惯性摩擦焊接头非对称性分析

应用无线测温系统和热电偶测温技术,试验测定了惯性摩擦焊旋转端和滑移端试件的温度场,探讨了惯性摩擦焊摩擦界面两侧温度分布的非对称性;统计分析了不同焊接条件下惯性摩擦焊试样焊接区域的几何特征及宏观形貌.结果表明,滑移端的温度及升温速率均高于旋转端,滑移端的轴向缩短量、飞边宽度以及热力影响区(TMAZ)宽度均大于旋转端.分析认为惯性摩擦焊摩擦结合界面两侧温度场的非对称性与焊接区域几何特征的非对称性紧密相连.     

斜拉网格结构的结构形式、应用及特性在国内的研究进展

斜拉网格结构是目前应用较为广泛的刚柔混合结构体系之一,由塔柱、拉索、网格结构组合而成。系统的对该类结构体系在我国的发展进行了回顾及展望。首先,对该混合结构的结构形式发展及部分工程应用进行了介绍;之后,分别回顾了斜拉平板网架结构和斜拉空间网壳结构的结构特性研究,从考虑结构几何非线性,参数振动和模态跃迁等因素,突出分析了斜拉空间网壳结构复杂的动力特性行为;最后,分析尚存的问题,对今后的发展进行了展望。     

基于有限单元柔度法和刚度法的几何非线性空间梁柱单元比较研究

分别基于有限单元柔度法和有限单元刚度法二阶分析理论,采用纤维模型梁柱单元编制了钢筋混凝土杆系结构二阶非线性分析程序;分别采用这两种方法对几个典型试验实例进行了计算机模拟分析,通过模拟分析结果的对比,对有限单元柔度法与有限单元刚度法处理几何非线性问题的效果与效率进行了比较研究.结果表明:对于几何非线性问题,尤其是对于处理下降段(非稳定阶段)问题,基于柔度法的梁柱单元无论从计算效率还是计算效果上都明显优于基于刚度法的梁柱单元,有限单元柔度法是目前处理杆系结构材料与几何双重非线性问题最为有效的分析方法.     

混凝土斜拉桥与T构协作体系的极限承载力研究

考虑结构的材料非线性和几何非线性,通过对协作体系金马大桥进行全过程非线性分析,得到了结构的极限承载力。研究了混凝土收缩徐变、加劲梁配筋率、斜拉索的安全系数、加载方式等因素对协作体系桥梁的极限承载力的影响,结果表明斜拉索的设计安全系数是很重要的影响因素,应加以重视;全桥和半桥加载时,弹塑性极限活荷载安全系数分别为21.4和9.67,表明金马大桥这种协作体系具有良好的极限承载能力;其弹塑性极限承载力远小于弹性极限承载力,研究结果可以为同类桥梁工程的设计和计算提供参考。     

基于二维振镜的动态目标实时跟踪与高保真信息采集系统

针对目前视觉跟踪平台研究中存在的大视野与高分辨力不可兼得以及高速运动目标跟踪难以实现等痛点问题,设计了一种基于二维振镜的新型视觉跟踪平台,可以在保证视野范围的前提下,兼顾高帧率和高分辨力特性,实现动态目标50 FPS的实时跟踪以及100倍放大后的高保真信息采集。首先,对基于二维振镜的光学系统进行几何建模,对光路变化与动态视角之间的耦合关系进行分析,完成了双相机协同系统的坐标系变换;其次,针对运动目标实时跟踪任务,采用一种基于动态模板匹配和卡尔曼滤波器的目标检测跟踪算法,以保证目标物体的快速、准确定位;最后,从动态视野范围、响应速度、跟踪目标定位精度及跟踪目标极限速度四个方面对系统性能进行评估,并选择多个典型场景对系统的应用领域进行分析。结果表明：该系统特殊的双相机协同工作模式和极快速的动态响应特性,使其很好地弥补了现有视觉跟踪平台的不足,在智能监控、智慧交通、国防军工等领域中具有广阔的应用前景和极高的研究价值。     

基于几何特征的高分辨率SAR图像飞机目标解译方法

针对高分辨率SAR（synthetic aperture radar）图像特性,提出了一种基于几何特征的飞机目标解译方法。首先,局部自相似性及DBSCAN（density based spatial clustering of application with noise）算法用于提取感兴趣的目标区域;其次,机翼和机身形成的“T”型结构采用霍夫变换进行提取;最后,结合基于水平集的精细部件分割和共线性、对称性等先验知识,飞机目标的发动机和机头等部件得以提取。得到飞机目标的关键几何参数以用于目标识别和解译。基于miniSAR图像的实验验证了方法的实用性和有效性。     

Perspectiva Geometrica

Mark Reynolds presents some drawings and constructions for those whose interests are in systems of perspective, and the role that grid making may have played in the development of perspective in the early Renaissance.     

Affine transformations for digitized spatial data in geology

Affine transformations are among the most basic and useful geometrical operations in computer applications in geology. Homogeneous coordinates extend their applicability. The methods are essential in handling digitized locational data and are applicable widely in other graphical applications such as calibrating data sets for plotting, and in shape comparison and spatial analysis. Affine transformations alter the length of lines and the angles between them, whereas straight lines remain straight, parallel lines remain parallel, and the ratio in which a point divides a line remains the same.Their geometrical significance indicates that they can be visualized readily, and the corresponding operations in matrix algebra provide a straightforward method of computer implementation. A transformation matrix is calculated from four calibration points, the coordinates of which are known before and after transformation. Multiplication of coordinates in the initial frame of reference by the transformation matrix converts them to coordinates in the new frame of reference. A listing of relevant FORTRAN programs is given, with examples.     

A hybrid model for weekday replacements with infant mortality failures

A hybrid availability model of a repairable system with infant mortality failures is proposed. The hybrid model can efficiently represent different types of state transitions by the use of a hierarchy of models: (1) a time-discretized component submodel, which provides a piecewise-linear failure rate during an operating interval; (2) a phased-mission model, which transforms the state probability vector according to repair activity; and (3) a combinatorial model, which is used to predict the number of working units among a collection of identical components. The modeling approach is illustrated by predicting the expected number of working components for a multiple-component system where replacement components are ordered at the end of business hours each weekday end. Replacement occurs on the next weekday morning.     

Ultimate Strengths of Partially Stabilized Zirconia Ceramics

Previous results for ultimate tensile fracture strengths of partially stabilized zirconia (PSZ) containing preexisting finite cracks are reformulated in terms of a new transformation-strengthening parameter. This allows a simplified method for estimating the strengths of bulk PSZ containing arbitrarysized, preexisting critical cracks.