Study On Variable Fidelity Model Of Bulbous Bow Resistance Reduction Optimization Based On Intelligent Optimization Method

The development of new ship types with excellent performance,energy conservation and consumption reduction,green and clean to reduce the resistance in the process of ship navigation has always been a hot topic of ship type optimization.The shape of the bulbous bow has a great influence on the resistance of the ship.The reasonable selection of the shape of the bulbous bow can reduce the resistance and improve the speed.Taking the shape drag reduction optimization of bulbous bow as the research goal,this paper constructs a gradient optimization framework of low and high-fidelity approximate model based on BP neural network and other approximate technologies,that is,Variable Fidelity Model(VFM)framework.The high-fidelity prediction results of a small number of sample points are used to modify the low-fidelity prediction results of a large number of sample points,so as to reduce the drag prediction time and ensure the calculation accuracy,The geometric shape of bulbous bow with excellent resistance performance can be found with less calculation cost.Taking the military destroyer DTMB 5415 and the civil container ship KCS as the research objects,this paper designs a fully parameterized hull geometric reconstruction scheme,and focuses on three geometric reconstruction methods of bulbous bow,namely,the ship form parameterization fusion technology based on visual programming environment,the free deformation method(FFD)and the parameterization method with the coordinate position of NURBS curve editing point as the variable.Two sets of self-designed hull geometry reconstruction programs based on visual programming environment are provided,which are the parametric fusion program of hull geometry and the surface deformation program of manipulating the coordinate position of curve editing points.A set of visualization program of profile fairing based on genetic algorithm is developed,which can solve the problem of medium-sized line fairing in geometric reconstruction.Through the geometric reconstruction examples of DTMB 5415 and KCS,it is proved that the ship form parametric geometric reconstruction method proposed in this paper can be better applied to ship form optimization.A series of sample ship types are generated by Hull geometric reconstruction technology,which are used as training samples of approximate models in VFM framework,and then low and high fidelity approximate model and modified model are constructed.Through the optimization technology,the optimization solutions of the linear dimensions of the bulbous bow of the two types of ships are found in the modified model,and the excellent hull shape line that reduces the resistance is obtained.Through the CFD numerical analysis,it is proved that the resistance performance of the optimized bulbous bow is better than that of the optimized bulbous bow.Taking DTMB 5415 and KCS as examples,the accuracy and applicability of the VFM frame in the optimization of bulbous bow shape are verified.The results of this study can provide a complete set of bulbous bow design system for ship designers,and the VFM frame can not only be used For the optimization of the bulbous bow shape,it can also be applied to the optimization of the whole ship shape line,with strong practicability.