A Study On A Parametric Expression Of Bulbous Bow Geometry And Its Optimization

For ships,the main way to reduce energy consumption is to reduce its resistance.Ship resistance can be divided into viscous resistance and wave making resistance.In the process of ship design,the reduction space of viscous resistance is limited,while wave making resistance has a large reduction space.At present,the most important way to reduce the wave making resistance is to install the bulbous bow,and the size and shape of the bulbous bow is the key to its resistance reduction performance.In the development process of new ships,there is often no data of mother ship.How to get a bulbous bow with good performance in the geometric space where bulbous bow is installed is embodied in the parameterization ability of bulbous bow.That is to say,a new bulbous bow shape can be obtained by determining several parameters.This paper presents a set of mathematical surface algorithm,which is applied to the parameterization of bulbous bow.Under the condition that the cross section of the ship’s bow is fixed,the parameters of bulbous bow can be reduced to five,which can change the bulbous bow’s length direction,width direction,height direction,nose point height and cross section longitudinally transformation.That is to say,a new bulbous bow shape can be generated by determining five parameters.In this paper,the method of bulbous bow parameterization is adopted and the idea of ship form optimization is introduced.Five parameters are used as optimization variables,potential flow module in SHIPFLOW is used as calculation solver of wave making resistance,and Multi Island genetic algorithm and basic genetic algorithm are used for optimization.The above tools are integrated into the optimization platform ISIGHT,and a set of bulbous bow parametric design method is finally formed.In the end of this paper,the bulbous bow of KCS and KVLCC2 is redesigned by the above-mentioned parametric design method.For the bulbous bow of KCS ship,the wave making resistance of this design scheme is reduced by 10.26% compared with the original scheme;For the bulbous bow of KVLCC2 ship,the wave making resistance of this design scheme is reduced by 15.32% compared with the original scheme.In both designs,the bulbous bow with less wave making resistance is obtained,which preliminarily verifies the effectiveness of this parametric design.