基于OpenGL实现NURBS汽车前盖曲面造型

分析了NURBS构造自由曲面的方法,结合汽车前盖曲面流线型知识,基于OpenGL技术,利用VC++开发工具进行汽车前盖曲面的造型。     

高级曲面造型的功能实现与现状

一、曲面设计基础复杂外形的产品设计和制造是任何CAD／CAM软件必须解决的重要问题，这实际上是曲线曲面理论在工程上的具体应用。从CAGD的几十年发展来看，各种理论方法和算法研究层出不穷，而且趋于问题的几何方面。例如，60年代末出现的Bener曲线曲面就是基于几何逼近的思想，对工业界的CAD应用产生了巨大影响。之后，B样条方法以其易于局部修改、形状控制灵活的特性克服了Bener的缺点，成为曲面造型的有效工具。另外，随着实体造型技术的不断成熟，曲面、实体迫切要求融合一体，即采用以精确曲面为壳的实体。这就需要以统一方法…     

二维半自由曲面造型技术与雕刻系统

描述二维自由曲面的造型技术，提出了基于区域填充拉伸、纹理映射、线状模型的造型方法，并对中国水墨画的浮雕造型方法进行了描述。自然物体表面模型的生成技术是二维半模型造型的技术关键，采用由影调到物体表面外形的恢复技术，有效地解决了从实体图象到模型表面的重建问题。     

基于NURBS曲线曲面造型理论的产品外形系统设计

为了设计一个适用于产品外形设计的系统,文中重点对曲线曲面造型模块进行了研究,在NURBS曲线曲面造型模块中融入了实体造型的功能,设计了便于扩充和维护的曲线曲面类层次结构,并讨论了曲面造型模块的应用流程,通过与数据导入导出功能的衔接实现了与其它造型软件之间的数据共享,提高了系统造型效率,缩短了产品设计周期。在内核的显示模块设计中,提出了一个包含两个显示链表的显示类结构,用以加快图形对象的显示速度。     

面向制造的CAD/CAM系统--设计、加工编程软件Space-E

一、Space-E系统的基本构成 Space-E系统的造型功能提供了灵活的复合建模方式,即把严谨的实体造型和灵活的曲面造型相融合,提供了丰富的曲线曲面生成功能,以及多种快捷的实体生成功能,能够充分满足工业设计的需要,为用户提供自由直观的建模环境.     

自由曲面光滑拼接的数值优化方法

研究了B样条曲面的光滑拼接问题，介绍了参数曲面几何连续性的定义，提出了2种在B样条曲面间实现 光滑拼接的数值优化算法，即调整邻接曲面的公共边界曲线和调整其中一个曲面的邻近边界的控制顶点。实验结果表明，灵活使用文中的方法修改曲面外形可有效地解决曲面造型中的相关问题。     

MESSAGE——具有自由曲面造型功能的立体造型系统

MESSAGE是一具有自由曲面造型功能的立体造型系统,它能够处理二次曲面、旋转曲面、 广义sweeping曲面、自由曲面以及由平面和上述曲面围成的三维物体,系统以平面及双三次 有理B样条曲面为基本曲面模型,提供了布尔运算、glue运算及多种局部修改运算.系统还 具有一个独立的几何数据库,可以支持一些重要的工程应用.     

面向制造的CAD/CAM系统——设计、加工编程软件Space-E

一、Space-E系统的基本构成 　　Space-E系统的造型功能提供了灵活的复合建模方式,即把严谨的实体造型和灵活的曲面造型相融合,提供了丰富的曲线曲面生成功能,以及多种快捷的实体生成功能,能够充分满足工业设计的需要,为用户提供自由直观的建模环境.……     

数控加工刀具轨迹生成方法探讨

目前,零件造型的方法主要有三种:线架造型、曲面造型和实体造型.在数控加工中,通常采用曲面造型和实体造型相结合的方法来进行.本文就在CAXA制造工程师软件中进行实体造型零件的数控加工曲面时,刀具轨迹生成的方法进行探讨.……     

数控加工刀具轨迹生成方法探讨

目前,零件造型的方法主要有三种:线架造型、曲面造型和实体造型.在数控加工中,通常采用曲面造型和实体造型相结合的方法来进行.本文就在CAXA制造工程师软件中进行实体造型零件的数控加工曲面时,刀具轨迹生成的方法进行探讨.     

附加自由曲面构造框架及其有效性维护的研究*

在对HUST-CAID(哈尔滨理工大学计算机辅助工业造型设计)系统进行研究的基础上,首先引入了自由曲面特征,然后结合HUST-CAID系统定义了自由曲面特征的分类和参数化,应用这种分类和参数化的方法创建了一个自由曲面特征,提出了一种基于FFDP配置的附加自由曲面特征的构造框架。此框架可以使自由曲面整体模型的构造完全参数化。最后建立了基于这个框架构造的自由曲面附加特征的有效性维护机制,从而达到对自由曲面附加特征进行有效性维护的目的。     

基于特征造型的自由曲面特征及约束求解的研究

在对HUST-CAID（哈尔滨理工大学计算机辅助工业造型设计）系统进行研究的基础上，首先引入了自由曲面特征。然后结合HUST—CAID系统定义了自由曲面特征的分类和参数化，同时系统为用户提供了一组适当的参数，使用户能够直观的设计任意曲面，而不必参与曲面的底层设计。当用户修改参数时，系统就会自动提供相应的反馈。为了求解出与约束一致的图形，还给出了一种新颖的原型驱动约束求解算法，并在HUST—CAID系统中进行了仿真实验，结果显示，此算法能够有效地简化约束求解和特征造型的过程。     

Feature-based 3D non-manifold freeform object construction

This paper presents a novel technique for modeling a 3D non-manifold freeform model around a 3D reference model. To represent both the design abstractions and the incomplete topological information, a new non-manifold data structure is first defined. Our data structure embodies the functional vitalities of both the boundary representation data structure and the complex-based data structure. Along with our data structure, a set of topological operators is defined to manipulate the entities in the data structure. Based on the non-manifold data structure and the topological operators, we develop a technique to construct 3D freeform objects around a reference model. Intuitive 2D sketches are adopted to specify the detailed profile of the object constructed. The construction method is feature-based – every reference model has pre-defined features, and the feature template of the constructed object is related to the features of the reference model by feature node encoding. Therefore, the surfaces derived from one reference model can be regenerated automatically on another reference model with the same features. The geometry coverage of our geometric modeling approach includes both manifold and non-manifold 3D freeform objects.     

自由特征模型参数化研究

为了更高效直观地对自由特征形状进行建模,对自由特征形体及自由特征定义点进行参数化,提出了一种通过封装参数和约束创建自由特征体特征的方法。在自由特征形状的定义中,建立数值参数和最终特征形状几何属性的映射关系。在轨迹线上提取特征定义点,在各点处建立横截面,对横截面进行蒙皮和扫掠运算,生成和基曲面无缝连接的自由形状体特征。     

自由曲面特征的定义与识别技术的研究

结合自主开发的HUST-CAID（哈尔滨理工大学计算机辅助工业造型设计）系统的特点,引入自由曲面特征,给出了自由曲面特征的参数化定义,并在此基础上对自由曲面特征识别进行研究,先是给出自由曲面特征识别的定义,接着提出了基于曲线的特征识别的算法。该方法将基于曲线的特征以二维参数的形式给出定义,使其能在二维平面上研究,通过重构特征的剖面模板库,从而利用目标特征与模板特征匹配实现了特征识别。     

自由曲面特征模型中的数值和曲线参数*

成功的特征模型系统,在很大程度上取决于是否能给用户提供友好的方式来指定和改变特征模型,针对这一点,给出了两个新的功能：a）利用数值参数和曲线参数来指定和改变自由曲面特征模型;b）除了特征模型中现有的参数,其他参数可以添加到特征模型,包括特征之间的交叉曲线。为了提供这些功能,提出了一个新的三个层次的结构,最高层次为不可估计模型,最低层次为可评估的模型,中间层次为部分评估模型,后者链接最高层次的特征和最低层次的几何模型,并且也提供了最高层次和最低层次几何模型中的特征定义的交互。     

Creation of user-defined freeform feature from surface models based on characteristic curves

This paper proposes a novel method for the creation of user-defined freeform feature (UDFFF) from existing surface model. The developed methodology has four major steps: selecting the region of interest (ROI), obtaining the characteristic curves from the surface model, reconstructing the ROI surface, and parameterizing the UDFFF. To quickly create UDFFF on the ROI, the representation of freeform feature based on characteristic curves is proposed. First, the characteristic curves of ROI are obtained automatically or by a small amount of human–computer interaction. In particular, user can directly and easily draw the curves on surface to satisfy the designer's requirements. Second, from the set of characteristic curves that is obtained, freeform surface is reconstructed by a suitable surface generation method, e.g., sweeping, revolving, skinning, and filling. Finally, parameterization of the freeform feature is configured, which primarily involves establishing parameters and building the mappings between feature parameters and shape data. Moreover, according to the degrees of freedom, two types of parameterization of freeform features may be described: one (low degrees of freedom) can be accurately described by the characteristic curves and the other (high degrees of freedom) can be approximated with these curves. The proposed UDFFF creation method has been tested with examples based on the surface models. Experience with our prototype system indicates that it allows untrained users to create UDFFFs from the surface models.     

Numeric and curve parameters for freeform surface feature models

The success of feature modelling systems depends to a large extent on offering user-friendly ways for specifying and varying feature models. In this paper, several new facilities are introduced for this.Numeric and curve parameters are presented for specification and variation of freeform surface feature models. Several properties of the parameters can be defined, such as the direction of evaluation for a curve parameter. In addition to parameters present in features, other parameters can be added to a feature model, including intersection curves between features.To provide these facilities, a new three-level structure is introduced, which includes a partially evaluated model that can capture new generic model entities, including feature intersection curves. The work has been implemented in a prototype surface feature modelling system with functionality for feature class definition, feature model creation, and advanced feature model variation through the new types of parameters.     

Interactive design and simulation of tubular supporting structure

This paper presents a system for design and simulation of supporting tube structure. We model each freeform tube component as a swept surface, and employ boundary control and skeletal control to manipulate its cross-sections and its embedding respectively. With the parametrization of the swept surface, a quadrilateral mesh consisting of nine-node general shell elements is automatically generated and the stress distribution of the structure is simulated using the finite element method. In order to accelerate the complex finite element simulation, we adopt a two-level subspace simulation strategy, which constructs a secondary complementary subspace to improve the subspace simulation accuracy. Together with the domain decomposition method, our system is able to provide interactive feedback for parametric freeform tube editing. Experiments show that our system is able to predict the structural character of the tube structure efficiently and accurately.