A NURBS-Based Computational Tool for Hydrodynamic Optimization of Ship Hull Forms

NURBS stands for a "Non-Uniform Rational B-Spline" type of surface. Ship hull forms are represented by NURBS in most of the modern Computer Aided Ship Design (CASD) environments. Computational fluid dynamics (CFD) based hull-form hydrodynamic optimization relies on CFD solvers to evaluate the objective functions in terms of the flow around the ship hull that is discretized by meshes. In order to conduct CFD-based hull-form hydrodynamic optimization efficiently and automatically, it is essential to develop an accurate and effective NURBS-based hull-surface modification technique and an automatic mesh generation tool. A.;NURBS-based computational tool for hydrodynamic optimization of ship hull forms is developed in this dissertation. A new hull surface modification technique is developed to modify the hull form within NURBS in the design optimization process, which ensures: (i) Only a small number of design variables are required to reduce the number of objective function evaluations; (ii) Large variation of hull forms can be obtained to produce different type of hull forms; (iii) Modified region can join the original design smoothly without discontinuities when only a part of the hull needs to be optimized; (iv) Practical hull form (both three-dimensional fairness and manufacture practicability) can be preserved and various geometrical constraints can be easily implemented in the optimization process. In addition, a NURBS-based grid generation tool is developed to discretize hull surface and generate the mesh required for the CFD simulation of the flow around the hull.;Hydrodynamic design of ships involves several stages, from preliminary and early-stage design to late-stage and final design. As the objective of this study is to develop a practical hydrodynamic optimization tool for the design of a ship with reduced drag at the early design stage, a practical design-oriented CFD tool (Code SSF), based on a new theory called Neumann-Michell (NM) theory, is used to compute the steady flow about a ship and evaluate the objective function that measures the wave drag and/or total drag. Even though SSF is a highly efficient CFD tool, the need to conduct hull form optimization for several design speeds with further reduced computing time prompted the development of an approximation model, i.e. a response surface, in which only a limited number of objective function evaluations are done using CFD solver directly. Based on the response surface, An ANalysis of VAriable (ANOVA) functionality is developed to analyze the importance of each design variable. An evolutionary-based optimization solver is used to find the optimal hull form on the response surface.;The computational tool developed in this study ensures the seamless integration of CASD, CFD and optimization techniques into the hydrodynamic optimization of ship hull forms. The applications of the tool on several real life ships demonstrate that the present tool provides an effective and inexpensive way to optimize hull forms at the early design stage. It also offers helpful analyses on the importance of different design variables. Due to its modularity, the developed computational tool can be extended to study the optimization problem in terms of other hydrodynamic performance.