The Acoustic Black Hole (ABH) is a technique for passive vibration control that was recently developed within the Structural Dynamics and Vibroacoustics communities. From a general perspective, the ABH effect is achieved by embedding a local inhomogeneity in a thin-walled structure, typically a beam or a plate. This inhomogeneity is characterized by a variation of the geometric properties (although

The traditional linear vibration isolation system has the effect of vibration isolation only on the condition that the excitation frequency is more than 2ωn. Quasi-zero stiffness vibration isolation system has the characteristic of “high static and low dynamic”, which can effectively solve this problem. When subjected to static load, the system has high stiffness to provide enough support force for

This paper presents a closed-form frequency equation that predicts the modal coupling between the adjacent axial and bending modes of a beam with a transverse open crack. The final form of the proposed frequency equation is simply expressed in terms of the uncoupled frequency equations of intact and cracked beams for any type of support condition of the beam by introducing an axial–bending modal coupling

We present a general formulation for problems of sliding structures and axially moving beams that undergo large deformations. The formulation relies on a coordinate transformation that facilitates the analysis of beams characterized by a large sliding motion, for which conventional approaches typically become inefficient. The transformation maps variable domains in the material coordinate, which result

This paper proposes a proportional viscous damping model that is computationally very efficient for response history analysis of a large-scale structure with a large number of degrees of freedom. The proposed model is based on a bell-shaped basis function parameterized by the frequency and damping ratio at its peak. Any damping ratio curve in the frequency domain can be easily matched by adding several

A fluid-structure interaction scheme for numerical simulation of actively controlled bridges subject to flutter instability is proposed in this work. In order to suppress or attenuate dynamic instabilities induced by the wind action on long-span bridges, control systems are proposed considering aerodynamic appendices and winglets attached to the deck structure, where control forces are continuously

In this work we carry out a numerical study of the influence of the upstream Mach number on the flutter of a three-dimensional, cantilevered, flexible plate subject to a subsonic, inviscid, open flow. We have assumed a linear elastic model for the plate and that the fluid flow is governed by the linearized potential theory. The fluid equations are solved by means of a doublet point method to obtain

A new method is proposed for precise shaping of the acoustic radiation of a vibrating plate. The potential applications of this method are: to optimize acoustic radiation of a plate employed as a sound source; and to enhance transmission loss of a plate used as a noise barrier, both in passive or active control solutions. The proposed method is based on mounting several additional ribs and masses (passive

Helmholtz resonators are commonly used as narrowband sound absorbers in room acoustics applications. Previous research has shown that Helmholtz resonators can also be used to improve the sound transmission loss of double walls. The focus of this paper is the broadband improvement of the transmission loss of double walls in the low frequency region by tuning the Helmholtz resonators inside the cavity

Acoustic black hole (ABH) indentations have proven to be an efficient way for reducing vibrations on straight beams and plates. However, many built-up structures in the naval and aerospace sectors involve curved beams and shells, so there is a need to check whether the ABH effect could be also beneficial for them. To date, such issue has not been yet addressed and in this work some initial steps are

Laser Doppler Vibrometer (LDV) has been performed as a tool to observe stress fields of ultrasound longitudinal wave inside transparent solids due to its high sensitivity and intuitiveness. Besides, this method is only sensitive to dynamic stress and has no response to static stress, so it has the advantage of not being affected by residual stress in transparent solids. However, this method has limitations

The self-noise of an isolated controlled-diffusion aerofoil is investigated using direct noise computations. The high-order finite difference solver HiPSTAR is used to conduct four large eddy simulations and one direct numerical simulation. The motivation is to investigate the multiple sources of aerofoil self-noise on a realistic compressor blade geometry, the physical mechanisms leading to the generation

This paper investigates the additional damping effect that vehicle-bridge interaction (VBI) has on the vibration of bridges. It also establishes a generic analytical expression that accurately predicts the additional damping effect for a broad class of (conventional and high-speed) train-bridge systems. The analysis adopts the classic assumption of continuous contact between the rails and the wheels

This paper presents solutions and comparisons for guided wave motion (Lamb and shear horizontal) due to tensile and shear cracks in an isotropic plate using elastodynamic reciprocity. Cracks are treated as point sources, which for the ease of wave motion analysis have equivalent body force representations. The paper then outlines the use of elastodynamic reciprocity for obtaining the wave motion due

Both the hydrodynamic and acoustic pressure on automotive front side window have the potential contribution to the interior sound pressure of the vehicle. The corrected force analysis technique (CFAT) is employed to extract the acoustic pressure on front side window. The sensitivity of all pressure fluctuation inside and outside the vehicle to the variation of wind speed, yaw angle and the geometry

Broadband stochastic excitations from environment such as seismic activities, sea waves, wind gusts, and tremors can lead to the terrible damages of tall structures and buildings which usually have a low amount of vibration damping. Tuned liquid dampers (TLD) have been considered for around thirty years regarding their ability for passive suppression and absorb the vibration energy in such structures

New theorems for moments of the first passage time of one dimensional nonlinear stochastic processes with an entrance boundary xe are formulated. This important class of one dimensional stochastic processes results among others from approximations of the energy or amplitude of second order nonlinear stochastic differential equations. Since the diffusion of a stochastic process vanishes at an entrance

In numerous engineering structures with local nonlinearities, the nonlinear effects are usually localized and most parts of the structures behave linearly. Considering this, a reduced-order modelling technique for generally damped systems with localized nonlinearities is proposed. Firstly, the linear parts with non-proportional damping of the system is separated to form one component, which can be

This paper presents a consistent corotational formulation for the geometric nonlinear dynamic analysis of 2D sliding beams. Compared with the works of previously published papers, the same cubic shape functions are used to derive the elastic force vector and the inertia force vector. Consequently, the consistency of the element is ensured. The shape functions are used to describe the local displacements

This study investigates the amplitude dependent damping behaviour of the fundamental mode for composite tubes under dynamic excitations. For this purpose, a closed form solution of damping ratio is derived for a cantilever tube subjected to harmonic base excitation while accounting for stress fields, material properties and cross-sectional configurations of the member. Shake table experiments are performed

An experimental-based approach to flutter speed uncertainty quantification in aeroelastic systems is developed. The proposed technique considers uncertainty from a post-manufacture perspective. Variability due to manufacturing tolerances, damage and degradation is formulated as a stochastic structural modification to a single set of measured receptance data. The Sherman-Morrison formula is exploited

For floating bodies in shallow sea, the prediction of acoustic radiation requires consideration of complex acoustic environments. Generally, the influence of the sea surface, seabed and sound speed profile cannot be neglected. In this paper, a relevant calculation method in shallow sea considering the sound speed profile is developed by introducing the Green's function corresponding to a complex ocean

Fricative/s/is known to be pronounced by jet generation and subsequent impact on walls of the oral cavity. The prediction of acoustic characteristics of/s/is an ongoing research topic due to the aeroacoustic nature of the sound source. In this study, acoustic characteristics are modeled using the multimodal theory with monopole and dipole sources positioned in the oral tract waveguide. The oral tract

In this paper, a novel approach to model updating for a large-scale railway bridge using orthogonal diagonalization (OD) coupled with an improved particle swarm optimization (IPSO) is proposed. Particle swarm optimization (PSO) is a well-known and widely applied evolutionary algorithm. However, as other evolutionary algorithms (EAs), PSO has two main drawbacks that may reduce its capability to tackle

This paper presents a nonlinear multi-modal energy harvester and vibration absorber (EHVA) for both energy harvesting and vibration suppressing in low-medium frequency band. Two different methods are applied to broaden the effective bandwidth. Not only the multi-modal shapes of EHVA are designed, but also the hysteresis property of nonlinear softening spring is realized by a novel permanent magnets

The fluid insert technology is an active noise reduction technique that has been shown to successfully reduce supersonic jet noise in model scale nozzles. The goal of this paper is to better understand the noise reduction mechanisms of fluid insert jets using Doak's Momentum Potential Theory and Spectral Proper Orthogonal Decomposition applied to an LES database. It is found that the use of fluid inserts

To improve the passive control effect on low frequency micro-vibration of structures with high static support stiffness, this paper proposed a high-static-low-dynamics stiffness vibration isolator (HSLDs-VI). This device is equipped with a magnetic negative stiffness mechanism that can provide high magnetic negative stiffness to counteract high static stiffness. The magnetic mechanism is composed of

Damping of coupled bending-torsion beam vibrations is realized by local actuators, operating axially on an end cross-section of a fully three-dimensional structure by a collective positive position feedback control with a spatial filter that specifically targets the out-of-plane warping component of the coupled response. To reduce the computational effort, a beam element model is introduced, in which

This paper proposes a method to estimate the rotational stiffness at the coupled points of an assembled system. Conventional test-based rotational stiffness evaluation methods are sensitive to measurement errors and require a separate jig for testing. In contrast, as the proposed method uses the natural frequency shift phenomenon resulting from the addition of mass, the measurement error is relatively

Dynamically large structures can have many closely spaced modes. A particular example is an extruded aluminium panel used for building high-speed trains. Such a structure may be modelled deterministically with a large number of degrees of freedom (dofs), or statistically represented as a statistical energy analysis (SEA) system having particular SEA parameters. In both cases, experimental modal parameter

Data integrity has become more critical with the growth in remote semi-automated machine health monitoring. The mounted resonance frequency of an accelerometer, if correctly mounted on a flat surface, is normally quite repeatable, for example at different locations on the same object. A method has recently been developed which largely separates forcing and transfer functions in response signals, by

In this paper, a method for crack detection in beams is proposed by applying the concept of defect modes in band gaps of imperfect phononic crystals (PCs). In the proposed crack detection method, a periodic array of concentrated masses is attached on a straight beam to generate the Bragg band gaps. Then, a crack in the beam might induce the defect modes in some of the band gaps, whose frequency depends

Many convex regularization methods, such as the classical Tikhonov regularization based on l2-norm penalty and the standard sparse regularization method based on l1-norm penalty, have been widely investigated for impact force identification. However, in many practical applications, these regularization methods commonly underestimate the true solution. In this paper, we propose a non-convex sparse regularization

The present work aims at finding an approach to calculate fatigue damage from three-dimensional vibration measurements, with a key objective to define a reliable measurement quantity to predict local stresses. Existing theoretical concepts highlight an exploitable relation to modal velocity. A hysteresis counting based on velocity measurements as well as damage accumulation using S–N curves is proposed

The paper deals with the steady state responses of an infinite Euler-Bernoulli beam resting on a nonlinear foundation under a harmonic moving load. Greatly different from previous works, the nonlinear partial differential governing equation of the beam motion is converted to two nonlinear Volterra integral equations by using the Fourier transform, residues Theorem and the convolution theorem. The Volterra

This paper presents a theoretical study on the scaling laws of electromagnetic and piezoelectric seismic vibration energy harvesters, which are assembled from discrete components. The scaling laws are therefore derived for the so called meso-scale range, which is typical of devices built from distinct elements. Isotropic scaling is considered for both harvesters such that the shape of the components

Acoustic exterior problems are in this paper solved numerically using the Astley-Leis infinite element method (IFEM). Normal modes can be determined thanks to the frequency independence of the system matrices. Convergence properties of the harmonic sound pressure solution as well as of normal mode eigenvalues are investigated for two-dimensional elliptical computational domains to estimate the essential

While simulations of the measured biodynamic responses of the whole human body or body segments to vibration are conventionally interpreted as summaries of biodynamic measurements, and the resulting models are considered quantitative, this study looked at these simulations from a different angle: model calibration. The specific aims of this study are to review and clarify the theoretical basis for

Breath sounds are often used to aid in the diagnosis of pulmonary disease. Mechanical and numerical models could be used to enhance our understanding of relevant sound transmission phenomena. Sound transmission in an airway mimicking phantom was investigated using a mechanical model with a branching airway network embedded in a compliant viscoelastic medium. The Horsfield self-consistent model for

This paper provides new formulations to derive the impulse response matrix, which is then used in the problem of load identification with application to wind induced vibration. The applied loads are inversely identified based on the measured structural responses by solving the associated discrete ill-posed problem. To this end - based on an existing parametric structural model - the impulse response

The relationship between the vibration transmissibility and driving-point response functions (DPRFs) of the human body is important for understanding vibration exposures of the system and for developing valid models. This study identified their theoretical relationship and demonstrated that the sum of the DPRFs can be expressed as a linear combination of the transmissibility functions of the individual

The method of tailored Green's functions advocated by Doak (Proceedings of the Royal Society A254 (1960) 129 - 145.) for the solution of aeroacoustic problems is used to analyse the contribution of the mucosal wave to self-sustained modulation of air flow through the glottis during the production of voiced speech. The amplitude and phase of the aerodynamic surface force that maintains vocal fold vibration

The objectives of this study were to develop models of the hand-arm system in the three orthogonal directions (xh, yh , and zh ) and to enhance the understanding of the hand vibration dynamics. A four-degrees-of-freedom (DOF) model and 5-DOF model were used in the simulation for each direction. The driving-point mechanical impedances distributed at the fingers and palm of the hand reported in a previous

Model updating procedures are applied in order to improve the matching between experimental data and corresponding model output. The updated, i.e. improved, finite element (FE) model can be used for more reliable predictions of the structural performance in the target mechanical environment. The discrepancies between the output of the FE-model and the results of tests are due to the uncertainties that

An analysis is made of the fluid-structure interactions involved in the production of voiced speech. It is usual to avoid time consuming numerical simulations of the aeroacoustics of the vocal tract and glottis by the introduction of Fant's 'reduced complexity' equation for the glottis volume velocity Q (G. Fant, Acoustic Theory of Speech Production, Mouton, The Hague 1960). A systematic derivation

The steady state response motion of a base excited cantilever beam with circular cross-section excited by a unidirectional displacement will fall along a straight line. However, achieving straight-line motion with a real cantilever beam of circular cross-section is difficult to accomplish. This is due to the fact that nonlinear effects, small deviations from circularity, asymmetric boundary conditions

The flow-induced vibrations of a single-layer vocal fold model were investigated as a function of vocal fold stiffness, and subglottal and supraglottal acoustic loading. Previously, it was reported that the single-layer vocal fold model failed to vibrate when short, clinically-relevant tracheal tubes were used. Moreover, it was reported that the model had a propensity to be acoustically driven, and

Quadratic matrix polynomials are fundamental to vibration analysis. Because of the predetermined interconnectivity among the constituent elements and the mandatory nonnegativity of the physical parameters, most given vibration systems will impose some inherent structure on the coefficients of the corresponding quadratic matrix polynomials. In the inverse problem of reconstructing a vibration system

Nonlinear dynamic analysis and model simulations are used to study the nonlinear dynamic characteristics of vocal folds with vocal tremor, which can typically be characterized by low frequency modulation and aperiodicity. Tremor voices from patients with disorders such as paresis, Parkinson's disease, hyperfunction, and adductor spasmodic dysphonia show low-dimensional characteristics, differing from