Research On NURBS Stream Curve And Lightweight Design Of Hull Surface

The hull surface design plays an important role in the ship design.Nowadays NURBS is the main method for ship design.But there are some defects such as the requirement for overmuch data or redundant definition data in current hull surface design method resulting in the inconvenient fairness and modification of hull surface.In addition,the geometric properties of curves and surfaces are still separate from the flow field information in hull surface design.And the designers' experiences are difficult to inherit to guide the optimization in the common optimization method.So the hull surface design fails to achieve intellectualized design purpose.Based on studying the features of hull surface,NURBS stream curve is studied and applied to the lightweight hull surface design by combining NURBS and stream curve and surface modeling method,replacing interpolation method with approximation method and designing reasonable intelligent solution strategy.The design instances of the full-scale ships indicate that this method is effective and feasible.To improve design efficiency and stability,the waterlines and the stem and stem contours approximation with as less control parameters as possible is studied in this dissertation.The mathematical model of their lightweight approximation is established.A framework of the quantum-behaved particle swarm optimization(QPSO)algorithm is constructed to solve these approximation problems.According to the approximate design features,the memory factor is introduced to improve the algorithm to solve the waterlines lightweight approximation design.Then,the immune quantum-behaved particle swarm optimization(IQPSO)is specifically designed by combining the immune operator of the immune genetic algorithm(IGA)with the QPSO algorithm.Meanwhile,the self-adaptive constraints evolution strategy(SACES)is proposed to improve the IQPSO algorithm.Finally,the self-adaptive approximation solving strategy is constructed and applied to solve the stem and stern contours approximation problems,a typical kind of complex nonlinear constrained optimization problems.The design efficiency of the related characteristic curves is improved.The concept of NURBS stream curve unit is proposed integrating NURBS and stream curve modeling method.Furthermore,a new NURBS stream curve modeling method based on other constraints,such as area,centroid of area,the eigenvalue of the flow filed,etc.,is proposed and used to solve the hull waterline design problem.It is realized to direct characteristic curves design preliminarily using the flow field information.Combining draught function and NURBS,the self-design method of ship hull surface based on the vertical parameterization is proposed.The hull surface can be designed with as less data as possible using this method and it is more suitable for the self-design of new ship form.During the characteristic curves design of ship hull surface,it is not easy to use knowledge-directed optimization algorithm and NURBS has not been integrated well with the parameterization,which result in the inefficient design process.To solve these problems,knowledge-directed optimization solution strategy is put forward.The guidance knowledge is proposed in the belief space of the cultural algorithm.The guidance knowledge is constituted using the gradually structuralizatation or quantification design intents(the artificial individual,the design constraint and the design objective),which leads to the optimization algorithm solution being guided in both the gene level and the population level directly or indirectly.So the designers' experiences can be derived in time.A lightweight design approach of hull surface approximation is proposed.The hull surface is generated by two steps of section curves approximation.The genetic algorithm with the adaptive alteration of the chromosome length is improved and applied to solve this optimization problem.Applying this method,the data used for hull surface design and approximation are reduced on and the design results satisfy the requirements of the engineering design.Based on the lightweight model of the control points distribution setting for the hull surface characteristic curves approximation,and the specially designed intelligent solution strategy,the proposing NURBS stream curve lightweight design method of hull surface provides a foundation for the reverse design method of hull surface.The lightweight definition data of hull surface and its characteristic curves are achieved.And the design efficiency and quality are improved.