The Wigley hull is considered as the initial ship, which can be globally deformed by shifting method and locally deformed by RBF (Radial Basis Function) method to generate a bulbous bow. Two optimization cases are given. In case 1, only shifting method is used, while in case 2, shifting and RBF methods are both used. The genetic algorithm is taken to obtain two optimal ships with minimum wave drag. Further validation by CFD solver naoe-FOAM-SJTU turns out that for the hull without bulbous bow, through combination of the two methods, a hull that has a much fewer wave drag can be obtained.
In the ship design process, hull form design is very important, which has attracted the attention of a large number of researchers and ship designers. In order to obtain a modified ship with better hydrodynamic performances, the initial hull should be optimized. In recent years, with the huge development of computer technology and calculation theories, the Simulation-Based-Design (SBD) approach is becoming possible rather than empirical or semi-empirical formulas. It is a new design way which integrates hull form modification method, numerical simulations and optimization technology.
Scholars at home and abroad have done a series of researches on hull form optimization problems, and achieved good results. Peri, Rossetti, and Campana (2001) regarded the total resistance and the bow wave amplitude as the objective functions of the geometry of a tanker bulbous bow, and used three different optimization algorithms to do the optimizations, and the optimization results are finally verified by the model test. Campana, Peri, Tahara, and Stern (2006) used the Non-Uniform Rational B-Spline (NURBS) surface modeling method to modify a bulbous bow, and the modified hulls were evaluated by RANS-based solver, and the bulbous bow was optimized. Zhang, Ma, and Ji (2009) used Rankine source method to calculate the wave-making resistance and Non-Linear Programming (NLP) as the optimization algorithm to get the optimal hull form with minimum wave-making resistance. Yang and Huang (2016) used surrogate models to perform three optimization cases and are validated by cross validation, where each sample point is evaluated from the surrogate model constructed by the rest of the sample points. Wu, Liu, Zhao, and Wan (2017) used Free-Form Deformation (FFD) method to change the bulbous bow shape of DTMB-5415 in order to obtain optimal hulls with better resistance performances in different speeds. Tezdogan, Zhang, Yigit, Liu, Xu, Lai, Kurt, Djatmiko, and Incecik (2018) used a hybrid algorithm to optimize the total resistance in calm water of a fishing boat, where two optimal hulls were obtained by two schemes.