Real-Time Simulation of a Rescue Ship Maneuvering in Short-Crested Irregular Waves

Research on the mathematical model and the real-time simulation of the ship motion is investigated. An equation of three degrees of freedom (DOF) nonlinear maneuvering motion is established by means of the unified model in short-crested irregular waves in deep water. The resistance and propulsion dynamics are modeled by the classical methods as well as forces and moments of the rudder and the viscous crossflow. The three-dimensional boundary element method (BEM) using Green function source is adopted to solve the boundary value problem (BVP) in the frequency domain. The added mass and potential damping coefficients are calculated by Cummins method, and the mean wave drift forces by far-field formulas along with numerical verifications. After that, the turning motions of two ships (a rescue ship NHJ111 and the Mariner) in calm water are performed, and the relative error is approximately 7% by comparing calculated results with the experimental data. The maneuvering motion of the Mariner in short-crested irregular waves is then carried out. The turning trajectory, surge speed, and drift forces agree well with the theoretical results in regular waves. Finally, the synchronous interpolation method with two-thread double-timer is conceived. The real-time maneuvering simulation of NHJ111 using the validated model is then realized. The developed method can lay the foundation for fast computations of predicting the rescue ship motions in waves.