Effects of wave direction on ship turning in regular waves

Abstract

In this study, we focused on the drift motion of a ship during turning in regular waves and investigated the effects of wave direction on ship turning and drifting. First, turning tests in regular waves were conducted using a bulk carrier model by systematically changing the wave direction and wavelength to capture drifting characteristics. Subsequently, long-duration turning simulations were performed to capture the drifting characteristics with a large heading angle change over 2000° in waves using the two-time scale method (Yasukawa, 2006b; Skejic and Faltinsen, 2008). The simulation results indicated that the ship constantly drifted in a particular direction with respect to the incident wave direction during turning when sufficient time had passed. This phenomenon can be understood analytically using new formulas derived for the drifting indices (drifting distance and drifting direction). According to the formulas, the ship turning trajectory is deformed in waves drifting in proportional to time. The drifting velocity and drifting direction were determined by combining the average velocity components (ship surge velocity, lateral velocity, and yaw rate) and the first-order velocity fluctuation components with turning circular frequency. The formulas for the drifting indices were verified through comparison with the simulation results.