Acoustooptic methods for measuring sound velocity

This paper gives a brief review of some studies of acoustooptic methods for measuring sound velocity in solids performed at the Department of Acoustoelectronics and Acoustooptics of the Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Science.     

An approach for velocity and position estimation through acceleration measurements

This paper proposes an approach for velocity and position estimation through acceleration measurements. In this approach, the noises of acceleration signal are removed through a smoothing process based on diffusion equation, a special partial differential equation (PDE). Then a mechanism is designed to remove abnormal deviations in the signal before and after integration. The proposed approach can substantially reduce the errors (drifts) accumulated from the integration of acceleration signal. Its effectiveness and superiority over other popular methods are validated by simulation and experimental results.     

An all-digital method for accurate measurements of mechanical deformations

In this paper, an experimental analysis method based on image treatment techniques for the quantitative evaluation of some polycrystal material deformations is presented. This method has been successfully developed for this purpose by adapting and developing algorithms suitable for the images under study. Details of the whole process as applied to a typical example are described and discussed.     

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.     

An attachment to SEM for 3-D surface topography measurements of uniform materials

The paper reports on a SEM-based system for quantitative three-dimensional (3-D) surface topography measurements. In comparison with commercial line-width measuring systems, this metrology instrument is designed to measure quantitatively both critical dimensions in horizontal plane and features height while allowing for full cross section reconstruction from backscattered electrons (BSE) signal. The philosophy behind this technique has been described previously, (Aristov et al. 1988, 1991). Now the system is operational at our Institute, and its characteristics just as design criteria, and some examples of application are presented.     

Radio-frequency probe for bubble size and velocity measurements

A radio frequency (rf) probe that can provide local void fraction and interface velocity measurements in a gas-liquid two-phase flow was developed. The probe response to bubble passage was investigated with single-bubble controlled experiments. For a fixed geometry, the probe response was dependent on the dielectric constant of the medium surrounding the probe tip (air or water) and on the frequency of the carrier signal supplied to the probe. Bubble lengths (< 1 cm) and average bubble approach velocities (< 160 cm/s) were independently measured by two light sources and detectors placed at a known distance from each other and sensing the passage of each bubble. By choosing a sensitive probe tip length of 2.75-3 mm, the rf probe output provided enough information to determine the bubble length and velocity. The results obtained by the two independent methods show reasonable agreement (+/-10%).     

A microwave method based on amplitude-only reflection measurements for permittivity determination of low-loss materials

A new method based on amplitude-only reflection measurements for complex permittivity determination of low-loss materials backed by a short-circuit termination is presented. There are two main advantages of the proposed method. First, it is insensitive to calibration plane shifts and phase uncertainties in reflection measurements of low-loss materials. Second, it does not require any additional test material with a thickness value different than that of the material under test. The disadvantage of the proposed method is that it is not convenient to apply for complex permittivity determination of dispersive low-loss materials. The method is validated by complex and amplitude-only scattering parameter measurements at X-band of a low-loss sample (polystyrene) fitted into a waveguide section. The method, as other non-resonant methods, can only provide a rough indication of the imaginary part of the permittivity for low-loss samples.     

A digital technique for measuring the velocity and attenuation of sound

A digital procedure for measuring the velocity and attenuation of sound in a wide temperature range is described. Commercially available digital instruments are used. Original Russian Text ? A.E. Petrova, S.M. Stishov, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 4, pp. 173–176.     

Optical probe for local void fraction and interface velocity measurements

In view of the importance of obtaining unsteady local void fraction and interface velocities in liquid-vapor two-phase flows, an optical probe with a controlled tip geometry was developed and is described. In order to minimize the disturbances caused to the flow field by the presence of the probe, its dimensions have been miniaturized. The electronic and hydrodynamic responses of the probe were investigated experimentally. The probe was found to be sensitive to both the interface velocities and the phase present at the probe tip. A possible explanation for the behavior of the probe is presented. Within the velocity range checked and with proper calibration, the optical probe described can be used to determine both local void fractions and interface velocities.     

一种小型水下高速运动体的自主测速方法

针对水下高速运动体自主测速困难的问题,基于涡轮转速与运动载体速度在一定范围内的线性关系,提出一种适用于小型水下高速运动体的自主测速方法.建立了基于力矩平衡的涡轮转动黏性数学模型,给出了模型求解方法,计算并获得了理论曲线.设计制作了原理样机,在高速水洞中进行了模拟实验.结果表明:在实验段测速线性度误差为3.89％,初生空化数约为1.02,在水下1 m以下环境,测量30节(55.56 km/h)以内的速度不会发生明显空化.该方法经初步验证切实可行.     

Obtaining flaw images by the SAFT method taking the variable velocity of sound in a test object into account

A modification of the SAFT method for obtaining flaw images in test objects containing three regions with different velocities of sound (SV) is proposed. Complex composite welded joints and repair welds are classified as objects in which the SV in a welded joint may differ from the velocity in a parent metal by >5%; therefore, a high-quality image of flaws can be obtained by taking different SVs into account. To solve this problem, a method for obtaining a test object with three regions with different SVs is proposed. The delays of propagating ultrasonic pulses were calculated using the Fermat principle. The results of reconstructing flaw images in a 300 welded joint from echo signals obtained as a result of numerical simulation by the finite-element method are presented. The images obtained by the SAFT method without taking different SVs into account are displaced from their true position, thus they do not allow determination of their coordinates and location. Consideration of different SVs allows one to obtain unshifted reflections of flaw images and, hence, evaluate the types and dimensions of flaws more accurately.     

Note: Measurement method for sound velocity of melts in large volume press and its application to liquid sodium up to 2.0 GPa

Based on large volume press and conventional pulse-echo ultrasonic technique, we have overcome the difficulty in determining the length of liquid specimen under high pressure, and the sound velocity in liquid Na has been measured up to 2 GPa. The P-V data deduced by our sound velocity results through equation of state is in an excellent agreement with previous data directly determined by piezometer method. This new experimental technique is convenient and ready for use, being expected to advance investigation on thermodynamic properties of liquid metals and other melts under high pressure.     

Simultaneous velocity profile and temperature profile measurements in microfluidics

Simultaneous non-intrusive temperature and velocity measurements in flows are of high technological interest, e. g. to study the heat transfer in microfluidic environments. However, a measurement system that offers a low velocity uncertainty and micrometre spatial resolution as well as highly accurate temperature measurements in a single device has not been demonstrated so far. In this work, this problem is solved by combining a Laser Doppler Velocity Profile Sensor (LDV-PS) with Laser-Induced Fluorescence (LIF). Seeding particles are employed, that contain the fluorescent dyes uranine and rhodamine B. The multiple dye approach eliminates the influence of the droplet size. Relative velocity uncertainties of down to 0.4% and a temperature uncertainty of down to 0.24 ${}^{\circ }$C with a spatial resolution of $10\mathrm{\mu }\mathrm{m}$ are achieved in a demonstration air flow experiment. The method has the potential to be optimised for different temperature ranges and uncertainty requirements, making it applicable on a wide range of thermal flows like fuel cells or microbioreactors. A better understanding of heat exchange processes can improve the energy efficiency of microfluidic devices.     

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.     

Heterodyne laser-Doppler line-sensor for highly resolved velocity measurements of shear flows

We report on the application of a heterodyne laser-Doppler line-sensor for spatially highly resolved shear flow measurements. The line-sensor employs a wavelength-division-multiplexing (WDM) technique, which generates a measurement volume with convergent and divergent fringes for two laser wavelengths, respectively. The evaluation of the ratio of the resulting two Doppler frequencies yields the particle velocity and position inside the measurement volume with a resolution of a few micrometers. A line sensor with directional discrimination was realized by using a heterodyne technique. The measurement signal is generated in the intermediate frequency band, allowing the evaluation of small velocities with high accuracy. We report on the measurement of laminar boundary layers and for the determination of the wall shear stress. Good agreement was obtained between the measured velocity and the Blasius solution.     

Design and characterization of optical heads for interferometric ballistic velocity measurements

The design of optical fiber based heads offering high accuracy and bandwidth for use in VISAR (velocity interferometer system for any reflector) experiments measuring ballistic velocities is described. A new, expanded, model for predicting the distance-dependent collection efficiency of the heads is presented. The model is shown to agree very well with experimental results, both within and outside the "depth of field". Various optical heads are demonstrated, to suit different experimental setups and conditions. Designs offering options for high bandwidths, accurate prealignment, and large stand-off distances are discussed. Results from a typical VISAR experiment are presented, verifying that our designs yield high-quality data.     

Improved instrumentation for blood flow velocity measurements in the microcirculation of small animals

Microcirculation is the generic name of vessels with internal diameter less than 100 microm of the circulatory system, whose main functions are tissue nutrition and oxygen supply. In microcirculatory studies, it is important to know the amount of oxyhemoglobin present in the blood and how fast it is moving. The present work describes improvements introduced in a classical hardware-based instrument that has usually been used to monitor blood flow velocity in the microcirculation of small animals. It consists of a virtual instrument that can be easily incorporated into existing hardware-based systems, contributing to reduce operator related biases and allowing digital processing and storage. The design and calibration of the modified instrument are described as well as in vitro and in vivo results obtained with electrical models and small animals, respectively. Results obtained in in vivo studies showed that this new system is able to detect a small reduction in blood flow velocity comparing arteries and arterioles (p <0.002) and a further reduction in capillaries (p<0.0001). A significant increase in velocity comparing capillaries and venules (p <0.001) and venules and veins (p <0.001) was also observed. These results are in close agreement with biophysical principles. Moreover, the improvements introduced in the device allowed us to clearly observe changes in blood flow introduced by a pharmacological intervention, suggesting that the system has enough temporal resolution to track these microcirculatory events. These results were also in close conformity to physiology, confirming the high scientific potential of the modified system and indicating that this instrument can also be useful for pharmacological evaluations.     

An improved single-parameter tip-timing method for turbomachinery blade vibration measurements using optical laser probes

This paper presents an improved analysis method for the interpretation of the vibration data measured at turbomachinery blade tips using optical laser probes. A multi-degree-of-freedom numerical simulator, which includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms and the characteristics of the optical probe, has been developed to assess the reliability of the various data processing techniques to identify the natural frequencies and mode shapes of bladed-disk assemblies. It has been demonstrated that the Zablotsky—Korostelev single parameter technique, which is a de-facto standard in the aerospace industries, has inherent limitations associated with it. An improved and more rigorous method is presented for deriving the blade arrival times and a non-linear solution technique is suggested for their numerical determination. Finally, the effect of blade mistuning on the accuracy of the proposed method is also investigated.     

羟基分子标记示踪速度测量中的强振动干扰抑制

针对在发动机实验环境中羟基分子标记示踪速度测量技术受到的强振动干扰问题,通过实验研究分析了标记激光与不同流场作用时产生的辐射光谱特性,设计了在实验中同时拍摄标记基准图像和移动图像的振动干扰抑制方法。对于一般流场,在实验中实时拍摄标记激光瑞利散射作为标记基准图像,而对于含有煤油大分子碳氢燃料的流场甚至是CH_4燃烧场,用标记激光诱导燃料在OH荧光辐射波段的辐射光作为标记基准图像。在超燃发动机的速度测量应用尝试表明,两种方案均可以达到抑制振动的目的。在相对干净的流场区域,前者得到的标记激光图像会受到壁面散射等干扰,基准位置提取不确定度约为0.06mm。在流场中未燃燃料含量比较丰富的区域,后者能够得到清晰的标记基准图像,基准位置提取不确定度可以降至0.03mm,与采用平均方法得到的基准位置提取不确定度相当。