Evolution of the partial image velocimetry measuring technique

Evolution of the non-intrusive flow measuring technique known as particle image velocimetry (PIV) is reviewed. Techniques for illuminating the flow field and recording the images are compared and the principles of image analysis outlined. Recent developments in stereoscopic and holographic PIV, application to vibration fields and fibre optic beam transmission are also discussed.     

Eliminating background noise effect in micro-resolution particle image velocimetry

A novel method is developed to improve the accuracy of micro-resolution particle image velocimetry (PIV) in microfluidics measurements. This method utilizes the Laplacian of Gaussian method and image-processing techniques to eliminate the background scattering noise. A high signal-to-noise ratio image has been obtained. This technique is especially suitable for improving micro-resolution PIV in micro, two-, or multiphase flow conditions, such as for submicron bubbly flow measurements in a microchannel. The method can easily be implemented with minimal modification of the conventional PlV system. The results of simulation and experiments demonstrated the feasibility of this, to our knowledge, new method.     

The use of high-speed PIV and holographic cinematography in the study of fiber suspension flows

High-speed particle image velocimetry (PIV) and digital holography were applied to dilute, rigid fiber suspensions without floc formation. PIV is suited to study the instantaneous interaction between the flow and the fiber motion down to the scale of the fiber. Based on the size difference between fibers and tracers, fibers were masked in the PIV images. However, this method is not always sufficient, and we propose a more elaborate method based on local cross-correlation between successive cropped images to track and remove fibers from the PIV images. Digital, inline holographic cinematography has the advantage of a relatively easy optical setup. Exploratory experiments were performed using a single-view, inline setup tracking fibers in 3D. Fiber holographic reconstructions were clear and enable accurate determination of fiber length and orientation. This is in contrast to the PIV images, where the fiber optical signature suffers from intensity saturation and reflections. However, to obtain the accurate 3D fiber orientations, a two-orthogonal view holography setup is needed. We propose combined PIV and holography to study the basic fiber-flow interaction mechanisms in turbulent flows.     

New metric for stereo image quality assessment based on HVS

Stereo image is regarded as an important trend of image technology, and there is an increasing need to develop efficient measures for stereo image quality evaluation. By analyzing the main properties of human visual system that is related to stereo image, a new metric based on human visual systems (HVSs) for stereo image quality assessment is proposed in this article. This method assesses stereo images from the perspective of image quality and stereo sense. The experimental results are presented to show that the proposed metric provides results consistent with the subjective assessment and thus can be employed to reflect image quality and stereo sense. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 301–307, 2010     

AFM image reconstruction for deformation measurements by digital image correlation

The scanner drift of the atomic force microscope (AFM) is a great disadvantage to the application of digital image correlation to micro/nano-scale deformation measurements. This paper has addressed the image distortion induced by the scanner drifts and developed a method to reconstruct AFM images for the successful use of AFM image correlation. It?presents such a method, that is to generate a corrected image from two correlated AFM images scanned at the angle of 0° and 90° respectively. The proposed method has been validated by the zero-deformation test. A buckling test of a thin plate under AFM has also been demonstrated. The in-plane displacement field at the centre point of the buckling plate has been successfully characterized by the application of the image correlation technique on reconstructed AFM images.     

Novel particle image velocimetry system based on three-color pulsed lamps and image processing

A novel particle image velocimetry (PIV) measurement system based on flashed lamps as light sources and digital reconstruction of particle positions by image processing is presented. Three different colors are used in order to distinguish, on a same photograph, the corresponding positions of each moving particle at three different instants of time. This solution can give significant advantages in several aerodynamic and hydrodynamic situations. In particular, it allows high flexibility for velocity measurements and independent settings of different acquisition parameters, like pulse powers and timing. Furthermore, the developed PIV measurement system is fully transportable, eye-safe, practical, and economical. The first hydrodynamics measurements achieved by using the proposed velocimetry measurement system are reported.     

Application of particle image velocimetry for measuring He II thermal counterflow jets

The particle image velocimetry (PIV) technique was successfully applied for measuring the velocity of a He II thermal counterflow jet. Neutrally buoyant hydrogen-deuterium solid particles were used as tracer particles for PIV measurement. In the application, the normal component velocity was measured. The jet velocity profile and spatial decay of the jet velocity were compared with those of turbulent round jets of ordinary viscous fluids. The velocity measured near the jet nozzle exit was compared with the theoretical prediction for the normal component flow velocity.     

Temperature and velocity measurement fields of fluids using a schlieren system

This paper proposes a combined method for two-dimensional temperature and velocity measurements in liquid and gas flow using a schlieren system. Temperature measurements are made by relating the intensity level of each pixel in a schlieren image to the corresponding knife-edge position measured at the exit focal plane of the schlieren system. The same schlieren images were also used to measure the velocity of the fluid flow. The measurement is made by using particle image velocimetry (PIV). The PIV software used in this work analyzes motion between consecutive schlieren frames to obtain velocity fields. The proposed technique was applied to measure the temperature and velocity fields in the natural convection of water provoked by a heated rectangular plate.     

基于PIV技术的复合流道板式结构实验

目的在包装工程流场测量的研究中,验证粒子图像测速(PIV)技术的可行性。方法用超白玻璃制作复合流道板式换热器的模型,基于PIV技术采集被测区域图像,应用互相关分析法进行计算,获得流场数据,并与数值模拟结果比对进行验证。结果实验结果流型清晰,数据和数值模拟基本一致。结论PIV技术可应用于流动复杂、非接触的包装工程类的流场测量,且超白玻璃是一种理想实验材料,能够为拓展该领域的探索思路提供参考。     

Phase-conjugate holographic system for high-resolution particle-image velocimetry

A novel holographic particle-image velocimeter system has been developed for the study of threedimensional (3-D) fluid velocity fields. The recording system produces 3-D particle images with a resolution, a signal-to-noise ratio, an accuracy, and derived velocity fields that are comparable to high-quality two-dimensional photographic particle-image velocimetry (PIV). The high image resolution is accomplished through the use of low f-number optics, a fringe-stabilized processing chemistry, and a phase conjugate play-back geometry that compensates for aberrations in the imaging system. In addition, the system employs a reference multiplexed, off-axis geometry for the determination of velocity directions with the cross-correlation technique, and a stereo camera geometry for the determination of the three velocity components. The combination of the imaging and reconstruction subsystems makes the analysis of volumetric PIV domains feasible.     

PIV血流场显示测速技术

通过分析多普勒测速技术与粒子图像测速技术的区别,从一个新角度把PIV全流场测速技术应用于血液流场的研究中。用激光片光源照亮血流粒子场,再计算确定实验系统光学参数,以获得最佳流场图片。对流场分析常用的互相关算法进行改进,辅以曲面拟合和误差修正,获得了亚像素级的全流场速度的大小和方向,并进一步计算出血流场的涡量分布和剪切率分布。为了验证改进的算法,对日本视频协会提供的PIV-STD序列标准图像进行仿真计算和误差分析,与原算法相比其速度矢量图的误差降低了2个百分点,流场速度值的平均误差小于±1%。该结果表明文中建立的方法是有效的,并可推广用于其它的流场分析。     

Eulerian-Lagrangian analysis for particle velocities and trajectories in a pure wave motion using particle image velocimetry

This paper investigates the velocity and the trajectory of water particles under surface waves, which propagate at a constant water depth, using particle image velocimetry (PIV). The vector fields and vertical distributions of velocities are presented at several phases in one wave cycle. The third-order Stokes wave theory was employed to express the physical quantities. The PIV technique's ability to measure both temporal and spatial variations of the velocity was proved after a series of attempts. This technique was applied to the prediction of particle trajectory in an Eulerian scheme. Furthermore, the measured particle path was compared with the positions found theoretically by integrating the Eulerian velocity to the higher order of a Taylor series expansion. The profile of average travelling distance is also presented with a solution of zero net mass flux in a closed wave flume.     

Cooperative matching paradigm for the analysis of stereo image sequences

A general framework for the analysis of sequences of stereo images is presented in this article. The proposed paradigm integrates spatial and temporal information to achieve robustness in establishing stereo correspondence from images that possess a limited number of salient features. Specifically, the recovery of dynamic stereo information, and thus, the reconstruction of a three-dimensional object structure, is accomplished using a feature-based approach. The multiset feature correspondence problem is cast into a four-dimensional problem which is subsequently solved using a greedy-type local search algorithm. No assumption is made about the type of motion. The proposed algorithm may be applied to process image sequences containing both rigid and nonrigid shapes. The efficacy of the proposed approach is tested using both synthetic data and real images of a live frog's ventricle acquired by a stereo light microscope. We also consider the incorporation of domain-specific knowledge to enhance the performance of the cooperative matching scheme. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 192–200, 1998     

Hybrid retinal image registration using phase correlation

Abstract

This paper deals with registration of retinal images, which were taken by high-resolution digital colour fundus cameras. The proposed method describes successful application of phase correlation method. It combines several basic steps — global correction of shift, rotation and scaling, detection of landmarks, their correspondences and finally image registration using second-order polynomial model. The method is tested on two sets of images. The first set contains images from the diabetic patients where many retinal pathologies can disturb the registration process. The second set contains images from healthy subjects, which were acquired by different illumination conditions. The method was evaluated using four different criteria - tree objective and one subjective. These criteria are also compared. The achieved registration accuracy of the landmarks position error is 1·13 and 0·93 pixels for respective image sets. Finally, the simple scheme for retinal pathology visualisation of registered fundus pairs is presented.     

Photometric reconstruction of a dynamic textured surface from just one color image acquisition

Textured surface analysis is essential for many applications. We present a three-dimensional recovery approach for real textured surfaces based on photometric stereo. The aim is to be able to measure the textured surfaces with a high degree of accuracy. For this, we use a color digital sensor and principles of color photometric stereo. This method uses a single color image, instead of a sequence of gray-scale images, to recover the surface of the three dimensions. It can thus be integrated into dynamic systems where there is significant relative motion between the object and the camera. To evaluate the performance of our method, we compare it on real textured surfaces to traditional photometric stereo using three images. We thus show that it is possible to have similar results with just one color image.     

Optical fiber array for the delivery of high peak-power laser pulses for fluid flow measurements

Fiber delivery of 64.7 mJ laser pulses (approximately 6 ns duration) from a Q-switched Nd:YAG laser operating at 532 nm is demonstrated. A custom diffractive optical element was used to shape the laser beam and facilitate coupling into a linear fiber array. This launch arrangement achieves an improvement in launch efficiency compared with a circular fiber bundle evaluated in previous work and the delivery of higher pulse energies is demonstrated. The bundle is capable of delivering light of sufficient pulse energy and, importantly, with suitable focusability, to generate a thin light sheet for the fluid flow measurement technique of particle image velocimetry (PIV). Fiber delivery offers an advantage, in terms of optical access, for the application of PIV to enclosed measurement volumes, such as the cylinder of a combustion engine.     

扩展核线模型在线阵CCD卫星遥感影像立体匹配中的应用

核线(epipolarity)是立体摄影测量分析像对几何关系的一个基本概念,在摄影测量的处理当中有着重要的应用价值,但经典的核线关系仅适用于框幅式中心投影影像.针对线阵CCD卫星遥感立体影像,将基于投影轨迹法的扩展核线模型引用到影像匹配中, 提出了一种基于动态核线的近似直线约束方法,实现了线阵CCD立体影像匹配的核线约束;在此核线模型应用的基础上,提出了一种基于核线的成像约束方法.试验结果表明前一种方法在匹配速度方面比传统方法有显著的提高,后一种方法在匹配精度、可靠性方面比传统方法有明显提高.     

Contrast-enhancement techniques for particle-image velocimetry

In video-based particle-image velocimetry (PIV) systems for fluid mechanics research, it is sometimes desirable to image seed particles to be smaller than a camera pixel. However, imaging to this size can lead to marginal image contrast such that significant numbers of erroneous velocity vectors can be computed, even for simple flow fields. A variety of image-enhancement techniques suitable for a low-cost PIV system that uses video cameras are examined and tested on three representative flows. Techniques such as linear contrast enhancement and histogram hyperbolization are shown to have good potential for improving the image contrast and hence the accuracy of the data-reduction process with only a 15% increase in the computational time. Some other schemes that were examined appear to be of little practical value in PIV applications. An automated shifting algorithm based on mass conservation is shown to be useful for displacing the second interrogation region in the direction of flow, which minimizes the number of uncorrelated particle images that contribute noise to the data-reduction process.     

Photon-limited image classification with a feedforward neural network

An application of neural networks to the classification of photon-limited images is reported. A three-level feedforward network architecture is employed in which the input units of the network correspond to the pixels of a two-dimensional image. The network is trained in a minicomputer by the use of the backpropagation technique. The statistics of the network components are analyzed, resulting in a method by which the probability of correct classification of a given input image can be calculated. Photon-limited images of printed characters are obtained with a photon-counting camera and are classified. The experimental results are in excellent agreement with theoretical predictions.     

聚合物真实黏度流变仪收缩流道轴向速度场的PIV实验研究及分析EI北大核心CSCD

为研究测量聚合物真实黏度流变仪收缩流道轴向速度分布规律,建立了收缩流道实验模型及实验方案。利用粒子图像测速(PIV)系统拍摄牛顿流体聚丁二烯在收缩流道流场中粒子的图像,利用Tecplot、Origin软件对图像和数据进行分析处理,得到聚合物真实黏度流变仪收缩流道的轴向速度曲线。同时将PIV实验、Polyflow仿真、理论计算结果相比较,发现三者规律基本吻合。证明了从PIV实验中得到牛顿流体聚丁二烯收缩流道速度场的方法是可行的。