三维电子散斑干涉载频调制及其在柴油机上的应用

将电子散斑干涉场的三维载波调制技术应用到三维物体变形测量中.用水平方向、竖直方向及垂直试件表面的三路相干光分别照明物体，在水平和竖直方向通过控制反射镜的微小偏转引入载波，实现位移场干涉条纹的调制；利用物体的微小偏转实现离面位移场干涉条纹的调制；结合傅里叶变换法，分别解调出变形场的位相，从而实现了物体三维变形场的精确测量.将该技术应用到柴油机油泵的三维位移测量上，成功测量了油泵的三维位移场.     

一种新型单帧彩色复合光栅投影的实时三维测量方法

提出了一种新型单帧彩色复合光栅投影的实时三维测量方法。采用三帧具有π2的相移正弦条纹分别编码到红色(R)、绿色(G)和蓝色(B)三个颜色通道中,组合成单帧彩色复合光栅,当该彩色复合光栅投影到待测物体上,仅需获取单帧彩色变形条纹并从中分离出相应的具有π2相移的三帧单色相移变形条纹,由于不同颜色通道之间存在颜色串扰以及色度不均衡问题,采用最小二乘法对分离出的三帧单色相移变形条纹直流项进行背景一致性校正,从而获得三帧校正后的单色相移变形条纹,运用所建立的三维重构物理模型,即可恢复物体的三维形貌。实验验证了该方法的可行性和实用性。进一步的实验表明,该方法的测量精度优于传统单帧彩色PMP。因为所提方法仅需一帧彩色复合光栅即可恢复物体的三维形貌,在实时三维测量中具有很好的应用前景。     

基于优化电子散斑光谱的三维物体测量研究

用激光光束直接照射到测试表面,再用CCD采其变形前后表面散斑颗粒干涉形成的条纹,条纹图解析为测量点的位移量和变形量,进而得到其离面位移,在优化算法的时候采用π位相技术获取另一个π相移的变形条纹图像,将面内位移与离面位移分离,为了消除零级分量,让投影光栅移动1/2个周期.通过Matlab和四步位相算法给出了三维空间模型,得出变形后物体的离面位移数据.实验仿真数据表明其能够稳定地测量物体变形场三维分量,误差较低.     

基于相位预测的在线三维测量像素匹配方法

物体的运动使变形条纹图中物体像素点不对应,因此需要对物体做像素匹配。提出了一种基于相位预测的在线三维测量像素匹配方法。仅投一帧正弦光栅条纹到在线运动的物体上,CCD同步采集相同步距时刻受物体调制的变形条纹图。采用傅里叶变换轮廓术(FTP)方法对采集的变形条纹预测物体不同位置的相位信息,并以该相位信息的特征做像素匹配,实现了物体在各帧条纹图中的像素一一对应,同时匹配后的变形条纹产生等效的等步相移,进而采用等步长相移算法来重构在线运动物体的三维面形。计算机模拟与实验验证了该方法的有效性和可行性。同时,与在线FTP方法进行比较,在线FTP方法和本文方法的均方根误差分别为1.013mm和0.024mm,表明该方法对在线三维测量具有较高的测量精度。     

一种分析薄膜振动模式的结构光条纹时间平均法

提出了一种用于振动物体表面快速测量的光学测试系统和方法。该系统采用结构光三维传感技术,利用时间平均法来实现对振动表面的测量和振动模式分析。用低帧频商用CCD相机记录由光栅投影到振动物体表面上形成的一系列变形正弦条纹,对获取的一帧变形条纹经过二维傅里叶变换、频谱滤波、逆傅里叶变换等处理得到调制物体振幅的零级贝塞尔函数分布。给出了该方法的理论分析,推导了相应的计算公式。计算机模拟和实验验证了该方法的可行性。实验证明,该方法具有数据获取速度快,全场非接触测量以及实验装置简单等优点。     

基于改进网格运动统计特征的在线三维测量

为了解决在线三维测量技术中像素匹配耗时长,准确率低等问题,提出了一种基于改进网格运动统计特征的像素匹配算法。该方法只需一帧固定的正弦光栅投影到被测物体上,由摄影系统连续采集五帧物体在相等位移下的变形条纹图,提取出相应的调制度信息,并利用快速旋转不变性特征算法提取图像的特征点匹配对,然后利用改进的网格运动统计特征算法来实现误匹配对的剔除。最后根据在线三维测量中对其精度要求很高的特点,取其出现位移量最多的值以获得一组相移量相等的条纹图,采用等步相移算法重建出在线移动物体的三维形貌。大量实验验证了该方法的可行性和有效性,与传统的在线傅里叶变换轮廓术算法进行对比,所提方法的鲁棒性更高,能够恢复出更高精度的三维面形。     

利用强度调制消除零频的傅里叶变换轮廓测量

采用双色正弦条纹投影的傅里叶变换轮廓术中零频分量的扩展对有用基频分量有影响,为此提出一种新型的基于强度调制的零频消除方法提高测量准确度和范围.通过采集一帧变形彩色条纹图并分离颜色通道获得两幅相位差为π的条纹图,对变形条纹做强度调制校正,进而消除零频分量,实现高度解析.理论模拟和实验测试均验证了此方法的有效性.相比传统的相移消除零频分量的方法,此方法具有显著的速度优势,适合于三维物体的实时测量.     

基于相位追踪的水中物体三维面形测量

提出一种基于相位追踪和光线迫迹算法测量水中物体三维形貌的新方法.该方法利用正弦面结构光来记录物体的三维面形数据,首先由投影仪投出止弦条纹图来调制淹没于水中物体的三维信息,摄像机拍摄获得物体表面的变形条纹图,然后利用相位追踪算法确定投影条纹和变形条纹之间的对应点,最后对相应的匹配点对进行光线追迹计算后,可以恢复出物体的三维形貌.由于使用面结构光进行测量,无需移动装置来实现对物体的一维或二维全场扫描,这样既节约了经济成本又缩短了测量时间.利用该方法进行了实际测量,得到了较好的重建结果,证明了本方法的正确性和可行性.     

基于椭圆形光强分布光栅投影的三维面形测量方法

基于椭圆形光强分布光栅投影测量物体三维面形的方法,将椭圆形光强分布光栅投影到被测物体表面,用摄像机获取变形条纹图,通过系统参量和条纹图携带的相位信息求解出物体的三维面形.推导出通过椭圆形光强分布光栅条纹求解相位的计算公式并对提出方法作了计算机仿真.实验结果表明该方法可以比较准确地测量物体的三维面形,在噪音较大的情况下测量结果仍具有较高准确度.     

基于椭圆形光强分布光栅投影的三维面形测量方法

基于椭圆形光强分布光栅投影测量物体三维面形的方法,将椭圆形光强分布光栅投影到被测物体表面,用摄像机获取变形条纹图,通过系统参量和条纹图携带的相位信息求解出物体的三维面形.推导出通过椭圆形光强分布光栅条纹求解相位的计算公式并对提出方法作了计算机仿真.实验结果表明该方法可以比较准确地测量物体的三维面形,在噪音较大的情况下测量结果仍具有较高准确度.     

Exponential discretization of the Perfectly Matched Layer (PML) absorbing boundary condition simulation in FD-TD 3D

We present the discretized equations of the 12 PML (perfectly matched layer) in the three-dimensional case using the Cartesian geometry. These equations can be used in different fields where Maxwell equations need to be solved.     

An Experimental Method to Decrease Heating Time in a Commercial Furnace

Abstract

The aim of this article is to present an experimental method to optimize the heating time in a furnace in order to show an example of the progression toward increasingly empirical solutions as the problems become progressively more unwieldy. During this experimental study, different cases are carefully chosen to compare and measure the effects of applying different enhancement methods of the heat transfer processes. It is found that changing the inner geometry by introducing radiant panels inside the heated chamber leads to important time savings in the heating process by increasing the convection rate in the furnace.     

Real time 3D visualization of ultrasonic data using a standard PC

This paper describes a flexible, software-based scan converter capable of rendering 3D volumetric data in real time on a standard PC. The display system is used in the remotely accessible and software-configurable multichannel ultrasound sampling system (RASMUS system) developed at the Center for Fast Ultrasound Imaging. The display system is split into two modules: data transfer and display. These two modules are independent and communicate using shared memory and a predefined set of functions. It is, thus, possible to use the display program with a different data-transfer module which is tailored to another source of data (scanner, database, etc.). The data-transfer module of the RASMUS system is based on a digital signal processor from Analog Devices--ADSP 21060. The beamformer is connected to a PC via the link channels of the ADSP. A direct memory access channel transfers the data from the ADSP to a memory buffer. The display module, which is based on OpenGL, uses this memory buffer as a texture map that is passed to the graphics board. The scan conversion, image interpolation, and logarithmic compression are performed by the graphics board, thus reducing the load on the main processor to a minimum. The scan conversion is done by mapping the ultrasonic data to polygons. The format of the image is determined only by the coordinates of the polygons allowing for any kind of geometry to be displayed on the screen. Data from color flow mapping is added by alpha-blending. The 3D data are displayed either as cross-sectional planes, or as a fully rendered 3D volume displayed as a pyramid. All sides of the pyramid can be changed to reveal B-mode or C-mode scans, and the pyramid can be rotated in all directions in real time.     

Visualization of 3D variable in time object based on data gathered by active measurement system

The recent needs of analysis and visualization of variable in time real 3D objects in many applications require development of new approach towards combining rapid 3D shape acquisition and the methodology of data processing in order to perform visualization and analysis of real 3D dynamic objects. In this paper, the general concept of visualization system of data gathered by means of optical 4D (x,y,z,t) shape measurement system is presented. The concept of a virtual camera, as the mean for interactive object visualization is introduced. The experimental results for processing of simulated and real variable in time 3D object are presented and discussed. The directions of future works focused on full implementation of the concept are introduced.     

Optoranger: A 3D pattern matching method for bin picking applications

This paper presents a new method, based on 3D vision, for the recognition of free-form objects in the presence of clutters and occlusions, ideal for robotic bin picking tasks. The method can be considered as a compromise between complexity and effectiveness. A 3D point cloud representing the scene is generated by a triangulation-based scanning system, where a fast camera acquires a blade projected by a laser source. Image segmentation is based on 2D images, and on the estimation of the distances between point pairs, to search for empty areas. Object recognition is performed using commercial software libraries integrated with custom-developed segmentation algorithms, and a database of model clouds created by means of the same scanning system.Experiments carried out to verify the performance of the method have been designed by randomly placing objects of different types in the Robot work area. The preliminary results demonstrate the excellent ability of the system to perform the bin picking procedure, and the reliability of the method proposed for automatic recognition of identity, position and orientation of the objects.     

Vibration and instability of a single-walled carbon nanotube in a three-dimensional magnetic field

The vibration and instability of a single-walled carbon nanotube (SWCNT) under a general magnetic field are of particular interest to researchers. Using nonlocal Rayleigh beam theory and Maxwell’s equations, the dimensionless governing equations pertinent to the free vibration of a SWCNT due to a general magnetic field were derived. The effects of the longitudinal and transverse magnetic fields on the longitudinal and flexural frequencies as well as their corresponding phase velocities were addressed and are discussed below. The critical transverse magnetic field (CTMF) associated with the lateral buckling of the SWCNT was obtained. The obtained results reveal that the CTMF increases with the longitudinally induced magnetic field. Further, its value decreases as the effect of the small-scale parameter increases.     

CFD modeling of a biogas fuelled SOFC

Mathematical modeling of transport and electrochemical phenomena within SOFCs can lead to improved understanding of the involved physical, electrical, and chemical processes and represents a powerful tool for their development. In this context, the present work illustrates a three-dimensional CFD simulation of a planar SOFC unit cell fuelled by modeled biogas/steam mixtures. The simulations estimate the distribution of gas species, the current densities and the potentials, as well as the temperature gradients and confirm that equimolar CH₄/CO₂ biogas leads to improved performance, while minimal steam addition can prevent carbon deposition.     

Mott–Hubbard transition in a 2D He fluid monolayer

We discuss recent observations of the heat capacity and magnetization of a fluid ³He monolayer adsorbed on graphite plated with a bilayer of HD. Approaching the density at which the monolayer solidifies into a commensurate solid, we observe an apparent divergence of the effective mass. However, the inferred values of F₀^a tend to a constant. We interpret this in terms of a Mott–Hubbard transition between a 2D Fermi liquid and a magnetically disordered solid occurring via the Brinkman–Rice–Anderson–Vollhardt scenario.     

Precision verification of a simplified three-dimensional DIC method

The traditional three-dimensional (3D) digital image measurement technique uses at least two images captured from different positions to determine the 3D coordinate of an object. One disadvantage of this method is that the mechanical and optical properties of the image capture devices are not fully identical, and the calibration procedure is quite complicated. This paper introduces a simplified 3D digital image correlation (DIC) method, in which only one image capture device is used. The theoretical measurement error equation is derived and experimentally verified. Experimental results show that distortion correction plays an important role in the improvement of measurement precision. After a radial distortion correction, the measurement precision of the object distance can reach 0.0043%. The optimal camera spacing should be set from 1/50 to 1/30 of the object distance, to obtain a satisfactory precision.     

基于海量散乱点数据三维显示新算法的研究

逆向工程中基于海量散乱点的三维模型重建,在许多应用中具有重要意义.由于测量系统精度的限制和测量数据无法直接与三维显示系统相结合,这也成为逆向工程发展的一个瓶颈.对传统的基于多边形网格的生成过程及Bezier插值细化进行了深入的研究,分析了其中的缺点和不足,并在此基础上提出了三维显示模型构建的新算法,即单层串珠算法、相邻...