共查询到19条相似文献,搜索用时 164 毫秒
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文章给出了基于C-B样条的由网格数据产生三角形和四边形曲面片的方法,C-B样条是由基底函数{sin t,cos t,t,1}导出的一种新型样条曲线,它可以克服现在正在使用的B样条和有理B样条为了满足数据网格的拓扑结构而增加多余的控制点,求导求积分复杂繁琐,阶数过高,从而讨论其连续拼接时增加了困难等缺点,如何将它推广成曲面就成为一个重要问题。作者利用边-顶点方法构造插值算子,再将这些算子进行凸性组合,将C-B样条曲线推广成三角形曲面片和四边形曲面片,它可以用于CAD的逆向工程中散乱数据的曲面重构。 相似文献
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带参数的二次三角多项式样条曲线 总被引:10,自引:0,他引:10
给出了带有参数λ的二次三角多项式样条曲线。与三次B样条曲线类似,曲线的每一段由相继的4个控制顶点生成。对于等距节点,在一般情形下,曲线达到了C1连续,而当λ=1时,曲线达到了C3连续。λ有明确的几何意义,λ越大,曲线越逼近控制多边形。还给出了用此种曲线表示椭圆和整圆的方法,在相同的控制顶点下,可生成一簇椭圆弧和圆弧。 相似文献
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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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将轴变形方法引入B样条造型,以促进多肢物体如人体的建模。基本轴映射模型主要针对简单形体造型。为方便用户操作,它将B样条曲面的表面关键点分组映射至轴线上,而关键点被用来定义和操纵轴线及曲面的形状。为适应复杂的造型需求,将基本轴映射模型组合为复合轴映射模型,定义了模型间的连接关系和过渡曲面。测试表明,B样条轴映射模型可以实现简易、直观的多肢物体实时交互造型,并具有通用性和复用性。 相似文献
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在数控加工领域,由于加工刀具一般采用的是球刀,因此在加工非圆的曲面时采用的是用圆弧拟合的方法转换成圆弧加工,理论拟合精度决定了加工误差;圆弧拟合椭圆有无数解,针对八心圆弧拟合椭圆没有准确的误差算法导致拟合椭圆的精度较模糊这一问题,根据图形学理论提出了等差拟合弧的概念,确定了八心圆弧拟合椭圆的定解区间,导出了拟合椭圆的八心圆弧法向误差超越方程解析式,并用二分法求解,在AutoCAD环境下应用Visual LISP语言编程,求解出根据法向误差确定八心圆弧拟合椭圆的最小误差带,从而确定八心圆弧拟合椭圆的最优解,使八心圆弧是否可以拟合给定形状公差的椭圆有了准确的判断依据. 相似文献
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基于NURBS的PDE曲面构造法研究及应用 总被引:2,自引:0,他引:2
由非均匀有理B样条曲线曲面给定边界条件,用偏微分方程来构造曲面,以参数“a”控制其整体形状,本文分析其思路原理及过程,并列举了在CAD上的应用,最后分析了优缺点。 相似文献
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针对CE-Bézier曲面造型中复杂曲面难以用单一曲面来表示的问题,通过分析CE-Bézier曲线的唯一性,提出了一种新的CE-Bézier曲面的光滑拼接技术。首先,在分析第1类CE-Bézier曲线基函数及其端点性质的基础上,对第1类CE-Bézier曲线的唯一性进行了研究,得出了对于同一条第1类CE-Bézier曲线可以有很多组不相同的控制顶点和形状参数与之对应的结论;其次,利用该结论进一步给出了两相邻第1类CE-Bézier曲面片间G1光滑拼接的一般几何条件,并通过合理地选取形状参数,进一步简化了该曲面的G1拼接条件;最后,给出了第1类CE-Bézier曲面光滑拼接的几何造型实例。实例结果表明,该方法简单、直观、易实现,有效地增强了CE-Bézier方法表达复杂曲线曲面的能力,可广泛地应用于工程复杂曲面的造型系统中。 相似文献
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"广义形体分析法"是"工程图学"课程改革的一种探索性创新思维方法,它将课程核心内容整体分解为几何元素、几何结构、功能组合、零件装配、知识与技能等5个块元。介绍了基于"广义形体分析法"的高职"工程图学"课程改革方案及其实现关键,进行了改革的初步探索和实践,取得了较好的成效。实践结果表明,该方法能有效提升图学基础与应用的教学效果,有助于职业快速适应、逻辑思维形成及创新能力提升。 相似文献
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传统的线性四点插值细分方法不能表示圆等非多项式曲线,为了解决这种问题,基于几何特性提出了一种带有一个参数的四点插值型曲线细分方法。细分过程中,过相邻三插值点作圆,过相邻二插值点的圆弧有两个中点,将其加权平均得到新插值点,文中给出了插值公式和算法描述。所给方法具有还圆性,可以实现保凸性。实例分析对比了本方法与多种细分方法的差异,说明本方法是有效的,当参数取值较小时,曲线靠近控制多边形。 相似文献
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Generation of on-axis and off-axis conic surfaces of revolution by applying a tubular tool 总被引:4,自引:0,他引:4
A new technique, fabrication of aspherical ultraprecise surfaces using a tube, is applied to the generation of conic surfaces of revolution, which also demonstrates that it is possible to generate different kinds of surfaces with the same tube. Surfaces are considered that are generated with the same tube with an elliptical edge but with different off-axis distances and different angles between the tube and the surface. Subsequently it is shown that the generated surface is always a radial section of a conic surface. In addition it is proven that the shape of the generated conic surface is independent of the off-axis distance. With each elliptical tube edge a range of different conic surfaces can be made depending on the angle between tube and surface. The more the tube edge resembles a circle, the larger will be the range of different surfaces. For each tube an angle between the tube and the surface exists at which it generates an on- or off-axis part of a semi-ellipsoid. Finally, an optimization technique is presented for the determination of the best combination of process-determining parameters for the generation of a certain conic surface. 相似文献
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NURBS曲面的过渡曲面生成 总被引:4,自引:1,他引:3
曲面过渡是几何造型的关键技术之一,本文提出的NURBS曲面的过渡曲面生成方法,能够处理曲面内具有不同连续性的情况,解决了NURBS曲面的等半径,变半径过渡及三面过渡问题,并在超人CAD/CAM系统中实现。 相似文献
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While conventional engineering transforms engineering concepts into real parts, in reverse engineering real parts are transformed into engineering models. The construction of a surface from three-dimensional (3D) measuring data points is an important problem in reverse engineering. This paper presents a reconstruction method for the sculptured surfaces from the 3D measuring data points. The surface reconstruction scheme is presented based on a neural network. The reconstruction of the existing surfaces is realized by training the network. A series of measuring points from existing sculptured surfaces is used as a training set. Once the neural network has been trained, it serves as a geometric model to generate all the points that are needed. However, the learning rate for the neural network is relatively slow, and the learning accuracy is often unacceptably low. In this paper, to improve the performance of the neural network, a pre-processor is proposed before the input layer. The pre-processor maps the input into the larger space by generating a set of linearly independent values. The effect of the pre-processor is to increase modelling accuracy, and reduce learning time. Based on this method, experimental results are given to show that the reconstructed surfaces are faithful to the original data points. The proposed scheme is useful for regular or irregular digitized data. 相似文献
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组合体及其形体分析法的基本理论问题探讨 总被引:5,自引:0,他引:5
传统工程制图教材关于组合体及其形体分析法的有关理论存在不足之处,本文在阐述组合体概念特有属性的基础上,探讨了叠加体的分解与组合、切割体的形成及虚体补合等涉及的各种表面连接关系。 相似文献
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Xianyun Qin Jianming Zhang Guangyao Li Xiaomin Sheng Qiao Song Donghui Mu 《Engineering Analysis with Boundary Elements》2010,34(11):934-943
This work presents a new implementation of the boundary face method (BFM) with shape functions from surface elements on the geometry directly like the boundary element method (BEM). The conventional BEM uses the standard elements for boundary integration and approximation of the geometry, and thus introduces errors in geometry. In this paper, the BFM is implemented directly based on the boundary representation data structure (B-rep) that is used in most CAD packages for geometry modeling. Each bounding surface of geometry model is represented as parametric form by the geometric map between the parametric space and the physical space. Both boundary integration and variable approximation are performed in the parametric space. The integrand quantities are calculated directly from the faces rather than from elements, and thus no geometric error will be introduced. The approximation scheme in the parametric space based on the surface element is discussed. In order to deal with thin and slender structures, an adaptive integration scheme has been developed. An adaptive method for generating surface elements has also been developed. We have developed an interface between BFM and UG-NX(R). Numerical examples involving complicated geometries have demonstrated that the integration of BFM and UG-NX(R) is successful. Some examples have also revealed that the BFM possesses higher accuracy and is less sensitive to the coarseness of the mesh than the BEM. 相似文献