Prediction And Optimization Of Ship Hydrodynamics Using CFD Technology

The CFD method has attracted wide attention in various fields due to its advantages of high accuracy,wide applicability,stable calculation results,high repeatability,low cost and short cycle.The CFD method mainly focuses on three aspects in the research of ship hydrodynamic performance:ship hydrodynamic performance prediction,mechanism study of ship hydrodynamic and optimization of ship hydrodynamic.In this paper,the CFD method is used to study the prediction,mechanism and optimization of ship hydrodynamic.First,the basic principles of CFD described.According to the characteristics of ship hydrodynamics,the control equation,finite volume discrete,boundary condition and turbulence model are described in detail.In addition,CFD uncertainty analysis was carried out.In this paper,a multifactor CFD uncertainty analysis method which can take into account the interaction between factors is proposed,and the method is used to carry out the uncertainty analysis for the prediction of total static water resistance of ships.The uncertainty analysis cover four factors including mesh size,time step,grid form and turbulence model.This method is an improvement on the original method.In this method,the uncertainty analysis of each factor is carried out at the same time.Due to the simultaneous analysis of each factor,the problem that other factor parameter setting depends on experience is solved.Secondly,the CFD method is used to predict the hydrodynamic performance of ships,including ship hydrostatic resistance,propeller hydrodynamic performance,maneuverability and seakeeping performance.Based on the prediction of ship hydrodynamic performance,the advantages of CFD method are given full play to the study on the mechanism of the hydrodynamic performance of three special ships.It includes the influence of ship’s pitch and heave on the prediction precision of total static water resistance,the problem of propeller scale effect and the causes of the uneven of the load on propellers of four propeller vessel.Study on the influence of ship’s pitch and heave on the prediction precision of total static water resistance is carried out through comparing the results of two ships.For the problem of propeller scale effect,the advantages of numerical calculation are given full play.The results show that under the condition of full similarity,the scale effect of model scale and real scale propeller is basically eliminated.In the study of the inhomogeneity of the load distribution of the inner and outer propellers of the four-propeller vessel,it is found that there are three areas around the propeller:wake area,acceleration area and deceleration area.The wake area is the area behind the propeller(within the range of the propeller disc).The propeller load in this area will be greatly reduced.The front area of the propeller is the acceleration area.The fluid in the area accelerates and the propeller load in the area decreases.The area behind the propeller except the wake area is the deceleration area.The fluid decelerates in this area,and the propeller load arranged in this area increases.The mechanism of the uneven distribution of load on the inner and outer OARS of the four OARS is revealed.Finally,a new method of hull geometry reconstruction,self-blending method,is proposed,which is the key technology of ship hydrodynamic performance optimization.The self-blending method takes the original ship cross section as the basic unit for blending operation,and generates a new hull cross section.This method has the characteristics of less parameters,large deformation space,smooth surface after reconstruction and practicability of reconstructed surface.Combined with CFD method and genetic algorithm,it is used to optimize the hydrodynamic performance of ships,including local hull shape optimization,whole ship hull optimization and multi-objective optimization.