内凹和外凸轮廓切挤复合精整时的材料流动分析

目的为了探索零件精整面的成形规律,研究2种轮廓的材料流动情况。方法利用有限元模拟方法进行研究,根据精整轮廓的不同特点,首先对切挤复合精整中的变形区进行了分析,接着对外凸和内凹轮廓零件切挤复合精整时的材料流动进行了研究,得出了材料变形区的流动、剪切滑移等的规律。结果变形区可以细分为主变形区、新面形成区、废料变形区和剪切滑移区等;内凹轮廓精整处于稳定精整阶段时,基体材料内部有涡流现象出现,然而,在外凸轮廓精整的整个过程中,基体材料都没有形成涡流,涡流可以提高静水压应力,抑制裂纹的产生,促使得到光洁度较好的零件;在整个精整过程中,外凸轮廓零件材料相比于内凹轮廓在精整方向上滑移了较长的距离,才能移动到新成形表面,内凹轮廓变形区材料所受应力多为压应力。结论内凹比外凸轮廓精整易得到较好的成形质量。     

Image fusion based on wavelet transform and gray-level features

Image fusion makes the fused image more reliable and intelligible, and more suitable for human vision and computer detection, classification, recognition and understanding. This paper proposes a pixel-level image fusion method for merging two source images of the same scene using wavelet transform and gray-level features (GLF). First, a three-level discrete two-dimensional wavelet transform is used to decompose the two source images into low-frequency image components and horizontal, vertical, and diagonal high-frequency components. Then, the spatial frequency correlation coefficient is used to determine the pixel fusion rule to apply to each of the low-frequency images, and the correlation coefficient of the GLF is used to determine the pixel fusion rule to apply to each of the high-frequency images. Finally, the fused image is reconstructed using inverse wavelet transform. The results of the experiments conducted indicate that the proposed method is more effective than relevant conventional methods.     

Target segmentation in active polarimetric images by use of statistical active contours

We address the problem of target segmentation in active polarimetric images, which can reveal contrasts that do not appear in standard intensity images. However, these images are perturbed by strong specklelike noise. For the purpose of segmentation we thus use statistical active contours, which are known to possess noise robustness properties. The polarimetric imagers we consider acquire two different images of the same scene so as to form a two-channel image (TCI). These two images can be combined to form the orthogonal state contrast image (OSCI), which represents the degree of polarization of the backscattered light if its coherency matrix is diagonal. We characterize the segmentation performance of the statistical active contour procedure on the TCI and on the OSCI. In particular, we show that if the illumination beam is spatially nonuniform, it is more efficient to perform the segmentation on the OSCI, which is independent of the spatial variations of the illumination.     

刀具轮廓亚像素精度阈值分割算法研究

提取亚像素精度边缘轮廓是完成刀具几何参数精确测量的重要环节。该文研究了一种简单有效的方法,该算法基于灰度阈值分割定位像素级边缘,并经双线性插值法细分完成亚像素边缘轮廓的提取。最后设计实验对比分析了该算法以及基于Canny和Sobel算子的亚像素边缘检测算法所提取轮廓的特点。结果表明在准确的前提下,对高对比度图像应用该算法后,能比后两者更快速地完成边缘轮廓提取。     

Characteristics of pixel arrangements in various rhombuses for full-parallax three-dimensional image generation

In full-parallax three-dimensional (3-D) imaging systems, the pixel cells often have the shape of a rhombus. Proper arrangement of pixels in these rhombic-shaped cells is important to maximize the quality of displayable 3-D images with a given display panel. The possible number of pixel arrangements in a rhombic cell with a definite dimension is found by considering the number of possible crossings between parallel line families forming the pixel cells, when the slopes of the lines are approximated by the ratio between the number of pixels in the vertical and horizontal directions. To make the rhombic cell have a uniquely defined pixel arrangement, its horizontal and vertical dimensions should be equal to the even multiple of the pixel dimension in their corresponding direction.     

Self-similarity and finite-size effects in nano-indentation of highly cross-linked polymers

The scalability of thermomechanical polymer deformations in the sub-10 nm regime is of particular importance for nano-imprint techniques, hardness measurements of thin films by nano-indentations, and scanning-probe-based thermomechanical data storage. We investigate nano-indentation in the sub-10?nm regime performed on highly cross-linked polymer films of different thicknesses. It is shown that the lateral and vertical geometric characteristics of the indents independently scale down to an indent depth of 1?nm and that the scaling parameters are functions of the film thickness and the temperature of the indenter. However, in the limit of shallow indents the scaling of the cross-coupling between lateral and vertical dimensions is lost. It is argued that the breakdown of self-similarity is due to a minimum strain requirement originating from the co-operative nature of the polymer response induced by α transitions which lock the indent in the deformed state. The results shed new light on the fundamental processes and size effects involved in nanoscale plastic replication, in general.     

一种基于轮廓配准的包装缺陷检测方法

提出了一种基于包装图像轮廓配准的包装缺陷检测方法.该方法先对包装图像进行轮廓提取,计算目标轮廓的质心,从而得到配准平移参量.围绕目标质心每隔一定角度抽得质心到轮廓的距离值,得到一个距离值的序列.通过计算标准图像和待配准图像的距离值序列的圆周相关的最大值来确定旋转的角度.然后对已配准的包装图像进行缺陷检测,实验证明,本方法对包装缺陷的检测是快速的,有效的.     

饱和分数导数型粘弹性土层竖向振动放大效应

将土骨架视为具有分数阶导数本构关系的粘弹性体,采用Biot动力固结方程,在频率域内研究了饱和分数导数粘弹性土层的土骨架粘性、土层厚度等对竖向振动放大系数的影响。通过动力控制方程解耦和边界条件束缚,给出了经典弹性饱和土、分数导数型粘弹性饱和土和经典粘弹性饱和土三种情况下饱和土层的位移、应力和孔压解析表达式。考察了饱和土各物理和几何参数对竖向振动放大系数的影响,结果表明:在不同土层厚度时,经典弹性饱和土、分数导数型粘弹性饱和土及经典粘弹性饱和土的竖向振动放大系数各不相同;分数导数模型的材料参数对振动放大系数有较大影响。     

噪声和振动等舒适度曲线的快速确定方法

噪声和振动是车辆、船舶和飞机等交通工具舱室内部影响人体舒适性的重要因素。噪声和振动的等舒适度曲线是舱室减振降噪设计的重要指标。提出一种噪声和振动等舒适度曲线的快速确定方法,即通过不完整的交叉主观评价实验,确定噪声和振动的主观不舒适度随两者客观幅值的增长率,再通过增长率的比值,计算确定噪声和振动的舒适度等效曲线。相对于传统的完整交叉主观评价实验,该方法在保证预测模型准确率的情况下减小了实验时长和数据分析的工作量。     

纹理贴图模型的彩色截面轮廓生成算法研究

针对彩色3D打印彩色轮廓生成问题,本文提出一种基于纹理贴图模型的彩色轮廓生成算法。根据平面投影法建立纹理和三维模型的映射关系,接着对该模型进行切片处理取得轮廓顶点的几何信息和纹理信息;并根据轮廓顶点和纹理图片的映射关系,插值出顶点间色彩信息;同时给出一种内外轮廓的快速识别算法,并提出一种基于偏置算法的彩色轮廓偏置方法,形成颜色厚度,消除阶梯效应。     

偏流角误差对TDI CCD相机成像的影响与仿真

本文分析了TDI CCD相机的偏流角调整过程和偏流角误差匹配的影响因素,依据偏流角误差导致的姿态稳定度偏差对相机成像质量的影响,建立推扫相机像点与物点一一对应的数学模型,根据TDI CCD成像时超出对应像素的横向与纵向偏移量的累加计算,仿真卫星姿态稳定度改变时相机的成像;同时,利用单轴气浮转台和面阵CCD进行成像实验,将实验条件的像移速度与仿真条件的像移速度匹配,并对面阵CCD成像进行偏移量的累加,模拟推扫CCD成像,最后利用图像对比度和互相关相似性测度分析仿真成像与实验成像质量。仿真成像与实验成像在对比度和互相关相似性测度上相差为0．03左右,能较好满足地面卫星相机连调试验的图像仿真。     

Dimensional instability of cement bonded particleboard: SEM and image analysis

Scanning electron microscope (SEM) and image analysis were applied to quantify the structure of commercial cement bonded particleboard (CBPB) to obtain a more fundamental understanding of the instability of CBPB and to provide a basis of information for modelling the stress–strain behaviour of CBPB. Surfaces through the thickness of the board and vertically within the board were analysed mainly with respect to the distribution, size, shape and percent area occupied by individual components (void, cement paste and wood chips). Results showed that the area occupied by wood chips 1) increased from the surface to the core layer (from 34 to 49%), 2) was 5% higher for vertical surfaces than for horizontal surfaces, 3) but was in total only about 40%; this is much lower than the volume fraction (about 75%) of raw materials used in the manufacture of CBPB. This confirms the mechanism/organisation of mat formation, showing the more significant effect of wood chips on thickness than on length changes with changing moisture content and indicating that the wood chips are compressed in CBPB. The wood chips nearly all lie flat in the horizontal planes throughout the board thickness and were randomly distributed on the horizontal plane. The mean angle was about 10.7° between wood chips and the horizontal surface and about 44.7° between wood chips and the longitudinal direction within a horizontal plane, verifying that the change in thickness should be much higher than that in length or width, and the change in length and width should be similar. The size and shape of the wood chips were very different among six horizontal layers and between the horizontal and the vertical layers.     

Width-independent fast skeletonization algorithm for binary pictures

An effective algorithm of skeletonization for digital binary pictures based on input-time-tracing principle and sequential decomposition of input picture into simple parts is described. The proposed algorithm is fast and requires no image memory. Its computing complexity does not depend on the thickness of picture patterns and is determined not by the number of picture pixels but by the essentially small number of horizontal and vertical lines constituting the contour of the picture.     

有多层立杆的双排碗扣式脚手架稳定性分析

根据双排碗扣式钢管脚手架的受力性能,在铰接单杆理论的基础上,针对连墙件竖向间距较大,立杆层数较多,且未设廊道斜杆的情况,综合考虑了连墙件间立杆、多层水平杆和碗扣的整体效应,推导出架体稳定承载力的解析解。考虑整体效应后,架体的计算承载力与铰接理论相比有较大提高,更符合真实承载力,且与有限元结果吻合较好,此方法适用于碗扣式钢管脚手架设计计算中。     

Image tracking of motorcycles and vehicles on urban roads and its application to traffic monitoring and enforcement

Abstract

Image tracking has increasingly gained attention for use in vision‐based traffic monitoring and surveillance applications. For many cities in Asia countries, it is desirable to detect multiple motorcycles as well as cars for urban traffic monitoring and enforcement. In this paper, a novel contour initialization and tracking algorithm is presented to track multiple motorcycles and vehicles at any position on the roadway. This method has the capability to detect moving vehicles of various sizes and to generate their initial contours for image tracking. The proposed method is not constrained by lane boundaries or vehicle size. To track vehicles on roadways, dynamic models are designed to predict the horizontal and vertical positions of vehicle contours. A Kalman filter is designed to update the prediction based on real‐time image measurement. Practical experimental studies using video clips are presented to evaluate the performance of the proposed method. Traffic parameters such as traffic flow, vehicle speeds and traffic density are obtained with satisfactory accuracy.     

Effect of cyclic shearing on shear localisation in granular bodies

Cyclic shearing of an infinite narrow layer of dry and cohesionless sand between two very rough boundaries under constant vertical pressure is numerically modelled with the finite element method using a polar hypoplastic constitutive relation. The constitutive relation was obtained through an extension of a non-polar model by polar quantities, viz. particle rotations, curvatures, couple stresses using the mean grain diameter as a characteristic length. The proposed model captures the essential mechanical features of granular bodies in a wide range of densities and pressures with a single set of constants. The material constants can be easily determined from granulometric properties and laboratory tests. The attention of numerical simulations is laid on the influence of number of cycles on the thickness of an induced shear zone for both an initially dense and loose granular specimen. In addition, the effect of a stochastic distribution of the initial void ratio on shear localisation is demonstrated.KeywordsGranular material, Cyclic shearing, Polar hypoplasticity, Finite element method, Shear localisation     

结合Zernike矩的多尺度模板形状匹配

针对形状匹配中小波表达对起始点依赖的问题,提出一种结合Zernike矩的多尺度模板进行形状匹配的方法。该算法对输入图像进行预处理后提取目标轮廓,经过归一化处理得到目标形状的平移、尺度不变的链状表达,再通过小波变换进行多尺度分析;引入Zernike矩,利用Zernike矩的特性,实现小波表达的旋转不变性,解决了小波变换对起始点的依赖。匹配过程是以小波表达的各阶Zernike矩为特征向量,在由粗到精的尺度上进行的。实验结果表明,对于同一目标,原图像与旋转不同角度的图像的正确匹配率为91％。该算法适用于轮廓较明显的目标。     

双重主动轮廓图像分割

本文首先利用小波变换得到原图像的粗分辨逼近,在粗分辨逼近中得到图像的一个粗尺度分割。由于逼近图像中噪声下降,尺寸减少,使得算法对参数的选取不太敏感,而且收敛速度加快。然后将第一次分割结果通过小波反变换返回到原始尺度上,将得到的近似轮廓曲线作为初始水平集函数再在原图像中演化得到更准确的分割,这样就得到了一种双重主动轮廓图像分割算法。由于初始轮廓曲线非常接近真实的轮廓曲线,所以很快就可以收敛到真实的轮廓。理论分析和数值结果表明,双重主动轮廓分割算法可以快速有效地分离出感兴趣目标。