Global optimization of trimaran hull form to get minimum resistance by slender body method

Abstract

In the current paper, different geometrical parameters of the trimaran hull ship are investigated to achieve the optimal points of geometry parameters. Considering the fixed displacement volume, the values of the longitudinal center of buoyancy, block coefficient, midsection coefficient as well as the side hull length and position are computed and using Lackenby shift transformation, the geometry is reconstructed during the optimization process. It is then necessary to compute the ship resistance of the reconstructed geometry which is hereby accomplished by slender body method. Subsequently, D-optimal method is used for finding the best parameters to achieving minimum resistance at cruise and sprint speeds. Two strategies are pursued to find optimum value of design variable: trimaran hull transformation and separated hull approach. Generally, a hull optimization process takes huge time and depending on the applied methodology, it might take somewhere between 6 months and 2 years. However, through slender body method and design of experiment study, proposed in this paper, the total time of global optimization process is only 1 week. Meanwhile, 9.1% resistance reduction at cruise speed and 2.24% resistance reduction at sprint speed is achieved. Hence, a successful ship hull optimization with suitable computational time and effort is the novelty of the current work. The conducted optimization indicates that two parameters of longitudinal center of buoyancy and block coefficient have significant effect on the total resistance. Comparison of the original and optimized hull signals the validity and superiority of the proposed optimization strategy, which can be extended to other maritime industrial projects.