CFD-based optimization of a displacement trimaran hull for improving its calm water and wavy condition resistance

Abstract

This paper presents a multi-objective shape optimization approach for improving the bow region of a trimaran ship hull. A CFD-based design study is conducted to reduce the total resistance of trimaran ship hull in calm water and wavy condition. Accordingly, a practical multi-objective optimization platform is established and developed for ship hull modification. In addition, the hullform of a displacement trimaran ship with inverted bow is modified as a case study. Six objective functions are utilized in the present study by considering the weighted sum optimization method. Reduction of total resistance at two cruise and sprint speeds in calm water, reduction of resistance in two different wave conditions, and two cruise and sprint speeds are the six objectives of the study. Two aspects of ship hydrodynamics, resistance, and seakeeping are the disciplines that are considered through the proposed optimization process. Ship hull parametrization is performed by Arbitrary Shape Deformation (ASD) technique that defines the input variables for optimization process. The geometry reconstruction step connects to CFD solver in order to calculate the response of the optimization cycle. An innovative Simcenter SHERPA algorithm is employed to optimize the design objectives. The optimization results show a 3.14% reduction in the aggregated objective function. Generated waves around the hulls of the optimized trimaran have constructive interaction and diminish each other in calm water. A forefoot angle and sharper nose are created at bow region of the optimized hullform. Moreover, the comparison between baseline and optimized trimaran hull confirms the validity of the proposed optimization design strategy.