Ship Motions From Unsteady Maneuvering in Two-Dimensional Waves: Part I—Numerical Simulations

Numerically simulating the six-degrees-of-freedom response motions of a ship executing an unsteady maneuver in a two-dimensional wave environment is one of the most challenging tasks in seakeeping. Mathematical difficulties may occur for several reasons. For example, the rapid change in encounter frequencies may cause a numerical dynamics imbalance. Furthermore, in order to predict the ship’s track (ship heading) accurately, the rudder forces and two-dimensional drift forces must be predicted accurately; otherwise, erroneously predicted headings can ultimately lead to obtaining entirely different ship motions. To overcome these problems, we added a well-behaved, pre-conditional iterative method into the hybrid flow-based, fully-nonlinear ship motion model, DiSSEL (Digital, Self-consistent Ship Experimental Laboratory), in a two-dimensional wave environment. DiSSEL includes two components: a ship-wave interactions model (Lin et al., 2005[1], Lin and Kuang, 2006[2]), and a solid body motions interactions model (Lin and Kuang 2010[3]). The rudder and appendage forces (Lin et al, 2010[4]) are included in the solid body motions component. This refined model is able to overcome the mathematical dynamics imbalance when the encounter frequency rapidly changes as well as accurately calculate the forces on the hull and rudders. Finally the simulations of ship response motions at various relative headings and at various forward speeds in a two-dimensional seaway will be benchmarked against experimental model data for the test cases.