Development Of Ship Heave And Pitch Motions Evaluation Program And Application In Ship Hull Form Optimization

Ship hydrodynamic performance evaluation is an important part in ship hull form optimization,and rapid and accurate evaluation method is an important topic in the field of ship hull form optimization.For the hull form optimization with the aim of seakeeping,a set of seakeeping evaluation program which can rapidly calculate ship motions of each degree of freedom in waves is the basis of ship hull form optimization.At present,although ship motion calculation method based on viscous flow theory can accurately evaluate the motions of ship,the calculation time is long and a lot of calculation resources are needed,which leads to the long optimization period of ship hull form and the low fault tolerance of ship hull deformation.Therefore,the methods based on potential flow theory,which can realize fast calculation,is very suitable for ship hull form optimization,and the strip method,whose development is relatively mature,can further reduce the calculation time and obtain satisfactory evaluation results.Based on the strip theory,this paper develops a set of C-language program for calculating the heave and pitch motions of a ship in a regular wave at a certain speed.In the calculation of the hydrodynamic coefficients of the two-dimensional sections of the ship,the added mass and the damping coefficient of each section of unit length are obtained by using the Tasai graphics,which are based on the Lewis section method.According to the principle and formula of the strip method,the hydrodynamic coefficients of heave,pitch and their coupling motions and the wave force（moment）of the ship are solved.When they are substituted in the differential equation group of heave and pitch motions,the special solutions are solved,which can obtain the heave and pitching motion amplitude response of the ship under a certain wave condition.In order to verify the effectiveness of the program in this paper,the numerical ship model Wigley and the standard ship model Series60 are calculated by the program,and the hydrodynamic coefficients of heave,pitch and their coupled motions,the wave force and moment at each encounter frequency are solved.By comparing the results with the experiment values,it is proved that the program can calculate heave and pitch motions rapidly and effectively,which can be further applied to ship hull form optimization.Then,a ship hull form optimization design with the aim of reducing heave motion is applied to the standard ship model KCS.Ship hull is deformed by translation method,and a series of sample ships are obtained.Then the heave amplitude of each sample ship is obtained by self-designed program,and a Kriging approximation model is established.The optimal ship form is solved by the genetic method,and the optimized ship form is verified by using the naoe-FOAM-SJTU solver based on the viscous flow theory.The results show that this optimization design reduces the heave motion amplitude of the KCS in the wave,and proves that the program can be applied to ship hull form optimization.