A Research On The Ship Hull Form Optimization Using Viscous CFD And Genetic Algorithm

Optimization of hull form is based on the geometry changes to the hull in order to attainbetter performance of the ship. The traditional method for improvement in the ship hull formis to produce an initial hull form and test it in towing tank to obtain flow around the hull andthen modifying the hull with improvements and test it again. With the development of fastcomputers and Computational Fluid Dynamics (CFD) based methodologies the initial analysisis carried out more robustly and accurately with CFD tools. In recent years CFD applicationshas been used extensively for the calculation of flow field around ship hull, and it has becomean important tool for designers and engineers in ship industry.Optimization of a hull form is generally based on optimizing the offset of the initial hull;another way to improve the resistance of the hull is to change in geometry of the hull whichcan change the flow around the hull. In this research work, hull form of a ship is optimized fortotal resistance using CFD as calculation tool and Genetic Algorithm as optimization tool.CFD based optimization consist of following major steps:Automatic generation of geometry based on design parametersAutomatic generation of meshAutomatic analysis of fluid flow to calculate required objective functionAn optimization tool to evaluate the cost for optimization.For optimization, integration of Genetic Algorithm program, written in MATLAB, hasbeen carried out with geometry&meshing software GAMBIT and CFD analysis softwareFLUENT. Journaling feature of Gambit is used for the generation of geometry and mesh.FLUENT journaling is used for automatic calculation of total resistance of hull form. Twoship hulls (mono-hull and trimaran hull) are optimized to obtain low resistance hull forms.The mono-hull Series60(Cb=0.6) is selected for optimization with the addition of bulbousbow. The hydrodynamic effect of bulbous bow depends mainly on the flow change aroundbow of hull. Geometrically, in addition to the main part of the hull, this hydrodynamic effectis a function of bulb size or volume (i.e. longitudinal distribution of volume along length ofbulb and the form of bulb). The vertical distribution of bulb volume and its distance to thefree-surface affect the amplitude of the wave system along hull. The longitudinal distribution of the bulb volume along the length will create the phase shift between bulb and hull waves.The appropriate selection of these geometric parameters can create favorable interference ofbulb and hull waves, resulting in a decrease in wave resistance. Different geometries ofadditive bulbous bow have been incorporated in original hull based on design parameters.These design variables are optimized to achieve a minimum cost function of “totalresistance”.For second hull, trimaran FA1is taken for optimization. In this optimization, lines of themain hull of trimaran are optimized. A total of eight optimization cases are presented fortrimaran. For the first six cases, objective function in selected as minimizing of totalresistance, while for the last two cases objective function is selected as minimizing of totalresistance per unit displacement. The first four cases are based on the optimization of mainhull bulbous bow form controlling points; a total number of24points are individuallyevaluated for optimization. For the fifth case, six bow station lines of main hull are optimized;a total number of85points are individually evaluated. For the sixth case, along with the mainhull bulbous bow points, bulbous bow length has also been optimized. For the seventh case,24bulbous bow points are individually evaluated for an objective function of total resistanceper unit displacement. For the eighth case,24bulbous bow points are divided into four groups(based on water lines) and these groups are optimized for both objective functions (i.e. totalresistance and total resistance per unit displacement).The results for both ship hull optimizations are compared with the available experimentalresults. The results show that the integration of Genetic Algorithm with CFD tools proves tobe effective for hull form optimization.