A Study on Mathematical Models for Manoeuvring Motions : In Reference to Longitudinal Force and stern Flow

Abstract

With trends of energy-saving ship design through lower-powered and lower-speed specifications, ship's manoeuvring characteristics are becoming more closely related with its propulsive performance. That is, under environmental forces due to wind, sea, and current, ship's course-keeping ability is unseparably connected with ahead resistance increase which can result in apparent drop in the service speed. It may be advised, therefore, that the mathematical models for simulation study on manoeuvring motions will be capable of dealing with propulsive performance as well. To cope with these demands, basic investigation is made on two mathematical models; a simplified one in which variations of longitudinal force and stern flow due to sway-yaw motions are simply expressed and MMG-type one in which expression of wake due to sway-yaw motions is modified. These models are derived so as to fully utilize experimental results about propulsive performance. In the present paper, various simulation including full-scale prediction is made to clarify applicability and effectiveness of the two mathematical models especially for manoeuvring motions. And it is shown that in spite of simple expressions mentioned above, simplified mathematical model is as effective as MMG-type one. It is considered that these mathematica1 models with assured reliability in prediction of manoeuvring motions will be effective for evaluation of ship manoeuvrability related with propulsive performance