Particle Velocity Measurements Research Articles

Decimeter-scale particle characterization in the coma of 73P/Schwassmann-Wachmann 3 using dual-wavelength radar observations

We investigate the centimeter-to-decimeter-scale particle size distribution and dynamics in the coma of Comet 73P/Schwassmann-Wachmann 3 using radar observations obtained shortly after the comet's disintegration in May 2006. We derive the particle size distribution power-law index in the comae of fragments B and C using radar cross sections and circular-polarization ratios observed at S and X bands (2.38 GHz and 8.56 GHz, respectively), and show day-to-day changes in the number of contributing particles. We test three irregular particle morphologies, but find that the particle shape plays a relatively minor role. The power-law indices from 4.0 to 4.8 and major-axis diameters up to about 30 cm provide the best fits to the radar observations, the values depending on the particle shape and the observed radial velocity. A majority of the measured particle velocities exceed the escape velocity of the nuclei.

Particle velocity measurement method of dense-phase gas–solid flow based on an electrostatic sensor array

Particle velocity is an important parameter of dense-phase gas–solid flow for both monitoring and control purposes. This paper presents a recent development in the noncontact measurement of solid particle velocity using an electrostatic sensor array (ESA). The electrostatic sensor array with eight electrodes is used to collect electrostatic signals generated by the moving charged particles. A velocity measurement method based on the tomography technique is presented, which measures the velocity of solid particles in the horizontal pipeline. The simulated model of the ESA with eight electrodes is built, and the sensing area of the ESA is mapped onto 13 pixels of equal area. Simulation tests are then conducted to evaluate the feasibility and accuracy of the velocity measurement at different positions. Finally, experimental tests are conducted on the horizontal conveying pipeline of a high- pressure dense-phase pneumatic conveying pilot system. Results indicate that the proposed method is capable of measuring the spatial average velocity of pulverized coal over the cross-sectional area of pipe with a relative error within ±7% for the conditions of particles tending to be of uniform distribution. In addition, the effect of moisture on velocity measurement is investigated.

An Economical Approach to Cold Spray Using In-line Nitrogen–Helium Blending

The cold gas dynamic spraying process provides an advantageous solution to the deposition, and additive manufacturing, of metals. Namely, it provides a reduced reactive environment, simple operation, and high deposition rates. It is known that the deposition efficiency of the cold spray process can be substantially increased using helium instead of nitrogen as the process gas. However, the use of pure helium can be cost prohibitive and commercially available helium recovery systems constitute a major capital investment and cannot be used with portable systems. This work focuses on the development and use of a novel, in-line gas mixing system, designed to provide a blend of nitrogen and helium at any ratio. Deposits produced with different gas ratios are investigated through particle velocity measurements, deposition efficiency, coating porosity, and coating hardness. The experimental results show that helium, even in lower percentages, can have a significant effect on deposition efficiency and coating quality. From the results, a cost model is presented which, when provided experimental values and user costs, can be used to identify the nitrogen–helium ratio that will produce the lowest overall coating cost.

Selection and Evolution of MEMS Accelerometer Sensor for Measurement of Blast-Induced Peak Particle Velocity

An ambiguous ground vibration caused by blasting operation is undesirable and results in grievous damage to surrounding structures, residential premises, and other sensitive sites. Consequently, proper monitoring of ambiguous ground vibration is an indispensable prerequisite to pinpoint the safe limits in and around mines to reduce their hazardous effects. The recently proliferated microelectro-mechanical-system (MEMS) based accelerometer sensors are becoming widely prevalent in vibration and condition monitoring applications. In this article, a three-axis, low- g , high-accuracy, inexpensive MEMS accelerometer has been selected and evaluated to measure blast-induced ground vibration. In addition, a global system for a mobile SIM 800 device is used as a radio frequency module and integrated to design an effective test setup. The experiment has been carried out by installing test setup at Mine-A, and the obtained results ensure that the peak particle velocity ranges from 0.19 to 8.60 mms at different monitoring locations.

Evaluation of Heat Transfer Transport Coefficient for Cold Spray Through Computational Fluid Dynamics and Particle In-Flight Temperature Measurement Using a High-Speed IR Camera

This work aims at obtaining experimental particle temperature readings during the cold spray (CS) process using a high-speed, high-definition infrared (IR) camera for multiple gas stagnation parameters to infer the suitability and accuracy of Nusselt number and drag coefficient correlations widely used in CS modeling. Measured particle temperatures are compared with values obtained through numerical modeling. Measured particle velocity using recorded data from the IR camera, based on particle streak and particle tracking velocimetry methods, is compared to values obtained from simulations. Additionally, particle velocities acquired using a Cold Spray Meter are also considered. Results demonstrate that only one of all common Nusselt correlations typically used in CS modeling results in accurate particle temperature predictions. Furthermore, the study shows that the drag coefficient correlation must incorporate the particle Mach number in order to provide acceptable particle velocity predictions.

Diagnostic system «Yuna» for disperse phase properties control in plasma and laser powder deposition processes

The possibilities of using the optical diagnostic complex «Yuna» for studying the characteristics of a disperse phase gas-powder jets under conditions of thermal spraying, laser cladding, as well as modeling physical experiments with cold gas-powder jets are presented. The optical system allows measurements of particles larger than 10 μm, the measureable velocities range is 1-1000 m/s, measureable temperature range is 1500-5000 K, and the field of view size can vary from 1 to 20 cm. The particle velocity measurements are performed using the Particle Track Velocimetry (PTV) method, and temperature measurements - using the Spectral-Brightness Pyrometry (SBP) method. For diagnostics of gas-powder flows with cold particles, a pulsed LED illumination system is used. Various examples of the application of the diagnostic system for investigation of hot and cold gas-powder flows are presented.

La turbulencia asociada con velocidades orbitales de olas que aún no rompen

Ocean-atmosphere exchange processes are known to decisively determine the sea state, the weather and our planet´s climate. With the ultimate goal of a better understanding of the processes contributing with turbulent kinetic energy into both boundary layers above and below the sea surface, we approach the ocean surface wave phenomenon, and in particular we study the non-breaking waves potential effect. Therefore, measurement of particle velocities were made in a fluid under non-breaking waves, for the purpose of detecting turbulence and its association with the wave steepness. A total of 184 experiments were analyzed, each one with a duration of 3.5 minutes and the presence of approximately monochromatic waves with varying steepness (0.012-0.273). The measurements were carried out in a wave tank with dimensions of 12.26 m × 0.55 m x 0.32 m using an acoustic velocimeter (Vectrino Profiler, Nortek). The u, v and w components of velocity were measured on a 3.5 cm long fluid column in 35 cells of 1 mm in height. During the experiments, the voleocity profile between 1.5 cm and 8.6 cm depth was obtained, referred to the water level in the wave tank (h = 48.6 cm ± 0.5 cm). The waves propagated in deep waters (h/λ > 0.5), where λ is the wave length. Only u(t, z) and w(t, z) components were considered for the analysis since, waves are practical two-dimensional (v(t, z) = 0). Power spectra were calculated in as function of frequency corresponding to u'(t, z) and w'(t, z) turbulent fluctuations, an inertial subrange (isotropic turbulence) was detected in the most of the spectra, for certain depths regardless of the wave steepness. Results from turbulent fluctuations frequency spectra show that eddy size involved in transferring energy to smaller ones, increases with the wave slope.

Miniature all-fibre microflown directional acoustic sensor based on crossed self-heated micro-Co2+-doped optical fibre Bragg gratings

The large size and electromagnetic interference of microphone arrays are long standing challenges for sound source localization. Here, an all-fibre vector acoustic sensor based on crossed microfiber Bragg gratings (micro-FBGs) has been proposed and experimentally demonstrated that enables the two-dimensional sound source localization with a size less than 1.5 mm. Two micro-FBGs inscribed in the Co2+-doped fibre are fabricated through a hydrofluoric acid solution, which are placed parallel to each other to form a micro-FBG pair. Based on the self-heating and asymmetric temperature distribution of two Co2+-doped fibres, the crossed micro-FBGs provide a direct two-dimensional measurement of the acoustic particle velocity. The experimental results show that an orientation sensitivity of 1.57 mV/deg for the micro-FBGs is achieved with a figure-of-eight response of the acoustic source direction. Meanwhile, the direction responses of two crossed pairs of micro-FBGs are exactly orthogonal to each other, which could detect the sound source localization. The all-fibre vector acoustic sensor is immune to electromagnetic interference, which appears to have a variety of potential applications, including research in acoustic communication, pipeline monitoring and navigation, etc.

A primer on vector hydrophones

Vector hydrophones are used by the military to track submarines, and, more recently, by scientists attempting to measure the influence of particle velocity on the behaviour of fish. Despite being in use for decades, vector hydrophones remain poorly understood by both communities. The problem is particularly acute for those aiming to measure particle velocity because vector hydrophones do not measure particle velocity directly; rather they measure pressure difference, the force that creates particle velocity. Topics covered will be the two types of vector hydrophone and why only one works well at low frequencies, the importance of knowing the phase of the directional channels relative to each other and to the pressure hydrophone, how bearings are determined, calibration of vector hydrophones and near-field effects, the magnitude of particle velocity for typical sound pressure levels, why bigger is better for mechanical noise, why neutral buoyancy is unnecessary and undesirable, and best practice for mounting.

Characterization of bottom parameters in the New England Mud Patch using geophone and hydrophone measurements

Measurements of acoustic pressure and particle velocity were made during the Seabed Characterization Experiment (SCEx) in the New England Mud Patch south of Cape Cod in about 70 meters of water. The University of Rhode Island and Woods Hole Oceanographic Institution deployed the “geosled” with a four-element geophone array, a tetrahedral array of four hydrophones, and several hydrophone receive units (SHRUs). In addition, a new low frequency source, interface Wave Sediment Profiler (iWaSP) was deployed to excite interface waves (Scholte waves). The iWaSP system consists of a source to generate the interface wave and a four-element accelerometer receive array. Modal arrivals from broadband sources (SUS and CSS) on geophones and hydrophones will be presented and compared. The individual arrivals on the sensors will be identified though seismo-acoustic modeling. Based on the propagation paths of the various waves (compressional, shear and Scholte waves), geoacoustic parameters will be estimated. Seismic data collected at the location will be used to constrain the model parameters in the inversion. Sediment data from cores, other in-situ measurements and inversions using other types of data will be used to compare and validate our inversions. [Work supported by Office of Naval Research.]

Statistical inference approach applied to simultaneous vertical particle velocity and acoustic pressure measurements from SUS explosive sources made in the New England Mudpatch

Pressure and particle velocity time series were measured in the New England “Mudpatch” in the Spring of 2017. The time series were generated from Signal Underwater Sound (SUS) MK-64 explosive sources and recorded by a bottom-mounted L-shaped array of hydrophones and a vector sensor system that recorded both pressure and particle velocity (1.3 m off the bottom) in a separate location. A maximum entropy approach was utilized to infer the marginal probability distributions of geo-acoustic parameter values of the seabed using both the particle velocity and the pressure. The seabed consists of a surface layer of mud over sand whose thicknesses are range- and azimuth dependent. The modeled vertical component of particle velocity is computed by a three-point derivative of the pressure fields generated by RAM-PE along the vertical axes centered at the depth of the vector sensor. The two-way travel time CHIRP data for the multiple range and azimuth-dependent sediment layers provide a constraint for the sediment th...

Airborne vector sensor experiments within an anechoic chamber

A technique to measure acoustic particle velocity in air is demonstrated in a controlled set of experiments conducted within an anechoic chamber at the Army Research Lab (ARL-Adelphi). This air-borne vector sensor measures acoustic pressure with an omnidirectional microphone and the 3D acceleration of a lightweight, rigid sphere with an embedded high-sensitivity tri-axial accelerometer. Two experiments are presented to demonstrate fundamental properties of the acoustic vector field: sound directionality, and the relative phase of pressure and particle velocity in the near to far field transition. Directional studies are implemented in the far-field of a speaker producing tones, defined by kr>>1, where r is the range from the speaker and k is the acoustic wavenumber. The pressure-velocity phase relationship is examined through the transition kr << 1, kr = 1, and then kr >> 1 by changing frequency and sensor range. For comparison, a tri-axial Microflown sensor simultaneously recorded the acoustic field. As neither sensor measures particle velocity directly, the phase characteristics of sensors depend on the sensing technique and corrections must be made to account for the true phase of particle velocity. Advantages and disadvantages of each method are discussed.

Measurement of abrasive particle velocity and size distribution in high pressure abrasive slurry and water micro-jets using a modified dual disc anemometer

In both abrasive water jet (AWJ) and high pressure abrasive slurry jet (HASJ) machining, garnet abrasive particles are mixed with water and the resulting jet can contain particles travelling with a wide range of velocities. Previous investigations have suggested that a dual disc anemometer (DDA) can be used to provide an assessment of the average particle velocity within the jets. This paper presents an in-depth analysis of the DDA test by considering the distribution and size of impact craters on the recording disc, and by modeling the size of the slurry slug incident to it. Procedures are presented to assess the accuracy of the determined average velocity, and to determine the histogram of particle velocities within the jet. A modification to the anemometer is introduced which also allows determination of the particle size-velocity correlation. Results are presented for both HASJ and AWJ under typical process conditions, and compared to existing analytical models of abrasive particle velocity from the literature, with good agreement.

Adaptive EMD based induction signal extraction of electrostatic sensor for particle velocity measurement

As the fluid movement, particles transporting in the pipeline will produce electrostatic charge. The electrostatic induction signal has been widely applied in measuring the flow parameters of pneumatic conveying due to its symmetry characteristic and simplicity. However, due to the weak signal and the complexity of the particles in the flow process, the electrostatic signal is easy to be disturbed by the environment, which affects the accuracy of particle flow parameter measurement. In this paper, an adaptive EMD method for extracting electrostatic induction signals of gas solid two-phase flow is proposed. The real IMF components and the IMF components which belong to noise are decomposed adaptively. Then according to the correlation coefficient of autocorrelation function, the corresponding IMF components are selected to reconstruct the electrostatic induction signal. The results show that in the gas-solid two-phase flow experiment, compared with the measurement signals, the mean relative standard deviation of cross-correlation velocity is reduced from 2.87% to 2.61%. This study is conducive to the accurate measurement of gas-solid two-phase flow parameters and provides an effective help for the electrostatic signal analysis of gas-solid two-phase flow.

Heterodyne transverse velocimetry for pressure-shear plate impact experiments

Pressure-shear plate impact experiments have traditionally relied on free space beam interferometers to measure transverse and normal particle velocities at the rear surface of the target plate. Here, we present two different interferometry schemes that leverage heterodyne techniques, which enable the simultaneous measurement of normal and transverse velocities using short-time Fourier transforms. Both techniques rely on diffracted 1st order beams that are generated by a specular, metallic grating deposited on the rear surface of the target plate. The diffracted beam photonic Doppler velocimetry technique interferes each 1st order beam with a reference of slightly higher wavelength to create a constant carrier frequency at zero particle velocity. The second technique interferes the 1st order beams with each other and employs an acousto-optic frequency shifter on the +1st order beam to create a heterodyne transverse velocimeter. For both interferometer techniques, the 0th order beam is interfered in a heterodyne photonic Doppler velocimetry arrangement to obtain a measurement of the normal particle velocity. An overview of both configurations is presented along with a derivation of the interferometer sensitivities to transverse and normal particle velocities as well as design guidelines for the optical system. Results from normal impact experiments conducted on Y-cut quartz are presented as the experimental validation of the two proposed techniques.

Influence of the time interval on image-based measurement of bed-load transport

ABSTRACTThe influence of the time interval (Δt) between two successive images on measurement of bed-load dynamics has been investigated both analytically and experimentally. The analytical approach is based on simplifying bed-load motion to follow a “flight-rest” pattern. The experimental work involves measuring bed-load transport in a closed channel with a particle imaging technique. The two approaches are consistent in revealing the influence of Δt on measurement results. It is shown that an increase in Δt leads to reduction in measured particle velocity and increase in the measured number of moving particles as well as the flight time. The measured flight length and bed-load transport rate are not directly affected by Δt. The influence of Δt needs to be fully addressed in image-based measurement of bed-load transport.

Pressure and particle velocity measurements from a broad band source at ranges 1–10 km

The IVAR system (Intensity Vector Autonomous Recorder) is a bottom deployed system developed for first-use in the Sediment Characterization Experiment (SCE17), conducted on the New England Mud Patch [40°28’ N, 70°35’ W] in spring 2017. IVAR continuously and coherently records four channels of acoustic data, three from a tri-axial accelerometer embedded in a neutrally buoyant sphere (diameter 10 cm) and one from an omnidirectional hydrophone positioned 10 cm above the centroid of the sphere positioned 1.2 m above the seafloor. The connection of these measurements to understanding seabed properties as part of SCE17 has been discussed previously. Here, emphasis is placed on documenting pressure and particle velocity signals as these quantities evolve with range from a broad band explosive source (Mk64 SUS charge). We explore the phase relation between pressure and components of particle velocity through study of active (in phase) and reactive (out of phase) intensity, as well as corresponding non-dimensional indices of the acoustic vector field, and discuss how these are influenced by propagation conditions. The work has relevance to both the ongoing geoacoustic studies from SCE17 as well as to studies on the sensitivity of fish to acoustic particle velocity generated by explosions.The IVAR system (Intensity Vector Autonomous Recorder) is a bottom deployed system developed for first-use in the Sediment Characterization Experiment (SCE17), conducted on the New England Mud Patch [40°28’ N, 70°35’ W] in spring 2017. IVAR continuously and coherently records four channels of acoustic data, three from a tri-axial accelerometer embedded in a neutrally buoyant sphere (diameter 10 cm) and one from an omnidirectional hydrophone positioned 10 cm above the centroid of the sphere positioned 1.2 m above the seafloor. The connection of these measurements to understanding seabed properties as part of SCE17 has been discussed previously. Here, emphasis is placed on documenting pressure and particle velocity signals as these quantities evolve with range from a broad band explosive source (Mk64 SUS charge). We explore the phase relation between pressure and components of particle velocity through study of active (in phase) and reactive (out of phase) intensity, as well as corresponding non-dimensional...

Inversions for sediment parameters using geophone and tetrahedral array measurements in the New England Mud Patch

Measurements of acoustic pressure and particle velocity were made during the Seabed Characterization Experiment (SCEx) in the New England Mud Patch south of Cape Cod in about 70 meters of water. The University of Rhode Island and Wood Hole Oceanographic Institution deployed the “geosled” with a four-element geophone array, a tetrahedral array of four hydrophones, and several hydrophone receive units (SHRUs). In addition, a new low frequency source, interface Wave Sediment Profiler (iWaSP) was deployed to excite interface waves (Scholte waves). The iWaSP system consists of a source to generate the interface wave and a four-element accelerometer receive array. Results of inversions for geoacoustic parameters will be presented. Arrival time dispersion from broadband sources (SUS and CSS) and iWaSP will be used for these inversions. Both p-wave and Scholte wave arrivals will be investigated using the geophone and hydrophone data. Seismic data collected at the location will be used to constrain the model parameters in the inversion. Sediment data from cores, other in-situ measurements and inversions using other types of data will be used to compare and validate our inversions. [Work supported by Office of Naval Research.]

CFDEM modelling of particle heating and acceleration in cold spraying

Cold spraying is a promising approach for the processing of refractory metals. A powder material is accelerated and heated in the gas flow of a supersonic nozzle to velocities that are sufficient to obtain cohesion of the particles to a substrate due to plastic deformation. The cohesion behavior of the particles is mainly determined by their velocity and temperature. These are controlled by the pressure and temperature of the gas at the nozzle entrance. A correlation of the process parameters gas pressure and temperature with the particle velocity and temperature is possible based upon numerical simulations. In this contribution a CFDEM simulation model for particle heating and acceleration based on OpenFOAM and LIGGGHTS is presented. CFDEMcoupling combines computational fluid dynamic (CFD) calculation of the gas flow based on the finite volume method with a description of the particles based on the discrete element method (DEM). The predictions of the simulation model are verified based on an analytical description of the cold spray nozzle and validated by experimentally measured particle velocities. Based on this experimental validation the drag model of Koch and Hill appears best suited for a CFDEM modelling of cold spraying.

Towards acoustic particle velocity sensors in air using entrained balloons: Measurements and modeling.

In this article, the feasibility of using balloons for the measurement of acoustic particle velocity in air is investigated by exploring the behavior of an elastic balloon in air as it vibrates in response to an incident acoustic wave. This is motivated by the frequent use of neutrally buoyant spheres as underwater inertial particle velocity sensors. The results of experiments performed in an anechoic chamber are presented, in which a pair of laser Doppler vibrometers simultaneously captured the velocities of the front and back surfaces of a Mylar balloon in an acoustic field. From phase measurements, the motion is described in terms of contributions from odd-order vibration modes (including bulk translation) and even-order vibration modes. The measured entrainment factors for the balloon are seen to be in good agreement with a physical model based on the scattering from an entrained rigid sphere. This demonstrates the feasibility of using entrained balloons for direct measurement of acoustic particle velocity in air.