三角形约束的平面二次曲线的NURBS表示

非均匀有理Ｂ样条（ＮＵＲＢＳ）是ＣＡＤ设计中广泛使用的技术。本基于平面几何知识给出了三角形约束的圆与椭圆曲线的ＮＵＲＢＳ表示,为工程设计中使用这类曲线提供了可计算性。     

Analysis of end point vibrations of a two-link manipulator by integrated CAD/CAE procedures

In this work, the effect of flexibility on the trajectory of a planar two-link manipulator is studied using integrated computer-aided design/analysis (CAD/CAE) procedures. The solid models and finite element models of the parts of the manipulator are created by using the CAD/CAE software I-DEAS. The assembly is defined, and knowing the payload and the end point trajectory, the velocities and accelerations of the parts, joint forces and driving torques are calculated using the rigid body dynamics. All the time dependent nodal forces acting on the parts including distributed gravity and inertia forces are created in files with the I-DEAS program file format. The finite element vibration analysis of the parts is performed by I-DEAS. The end point vibrations and the deviations from the rigid-body trajectory are analyzed for different types of end point acceleration curves. A circular trajectory is considered as an example. It is observed that the precision of the manipulator can be increased by testing different end point acceleration curves without changing the trajectory and the duration of the end point work. The procedure explained in this work can be used for this purpose successfully.     

The non-solvability by radicals of generic 3-connected planar Laman graphs

We show that planar embeddable -connected Laman graphs are generically non-soluble. A Laman graph represents a configuration of points on the Euclidean plane with just enough distance specifications between them to ensure rigidity. Formally, a Laman graph is a maximally independent graph, that is, one that satisfies the vertex-edge count together with a corresponding inequality for each subgraph. The following main theorem of the paper resolves a conjecture of Owen (1991) in the planar case. Let be a maximally independent -connected planar graph, with more than 3 vertices, together with a realisable assignment of generic distances for the edges which includes a normalised unit length (base) edge. Then, for any solution configuration for these distances on a plane, with the base edge vertices placed at rational points, not all coordinates of the vertices lie in a radical extension of the distance field.

     

Detection of diminished response to cold pressor test in smokers: Assessment using phase-contrast cine magnetic resonance imaging of the coronary sinus

Purpose

The purposes of this study were to evaluate the reproducibility for measuring the cold pressor test (CPT)-induced myocardial blood flow (MBF) alteration using phase-contrast (PC) cine MRI, and to determine if this approach could detect altered MBF response to CPT in smokers.

Materials and methods

After obtaining informed consent, ten healthy male non-smokers (mean age: 28 ± 5 years) and ten age-matched male smokers (smoking duration ≥ 5 years, mean age: 28 ± 3 years) were examined in this institutional review board approved study. Breath-hold PC cine MR images of the coronary sinus were obtained with a 3 T MR imager with 32 channel coils at rest and during a CPT performed after immersing one foot in ice water. MBF was calculated as coronary sinus flow divided by the left ventricular (LV) mass which was given as a total LV myocardial volume measured on cine MRI multiplied by the specific gravity (1.05 g/mL).

Results

In non-smokers, MBF was 0.86 ± 0.25 mL/min/g at rest, with a significant increase to 1.20 ± 0.36 mL/min/g seen during CPT (percentage change of MBF (?MBF (%)); 39.2% ± 14.4%, p < 0.001). Inter-study reproducibility for ?MBF (%) measurements by different MR technologist was good, as indicated by the intraclass correlation coefficient of 0.93 and reproducibility coefficient of 10.5%. There was no significant difference between smokers and non-smokers for resting MBF (0.85 ± 0.32 mL/min/g, p = 0.91). However, ?MBF (%) in smokers was significantly reduced (-4.0 ± 32.2% vs. 39.2 ± 14.4%, p = 0.011).

Conclusion

PC cine MRI can be used to reproducibly quantify MBF response to CPT and to detect impaired flow response in smokers. This MR approach may be useful for monitoring the sequential change of coronary blood flow in various potentially pathologic conditions and for investigating its relationship with cardiovascular risk.     

New Voronoi Diagram Algorithm of Multiply-Connected Planar Areas in the Selective Laser Melting

This paper studies the practical generation of Voronoi diagrams for multiply-connected planar areas bounded by line segments. The core of the algorithm was calculating Voronoi polygon of every Voronoi object in planar areas independently. The main approach had two steps. The first step was calculating all relevant bisectors of every Voronoi object. The second was combining obtained bisectors into completed Voronoi polygons individually. All code was implemented in Visual C++ platform. The resulting code was extensively tested in real-world data and its practical running time grew only linearly. Three statistical CPU-consumption charts had been drawn with the Voronoi diagrams computation data, and compared with other published codes for computing Voronoi diagrams. The algorithm was applied to compute offsetting of slice area consisting of large-scale line segments for the selective laser melting (SLM) trajectory scanning technology which is a kind of rapid prototyping (RP). The experimental results of offsetting for slice area based on Voronoi diagrams show that the approach is effective and simple for polygon offsetting problems. The method is helpful to those offsetting work and can provide more effective offsetting solution.     

计算机辅助成组技术的研究

成组技术(GT)是改变多品种、中小批量生产落后面貌的卓有成效的技术、组织措施.实施成组技术的关健在于零件的排序、特征统计、分类归组及原有图纸、工艺工装的检索.本文针对上述几个关键问题的计算机解法进行了初步的探讨,其程序在IBM-PC计算机上运行获得了成功.     

用双三次COONS曲面拟合椭球面的设计（CAD）

双三次ＣＣＯＮＳ曲面具有足够的光滑性和连续性，计算方法简便，易于在计算机上实现。用双三次ＣＯＯＮＳ曲面拟合椭球面的设计用ＦＯＲＴＲＡＮ７７编写，包括一个主程序和三个子程序（ｖｗ，ａａ和ｍａｔ）。本程序具有操作方便，执行效率高的特点。     

CAD技术在有限元分析前处理中的应用

本文研究了三维实体在ＣＡＤ技术下的网格划分。针对相贯线这一难点进行了探索，并从中总结出了一套合理的解决办法，为解决工程结构中的圆角过渡等应力变化敏感部位的三维网格生成，提供了准确快捷的方法。     

地下矿生产日报CAD动态监视与管理系统

本文利用ＣＡＤ技术建立了地下矿生产日报动态监视系统。该系统采用ＣＡＤ技术形象直观地监视地下矿生产动态；应用多级模糊层次综合评价模型和灰色预测模型及时利用生产日报信息，迅速评价当天生产总体效果和准确预测未来生产发展状况。     

多级变速传动系统转速图在CAD中的参数表示法

本文对金属切削机床的多级变速传动系统转速图在CAD中的参数化表达形式进行了初步探讨,并通过对变速传动系统中传动组的基本要素分析,提出了转速图的参数化表达模式——变速传动式的概念。运用这个概念,在许多情况下,变速传动式可以代替转速图,即不必给出转速图就可以根据变速传动式进行变速传动系统的分析、计算和方案比较。