Research And Application Of The FVM In The Structural Vibration And Sound Radiation

In the noise control field,the precondition for the low noise design of equipment is to know the sound and vibration characteristic.The numerical simulation of structural vibration and sound radiation can provide the basis for optimizing the system.The numerical simulation of the structural vibration and sound radiation is multi-zone coupling problem,the key technologies of which contain the computational method of structural vibration,the computational method of sound radiation and multi-physics coupling mode.Based on the cell-vertex finite volume method(FVM),the main objective of the present thesis is to establish a unified numerical method for structural vibration,sound radiation and structural acoustic coupling by using the interface coupling conditions.The present numerical solution is formed as the general numerical simulation software.For the structural vibration problem,the computational domain is meshed with triangular elements,quadrilateral elements,tetrahedral elements,pentahedral elements and hexahedral elements.The basic equations of anisotropic elasticity are discretized by the cell-vertex FVM.The discretized equations are solved by the explicit and implicit algorithms.The computational procedure is built by Fortran programming language.Based on the dispersion analysis of the second-order displacement wave equation,the stability criterion of the pentahedral element is obtained.The linear quadrilateral element shape function is introduced instead of the constant one to improve the accuracy of the present method.The improvement is validated to be vital to avoid violent numerical oscillation of displacement field when applying to the point source problem.Comparison of the memory and the CPU time consuming of the present explicit FVM,implicit FVM and commercial software ANSYS has been done to evaluate the numerical performance of the present methods.For the sound radiation problem,the unified form of the classic acoustic wave equation,the static form of inhomogeneous medium acoustic wave equation and uniform flow acoustic wave equation is presented.The five kinds of elements are employed to build the cell-vertex FVM and the computational process for the sound filed.The explicit and implicit algorithms are formed.By discussing the dispersion relation of the classic acoustic wave equation,the criterions for five kinds of elements are provided to choose the optimized spatial and time step sizes.The effects of the spatial and time step sizes on the computational result are discussed.The present time domain impulse method is improved by the application of absorbing boundary condition.The modified impulse method reduces the length of the inlet and outlet tube restrictions and makes the data processing easier.The structural acoustic coupling problem is implemented according to normal components of particle acceleration continuity condition and normal traction equilibrium condition at the interface.An ordinal coupling algorithm is adopted.The cell-vertex FVM and the computational process for the structural acoustic coupling problem are built.Two treatments for the coupling interface are discussed.The effect of the improved treatment for the quadrilateral element on the structural acoustic coupling problem is discussed.Because the explicit scheme and the implicit scheme can be employed in the structural subdomain and acoustic subdomain,four types of solution combinations are formed.The numerical result shows that the explicit-explicit scheme and implicit-explicit scheme is stable.In order to improve the computational efficiency,a technique of different time steps is introduced.The computational structural vibration and acoustic radiation technologies based on the unstructured CVFVM are implemented in an in-house software.The software function,design idea,and program implementation process are discussed in detail.The present computational software is applied to predict the structural acoustic coupling system performance of the underwater infinite column,the enclosed cavity filled with water or air and the water muffler and the underwater structure.The present method can obtain the transient response and natural characteristics at the same time.The numerical results indicate that the software has the ability to simulate the process of the structural vibration and acoustic radiation and to predict the acoustic performance.