共查询到20条相似文献，搜索用时 15 毫秒
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一种trimmedNURBS曲面的裁剪方法 总被引：4，自引：1，他引：4
所研究trimmed NURBS曲面的裁剪方法分三步完成裁剪算法。其主要特点是将所有trimmed NURBS曲面与裁剪轮廓面的交线都转为封闭环,从而可以统一的方式处理各类裁剪问题。实验结果表明,该算法可方便地解决目前一些曲面造型系统对已裁剪的内部和外部边界无法再裁剪等问题,亦可应用于一般形式的trimmed参数曲面的裁剪操作。 相似文献
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Stefano Pippa Gianni Caligiana 《International journal for numerical methods in engineering》2005,62(4):495-515
In this paper a new method, called GradH‐Correction, for the generation of multi‐patch parametric surface meshes with controlled sizing gradation is presented. Such gradation is obtained performing a correction on the size values located on the vertices of the background mesh used to define the control space that governs the meshing process. In the presence of a multi‐patch surface, like shells of BREP solids, the proposed algorithm manages the whole composite surface simultaneously and as a unique entity. Sizing information can spread from a patch to its adjacent ones and the resulting size gradation is independent from the surface partitioning. Theoretical considerations lead to the assertion that, given a parameter λ, after performing a GradH‐Correction of level λ over the control space, the unit mesh constructed using the corrected control space is a mesh of gradation λ in the real space (target space). This means that the length ratio of any two adjacent edges of the mesh is bounded between 1/λ and λ. Numerical results show that meshes generated from corrected control spaces are of high quality and good gradation also when the background mesh has poor quality. However, due to mesh generator imprecision and theoretical limitations, guaranteed gradation is achieved only for the sizing specifications and not for the generated mesh. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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本文针对曲面造型系统中ＮＵＲＢＳ裁剪曲面的真实感显示需求，提出使用四叉树的数据结构和参数和空间映射的新技术，实现了光线跟踪技术的快速计算和图形的反走样处理，同时，参数域上的扫描线判断法能快速正确地识别曲面上的裁剪区域。 相似文献
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Ahmed Kovacevic 《International journal for numerical methods in engineering》2005,64(3):401-426
This paper describes some aspects of an advanced grid generation method used, with Computational Fluid Dynamics (CFD) procedures, to model three‐dimensional flow through screw compressors. The increased accuracy of the flow predictions thus derived, enable such machines to be designed with improved performance and for lower development costs. To achieve this, a wholly original boundary adaptation procedure has been developed, in order to allow for convenient mapping of the internal grid points of a screw compressor, which is sufficiently flexible to fit any arbitrary rotor profile. The procedure includes a practical transformation method, which adapts the computationally transformed region to produce a regular boundary distribution on the mesh boundaries. It also allows for subsequent generation of an algebraic grid, which enables the three‐dimensional domain of a screw compressor to be mapped regularly even in regions where the flow patterns are complex and the geometrical aspect ratio is high. This procedure enables more efficient use of a CFD solver for the estimation of the flow parameters within both oil free and oil injected screw compressors, with either ideal fluids or real fluids, with or without change of phase. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Frdric Noël 《International journal for numerical methods in engineering》2002,54(7):965-986
We describe a new geometric algorithm to map surfaces into a plane convex area. The mapping transformation is bijective; it redefines the whole surface as a unique bi‐parametric patch. Thus this mapping provides a global parametrization of the surface. The surfaces are issued from industrial CAD software; they are usually described by a large number of patches and there are many shortcomings. Indeed, the decomposition into patches depends on the algorithm of the geometric modelling system used for design and usually has no meaning for any technological application. Moreover, in many cases, the surface definition is not compatible, i.e. patches are not well connected, some patches are self‐intersecting or intersect each other. Many applications are hard to address because of these defects. In this paper we show how patch‐independent meshing techniques may be easily automated using a unique metric in a plane parametric space. Thus we provide an automatic procedure to build valid meshes over free‐form surfaces issued from industrial CAD software (Computer Aided Design: this terminology should refer to a large amount of software. For the scope of this paper we only refer to geometric modelling systems. Indeed geometric modelling systems remain the kernel of many CAD software). Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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裁剪曲面的三角化及图形显示 总被引：2，自引：0，他引：2
结合自主版权的超人ＣＡＤ／ＣＡＭ系统的开发，本文提出了一种适合于裁剪曲面图形显示的曲面三角化算法，该算法将曲面的三角化转化为曲面参数域的三角化，并将二维图形的集合运算与Ｄｅｌａｕｎａｙ三角剖分应有和于曲面参数域边界的处理，从而使裁剪曲面在边界上的三角形分布均匀。 相似文献
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裁剪曲面是基本图形交换规范（IGES）的主要内容，详细介绍了IGES文件中裁剪曲面的定义格式。在开放图形库（OpenGL）环境中，要求裁剪曲面外环必须是逆时针的，内环是顺时针的才能得到正确的显示结果，给出了平面任意多边形走向判定算法用来调整内外环的走向。此外，还给出了曲面控制点和裁剪曲线中直线段的调整方法，提供的实例证明了算法的有效性。 相似文献
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给出了一类可以保持几何与拓扑信息一致性的裁剪面的参数变换定理及其算法。首先,确定了参数变换对裁剪面表示信息的影响。然后,根据参数变换后几何与拓扑信息的一致性要求,给出了对裁剪面表示信息进行调整的方法。最后,通过建立参数变换的关系,以裁剪球面为例阐述了这类参数变换的具体实现方法。 相似文献
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C. K. Lee 《International journal for numerical methods in engineering》2001,50(4):787-807
A new procedure is suggested for controlling the element‐size distribution of surface meshes during automatic adaptive surface mesh generation. In order to ensure that the geometry of the surface can be accurately captured, the curvature properties of the surface are first analysed. Based on the principal curvatures and principal directions of the surface, the curvature element‐size requirement is defined in the form of a metric tensor field. This element‐size controlling metric tensor field, which can either be isotopic or anisotopic depending on the user requirement, is then employed to control the element size distribution during mesh generation. The suggested procedure is local, adaptive and can be easily used with many parametric surface mesh generators. As the proposed scheme defines the curvature element‐size requirement in an implicit manner, it can be combined with any other user defined element size specification using the standard metric intersection procedure. This eventually leads to a simple implementation procedure and a high computational efficiency. Numerical examples indicate that the new procedure can effectively control the element size of surfacemeshes in the cost of very little additional computational effort. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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本文首先论述了多面体拼合运算的分割方法和法矢投影法，重点介绍后者。然后将法矢投影法推广到由裁剪曲面表示的曲面实体拼合中，初步得到满意的结果。 相似文献
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P. COLOMBI A. BASSETTI A. NUSSBAUMER 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(1):59-66
Pre‐stress bonded composite patch is a promising technique to reinforce steel member damaged by fatigue. The effectiveness of this technique was verified by fatigue tests on notched steel plates. Results showed that the application of carbon fibre reinforced plastic (CFRP) strips and, eventually, the introduction of a compressive stress by pretension of the CFRP strips prior to bonding produced a significant increment of the remaining fatigue life. In this paper, the stress intensity factor in the notched plates is computed by a two‐dimensional finite element model in connection with the three‐layer technique in order to reduce the computational effort. Due to high stress concentration at the plate crack tip, debond is assumed at the adhesive–plate interface. The goal is to illustrate the influence of some reinforcement parameters such as the composite strip stiffness, the pre‐stress level, the adhesive layer thickness and the size of the debonded region on the effectiveness of the composite patch reinforcement. 相似文献
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在CAGD和CG中,代数曲线上指定曲线段的最优参数化是热点问题,而不是整条曲线。以最接近于弧长的参数化为最优的参数化评判标准,得到了二次代数曲线上的任意指定曲线段的最优或逼近最优的有理参数化公式,具有较强的自适应性。最后,通过实例对该方法与传统方法得到的参数化结果进行了对比。 相似文献
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Guang Zhu Yu Sheng Zhou Peng Bai Xian Song Meng Qingshen Jing Jun Chen Zhong Lin Wang 《Advanced materials (Deerfield Beach, Fla.)》2014,26(23):3788-3796
Effectively harvesting ambient mechanical energy is the key for realizing self‐powered and autonomous electronics, which addresses limitations of batteries and thus has tremendous applications in sensor networks, wireless devices, and wearable/implantable electronics, etc. Here, a thin‐film‐based micro‐grating triboelectric nanogenerator (MG‐TENG) is developed for high‐efficiency power generation through conversion of mechanical energy. The shape‐adaptive MG‐TENG relies on sliding electrification between complementary micro‐sized arrays of linear grating, which offers a unique and straightforward solution in harnessing energy from relative sliding motion between surfaces. Operating at a sliding velocity of 10 m/s, a MG‐TENG of 60 cm2 in overall area, 0.2 cm3 in volume and 0.6 g in weight can deliver an average output power of 3 W (power density of 50 mW cm?2 and 15 W cm?3) at an overall conversion efficiency of ～50%, making it a sufficient power supply to regular electronics, such as light bulbs. The scalable and cost‐effective MG‐TENG is practically applicable in not only harvesting various mechanical motions but also possibly power generation at a large scale. 相似文献