Vibro-Acoustic Analysis Of Flexible Panel And Its Coupled Cavity System With Consideration Of Complex Factors

Flexible panel structure and cavity coupling system can be found in various engineering fields,such as marine and astronautical engineering.A clear understanding on its dynamic characteristics and structural-acoustic coupling mechanism is the necessary prerequisite and foundation to develop the low noise design and noise control of such complicated systems.Along with the increasingly development of engineering technology,the boundary conditions,material properties,and system composition of the practical flexible structures become complicated.To deal with this problem,the dynamic behaviors of structural-acoustic coupling systems considering complex factors are studied in this thesis.To further study the in-plane vibration of rectangular panel structure,the non-uniform boundary condition with any distribution function is considered.The displacement functions for the in-plane vibration are determined by two-dimensional improved Fourier series method.Then the distribution function for the boundary conditions can be expanded into a set of Fourier series.Energy equations are employed to describe the in-plane dynamics of panel system.Through compared with the results from other method,the effectiveness and reliability of present theoretical model can be verificated.Then the in-plane free and forced vibration characteristics of the rectangular panel with four types of specific distribution functions for the boundary conditions which include linear function,quadratic function,sine function and cosine function are also analysis.Some numerical results are never presented before,which can be used as the reference of future research.The improved Fourier series solutions of the in-plane vibration of orthotropic rectangular panel with elastically restrained edges are firstly established.The obtained displacement function is smooth enough in the whole solution domain.By letting the solution accurately satisfy both the boundary conditions and the governing differential equations,the system characteristic equation of the in-plane vibration analysis of orthotropic rectangular panel is obtained.Numerical examples are presented to demonstrate the reliability and effectiveness of the current solution through the comparing with the results obtained from other analytical approach.The effect due to the boundary condition,aspect parameter and material property of the orthotropic rectangular panel is discussed,which lay a theoretical foundation for the optimization to the in-plane vibration analysis of complicated material.The coupling between bending and in-plane vibration of flexible panel structure become stronger in the case of really big thickness,the classical theory and relative modified theories of elastic panel are not applicable.In this study,the vibration characteristics are studied based on three-dimensional elasticity theory.Three-dimensional improved Fourier series method is used to model the three displacement fields in the thick rectangular panel.By introducing the elastic boundary restrains based on force balance principle,the dynamic characteristics of thick rectangular panel with elastically restrained edges is obtained using the Rayleigh-Ritz procedure.On this basis,the dynamic characteristics of the thick rectangular panel with different boundary conditions are discussed in details.The results show that the current method is able to make accurate and efficient prediction on the modal characteristics and forced response of such complicated cases.To remove the limitation of two single subsystems in present flexible panel-cavity coupling system,the prediction model of the structural-acoustic coupling characteristics of a three-dimensional cavity with flexible partition is proposed systematically.Based on the energy principle for the structural-acoustic coupling system,two-dimensional and three-dimensional improved Fourier series method are used to represent the displacement on the partition and the sound pressure inside the cavity in order to satisfy the requirement of continuity on the structural-acoustic coupling surfaces and structure boundaries.Then Rayleigh-Ritz procedure is employed for this structural-acoustic coupling system to obtain the equation of motion.In the numerical analysis,the natural frequencies,mode shapes and forced response for the structural-acoustic coupling system are presented.In addition,the different positions and boundary conditions of the partition are also discussed to further demonstrate deeply understand their influence to the modal properties of the coupled system.The analytical model of the complicated cavity with multiple partially partitions is established.The coupling system can be divided into three kinds of subsystem,and the virtual air panel assumption is first introduced into the improved Fourier series system to describe the interface between neighboring sub-cavities.Then the modal characteristics,forced response and energy transmission of the coupling system is solved by using Rayleigh-Ritz method based on the energy principle.The numerical calculation procedures provide modal characteristics and forced response of the complicated cavity with multiple partially partitions.The coupling system with different sub-system components,different length and boundary conditions of the partition is deeply analyzed,and the interior sound intensity distribution is plotted,which is convenient to illustrate the energy transmission form and structural-acoustic coupling mechanism of the coupling system.In the end,the experimental study on the dynamic characteristics of the cavity with flexible partition and partially flexible partition is performed.The frequency response functions of the coupling system are measured with the excitation of the acoustic source and concentrate force,respectively.The accuracy of the modeling method proposed in this study is verified through the comparison between the measured results and predicted results.The studies of this thesis can provide theoretical model for structure vibration and its coupled cavity system,the structural-acoustic characteristics of coupling system with complex factors are discussed based on the existing research,the relative numerical results afford the useful references for further optimize the theoretical model and introduce vibration and noise control technology.