【作者】 高雪瑶；

【导师】 孙立镌；

【作者基本信息】 哈尔滨理工大学 ， 计算机应用技术， 2009， 博士

【摘要】 特征造型技术能够为设计人员提供特定领域内高层次的概念设计与功能设计。传统的造型技术与参数化、变量化技术相结合,构成参数化、变量化特征造型系统。这类系统依赖于特征的创建历程,在设计后期,若要对产品模型进行修改,就需要按照设计历程完全重现一遍设计过程,导致模型设计的效率很低。与历程无关的造型技术是特征建模技术的补充。在与历程无关的造型系统中,设计人员只需关注最终的设计结果,而不必顾及设计的过程。研究与历程无关的特征造型技术,提高造型系统的操作灵活性和造型效率,是造型系统的一个新的发展方向,具有重要的理论意义和实际应用价值。对此,本文从以下几方面进行了研究:1.根据与历程无关造型的动态、可逆的特点,提出一种基于特征的拓扑元素命名与编码方法。特征的语义与属性在建模过程中保持不变,利用特征名对特征的拓扑面进行命名,然后根据拓扑边和拓扑点的邻接面对边和点进行命名。对于分裂的子面,以特征名为基础按照子面在父面参数域上的顺序对子面进行排序,对子面进行区分。当拓扑边发生分裂或曲面相交产生多条交线时,提出利用参考线进行区分的方法。根据拓扑元素的命名与标识方法,归纳出一种统一格式的拓扑元素编码方法。并提出虚拓扑元素和子边的概念,针对与历程无关模型操作的特点,根据虚拓扑元素和子边的定义方法,提出拓扑元素的继承、分裂与重合操作方法,通过保留模型中拓扑元素间的拓扑关系,实现与历程无关的模型操作过程。2.根据特征模型的操作方法,提出在模型编辑、修改过程中的模型处理与维护方法。将与历程无关的特征模型操作归纳为:平移、拉伸、旋转三种操作方法。对直接受模型操作影响的特征(或部分模型),若没有发生拓扑结构的改变,则直接通过约束求解得到结果模型并予以显示;若发生了拓扑结构的改变,则利用拓扑元素编码方法进行处理,对于分裂的拓扑元素,根据继承规则与分裂操作方法进行处理;对发生重合的拓扑元素,利用子边及虚拓扑元素进行重合操作的处理。对于间接受模型操作影响的特征(或部分模型),提出利用特征依赖图分析相关特征间存在的依赖关系,建立动态的特征修改优先准则,给出特征优先级的性质,根据特征修改优先准则和优先级性质生成正确的结果模型。并提出在模型操作过程中的有效性检查与恢复方法。3.建立与历程无关的模型修改过程中的约束求解机制。以几何实体的欧拉参数表达为基础,建立几何约束的基本定义,并推导常用工程几何约束的代数表达方程,以建立几何约束的数学模型。将几何约束的代数方程组转化为优化问题并利用优化法求解问题的解。提出了一种改进的混沌搜索策略,并将该方法与粒子群算法相结合,利用粒子群算法在初期收敛速度快的特点进行初步搜索,当算法陷入局部最优或找到较优解时,利用改进的混沌搜索策略激活并进行精细搜索,从而准确地找到最优解。4.研究了在与历程无关的造型过程中,特征模型的更新及显示策略。提出将模型的处理过程划分为“预处理”和“实际求解”两步的方法。用特征依赖图(FDG)存储特征信息及特征间的依赖、约束关系,提出将特征依赖图分解为受修改参数影响的“宏几何体”(由相关集确定)和不受影响的刚性体两部分。“宏几何体”是约束求解的主体,将其用几何约束图来表示,图中的每一个约束关系可由约束表达式来表示,并在局部坐标系下进行求解,并研究了在几何约束图中更新求解结果的方法。最后研究了将本文系统用于协同设计的方法。更多还原

【Abstract】 Feature modeling can provide high-level conception design and function design for designer in special domain. Parametric and variational feature modeling system is built by combining traditional modeling technique with parametric and variational technique. These systems depend on creation history of features, and the whole design process must be repeated according to the design history if the model needs to be modified in later design period. This results in the low efficiency of model design.History-independent modeling is complement to feature modeling. In history-independent modeling system, the designers only need to pay attention to design results, but not design process. The research on history-independent feature modeling and promoting flexibility and efficiency of modeling system is a new trend of modeling system, which has theoretical and practical significance. This thesis includes the following contents:Firstly, a method of naming and coding topological entities is proposed, which is based on features, and this method aims at dynamic and reversible characteristics of history-independent modeling. The semantic and attribute of feature is unchangeable in process of modeling. Topological face is named by using feature name, and topological edge and vertex are named by using adjacent faces of them. On the basis of feature name, the split sub-faces are distinguished according to the order that sub-faces are sorted on the parent face. References are used to distinguish the split edges and the multi-edges that produced by surfaces intersection. A uniform coding format is proposed, which is based on topological entities naming. The conception of virtual topological entity and sub-edge are proposed, then inherit, split and merge operation are processed which aim at characteristics of history-independent modeling. History-independent modeling operation is realized through maintaining relations between topological entities in the model. Secondly, model process and maintain methods during editing and modifying are proposed according to model operation methods. The history-independent feature model operations are summarized as translation, extension and rotation. For features or part models that are directly affected by model modification, the result model can be generated by constraint solving and to be displayed if there are no variations in topological structure. The model is processed based on topological entities coding when topological structures are changed. The split topological entities are processed according to inherit rules and split operation, and the merged topological entities are processed by utilizing sub-edges and virtual topological entities. For features or part models that are indirectly affected by model modification, the relations among these features are analyzed by making use of feature dependent graph (FDG). The dynamic feature modification precedence criteria are built and property of feature precedence is given. The appropriate result model is produced according to these criteria and property. Validity checking and recovery method during process of model modification are proposed.Thirdly, constraint solving mechanism is proposed in process of history-independent model modification. The basic definition of geometric constraint is built based on Euler parameter expressions of geometric entities. Then the algebraic equations of common project geometric constraints are derived to establish mathematic model of geometric constraints. The algebraic equations of geometric constraints are transformed into optimization problem and are solved by optimization method. An improved chaos search strategy is proposed, and which is introduced into particle swarm optimization algorithm (PSO). PSO searches solutions rapidly in early evolution period, which is used to search primary solutions. When the algorithm gets into the local extremum or finds preferable solutions, the improved chaos search strategy is used to activate the particles and to search the global best solutions accurately.At last, the update and display strategy of feature model is studied, which can satisfy history-independent modeling. The model process procedure is divided into two steps, namely pretreatment and practical solving. FDG is used to store feature information and relations of dependence and constraints between features. A method of decomposing FDG is proposed, which decomposes FDG into macro-geometry and rigid body. Macro-geometry is affected by the modified parameters, and rigid body is not affected. The macro-geometry is determined by correlation set, which is the principal part of constraint soling. The macro-geometry is expressed in geometric constraint graph. Each constraint relation can be expressed by constraint expressions and be solved in local coordinate system. After the constraints have been solved, the method of updating results in geometric constraint graph is studied. At last, the method of collaborative design based on the proposed system is studied.更多还原