Rearch On Multi-objective Hydrodynamic Optimization Of Channel Craft With Inlet Duct Effect

Channel crafts are developed from conventional monohull coasting craft,which have good seakeeping performance and are widely used in unmanned boats and patrol boats.Compared with monohull coasting craft of same scale,channel craft has better transverse static stability,longitudinal stability and seakeeping performance,but worse resistance performance.Therefore,the optimization design of channel crafthull,which pursues both excellent resistance and seakeeping performance,is one of the hot issues in current academic research.The interaction between water-jet inlet duct and crafthull is complicated,but the optimization of crafthull and inlet duct was carried out separately in traditional channel craft design.Therefore,the research on hydrodynamic performance optimization method for channel craft with inlet duct effect was carried out in this paper.The main research contents are as follows:(1)The key factors affecting simulation accuracy and efficiency were analyzed with a certain channel craft as the research object,and the hydrodynamic performance of channel craft was simulated with different turbulence models,numerical difference schemes,mesh encryption forms at free surface,and internal iterations.The numerical simulation results were compared with model test results.The influence of relevant factors on simulation accuracy and efficiency was defined,and the factors affecting hydrodynamic numerical simulation of channel craft were determined comprehensively to meet requirements in the subsequent optimization evaluation.(2)The hydrodynamic performance optimization of channel craft resistance and motion response in regular wave is multi-peak problem.In order to verify the calculation ability of different global optimization algorithms in multi-peak problem,Branin equation was taken as the verification object,and five global optimization methods,ASA,Evol,Pointer,PSO and MIGA,were used to calculate Branin equation.The convergence speed and global searching ability of different global optimization algorithms were compared and analyzed.On this basis,the global optimization algorithm used in optimization calculation of channel craft and inlet duct was determined.(3)By referring to the domestic and foreign research results about monohull coasting craft and combining with engineering design experience,several channel craft shape schemes were formed by uniform test design with five parameters as design variables,including deadrise angle of bottom,width of the channel,height of channel,the height and angle of wedge in the channel.The numerical simulation method for the hydrodynamic performance of channel craft was adopted to complete the hydrodynamic performance simulation of different channel craft shape schemes.An approximate model for hydrostatic resistance,wave drag increase and motion response value in regular waves of channel craft based on the above five key parameters was established.The weighted average function of hydrostatic resistance,wave drag increase and motion response value of channel craft in regular waves was taken as the optimization object.The multi-objective comprehensive optimization for resistance and seakeeping of channel craft was completed,and the multi-objective optimization effect of hydrodynamic performance such as resistance and seakeeping was achieved at least 4.33%.(4)The optimization method for the hydrodynamic performance of channel craft considering the waterjet inlet duct influence was carried out.Firstly,an approximate expression of the inlet duct efficiency suitable for the length Froude number greater than 0.6 was proposed based on the analysis of actual operating conditions of channel craft and combined with the research results and engineering experience of domestic and foreign scholars.Secondly,a simplified parametrization model of inlet duct with 9 parameters was proposed based on axial line of inlet duct and different section lofting.The fitting ability of the simplified model was verified by the classical pipeline problem.Based on the parameterized inlet duct model,the inlet duct efficiency was improved by8.34%.For the difference of crafthull optimization with and without inlet duct effects,the joint optimization of craft hull and inlet duct was realized by reoptimizing craft hull and inlet duct by integrating inlet duct into crafthull.(5)In view of the problem that pressure value at the bottom of channel craft is too conservative in the specification,the analysis of pressure distribution form and inflection point position was carried out.The distribution form of dynamic pressure changing with the longitudinal position was deduced according to two-dimensional flat potential flow theory.According to the relative relationship between maximum value and different longitudinal positions,the theoretical distribution form of dynamic pressure changing with the longitudinal position was formed.By comparing the theoretical analysis results with Kapryan’s test results,a new longitudinal load coefficient of bottom pressure was proposed,and the external load was reduced by 13.37%.By integrating resistance,wave drag increase,inlet duct efficiency and bottom pressure together,a multi-objective joint optimization was carried out.It was found that the hydrodynamic performance joint optimization of inlet duct and channel craft hull,such as resistance,wave drag increase and bottom pressure,has engineering value.