19th INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, 2-7 SEPTEMBER 2007 NUMERICAL COMPUTATION OF THE ACOUSTIC PRESSURE IN A COUPLED PLATE/FLUID PROBLEM. EXPERIMENTAL VALIDATION (original) (raw)
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Acta Acustica united with Acustica, 2010
This work deals with a coupled acoustic problem: a fluid contained in a cavity whose walls are all rigid except for the top, where a flexible plate is placed. The fluid is described by means of its pressure, meanwhile for the plate the Reissner-Mindlin model is used. A finite element method to solve this coupled problem, based on Lagrange hexahedral elements in the fluid and four node MITC elements in the plate is presented. A comparison between numerical and experimental results is presented. Then, the behaviour of an absorbing layer attached to the plate is described by using a wall impedance condition and also by means of two different fluid equivalent models. Again, a comparison between numerical and experimental results is presented for the covered problem.
Proceedings of the Eleventh International Conference on Computational Structures Technology, 2012
The wave finite element method (WFE) is investigated for the computation the acoustic radiation of stiffened or non-stiffened rectangular plates under arbitrary boundary conditions. The method aims at computing the forced response of periodic waveguides (e.g. rectangular plates that are homogeneous or that contains a periodic distribution of stiffeners) using numerical wave modes. A WFE-based strategy is proposed which uses the method of elementary radiators for expressing the radiation efficiencies of stiffened or non-stiffened baffled rectangular plates immersed in a light acoustic fluid. In addition, a model reduction strategy consisting in using reduced wave bases for computing these radiation efficiencies with small CPU times is proposed. Numerical experiments highlight the relevance of the strategies.
Finite element computation of the vibrations of a plate-fluid system with interface damping
Computer Methods in Applied Mechanics and Engineering, 2001
This paper deals with a finite element method to compute the vibrations of a coupled fluid-solid system subject to an external harmonic excitation. The system consists of an acoustic fluid and a plate, with a thin layer of a noise damping viscoelastic material separating both media. The fluid is described by displacement variables whereas the plate is modeled by Reissner-Mindlin equations. Face elements are used for the fluid and MITC3 elements for the bending of the plate. The effect of the damping material is taken into account by adequately relaxing the kinematic constraint on the fluid-solid interface. The non-linear eigenvalue problem arising from the free vibrations of the damped coupled system is also considered. The dispersion equation is deduced for the simpler case of a fluid in a hexahedral rigid cavity with an absorbing wall. This allows computing analytically its eigenvalues and eigenmodes and comparing them with the finite element solution. The numerical results show that the coupled finite element method neither produce spurious modes nor locks when the thickness of the plate becomes small. Finally the computed resonance frequencies are compared with those of the undamped problem and with the complex eigenvalues of the above non-linear spectral problem.
Zenodo (CERN European Organization for Nuclear Research), 2023
This work deals with a coupled acoustic problem involving a compressible fluid and a poroelastic material contained in a cavity whose walls are all rigid except for the top, where a flexible plate is placed. The fluid is described utilizing its acoustic pressure, whereas, for the plate, the Naghdi model is used. The mechanical behaviour of the absorbing layer attached to the plate is described by using a Biot-Allard model, where the governing equations are written in the displacement-based formulation. A comprehensive three-dimensional analysis is performed, comparing numerical and experimental results and showing the advantages of using the Biot-Allard poroelastic model over other fluid-equivalent formulations, such as the Allard-Champoux model.
Journal of Sound and Vibration, 2022
Predictions of the vibroacoustic response of a point-force excited baffled thin rectangular plate immersed in a heavy fluid and near a free surface are presented using an analytical model. The equations of motion are solved by Fourier analysis, where the eigenfunctions of plate vibration form the basis of spatial expansion for fluid loading. Vibroacoustic indicators, including the plate velocity, acoustic pressure, and acoustic power, are predicted using the analytical approach and verification is performed by comparison with finite element simulations. The results have shown that variations in the height of the free surface can have a significant effect on these indicators. From the vibration response, added mass effect due to heavy fluid loading is altered and further investigated with the explicit evaluation of an added mass ratio for different free surface heights for the first five plate modes. For a given height of a free surface, standing waves can form between the free surface and baffled plate at specific excitation frequencies and slightly alters the acoustic pressure spectra. This condition also presents an effect on the acoustic power, where the first standing wave frequency dictates the efficient sound radiation to the far field.
2002 Annual Conference Proceedings
In this study, the sound-structure interaction problem in a coupled structural-acoustic system has been investigated. The novelty of this investigation is embedded in using of Finite Element Method to calculate sound pressure level. The governing differential equation for the interaction of the acoustic cavity with the flexible wall (plate) is calculated. The modal analysis of such a problem is possible, an analysis in which the decoupled equations of motion for the cavity and the flexible wall can be obtained separately. In order to accomplish this task, the coupled structural-acoustic system has been decomposed to an acoustic component, a cavity with a rigid wall, and a structural component, a flexible wall (plate). The cavity modes (eigenvalues and eigenvectors) of the cavity with the rigid wall boundary condition and structural modes of the simply supported flexible plate in a vacuum are obtained by using the finite element method. The coupled structural-acoustic equation for the pressure inside the cavity is obtained in terms of the eigenmodes of the cavity and the flexible wall. The coupling method has been successfully implemented into two classical existing problems.
Formulation of nonlinear vibroacoustic problem : Application for the thin plates
2012
This work is related to geometrical nonlinearities applied to thin plates coupled with fluid-filled domain. Model reduction is performed to reduce the computation time. Reduced order model (ROM) is issued from the uncoupled linear problem and enriched with residues to describe the nonlinear behavior and coupling effects. To show the efficiency of the proposed method, numerical simulations in the case of an elastic plate closing an acoustic cavity are presented.
Acoustic and Dynamic Response of Unbaffled Plates of Arbitrary Shape
Applied Sciences, 2021
In this study, a method for determining the effects of fluids on the dynamic characteristics of an aerospace structure and the response of the structure when it is excited by the acoustical loads produced during a rocket launch, has been developed. Elevated acoustical loads are critical in the design of large lightweight structures, such as solar arrays and communication reflectors, because of the high acceleration levels. The acoustic field generated during rocket launch can be considered as a diffuse field composed of many uncorrelated incident plane waves traveling in different directions, which impinge on the structure. A boundary element method was used to calculate the pressure jump produced by an incoming plane wave on an unbaffled plate and the fluid–structure coupled loads generated through plate vibration. This method is based on Kirchhoff’s integral formulation of the Helmholtz equation for pressure fields. The generalized force matrix attributed to the fluid loads was th...
Acoustic forcing of flexural waves and acoustic fields for a thin plate in a fluid
2014
Consistency with conservation of energy for coupled acoustic fields and plate flexural waves, discussed in another paper for this conference, is used to derive the amplitude and phase of flexural and acoustic waves for an infinite thin plate – fluid system excited by an incident acoustic plane wave. The acoustic interaction of the plate – fluid system is defined by 1. specula reflection from the plate surface, 2.transmission through the plate material and 3. plate flexural waves taking in to account fluid loading. This reproduces the well-known peak in plate flexural wave amplitudes above the coincidence frequency where the trace wavenumber of the incident acoustic plane wave along the plate equals the plate – vacuum flexural wavenumber. This is essentially a resonance with the resonant frequency that varies with the direction of the incident plane wave. The width of the resonance is governed by fluid loading which manifests as radiation damping of the flexural waves. It is found th...
Acoustic and flexural wave energy conservation for a thin plate in a fluid
2014
Although the equations of flexural wave motion for a thin plate in a vacuum and a fluid are well known, it is not easy to find a discussion of energy conservation for plate flexural waves, particularly “leaky” waves where a plate and fluid can exchange energy. Nor are formulae easily found for acoustic and flexural wave kinetic energy density, potential energy density and energy density flux including the effect of leaky waves. This paper derives formulae for acoustic and flexural energy densities and energy density fluxes, and finds the energy conservation equation for the coupled thin plate – fluid system