Numerical Study of Ship Maneuvering in Irregular Waves Based on Two-Time-Scale Model

In severe sea conditions, ships are affected by various environmental factors such as wind, waves, and currents. The six-degree-of-freedom motions have an important influence on the ship’s maneuvering performance. This paper presents a mathematical model for ship maneuvering in irregular waves based on a two-time-scale method. The overall ship motion is divided into high-frequency seakeeping motion and low-frequency maneuvering motion. The high-frequency wave force is evaluated by the time-domain Rankine source method, and a set of four-degree-of-freedom equations is used to represent the low-frequency motion. As for the low-frequency motion, the wave drift force and moment are incorporated in the maneuvering equation to reflect the influence of waves on ship maneuvering. Two different time scales are used to solve these two types of motion equations, and a parallel time step format is adopted. The wave drift force and moment at each step are calculated for high-frequency wave motion. The constant and slow drift forces for low-frequency maneuvering motion is obtained through the empirical mode decomposition (EMD) of second-order wave loads within a certain period. In this paper, the maneuverability of the KVLCC2 container ship is numerically simulated based on the two-time-scale model. The turning motions in calm water are compared with the model test results for verification. Moreover, the motions with different rudder angles and steering rates are investigated in irregular waves for numerical analysis.