Investigation On The Finite Element Method Of Vibration From Finite Length Double Cylindrical Thin Shells

The research on the FEM for calculating the vibration of the double cylindrical thin shell structure has mainly been done in the dissertation. The elastic cylindrical shell is the typical structure of underwater vehicles. It is important to study the vibration of underwater elastic cylindrical shell in practice. At present, the radiated sound field from underwater structure vibration can be calculated by the combination of FEM and FEM+BEM. When the sound field is calculated by FEM, the whole calculated region has been meshed fully, which makes the calculation amount huge. When the sound field is calculated by FEM+BEM, the region of elastic structure can be meshed only. Compared to FEM, FEM+BEM has a great improvement. However, there is no acoustic finite element type in BEM. So the structure vibration problem, which the fluid exists in the double shells, can not be calculated by BEM only.Therefore, 3-D and 2-D fluid-solid coupling FEM algorithm have been developed in the dissertation. Meanwhile, the method to solve the large sparse matrix equation has been investigated.The developed type of finite elements is as follows: first, 3-D shell elements, including the triangular and quadrilateral elements; second, solid and fluid elements, including hexahedron, tetrahedron and prism elements; third, 2-D axis-symmetric elements. These types of the elements can be used to solve the vibration problem of coupling structures consisting of the double shell, the ribs in the shell, the fluid between double shells.The numerical validation has been done on the developed finite element algorithm in the paper. The results are consistent with that solved by ANSYS. At the same time, the numerical calculation of the spherical model's vibration has been done by the self-developed algorithm. Compared to the analytical solution, the error of the self-developed algorithm is less.