Finite Element Fluid-structure Interaction Method For The Analysis Of Vibration Noise Reduction Of The Small Mechanical Structure

Because of high strength, large damping and high quality, damping composite structures are widely used in the field of ship, aviation, and machinery, etc. The design, damping mechanism, dynamic characteristics and acoustic radiation of impedance compound sound absorption structures is central issue, as well as difficulty. The purpose of this dissertation is to design an impedance compound small mechanical structure. And with the numerical calculation, the good sound absorption and vibration reduction effect of the small mechanical structure is demonstrated from the theoretical point of view.Firstly, the small mechanical fluid-structure finite element model is established, and through the finite element analysis of fluid-solid coupling numerical algorithm the acoustic characteristic curve of the top and bottom plate is calculated. Then the small mechanical resonance frequency is concluded. At the same time, the working frequency range for the small mechanical structure is provided.Secondly, given that the micro pore is decimillimetre, it is impossible to establish its finite element model. Studying the sound absorption mechanism of the micro perforation plate and porous medium respectively, it is obvious that there are some similarities between them. So with the mature theory of porous media, the mathematical model for the acoustic impedance of the micro perforated panel by the thought of equivalent porous medium model of micro perforated panel is established. Compared with the Rayleigh microtubules impedance model, the conclusion that the equivalent acoustic impedance model is feasible is proved.Thirdly, through the homogeneous continuous impedance boundary conditions, acoustic admittance relationship between the up and down cavity for the small mechanical structure is built. And in this way, the damping mechanism of micro perforation plate is introduced into the fluid-structure coupling finite element model. With finite element analysis of fluid-solid coupling numerical algorithm, the small mechanical dynamic characteristic curve under harmonic excitation is calculated on condition that the micro perforation plate is embedded.Fourthly, the upper and lower sheet transfer function is obtained through MATLAB simulation. Changing the thickness of sheets and the length of blocks, the thickness of the up and down sheets and the length of the up and down blocks as the main factors that influence the transfer function coefficients are found.Fifthly, using the finite element fluid-solid coupling numerical algorithm, the bilinear interpolation method which is semi-analytical numerical algorithm is verified. As a result, the bilinear interpolation method has some error. But bilinear interpolation method is more simple and efficient than fluid-solid coupling finite element algorithm and also saves resources. Bilinear interpolation method is of high application value. And in this dissertation, the validation process of bilinear interpolation method is to find out the reasons of the error and its correction scheme.Finally, using the method of PML, the finite element model of truncation for the small mechanical structure that works in the infinite fluid domain is established. And through the finite element numerical algorithm, sound pressure of radiation produced by small mechanical vibration is gotten.