Investigation On Hull Form Optimization Under Typical Sea Conditions

Ship hull form optimization generally based on calm water resistance, and rapidity incalm water is used to pick out the favored hull form design. But in most of the time, a ship issailing in different sea conditions, and will influenced by the added resistance due to waves,so a good rapidity performance in calm water can’t be accounted for a same one in waves. Inaddition, decreasing the resistance and engine power is also the key to reduce fuelconsumption and carbon emissions. In this paper, based on an established optimizationsystem which is integrate the computations of resistance in calm water and added resistancedue to waves, a numerical optimization example for a300000DWT oil tanker is provided.Hull form with optimal resistance performance is obtained by means of the integratedapproach, and verified by the results of numerical computations and model tests.Firstly, on the basis of systematic exposition of the methods for computing resistance incalm water and added resistance due to waves, as well as hull form optimization, the researchtarget of developing the integrated optimization system based on SBD technology forreducing total resistance in waves is proposed.Secondly, the numerical computation procedure of total resistance in waves adopted inthe integrated optimization system is introduced in detail, and model test results are used toverify the precision and sensibility of numerical method applied to variety hull form designs.The result shows that this method can predict the tendency of ship hull resistance for differenthull form designs correctly, though some errors exist.Thirdly, by using the interface program developed in this paper, which has yet beenproven to be effective by comparing geometric models before and after transformation, thesoftwares of computing added resistance due to waves are integrated into Friendship. Thatadopted examples also show that Cubic B-spline Curve can be used to fit the ship hull linesappropriatelyFourthly, based on the established fully parametric hull model of a300000DWT tankerin the Friendship software, a numerical optimization model is obtained by integrating thecomputations of resistance in calm water and added resistance due to waves. With the Designof Experiment (DOE) and genetic algorithm, the resistance in calm water and added resistance due to waves are all reduced after the optimization, which is verified by comparingwith the numerical computation results and model test results of the original hull form and aformer modified hull form. The developed automatic integrated optimization system based onparametric hull form design breaks though the traditional mode that ship hull formoptimization mainly depends on designers’ experience, and improves the efficiency ofoptimizations obviously.Lastly, some research work with respect to computation of added resistance for a shipsailing in short waves is carried out. Based on overset gird technology and SST k-w turbulentmodel, RANS and motion equations are solved with Level set method for treatment of wavesurface. The computation precision is verified by model test results of KVLCC2, whichshows that some errors exist between the results of computations and model tests yet, andfurther more studies are needed.