서보모터를 이용한 자유항주용 부가추력장치 개발

Abstract

Scale effects on the prediction of maneuvering performance of a ship by free model tests have been still in controversy. If a free model tests is carried out according to Froude’s law of similarity, there are two different aspects of scale effects during free model tests. Decreased velocity into the propeller and rudder due to thicker boundary layer and increased propeller slip stream due to high propeller loading at the model propulsion point. As a result of these scale effects, rudder effectiveness of a model is generally overestimated than a real ship. In this study, a new additional towing device has been developed for free model tests to be able to apply a frictional force correction by providing an additional towing force to a free model with a servo motor system. The system can apply precise towing forces with the feedback control of measured towing force by a load-cell. The new system is more convenient and useful for wide application compared with air-fan and air-jet system, which requires calibration of the system for exact force and might induce an unwanted fin effect during tests. To test the performance newly-developed additional towing device (ATD), free model tests are carried out on KRISO container ship (KCS). The features of ATD and the results of free model tests are described in this paper.