Study On Sound Radiation From Periodically Stiffened Thin Plate By Numerical Method

The structure of stiffened plate and shell has a wide application in the fields of ship, mechanical engineering, aerospace and so on, with the features of big stiffness, light weight, good mechanical performances. The vibration and acoustic radiation becomes one of the main sources of noise pollution that generated by stiffened-plate structure forced by outside excitement in the fluid. Therefore, the research on the underwater structure's vibration and acoustic radiation gets more and more people's emphasis presently. The common forms of stiffened-plate structure are stiffened periodically in one dimension or two dimensions. Stiffening can improve plate's stability, also reduce structure's acoustic radiation in some particular frequency areas. Statistical energy method and dynamic stiffness method are used to calculate structure's acoustic radiation in the high frequency area. And for the low frequency area, people mainly use FEM, BEM and coupled FEM/BEM.In this paper, coupled FEM/BEM is used to research and analyze the acoustic natures of three kinds of periodically stiffened plate. At first, it introduces the concepts of acoustic pressure, particle's vibrating velocity, acoustic intense, etc. Then the finite element models of three kinds of coupled structures are established: coupled structure of plate and stiffeners, coupled structure of plate and quadrate entity, coupled structure of plate and circle entity. Those three kinds of stiffened structures are distributed in two dimensions on plate, and the coupled structure of plate and stiffeners is the common two-dimensional periodically stiffened plate. The element's natures are prescribed and the grids are divided for the three different models by using the ANSYS software. After that, it gives specific introduce to calculation of the BEM in structure acoustics. It mainly derive Rayleigh integral equation based on surface, and discretize it. For the singular integral nature appearing after discretizing the BEM integral equation, degenerating element is used to eliminate it. And the SECHIEF method is applied to solve the non-sole problem and multiple-frequency calculation problems. On the basis of analyzing deeply the couples theory of BEM and FEM, it derive specifically the coupled equation of structure and acoustic field, gives the expression of SPL, SVL and SIL for the structure's acoustic radiation in the fluid. At last, it imports the three kinds of periodically stiffened plate divided in the ANSYS software into SYSNOISE software, which is used specially in the analysis of vibration and noise, to calculate the influence of different boundary conditions, different fluid fields and different incidence angles for the outside excitement on the SPL, SVL and SIL for the structure's acoustic radiation, the results are also analyzed.