A practical multi-objective optimization tool, named OPTShip-SJTU, is utilized here to optimize both of the resistance and seakeeping performance for a surface combatant DTMB Model 5415. During the optimization procedure, free-form deformation (FFD) method is used as parametric hull surface modification technique to produce a series of alternative hull forms subjected to geometric constrains. The Neumann-Michell (NM) theory and an extension of Bales seakeeping ranking method are implemented in the evaluation module of the tool, and to predict the wave-making drag and Bales seakeeping rank factor R respectively. An optimized Latin hypercube sampling (OLHS) method is employed to generate 60 samples within the design space, and an approximation model is established in terms of these samples and corresponding predictions. A muti-objective genetic algorithm, NSGA-??, is adopted to produce pareto-optimal front. The numerical optimization results are analyzed, and the availability of the OPTShip- SJTU is confirmed by this application.
The optimization of hull forms to improve the hydrodynamic performances has attracted attention in the recent years. In the past, a large number of alternative hulls were proposed according to the experience of ship designers and tested by model experiments before the final design was obtained, obviously, this method is in low effect and uneconomical. At present, with the rapid development of numerical methods and optimization algorithms, advanced modification methods, evaluation tools and optimizers have been proposed and integrated together to form various numerical optimization platforms, and they have been presented in a huge body of literature.
Kim et al. (2010) used two approaches including shifting method and radial basis function interpolation to modify the hull surface, and a practical CFD tool and Bales seakeeping ranking method were used to predict the objective functions associated with resistance and seakeeping. Eventually, valid results were obtained using the MOGA algorithm for optimization. Tahara et al. (2011) took a fast catamaran as the initial design and the numerical optimization was performed based on an URANS solver, a potential flow solver and global optimization (GO) algorithms. The HSSL-B geometry was successfully optimized and an experimental campaign was carried out for validation. Zhang et al. (2015) studied the minimum total resistance hull form design method based on potential flow theory of wave-making resistance and considering the effects of tail viscous separation, and the nonlinear programming method was chosen as the optimization scheme. Campana et al. (2006) present the fundamental elements of a SBD environment for shape optimization. Both of the CFDSHIP-Iowa and MGShip were used as simulation tools, and CAD-free and CAD-based techniques had been adopted for shape grid manipulation. Additionally, GA approach was utilized in the computations and approximation model management optimization (AMMO) was employed to reduce the computational efforts. Based on above techniques, our in-house hydrodynamic optimization tool, OPTShip-SJTU, was developed for numerical multi-objective optimization of ship hull (Wu, Liu and Wan, 2015).