An Experimental Study on the Characteristics of Drag Force acting on a Flat Plate under Transitional and Irregular Oscillations

Abstract

In order to guarantee the safety of vessels, it is very important to understand the characteristics of roll damping and to estimate it accurately. Because it affects the occurrence of parametric rolling and its amplitude significantly. However, it is very complicated to calculate roll damping theoretically, because of significant viscous components caused by vortex shedding. It is well-known that there is a prediction method of roll damping proposed by Ikeda for conventional displacement type mono-hull vessels, barge ships and small hard chine fishing boats. It has been developed based on theoretical and experimental backgrounds for regular roll motion. Therefore, it is difficult to apply it to computer simulation of transitional or irregular roll motion (i.e. roll motion and parametric rolling in irregular waves, broaching to capsize etc).The purpose of this study is to investigate the characteristics of drag force acting on a flat plate under transitional and irregular oscillation as a basic study, and to develop an estimation method of bilge-keel roll damping in time domain. First, under transitional motion, the characteristic of drag coefficient of flat plate at low Kc number is investigated experimentally. Second,using a forced sway motion device, the characteristic of drag coefficient of flat plate under transitional regular sway motion is investigated. Finally, based on the measured results, an estimation method of drag force of flat plate in time domain is proposed.