【作者】 刘鹏；

【导师】 胡铁牛；

【作者基本信息】 上海交通大学 ， 船舶与海洋结构物设计制造， 2012， 硕士

【摘要】 数学线型生成方法进行船舶外形曲面表达,已经成为船舶设计的重要手段,以此为基础的曲面造型软件成为船舶设计制造过程中极为重要的工具。但是目前的数学线型生成方法在进行船型设计时多是整体生成和修改船型,无法令人满意地解决数学船型曲面的局部修改问题。为此,论文提出了一种简便、多功能的曲面局部修改法,该法基于非均匀有理B样条(NURBS)曲面,可以在指定边界内生成满足要求的曲面,并与边界外的曲面光顺连接。运用该方法既能灵活方便解决曲面修改问题,又能结合进数学船型软件内部,便于后续计算的进行。在分析国内外曲面修改研究现状的基础上,论文阐述了其理论基础——NURBS曲面的相关算法,对曲面局部修改具体过程和控制参数对目标特征值的影响进行了研究,并将局部修改法应用于某船体尾部修改过程中,最后探讨了局部修改法的扩展应用。论文的创新点和关键在于边界的固定和控制参数的调整。要完成局部修改,首先应该固定住边界,并保证边界内外曲面的光顺连接。论文对之前的边界处理方法进行了总结分析,并创新性的提出了通过曲面拼接和细化曲面相结合的方法来固定边界,保证了曲面修改的局部性和局部曲面与外部曲面的光顺连接。控制顶点移动方程组的建立使得新曲面的表达简单直接,应用最小二乘法即可求得控制顶点及其权因子的变化量,可以方便的达到满意的修改效果。为了对修改过程的控制提供指导,论文针对控制参数对目标特征值影响的定性分析与定量计算进行了研究,解决了确定调整控制顶点范围的关键问题,避免了修改过程的盲目和繁琐。边界内外曲面的统一表达为后续性能计算奠定了有利基础。根据本方法的研究思路及数学模型用Visual Basic语言开发了相应的计算模块及程序。包括曲线曲面的表达及反算,边界的表达及固定,曲面的修改和控制参数对目标特征值的影响计算等。由于计算公式的抽象和非直观性,论文采用FreeShip所带图形显示平台作为显示工具来加强软件的图形功能,使显示的曲面直观清晰,也便于判断修改,可作为后续设计的重要工具。为了验证局部修改法的修改效果和实用性,论文对某船体曲面的船尾形状进行了局部修改,并对其修改后的曲率和几何变化进行了验证,结果显示经过修改得到了一个满足设计要求、光顺平滑的船体新曲面。针对该算例的修改计算,可知该局部修改法确是方便实用的,可以根据设计者的修改要求获得满意的曲面形状。本法用途广泛,不仅可以用于曲面修改,也可用于曲面设计,当边界为曲面上指定曲线时可实现局部曲面的修改,当边界为整个曲面边线时,则可以生成曲面;应用范围广,并不局限于船体曲面的修改及设计,同样适用于其他的领域,例如航空、汽车、机械设计等等。因此论文最后对局部修改法的扩展应用进行了探讨,将其应用于变边界曲面修改和船体曲面的分片生成,对应用过程中的具体操作进行了阐述。更多还原

【Abstract】 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.更多还原