Vibro-acoustic Transmission Research Articles

Two methods to improve sound transmission loss in the coincidence region

The building acoustics industry has seen little development away from traditional homogeneous materials. With the inevitable densification of housing, the severity of noise pollution within residential living environments is escalating. While the insulation of high-frequency audible sound through walls is often relatively good between 1 to 5kHz, the overall acoustic performance classification of lightweight wall systems often suffers in this region due to the coincidence effect. This effect results from a more efficient coupling between the incident sound waves and the bending waves initiated within the wall panels. We present an investigation into two contrasting methods to improve the coincidence region. These are i) a multi-layer approach, and ii) the introduction of periodic and quasi-periodic geometrical patterns in the distribution of the mass of the panels. These methods are intended to improve the attenuation of the bending waves by altering a panel's effective stiffness and creating band gaps due to back scattering. Diffuse field results were then used to verify computational models of vibroacoustic transmission based on two different approaches. The experimental and modelling results are in good qualitative agreement and indicate that the addition of impedance change features or surface variations sees a band of significantly attenuation within the targeted band indicating an effective method for either removing or shifting the coincidence effect outside of the most important part of the audible frequency region.

Exploring pulse mitigation in heterogeneous granular metamaterials

Recognizing the need for effective control of vibration and sound propagation in various industries, this study investigates the potential of designing heterogeneous granular networks for vibroacoustic transmission mitigation. It introduces new models of granular systems: decorated, stepped, and tapered 2-level branching structures. The research assesses changes in particle size (5–10 mm radii) and material properties (density and Young's Modulus) to create finely-tuned composites that significantly modulate pulse waves. The discrete element method predicts wave propagation in these granular metamaterials, comparing monodispersed chains, conventional chain networks, and the proposed heterogeneous structures. Their pulse diffusion capacity is evaluated, showing how collective responses can be adjusted by altering physical parameters like particle size and composition. Preliminary findings underscore the utility of these configurations in advancing the development of elastic and acoustic metamaterials, demonstrating a peak amplitude reduction more than five times greater than an equivalent monomer system. With versatility across a wide frequency range, these metamaterials could pioneer a new direction in impact mitigation.

Mechanical effect of reconstructed shapes of autologous ossicles on middle ear acoustic transmission.

Conductive hearing loss is caused by a variety of defects, such as chronic otitis media, osteosclerosis, and malformation of the ossicles. In such cases, the defective bones of the middle ear are often surgically reconstructed using artificial ossicles to increase the hearing ability. However, in some cases, the surgical procedure does not result in increased hearing, especially in a difficult case, for example, when only the footplate of the stapes remains and all of the other bones are destroyed. Herein, the appropriate shapes of the reconstructed autologous ossicles, which are suitable for various types of middle-ear defects, can be determined by adopting an updating calculation based on a method that combines numerical prediction of the vibroacoustic transmission and optimization. In this study, the vibroacoustic transmission characteristics were calculated for bone models of the human middle ear by using the finite element method (FEM), after which Bayesian optimization (BO) was applied. The effect of the shape of artificial autologous ossicles on the acoustic transmission characteristics of the middle ear was investigated with the combined FEM and BO method. The results suggested that the volume of the artificial autologous ossicles especially has a great influence on the numerically obtained hearing levels.

Vibroacoustic Transfer Characteristics of Underwater Cylindrical Shells Containing Complex Internal Elastic Coupled Systems

Cylindrical shells containing complex elastic coupling systems are the main structural form of underwater vehicles. Therefore, in this paper, the vibroacoustic radiation problem of underwater cylindrical shells containing complex internal elastic coupling systems is studied. Firstly, the dynamics model of the complex elastic coupled system is established through the method of integrated conductivity. The sound pressure distribution law and the general magnitude relationship between the performance index of hydroacoustic radiation and vibration isolation are investigated through numerical simulation. A strategy of global sensitivity analysis and related parameter optimization is carried out, by applying the Sobol’ method to the dynamics model. It could be concluded that the main flap of sound pressure at low and medium frequencies appears in the direction of the excitation force or the perpendicular to the excitation force, the magnitudes correspondence between the vibration level drop—power flow—hydroacoustic radiation at low frequencies can be expressed as a relatively simple function, and the vibroacoustic transmission of the system at lower order resonance frequencies is dominated by the parameter configuration of the vibration isolation device, while at higher frequencies is more influenced by the modalities of the base structure. The transfer power flow and the level drop are used as objective functions to optimise the acoustic radiation index of the coupled system, with the best results obtained when the transfer power flow and the level drop are used together as objective functions.

An active metamaterial cell concept for nonreciprocal vibroacoustic transmission

The challenge of inducing stable and robust nonreciprocal transmission of sound is seen as an important milestone on the path towards developing active acoustic metamaterials. Structures that can transmit sound or vibration in a nonreciprocal manner may be considered analogous to an electrical diode and could be useful in many applications, such as noise control and the development of invisible acoustic sensors and acoustic cloaking. This paper focuses on conceptual development and experimental validation of an active metamaterial cell that does not obey the reciprocity principle. The structural cell considered, when activated, significantly attenuates vibration transmission through it in one direction and increases it in the opposite direction. The effect is present in a broad frequency band. The loss of reciprocity is induced by using two concurrent velocity feedback loops with non-collocated sensor-actuator pairs. Inertial accelerometers with time-integrated outputs are used in conjunction with miniature electrodynamic force actuators. The study is first carried out theoretically, using an electromechanically fully coupled lumped parameter model of an otherwise flexible active structure. The derived model is used to conduct analysis of the control system stability and performance. Given that a non-collocated transducer arrangement is considered, special attention is paid to the selection of parameters of the passive system which ensure satisfactory gain margins when the system is made active. In fact, criteria for unconditional stability are derived analytically, in terms of two simple inequalities for the system with idealised sensor-actuator pairs. For realistic transducers, however, unconditional stability is not possible. Nevertheless, if the two inequalities are respected, useful gain margins of the active system can be expected. This is validated experimentally using a dedicated 3D-printed measurement test rig. A substantial reduction of vibration transmission in the desired direction, accompanied by an increase in the opposite one, is recorded experimentally. These results suggest that the control scheme proposed could be used to design an active acoustic metamaterial, which would enable the significantly different transmission of sound depending on the direction it enters such a system.

Homogenization of the vibro–acoustic transmission on periodically perforated elastic plates with arrays of resonators

The paper is devoted to the homogenization of the vibroacoustic fluid-structure interaction problem in a layer which consists of a perforated plate and a surrounding acoustic fluid. As the major novelty of the problem, we consider a plate with metamaterial properties due to embedded arrays of soft elastic inclusions serving for resonators. Such structures enable to suppress the acoustic transmission for selected frequency bands. Asymptotic analysis with respect to the layer thickness, proportional to the Reissner-Mindlin plate thickness and to the perforation period, yields a model of the homogenized metasurface. An efficient method is proposed for computing frequency-dependent effective parameters involved in the homogenized model of the layer. The derived model of the layer is intended to serve transmission conditions of the homogenized interface associated with the plate separating two fluid-filled subdomains in the global problem of the acoustic wave propagation. This model application as the homogenized interface allows for a significant reduction of the computational model. Numerical illustrations are presented.

Effect of shapes of reconstructed middle ear on sound transmission

The conductive hearing loss, which are caused by malfunctions of some parts along the auditory transmission path, quite decreases the quality of life. The conductive hearing loss is caused by a variety of defects or injuries such as the chronic otitis media, osteosclerosis, and malformation of ossicle. In such cases, the defected bones of the middle ear are often surgically reconstructed by using the artificial ear ossicles in order to increase the hearing ability. However, some artificial ear ossicles cannot work well, and the surgical procedure does not result in an increase of hearing, especially in such a difficult case of symptom, when only the bottom plate of the stapes are remained and all of the other bones are destroyed. Herein, the appropriate shapes of the artificial ear ossicle, which are suitable for various cases of the middle ear defects, can be determined by adopting the numerical prediction of the vibroacoustic transmission of sounds via the bones. In this study, the vibroacoustic transmission characteristics via the bone models of the human middle ear are calculated by using the finite-element method (FEM).

Study for the interaction between the medium in the middle ear and vibro-acoustic transmission

This study presented a quantitative evaluation index related to sound response for diagnosis of middle ear condition. The signal transmission paths for human perception of sound are divided into bone conduction and air conduction, respectively, depending on the path through which vibration and sound are transmitted. The components of auditory system that can affect the sound signal variability include temporal bone, ear canal, eardrum, and middle ear cavity. The specific acoustic impedances were obtained through simple geometric model of the auditory components, and the sound transmission mechanism was implemented through the outer-middle ear circuit model. The frequency range corresponding to the resonance characteristics of each components were calculated. The response difference for the medium of middle ear was confirmed by deriving frequency response function between the input sound and the output sound in the frequency domain through the transfer function method. The reliability of the algorithm was confirmed through the ROC curve, and individual evaluation indexes were derived according to the priority factor between classification accuracy and error rate.

Prediction of vibroacoustic transmission characteristics through double-plate floor structures by using finite-difference time-domain analysis

Prediction of vibroacoustic transmission characteristics through double-plate floor structures by using finite-difference time-domain analysis

Homogenization of the vibro–acoustic transmission on perforated plates

The paper deals with modelling of acoustic waves which propagate in inviscid fluids interacting with perforated elastic plates. The plate can be replaced by an interface on which transmission conditions are derived by homogenization of a problem describing vibroacoustic fluid-structure interactions in a transmission layer in which the plate is embedded. The Reissner-Mindlin theory of plates is adopted for periodic perforations designed by arbitrary cylindrical holes with axes orthogonal to the plate midplane. The homogenized model of the vibroacoustic transmission is obtained using the two-scale asymptotic analysis with respect to the layer thickness which is proportional to the plate thickness and to the perforation period. The nonlocal, implicit transmission conditions involve a jump in the acoustic potential and its normal one-side derivatives across the interface which represents the plate with a given thickness. The homogenized model was implemented using the finite element method and validated using direct numerical simulations of the non-homogenized problem. Numerical illustrations of the vibroacoustic transmission are presented.

Global sensitivity analysis of analytical vibroacoustic transmission models

Noise reduction issues arise in many engineering problems. One typical vibroacoustic problem is the transmission loss (TL) optimisation and control. The TL depends mainly on the mechanical parameters of the considered media. At early stages of the design, such parameters are not well known. Decision making tools are therefore needed to tackle this issue. In this paper, we consider the use of the Fourier Amplitude Sensitivity Test (FAST) for the analysis of the impact of mechanical parameters on features of interest. FAST is implemented with several structural configurations. FAST method is used to estimate the relative influence of the model parameters while assuming some uncertainty or variability on their values. The method offers a way to synthesize the results of a multiparametric analysis with large variability. Results are presented for transmission loss of isotropic, orthotropic and sandwich plates excited by a diffuse field on one side. Qualitative trends found to agree with the physical expectation. Design rules can then be set up for vibroacoustic indicators. The case of a sandwich plate is taken as an example of the use of this method inside an optimisation process and for uncertainty quantification.

Prediction of Interior Noise in a Sedan Due to Exterior Flow

Aero-vibro-acoustic prediction of interior noise associated with exterior flow requires accurate predictions of both fluctuating surface pressures across the exterior of a vehicle and efficient models of the vibro-acoustic transmission of these surface pressures to the interior of a vehicle. The simulation strategy used in this paper combines both CFD and vibro-acoustic methods. An accurate excitation field (which accounts for both hydrodynamic and acoustic pressure fluctuations) is calculated with a hybrid CAA approach based on an incompressible unsteady flow field with an additional acoustic wave equation. To obtain the interior noise level at the driver's ears a vibro-acoustic model is used to calculate the response of the structure and interior cavities. The aero-vibro-acoustic simulation strategy is demonstrated for a Mercedes-Benz S-class and the predictions are compared to experimental wind tunnel measurements.

A graph cut strategy for transmission path problems in statistical energy analysis

In this paper, it is shown how a strategy based on algorithms for computing cuts in undirected networks, can be applied to reduce energy transmission in realistic statistical energy analysis (SEA) models, with the sole modification of a limited number of internal and coupling loss factors. The frequency dependent case of SEA systems with multiple sources and targets is considered. A mathematical justification for the strategy is also provided, which relies on an analysis of the series expansion of the energy vector, in terms of the powers of the SEA graph adjacency matrix. A numerical example of vibroacoustic transmission in a simple test building has been included to show the performance of the approach.

Modes of Wave Propagation and Dispersion Relations in a Cylindrical Shell

This paper reinvestigates the classic problem of the dispersion relations of a cylindrical shell by obtaining a complete set of analytical solutions, based on Flügge’s theory, for all orders of circular harmonics, n=0,1,2,…,∞. The traditional numerical root search process, which requires considerable computational effort, is no longer needed. Solutions of the modal patterns (eigenvectors) for all propagating (and nonpropagating) modes are particularly emphasized, because a complete set of properly normalized eigenvectors are crucial for solving the vibration problem of a finite shell under various admissible boundary conditions. The dispersion relations and the associated eigenvectors are also the means by which to construct transfer matrices used to analyze the vibroacoustic transmission in cylindrical shell structures or pipe-hose systems. The eigenvectors obtained from the conventional method in shell analysis are not as conveniently normalized as those commonly used in mathematical physics. The present research proposes a new alternative method to find eigenvectors that are normalized such that their norms equal unity. A parallel display of the dispersion curves and the associated modal patterns has been used in the discussion and shown to provide a more insightful understanding of the wave phenomena in a cylindrical shell.

On-resonance transmissibility methodology for quantifying the structure-borne road noise of an automotive suspension assembly

In this paper, a methodology is presented for the analysis of the structure-borne noise transmission paths for an automotive suspension assembly. First, a fully-instrumented test bench consisting of a wheel/suspension/lower suspension A-arm assembly was designed in order to identify the vibro-acoustic transmission paths (up to 250 Hz) for white noise excitation of the wheel. Second, frequency response function measurements between the excitation signal and each suspension/chassis linkages are used to characterize the different transmission paths that transmit energy through the chassis of the car. Finally, a synthesis of the major resonances of the suspension is drawn, with the objective of indicating which suspension transfer paths contribute the most to the structural forces transmitted to the chassis. On-resonance force transmissibility factors (ORTF) were calculated to provide an overall classification of the system resonances to the vibration transmission through the individual suspension linkages and in all axes.

EXPERIMENTAL DETERMINATION OF PASS-BY NOISE CONTRIBUTIONS FROM THE BOGIES AND SUPERSTRUCTURE OF A FREIGHT WAGON

Pass-by noise from freight trains on straight tracks is dominated by rolling noise. The main contributions are generally accepted to originate from vibrations of the track and the wheels. However, there is uncertainty about the contributions from the bogie and the wagon superstructure. This article describes experimental methods to determine these. The methods combine vibration measurements on a rolling wagon and measurements of structural and of vibro-acoustical transfer functions under static conditions. Firstly, an inverse method is used to determine the equivalent structural excitation of a wagon. Secondly, two reciprocity methods are described for detailed vibro-acoustic transmission path analysis, with the wagon parts excited by the equivalent forces. As an example, some data will be shown from experiments on a widely used freight wagon. It appears that the contributions from two bogies and from the wagon superstructure are respectively 20 and 30dB(A) lower than the measured pass-by noise levels. Detailed information is obtained about the ranking of sub-areas which contribute to the sound radiation. The results illustrate the practical value of the methods even in the case of weak partial sources.

Prediction of the vibro-acoustic transmission loss of planar hose-pipe systems

Vibro-acoustic energy travels through hose walls as longitudinal waves and flexural waves, apart from the sound waves through the fluid medium inside. Longitudinal waves in the hose wall are coupled to the sound waves inside by means of the hose-wall Poisson’s ratio. Both in turn get coupled to bending or flexural waves because of the energy transfer or interaction at the bends. For any of these three types of waves incident on one end of a hose, waves of all the three types may be transmitted on the other end because of their dynamical coupling with one another. Therefore, in the present paper, expressions have been derived for the 3×3 transmission loss matrix for a two-dimensional or planar piping system in terms of elements of the overall 8×8 transfer matrix of the system. These expressions have then been used in a comprehensive computer program to evaluate the vibro-acoustic performance of hoses, with particular application to the automotive climate control systems with gaseous as well as liquid media. Finally, parametric studies have been made that have led to some general design guidelines.