An efficient finite element approach to examine the free vibration characteristics of liquid tankages in space launch vehicles

This paper deals with the development of an efficient finite element method to study the dynamic characteristics of structures containing fluid. Structural and fluid domains are discretized with 8-node plate/shell element and 20 node brick element respectively. The inviscid incompressible fluid is assumed under irrotational motion. Proper care is taken to eliminate the pressure at fluid–structure interfaces. Mass due to fluid–structure interaction is merged with structural mass and expressed the added mass in terms of inverted fluid stiffness matrix with pre- and post- multiplication of area coefficient matrix. An appropriate node numbering scheme is adopted for idealizing the structural domain and subsequently the fluid domain to gain the computational efficiency and reduction in the storage required for the added mass matrix. The adequacy of the present approach is demonstrated by considering the free vibrations of clamped cantilever plate and clamped-free open-ended cylindrical tanks and partially filled liquid tankages having common bulk head.