共查询到18条相似文献,搜索用时 109 毫秒
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针对反求工程中由于点云数据的不完整而产生的三角网格孔洞,提出了一种三角网格模型孔洞的空间修补算法。在提取孔洞边界特征后进行边界预处理,建立孔洞边界特征平面,并将孔洞边界向该平面投影;逐次寻找投影多边形中夹角最小的对应空间边界点作为网格生长点进行修补,直至新增的三角网格覆盖原有的孔洞;以孔洞边界周围的网格顶点作为采样点,对新增的孔洞网格顶点位置进行最小二乘拟合调整,以实现孔洞的准确修补。通过实例验证,说明该方法具有较好的孔洞修补精度和稳定性。 相似文献
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基于最小二乘支持向量机的三角网格修补算法 总被引:1,自引:0,他引:1
为实现点云数据孔洞区域的修补,提出了一种基于最小二乘支持向量机的三角网格曲面孔洞修补算法。首先检测出孔洞,采集孔洞边界周围的三角片顶点作为学习样本训练最小二乘支持向量机模型;然后对孔洞多边形进行平面填充,获得新增三角片的顶点,并用已训练好的最小二乘支持向量机模型将其优化,最终实现孔洞的修补。实验结果表明,该方法的精度和处理速度优于人工神经网络,具有一定的实用性,为孔洞修补研究提供了一种新思路。 相似文献
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三维封闭三角网格模型的缺失实体孔洞修复算法 总被引:1,自引:0,他引:1
提出一种针对三维封闭三角网格模型的缺失实体孔洞修复算法,由初始导引点出发,根据几何特征搜索孔洞边界,并以水平集方法扩展边界,获取目标问题区域。基于边界采样和投影方法建立代理曲面,实现了内环三角化细分和三维网格表面的自由变形。通过合并环间区域和引入边缘约束的平滑过程,得到缺失实体孔洞的上缝合面。在此基础上向内扩展,获取孔洞下表面边界轮廓,搜索出上下边界环之间的三角网格区域,并利用同样的方法构建缺失实体孔洞的下缝合面。最终,连接上下缝合面以及两个边界轮廓环之间的三角网格区域得到修复实体。试验制作的样件表明,算法能简化人工交互设计的步骤,生成高质量的修补结果。 相似文献
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针对复杂网格曲面分型线提取精度和效率不高的问题,根据非封闭自由曲面和封闭自由曲面的拓扑信息和几何特点,提出了2种基于投影方法的分型线提取算法. 对非封闭模型,首先将模型投影到平面并重新三角网格化,然后提取投影三角网格的边界,最后以平面三角网格的边界为检索信息在原始网格中检索得到自由曲面的分型线. 对封闭模型,根据模具分模的几何原理,提出通过建立封闭自由曲面凹模和凸模离散几何模型的方法提取封闭自由曲面的分型点,然后通过一环邻域点搜索法对分型点排序,得到分型线. 实验结果和数据分析表明,两种方法可以精确、高效地提取非封闭和封闭自由曲面的分型线,并可以确保分型点都是三角网格曲面的顶点. 相似文献
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本文介绍了一种利用网格孔洞的边界元而有效填充网格孔洞的算法。由于在孔洞的修补过程中 ,修补网格的信息不完整 ,所以 ,修补后的网格形状很大程度上依赖于修补算法和初始信息的确定。本文阐述了一种简单而有效的网格孔洞的修补算法。用该算法所生成的网格保持了在孔洞边界的光滑过渡 ,并可以满足一般机械制造工程上的需要 ,在快速原型制造、有限元分析中有重要的实际应用价值。 相似文献
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针对三角网格模型存在的孔洞问题提出一种基于变分隐式曲面的孔洞修补算法。首先,利用孔洞边界信息构造插值孔洞边界的变分隐式曲面并将其网格化,得到初始孔洞网格,再利用边界点裁剪初始孔洞网格,最后把裁剪后的孔洞网格与初始网格拓扑合并,完成孔洞修补。算法充分考虑了孔洞周围的信息,使得孔洞网格与原始网格光滑连接,取得了比较好的效果。 相似文献
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Zhu Y Phillips R Griffiths JG Viant W Mohsen A Bielby M 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2002,216(5):323-332
In intramedullary nail (IMN) surgical operations, one of the main efforts for surgeons is to find the axes of two distal holes. Two distal holes on an IMN, which are inside the intramedullary canal of a patient's femur, can only be seen in a lateral X-ray view. For the standard surgical procedure, the localization of the distal hole axes is a trial-and-error process which results in a long surgical time and large dose of X-ray exposure. In this paper, an algorithm to derive the three-dimensional position and orientation of the distal hole axis was developed. The algorithm first derives the nail axis through two X-ray images. Then the distal hole axis is calculated through projecting back the hole boundary on the X-ray image from a lateral view to three-dimensional space. A least-squares method is used to determine the centres of the front hole and the back hole through iteration. The algorithm has been tested with real data and it was robust. 相似文献
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The existing investigations on piezoelectric materials containing an elliptic hole mainly focus on remote uniform tensile loads. In order to have a better understanding of the fracture behavior of piezoelectric materials under different loading conditions, theoretical and numerical solutions are presented for an elliptic hole in transversely isotropic piezoelectric materials subjected to uniform internal shearing forces based on the complex potential approach. By solving ten variable linear equations, the analytical solutions inside and outside the hole satisfying the permeable electric boundary conditions are obtained. Taking PZT-4 ceramic into consideration, numerical results of electro-elastic fields along the edge of the hole and axes, and the electric displacements in the hole are presented. Comparison with stresses in transverse isotropic elastic materials shows that the hoop stress at the ends of major axis in two kinds of material equals zero for the various ratios of major to minor axis lengths; If the ratio is greater than 1, the hoop stress in piezoelectric materials is smaller than that in elastic materials, and if the ratio is smaller than 1, the hoop stress in piezoelectric materials is greater than that in elastic materials; When it is a circle hole, the shearing stress in two materials along axes is the same. The distribution of electric displacement components shows that the vertical electric displacement in the hole and along axes in the material is always zero though under the permeable electric boundary condition; The horizontal and vertical electric displacement components along the edge of the hole are symmetrical and antisymmetrical about horizontal axis, respectively. The stress and electric displacement distribution tends to zero at distances far from the elliptical hole, which conforms to the conclusion usually made on the basis of Saint-Venant’s principle. Unlike the existing work, uniform shearing forces acting on the edge of the hole, and the distribution of electro-elastic fields 相似文献
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对当前反求工程关键技术之一的特征提取技术进展作了综述.特征提取分为边界特征提取和过渡特征提取,前者分为基于点云的提取和基于三角网格的提取;后者分为等半径过渡特征提取和变半径过渡特征提取.分析和比较不同提取技术的优缺点,最后再介绍一种用于提取变半径过渡特征的多阈值精度比较法. 相似文献
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Exact solutions for piezoelectric materials with an elliptic hole or a crack under uniform internal pressure 总被引:3,自引:1,他引:2
The existing investigations on piezoelectric materials containing an elliptic hole or a crack mainly focus on remote uniform tensile loads.In order to have a better understanding for the fracture behavior of piezoelectric materials under different loading conditions,theoretical and numerical solutions are presented for an elliptic hole or a crack in transversely isotropic piezoelectric materials subjected to uniform internal pressure and remote electro-mechanical loads.On the basis of the complex variable approach,analytical solutions of the elastic and electric fields inside and outside the defect are derived by satisfying permeable electric boundary condition at the surface of the elliptical hole.As an example of PZT-4 ceramics,numerical results of electro-elastic fields inside and outside the crack under various electric boundary conditions and electro-mechanical loads are given,and graphs of the electro-elastic fields in the vicinity of the crack tip are presented.The non-singular term is compared to the asymptotic one in the figures.It is shown that the dielectric constant of the air in the crack has no effect on the electric displacement component perpendicular to the crack,and the stresses in the piezoelectric material depend on the material properties and the mechanical loads on the crack surface and at infinity,but not on the electric loads at infinity.The figures obtained are strikingly similar to the available results.Unlike the existing work,the existence of electric fields inside an elliptic hole or a crack is considered,and the piezoelectric solid is subjected to complicated electro-mechanical loads. 相似文献
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提出一种针对任意多边形边界内嵌任意形状、任意多个内特征的“递归式”三维平面三角划分方法 ,该算法主要应用于产品概念设计中零件的可视化处理。在提出“有效线段”概念及相关三维平面“内外点的判定”方法的基础上 ,提出针对不同内外特征形状的一整套三角划分方法。较之一般的三角剖分算法 ,本方法着重提高了算法的简单性、通用性及处理问题的有效性 ,本文的研究成果已成功应用于“86 3”课题 :基于广义映射原理的绿色产品设计自动化软件系统中 相似文献
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The present article proposes a technique to improve the performance of textured hydrostatic thrust bearings with the use of oil supply holes. The article provides a comparison between smooth and surface-textured hydrostatic thrust bearings. To get an accurate prediction of the caviation regime, the Jakobsson-Floberg-Olsson (JFO) mass conservation algorithm has been used instead of the Reynolds boundary conditions. It has been observed that surface texture results in a significant decrease in friction power loss along with an improvement in other performance parameters. The study also reveals that the location of the supply hole for the lubricant system significantly affects the bearing performance. 相似文献