Research On The Sound Radiation From Plates And The Sound Transmission Of Panels Based On The Coupled Sound Space-panel System

The sound insulation structures are widely adopted to passively control the sound transmission throught the coupled sound spaces.The transmission loss(TL)of those structures has been studied by researchers for almost a half century in which the experimental and analytical methods are the mainly two ways to be used.However,the later one is more widely adopted to derive the TL since it is much a timesaving and economical way to do the same study.Interaction between acoustic space and flexible structures is an important problem to study the sound transmission of those panel structures.In this thesis,the sound radiation of panels and interaction between sound space and panels are deeply studied to derive the characteristic of the sound transmission through the panels or apertures.The sound radiation from elastically restrained plates is studied using the Spectro-Geometric Method(SGM),which is a meshless and parametric modeling technique.By adopting the Rayleigh-Ritz procedure and the Rayleigh integral,a vibro-acoustic coupling system is established.This model studies the situation when the plate is immersed in heavy fluid,such as water,in which the strong coupling between the structure and acoustic media should be fully considered.The influence of the boundary conditions on the radiated sound power and sound reduction provided by the decoupling layer based on the locally reacting model is studied.The non-uniform distributed decoupling layer is also studied to analyze the sound reduction effect.The sound intensity on the outer surface of the decoupling layer is investigated and tends to be uniform along the plate scale with increasing thickness of the decoupling layer.The break-out sound from a cavity via an elastically mounted panel is predicted in this paper.The vibroacoustic system model is also derived based on SGM in which the solution over each sub-domain is invariably expressed as a modified Fourier series expansion.Unlike the traditional modal superposition methods,the continuity of the normal velocities is faithfully enforced on the interfaces between the flexible panel and the(interior and exterior)acoustic media.A fully-coupled vibro-acoustic system is obtained by taking into account the strong coupling between the vibration of the elastic panel and the sound fields on the both sides.The typical time-consuming calculations of quadruple integrals encountered in determining the sound power radiation from a panel has been effectively avoided by reducing them,via Discrete Cosine Transform(DCT),into a number of single integrals which are subsequently calculated analytically in a closed form.Several numerical examples are presented to validate the system model,understand the effects on the sound transmissions of panel mounting conditions,and demonstrate the dependence on the size of source room of the"measured" transmission loss.Experimental determination of the acoustic characteristics of a sound insulation panel often requires a standard measurement suite consisting of two rooms connected via a window onto which the panel is mounted.While such a facility is quite expensive to build and maintain,the measurement results can show a significant variance,especially at low frequencies.To better understand the variance of the results and identify the directions for improving the sound insulation designs and applications,a virtual testing capability is developed based on an analytical parametric model.This model consists of a source room,a receiving room,and a partition wall with a mounting window.This model can be effectively used to virtually test the acoustic performance of sound insulation designs under different environments and application conditions.Modeling sound transmission among acoustic media through mix separations,consisting of both flexible structures and apertures,is a challenging task.In the present works,a virtual panel treatment is proposed to model the apertures in such complex vibroacoustic systems.The eigenfrequencies and modal shapes of plates with cut-outs of any shapes are studied by setting the density of cut-outs to be infinitely small.Hamilton's principle is used with the Fourier series that does not depend on the shape or the number of cut-outs.The results obtained by this method are validated against those derived by the finite element method.The panel in the vibroacoustic system is replaced by the one with cut-outs to get the new vibroacoutic system consisting of both panels and apertures.The continuity of the sound pressure at the points located on the both sides of the apertures is validated to draw the conclusion that the virtual panel treatment is accurate to handle those problems.The effects of the sizes of the cut-outs and boundaries of the panel on the coupled systems are studied.A unified approach is presented to study the acoustic characteristics of the cavity with arbitrarily shapes by transforming the cavity into a rectangular one.The rectangular cavity in the cavity-panel-cavity model is replaced by the irregular one to derive the unified vibroacoustic coupling system which could act as the new sound transmission suite.The coupling system that a panel is backed by the irregular cavity is also studied.The sound power impinging upon and radiated from the panel are analyzed with the shape of the cavity changing.To validate the model established in this thesis,experimental tests are performed including the models of:cavity-panel-cavity and cavity-apertures-cavity in which the rectangular cavity and the irregular cavity are both setup.The results obtained by the method proposed in this thesis and those derived by the experiments match very well.The errors in the comparison are also analyzed.