A NURBS-based Hull Form Optimization For Resistance

With the development of Computational Fuild Dynamics(CFD),high performance computing and optimization technology,the CFD-based hydrodynamic optimization of ship hull form has been developed rapidly,which will play an important role in the fields of green and intelligent ships.In the modern computer-aided ship design system(CASD),ships are mostly represented by Non-Uniform Rational B-Spline(NURBS)surfaces and saved in IGES file format according to the international standard.The NURBS surface is able to represent any complex surface in a unified mathematical expression.The local deformation of NURBS surface can be achieved by simply moving NURBS control points or changing weight factor.In order to intergrate with the modern computer-aided ship design system,it is necessary to develop a NURBS-based ship hull form optimization technique for hydrodynamic performance.Ship geometry remodeling,mesh regeneration and hydrodynamic performance optimization can be performed based on NURBS surface.Since meshes are regenerated for each candidate hull,the quality of mehes can be guaranteed and avoid producing skewed meshes that happens in the deformation of hull surfaces represented by discrete meshes because of large deformation.The following modules are developed in this paper based on C language: IGES file reading and writing processor,NURBS-based hull surface representation and manipulation library,NURBS-based hull surface deformation method,mesh generation module.These modules are intergrated with the existing CFD solver,surrogate model and optimization algorithm,which forms a NURBS-based ship hull form optimization tool for hydrodynamic performance.It fuses CAD system,CFD method and optimization technology.To validate the reliability and effectivity,it has been applied to the optimization of standard ship model in terms of resistance.The optimization results demonstrate that the NURBS-based ship hull form optimization tool can extract the information of NURBS surface directly from IGES file and the optimal ship can be saved in IGES file format for subsequent design and manufacture.The basic NURBS algorithms are able to pre-process parent ship surfaces properly.Using radial basis function method and Free-Form deformation method to move NURBS control points can achieve flexible deformation and reduce the number of design variables simultaneously.The mesh generation module can control grid refinement level to guarantee the quality of meshes.All of these modules extend the function of in-house ship hull form optimization solver named OPTShip-SJTU,making it possible to solve more complex engineering optimization problems.