三维造型系统中剖视的研究与实现

结合三维实体造型的特点，介绍了剖视图与剖切面的分类。通过分析应用要求，提出了利用三维实体上的元素(点、线、面)构造剖切面，以及对剖切面进行精确定位的方法。进而利用系统的参数化机制，将剖切结果表达为剖切过程的描述，从而实现了实例的修改后剖切结果的自动更新。实践证明，整个剖视过程灵活可靠，能够满足应用要求。     

制图国家标准中有关剖视图概念的探讨

在“机械制图”教学中，学生往往误认为半剖视图仅是剖视图的一种画法，而不是一种剖切方法；误认为剖视图中的剖切符号仅表示剖切面的位置，而不是表示剖切范围这样一些基本概念。错误发生的重要原因是：在《技术制图》国家标准中，剖切方法和画法表述混乱；《机械制图》国家标准中有关剖视图的标注的表述不确切。建议对国家标准有关内容的表述进行相应的修改，以使概念和定义表述更加科学、严谨和相统一，从而提高工程图样表达的正确性和准确性。     

制图标准中剖切面后结构画法的探讨

针对机械制图标准中有关旋转剖视图画法的规定,围绕剖视图中剖切面后结构的画法,提出了"剖切面后的其他结构"和"剖切结构及其有关部分"的具体界限,当一些结构没有直接被剖切到时,若它所在的形体的轴线为两剖切面的交线,应按剖切面后的其他结构,按原来的位置投射;否则应按照"剖切结构及其有关部分",随其所在结构旋转到新的位置,使画法进一步明确。针对有些学者建议,删去制图标准中"剖切面后面的其他结构,应按原位置投射"的规定,认为不能删去,并证明了自己的观点。     

关于国标中剖视图内容不断完善的分析与建议

运用逻辑学关于“划分”、“概念间的关系”和“下定义”的有关原理,分析了近30年中国家标准中关于剖视图分类演变的进程,对剖视图的分类趋向科学性予以肯定,指出近代国标中关于剖视图分类存在的问题。在此基础上,阐明符合逻辑学的剖视图定义结构,并对剖视图标注中剖切符号的图示提出了改进建议。使得各类剖视图的定义更确切、科学,表达更方便、明了,绘图更容易。     

基于ObjectARX开发工程图模块的研究

三维实体建模在机械产品的设计过程中得到了广泛应用,但二维工程图仍是当前指导生产和进行技术交流必不可少的文件。为了从三维实体模型快速得到二维工程图,利用ObjectARX二次开发工具,在AutoCAD平台上开发工程图模块,实现了实体模型向工程图的快速转化以及自动标注。工程图生成在模型空间,方便后续操作。通过实例证明该工程图模块能够从特征实体模型中提取工程图的相关信息,快速生成二维工程图,大大提高用户的工作效率。     

CATIA V5中三维实体模型的二维工程图表达

介绍了在CATIA V5软件中创建二维工程图的两种方法。详细阐述了在Drafting（工程图）模块下由三维实体模型直接创建各种视图、剖视图及断面图的方法。分析所得二维工程图在图样表达上与现行国家标准图样画法不一致的地方,并提出相应的解决办法。本文内容对在三维模式下创建符合国家标准规范的工程图具有一定参考价值。     

关于剖切面及其剖切方法划分的标准化

根据逻辑学关于褐示概念外延的划分原理,剖析了现行机械制图国家标准关于剖切面及其剖切方法分类的逻辑错误,提出了剖切面及其剖切方法严密,完整,清楚的划分方法。     

三维重建中的剖视图处理

剖视图处理能够有助于更好地理解视图,提高三维重建的效率。基于对剖视图自身特点的分析,提出了三维重建中对剖视图的处理算法,即通过剖视图信息的智能提取生成基元体,将基元体同由视图轮廓生成的参照体进行布尔运算,从而得到最终的目标体。算法能够处理包括全剖视图、半剖视图以及平行剖视图在内的剖视图,最后给出了应用算例以验证算法的可行性。     

横向剖切法构造B样条曲面在炮口制退器曲面设计中的应用

本文采用横向剖切面面而得到截线的方法来构造Ｂ样条曲面，从而实现炮口爱器的构形。此外，本文还结合实例说明了用此方法进行造型设计的技术。     

Pro／E下用于创建注塑模具型腔的三维模型设计

一件塑料制品，在Part／Design模块下进行三维实体模型设计时，可以采用不同的特征构造方法和步骤进行设计，如果在进行三维实体模型设计时，考虑到后续模块的特点，就可以使整个设计简捷高效，降低模具的设计周期和成本，从而提高市场竞争能力。本文针对Pro／E下用于创建注塑模具型腔的三维塑件实体模型设计进行了探讨。     

An Edge Detection Algorithm for Photoelasticity Analysis

Abstract: Photoelasticity has become a modern tool of stress analysis which is capable of competing with other tools employed currently, including finite element analysis. Improved model production and automated fringe analysis allow us to perform investigations of complex models, speeding up the rate of analysis and reducing the action by users, consequently automating the whole process. However, before automated fringe analysis, the mask of the model should be extracted. The authors discuss the development of a new algorithm to detect the mask of the model by analysing isochromatic fringe patterns used in photoelasticity. It is important to know the mask of the model for its analysis and to obtain a stress map. Unlike the available edge algorithms or any other techniques used to detect a model's mask, the proposed algorithm was developed to minimise user action, allowing the process to be automated. There is a major difference between the area of the background and area of the model from the point of view of image processing. Grey level of points inside the background region are distributed along the tilted plane with low total variance, and those points inside the model regions are distributed along the isochromatic fringes having the shape of a wave. The variance of certain areas is measured with respect to the approximated plane created over such area from the grey level of each point. Areas having low variance are then selected and extended to true boundaries based on the fact that edges are characterised by a huge jump in the grey level. The proposed method is validated experimentally for a plate with multiple cutouts in a dark field and a circular disc under diametric compressive load with frozen stress in white field.     

The measurement of the distribution of residual stresses through the thickness of a welded joint

A new method for the measurement of residual stresses in welded joints of complex cross section is described. The method involves the measurement of strain changes in the body as a narrow slot is cut in the plane of interest, in small increments of depth. A finite element model of the cross section is used to relate the strain changes at the measurement points to the residual stresses across the slot plane.
The accuracy of the method is demonstrated by using it to measure a known residual stress field in a cold bent bar. The method has been used in combination with a block removal technique to measure the through wall distribution of axial residual stresses at a circumferential butt weld in a cylinder with a protruding root bead. It could also be applied to the measurement of residual stresses in other joint configurations, such as fillet welds or T-butt welds.     

The linear-wave response of a periodic array of floating elastic plates

The problem of an infinite periodic array of identical floating elastic plates subject to forcing from plane incident waves is considered. This study is motivated by the problem of trying to model wave propagation in the marginal ice zone, a region of ocean consisting of an arbitrary packing of floating ice sheets. It is shown that the problem considered can be formulated exactly in terms of the solution to an integral equation in a manner similar to that used for the problem of wave scattering by a single elastic floating plate, the key difference here being the use of a modified periodic Green function. The convergence of this Green function in its original form is poor, but can be accelerated by a transformation. It is shown that the results from the method satisfy energy conservation and that in the particular case of a fixed rigid rectangular plate which spans the periodicity uniformly the solution reduces to that for a two-dimensional rigid dock. Solutions for a range of elastic-plate geometries are also presented.     

支持模型重用的三维参数化特征造型

本文提出了三维参数化特征造型的一种新的思路和方法。特征分为广义几何特征和应用特征，应用特征的几何信息可用广义几何特征表示；三维参数化特征建立在浮动基准体系上，在勾画平面上勾画二维参数化轮廓，勾画时可以引用三维模型在勾画平面上的投影，勾画轮廓经过广义扫描生成三维参数化特征，特征的定义过程用过程语义描述；隐式基准和虚索引对象为特征“剪贴”的实现提供了必要的保证，同时特征“剪贴”支持模型的重用、应用特征库的定义和用这些应用特征进行设计。     

基于人机工程学的键盘设计

运用人机工程学原理展开对台式电脑键盘的深入设计.从键盘的平面布局、主键盘区、编辑与定位键盘区和数字辅助键盘区的按键搭配、定位键、色彩以及整体设计等角度,对键盘进行了改进和完善.进一步体现了键盘的人性化设计,大大提高了键盘作业的效率.     

Mechanical Properties of a Novel Zero Poisson's Ratio Honeycomb

In this paper, a novel honeycomb is proposed by embedding a rib into every cell of the existing zero Poisson's ratio (ZPR) configuration, semi re‐entrant honeycomb (SRH). Analytical model is developed to investigate the in‐plane mechanical properties of the new honeycomb, and the resulting theoretical expressions are compared with the experimental tests and numerical results obtained from two different finite element (FE) models (3D beam model and 3D solid model), leading to a good correlation. FE analysis, analytical modeling, and experimental tests of the new honeycomb show that it can achieve ZPR effect in two principal directions. For further studies, parameters analyses are carried out to explore the dependence of the in‐plane mechanical properties versus the geometric parameters. The results show that bending is the dominated deformation model when the new honeycomb is compressed along the x‐ direction, while stretch controlled in the y‐ directional compression. It is remarkable that the new proposed honeycomb features superior specific stiffness and more flexible in mechanical properties tailoring compared to the other ZPR honeycombs in the literature. Given these benefits, the new honeycomb may be promising in some practical applications.

     

Convective instability in a horizontal fluid layer with a permeable barrier under conditions of arbitrary boundary heat conduction

We examine the effect on the convective stability of a plane horizontal fluid layer from the resistance of a permeable barrier positioned in the middle of the layer, and from the heat conduction of a solid block surrounding that layer.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 3, pp. 410–414, March, 1991.     

Phase plane analysis of one-dimensional reaction diffusion waves with degenerate reaction terms

This paper demonstrates the existence of a minimum wave speed for reaction diffusion systems whose permanent form travelling wave solutions satisfy the nonlinear ordinary differential equation u' + cu' + f ( u , u' ; c ) = 0 when there are two equilibrium points, one of which is not hyperbolic, under certain restrictions on the behaviour of f . It also shows how to construct a trapping region in the phase plane, which leads to an upper bound on the value of the minimum wave speed. This class of systems includes autocatalytic reactions of order greater than one and combustion waves in premixed gaseous and solid fuels.