approximated internal dynamics equation characterized by eigenvalues that all reside in the left half of the complex plane. Knowing the desired time evolution of the system output coordinates, a stable computation of the required feedforward input term is performed.

Electromechanical coupling is a measure of the efficiency of conversion between electric and vibration energy. The crucial problem in the design of energy collection is the design and modelling of an electro-mechanical coupling. This paper shows that electromechanical coupling in electromagnetic energy harvesters is inherently nonlinear and can be easily modified. The design of the electromechanical coupling function through the special construction of coils and magnet-spacers is proposed. In order to demonstrate the effectiveness of the harvester with the proposed electromechanical models, numerical results are presented.

In this paper, a distributed model in terms of neutral-type time-delay equations is presented to investigate the global nonlinear axial-torsional dynamical behavior of a drilling string. A rate-independent bit-rock interaction law is employed for both cutting and frictional forces at the bit. A model is proposed for the estimation of the depth of cut which is valid in the case of bit bouncing and the bit reverse rotation. Illustrative simulation results are presented for a representative case study, which demonstrate the existence of the bit-bounce and reverse-rotation in some practical operating conditions, and indicates the need for taking the resulting multiple regenerative effects into account.

Rotor-bearing systems are important components of aircraft engines of which vibration response must be analyzed under normal and disturbed conditions. Due to the existence of strong nonlinearity from squeeze film dampers and ball bearings, it is often very time consuming to evaluate the vibration of the rotor excited by unbalanced mass, which makes efficient and reliable modeling reduction is pivotal to rotordynamic analyses. In this paper, the nonlinear vibration and dynamical behavior of a twin-spool rotor assembly supported on bearings and squeeze film dampers with centralizing springs is investigated through the post-processed nonlinear Galerkin method. The rotor is spatially discretized with the finite element method, and the nonlinear governing equation of motion of the system is derived. To reduce the scale of the full-sized model, the post-processed nonlinear Galerkin method is employed to project the original system onto a low-dimensional sub-manifold with a relatively smaller number of degrees of freedom. The convergence of the nonlinear Galerkin method is verified through comparisons energy between the original and the reduced systems. The optimal choice of the number of master modes is determined to form the reduced model for nonlinear vibration analyses. Through the NGM the vibration of the system is solved, and the amplitude-frequency response, bifurcation and the Poincaré map are obtained to demonstrate the complexity in the rotor dynamics.

Subsea production systems design requires estimates of hydrodynamic loads related to characteristics of structures and the external flow. The current work investigates flow-induced forces for a group of stationary rigid structures modelled in 2D including one structure with a squared cross-section and three smaller circular cylinders located in proximity of each other. Uniform flow and planar sheared flow conditions are considered in this work, with three different arrangements of smaller structures. Flow characteristics are obtained using CFD method and k-ω SST turbulence model. Simulation results include time histories of hydrodynamic coefficients, FFT data and velocity fields. Results for the planar sheared flow in the cases considered show a reduction of mean drag coefficients, increase of frequencies and amplitudes of the fluctuating drag and lift coefficients compared to values observed for the uniform flow.

The driving wheelsets are used on the railway traction vehicles to support the vehicle’s weight, for traction and braking purpose. Most commonly, a driving wheelset consists of the axle on which the two wheels and the driving gear are rigidly attached. The driving wheelset longitudinal vibrations are important for the locomotive performance from the traction point of view. This vibration may be caused by the friction forces at wheel level, the torque from the motor or from the drive system, and the steering system of the wheelset. In this paper, a basic mechanical model of a driving rigid wheelset, including the rotor dynamics and elasticity of the driven shaft and the steering system is considered to point out some aspect of the longitudinal vibration when the wheelset is running on adhesion limit. Using a numerical method for solving the nonlinear equations of motion, the limit cycle which appears at the adherence limit and the influence of the steering damping are presented.

Rotor-stator rubbing phenomenon is a very common fault in various engineering applications. Usually, the stator supports are assumed to be symmetric, however, in some conditions, the stator support stiffness is anisotropic in nature. In this paper, an approximate analytical solution for the rub interactions between a Jeffcott rotor and an asymmetrically supported stator is introduced. The present problem is a good example of piecewise nonlinear dynamics in which contact causes the system to switch between linear and nonlinear dynamic behavior. To evaluate an analytical solution to the contact equations, Taylor’s expansion is used to linearize the contact forces. Then, an analytical solution is introduced based on this approximation. To investigate the validity of the present model, the proposed approximate analytical solution is compared with the numerical solution obtained using direct numerical integration for the same problem. The results show that the proposed piecewise analytical solution is efficient in evaluating the system response for both periodic and chaotic responses.

The dynamics of a harmonically base-excited two pendula system, is investigated for the practical application of energy harvesting from rotatory motions [1, 2]. The central aim of this study is to identify system parameter ranges for which pendulum rotations exist. The external harmonic excitation amplitude and frequency, and the difference in pendulums lengths are the system parameters which have been varied thresholds. Bifurcation analysis has been performed for the identification of values beyond which rotations exist, and the study of corresponding bifurcation points has been conducted with computational tool ABESPOL, developed at the Centre for Applied Dynamics Research (CADR) of the University of Aberdeen [3]. Direct simulations and one-parameter continuation analysis were performed with ABESPOL and some results were corroborated with direct numerical integration in Matlab, based on a Runge-Kutta algorithm. One parameter continuation results showed complex bifurcation scenarios for antiphase rotatory motions, presenting evidence of existence and form of representation. Further results showed that pendulum rotations, in phase and antiphase, co-exist with oscillatory motions. Therefore, the basins of attraction have been computed, enabling attractors to be targeted so as to enable antiphase rotatory motion.

In this paper the elastic dynamic load factor in structural dynamic is revisited. The existing literature in which the response exists only for isosceles triangular pulse and shock load pulse is criticized.A new pulse shape parameter is introduced by which both isosceles triangle impulse and shock load impulse and other unsymmetrical pulses can be expressed. This enables the elastic Dynamic Load Factor (DLF) to be computed versus the pulse shape parameter.Thereafter a surrogate model is found by which the load factor can be computed via pulse duration, natural period and pulse parameter. The conservative values of the load factor extracted from the surrogate model and can be used for structural dynamic aspect of the design.In numerical examples the Single Degree Of Freedom (SDOF )model subjected to blast loading is investigated. It is shown that numerical scheme for elastic dynamic load factor in this paper is very accurate. The accuracy is demonstrated in case when isosceles triangular pulse blast load is applied. Moreover, by introducing the pulse shape index parameter, any unsymmetrical pulse can be expressed and their response can be determined.Two types of surrogate functions are introduced to substitute the elastic DLF data. It is concluded that nonlinear low order surrogate functions are not accurate enough to predict elastic DLF. However, higher order surrogate polynomials are very accurate and can be used in computational design of protective structures.

The aim of this paper is to present the initial results of feasibility studies aimed at optimising the towing configuration of a novel, complex shape (pyramid based) and thereby untested design of floating wind farm anchor during underwater towing. The study was carried out in the real physics Marine Simulator, at the National Decommissioning Centre. This enables us to study in detail, the drag/lift forces acting on the towed anchor/s, determine the optimal anchor installation arrangement (orientation, depth, position of towing cables, number of anchors towed together in an array) and establish the effects of the operational (towing velocity, drag) and environmental conditions (sea states, significant wave height, peak wave period) on the anchor’s trajectory. The model developed is validated with computational fluid dynamics analysis to obtain representative drag and lift coefficients for the anchor during towing. Thus, this paper focuses on the calibration process to ensure robustness and relevance of the developed model in the simulator. Consistent results for the drag and lift coefficient were obtained for a range of towing speeds (0,25–3 m/s). The towing dynamics, forces acting on the anchor and the final configuration (e.g. water depth, offset angle) were obtained which in turn will allow the optimal conditions and requirements (e.g. equipment, vessel type etc.) to be recommend-ed in future studies.

The steady-state vehicle-track interaction or the interaction of the moving train with rail defects may result in unstable vibrations. The interaction of the moving train with such track defects induces additional dynamic stresses in the track system that may prove harmful for the structural health of the track. In this paper, a new iterative approach is proposed for analyzing the coupled equations of the vehicle-track system. The proposed approach can account for the wheel/rail contact loss. The results show that the proposed approach is computationally efficient and can be employed to study the effect of a wide range of track defects on the vehicle-track response. As an example, the vehicle-track response is obtained for the case where the wheel is traversing a rail-head corrugation. A loss of contact is observed when the wheel encounters the rail-head corrugation. The wheel-rail contact loss results in high impact loads over the rail beam leading to a sudden increase in rail beam deflections (by up to 85% and 57% for the undamped and damped cases, respectively).

The application of mechanically stabilized layers with stiff geogrids is an effective way for sustainable and durable construction of under sleeper structures in railways. The paper explains the basics of the theory of mechanical stabilization of granular material by geogrids. Determining the mechanical properties of mechanically stabilized layers is still a practical problem. The paper describes possible laboratory approaches combined with inverse analysis of the 3D finite element method. Smaller laboratory models are used to observe differences in the performance of different geogrids even with different grain fills. Parameters describing these differences were specified and demonstrated in specific laboratory models. The inverse finite element method was used to calibrate the measured parameters with those modelled. Some approximation of the mechanical properties of the mechanically stabilized material, such as the modulus of deformation and the Poisson’s ratio, has been achieved. Determining the mechanical parameters of mechanically stabilized layers with geogrids is very useful for evaluating their possible contribution to the structure under the sleeper in comparison with unstabilized granular material. A new innovative generation of stiff geogrids was included in the research.

Numerical modelling of railway tracks is important to understand the true behaviour of tracks and define strategies to reduce the impact of the generated forces at the wheel-rail interface on ride quality and other effects such as ground-borne noise and vibration. Most modern railway tracks use rail pads to reduce the train’s impact on the track infrastructure and to improve the dynamic behaviour of railway tracks. The rail pads provide other functions for the tracks as they modify and smooth the perceived roughness by the wheels due to tracks unevenness. Capturing the true behaviour of rail pads is significantly important to improve the accuracy of models of railway tracks. This paper utilizes a model of a track based on discretely supported beam to anlayse the behaviour of rail pads under quasi-static and dynamic loads by modelling the dynamic behaviour of the rail beam under the action of a wheel-mass and with harmonic excitation induced through relative displacement between the wheel-mass and the beam. Information and properties of rail pads as well as other track’s components are taken from the literature. The quasi-static loads are calculated based on typical information of trains. The developed model is used to examine the extent of deformation of railpads and whether this deformation is associated with linear or non-linear behaviour of the railpads.

Interpretation of acceleration time-series from rolling-element bearings is sometimes challenging if no prior knowledge of the system is available. The evaluation must adapt operational conditions or the actual value of operational parameters. In our analysis, we apply the machine learning methods and statistical indicators in the diagnosis of dynamical response in the self-aligning ball bearing with different radial internal clearance. Machine learning methods are applied for the quantification of the acceleration time-series with statistical indicators and their assignation to the specific state or clearance value. The results of the analysis allow recognizing the bearing’s condition and the clearance value based on experimental acceleration time-series. Additionally, confusion matrices are presented for showing the accuracy of proposed methods. The results of applied Machine Learning methods are on the level of around 80% in classifying the dynamical response to the specific radial clearance. The motivation of the research is to introduce it to on-site practice in the test rig.

Maglev trains are modern railway transport systems that utilize non-contact magnetic forces for levitation and propulsion. Owing to the advantage of being wear-free, they can travel at a speed that is much higher than conventional wheeled trains with lower noise emissions. For city and inter-city maglev lines, maglev trains often operate on multi-span elevated bridges. The dynamic response of the coupled maglev train-bridge system is of great interest to researchers and engineers to ensure safe travel with the ever-increasing demand for higher operating speeds from the society. This study employs the moving element analysis to efficiently compute the dynamic response of a maglev vehicle traversing a multi-span bridge with each span modeled as a simply supported beam with rotational springs connecting to the adjacent spans. The vehicle is modeled by employing the multi-body system. The vehicle and the bridge are coupled via electromagnetic forces. The accuracy of the proposed computational model is examined by comparison with results obtained using the equivalent finite element model. Parametric studies are carried out to investigate the effect of various factors on the dynamic response of the coupled system. These include the speed of the train, the bridge span length and the stiffness of the suspension system.

The previously developed model “beam inside beam” used for rail head vibrations analysis is extended by assumptions regarding viscoelastic nonlinear properties of the system. The coupled system of dynamic differential equations describes the beam-foundation structure subjected to distributed forces travelling along a beam. The upper beam, although arbitrarily distinguished, is not separated from the whole beam. This layer is considered as a vibration generator for the whole beam longitudinal axis. An assumption of nonlinear foundation stiffness is introduced as an important extension compared to existing solutions. This nonlinear system is solved by using a hybrid method based on the Adomian’s decomposition combined with a wavelet based approximation. Although description of the problem was already presented before, a new solution along with computational examples are important contribution to the field and the main novelty of the paper. The theoretical parameters used in the analysis are taken from the literature and although being close to real structures they should be validated by experimental measurements. The aim of this parametrical study is to compare the new “beam inside beam” model with classical system of double-beam resting on nonlinear foundation. This work is left however for future study.

Monitoring of roads is considered the first step in establishing a successful road maintenance program, which includes scheduling adequate maintenance to a certain road section at the right time. Road monitoring assesses the road’s condition for later analysis, which helps the prioritization of maintenance activities. Optimizing the process of scheduling and prioritizing maintenance activities is driven by cost-efficiency and is critical for preserving the overall road networks’ health and smooth operation. However, the implementation of road monitoring, using traditional equipment such as profilometers, total stations, and automated road meters, could be exceedingly time-consuming. This research proposes the usage of Artificial Neural Networks (ANNs) and dynamic vehicle accelerations to reconstruct road defects in a time/cost-effective manner. A multi-degree of freedom numerical model is used to simulate the dynamics of a vehicle passing on various road defects such as potholes and speed bumps. These road defects are reconstructed by using two different methods. The first method employs a frequency domain approach to inversely reconstruct the road defects numerically. The second method uses ANNs to reconstruct the road defects with time histories of the vehicle’s acceleration as the input to the network. The ANN model was trained by dynamic vehicle accelerations as inputs and various road defect profiles as outputs. Both methods were later compared on the basis of their accuracy and efficiency, and the ANN method was found to be more promising for implementation on experimental data.

A relatively standard brake system used on a metro vehicle showed abnormal noise and vibrations in service. Beyond passenger’s annoyance, this led to both brake calliper levers failures and premature wear of brake pads.No similar problems appeared during test benches performed by the manufacturer before and a reinforced version of the levers prevented failures nevertheless leaving unchanged high noise and vibration effects during braking. Several pads were tested without success.The paper shows how the problem was solved by means of a dynamic analysis of all the components involved and a minor redesign of a component. The impact on the existing fleet in terms of retrofit costs and times in described as well.

Ground vibration generated by rail and road traffic is a major source of environmental noise and vibration pollution in the low-frequency range. A promising and cost-effective mitigation method could be the use of heavy masses placed as an array on the ground surface near the road or track, these could be concrete or stone blocks, or specially designed brick walls, for example. This work concerns the effectiveness of such “blocking” masses. We consider propagating waves in a finite depth elastic layer assuming plane strain conditions. Given that the masses are considered solid objects we may place these on the surface, embedded or submerged in the elastic medium where a finite element method is considered as a computational solution technique. Next, we may assume the masses are aligned as a periodic infinite array and enforce periodic boundary conditions around a “unit-cell”. By consideration of propagating waves via Floquet-Bloch theory we shall investigate the existence or lack thereof of propagating surface and body waves. This analysis supports a semi-analytical lumped-parameter method assuming the blocking masses are point masses situated on an elastic waveuide. The work is enhanced by an example highlighting advantages and disadvantages of multiple-mass scatterers in terms of possible stopband intervals related to propagating surface waves.

Hyperloop is an emerging high-speed transportation system in which air resistance is minimised by having the vehicle travel inside a de-pressurised tube supported by columns. This design leads to a strong periodic variation of the stiffness (among other parameters) experienced by the vehicle. Also, along its route, the Hyperloop will encounter so-called transition zones (e.g., junctions, bridges, etc.), where the properties (e.g., support stiffness) are different than for the rest of the structure. In railway engineering, increased degradation is seen in the vicinity of these transition zones, leading to increased frequency of maintenance. This work investigates response amplification mechanisms in a Hyperloop system that arise due to the combination of a transition zone and the structure having a periodic nature. The amplification mechanisms investigated here can help prevent degradation of the Hyperloop tube close to transition zones as well as fatigue and wear of the vehicle.

Rotordynamics and periodic mechanical structures - or mechanical metastructres - are two widely explored fields of knowledge in dynamical systems, each being its own universe with very specific practices and interests. The latter has been of particularly growing interest to the scientific community over the past years, and its expansion has found several intersections with the most diverse fields of study, such as acoustics, optics and seismology. However, the combination of mechanical metastructures and rotating axially symmetric systems - rotordynamics - is still a largely unexplored subject. In this work we propose the study of a simple rotor system with periodically attached resonators. Its dynamical behavior is investigated using the system’s transfer matrix. The gyroscopic effects acting both on the rotor and the resonators create interesting phenomena such as polarization of the whirl modes and ‘invisibility’ effects. A rainbow-type arrangement of resonators is also explored for translational and flexural resonators, showing good enhancement of attenuation performance. The interaction between resonators modes and rotor modes is explored and the impacts on vibration transmissibility is evaluated. The translational resonators showed significantly superior attenuation performance, both in amplitude and bandwidth. However, unique effects such as polarized invisibility and speed dependent bandgap formation where only achievable for the flexural resonators.

Metamaterials are artificial structures which have been engineered to have properties that are not common in nature. So-called locally resonant metamaterials are comprised of a host structure in or onto which resonant structures are added on a sub-wavelength scale. Their interaction leads to stopbands, which are frequency ranges in which no free wave propagation is allowed, causing strong vibration reduction. These stopbands are typically predicted using the finite element method, assuming that geometry and material properties are known.At present, locally resonant metamaterials are mainly produced as ad-hoc demonstrators to validate academic findings. However, the currently used manufacturing approaches are not suited for mass production. Additionally, manufacturing induced changes in LRM geometry and material properties are hard to account for in the early design process, resulting in an off-design metamaterial performance.To enable widely applicable locally resonant metamaterial solutions with robust performance by design, injection moulding is a promising manufacturing process, as it comes with low cycle times and costs when used for mass production. Although good process repeatability in terms of the dynamic response of produced resonators recently has been shown, significant off-design performance can still be present due to imprecise knowledge on geometry and material properties of the realisations after manufacturing. To address this gap, this paper proposes the use of dedicated injection moulding process simulations to update structural dynamic finite element metamaterial models. Based on three resonator realisations it is shown that incorporating the outcomes of process simulations can clearly improve the resonance frequency predictions of manufactured resonators.

Acoustic meta-structure represents a class of composite structure characterized by local resonators that improve the sound absorption. In recent years, the interest for these complex systems is tremendously risen, above all for their capacity to alter waves in low-frequency ranges. Local resonators are generally based on quarter-wavelength resonance, which leads to not negligible problems: the narrow bandwidth of influence and the fact that for low-frequency design, the quarter-wavelength means a wave path too big for conventional problems where limited thickness is a requirement.Labyrinth resonators (LRs) can be the perfect solution in order to overcome these problems: the tube follows a labyrinth path that enables the resonance effect without increasing too much the sample thickness. The whole length can be stretched in other directions rather than along the thickness.Even though the resonance behavior of quarter-wavelength tubes and labyrinth resonators is quite similar, the analytical formula of quarter-wavelength tubes is not overall able to predict the natural frequency of LRs. The scope of this project is to prove that labyrinth resonance frequency cannot be predicted through conventional quarter-wavelength formula, maynly because natural frequency depends just on tube length. Moreover, a new analytical formula is proposed by considering the main parameters of labyrinth resonators: number of labyrinth branches, dimension of the single-port air-inlet, and the total length of the labyrinth.

This paper concerns a potential application of vibration control using nonlinearity. In this paper, a nonlinear boundary problem for a thin rod is considered. An incident wave propagates along the rod at frequency $$\omega$$ ω giving rise to an infinite number of reflected waves with frequencies $$n\omega$$ n ω . This paper concerns the reflected waves produced by multiple waves at frequencies $$n\omega$$ n ω incident on the boundary of a semi-infinite rod with linear and cubic nonlinear stiffnesses. Equations are truncated including the third harmonic and solved using the harmonic balance method for the case with two reflected and two incident waves. The effects of different parameters on the magnitudes of the reflected waves are studied. It is shown that the phase difference between the incident waves affects the reflected waves’ behaviour. Numerical examples are presented to find the conditions at which the magnitude of the reflected wave of the 1st harmonic is minimum and the maximum energy leaks from the 1st harmonic to the 3rd harmonic. The results show that the presence of the second incident wave can decrease the magnitude of the reflected wave of the 1st harmonic.

Metamaterials are employed to reduce vibration levels by exploiting the effects of structural periodicity. When structural elements are arranged in a periodic pattern, they act as mechanical filters, creating stop-bands. The term stop-band is often used for infinite structures, but a more appropriate term for a finite structure is attenuation band. A way of obtaining this effect is by attaching vibration absorbers, which create a local resonance stop-band plus a Bragg stop-band. The local resonance stop-band is controlled only by the properties of the attached device. The Bragg stop-band depends on the interaction between the host cell and the device. The combination of these two effects can create an attenuation zone – the so-called super attenuation band. Recent works on finite mono-coupled metamaterials have shown that asymmetric periodic structures have better attenuation properties when compared to the symmetric ones, if they are correctly orientated. This paper investigates the formation of a super attenuation band in a finite mono-coupled structure using vibration absorbers. The system is defined by the formation of a cell, which repeats along with the whole structure. The cell can be divided into sub-cells with equal or different dynamic properties. The dynamic features to form the super attenuation band are determined from the displacement transmissibility of a single cell. This analysis is extended to several cells. The results show that a super attenuation band can only occur when each attached vibration absorber is optimally tuned to its corresponding host cell in a structure comprising cells with dynamical asymmetry.

A modified formulation of Floquet propagator is proposed to analyze free wave motion in homogeneous and periodic waveguides both in the Cartesian and in the polar coordinates. For homogeneous waveguides, it substantiates the application of a Wave Finite Element Method in polar coordinates. For radially periodic waveguides, it facilitates the application of conventional (i.e., used in Cartesian coordinates) criterion to identify frequency-wise positions of pass- and stop-bands. The application of the proposed methodology is illustrated by a simple example of a wave propagation problem governed by the Helmholtz equation (a dilatation wave in a membrane).

This article analyzes wave propagation isolation and vibration attenuation strategies of a beam coupled to piezoelectric sensors periodically arranged in a given frequency band. Each piezo sensor is connected to a resonant shunt circuit. The influence on the attenuation band is due to a tunable shunt impedance associated with the corresponding piezo. Hence, the piezo’s resonate at different and neighbouring frequencies creates a tunable rainbow trap that can attenuate the energy within a bandgap characteristic. The smart metastructure is modelled by means of the spectral element method, which is a highly accurate method with a low computational cost. Flexural wave propagation is obtained using the Transfer Matrix Method with the scatter diagram plot. Results show the effect of broadband vibrations’ attenuation and propagating waves isolation. Moreover, the spectral range over which attenuation is achieved with the rainbow arrangements is on average wider than the usual metamaterials configurations.

In recent years, periodic structures such as metamaterials and phononic crystals have come to the fore in the search for innovative lightweight and compact noise and vibration solutions. The vibro-acoustic performance of these structures is often analyzed by means of dispersion curves and/or sound transmission loss calculations, using unit cell modeling. However, the link between these two performance indicators is not always straightforward. Recently, a first step to bridge this gap was taken by Yang et al. [12] who proposed a method which allows decomposing the sound transmission of infinite in-plane homogeneous media into a sum of wave mode contributions. Despite providing useful insights in the sound transmission of homogeneous structures, this method is limited to meshes with corner degrees-of-freedom only and hence not readily applicable to arbitrarily complex, inhomogeneous periodic structures. To expand the potential of this method towards identifying the most important transmission mechanisms in periodic media, this work extends the method towards periodic inhomogeneous structures represented by unit cells with arbitrarily complex meshes. The proposed methodology is applied to a periodic double panel partition thereby demonstrating its ability to provide new insights into the sound transmission mechanisms of periodic media/structures.

In this work, we explore the dynamic behaviour of a discrete model of a periodic structure under harmonic input with nonlinear stiffness. The periodic structure has a unit cell with three degrees of freedom. We devise an approach that replaces the linear stiffness characteristic of the structure with a nonlinear one in which the nonlinear stiffness coefficients provide the same strain energy. The effect of this approach on the frequency response is analysed using numerical simulation, focusing on band gaps. The approach to determining nonlinear stiffness coefficients is based on the concept of equivalent elastic strain energy. This is different from the common approach found in the literature of adding a cubic term to the linear one, resulting in an increase in the elastic deformation energy of the system. Once the strain energy of the linear system is determined, a family of possible nonlinear stiffness coefficients is found, parameterised by the ratio between the linear and cubic coefficients. This approach can be used with hardening or softening stiffness characteristics. With the nonlinear stiffness coefficients defined, the dynamic response of the metastructure shows the usual shift to high and low frequencies. In addition, some frequency ranges are shown where vibration levels can be greatly reduced when the ratio of nonlinear stiffness coefficients is increased, compared to the case where there are only linear springs. Also, it is shown that the addition of the nonlinear component in the structure can increase or decrease the distance between the resonant frequencies.

The ability of periodic structures to create stop-bands has shown great potential application in noise and vibration reduction. In mechanical and civil engineering, the studies on periodic structures typically deal with waveguides in Cartesian coordinates, while the effects of polar periodicity have been rarely analysed. However, the passive reduction of the vibrations generated from a localised excitation source on a large flexible structure can be obtained by exploiting radial periodicity effects. This paper investigates the vibration isolation properties of a plate made of a sequence of annuli with periodic alternating thickness. Two approaches are proposed and compared: the first implements a Wave Finite Element method to a small slice of the structure approximated by piecewise rectangular segments; the second deals with a standard FE model and the evaluation of the difference in the vibration before and after the insertion of n consequent periodic annuli in the finite uniform plate.

The scattering of guided waves through a coupling region is a crucial information when studying waveguides. In this paper, the second strain gradient theory (SSG) is used to describe wave transmission and reflection in a three-dimensional micro-sized medium. First, the constitutive relation of 3D SSG model is derived while six quintic Hermite polynomial shape functions are used for the displacement field. Then Hamilton’s principle is used for the weak formulation of the unit-cell’s stiffness matrix finite element stiffness, mass matrices and force vector. Eventually the wave diffusion (i.e. including reflection and transmission coefficients) are computed and discussed for various coupling conditions.

Recently, the interest in using hydrogen energy in city planning has been increasing due to the demand for environmental preservation. The primary objective of this study is to develop a conceptual design of an underground hydrogen pipeline monitoring system that improves the underground pipeline in safety, stability, and responsiveness. For this, the following research works are conducted sequentially; 1) definition of sensing information, 2) literature review, 3) deduction of conceptual design and its work process. As a result, DAS (Distributed Acoustic Sensing), DTS (Distributed Temperature Sensing) are selected as core technologies. Furthermore, a conceptual design and work process of the underground hydrogen pipeline monitoring system is developed based on the core technologies. It is expected that the application range and impact on the construction industry will be enormous due to the increasing interest in using hydrogen energy.

Since the requirements for constructing more stable and durable structures are increasing, structural health monitoring (SHM) is getting more importance nowadays. SHM relies on various methods to monitor a specific structure even live online or through direct observation of some structural parameters to decide whether a structure is damaged or not. Besides the need of getting reliable updates about the structure status, the need of making it more affordable for all types of projects is getting decisive. One of the simple implementations that are used for this purpose is to employ wave excitation at certain position of the structural part of interest and to observe the response at another predefined location of this part. After that, the observed wave propagation signal is used to calculate the damage index (DI) parameter which can be implemented in different algorithms for monitoring the current status and possibly predicting the remaining reliable operation of the structure. The signal processing procedure implemented in this work is based on the wavelet decomposition of the wave signal for the purpose of determining the energy of the propagating wave. This research is done as a part of a larger project that will study the possibility of detecting damages in different structures in general and in massive structures in specific. The paper investigates the possibilities and benefits of implementing the DI metric for monitoring the structural condition. The method will be demonstrated through a case study. Several models will be invoked to clarify its applicability. For the sake of clarity, the implementation will be done on 2D models. In addition, a 3D example based on finite element modeling should give the scope of using DI in a general case.

This work provides structural integrity of SA 387 pressure vessel steel subjected to tensile loading using acoustic emission (AE) monitoring. AE signals were detected and investigated using specialized system developed by Physical Acoustics. To detect the elastic waves released by the material under stress and owing to dislocation motion, two sensors were mounted on the surface of the specimen. AE parameters such as amplitude, energy, hits, counts, rise time and average frequency are considered in this study. Variations of these AE parameters are investigated across different regions on tensile curve such as micro-plastic deformation, yield, strain-hardening, necking and fracture by analyzing the overall acoustic signals. The results of this study revealed that intense AE signals are detected in micro-plastic as well as fracture regions. AE cumulative energy (AECE) and AE cumulative count (AECC) curves have shown sharp increment in micro-plastic deformation and fracture regions, whereas in rest of regions remained stable. The AE source is located using time difference of arrival (TDOA) method.

High-speed digital image correlation is a camera-based displacement measurement technique that has experienced increasing popularity for modal analysis. It is due to a high spatial density of measurement that provides an outstanding interpretation of mode shapes or operational deflection shapes. However, its sensitivity is typically lower than other techniques and transducers such as accelerometers or laser vibrometry. With these measurements, the estimation of any transfer function in the frequency domain is noisier in valley regions of the response, including anti-resonances. Therefore, an accurate analytical model of the response should be used for modal identification. Modal analysis algorithms perform an identification of the modal parameters and a reconstruction of the response based on the transfer function between force excitation and displacement response. This is called the frequency response function. However, force measurements are not available in many experiments, where the motion excitation is recorded instead. This is the case when the vibration is applied to the specimen through a motion in its base. This transfer function, also known as the transmissibility function, relates the motion of excitation and response, whose shape differs from the frequency response function. This difference in the response function is relevant in a relatively noisy measurement like using digital image correlation. Hence, in this work, a transformation of the transmissibility function into equivalent frequency response function, based on theoretical models, is performed prior to modal identification in base motion tests. More suitable experimental response functions are obtained, increasing the accurateness of the modal parameter estimation.

Earthquake-induced structural pounding has led to significant damages during previous earthquakes. This paper investigates the effect of pounding on the dynamic response of colliding high-rise buildings with different structural arrangements. Three 3-D buildings are considered in the study, including 5-storey building, 7-storey building and 9-storey building. Three pounding scenarios are also taken into account, i.e. pounding between 5-storey and 7-storey buildings, pounding between 5-storey and 9-storey buildings and pounding between 7-storey and 9-storey buildings. These three pounding scenarios are studied and compared with the no pounding case. The results show that the level of accelerations of colliding buildings significantly increases for all scenarios, as compared to the no pounding case. At the same time, displacements experience both increase and decrease, while the peak storey shears experience an increase due to pounding with few exceptions regarding the top storeys. Finally, pounding leads to the generation of dangerous impact forces with higher peak values experienced in taller buildings.

Damage is defined as any change to the material, geometry or boundary condition that can modify the structure’s properties or response. In the past, damage identification was performed through periodical inspection, non-destructive testing/non-destructive evaluation, or visual observation. Structural health monitoring (SHM) has emerged to transition from offline damage identification to near real-time and online damage assessment. Hence, SHM is a damage detection strategy to monitor a structure for a period using a series of continuous measurement devices, which then collect the system’s characteristics and subsequently perform statistical analysis to assess the current circumstances and health of the structure. One of the first steps for the study of SHM is damage detection followed by monitoring. Machine Learning (ML) techniques can be used to develop viable algorithms to make potential predictions. ML algorithms are therefore providing the tools needed to enhance the capabilities of SHM systems and provide intelligent solutions to past challenges. Preliminary studies have reviewed that the extension of ML into SHM has dramatically increased the system’s capabilities, providing innovative solutions to different research challenges. This work conducts a study of the use of ML to identify damage in a beam and discuss the challenge of usage, performance and implementation of each technique.

A supervised learning algorithm that uses neural networks is developed for localizing damages of beam structures. The equation of motion of beam is derived by Timoshenko’s theory and discretized by the finite element method. Damages are modelled by reducing the thickness of the beam at the damaged area. Training data for the supervised learning algorithm is generated by solving the equation of motion for variety of damages and external forces. Transverse displacements along the whole beam’s length for several instants of time are stored into one-dimensional vector and used as training data. It is shown that neural networks can successfully localize damages even for excitation frequencies that are not used in the training set.

Geosynthetics have been widely used in various geotechnical engineering applications to enhance the strength of geosystems, as well as the fact that they are economical and relatively easy to install. Separation, filtration, drainage, reinforcement and stabilization can be referred as the main functions of the geosynthetics.Regarding the reinforcement function, literature review shows that these materials can reduce the settlement and degradation of ballast. Placing geosynthetics under the ballast confines the aggregates via interlock or frictional resistance among ballast particles which then stiffen the surrounding aggregates and increase the shearing resistance of the composite system.This paper aims to present a case study where a geotextile was used for improving the subgrade bearing capacity and, therefore, reduce the settlements. The case study concerns a railway section between Elvas and Caia (border with Spain), about 11 km long. It is located at East Railway Line, a 140 km long railway line that connects Abrantes to Caia, serving as an alternative to the Center - North corridor with regard to the transport of goods. This paper describes the design, construction and installation issues related with the geotextile used.

Environmental protection has several aspects from the most popular like air or water pollution to landscape protection. One of the aspects of pollution which is neglected is protection against vibration. Meanwhile, vibrations are a pollution not only by Polish legislation but also in EU directives. One of the most subjective parameters to judge this level of vibration pollution is the human perception of vibration. It depends on individual perception which could be cause of age, sex, high of a person. Vibration excitation in buildings comes mainly from external sources such as: industrial machinery (building machines) such as vibration road rollers, pile driving etc. or transport excitation from roads, railways, subways or trams. Vibrations that are transmitted from the ground to building may influence the building structure but more often can result in discomfort of the occupants. Especially unexpected vibrations coming from transport vibration could be annoying. This paper aims to investigate if there is an influence between the type, train speed passing next to a building in which people live with the use of linear or non-linear regression. The article summarizes a lot of information that may be useful for designers or rail transport managers.

This paper reports an investigation into correlations between dynamic features of unvarnished and varnished new violins and their acoustic perceptual evaluation. Seven violins with modified plate thicknesses were tested before varnishing (in white) and after varnishing. During the first stage, the violins were dynamically tested and then acoustically evaluated by specialists in the field using a blind test. In the second stage, the testing procedure was resumed, but on the varnished violins. Thus, in the dynamic analysis of the violins were identified their signature modes, the dominant frequency, the frequency spectrum, the quality factor and their damping. In using perceptual acoustic analysis, five acoustic criteria were investigated (sound clarity, sound warmth, brightness of tone, equal sound on strings, amplitude of sounds), based on the musical audition of each violin studied, without the subjects seeing the violin or knowing their physical characteristics.

The paper deals with dynamic analysis of a two types of musical triangles, one made from stainless steel and other from alloy. The experimental method applied in this study consisted in exciting the structure with the impact hammer and recording the acoustic signals with the help of the microphone located near the sample, the acquired signals being subsequently processed in the program developed in Matlab. The time and frequency analysis showed for each drag, the frequency spectrum, the dominant frequency and the damping. Then, finite element analysis and damping simulation of the musical triangles was done with Simcenter 3D software, based on real properties of materials and experimental signals. The results between the experimental and the numerical analysis showed a good correlation between the two methods. Thus, it was observed that at the frequency of 878 Hz, the triangle vibrates in a torsional mode, followed by longitudinal vibrations (at the frequency of 1053 Hz), and at the dominant frequency, of 1877 Hz, the triangle vibrates in a transverse mode, in the plane or. The higher modes corresponding to the frequencies 3089 Hz and 3454 Hz are torsion modes.

The aim of this paper is to highlight the correlations between the anatomical quality of the resonant wood (spruce and maple) and the dynamic response of the violins. In this study were analyzed 28 violins, seven from each structural quality class of wood (A, B, C, D), according to the classification made by manufacturers. The violins were analyzed in terms of physical parameters (width of annual rings, proportion of late wood, proportion of early wood, wavelength of sycamore curly grains) after which they were dynamically tested, determining the dynamic parameters. The results of experimental investigations showed that the frequency response of violins is closely related to the anatomical quality of the wood in the structure of violin boards.

The present note considers the bowed string instruments of the violin family and focuses on the string-soundbox dynamical coupling in the low-frequency range, carrying out a numerical and an analytical modal approach in parallel and aiming at a simple theoretical model of the sound production. The numerical results show just slight aperiodic fluctuations of the amplitude and very slow phase shifts in comparison with the simple analytical solutions, suggesting the latter as a fairly realistic description of the instrument performances.

The influence of wood choices on the sound produced by string instruments is a recurrent issue in musical acoustics. Moreover, the intrinsic variability of wood’s mechanical properties requires considerable attention to any analysis attempt. This paper presents a numerical investigation of the wood mechanical properties variability influence on the sound synthesis of a simplified string instrument consisting of a single string coupled to a square soundboard. The adopted synthesis model is based on a hybrid modal approach that combines analytical expressions to describe the string vibration and numerical data obtained from a finite element analysis of the instrument soundboard. For the sound synthesis multiple sets of random wood mechanical properties are assumed. Samples are generated using Monte Carlo simulations and the synthesized sounds statistical moments are performed. Results show the influence of parametric uncertainty in the instrument sounds.

Sound propagation in ducts with elliptical cross sections and lined walls is considered using a modal decomposition approach. The acoustic fields can be described in terms of Mathieu functions and Mathieu radial functions but the use of impedance boundary conditions leads to a coupled system of infinite algebraic equations. As a result, coupling of modes with different orders arise. Expressions for the determination of the eigenvalues and eigenfunctions are derived in the general case and an approximation is introduced for small eccentricity (e < 0.3) that leads to the uncoupling of the system of equations and of the modes. For small eccentricity the eigenmodes and eigenvalues for the axial wavenumber determined were similar to those of ducts with circular cross section, which can be considered as the limiting case as the eccentricity tends to zero. The attenuation of modes is always larger in elliptical ducts when compared to circular ducts and the imaginary part of the axial wavenumber can be more than 20% higher in the examples shown. The real part of the axial wavenumber for elliptical ducts, however, can be either smaller or larger than for circular ducts, depending on the frequency and mode order. For ducts with larger eccentricities the amount of mode coupling depends on the value of the eccentricity.

Quasi-zero stiffness (QZS) indicates the characteristics of high static stiffness and low dynamic stiffness. In present study, the QZS vibration isolator has been theoretically investigated. A novel QZS vibration isolator, which consists of a vertical string, and three pairs of horizontal spring-cam-roller mechanisms, is proposed. The differential equation of the cam profile is derived. The expression of the restoring force (RF) is obtained by introducing the Gaussian function, and the dynamic characteristics of the isolator are analyzed. The results indicate that the vibration isolator meets the QZS characteristics. With the increase of the external excitation frequency, the amplitude of the system increases to the peak value, and then drops rapidly, finally decreases slowly. The force transmission rate has a similar trend that the initial value is one, and the vibration isolation effect occurs at a certain frequency. Generally, the proposed design of the QZS vibration isolator is feasible for vibration isolation in the low-frequency range.

In recent years, floating breakwaters are considered for protecting the offshore engineering structures in the deep sea. Further, to expand the capabilities of the horizontal plate breakwater, an elastic supported horizontal plate (ESHP) breakwater is developed as an eco-friendly and high energy dissipation structure. In this study, the wave dissipation effect of an ESHP breakwater is investigated with experimental tests. Then the hydrodynamic coefficients and the wave force acting on the breakwater are analyzed with a variable stiffness of support spring and wave conditions. The experimental study shows that the interaction between the radiation wave of the heaving plate and scattered waves causes additional vortex flow, and the wave height is reduced rapidly at the lee side of the breakwater. Then the wave dissipation mechanism of ESHP breakwater for incident waves with different incident wave heights is discussed. At last, the wave force changes due to plate motion are also revealed to ensure the robustness of the structure.

This study investigates the free vibration behaviour of simply supported square laminated composite plates with a square cut-out and straight fibre orientation designs. The cut-out is placed at the centre of the plate. Different cases are considered with fibre angles changed from $${0}^{\circ }$$ 0 ∘ to $${45}^{\circ }$$ 45 ∘ , at an interval of $${5}^{\circ }$$ 5 ∘ . The analytical method based on the first-order shear deformation laminate theory (FSDT) and the numerical method are both applied to obtain the free vibration properties in terms of the natural frequencies and mode shapes. The results obtained from these two methods are compared for verification. The effects of the cut-out size and fibre angles on the mode shapes are studied. It is found that the natural frequencies are influenced substantially by the size of cut-out and the fibre orientation, which can also be used to modify the mode shape and nodal line locations for the purpose of vibration suppression. With increasing the size of the cut-out of a square plate, the $${3}^{\mathrm{rd}}$$ 3 rd natural frequencies of the structure generally decrease. It is shown that the $${2}^{\mathrm{nd}}$$ 2 nd natural frequency increases with fibre angle increasing from $${0}^{\circ }$$ 0 ∘ to $${45}^{\circ }$$ 45 ∘ . The mode shape can also be tailored by the design of the fibre angle with the nodal line changing from being approximately the horizontal to the diagonal of the plate. The study provides some enhanced understanding on the free vibration properties of the laminated composite plate with a cut-out to achieve better dynamic designs.

The large rigid storage tanks are often used to store hazardous chemicals. It is very important to consider the non-linear load of strong wind or seismic excitation when designing the storage structure, because of the dangerous of petrochemical products. However, the large weight of the tank acted on the ground may cause foundation settlement over its service life. And above phenomenon is more serious in coastal areas. Meanwhile, when the planar tilt settlement of the tank is coupled with the external load such as ground motion, the local stress of the tank wall may exceed the allowable stress in related standard and lead to accident. Therefore, the sloshing phenomenon of storage tank under horizontal and tilting states is studied tentatively in this study. Three famous strong earthquake records are selected to test the dynamic response of storage tanks under different settlement conditions. And four different tilt angles are implemented. Through the overturning stability analysis, the maximum allowable tilt angle of the storage tank under dynamic load is given.

Laminated composite structures have superior material properties such as high stiffness and high strength-to-weight ratio and have been increasingly used in advanced structures such as automobiles to replace conventional metal structures to reduce weight for enhanced energy efficiency. Composite structures in practical working condition are often subjected to external excitation force, which can result in severe vibration problems. This paper investigates the vibration characteristics of rectangular laminated composite panels with various fiber orientations subjected to harmonic loading. Both free and forced vibration analysis have been carried out to obtain natural frequencies and the steady-state dynamic responses. Both analytical and numerical FE methods based on the first-order shear deformation theory (FSDT) are used to carry out vibration analysis. The numerical FE analysis is employed to validate the accuracy of proposed analytical method. The vibration transmission behaviour of laminated composite panels is compared with that of steel panels. It is found that fiber orientations have significant influence on vibration characteristics of laminated composite panels. The results explicitly show that natural frequencies and dynamic responses could be altered by designing fiber orientation for vibration mitigation. The findings provide some improved understanding on the structural design of laminated composite structures for enhanced vibration transmission behaviour.

This study investigates the vibration transmission and power dissipation behaviour of a mass-spring-damper system mounted on a conveyor belt. Coulomb friction exists between the mass and the belt moving at a constant velocity and acts as the external force for the mass. The steady-state power flow characteristics are obtained based on numerical integrations. The vibration energy dissipation at the contact interface and by the viscous damper is evaluated and quantified. The vibration transmission is measured by force transmissibility. For the system without the viscous damper, the instantaneous friction power can be positive or negative, depending on the motion characteristics of the mass. For the system with the viscous damper, in the steady-state motion, the vibration energy input caused by the friction can be dissipated by the viscous damper and also by the friction. Furthermore, effects of the magnitude of conveyor belt speed, damping ratio and friction force on the dynamic behaviour of systems are examined, and the power dissipation ratio of the system is analyzed. The results are expected to provide insights into the vibration transmission and suppression design of systems with friction.

This paper investigates the bandgap characteristics of inerter-based dual-resonator metamaterials and analyzes the low-frequency vibration suppression performance from the perspective of wave transmittance and vibration power flow. The studied metamaterial configuration is a one-dimensional mass-spring chain system with $$N$$ N identical lumped masses and each lumped mass has two resonators attached. Each unit cell of metamaterial is considered as a 1-DoF system with the effective mass varying with the excitation frequency, which can be negative in specific ranges of excitation frequencies. With dual resonators, dispersion relation diagrams show that there will be two separate bandgaps in which vibration transmission is suppressed, the frequency ranges for the bandgaps are similar to those for negative effective mass. Wave transmittance and power flow analysis also provides new perspectives to evaluate the dynamic characteristics. The results indicate that the wave transmittance is low and the energy is blocked within the bandgaps. The bandwidths of two bandgaps will not be influenced by cell position and the power transmittance of high excitation frequency is decreased as position number increases. The effect of inertance change on bandgap characteristics is examined and it shows that when the other parameters are the same, the two bandgaps are merged into one complete wide bandgap with identical inertance. These findings can provide a better understating of the dynamic behavior of dual-resonator metamaterials and their optimal design.

In this talk, a piezoelectric shunt damping is introduced to an acoustic black hole beam to form an acoustic black hole (ABH) piezoelectric composite structure, and its vibration characteristics are analyzed by a semi-analytical method. Based on the Hamilton principle, the Mexican hat wavelet is used as the shape function, and the energy method is used to solve the free and forced vibration of the acoustic black hole beam structure with PZT. The present results agree with those of the finite element method. To improve the effectiveness of the acoustic black hole, an external shunt circuit is connected to the PZT and shunt damping with the local resonance mechanism is introduced. The vibration characteristics of the beam with shunt damping and ordinary damping are compared and analyzed. The vibration suppression of ABH beam by piezoelectric shunt damping with different positions is discussed, and the optimal position is obtained. The designed acoustic black hole beam with shunt damping is significantly attenuated than the traditional damping layer acoustic black hole beam, which provides a new idea for the low-frequency vibration control of the acoustic black hole structure.

The current work involves testing the effect of using a flexible coupling between the engine and the generator on the rotational irregularity of an inverter generator Honda EU2200i. Simulation was carried on the generator’s engine Honda GXR120 Engine of 123 cm3 at 3000 rpm (6.3 Nm). An approach was developed and implemented in MATLAB environment. With reference to experimental setup, the calculated and simulated cylinder pressure curve shows a high degree of agreement. The key to higher electrical generator performance is the regularity of input speed. The obtained result of the present model shows that a higher degree of stability in the generator speed could be obtained with the introduction of a flexible coupling between the engine and the generator.

The transient vibration of the ship power propulsion system in polar conditions is considered from numerical analysis point of view. Besides linear components the models of the ship power propulsion includes damper components that typically leads to the models that are non-classically damped. Additionally, some components have relatively high ratio of the stiffness and mass and that push higher frequencies to the very high level. That is why implementation of classification rules than impose very small time step which as consequence has low numerical efficacy. The direct integration and modal superposition are compared and implemented to the practical example of the ship power propulsion. The procedure for handling non-classical damping and load which depend on position in modal superposition approach is developed, implemented and compared with direct approach. It is demonstrated that nonlinearities due to non-classical damping and displacement/position dependent forces can be efficiently handled with proposed procedure. The paper includes a case study of the electrically powered propulsion system that includes coupling and gear reducer.

Although railway system is the most sustainable mode of transport, with the lowest energy consumption, the noise induced by rail traffic in urban regions is a significant drawback. Mitigation of railway noise can be performed by different solutions, namely by the implementation of acoustic barriers. Although they offer a significant reduction in noise levels, their height makes people feel enclosed. Therefore, in the case of the railway infrastructure, the solution to the problem may lie in the use of barriers with a lower height placed close to the track. The purpose of this paper is to illustrate the development of a barrier solution to be used in a railway context through numerical modelling with Boundary Elements Method. The solutions developed were placed close to the track and have a low height (approximately 0.8m above the rail head). The geometry was defined, as mentioned, using 2D BEM from the numerical simulation of a sound wave. Thus, it was possible to match the inner face of the barrier with the geometry of the wavefront, favouring the normal reflection of the sound waves and directing the energy back to the track to take advantage of the acoustic properties of the ballast. The addition of a porous granular material on the inner face of the barrier, through the numerical simulation of an equivalent fluid and corresponding coupling to the acoustic medium, allows the control of reflections between the vehicle body and the barrier, increasing its acoustic efficiency. The solutions presented show great efficiency in terms of energy loss in the receivers with and without the barrier, i.e., in terms of Insertion Loss, the solutions presented give losses greater than 10 dB over a wide range of frequencies. In the case of the barrier with the presence of porous granular material, the barrier efficiency is even more remarkable with an increase of at least 5 dB compared to the solution without porous granular material.

Acoustic techniques remain the bedrock of pipeline leak detection, particularly for the water industry. The correlation technique, in which leak noise measurements are made at accessible locations on the pipe, either side of the leak, is used world-wide. Unfortunately, especially in the case of plastic pipes, access points are often not spaced closely enough for effective leak detection to take place. An alternative to sensing on the pipe is to measure directly on the ground surface, using discrete sensors such as geophones or accelerometers. However, to do this, the vibrational field on the ground, produced by the leak, needs to be fully understood. The present author, alongside colleagues, has developed an analytical model to show how axisymmetric elastic waves propagating within the pipe radiate to the ground surface. The model, only valid directly above the pipe, shows that, dependent on the soil properties, both a conical shear wave and a conical compressional wave may radiate into the soil, and thence propagate to the ground surface. Moreover, the axial dependence of the ground surface response mirrors the axial dependence of the waves propagating within the pipe. Here, a simplified analytical model of the conical pipe-radiated waves, which encapsulates the essential phase-related features of the more complex development described previously, is presented. This then allows a relatively simple extension to predict the off-axis ground surface as well as that directly above the pipe. Numerical simulations and experimental investigations are also carried out to demonstrate the potentialities of the proposed model to reveal the underlying physics through a simple way.

Inspection and preservation of buried water pipelines is of importance in the modern world. The wastage of water due to leaks is a global problem and existing technologies/methods to detect leaks in buried pipelines still face challenges, such as how to predict the bandwidth of measured leak noise using acoustic correlators, and what are the main factors affecting this frequency range. The leak noise bandwidth is useful information for operators to know before carrying out tests in the field, and currently there is no practical way of predicting this frequency range. This paper presents an approach to predict the bandwidth and investigates the main factors affecting it such as the distance between the sensors, wave speed and attenuation of the fluid-dominated wave, which is the main carrier of leak noise. To achieve this, a water-pipe-soil-sensor model is represented in terms of filters, allowing an investigation into the corresponding physical/geometric characteristics that affect the bandwidth of the measured leak noise. It is shown that the dominant factors are the material and geometry of the pipe, the properties of the surrounding soil and the type of transducer used.

The flexural guided wave modes in hollow cylinders can be used as a supplement to the axisymmetric guided wave testing. Thus, the excitation of specific flexural modes is essential to the guided wave testing with flexural modes. Because the wave motion of flexural modes in hollow cylinders can be approximately considered as Lamb waves or SH waves in plates propagating in a spiral path relative to the cylinder axis, helical excitation can be used to excite specific flexural modes by setting the helix angle of helical excitation. The forced responses of hollow cylinders under helical loads are analyzed with the classic Normal Mode Expansion (cNME) method, and then verified by numerical simulations. Taking the testing of an AISI 316L steel pipe as an example, helical excitation with a helical angle of 12.8° corresponding to the flexural mode T(1,1) at the excitation frequency of 50 kHz is applied, the theoretical predictions agree well with the finite element simulation results, validating the theoretical derivations.

This article examines the propagation properties of flexural wave in periodic pipelines. In order to realize the effect of boundary condition on stopbands, a pipe with two types of periodic supports is investigated: (i) pipe on translational and rotational springs, and (ii) pipe on simple supports restraint with rotational springs. Initially, the dispersion relationships for the corresponding homogeneous pipe with different boundary conditions are derived in the context of Bloch-Floquet theory of periodic structures. Successively, the accuracy of resulting band structures is verified based on the vibration transmission spectrum computed by finite element models. In the examined frequency range, both Bragg and resonance type of stopbands are evolved in the pipe with first kind of supports while in second case only Bragg type stopbands are emerged. The waves corresponding to frequency range other than stopbands indicate passbands and they can freely propagate through the pipe. Hence, in order to control a specific passband, a single-degree-of-freedom resonator is employed at the center of each span of the pipe. The width and position of stopband due to resonator depend upon the mass and stiffness properties of the resonator. Therefore, the stopbands properties can be tuned by means of properly adjusting parameters of the resonator. The dispersion relations provided herein are promising to realize the characteristics of flexural waves and to design the resonator for the similar periodic structures with different boundary conditions.

The colonisation of water pipes by macro-fouling organisms, such as barnacles and mussels, has presented a significant problem to industries drawing water from infested sources. Some of these creatures have been shown to be sensitive to low frequency sound and vibration, which have the potential to disrupt settlement and control population growth without the need for chemical interventions. The applicability of acoustic techniques to this problem is critically dependent on the achievable range of guided waves in the fluid or pipe wall which attenuate with distance from the actuation position due to mechanical losses.In this paper, fluid waves are considered owing to their typically lower attenuation rates. A fluid-filled pipe is modelled analytically as a 2D rigid walled duct. Higher order acoustic waves, which are dispersive immediately above cut-on, are focussed at a target position using a transient excitation. The input waveform is obtained by filtering and time-reversing the impulse response so as to compensate for dispersion thereby compressing the signal in time and space. Simulations show that peak pressures can be obtained that are more than an order of magnitude higher than those achievable by harmonic excitation. Future work will model focussing of waves in a 3D pipe with fluid-structure coupling for which experimental validation will be sought.

Buried pipes are used worldwide to transport water. Although they are convenient, a large amount of water is wasted during the transportation. To minimize such a problem, water companies apply different technologies to locate leaks in their pipe networks, where the buried pipe is usually located first. Electromagnetic techniques can be used to locate buried pipes, but their performance is limited by the moisture content of the surrounding soil. Active vibro-acoustic techniques have also been investigated to locate buried pipes, in which vibro-acoustic energy is introduced into the soil by an excitation source. Although they are promising, their practical application can be expensive and complex due to the setup of an excitation mechanism. The aim of this paper is to present a passive vibro-acoustic localization technique for buried water pipes, in which a leak is the source of excitation. The localization technique is based on the calculation of an approximate slope for the unwrapped phase between a pair of sensors placed on the ground surface. The performance of the two-sensor technique is tested with two datasets, one extracted from a numerical model of the buried pipe system and the other extracted from an experiment carried out on a test rig. The results highlight the potential of the two-sensor technique in locating buried water pipes.

The wave speed of pressure waves in water pipelines is sensitive to the reduction in pipe wall thickness and material strength, and it has been utilized as an indicator of water pipeline deterioration. These probing pressure waves are usually generated actively and is challenging to be incorporated into an automated senor network. This paper proposed a passive wave speed estimation method, which takes cross-correlation of the ambient noise in water pipeline networks measured by two synchronized pressure sensors to estimate the wave travel time. Field experiments were carried out in the operating water reticulation system at University of Canterbury campus for validation. In the experiments, pressure sensors were attached to fire hydrants to measure the ambient noise for 20 min. The experiment results indicate that pressure wave speed can be estimated using the proposed passive method, and the accuracy is at the same level compared with the conventional active method.

The acoustic camera is an established and highly effective device for localising acoustic sources by the use of a number of simultaneously acquired signals from an array of pressure sensors (microphones). The acoustic camera essentially provides for a highly directional sensor in which the signals arriving from the noise source in the steered main beam of the array are highly amplified relative to the background noise, which arrives at the camera from all directions outside the main beam and is therefore suppressed. The underlying principle of the acoustic camera is the beamforming data processing method which is widely applied in sensor array configurations and acts as a spatial filtering operation. The long term vision of the team is to develop an analogous device, termed here seismic camera, which allow to locate the direction of the noise sources generated from water leaks. This is an array of 3-axis geophones distributed on the ground in the vicinity of the suspected leak to localise and quantify water leaks with significantly greater accuracy and reliability than conventional methods that use just two sensors either side of the leak. The seismic camera differs from the acoustic camera since the array of data is vectorial (three axis geophones provide velocities instead of a scalar pressure field), two or more wave types (compressional, shear and surface waves) propagate simultaneously and the soil properties varies greatly with location, type and condition. In this preliminary feasibility study a time-domain solution calculated from the analytical elasticity equations is considered to generate the numerical data. The wave field is composed by spherical compressional waves radiating directly from the leak which is modelled here as a spherical cavity of radius a. The obtained numerical data is elaborated in order to look at the implementation of the Delay-and-Sum beamforming algorithm for the detection of the leak. Finally, the effects of wave reflection caused by a free surface and the sensor direction of measurement are discussed and it is shown that the beamforming algorithm works better and more precisely in infinity medium models, although the half-space model still presents satisfactory result.

Manifold vibrations in volumetric compressors systems are often the result of pressure pulsations and flow characteristics as well as compressor-generated mechanical vibrations. Standard methods of damping pressure pulsations in compressor installations using Helmholtz resonators focus on damping the main pulsation frequency resulting from compressor operation. Currently, in both refrigeration and industrial compressors, continuous operation with variable rotational speed of the compressor drive shaft is becoming a standard. As a result, the compressor, while working, generates pressure pulsations with different frequency values, which cannot be effectively suppressed using the standard method. In the works published in recent years, there are informations that shaped nozzles, introduced into the discharge manifold of compressor, can significantly affect the damping of pressure pulsations in a wide range of their frequencies. The production of damping nozzles using 3D printing techniques allows us to design unprecedented shapes. The article presents the effect of nozzles with complex shapes (impossible or difficult to produce using conventional methods) on the damping of pressure pulsations and pipeline vibrations.

The dynamic characterisation of elastic tubes is relevant to many fields in the industry. They are a key component for many processes involving fluid flow, heating, or cooling, etc., where grooves are frequently introduced to alter flow, and thus enhance heat transfer. Thin-walled tubes with helical features have been previously studied numerically and analytically, but experimental observation is still missing. In this paper, the wave propagation characteristics of a cylindrical tube with helicoidal grooves are investigated experimentally. The Wave Finite Element method is applied to a 3D model of this structure and a correlation method is used on a physical tube to experimentally observe the splitting of the degenerate dispersion branch into two. As opposed to a tube without grooves, both numerical and experimental methods show that the tubes with helicoidal grooves possess two distinctive but closely valued bending wave branches in the dispersion curves. The effect of the grooves is also visible in the mode shapes of the tubes of finite length, which will also be presented, where bending modes become unrestricted to lying in a single preferential direction.

Water loss has been one of the main concerns of water distribution companies in many countries for many years. Among the techniques used to detect and locate leaks in buried water pipes, leak-noise correlators are routinely employed. This method uses the measurements of pipe vibration due to leak noise that propagates along the pipe. Studies suggest that the predominantly fluid-borne wave carries most of the leak energy. In this paper, however, it is shown experimentally that two wave-types can propagate in an in-air plastic pipe when excited by a leak source. One wave-type is related to the predominantly fluid-borne wave, characterized by a low-frequency content. The other wave-type is predominant in the pipe wall. This wave is not well coupled to the fluid and has high-frequency content. A bespoke test rig is used to perform measurements and to collect pipe vibration data related to leak-noise under controlled conditions. The experimental data is used to show the presence of these two wave-types. Numerical results using the finite element method are also presented and validated against experimental data. Further, a discussion of the physics behind the phenomena is presented using analytical and numerical models.

For offshore wind turbines (OWTs), the monopile comprises the most common type of foundation and vibratory driving is one of the main techniques for monopile installation (and decommissioning). In practice, prior to pile installation, a pile driving analysis is performed to select the appropriate installation device and the relevant settings. However, pile penetration results from a complicated vibrator-pile-soil interaction and better understanding of the latter is necessary for an efficient installation process. During the course of installation, the interface and boundary conditions of the pile continuously alter due to the soil layering and the non-linearity of the soil reaction. In this paper, a set of experimental data from an onshore experimental campaign are employed in a numerical scheme to identify the pile strain field based on in vacuo modes of simpler yet related systems. By mapping the pile strain field onto physically-based shape functions, the evolution of the soil reaction during pile installation can be studied, in order to facilitate the back-analysis of driving records and, by extension, improve pile drivability and vibro-acoustics predictions.

Wave propagation in an elastic triangular lattice connected to a system of gyroscopic spinners is studied. The attention is focussed on waves travelling at the interface between two half-planes, where the spinners rotate in opposite directions. The relation describing the dispersive properties of these interfacial waves is given in closed form. These interfacial waves exist within a narrow frequency interval in the internal stop-band for the bulk medium, and are characterised by very low group velocity. The results of the dispersion analysis are confirmed by independent finite element simulations, which show that time-harmonic forces applied in proximity of the interface generate waves that are localised at the interface and do not propagate inside the bulk of the medium. In addition, these waves mainly propagate in one specific direction, that can be predicted from the dispersion curves and that can be reversed by changing the direction of rotation of the spinners. The model described here is an alternative to other elastic structures proposed in the literature and, considering its tuning properties, may be useful for different engineering applications including wave guiding, vibration isolation and energy harvesting.

The present paper studies the propagation behavior of shear wave through piezo-electro-magnetic material (PEMM) due to the impact of an impulsive point source at the lower boundary of PEMM. The PEMM lies between an isotropic viscoelastic layer and an isotropic heterogeneous half-space. Green’s function technique along with Fourier’s transformation has been employed to obtain the dispersion equation. For some particular cases, dispersion equation has been obtained and is validated and matched with pre-established standard results. The effects of viscoelasticity and functional gradient parameters on the phase velocity of propagating wave are shown graphically through numerical computations.

Nonlinear normal modes (NNMs) provide a useful framework for understanding nonlinear vibrations. This article discusses the NNMs of cyclically symmetric piecewise linear systems possessing N degrees of freedom. Such structures find practical applications, for example, in modeling turbomachine blade assemblies. We compute the system’s NNMs via a shooting-based method. In contrast to standard applications of this technique, our nonlinear system does not possess a clear underlying linear system, which is required to initiate the numerical method. To overcome this, we propose a linear system that incorporates cyclic symmetry and tends to the nonlinear system in the limiting case. This methodology is used to compute the NNMs of systems with 3 and 7 degrees of freedom. These examples show that the underlying linear system provides significant qualitative inferences about the NNMs, such as their mode shapes. Further, the NNMs split into groups with different frequencies based on their nodal diameters. These observations are generalized to the N degree of freedom case.

This paper presents the analysis and simulation of the properties of microstrip antennas based on metamaterial. The Matlab and Antenna Toolbox software environments were used for the simulations. CuFlon metamaterial was chosen for the simulations and subsequent fabrication of microstrip antennas. The following antennas and antenna arrays were selected: dipole, crossed dipole, microstrip antenna array with crossed dipoles, microstrip phased array for the frequency band from 1.5 GHz to 4 GHz were selected for simulations and subsequent practical experiments with CuFlon metamaterial. Problems of electromagnetic wave polarization are solved very often in practical applications, so it was necessary to take this aspect into account to the antenna design. Based on the results obtained in the simulations, the optimization of the designed antennas was performed and subsequently the antennas were fabricated. The power radiation patterns of the antennas were measured in an anechoic chamber, and the impedance and standing wave ratio were measured by a vector analyzer. The measured results were compared with the simulation results.

Numerical investigation of multi-stable vibrational energy harvesting under Gaussian white noise excitation is presented by solution of the corresponding Fokker-Planck (FP) equation. The effects of the system parameters, potential well function and noise intensity on the mean square voltage are studied. Under random excitation, for lower intensity of noise the energy harvester with single potential well outperforms the harvester with multiple deep potential wells. Beyond a threshold value of noise intensity, energy harvester with multiple well potentials outperforms as the jump from one potential well to another becomes more frequent with inter-well dynamics functioning. It is observed that the energy harvested can be optimized by suitable choice of the potential function, coupling parameters and the noise intensity.

MR fluid is being used, of late, in several applications such as vibration isolation, prosthetics and haptic devices. Application of a magnetic field controls the rheological properties of the MR fluid enabling pressure drop, high shear stress, and reversibility of these properties. The present work aims at designing a prosthetic ankle and utilizes a pressure drop formulation using the Bingham model. Subsequently, magnetostatic analysis is done for solving an approximate parametric magnetic model (PMM) assuming linear magnetic systems. The usage of PMM reduces the computation time. Finite element magnetostatic (FEMS) validation of PMM for fluid parameters has been done. Finally, the design parameters of the MR valve are optimized with a multi-objective genetic algorithm (MOGA). The selection of design parameters has been done considering anthropometric constraint of a below-knee amputee. The objective functions chosen for the optimization are to: (a) maximize pressure drop and (b) minimize mass of the damper valve, thus reducing the mass of the prosthetic ankle. The optimization results indicate effective trade-off solutions between pressure drop and mass of the damper. The most optimal design is arrived at by awarding higher priority to the mass of the MR damper.

In this paper, an approach was developed and implemented in MATLAB environment to define the effects of hydrogen addition to the combustion characteristics in SI engine. The current work involves predicting the combustion duration, the pressure and temperature and the mass of air entering the cylinder. Firstly, the combustion duration of air-fuel mixtures for different operating conditions is determined by simulation. High accuracy of the chosen model results was observer when it was compared with experimental results. Then, the Wiebe adjustable parameters were adopted to correspond to experimental data. To ensure the reliability of the modelling results, experimental results from the literature are used for comparison. Finally, a new method to predict the filling coefficient of cylinders for different hydrogen fraction is proposed and validated. Results show that these parameters are adopted effectively especially for low hydrogen fractions.

Solution for the long-wavelength region of the elastic vibration spectrum is obtained in an explicit form for a bi-layered plate based on recently proposed approach, which significantly simplifies both numeric and analytic studies of layered structures. We explore the behavior in the full range of elastic moduli, mass densities, and thicknesses of the layers on account of properly defined scaled parameters. The analysis reveals some non-trivial properties of the spectrum in composite free plates. In particular, it is shown that dependence of acoustic properties on material parameters of the added layer can be, rather unexpectedly, strongly non-monotonous. Thus, for a number of natural modes with the increase of a thickness ratio of a stiffer material the eigenfrequency may, e.g., decrease before it starts increasing, or have a sharp rise followed by a significant drop and only then resumes a steady growth. A quasi-oscillatory behavior is also possible. The property of avoided crossing between spectral branches allows to establish a continuous one-to-one correspondence between surface or interface modes and volume acoustic waves at shorter wavelengths, on one side, and fundamental or gapped modes at long wavelengths, on the other side. For composites with non-symmetric stacking the existence of a spectral property reminiscent of the A and S mode alternation of the Lamb solutions is demonstrated. We also discuss the implications of the above results to the electron-phonon heat exchange in composite nanostructures.

This work is dedicated to the research of the dynamic process in the fire automobile’s water cistern with different levels of filling. The work’s aim is to obtain data on the fluctuations of the dynamic system’s mass center that combines water and its tank during a fire automobile moving through a rough woodland at different speed. Determined data allow to predict the danger of fire automobile overturning under such conditions. During the solution of this task, the geometric configuration of the fire automobile cistern with water was modeled using the universal program complex LS-DYNA for computer modeling of dynamic systems. Time relations of cistern’s turn angles were set to recreate the dynamic impact on the fire automobile water cistern from the side of the rough woodland relief. The obtained relations were used as boundary conditions for recreating the dynamic impact of the rough woodland relief. The turning angles for the water cistern were determined depending on the relief bumps. The geometric form and parameters of these bumps were calculated using a pseudorandom number generator. Upon the explicit method and smoothed particles hydrodynamics method realized in LS-DYNA program code, the center mass fluctuating regularity for the water cistern of a fire automobile was determined in dependence of filling level and movement speed. This regularity can be used as a basis for predicting the danger of a fire automobile overturning as it moves through rough woodland.

This study evaluates the dimensional parameters (area and depth) of the swimming pool that yields to minimum roof displacement of the Reinforced Concrete (RC) building under seismic loading and also compares the roof displacement of the building considering the water as static dead load and dynamic load (considering sloshing of water). The frame model considered for this study are 10 storied Reinforced Concrete models with swimming pool centrally located at the roof. The area ratio (ratio of the area of the pool to the top floor area of the building) is varied from 0.2 to 0.8 with an increment of 0.1 and the depths of the pool considered are 1.22 m (4 feet), 1.35 m (4.5 feet), and 1.52 m (5 feet). The Linear Time History Analysis (LTHA) of the building is performed considering the three recorded earthquake time histories and eight different sinusoidal loadings. Two different approaches (IS 1893(Part 2): 2014 code method and Yu et al. 1999 Model) are used to represent fluid-structure interaction. The roof displacements are obtained minimum for the case when the area ratio is 0.4 and the depth is 4 feet (1.22 m). Furthermore, the results show that responses are different while considering water as static load and dynamic load.