Seakeeping optimization of trimaran outrigger layout based on NSGA-II

Abstract

The outrigger layout of a trimaran has a significant influence on its seakeeping performance. In this paper, the high-speed slender body potential flow theory (also named the 2D+t theory or 2.5D method) is applied to trimaran seakeeping calculations. A series of ship motion experiments were carried out in head regular waves for one trimaran with different outrigger layouts at the Froude numbers of 0.471 and 0.628. The experimental results have been compared with the simulation results derived from a 2.5D seakeeping prediction program to validate the 2.5D method. The enumeration method is used to study the influence of the outrigger layout on the seakeeping performance. Furthermore, the contour maps of the heave, pitch and roll motions are plotted at different forward speeds (Fn = 0.4 and Fn = 0.5). To improve the seakeeping performance of a trimaran in waves, a fast elitist non-dominated sorting genetic algorithm (NSGA-II) is adopted in this paper. Moreover, this paper proposes a fast optimization method for the trimaran outrigger layout by combining NSGA-II with the 2.5D seakeeping predicting method. Finally, taking a trimaran as an example, this paper provides the optimal outrigger layout with the minimum heave, pitch and roll motion.