Hydroelastic analysis of fluid storage tanks by using a boundary integral equation method

This paper presents a boundary integral equation method in conjunction with the method of images, in order to investigate the dynamic behaviour (wet frequencies and associated mode shapes) of fluid containing structures. In the analysis of the linear fluid-structure system, it is assumed that the fluid is ideal, and fluid forces are associated with inertial effects of the contained fluid. This implies that the fluid pressure on the wetted surface of the structure is in phase with the structural acceleration. The in vacuo dynamic properties of the dry structure are obtained by using standard finite element software. In the wet part of the analysis, the fluid-structure interaction effects are calculated in terms of the generalized added mass coefficients by use of the boundary integral equation method together with the method of images in order to impose the Φ=0 boundary condition on the free surface. In this study, three different test cases are considered: (i) a clamped-free cylindrical tank with a rigid bottom; (ii) a flexible circular plate in a rigid cylindrical tank and (iii) a flexible cylindrical shell with flexible end plates (hermetic can). The fluid storage tanks in this investigation are assumed partially or completely filled with water. To assess the influence of the contained fluid on the dynamic characteristics, the wet natural frequencies and associated mode shapes are calculated. The predictions compare well with available experimental and numerical data.