Study on fast interference wave resistance optimization method for trimaran outrigger layout

Abstract

The configuration of outriggers has a significant influence on the wave resistance of a trimaran. In this paper, slender ship theory is applied to calculate the wave resistance of trimarans. In order to improve the calculation accuracy, NURBS (Non-Uniform Rational B-Splines) method is introduced to molding the hull surface and the relative ideal results are obtained. On this basis, a series of 3D color maps of interference resistance (between main hull and outriggers) under different speeds and different displacement ratios are given to study the influence of the outrigger layout on the interference resistance. The results show that within an appropriate range, there is only one valley point of interference resistance exists in each 3D color map. For this reason, in combination with the characteristic of linear wave resistance has analytic expression, the steepest descent method can be applied to solve the problem of searching the outrigger layout with minimum wave resistance efficiently. Based on the above aspects, this paper proposes a fast trimaran outrigger layout resistance optimization method. By means of selecting an appropriate initial outrigger layout position, using trimaran wave resistance formula combined with steepest descent method, the minimum interference resistance layout in specific speed can be obtained efficiently. The results show a good precision of the optimal solution and an obvious promotion in computing efficiency compared to typical enumeration method.