共查询到19条相似文献,搜索用时 46 毫秒
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基于时间分辨的粒子图像测速技术(time-resolved particle image velocimetry, TR-PIV)是一种广泛应用的非接触式二维瞬时流场可视化测量技术。为了得到流场精细的瞬态空间结构和演变过程,提出了一种利用多光谱成像技术来提高流场测量的时间分辨率的方法。利用多个不同波长的脉冲激光照明流场中的同一测量区域,使用多光谱成像系统采集不同波长的粒子图像,经过图像分离,判决计算产生速度矢量场。为了验证这一原理的可行性,使用三种不同波长(488,532和632.8 nm)的单色光谱脉冲搭建了一套基于多光谱成像的TR-PIV系统,通过多波长激光脉冲之间时序的精确控制,将两帧图像之间的时间间隔从10 ms缩短至3.4 ms,时间分辨率提高了3倍。结果表明基于多光谱的TR-PIV测量系统在保持PIV技术瞬时全场测量特点的同时,时间分辨率大为提高。 相似文献
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对层析粒子图像测速(PIV)技术中示踪粒子成像部分进行理论分析,并结合真实风洞的相应参数,通过搭建模拟粒子成像平台的方法来进行研究。设计了一套体积为80 mm×100 mm×100 mm的激光照明系统,以提供粒子场的入射光强。建立了示踪粒子的三维成像模型,从而得到层析PIV系统的模拟图像。分析了影响PIV系统成像质量的相关因素。在单像素粒子数为0.007 7的情况下,通过真实粒子图像和模拟粒子图像比较,验证了该方法的正确性。 相似文献
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文中提出了用流场的一次曝光像的强度谱作为模板提取杨氏条纹,以获取尖锐的自相关分布的方法,并给出了该方法用于激光散斑测速和粒子像测速技术的计算机模拟结果以及粒子像测速的应用例子。 相似文献
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《光学学报》2020,(7)
粒子图像测速(PIV)作为一种非接触的、全局的间接流体力学测量技术,能够从图像中获取流体的速度场,从而揭示流体的运动规律。随着深度学习技术的发展,用深度学习技术来进行粒子图像测速具有很重要的研究价值和广泛的应用前景。基于光流神经网络,提出了一种改进型轻量级卷积神经网络,在提高粒子图像测速精度的同时,减小了模型的参数量,提高了测试速度。首先,将目前能够获取最优刚体估计的光流神经网络架构进行了改进,采用人工合成的粒子图像数据集进行有监督训练。然后,将训练得到的网络模型与当前最先进的用于粒子图像测速的深度学习模型进行对比评估。实验结果表明,本文提出的基于轻量化深度学习模型的粒子图像测速模型在不损失精度的同时,模型参数量减小了9.5%,测试速度提高了8.9%。 相似文献
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Developments of many cardiovascular problems have been shown to have a close relationship with arterial flow conditions.However,current ultrasound/Doppler imaging techniques cannot resolve the complex nature of arterial blood flow.We have recently developed a novel contrast-based echo particle imaging technique(Echo PIV) without angel dependence for non-invasively measuring multi-component flow vectors.This study introduces the Echo PIV principles,system characterization and utility examination to characterize hemodynamics in pipe laminar flow and rotating flow.Echo PIV measurement results show its capability to resolve the complex hemodynamics including proximal flow velocity vectors,and velocity mapping. The Echo PIV method provides an easy,direct and accurate means of quantitatively yet non-invasively characterizing the complex vascular hemodynamics. 相似文献
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A PC-based machine vision system for obtaining three-dimensional particle co-ordinates using a single camera is presented. Based on photogrammetric imaging, this system uniquely combines the advantages of stereo and orthogonal views to determine the accurate locations of the particles. A 3D cross-correlation algorithm has been implemented to follow the particles from frame to frame and compute the velocity vectors. Experiments have been carried out to obtain the velocity profiles in a cubical test section with an offset inlet and outlet. The results obtained from the experimental investigation were compared with numerical simulation data obtained from FLUENT and STAR-CD. 相似文献
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Driss Mgharaz Nawal RouchdiAbdelkader Boulezhar Marc Brunel 《Optics and Lasers in Engineering》2011,49(1):1-7
We have developed models to design actively Q-switched Yb-doped Double-Clad fiber lasers in various configurations. Based on these simulations, we present the design of two specific cavities: the first one is able to emit a pair of sub-nanosecond pulses separated by more than 500 ns for Particle Imagery Velocimetry applications. The time delay between the pulses can be adjusted by proper choice of the length of an un-doped fiber inserted in the cavity. The second cavity designed allows to emit long 150 ns pulses exceeding a few millijoules per pulse. Applications concern in this case materials science and combustion. In all cases, the rise time of the EOM is an essential parameter. 相似文献
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The temporal evolution of the velocity field of an unsteady fluid flow can be tracked by combining Particle Image Velocimetry (PIV) and high speed photography. Two alternative techniques for PIV are discussed: the classical light sheet technique and a method which makes use of the light scattered in forward direction. We applied time resolved PIV to investigate the flow around cavitation bubbles during their collapse near a solid boundary. The light source was an argon laser with an external acousto-optic deflector which produces series of short pulses. Using a drum camera for high speed photography, we achieved a temporal resolution of10 kHz and a spatial resolution of better than2 points/mm2. Velocities could be determined without directional ambiguity in a range from2 m/s to30 m/s. 相似文献
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An image-shifting technique based on grey-scale classification for particle image velocimetry 总被引:3,自引:0,他引:3
The image-shifting techniques are used to overcome the directional ambiguity of particle image displacement in the measurement of particle image velocimetry (PIV). This paper proposes an image-shifting technique based on grey-scale classification for PIV. By calculating the unified grey-scale statistical frequency of each interrogated unit, the directional ambiguity is resolved without any special requirement of the camera, and the particle image displacement is calculated synchronously. This image-shifting technique can be realized by controlling the difference in the light intensity of two lasers. Using this new technique, a PIV system was developed and used to measure the diesel spray flow. The displacement vector map of fuel particle in the spray flow was obtained, and the structure of the spray flow was investigated. The application confirmed that the image-shifting technique is viable and effective. 相似文献
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This paper summarises the development of particle image velocimetry (PIV) over the last decade and describes its applications as an effective measuring technique for mapping complex flow fields. A review of work in the field is given. Current aerodynamic and hydrodynamic investigation by the authors exploiting the method are described and used as illustration. 相似文献
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Sai Sandeep Dammati Yoram Kozak Cal Rising Jonathan Reyes Kareem A. Ahmed Alexei Y. Poludnenko 《Proceedings of the Combustion Institute》2021,38(3):3671-3681
We numerically investigate the accuracy of the Particle Image Velocimetry (PIV) technique for the flow characterization in high-speed, compressible regimes, in particular in gas-phase detonations. We carry out synthetic PIV reconstruction of the flow field in a two-dimensional, planar detonation propagating under atmospheric conditions and modelled using single-step Arrhenius kinetics. The flow is uniformly seeded with monodispersed Al2O3 particles with sizes 50 and 200 nm, along with initially co-located massless Lagrangian tracer particles. The effect of massive particles on the detonation speed and thermodynamic state of the flow is investigated and is found to be negligible. We further assess the ability of massive particles to sample the flow field and while it is found that 50 nm particles sample the flow field better than the 200 nm ones, they also exhibit significant clustering. By comparing the trajectories of massive particles with those of massless tracers, it is shown that almost all massive particles rapidly diverge from the actual flow pathlines. Finally, we quantify the accuracy of the PIV reconstruction of the velocity field in comparison with the actual velocity field in the numerical simulations. It is shown that while PIV is generally capable of capturing the bulk flow features in the streamwise direction, its accuracy is not sufficient to characterize the transverse velocity component or velocity fluctuations. 相似文献
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Brownian motion and correlation in particle image velocimetry 总被引:8,自引:0,他引:8
In particle image velocimetry applications involving either low velocities or small seed particles, Brownian motion can be significant. This paper addresses the effects of Brownian motion. First, general equations describing cross-correlation particle image velocimetry are derived that include Brownian motion. When light-sheet illumination particle image velocimetry (PIV) is used Brownian motion diminishes the signal strength. A parameter describing this effect is introduced, and a weighting function describing the contribution to the measured velocity as a function of position is derived. The latter is unaffected by Brownian motion. Microscopic PIV Brownian motion also diminishes the signal strength. The weighting function for microscopic PIV is found to depend on Brownian motion, thus affecting an important experimental parameter, the depth of correlation. For both light-sheet illumination and microscopic PIV, a major consequence of Brownian motion is the spreading of the correlation signal peak. Because the magnitude of the spreading is dependent on temperature, PIV can, in principle, be used to simultaneously measure velocity and temperature. The location of the signal peak provides the velocity data, while the spreading of the peak yields temperature. 相似文献
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P. V. Farrell 《Optics and Lasers in Engineering》1992,17(3-5):187-207
Application of particle image velocimetry (PIV) techniques for measurement of fluid velocities typically requires two steps. The first of these is the photography step, in which two exposures of a particle field, displaced between the exposures, are taken. The second step is the evaluation of the double-exposure particle pattern and production of appropriate particle velocities. Each of these steps involves optimization, which is usually specific to the experiment being conducted, and there is significant interaction between photographic parameters and evaluation characteristics. This paper will focus on the latter step, that of evaluation of the double-exposure photograph. In several parts of a PIV system, some performance advantage may be obtained by increasing use of optical processing over conventional digital image processing. Among the processes for which a performance advantage may be obtained are parallel or multiplex image interrogation and the evaluation of the Young's fringe pattern obtained from the scattered pattern from the double-exposure photograph. This paper will discuss parallel image interrogation and compare the performance of optical and numerical Fourier transform analysis of Young's fringes using speckle images. 相似文献