常见复杂物体轴测投影视觉事件及其计算

本文首先提出复杂物体轴测投影形态图计算时的投影空间为二维空间，并以投影球（高斯球）模型作为轴测投影的投影空间模型。然后全面分析了复杂物体轴测投影视觉事件的形成和类型，提出其视觉事件有八类十六种。最后建立了各种视觉事件的确定方法和计算公式，从而为复杂物体轴测投影形态图的计算提供了理论依据。     

曲面体轴测图的一种画法

指出了传统的轴测图的绘制方法对于曲面体的困难,提出了一种新的绘制曲面体轴测图的综合方法。在AutoCAD中不用坐标变换,也不用UCS系统及三维造型技术,充分利用已有的(用AutoCAD绘制的)正投影图的图形资源和AutoCAD强大的二维图形的编辑功能,并在数学分析的基础上与程序设计有机地结合起来,通过对圆的轴测投影的研究,快速实现了对曲面体的各种类型轴测图的绘制,方法易于掌握。     

复合轴测图的精确绘制

在制图教材的编写中,以及制图课件的制作中,轴测图的绘制占据了很大的工作量.其中某些轴测图还嵌套着正投影图或轴测图,对于这种复合轴测图,用手工或二维绘图工具软件很难精确绘制.AutoCAD是目前广泛使用的计算机辅助设计软件,可以方便地进行二维和三维工程图样的设计,借助于AutoCAD精确的三维数学建模方式,介绍了生成复合轴测图的方法和技巧,并给出了范例,这对新教材的立体插图绘制,课件制作具有很好的实用性.     

关于轴测投影变形系数和轴间角的图解问题

变形系数和轴间角是绘制轴测图的主要依据。历史上曾有过不少人在这方面作过贡献──得到某种关系或提供某种图解方法。这里将全面系统地研究这方面的问题。一、轴测投影由四个独立的参数确定(一)为了便于分析,以视向P的反方向A为投影方向,并假定轴测投影平而F在物体和观察者之间。也就是在第三分角里研究问题,如图1。为了便于作图,在选坐标系时,应使     

用AutoCAD绘制正等轴测图

介绍了用AutoCAD2005软件画支架正等轴测图及对其标注尺寸、注写文字的方法和技巧，对AutoCAD软件用户正确和快捷地绘制正等轴测图大有帮助。     

波尔克定理与轴测投影过程的程序模拟

从投影的基本概念出发,以波尔克-施瓦兹定理为计算依据,以CAD为图形支撑工具,可以实现轴测投影过程的程序模拟,自动创建各类轴测图,也包括所有基本视图和辅助视图.制图教学辅助软件ACAD Projector采用了对线、面、实体的灵活操控,精确重现投影基本规律中的投影线、投影面、实体之间的空间关系,实现了各类轴测投影的创建与反求.这种处理方法为三维重建和投影技术研究提供了新的思路.     

四维轴测图计算机显示的数学基础

作者在1983年提出了“四维正等轴测投影”的思想之后,本文又提出了四维轴测图计算机显示的数学方法,研究了四维空间旋转变换及变换规律和方法;并对四维正等轴测轴进行了优化处理,找到一种既简便又较直观的四维正等轴测图的轴向角及变形系数。     

轴测投影与透视投影的互换

建筑表面图常用的轴测投影与透视投影具有不同的优点，也具有着可以相互变换的几何特性，在计算机绘图的造型建模中也存在着这种互相转换。笔者阐述了建立以上投影互换的条件和作图方法，并且分析了这个系统中不同的互换型式。这些透视学的投影知识，有助于建筑师创建对建筑物的最佳视图，有助于提高建筑师的艺术与图学素养，拓宽和发展建筑的表现手段。     

体视变形和绘图误差

本文论述了体视变形的原理,分析了产生体视变形的三个因素:视点偏移、眼基线误差、图对间隔误差。介绍了体视变形在体视图绘制、缩印、立体电影和幻灯中的一些应用。为制作和观察体视图以及开拓其应用提供了理论依据。     

轴测投影变换矩阵的研究

在本文中,根据空间物体、投影方向、投影面和坐标系的关系,推导了包括正轴测投影和斜轴测投影的统一轴测投影变换阵。根据该变换矩阵可以导出各种轴测投影变换矩阵。根据物体的形状确定投影方向,并根据该变换矩阵可以获得物体的最清晰的轴测图。     

斜高线及其在三点透视作图中的应用研究

透视作图的关键在于如何确定3个主向灭点等作图参数的位置，然后合理地获取透视高度。传统的视线法需借助侧面投影求作建筑物高度棱线的透视。笔者基于量点法的透视作图，提出了斜高线的概念，证明了斜高线、真高线与透视高度的对应关系，并就其在三点透视作图中的应用进行了有效的研究。     

Oblique laser-sheet visualization

A laser-sheet visualization technique is demonstrated in which the laser and camera systems are integrated into a single unit, reducing the need for optical access to a single optical port. The technique is based on the photographing of a plane oblique to the camera optical axis and has been successfully applied to the quarl region of a power-station pulverized coal burner. The geometry of oblique photographing is presented.     

Oblique impact modeling of fuzes

This paper presents the results of a combined experimental, numerical, and analytical investigation of a low-speed (198 m/s) oblique impact of a cylindrical steel projectile into an aluminum-brass composite fuze simulant. The numerical simulations were performed prior to the experiments using the Lagrangian hydrocode EPIC92. The results indicate that projectile hardness and impact point strongly influence the mechanism by which the fuze deforms. An experiment was then conducted in order to evaluate the predictive capabilities of the hydrocode. The experimental results generally corroborate the hydrocode results during the initial stages of the impact but depart significantly at later stages of the penetration. Possible causes for the observed differences between the experiment and the simulation include, (i) the absence of a global fracture modeling capability in the hydrocode, and (ii) boundary condition differences between experiment and simulation. The hydrocode predicts that 91% of the projectile kinetic energy is converted into target plastic work. This result compares well with predictions based upon an analytical model of an elastic-plastic beam bent by an end load.     

Oblique impact testing of bicycle helmets

The performance of bicycle helmets was investigated in oblique impacts with a simulated road surface. The linear and rotational accelerations of a headform, fitted with a compliant scalp and a wig, were measured. The peak rotational accelerations, the order of 5 krad s⁻² when the tangential velocity component was 4 m s⁻¹, were only slightly greater than in comparable direct impact tests. Oblique impact tests were possible on the front lower edge of the helmet, a site commonly struck in crashes, without the headform striking the ‘road’. Data characterizing the frictional response at the road/shell and helmet/head interfaces, were generated for interpretation via FEA modelling.     

Oblique hypervelocity impacts into graphite

Investigations have been conducted into the morphology of craters formed by impacts of aluminium and HDPE projectiles at oblique angles to graphite target plates. The experiments were conducted with a two-stage gas gun capable of launching projectiles of differing density and strength to speeds of about 6 kms⁻¹ at right angles into target plates. It was found that, as the impact angle is decreased from the normal, the crater dimensions scaled as the normal component of the impact velocity as predicted by the ‘2/3 power law’ until a critical normal velocity was reached below which the conditions for a hypervelocity impact no longer apply. In this regime, new scaling laws were derived for the crater dimensions. It was also possible to identify a fragmentation angle below which the projectile remains intact as it ricochets across the target surface.     

On Oblique Cutting of Cellular Elastic materials

It is shown that the previously developed model for the direct cutting of cellular plane allows to investigate also the more general case of 3D oblique cutting after replacing the coefficient of friction at the cutter faces by its effective value. The numerical results illustrate the advantages and disadvantages of the oblique cutting regime. This revised version was published online in August 2006 with corrections to the Cover Date.     

颈椎椎间孔侧偏角度的研究

目的:测量颈椎椎间孔侧偏角度,研究颈椎斜位片在显示椎间孔中的作用,寻找清晰显示颈椎椎间孔的最佳投照角度。方法:选择无颈部病变者39例,做颈椎椎间孔螺旋CT扫描,层厚2-5mm。选取第二颈椎到第七颈椎之间的椎间孔,利用PPT文稿和Photoshop等工具进行测量。结果:颈椎椎间孔的侧偏角度悬殊较大,传统的45度斜位片并不适用于所有被检查者。结论:颈椎椎间孔侧偏角度因个体而异,对颈椎椎间孔的显示点片或直接查CT、MRI更好。     

吸波涂层斜入射特性研究

简要分析了吸波涂层（RAC）的斜入射特性，研究了几种吸波涂层在不同入射角（θi)下的吸波性能，指出在常规进气道等凹型腔体中使用RAC的主要要求是提高涂层的垂直极化性能。