Structural-acoustic Coupling Research Articles

Experimental and Theoretical Study of a Structural-Acoustic Coupling System (Minimization of Sound Pressure Level of Acoustic Tube by Dynamic Vibration Absorber)

Experimental and Theoretical Study of a Structural-Acoustic Coupling System (Minimization of Sound Pressure Level of Acoustic Tube by Dynamic Vibration Absorber)

A FINITE ELEMENT STRUCTURAL-ACOUSTIC MODEL OF COUPLED MEMBRANES

A simple model displaying structural-acoustic behavior is considered. The model comprises of two parallel infinitely-long flat membranes lying on elastic foundations and the acoustic medium separating them. The structural-acoustic coupling manifests itself in that a vibrational excitation of one of the membranes triggers vibrations in the other. The governing equations are stated, and the associated finite element formulation is constructed. The model is then analyzed numerically and its vibrational properties are investigated. The proposed model is especially simple, being two-dimensional and involving a small number of parameters, but at the same time it brings to light some important features associated with structural-acoustic coupling. Therefore it may serve as a benchmark for evaluating structural-acoustic numerical schemes and as an educational tool for studying structural-acoustic coupling in a simple context.

Cracked structure-acoustic coupling problems by hybrid fractal FE and BE methods

Evaluation of the sound-structure interaction is important for effective control of noise and vibration in structural acoustic systems. Cracked elastic structure-sound interaction problems are studied by employing the hybrid fractal FEM and BEM. The degrees of freedom of the system can be reduced greatly through adopting fractal FEM in discretizing the cracked elastic structure; while the exterior acoustic field is calculated by BEM, which automatically satisfies Sommerfeld’s radiation condition. Numerical examples are given and show that the resonant frequencies of the structure-acoustic coupled system decrease as the depth of the crack increases, and that the crack has a significant effect on the acoustical field in the vicinity of the crack tip.

박막을 이용한 저주파수 영역 덕트 소음 저감 방법

Two noise reduction systems are proposed in order to overcome the geometric restriction of the reactive muffler such as an expansion chamber. First, membrane is installed as a part of a duct wall and an air cavity is covered outside membrane. Second, membrane is installed inside a duct, which gives no volume change of the duct. Structural-acoustic coupling between membrane and fluid inside the cavity and duct causes rapid impedance mismatching and thereby reflected wave. Theoretical prediction is conducted by using modal expansion approach. The results are compared with the experimental results, which show better noise reduction performance than an expansion chamber.

Use of statistical energy analysis for the prediction of Sabine absorption coefficient of modally reactive panels

Statistical energy analysis (SEA) is used to establish a relationship between the Sabine absorption coefficient of a modally reactive panel and the coupling of the panel with the sound field in a room. The acoustic-structural coupling is described by the coupling loss factors between the panel and the room. The application of the consistency relationship in SEA, which is based on the reciprocity principle, is shown to enable the coupling loss factors to be determined by directly exciting either the panel or the room. Each way of driving the acoustic-structural coupled system produces different values of the coupling loss factors and thus, of the absorption coefficient. The nature of discrepancy between the results of both ways of exciting the system is explained by using distributions of energy among structural modes of the panel and acoustic modes of the sound field, as well as distributions of modal coupling-loss factor among acoustic-structural coupled pairs of the modes. This paper provides an insight into the effect of the use of the consistency relationship on the prediction of the Sabine absorption coefficient of modally reactive panels by SEA.

Device for reducing structural-acoustic coupling between the diaphragm vibration field and the enclosure acoustic modes

A novel cap for a telephone unit is provided to de-couple the loudspeaker diaphragm from the acoustic resonance in the enclosure and dampen the first resonant frequency of the diaphragm. The cap has a flange located at an outer edge thereof and a cavity provided in the cap. The cap cavity is sized to house an acoustical speaker that is directed outwardly through an aperture in an outer casing of the telephone unit. The flange of the cap is coupled to the outer casing so that the cap covers the aperture. A gap is provided between the cap and the outer casing.

Parametric design sensitivity analysis of high-frequency structural-acoustic problems using energy finite element method

A design sensitivity analysis of high-frequency structural-acoustic problems is formulated and presented. The energy finite element method (EFEM) is used to predict structural-acoustic responses in the high frequency range, where the coupling between structural junctions and the structural-acoustic interface are modelled using power transfer coefficients. The continuum design sensitivity formulation is derived from the governing equation of EFEM and the discrete method is applied in the variation of the structural-structural and structural-acoustic coupling matrices. The direct differentiation and adjoint variable method are both developed for the sensitivity analysis, where the difficulty of the adjoint variable method is overcome by solving a transposed system equation. Parametric design variables such as panel thickness and material damping are considered for sensitivity analysis, and numerical sensitivity results show excellent agreement as compared to analytical finite difference results.

Experimental and Theoretical Study of a Structural-Acoustic Coupling System (Acoustic Tube Coupled at One End with a Flexible Panel with a Spring-Mass System Attached)

Experimental and Theoretical Study of a Structural-Acoustic Coupling System (Acoustic Tube Coupled at One End with a Flexible Panel with a Spring-Mass System Attached)

다물체계내 유연체의 구조기인 소음해석

This paper presents the method for structure borne noise analysis of a flexible body in multibody system. The proposed method is the superposition method using the flexible multibody dynamic analysis and the finite element one. This method is executed in 3 steps. In the 1st step, time dependent quantities such as dynamic loads, modal coordinates and gross body motion of the flexible body are calculated through a flexible multibody dynamic analysis. And frequency response functions of those time dependent quantities are computed through Fourier transforms. In the 2nd step, acoustic pressure coefficients are obtained through structure-acoustic coupling analyses by the finite element method. In the final step, frequency responses of acoustic pressure at the acoustic nodes are recovered through linear superposition of frequency response functions with acoustic pressure coefficients. The accuracy of the proposed method is verified in the numerical example of a simple car model.

An analytical and experimental investigation of active structural acoustic control of noise transmission through double panel systems

An analytical and experimental investigation of active control of sound transmission through double panel systems has been performed. The technique used was active structural acoustic control (ASAC) where the control inputs, in the form of piezoelectric actuators, were applied to the structure while the radiating pressure field was minimized. Results verify earlier experimental investigations and indicate the application of control inputs to the radiating panel of the double panel system resulted in greater transmission loss (TL) due to its direct effect on the nature of the structural-acoustic (or radiation) coupling between the radiating panel and the receiving acoustic space. Increased control performance was seen in a double panel system consisting of a stiffer radiating panel due to its lower modal density and also as a result of better impedance matching between the piezoelectric actuator and the radiating plate. In general the results validate the ASAC approach for double panel systems, demonstrating that it is possible to take advantage of double panel system passive behavior to enhance control performance, and provide design guidelines.

Impacts of structural–acoustic coupling on the performance of energy density-based active sound transmission control

This paper investigates numerically the performance of the active sound transmission control into a rectangular cavity through a flexible panel under the energy density-based error-sensing algorithm. Full coupling between the sound transmitting panel and the enclosed space is considered. A pure vibration actuator, a pure acoustic source and a combined control source system are used as the secondary control source in the active control and their performances are studied. Formulae for the coupled eigenfrequencies of the cavity and the flexible panel are also derived. The strength of the structural–acoustic coupling, the ratio between the first eigenfrequencies of the cavity and the panel and the difference between the excitation frequency and the coupled eigenfrequencies, especially the latter, are found to have crucial impacts on the performance of the active control regardless the type of control source used.

Investigation of the Sound Transmission into an Advanced Grid-Stiffened Structure

The noise transmission behavior of an advanced grid-stiffened (AGS) composite structure has been investigated by combining numerical and experimental methods. Structural-acoustic coupling was found to be light, permitting separate analysis of the structure and acoustic cavity. Finite element analysis permitted the resonant frequencies of acoustic cavity and structure to be calculated, which play an important role for noise transmission through the structure. Acoustic mode shapes permitted internal coincidence frequencies to be estimated and provided insight into modal pressure distributions, when considering payload location. Experimental structural and acoustic modal analysis permitted the resonant frequencies and damping ratios for the structure and cavity to be determined, which in turn were used to corroborate the FEA model. Finally, direct measurement of the noise transmission was performed based on noise reduction spectrum (NRS), which is calculated from spatial averages of the RMS acoustic pressures inside and outside of the shell. It was found that the NRS was dominated by acoustic resonances, which were marked by sharp dips in the NRS curve. Internal coincidence of the axial wavenumbers was also found to be a significant mechanism for noise transmission. External coincidence and ring frequencies were found to provide less of an impact on the overall NRS for the structure.

Active vibration control for structural–acoustic coupling system of a 3-D vehicle cabin model

This paper presents an active vibration control system for use with structural–acoustic coupling system using piezoelectric actuators and piezoelectric sensors. For modelling a complicated 3-D vehicle cabin model, the structural–acoustic coupling system is analyzed by combining the structural data from modal testing with the acoustic data from the finite element method. Through the structural–acoustic analysis program, the control plate and the control modes are selected, which are most effective for attenuating its noise. A robust LQG controller with two sensor signal filters is designed to remove the experimental problems such as the spillover effect due to uncontrolled modes. The robust LQG controller for the structural–acoustic coupling system can reduce the interior noise of the cavity as well as the structural vibration of the cabin.

Simultaneous Structural-Control Optimization of a Coupled Structural-Acoustic Enclosure

Simultaneous structural-control optimization of a coupled structural-acoustic enclosure is investigated in this paper. The whole system has a rectangular parallelepiped sound field of which the entire bottom face and the partial top face are covered with two elastic plates while the other boundaries are enclosed with rigid walls. Two point forces applied on the two plates are used as disturbance and control inputs respectively. In the sound field, one sound sensor is placed to measure the sound pressure output. Feedback H 1 control is used to generate the control input signal to reduce the noise at the sensor spot induced by the disturbance. The coupled structural-acoustic enclosure is modeled by the finite element method. The element thickness parameters of the top elastic plate along with the controller parameters are adopted as design variables for the simultaneous optimization in which the closed-loop H 1 norm is minimized. To solve the simultaneous design problem, a nested approach is used in which the controller syntheses are considered as subprocesses included in the main optimization process dealing with the structural design variables. Moreover, since the matrices are unsymmetrical for structural-acoustic coupling problems, indirect modal analysis is used to reduce the computational cost instead of the direct method. Numerical example shows that the system performance is improved significantly by the simultaneous optimization. The effectiveness and potentiality of the design approach presented in this paper are also demonstrated by the results.

Noise Reduction Techniques for Close-fitting Enclosures at Structural/Acoustic Resonance

In this paper, a close-fitting enclosure model is used to prove the existence of a common structural-acoustic coupling experimentally, which deteriorates the insertion loss performance but was not considered in the formulas developed by Refs.(1)-(3) and the classical formula used in Refs.(4)-(6). The experimental results show that an enclosure, which first anti-symmetric structural and acoustic resonant frequencies do not coincide or nearly coincide, can avoid strong structural-acoustic couplings within the air cavity. At the acoustic resonance frequencies, the insertion loss performance of an enclosure can be improved by using the aluminum fiberboard, porous aluminum, and perforated aluminum panel to absorb the sound energy. Stiffener is useful to enhance the insertion loss ability of an enclosure if the dominant frequency bands of the noise are below the first structural resonant frequency. For having good damping effect to suppress the noise radiation at structural resonant frequencies, an enclosure should be mounted with both stiffeners and damping treatments.

Experimental and Theoretical Study of a Structural-Acoustic Coupling System (Acoustic Tube with Two Flexible Panels in Opposite Sides)

In a previous paper, to clarify features of the sound field of a structure-acoustic coupling system, a rectangular parallelepiped with a flexible panel at one side is analyzed. From a practical view-point, a parallelepiped with many flexible panels is also important. In this paper, a rectangular parallelepiped with two flexible panels in opposite sides is considered. First, experimental study is conducted. Two features worth noting are found. One is that there is in the response curve two fixed points, which is unaltered by a modification of the structure. The other is that the sine modal shape can exists, whose existence is confirmed in the usual structure only when its both ends are open. Then, theoretical study is made using a one-dimentional mathematical model. It is found that this model can explain the features mentioned above.

Experimental and Theoretical Study of a Structural-Acoustic Coupling System (Acoustic Tube with a Flexible Panel at One End)

Experimental and Theoretical Study of a Structural-Acoustic Coupling System (Acoustic Tube with a Flexible Panel at One End)

Developments in structural-acoustic optimization for passive noise control

Low noise constructions receive more and more attention in highly industrialized countries. Consequently, decrease of noise radiation challenges a growing community of engineers. One of the most efficient techniques for finding quiet structures consists in numerical optimization. Herein, we consider structural-acoustic optimization understood as an (iterative) minimum search of a specified objective (or cost) function by modifying certain design variables. Obviously, a coupled problem must be solved to evaluate the objective function. In this paper, we will start with a review of structural and acoustic analysis techniques using numerical methods like the finite- and/or the boundary-element method. This is followed by a survey of techniques for structural-acoustic coupling. We will then discuss objective functions. Often, the average sound pressure at one or a few points in a frequency interval accounts for the objective function for interior problems, wheareas the average sound power is mostly used for external problems. The analysis part will be completed by review of sensitivity analysis and special techniques. We will then discuss applications of structural-acoustic optimization. Starting with a review of related work in pure structural optimization and in pure acoustic optimization, we will categorize the problems of optimization in structural acoustics. A suitable distinction consists in academic and more applied examples. Academic examples iclude simple structures like beams, rectangular or circular plates and boxes; real industrial applications consider problems like that of a fuselage, bells, loudspeaker diaphragms and components of vehicle structures. Various different types of variables are used as design parameters. Quite often, locally defined plate or shell thickness or discrete point masses are chosen. Furthermore, all kinds of structural material parameters, beam cross sections, spring characteristics and shell geometry account for suitable design modifications. This is followed by a listing of constraints that have been applied. After that, we will discuss strategies of optimization. Starting with a formulation of the optimization problem we review aspects of multiobjective optimization, approximation concepts and optimization methods in general. In a final chapter, results are categorized and discussed. Very often, quite large decreases of noise radiation have been reported. However, even small gains should be highly appreciated in some cases of certain support conditions, complexity of simulation, model and large frequency ranges. Optimization outcomes are categorized with respect to objective functions, optimization methods, variables and groups of problems, the latter with particular focus on industrial applications. More specifically, a close-up look at vehicle panel shell geometry optimization is presented. Review of results is completed with a section on experimental validation of optimization gains. The conclusions bring together a number of open problems in the field.

Structural-acoustic coupling effect on the nonlinear natural frequency of a rectangular box with one flexible plate

The nonlinear natural frequency of a rectangular box, which consists of one flexible plate and five rigid plates, is studied in this paper. The flexible plate is assumed to vibrate like a simple piston. The behavior of the structural-acoustic coupling between the flexible plate and the air cavity is analyzed by using the proposed finite element modal method. The system finite element equation is reduced and expressed in terms of the modal coordinates with small degrees of freedom by using the proposed reduction method. The system nonlinear stiffness matrix representing the large amplitude vibration can be transformed to be a constant modal matrix. The natural frequencies are determined by using the harmonic balance method to solve the eigenvalue equations of the structural-acoustic system. The effect of the cavity depth on the natural frequencies and convergence studies are discussed in detail.

Double-layer structural-acoustic coupling for cylindrical shell by using a combination of WDA and BIE

This work formulates the double-layer structural-acoustic coupling problem for cylindrical shell by using a combination of the wave-number domain approach (WDA) and the boundary integral equation (BIE). Expressions for the spectral radial velocity of the outer surface of a finite fluid-filled/submerged (FFS) cylindrical thin shell are formulated by means of the transfer matrix equation in wave-number domain. It is shown that the spectral variables on the inner surface of the shell are related to those on the outer surface of the shell. The far field sound radiation from this kind of shell is numerically evaluated for various fluid cases. An experimental verification is performed, and a good correlation between the theoretical results and the experimental results shows that the theoretical study work in this paper is correct.