On a Method to Calculate Hull Response of High Speed Vessels in Waves Taking Account of Slamming

Abstract

This paper proposes a new method to simulate slamming impact. loads and ship response of a high-speed vessel in waves. Many non-linear analysis methods have been proposed and reported for simulation of slamming of ships, in which hydrodynamic impact loads are determined by means of Karman type impact model. It means that wrater pile up is not taken account of in water surface impact. process. On the other hand, model experiments and numerical analyses of water impact of wedges show very good agreements with water impact theory by Wagner, in which water pile up plays an important role. This implies that calculation of proper impact loads is not expected by these non-linear analysis methods. A new approach have been tried to improve this inconvenience.Wagner type impact model is adopted in the new method, together with threshold velocity of water impact to judge occurrence of water impact. Threshold velocity of water impact is derived for wedges with various deadrise angles, of which model test was carried out for the validation.A new concept of equi-added-mass lines is introduced to take account of the hull form to compute substantial relative velocity between hull and wave surface. This corresponds to a method to derive relative vertical velocity of an inclined prismatic body with a wedge section advancing forward on calm water surface. Using this method, substantial relative velocity can be computed taking account of ship speed, and loads derived by the method include the lift force induced by ship speed.These are incorporated in a new non-linear analysis method. It is confirmed that loads derived by this method for a ship section are equivalent to the loads derived by Stavovy & Chuang's method, which is so-called an impact theory to calculate three-dimensional impact. pressure. A comparison is made between the results of this method and model tests for hull response of a 40 m patrol boat in regular waves. The results show comparatively good agreements in motions in waves. But, it shows there is much room for improvements in treatments of piled up water and waves the ship induces.This method is applied well to simulate hull response of such high-speed vessels like patrol boats, and this method is expected to apply also to other ships like container ships.