Experimental Study of Hydrodynamic Lateral Force about a Model Ship Berthing at a Quay

Abstract

It is important to know the lateral added masses of ships which are either moving laterally to ward a quay or are moored near the quay, because the existence of the quay will alter that portion of potential flow component of the hydrodynamic lateral force which is caused by lateral acceleration. Furthermore, the other portion of this component, which is generated by lateral velocity, depends on the rate of change in the added mass. The remaining component in the force equation is viscous drag force which varies with velocity. Theoretical studies of the hydrodynamic lateral force operating in a restricted water area having a side wall have been conducted by Fujino [2,3] and Nonaka [4]. Experimental studies, however, have seldom been carried out, with the exception of Tsuji's research [5] which deals with lateral force at constant speed. This paper deals with model experiments of a 225GT fish carrier boat. These were carried out using lateral accelerating tests, and changes in the lateral added mass as affected by the quay were analysed. The equation of motion for the analysis is: m(dv)/(dt)=-m_y(s)(dv)/(dt)-(dm_y(s))/(dt)v-C_D・1/2・ρLd_m∣v∣v+Y_E, where s is the distance from the quay to the side wall of the ship. We drew the following conclusions: 1) the lateral added mass affected by the quay is from 2 to 4 times the added mass in open water, in accordance with the gap between the quay and the ship. This range corresponds to 0.1 to 0.0 times the ship breadth. 2) the cross flow drag cofficient C_D under conditions of accelerating motion is about 10% greater than under constant speed motion.