Multi-objective optimization of ship hull modification based on resistance and wake field improvement: combination of adjoint solver and CAD-CFD-based approach

This paper presents an investigation to modify a trimaran ship hullform based on resistance and wake field improvement. Combination of adjoint solver and CAD-based optimization platform is a novel strategy for ship hull optimization, which has been proposed in the present paper. Adjoint solver recognizes significant regions of the geometry surface based on calm water behavior. After that, a CAD-based optimization platform using Free Form Deformation (FFD) technique is implemented in introduced important region from adjoint solver. Consequently, a useful multi-objective optimization platform is created and developed. The ship hull parametrization includes two aspects: first, shape optimization by using Free Form Deformation technique and second, sidehull arrangement and its length. Accordingly, eleven design variables are defined for geometry regeneration in optimization process. The geometry reconstruction step of FFD is connected to CFD solver in order to calculate the objective functions. A Non-dominated Sorting Genetic Algorithm III (NSGA-III) is employed to optimize hullform objectives and find corresponding optimized variables. The optimization results show a 13.3% reduction in the total resistance and 7.58% reduction of wake coefficient for optimized hullform. Asymmetric sidehull, the sharper bow shape for an inverted bow, flat bottom in stern region, suitable sidehull arrangement and its length are the modifications of the optimization process. Besides, the comparison between initial and optimized hull demonstrates the validity of the proposed optimization design strategy with efficient computational time and effort.