On the frequency and dynamic analyses of complex cylindrical shells submerged in fluid: An axisymmetric FEM/BEM method

For the ribbed and variable-thickness cylindrical shell with endplates in the fluid, this paper develops an efficient and applicable axisymmetric FEM/BEM method for frequency and dynamic analyses of such a structure, which is widely used in the aerospace, civil, and ocean engineering. Axisymmetric finite elements are employed for the discretization of cylindrical shells, endplates, and ribs to obtain the mass and stiffness matrices of the structure. Accordingly, axisymmetric boundary elements are developed for the fluid pressures on the structural surface. And they are transformed into the equivalent nodal forces to obtain the fluid-added mass matrix and the fluid–structure coupling equations of the system. The frequencies and modes are calculated by eigenvalue analysis. In the presented method, only the displacements on the structural meridians need to be solved, effectively reducing the computational effort. Since the mass and stiffness matrices and the system modes are obtained, the modal superposition method is used to solve the dynamical response of the system subject to force excitation, so that the complicated solution for fluid forces is avoided. The results show that the method is accurate and efficient and has significant engineering potential.