Study On Optimization Of Ship Resistance And Wake Non-Uniformity Based On CFD Approximation Model

With the prosperity of international trade in recent years,the shipping industry is becoming one of the world’s most serious sources of greenhouse gas emissions.Hull form optimization,as an effective energy-saving technical means,has attracted more and more attention from ship designers.The traditional process of hull form optimization requires CFD（Computational Fluid Dynamics）technology to assess the hydrodynamic performance for each hull form plan,which will consume a lot of calculation time and calculation resources,and it is difficult to meet engineering needs.Therefore,it is of great engineering significance to adopt an appropriate approximation model to solve the problems of time consumption and calculation cost caused by CFD hydrodynamic calculation during the traditional hull form optimization.Firstly,this paper introduces the theory and method for calculating the hydrodynamic performance of ships.Taking KCS container ships as the object,the effects of different grid numbers on the numerical calculation results are explored.Secondly,this paper explores the application of the radial basis function interpolation method to the deformation of two-dimensional grid points,and compares the effects of different radial basis functions on the grid point deformation.It provides a suitable radial basis function for subsequent hull surface deformation.Then,taking the wave resistance of medium-to-high-speed KCS container ships as the optimization goal,RSM（Response Surface Methodology）,Kriging methd,and RBFNN（Radial Basis Function Neural Network）were used to construct approximation models to predict the wave resistance coefficient of the KCS ship based on the CFD method.And the error results and fitting conditions of the three approximate models are analyzed.Based on the above three approximation models,the bow of the KCS ship is optimized,the influence of different design variables on the response value are analyzed,and the trend recommendations are proposed for the design of the bow shape of the KCS ship based on the optimization results.Finally,taking the low-speed and large-scale multi-purpose ship as the research object and according to the different resistance components affected by the shape of the bow and stern,the bow was optimized with the wave resistance as the optimization target,and the stern was optimized with the total resistance and the wake non-uniformity at the propeller disk as the optimization targets.In order to verify the reliability of the optimization results,the high-precision CFD solver STAR CCM + was used to calculate the resistance of the optimized ship based on the VOF method and the double model method,respectively.The calculation results show that the optimized bow has a certain resistance reduction effect on the multi-purpose ship,and the optimized stern can obtain a more uniform wake at the propeller disk while the resistance performance is basically not affected.