Study On Local Modify Method For Ship Hull Surface

Mathematics line generation used in ship surface express has become an important method of ship design. Surface modeling software based on this method has played a key role in ship design and manufacture. However, nowadays the methods used are all in allusion to global generation and modification, which can't precisely meet the local modify target. Therefore, this thesis puts forward a simply and multipurpose local modify method, which is based on NURBS surface. We could generate content surface within boundary. Not only can solve the local modification problem conveniently, but also can be combined into modeling software to carry out follow-up calculation.After analyzing the research status about surface modify method, the thesis expound the rational--the relevant algorithm of NURBS surface. Do some research about influence of controls parameter on target characteristic. Then apply the local modify method to modification of one ship stern. Finally, discuss the extended application of this method.The key and innovations of local modify method are fixing boundary and adjusting controls parameter. To finish the surface modification, we should fix the boundary and ensure the smoothly connect of the surfaces in and out the boundary. After summarizing and analyzing the foregone boundary treatments, the thesis using surface joining and subdivision combined method to fix boundary, which assure the fairing joining of surfaces within and outside boundary. The simultaneous equation of moving control points makes the express simple and direct, we can get the change value of the control points and weights using least square method. The qualitative and quantitative analysis of influence of controls parameter on target characteristics solve the key problem about which points should be moved. This provide direction of practical application. The uniform expression of the whole surface provide the foundation for follow-up calculation.All the calculation modules are compiled by VB language, which provide important tools for the design. Because of the abstract of the computational formula, the graph display based on FreeShip is provided.The thesis has a test to verify the modify method by change a ship's stern, and get a new ship surface which meets design demands. At last, we get a fair and smooth surface。On these grounds, we know this method is convenience and practical, it can be used to get a satisfactory surface according to the designer's demand.The local modify method is broadspectrum. When the boundary is the appoint line on the surface, it can achieve the local modify target. When the boundary is the surface edge, it can be used to produce the surface. This method is with wide application. It can not only be use to ship surface modify, but also in other fields. At last, the thesis discuss the expanding apply of the local modify method, and apply it to variational boundary surface modification and ship surface patches design.