Numerical analysis of three-dimensional sloshing with random excitations

Abstract

Liquefied natural gas (LNG) carriers have played, and will continue to play, a key role in ocean gas transportation with the increasing demand for energy. Safe operation of LNG carriers requires knowledge of global and local pressures imposed by the sloshing liquid. As LNG carriers are required to operate in different environmental condition, safety is the primary consideration in such operations. LNG carriers are subjected to often significant sloshing loads during their operational life. As it moves across the ocean, the motion of the LNG carriers causes the liquid in the containers to slosh. Liquid sloshing may cause large internal stresses and deformation in the walls of containers, particularly when the external forcing frequencies of the ship are close to the natural sloshing frequencies. This effect is sometimes critical in ship design. A three-dimensional (3D) sloshing problem is analyzed by the linear wave velocity potential theory based on the boundary element method (BEM). When the rectangular tank is undergoing one-dimensional motion, the calculated results are found to be in very good agreement with other published data that assess the accuracy and applicability of the method. Extensive calculation has been made for the tank in two-dimensional (2D) motion. Then random sloshing problem, sloshing in a 3D rectangular container, is further simulated and discussed. In this case, the container filled with liquid is subjected to specified random horizontal oscillations. Both wave elevation and hydrodynamic force are obtained. The spectra of random waves and forces have also been investigated and results are compared between the analytical solutions.