Reduced order method for ship roll motion prediction based on viscosity equivalence

Aiming at the classical roll problem in the seakeeping performance of a ship, this paper presents a viscosity-equivalent reduced order method (VEROM) for roll motion prediction. This method identifies the nonlinear roll damping characteristics based on a viscous flow and nonviscous models solving the N-S and Euler equations, respectively. In this method, the hydrodynamic moment under different motion amplitudes is predicted from a new type of forced motion whose amplitude increases with time. First, the viscous flow and inviscid models are used to simulate the forced amplification motion of the hull and predict the hydrodynamic moment under different motion amplitudes, respectively. Furthermore, the energy equivalent method is used to obtain the correction function of ship rolling damping with KC number. In the prediction of rolling motion response, the inviscid fluid is solved on the basis of the Euler equation, and the rolling damping is corrected in real time by using the obtained damping correction function to improve the prediction accuracy. VEROM and RANS viscous models are used to predict the roll response of the midship section of a typical hull in waves to verify the effectiveness of the proposed method. Comparison results show that the forecast accuracy of the VEROM model is comparable to that of the RANS model. However, the computational efficiency can reach more than 20 times of the RANS model. © 2023 Editorial Board of Journal of Harbin Engineering. All rights reserved.