Optimization of an algorithm for measurements of velocity vector components using a three-wire sensor

Hot-wire measurements of velocity vector components use a sensor with three orthogonal wires, taking advantage of an anisotropic effect of wire sensitivity. The sensor is connected to a three-channel anemometric circuit and a data acquisition and processing system. Velocity vector components are obtained from measurement signals, using a modified algorithm for measuring velocity vector components enabling the minimization of measurement errors described in this paper. The standard deviation of the relative error was significantly reduced in comparison with the classical algorithm.     

Determination of the velocity and size of bubbles in two-phase flows by using a laser doppler anemometer

Natural oscillations of a spherical interface between a gas and a liquid in a bubble are registered. A possibility of measuring the geometric parameters of stationary and moving particles of the disperse phase by a laser Doppler anemometer is demonstrated. A method for simultaneous determination of the size and velocity of a bubble or a droplet in a two-phase flow is developed. The mean sizes of a group of bubbles settled on a ruler are compared: the results are obtained by two independent methods, i.e., by analyzing the image and by processing the Doppler signal containing information about the natural oscillations of the spherical interface between the media. A possibility of using a laser Doppler anemometer for simultaneous measurements of the velocity and size of bubbles or droplets in a two-phase flow is confirmed.     

Load/unload measurements using laser doppler vibrometry and acoustic emission

The dynamics of the load/unload process are studied using a so-called ‘periscope approach’ which allows us to follow the slider motion during load/unload (L/UL) with the beam of a Laser Doppler Vibrometer (LDV). LDV signals and acoustic emission signals are obtained for three different slider airbearing designs and for load/unload conditions with different vertical velocities and spindle speeds. The load process is investigated statistically using the acoustic emission signal in order to determine the effect of vertical load speed and spindle speed on the probability of contacts between slider and disk.The results indicate that small vertical load speeds decrease the number of head/disk contacts, and that slider designs with a cavity centered close to the trailing edge enable a smooth unloading process.     

Measuring two-dimensional components of a flow velocity vector using a hot-wire probe

The article presents a single-hot-wire probe adapted to detect the direction of flow velocity. The modification consists of the introduction of a third support which allows to measure voltage at the central point of the wire. The sign of voltage difference DeltaU between both parts of the wire is the measure of the direction of flow velocity in a system of coordinates associated with the probe.     

Water jet velocity uncertainty in laser Doppler velocimetry measurements

The present work deals with the uncertainty evaluation in water jet velocity measurements carried out by means of a laser Doppler dual-incident-beam velocimeter in reference-beam configuration developed at the WJLab (Water Jet Laboratory of Dipartimento di Meccanica of Politecnico di Milano). The applied experimental procedure makes it possible to calculate the measurement uncertainty through the determination of its various components. Once uncertainty is known, the laser Doppler system is suitable for objective and significant velocity evaluations but also for improvements allowed by the knowledge of the most effective uncertainty sources. Such a subject is typically not considered by the specific water jet literature, but is becoming more and more important due to the evolution of water jet machining towards high precision applications.     

Reproducing aircraft structural components using laser scanning

In the past few years, laser scanning has become a popular digitising tool for rapidly manufacturing commercial products, moulds and dies, and industrial parts. This popularity can be attributed to continual improvement in the accuracy and reliability of the technology. In this study, the re-engineering and re-manufacturing capabilities of laser scanning systems in aircraft structural components manufacturing are evaluated. The study includes surveying state-of-the-art laser scanning systems; scanning, modelling, and machining a sample aircraft structural component; comparing the duplicated model/part with the original model/part; and estimating savings achieved by laser scanning. The significant findings from this study include the following:Laser scanning technologies have matured to a stage at which they can capture and reproduce volumetric features, such as pockets, slots, steps, irregular cavities, bosses, etc., typically present in aircraft structural components.Laser scanning technologies, through both re-engineering and re-manufacturing approaches, can dramatically reduce the part turnround time and skill levels required to replicate aircraft structural components.     

Acoustic velocity measurements in resonators of thermoacoustic systems using hot-wire anemometry

Acoustic velocity measurements in resonators of thermoacoustic systems using hot-wire anemometry technique flow are presented. The hot-wire calibration is based on the determination of the acoustic velocity reference value through an acoustic pressure measurement and their relationship using a linear acoustic model. In this model, an analytical approach involving the coupling between the sound source and the resonant cavity effects and the viscous and the thermal effects in the boundary layers is used. The amplitude and phase calibrations are reported for the first time, simultaneously, either by varying the sound source input voltage for a fixed frequency, or by varying the frequency for a given source input voltage. The amplitude calibration is detailed by using a filtering technique to eliminate either the acoustic streaming effects or the anemometer basic electric voltage variations effects. This provides a simple way to an amplitude calibration with good accuracy when measuring an average of a stationary oscillating velocity. The phase calibration is proposed here by considering the phase difference between the microphone and the hot-wire anemometer output signals. The results obtained by using a simple fluid-filled resonant cavity are encouraging on the feasibility of this method to carry out a first-order acoustic velocity measurement. However, the complexity of the dynamic calibration due to that of the heat transfer mechanism around the hot-wire probe in various frequency ranges clearly merits more investigation.     

用激光外差技术高精度测量目标速度

搭建了外差探测实验平台,分别选用漫反射目标及类简谐运动模型作匀转速运动及变速运动的测量目标,应用激光外差探测技术实现了对匀转速运动及变速运动物体的速度测量.在匀转速测量过程中,同时采用外差探测法和振幅调制法测量了漫反射目标正负两个方向转动的速度,共得到133组不同的转速结果.通过调整实验系统,亦实现了对类简谐运动目标的...     

基于双光束-双散射的激光多普勒水流速测量

激光多普勒水流速仪是一种非接触、高精度的测量仪器,但由于技术和集成度等原因还仅限于研究所和高校使用。文中介绍了一种双光束-双散射法测量流体速度,利用此种光路测量法可以提高集成度、促进激光技术的普及;还可以解决常规测量法难以解决的问题,例如风洞的风速测量等。通过实验验证了这种方法的可行性。     

Confocal microscopic image sequence compression using vector quantization and three-dimensional pyramid

The three-dimensional (3-D) pyramid compressor project at the University of Glasgow has developed a compressor for images obtained from confocal laser scanning microscopy (CLSM) device. The proposed method using a combination of image pyramid coder and vector quantization techniques has good performance at compressing confocal volume image data. An experiment was conducted on several kinds of CLSM data using the presented compressor compared with other well-known volume data compressors, such as MPEG-1. The results showed that the 3-D pyramid compressor gave a higher subjective and objective image quality of reconstructed images at the same compression ratio, and presented more acceptable results when applying image processing filters on reconstructed images.     

Surface wave velocity measurement using reflections from laser scribed grooves

The measurement of ultrasonic surface wave (USW) velocity is difficult using the pulse overlap method (POM) in the presence of an externally applied stress. Coupling variations between the sample and the transducer cause nonuniform distortions of the two received pulses which makes the overlap condition difficult to determine over an extended stress range. The adaptation in this paper of a single transducer configuration to generate and detect the USW eliminates coupling variations between two or more transducers. In addition, two parallel, precisely positioned and contoured grooves are laser scribed on the sample surface to provide the necessary overlap echoes. Since both echoes are reflected only once by identical grooves and are equally affected by the distortions due to coupling variations, the overlap condition is relatively unaffected by the external stress and the accuracy of the USW velocity measurement is increased significantly.     

Improvement and validity of shock measurements using heterodyne laser interferometer

The improvement and validity of shock measurements using only the laser head (heterodyne laser interferometer) of a commercial laser Doppler vibrometer was investigated by comparing acceleration waveforms measured by a homodyne laser interferometer with those measured by a heterodyne laser interferometer. The acceleration waveforms were generated from the displacement waveforms obtained with a reference quadrature homodyne laser interferometer by applying a numeric differentiation process twice. The differences between the two acceleration waveforms were found to be small with the measurement uncertainty in case of high acceleration level. In a further investigation, the accuracy of the shock measurements taken by the homodyne and heterodyne laser interferometers were compared in computational simulation. The results indicated that the accuracy of the heterodyne laser interferometer was superior to that of the homodyne laser interferometer.     

Two-dimensional fringe projection for three-dimensional shape measurements by using the CWT phase gradient method

This paper describes an optical measurement technique for the two-dimensional fringe pattern (by introducing the carrier frequencies in two spatial directions x and y) by the continuous wavelet transform (CWT) phase gradient method. Such transforms based on the Morlet and Paul wavelets have been applied to image rows and columns one by one and then added to find the final phase distribution, without using any unwrapping algorithms. This technique is compared with the S-transform phase gradient method. Numerical simulations and actual experiments are carried out to show the validity of this technique for finding the phase distributions.     

薄膜谐振Lamb波传感器测量液体流速矢量的方法

针对液体流速测量领域中微型流量传感器高品质因数、高灵敏度的性能要求。本文设计一种双端增强型薄膜谐振结构实现Lamb波传感器的高品质因数,利用传感器反对称模式(A01模式)在薄膜-液体界面处的消逝波实现液体流速矢量测量。所制作的双端增强型薄膜谐振Lamb传感器A01模式的主峰品质因数为703,A01模式的频率移动量与液体流速大小存在线性关系,频率移动方向与液体流动方向存在对应关系。流速实测灵敏度约为270 Hz/mm/s,传感器稳定性噪声小于0.2Hz,流速最低检测极限值(LOD)为2.2μm/s,流量最低检测极限值(LOD)为18.3nL/min。结果表明,双端增强型薄膜谐振Lamb波传感器可以实现液体流速高灵敏度矢量测量。     

Probe and method for simultaneous measurements of 'true' instantaneous temperature and three velocity components in turbulent flow

In the measurement of turbulent flows the need has always existed to obtain correct instantaneous values of temperature and three components of velocity at a particular point. Many proposed lengthy approximate correction methods that attempt to account for 'nonlinear' effects (cross contamination between different quantities) in hot-wire measurements cannot be considered satisfactory. The availability of powerful digital computers for theoretical and experimental studies has placed pressure on experimentalists to develop better probes and methods. This paper attempts to answer these pressures by describing the development of a special four-wire probe and a method of processing the obtained signals. The use of four 0.625-microm-diam sensors makes the probe practically interference free. The processing method is based on the simultaneous solution of four complete nonlinear response equations for the sensors, yielding in principle exact instantaneous values of velocity components and temperature. Additional features of the processing method include: instantaneous full correction for tunnel free stream velocity and temperature fluctuations, first-order correction for dc drifts of the signals during data acquisition, subtraction of all 60-Hz related noise, and correction for streamwise displacement of sensors based on instantaneous streamwise velocity.     

Development of an optical three-dimensional laser tracker using dual modulated laser diodes and a signal detector

Laser trackers are widely used in industry for tasks such as the assembly of airplanes and automobiles, contour measurement, and robot calibration. However, laser trackers are expensive, and the corresponding solution procedure is very complex. The influence of measurement uncertainties is also significant. This study proposes a three-dimensional space position measurement system which consists of two tracking modules, a zero tracking angle return subsystem, and a target quadrant photodiode (QPD). The target QPD is placed on the object being tracked. The origin locking method is used to keep the rays on the origin of the target QPD. The position of the target QPD is determined using triangulation since the two laser rays are projected onto one QPD. Modulation and demodulation are utilized to separate the coupled positional values. The experiment results show that measurement errors in the X, Y, and Z directions are less than ±0.05% when the measured object was moved by 300, 300, and 200 mm in the X, Y, and Z axes, respectively. The theoretical measurement error estimated from the measurement model is between ±0.02% and ±0.07% within the defined measurable range. The proposed system can be applied to the measurements of machine tools and robot arms.     

雷尼绍与多普勒激光干涉仪测量方法比较

介绍了雷尼绍激光干涉仪和多普勒激光干涉仪的测量原理,并对这两种激光干涉仪的测量方法进行了比较。结果表明,当只需要测量机床的线性定位精度时,两者都比较适合。当需要测量机床的所有几何误差时,由于多普勒激光干涉仪采用了激光向量技术,测量周期大大缩短,测量效率较高。     

Rotating microchannel flow velocity measurements using the stationary micro-PIV technique with application to lab-on-a-CD devices

The measurement of microfluidic flows is an essential instrument to understand the governing physical mechanisms at small scales. This fact has motivated the adaptation of well-established “macroscale” experimental technics to deal with the specificities of microfluidic flows; a prominent example is the micro particle image velocimetry (micro-PIV) technique. In a different manner, the progress experienced by experimental techniques to measure flows in rotating frames has been more limited, with most studies concerned with macroscale turbomachinery applications. It turns out that the scale reduction in this field establishes a new and important flow class, known as centrigually-driven microfluidics, with application to lab-on-a-CD devices. However, the experimental characterization of rotating microflows has been, so far, limited to bulk flow measurements and/or visualization practices. For that reason, in this work, we propose extending the stationary micro-PIV technique to undertake quantitative, whole-field, velocity measurements inside rotating microchannel flow platforms. For this task, actual lab-on-a-CD prototypes are used. This work develops in two parts. First, we describe the most relevant changes in the micro-PIV equipment viewing the introduction of the test section rotation, namely: (i) hardware changes related to the micro-PIV/CD synchronization and (ii) software changes aiming at the preservation of the velocity measurement accuracy, through the removal of the circumferential velocity component. While this last step follows a well-known methodology, called image de-rotation, we propose tackling it in a new and automated fashion by means of the image registration method, whose implementation and advantages are explained in detail here. The second part of this work evaluates the capabilities of the modified micro-PIV technique by critically assessing the results of preliminary tests undertaken in dynamical regimes where rotation is dominant. Here, we present for the first time velocity profile measurements of centrifugally-driven microchannel flows, which display marked structural differences from classical stationary pressure-driven flows. The quality of these experimental profiles is further examined through comparisons with computational fluid dynamics simulations, based on the lattice Boltzmann method. Overall, this study indicates the effectiveness of the proposed micro-PIV system, which is able to accurately capture the most relevant physical features of rotating microfluidic flows over regions sufficiently far away from the walls. On the other hand, inside the boundary layers, the present micro-PIV measurements remain difficult to execute; the reasons for this limitation are discussed and clearly identified in the present preliminary studies, which pave the way for future studies in the field.     

基于激光散斑的多普勒效应实验装置设计

本系统基于散斑干涉技术。通过LabVIEW和Matlab混合编程。设计了处理数字散斑的系统。通过Matlab实现图像处理程序调用。在LabVIEW下进行散斑图像采集和图像处理参数的设定。完成散斑图的处理。本系统设计理念新颖。采用了基于CCD的非接触测量。能够实现实时测量。该系统的原理可以应用于生物医学光学成像、微小粒子测量等领域。     

Simultaneous measurements of the distance and velocity of diffusely scattering objects by active laser interferometry with linear frequency modulation

The possibility of simultaneous measurements of the distance and velocity of diffusely scattering objects by active laser interferometry with frequency modulation is theoretically shown and experimentally substantiated.