An experimental investigation of high velocity impact

The temperature increase due to shock compression is measured for three metals: 1100 aluminum, commercially pure copper, and Armco iron. Spherical shock waves are generated by the impact of projectiles (with identical target material) at velocities from 2700 to 5000 feet per second. The thermocouple response to these shock induced temperatures generally occur in less than three microseconds. The measured temperature increase is predicted with fair accuracy by the progressive wave similarity method. The pressure effect and charge effect on thermocouple are discussed.     

Laboratory measurement of suspended sediment concentration using an Acoustic Concentration Profiler (ACP)

Vertical profiles of suspended sediment concentration have been gathered in a laboratory flume using a 2.25 MHz acoustic transducer. The acoustic concentration profiler (ACP) was calibrated in a vertical duct for homogeneous concentrations of two uniformly sized sediments. The transducer was then transferred to a 6 m horizontal flume where concentration profiles were measured in steady and unsteady flows. For the steady flow tests, concentration measurements made with the ACP and with suction samplers are compared. The results demonstrate that the ACP provides an accurate method of non-intrusively measuring sediment concentrations of more than 2.5% by volume. Received: 24 September 1998/Accepted: 12 April 1999     

An improved method for measuring velocity and concentration by thermo-anemometry in turbulent helium-air mixtures

 A hot wire/film probe is used with new operating conditions for measurements of velocity and concentration in helium/air mixtures. With the upstream wire much more overheated than the downstream film, the sensing elements behave almost independently and the calibration map is composed of clearly distinct iso-velocity and iso-concentration curves. This behaviour is largely explained by the difference in the heated elements’ diameters. Tests of the probe in a turbulent boundary layer with large density variations indicate very satisfactory measurements. The domain of use for the probe is considerably extended with these new operating conditions. Received: 8 January 1996/Accepted: 29 May 1996     

An automated simultaneous measurement of thickness and wave velocity by ultrasound

The measurement of wave velocity in a sample requires an accurate determination of the sample thickness at the points of interrogation. The theory of an automated technique is presented. In its application, the thickness of the sample is first calculated by the knowledge of the wave velocity in the immersion fluid. This thickness is then used to calculate the wave velocity in the sample. The results of the application of the technique to isotropic and anisotropic materials are presented.     

Holographic sensor for measurement of wall velocity gradients

Time-resolved measurements of skin friction and boundary layer turbulence are important to the design of more fuel efficient aircraft. In this paper we describe the design and testing of a holographic fan fringe sensor that can non-intrusively measure time-resolved velocity gradients near an aerodynamic surface. The holographic sensor produces a set of optical interference fringes inside the viscous sub-layer that form a fan rather than a linear array. Particles scattering light in the sub-layer produce a Doppler frequency that is a direct measurement of the velocity gradient and is proportional to aerodynamic shear stress and skin friction. The holographic recording condenses the optics necessary to form the fringes into a small 3–5 mm package, eliminates the need for optical access from behind the model, and produces a compact and robust sensor.     

An analytical model for high velocity impacts on thin CFRPs woven laminated plates

An analytical model to study the impact process of a spherical projectile penetrating at high velocity into a carbon/epoxy plain woven laminate is developed in this work. The model is based on an energy balance, where the kinetic energy of the projectile is absorbed by the laminate by three different mechanisms: laminate crushing, linear momentum transfer and tensile fiber failure. A non-homogeneous differential equation is obtained. A subsequent simplification using regular perturbation analysis gives a closed-form solution that allows the approximative calculation of the residual velocity and hence the ballistic limit. The model is validated with the results of experimental tests in which the residual velocity is measured by means of high speed cameras.     

In-line imaging measurements of particle size,velocity and concentration in a particulate two-phase flow

A novel method is developed for in-line measurements of particle size, velocity and concentration in a dilute, particulate two-phase flow based on trajectory image processing. The measurement system consists of a common industrial CCD camera, an inexpensive LED light and a telecentric lens. In this work, the image pre-processing steps include stitching, illumination correction, binarization, denoising, and the elimination of unreal and defocused particles. A top-hat transformation is found to be very effective for the binarization of images with non-uniform background illumination. Particle trajectories measured within a certain exposure time are used to directly obtain particle size and velocity. The particle concentration is calculated by using the statistics of recognized particles within the field of view. We validate our method by analyzing experiments in a gas-droplet cyclone separator. This in-line image processing method can significantly reduce the measurement cost and avoid the data inversion process involved in the light scattering method.     

In-line imaging measurements of particle size,velocity and concentration in a particulate two-phase flow

A novel method is developed for in-line measurements of particle size, velocity and concentration in a dilute, particulate two-phase flow based on trajectory image processing. The measurement system consists of a common industrial CCD camera, an inexpensive LED light and a telecentric lens. In this work, the image pre-processing steps include stitching, illumination correction, binarization, denoising, and the elimination of unreal and defocused particles. A top-hat transformation is found to be very effective for the binarization of images with non-uniform background illumination. Particle trajectories measured within a certain exposure time are used to directly obtain particle size and velocity. The particle concentration is calculated by using the statistics of recognized particles within the field of view. We validate our method by analyzing experiments in a gas-droplet cyclone separator. This in-line image processing method can significantly reduce the measurement cost and avoid the data inversion process involved in the light scattering method.     

An assessment of high-power light-emitting diodes for high frame rate schlieren imaging

The feasibility of using high-power light-emitting diodes (LED) as a light source for high frame rate schlieren imaging is investigated. Continuous sequences of high-intensity light pulses are achieved by overdriving the LED with current pulses up to a factor of ten beyond its specifications. In comparison to commonly used pulsed light sources such as gas discharge lamps and pulsed lasers, the pulsed LED has several attractive advantages: the pulse-to-pulse intensity variation is on the same order of magnitude as the detector (camera) noise permitting quantitative intensity measurements. The LED??s narrow emission bandwidth reduces chromatic abberations, yet it is spectrally wide enough to prevent the appearance of speckle and diffraction effects in the images. Most importantly, the essentially lag-free light emission within tens of nanoseconds of the applied current pulse allows the LED to be operated at varying frequencies (i.e., asynchronously), which generally is not possible with neither lasers nor discharge lamps. The pulsed LED source, driven by a simple driver circuit, is demonstrated on two schlieren imaging setups. The first configuration visualizes the temporal evolution of shock structures and sound waves of an under-expanded jet that is impinging on a rigid surface at frame rates of 500?kHz to 1?MHz. In a second application, long sequences of several thousand high-resolution images are acquired on a free jet at a frame rate of 1?kHz. The low-intensity fluctuation and large sample number allow a reliable computation of two-point correlation data from the image sequences.     

An LIF line scan system for the measurement of scalar concentration in a continuously operated stirred tank

 An LIF line scan system is presented and used to obtain unobtrusive mean and angle resolved concentration measurements in a continuously operated stirred tank agitated with a single Rushton turbine. The measurements showed that the trailing vortex structures caused regions of elevated concentrations gradients and concentration fluctuations between blade passages. In addition, on the centre line of the tank, whilst macromixing was always complete, micromixing was less complete than in other regions of the tank. Compared to point measurement techniques, the line scan system made data collection more comprehensive and convenient and the determination of a line of data allows the possibility of the correction of beam attenuation and the extension of the technique to a larger scale. Received: 25 July 1997/Accepted: 15 October 1997     

An economical droplet fog generator suitable for laser Doppler anemometry and particle imaging velocity seeding

An inexpensive device for generating fogs of micron-sized droplets is described. The liquid does not pass through small orifices. It is easily constructed and suitable for liquids containing particulates, seeding high-pressure environments and laser Doppler anemometry, and particle imaging velocimetry. Phase Doppler anemometry measurements show size distributions as a function of pressure for three working fluids. The device consistently produced a narrow size range with a mean diameter of a few microns.     

Effect of the measurement volume in turbulent pipe flow measurement by the ultrasonic velocity profile method (mean velocity profile and Reynolds stress measurement)

 The ultrasonic velocity profile measurement method has some favorable advantages over the conventional flow measurement methods, such as measurement of the instantaneous velocity profile over the measuring line and its applicability to opaque liquids. The method has another advantage of being non-intrusive. Hence, it is applicable to various flow conditions, although it requires a relatively large measurement volume. In this paper, the effects of the measurement volume on the mean velocity profile and the Reynolds stress measurement have been investigated for fully developed turbulent flows in a vertical pipe. The results were then compared with data obtained by direct numerical simulation. Received: 9 March 2000 / Accepted: 27 March 2001 Published online: 29 November 2001     

On the use of electrochemical sensors for local velocity measurement of viscoelastic fluids

Some problems connected with the application of the electrochemical method of measuring local velocity of viscoelastic polymer solutions have been presented and discussed. On the basis of the analysis of changes in the fluid flow structure due to viscoelastic properties, a modified Eq. (8) which describes the local mass transfer coefficients for wedge shape electrochemical probes has been obtained. On the basis of Eq. (8), own modification of the construction of electrochemical measuring probes has been proposed. The reliability of the proposed method has been successfully experimentally verified by the comparison of the obtained free jet velocity profiles with the literature data referring to results obtained by the laser-Doppler technique.

---

Über die Anwendung der elektrochemischen Methode zur Messung der örtlichen Geschwindigkeiten von viskoelastischen Flüssigkeiten

Zusammenfassung Einige Probleme, die mit der Anwendung der elektrochemischen Methode der Messung der örtlichen Geschwindigkeiten von viskoelastischen Polymerlösungen verbunden sind, wurden dargestellt und diskutiert. Auf Grund der Analyse von Strömungsstrukturänderungen, die auf die viskoelastischen Eigenschaften zurückzuführen sind, wurde die modifizierte Gl. (8), welche die örtlichen Stoffübergangskoeffizienten für keilförmige elektrochemische Meßsonden beschreibt, erreicht. Auf Grund der Gl. (8) wurde eine eigene Modifikation der Konstruktion von elektrochemischen Meßsonden vorgeschlagen. Die Zuverlässigkeit der vorgeschlagenen Methode wurde experimentell, durch den Vergleich der Geschwindigkeitsprofile der freien Strahlen mit den in der Literatur angegebenen Daten über die mittels der Laser-Dopplerschen Technik gewonnenen Ergebnisse, erfolgreich geprüft.

     

多级炸药爆轰高速驱动技术的Gurney模型优化分析

利用多级炸药 飞片装置可得到速度在10km/s以上、直径数厘米的末级平面飞片,在高压物态方程和高速碰撞等实验研究中有重要应用前景。改进了爆炸驱动的Gurney模型,推广用于典型的二级爆轰驱动(前级飞片 炸药层 后级飞片)装置的分析,得到前、后级飞片终速度的计算公式,与实验结果符合较好。根据对炸药层厚度优化计算结果的讨论可知,对于综合利用前级飞片动能和炸药层能量最有利的后级飞片速度处于2～3倍Gurney速度的范围。前级飞片速度很高时,后级飞片速度趋于两者直接弹性碰撞的结果。     

Voronoï imaging methods for the measurement of granular flows

A set of digital imaging methods derived from the Voronoï diagram is proposed and tested on various liquid–granular flow applications. The methods include a novel pattern-based particle-tracking algorithm, as well as estimators of the three-dimensional granular concentration from two-dimensional images. The proposed algorithms are able to resolve individual grain motions even for rapid shear flows involving dense, fluctuating granular ensembles. Full automation is achieved, allowing the derivation of accurate statistics from large sets of individual measurements, as well as the construction of complete sets of grain trajectories. Results are presented for different applications: homogeneous fluidization, steady uniform debris flow, and unsteady debris surges.     

测量炸药旁侧爆轰波速度的啁啾光纤布拉格光栅传感器技术

提出了一种适用于啁啾光纤布拉格光栅CFBG(chirped fiber Bragg grating)传感器测量爆轰波速度的实验公式,该公式考虑了ASE(amplified spontaneous emission)光源的光谱、CFBG的平坦度对测量的影响;研究了CFBG的反射谱线宽与长度的理论关系,并设计了测量CFBG反射谱线宽的实验装置,从而可计算出CFBG长度。搭建了测量CFBG传感器系统常数的实验装置,并利用实验数据拟合了系统常数;用CFBG传感器测量了RDX/TNT(60/40)的旁侧爆轰波速度,与其爆速有3.4%的差异。     

Effect of the pulse trajectory on ultrasonic fluid velocity measurement

In a general situation a non-uniform velocity field gives rise to a shift of the otherwise straight acoustic pulse trajectory between the transmitter and receiver transducers of a sonic anemometer. The aim of this paper is to determine the effects of trajectory shifts on the velocity as measured by the sonic anemometer. This determination has been accomplished by developing a mathematical model of the measuring process carried out by sonic anemometers; a model which includes the non-straight trajectory effect. The problem is solved by small perturbation techniques, based on the relevant small parameter of the problem, the Mach number of the reference flow, M. As part of the solution, a general analytical expression for the deviations of the computed measured speed from the nominal speed has been obtained. The correction terms of both the transit time and of the measured speed are of M ² order in rotational velocity field. The method has been applied to three simple, paradigmatic flows: one-directional horizontal and vertical shear flows, and mixed with a uniform horizontal flow.     

On the measurement of lateral velocity derivatives in turbulent flows

Direct numerical simulation data for the lateral velocity derivative u/y at the centreline of a fully developed turbulent channel flow provide reasonable support for Wyngaard's analysis of the error involved in measuring this quantity using parallel hot wires. Numerical data in the wall region of the channel flow also provide a useful indication of how to select the separation between the wires. Justification for this choice is obtained by comparing several measured statistics of u/y with the corresponding numerical data.     

An approach for obtaining approximate formulas for the Rayleigh wave velocity

In this paper, we introduce an approach for finding analytical approximate formulas for the Rayleigh wave velocity for isotropic elastic solids and anisotropic elastic media as well. The approach is based on the least-square principle. To demonstrate its application, we applied it in order to obtain an explanation for Bergmann’s approximation, the earliest known approximation of the Rayleigh wave velocity for isotropic elastic solids, and used it to establish a new approximation. By employing this approach, the best approximate polynomials of the second order of the cubic power and the quartic power in the interval [0, 1] were found. By using the best approximate polynomial of the second order of the cubic power, we derived an approximate formula for the Rayleigh wave speed in isotropic elastic solids which is slightly better than the one given recently by Rahman and Michelitsch by employing Lanczos’s approximation. Also by using this second order polynomial, analytical approximate expressions for orthotropic, incompressible and compressible elastic solids were found. For incompressible case, it is shown that the approximation is comparable with Rahman and Michelitsch’s approximation, while for the compressible case, it is shown that our approximate formulas are more accurate than Mozhaev’s ones. Remarkably, by using the best approximate polynomials of the second order of the cubic power and the quartic power in the interval [0, 1], we derived an approximate formula of the Rayleigh wave velocity in incompressible monoclinic materials, where the explicit exact formulas of the Rayleigh wave velocity so far are not available.