Free fall water entry of a cone in three degrees of freedom

Abstract

The hydrodynamic problem of a three dimensional cone entering water in three degrees of freedom is analysed based on the incompressible velocity potential theory. The effect of horizontal motion and rotational motion on the entry process is investigated. The problem is solved through the boundary element method in the time domain. Two physical coordinate systems are constructed. One is the body-fixed system for the solution of fluid velocities and free surface tracking, and the other is the space-fixed system for equations of motion. To match the extremely small wetted surface at the initial stage, the former frame is stretched based on the ratio of physical coordinates and vertical travelled distance. The auxiliary function method is used to decouple the nonlinear mutual dependence between fluid loads and the body motion. Detailed results for cone motion, impact pressure and free surface are provided, and in-depth discussion on the effect of the horizontal motion and rotational motion is given.