Numerical investigation of hydrodynamic forces acting on the non-stepped and double-stepped planing hulls during yawed steady motion

Abstract

This article focuses on the steady motion of yawed planing hulls with emphasis on the effects of adding steps to the bottom of these vessels on the hydrodynamic forces and moments acting on the boat. To analyze the problem, the Ansys-CFX software is used and three different planing hulls are investigated in steady yawed condition. The main targeted results include hydrodynamic forces and moments acting on the boat at different yaw angles and beam Froude numbers which provide important insights regarding the effects of loading and adding step on these forces and moments. The numerically predicted sway forces are compared against experimental data, suggesting that the current numerical model predicts sway and surge forces with reasonable accuracy. Moreover, it is observed that surge force coefficient of the investigated prismatic planing hull with light loading condition does not change significantly when the hull is relocated in a yaw angle, while it is remarkably affected when the boat is heavy. Furthermore, it is observed that this prismatic planing hull has smaller rolling moment in a steady yawed motion, when it moves at larger beam Froude number. Meanwhile, the computed yawing moments of this hull indicate that an increase in speed does not change this moment notably, while an increase in its weight yields larger yawing moment. Comparison of the results of stepped and non-stepped planing hulls indicates that surge force coefficient of the stepped hull is larger, while its sway force and rolling moment are smaller. This is mainly caused by the shape of the interrupted wetted surface and larger number of maximum pressure area in the stepped planing hull. Finally, it is concluded that there is no significant difference between the yawing moment of the investigated stepped and non-stepped planing hulls.