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用能量优化方法构造N边域曲面 总被引:10,自引:2,他引:8
本文以物理变形模型基础,利用二次优化方法构造N边域曲面,得到满足N条边界曲线约束的以B样条表示的曲面。用该法生成的B样条曲面不仅精确地符合N条边界曲线约束,而且其幂次不高于各边界曲线,因而比一般方法更具有实用价值。文中详细地阐述了该法的基本思路和实现方法,并给出了应用实例。 相似文献
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虚拟原型工具作为可行的设计工具已经吸引了整个行业的关注。最重要的一个挑战是研究机构延长虚拟现实技术的功能,并超出它现在的人机工程学和设计评审范围。文章提出的一种研究是一个更大的研究项目的一部分,维修性评估目的是为了完成在虚拟原型上的维修性评估。文章论述了设计和实现一个几何约束管理,已被设计用来支持在虚拟环境下的物理实在性和交互式的装配和拆卸任务。约束管理所使用的关键技术是直接的相互作用、自动约束识别,约束补偿和受约束的运动。各种最优化技术已经应用于实现实时互动的大型工业模型。 相似文献
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基于特征的参数化设计和实体模型编辑的研究 总被引:9,自引:0,他引:9
本文概述和研究了基于特征的模型表示、特征的生成方法与手段、特征参数和约束尺寸的变量命名机制、约束关系的求解方法后,提出基于面向装配设计的抽取零件模型策略和重用CSG树技术,实现实体模型编辑与其历程树无关和加速实体模型生成,大大提高后期设计修改的灵活性,满足交互式设计需要。 相似文献
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为在低端计算平台上实现实时的虚拟人运动仿真,提出了一种基于限时梯度投影法的虚拟人运动生成方法。不同于传统的基于Jacobian 矩阵广义逆的逆向运动学方法,该方法在合成末端效应器运动轨迹的基础上,通过将逆向运动学问题转变为约束非线性规划问题,有效克服了计算Jacobian 矩阵广义逆所导致的计算复杂度高、多解及奇异性等问题。同时,通过动态调整系统每帧的规划时间,可同时达到非线性函数局部线性化和限时求解的双重目的。文章最后以人体行走运动为例,在PC 平台上实现了一个虚拟人的行走运动仿真系统。 相似文献
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目的 由于计算的难度与精度问题,在求解布局的过程中通常不考虑待布局元素面积的大小和形状的几何约束问题,导致求解的布局结果是理论上的,无法达到真正实用的目的。为提高界面布局优化方法生成布局方案的可用性,提出了一种集成启发式算法、多属性决策(MAMD)和整数线性规划(ILP)的方法。方法 首先,在获取到待布局元素间相关性、待布局元素的使用频率和面积等数据情况下,使用遗传算法(GA)通过改变待布局元素几何约束的参数生成一组备选布局方案;其次,将交互成本、GA寻优所花费的时间、有效性、效率和满意度作为评价界面布局的五个指标,根据TOPSIS、AHP和数据包络分析(DEA)等多属性决策方法对所有备选布局方案进行排序;最后,使用ILP方法获取一致性排序。结果 获得一个有效、具有高可用性的布局方案。结论 根据实验结果可知,该方法寻到的最优布局方案比原始方案有效地降低了交互成本和算法寻优的时间,提高了布局方案的可用性。 相似文献
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基于FRG的约束模型管理 总被引:1,自引:0,他引:1
为实现设计环境的自然化和智能化,本文将特征模型分为模型描述和模型数据两个层次,模型描述是基于约束的,故称为约束模型,并定义为满足一定约束关系集的特征集合。 相似文献
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基于约束矩阵的几何约束传播研究 总被引:1,自引:0,他引:1
为了保证几何约束系统的一致性和几何约束求解的正确性,对几何约束传播进行了研究,指出几何约束传播是几何约束系统的本质特征。提出了几何约束矩阵和约束传播矩阵来表达和揭示约束传播的内在机制,并提出了一种闭环约束识别的新方法。通过约束传播分析,为几何约束求解引擎的实现提供了理论依据和快速算法。 相似文献
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传统的形状及位置表示模型通常是建立在低层次的无应用意义的几何拓扑元素之上,因而无法很好地支持计算机辅助设计(CAD)向实用化和智能化方向发展。本文提出了一种非数值化的基于约束的产品形位描述模型,并对该模型中存在的一些问题进行了深入的讨论。该模型符合设计人员实际设计思维与过程,同时也支持高层次产品设计信息以及产品的设计过程信息,因而为传统CAD系统向新一代实用化智能化CAD系统过渡提供了一个良好的产品形位表示模型。 相似文献
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Continuum structural topological optimizations with stress constraints based on an active constraint technique 下载免费PDF全文
Jian Hua Rong Ting Ting Xiao Liao Hong Yu Xuan Pei Rong Ya Jun Xie 《International journal for numerical methods in engineering》2016,108(4):326-360
Stress‐related problems have not been given the same attention as the minimum compliance topological optimization problem in the literature. Continuum structural topological optimization with stress constraints is of wide engineering application prospect, in which there still are many problems to solve, such as the stress concentration, an equivalent approximate optimization model and etc. A new and effective topological optimization method of continuum structures with the stress constraints and the objective function being the structural volume has been presented in this paper. To solve the stress concentration issue, an approximate stress gradient evaluation for any element is introduced, and a total aggregation normalized stress gradient constraint is constructed for the optimized structure under the r?th load case. To obtain stable convergent series solutions and enhance the control on the stress level, two p‐norm global stress constraint functions with different indexes are adopted, and some weighting p‐norm global stress constraint functions are introduced for any load case. And an equivalent topological optimization model with reduced stress constraints is constructed,being incorporated with the rational approximation for material properties, an active constraint technique, a trust region scheme, and an effective local stress approach like the qp approach to resolve the stress singularity phenomenon. Hence, a set of stress quadratic explicit approximations are constructed, based on stress sensitivities and the method of moving asymptotes. A set of algorithm for the one level optimization problem with artificial variables and many possible non‐active design variables is proposed by adopting an inequality constrained nonlinear programming method with simple trust regions, based on the primal‐dual theory, in which the non‐smooth expressions of the design variable solutions are reformulated as smoothing functions of the Lagrange multipliers by using a novel smoothing function. Finally, a two‐level optimization design scheme with active constraint technique, i.e. varied constraint limits, is proposed to deal with the aggregation constraints that always are of loose constraint (non active constraint) features in the conventional structural optimization method. A novel structural topological optimization method with stress constraints and its algorithm are formed, and examples are provided to demonstrate that the proposed method is feasible and very effective. © 2016 The Authors. International Journal for Numerical Methods in Engineering published by John Wiley & Sons Ltd. 相似文献
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Yishay Spector 《国际生产研究杂志》2013,51(11):3387-3394
This paper addresses the issue of business model (BM) management and its relationship to the theory of constraints (TOC). Coman and Ronen (Coman, A. and Ronen,B., 2007. Managing strategic and tactical constraints in the hi-tech industry. International Journal of Production Research, 38(7), 1631–1639) have extended TOC methodology to include the alignment of the organisation's competencies with the business arena's strategic constraints. The aim of this paper is to take TOC one step further and to combine it with the business models theory. Business models have become important value creators due to the proliferation of new and innovative business models (i.e. new ways of creating value). New firms with new business models are threatening and replacing established companies and conventional ways of doing business. Among these are the music, publishing, books, retail, airline and many other industries. This paper argues that in the wake of the World Wide Web, contract manufacturing and globalisation it not enough to manage the firms (internal, external or strategic) constraints. In addition, the management of the firm's BM as a potential constraint is a key factor in the modern management theory. 相似文献
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Three‐dimensional analyses of in‐plane and out‐of‐plane crack‐tip constraint characterization for fracture specimens 下载免费PDF全文
M Y Mu G Z Wang S T Tu F Z Xuan 《Fatigue & Fracture of Engineering Materials & Structures》2016,39(12):1461-1476
Three‐dimensional elastic–plastic finite element analyses have been conducted for 21 experimental specimens with different in‐plane and out‐of‐plane constraints in the literature. The distributions of five constraint parameters (namely T‐stress, Q, h, Tz and Ap) along crack fronts (specimen thickness) for the specimens were calculated. The capability and applicability of the parameters for characterizing in‐plane and out‐of‐plane crack‐tip constraints and establishing unified correlation with fracture toughness of a steel were investigated. The results show that the four constraint parameters (T‐stress, Q, h and Tz) based on crack‐tip stress fields are only sensitive to in‐plane or out‐of‐plane constraints. Therefore, the monotonic unified correlation curves with fracture toughness (toughness loci) cannot obtained by using them. The parameter Ap based on crack‐tip equivalent plastic strain is sensitive to both in‐plane and out‐of‐plane constraints, and may effectively characterize both of them. The monotonic unified correlation curves with fracture toughness can be obtained by using Ap. In structural integrity assessments, the correlation curves may be used in the failure assessment diagram (FAD) methodology for incorporating both in‐plane and out‐of‐plane constraint effects in structures for improving accuracy. 相似文献
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AutoCAD系统为每个实体对象提供了唯一的标识符(ID)。笔者基于ARX技术对AutoCAD图形数据库的访问机理,通过实体标识符(ID)及实体对象的特征点、图元几何约束及图元间的约束联动,实现了图元实体驱动的参数化变动设计;通过尺寸实体对象标识符(ID)及尺寸与图元的约束关系,实现了尺寸驱动的参数化变动设计。此方法在水利工程流道CAD中加以了应用,其效果良好。 相似文献
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将源自控制工程的约束观点引入色彩设计的研究范畴,提出了色彩约束的新理念。在阐述色彩约束的内涵基础上,分析了其在物理属性、色彩心理、色彩文化中的表现特点,归纳了其在色彩创作实践中的应用价值。同时,将偶发性色彩作为反约束的典型案例提出,对比并探讨了2者的差异和关联,指出色彩约束与反约束在理论上是互为补充、相辅相成的,在实践中应各取所长、结合运用,以形成色彩设计更多样的创新图式。 相似文献