Broaching Prediction Using an Improved System-Based Approach

摘要

This paper reports the improvements of simulation model for ship motions in following and quartering waves. The authors use a wave-piercing tumblehome vessel as a subject ship. The existing 4-DoF (degrees of freedom) model shows some limitation in its capability for predicting broaching of this vessel. In a free-running model experiment for the vessel, we observed rudder exposition from water in the way to broaching. This rudder exposure can significantly reduce rudder force. To express rudder exposure, we should take account of not only roll but also pitch and heave. Therefore the authors develop a 6-DoF model. With the heave and pitch motion, we can calculate the local draught variation for calculating wave exiting forces and moments. Roll restoring variations are one of the important factors to estimate roll motions. Therefore we theoretically estimate restoring variations in wave then we found the tendency of variation dramatically changes due to the roll angle. Submergence of superstructure can be important for that variation. We also consider the variation of manoeuvring coefficients and rudder forces in waves which are relevant to broaching. To estimate these variations, we conduct PMM tests, straight-line tests and rudder angle tests in waves using a scale model of subject ship. With some of these improvements, we obtain better agreements with experimental results than existing 4-DoF model.