Research On Hull Form Optimization And Navigation Characteristics Of CNG Ship Based On Viscous Flow CFD

With the growing voice of the world shipping industry for energy conservation and emission reduction of ships,more and more attention has been paid to the research and development of energy-saving ships.CFD-based optimization method is one of the most important methods for ship designers.Different from the traditional parent ship modification method,the CFD-based hull form optimization design method combines the shape change technology with the numerical simulation method,which can effectively improve the quality of ship form design and save a lot of design costs.There is an inevitable connection between ship type and ship hydrodynamic performance.One of the important indicators to evaluate whether the ship type is good or not is hydrodynamic performance.The rapidity,seakeeping and maneuverability of the ship are the main performance of ship hydrodynamic.Ship navigation performance prediction is an important part of ship design,and hydrodynamic performance research is the basis of ship navigation performance prediction technology.Based on this,the main research contents of this paper are as follows:Firstly,this paper establishes an automatic optimization system of ship shape based on parameterization.Taking CNG ship as an example,The hull model is generated by parametric modeling,and the rapid deformation of the hull can be realized by controlling parameters,so as to generate a variety of ship types and provide a variety of solutions for hull lines optimization.On this basis,CFD technology is used to establish an optimizing platform based on viscous flow field,taking the total resistance performance as the goal,the bulbous bow of CNG ship is optimized,the optimization algorithms based on Sobol and NSGA-II are used,the differences between the two optimization algorithms are compared and analyzed.The influence of design variables on the optimization results is analyzed.The results show that the optimization algorithm based on Sobol is more suitable for the shape optimization of bulbous bow,and the deformation of the height direction of the bulbous bow has no significant effect on the resistance.Secondly,the hydrodynamic performance of the optimized ship in oblique towing is analyzed.The hydrodynamic performance of the optimized CNG hull-rudder system and hull-propeller-rudder system under oblique navigation is studied by using the numerical method based on RANS equations.The RANS k-ω turbulence model is adopted,and the overset grid technology is applied to consider the influence of free surface on ship motion.The propeller is processed by Moving Reference Frames.The based on the analysis of rudder surface pressure,free surface waveform and flow field around the ship under different drift angles,the interaction of CNG hull-propeller-rudder is analyzed.Finally,the acceleration characteristics of the ship are analyzed.The viscous flow CFD method is also used to simulate the nonlinear navigation process of CNG ship,application of overset mesh technology,ignoring the influence of free surface on ship motion,and the propeller is treated by sliding grid.The hydrodynamic performance of ship propeller with different acceleration rotation and constant rotation is analyzed.The influence of propeller rotation effect on ship navigation resistance and propeller hydrodynamic force is analyzed.