Three-dimensional Particle Velocity Research Articles

Revolutionizing Our Understanding of Particle Energization in Space Plasmas Using On-Board Wave-Particle Correlator Instrumentation

A leap forward in our understanding of particle energization in plasmas throughout the heliosphere is essential to answer longstanding questions in heliophysics, including the heating of the solar corona, acceleration of the solar wind, and energization of particles that lead to observable phenomena, such as the Earth’s aurora. The low densities and high temperatures of typical heliospheric environments lead to weakly collisional plasma conditions. Under these conditions, the energization of particles occurs primarily through collisionless interactions between the electromagnetic fields and the individual plasma particles with energies characteristic of a particular interaction. To understand how the plasma heating and particle acceleration impacts the macroscopic evolution of the heliosphere, impacting phenomena such as extreme space weather, it is critical to understand these collisionless wave-particle interactions on the characteristic ion and electron kinetic timescales. Such understanding requires high-cadence measurements of both the electromagnetic fields and the three-dimensional particle velocity distributions. Although existing instrument technology enables these measurements, a major challenge to maximize the scientific return from these measurements is the limited amount of data that can be transmitted to the ground due to telemetry constraints. A valuable, but underutilized, approach to overcome this limitation is to compute on-board correlations of the maximum-cadence field and particle measurements to improve the sampling time by several orders of magnitude. Here we review the fundamentals of the innovative field-particle correlation technique, present a formulation of the technique that can be implemented as an on-board wave-particle correlator, and estimate results that can be achieved with existing instrumental capabilities for particle velocity distribution measurements.

A Vector Sensor-Based Acoustic Characterization System for Marine Renewable Energy

NoiseSpotter is a passive acoustic monitoring system that characterizes, classifies, and geo-locates anthropogenic and natural sounds in near real time. It was developed with the primary goal of supporting the evaluation of potential acoustic effects of offshore renewable energy projects. The system consists of a compact array of three acoustic vector sensors, which measures acoustic pressure and the three-dimensional particle velocity vector associated with the propagation of an acoustic wave, thereby inherently providing bearing information to an underwater source of sound. By utilizing an array of three vector sensors, the application of beamforming techniques can provide sound source localization, allowing for characterization of the acoustic signature of specific underwater acoustic sources. Here, performance characteristics of the system are presented, using data from controlled acoustic transmissions in a quiet environment and ambient noise measurements in an energetic tidal channel in the presence of non-acoustic flow noise. Data quality is demonstrated by the ability to reduce non-acoustic flow noise contamination, while system utility is shown by the ability to characterize and localize sources of sound in the underwater environment.

Geoacoustic inversion of the acoustic-pressure vertical phase gradient from a single vector sensor.

A vector sensor can provide measurements of ocean acoustic fields in terms of the acoustic pressure and three-dimensional particle velocity, providing potentially highly-informative data for applications such as geoacoustic inversion. This paper applies nonlinear Bayesian inversion to vector sensor data to estimate seabed geoacoustic properties and uncertainties in South China Sea. Linear-frequency-modulated source transmissions, recorded as acoustic pressure and vertical particle velocity, are processed to estimate the vertical phase gradient of acoustic pressure at multiple frequencies as the inversion data. An advantage of this type of data is that it can be modeled without knowledge of the source spectrum, allowing inversion with an unknown source and a single sensor. Geoacoustic inversion of phase-gradient data is carried out and compared to inversion of the vertical acoustic impedance, another type of vector-sensor data, independent of the source spectrum, which has been considered previously. Model selection for the optimal number of seabed sediment layers is carried out using Bayesian information criterion, and parameter estimates, uncertainties, and correlations are calculated using delayed-rejection adaptive Metropolis-Hastings sampling. Results indicate a three-layer seabed model (including the semi-infinite basement), with properties in agreement with independent measurements including a high-resolution seismic profile and surficial sediment type from a core.

Geoacoustic inversion of the pressure gradient data using a single vector sensor

A vector sensor has the capability of obtaining the acoustic field involving the sound pressure and three-dimensional particle velocities simultaneously, which means that there exists a potential to extract deep information for further applications like direction of arrival (DOA), positioning, classification, geoacoustic inversion, etc. This paper applies a nonlinear Bayesian approach to the pressure gradient data for geoacoustic properties of South China Sea, about which the experiment took place in July of 2013 in South China Sea of nearly 90 m depth. Recorded linear frequency modulation (LFM) signals of the pressure and vertical particle velocity are windowed and processed together to estimate the pressure gradient in the vertical direction at multiple frequencies as the observation data. After the optimal sediment model is selected based on BIC (Bayesian Information Criterion) using adaptive simplex simulated annealing (ASSA), delayed rejection adaptive Metropolis (DRAM), a Markov chain Monte Carlo (MCMC) sampling method, is used not only to provide a maximum a-posteriori (MAP) parameters estimates but also to quantify the parameters uncertainties and inter-parameter relationships. [Work supported by the National Natural Science Foundation (Grant No. 61531012).]

Acoustic vector sensor: reviews and future perspectives

Acoustic vector sensor (AVS) has been recently researched and developed for acoustic wave capturing and signal processing. Conventional array generally employs spatially displayed sensors for signal enhancement, source localisation, target tracking, etc. However, the large size usually limits its implementations on some portable devices. AVS which generally includes one omni-directional sensor and three orthogonally co-located directional sensors has been recently introduced. An AVS is able to provide the four-dimensional information of sound field in space: the acoustic pressure and its three-dimensional particle velocities. A compact assembled AVS could be as small as a match head and the weight can be <;50 g. Benefits from these properties, AVS tends to be more attractive for exploitation and commercialisation than conventional sensor array. To have a well understanding of the research progress on AVS, an overview on its recent developments is first given in this study. Then, discussions of challenges on AVS and extensions on its possible future prospects are presented.

Lattice Boltzmann Simulation of Two- and Three-Dimensional Incompressible Thermal Flows

This work is concerned with the application of the thermal lattice Boltzmann method (TLBM) to compute incompressible two- and three-dimensional flows in cavities. Two convection test cases, namely, the laminar flow in a differentially heated square cavity and a cubic cavity, are numerically analyzed through TLBM. The internal energy density distribution function approach with two three-dimensional particle velocity models, namely, the 15-velocity and the 19-velocity, and a two-dimensional model, namely, the nine-velocity, have been used in the present work. Computations are carried out for laminar flows in a differentially heated square cavity and a cubical cavity (Rayleigh numbers = 103 to 105). The boundary conditions used are stable and of good accuracy. To lend credibility to the thermal lattice Boltzmann model square cavity results, they are further compared with those obtained from a finite-difference-based code developed for this purpose.

Second-Order Statistics-Based Multi-Parameter Estimation of Near-Field Acoustic Sources

In this paper, a new approach based on the second-order statistics (SOS) and acoustic vector sensor (AVS) array is proposed, for localization estimation of near-field acoustic narrowband sources. Firstly, we choose the centrosymmetric uniform linear-array as the AVS arrangement, and the array is consistent with the coordinate axis direction of the acoustic vector-sensor. This estimation method makes good use of the acquisition information from the AVS, such as one-dimensional sound pressure and three-dimensional particle velocity, and has shown preferable performance for the parameter estimation of direction-of-arrival (DOA) and range of target acoustic sources in the near field. The estimation algorithm expands the near-field array manifold of one single acoustic vector sensor to the acoustic vector-sensor’s uniform linear-array, and the near-field acoustic vector sensor linear array output model is deduced. The autocorrelation and cross-correlation function of the velocity field and the pressure field are used to construct the rotational invariance frame, which helps to extract the expected information. Consequently, the closed-form solutions of the incident source’s DOA and range are derived explicitly through the parameter pairing operation. The proposed method reduces the computational burden and has good spatial recognition ability and high resolution in the case of limited array elements. It also has better engineering application prospect. Eventually, the performance of the method is verified by Monte Carlo simulation experiments.

Statistical properties of kinetic and total energy densities in reverberant spaces

Many acoustical measurements, e.g., measurement of sound power and transmission loss, rely on determining the total sound energy in a reverberation room. The total energy is usually approximated by measuring the mean-square pressure (i.e., the potential energy density) at a number of discrete positions. The idea of measuring the total energy density instead of the potential energy density on the assumption that the former quantity varies less with position than the latter goes back to the 1930s. However, the phenomenon was not analyzed until the late 1970s and then only for the region of high modal overlap, and this analysis has never been published. Moreover, until fairly recently, measurement of the total sound energy density required an elaborate experimental arrangement based on finite-difference approximations using at least four amplitude and phase matched pressure microphones. With the advent of a three-dimensional particle velocity transducer, it has become somewhat easier to measure total rather than only potential energy density in a sound field. This paper examines the ensemble statistics of kinetic and total sound energy densities in reverberant enclosures theoretically, experimentally, and numerically.

Pressure gradient effect on a particle velocity distribution

[1] In space plasma missions, measurements of the three-dimensional particle velocity distribution are used to examine the dynamical evolution of plasmas. The first velocity moment of the measured particle velocity distribution is often regarded as the bulk flow of the population. Accurate determination of bulk flows is crucial if the frozen-in-condition is judged by E + V × B = 0, where E is the electric field, V is the bulk flow, and B is the magnetic field. In this paper, we show that this first velocity moment computed from the measured particle velocity distribution can deviate substantially from the bulk motion of the particle population when a significant pressure gradient exists near the measurement location. The discrepancy, which arises from the diamagnetic drift with a finite Larmor radius effect, increases with increasing energy range used in the computation. The result calls for caution in the proper interpretation of this velocity moment and suggests a means to avoid error in the determination of bulk flow due to pressure gradient effects.

Analysis of a three-dimensional particle velocity sensor for design optimization

The omni-directional sensitivity pattern of an integrated, three-dimensional acoustic sensor consisting of four hot-wire particle velocity sensors is analyzed theoretically and experimentally. The influence of the probe surface on the measured direction of particle velocity is investigated and a description of the gas flow profile around the integrated sensor is presented. A theoretical model describing the fluid flow in the vicinity of a simplified geometry, a plate of finite width, is shown to give a relatively adequate description for the gas flow around the probe. The analysis results in a number of design rules to optimize the device performance.

The characteristics of the particle position along an optical axis in particle holography

Particle diagnostics involving three-dimensional distributions are important topics in many engineering fields. The holographic particle velocimetry system is a promising optical tool for measuring three-dimensional particle velocities. One of the inherent limitations of particle holography is the very long depth of field of particle images, which causes considerable difficulty in the determination of particle positions along the optical axis. In this study, diffused illumination holography was adopted as a tool for analysing the characteristics of particles. The prerequisites for a more precise determination of the velocities of particles are a profound understanding of image properties and of the focusing parameter used to determine the particle position along an optical axis. For this purpose, the characteristics of speckles and particle images were investigated with respect to variations in hologram aperture and particle position along the optical axis. Based on our findings, we introduced three auto-focusing parameters corresponding to the sizes of particles, namely, correlation coefficient, sharpness index and depth intensity, to determine the focal plane of a particle along the optical axis. To investigate the suitability of these parameters, the plane image of a dot array screen containing different dot sizes was recorded and the positions of each dot along the optical axis were evaluated. In addition, the effect of particle distance from the holographic film was examined by changing the distance between the screen and the holographic film. All measurement results verified that the evaluated positions throughout the suggested auto-focusing parameters remain within acceptable error ranges. These research results may provide fundamental information for the development of a holographic velocimetry system based on automatic image processing.

Retrieval of Three-Dimensional Particle Velocity from Airborne Doppler Radar Data

Abstract A technique has been developed for the retrieval of three-dimensional particle velocities from Doppler data obtained with an airborne radar. The 95-GHz radar was mounted on the University of Wyoming KingAir aircraft. The retrieval technique is derived from the velocity azimuth display (VAD) analysis and is termed the airborne velocity azimuth display (AVAD). Data for this analysis are taken when the radar beam is scanned by the turning of the aircraft. As in VAD analysis, a functional form for the horizontal variation of the velocity of the scatterers must be assumed. The components of the velocity field are then determined using a least squares fit to the Doppler velocities. The AVAD technique differs from VAD analysis because of the mobility of the platform and its proximity to regions of interest, and it is due to geometric considerations dictated by the turning of the aircraft. The analysis region is only a few kilometers in diameter—considerably smaller than for a ground-based VAD analysis. ...

The Seafloor Borehole Array Seismic System (SEABASS) and VLF ambient noise

The Seafloor Borehole Array Seismic System (SEABASS) has been developed to measure the pressure and threedimensional particle velocity of the VLF sound field (2–50 Hz) below the seafloor in the deep ocean. The system consists of four three-component borehole seismometers (with an optional hydrophone). a borehole digitizing unit, and a seafloor control and recording package. The system can be deployed using a wireline re-entry capability from a conventional research vessel in Deep Sea Drilling Project (DSDP) and Ocean Drilling Project (ODP) boreholes. Data from below the seafloor are acquired either onboard the research vessel via coaxial tether or remotely on the seafloor in a self-contained package. If necessary the data module from the seafloor package can be released independently and recovered on the surface. This paper describes the engineering specifications of SEABASS, the tests that were carried out, and preliminary results from an actual deep sea deployment. VLF ambient noise levels beneath the seafloor acquired on the Low Frequency Acoustic-Seismic Experiment (LFASE) are within 20 dB of levels from previous seafloor borehole seismic experiments and from land borehole measurements. The ambient noise observed on LFASE decreases by up to 12 dB in the upper 100 m of the seafloor in a sedimentary environment.

Experimental studies of the development of quasi-two-dimensional turbulence in stably stratified fluid

Abstract Quasi-two-dimensional turbulence was generated by towing an array of vertical cylinders through a tank which was filled with a two-layer stratified fluid. Sugar and Epsom salts were used, to give matching refractive indices for the two layers. The interface between the two layers was seeded with approximately 1000 neutrally buoyant particles. The evolution of this quasi-two-dimensional turbulence was visualized by photographing the fluorescent particles illuminated by a horizontal laser sheet traversing in the vertical direction. The three-dimensional particle velocity was obtained by digitizing the streaks. The evolution of the velocity correlations, length scales, one-dimensional and two-dimensional velocity and vorticity spectra were obtained for N = 5.72 s−1, N = 4.43 s−1, and N = 2.55 s−1 (where N is the Brunt-Vaisala frequency). The results showed the physical process of inverse energy cascading and the formation of dominant vortical structures under the influence of density stratification. Compared with idealized two-dimensional turbulence, the flow is highly dissipative at high N, as a result of the frictional dissipation between the interface and the unstratified layers.

Particle velocity measurements in a circulating fluidized bed

In recent years, circulating fluidized beds (CFBs) have been extensively employed in a variety of industrial applications related to coal combustion and gasification, solid waste incineration, catalytic cracking of oil, and so on. To accomplish successful and reliable operation of CFBs, a number of investigations pertaining to different hydrodynamic aspects have been undertaken. Many of these are referenced in the monograph of Basu and Fraser (1991), review of Horio (1991), and the article of Mahalingam and Kolar (1991). The gross hydrodynamic features of CFBs are generally understood, but the detailed structure is established only to a limited extent. Some advancements in this direction have been made in recent years by Yang et al. (1991), Horio et al. (1988), and others. Detailed researches in this direction have been made in recent years by Yang et al. (1991), Horio et al. (1988), and others. Detailed researches in this direction will considerably help in the optimum and economic designs of CFB boilers. To aid in this direction, the authors have measured the three-dimensional particle velocities in a square-section CFB cold model under certain operating conditions at ambient temperature and pressure. Particle turbulent intensities and bed cross-sectional averaged voidage along its height are alsomore » measured. A majority of the investigations have been conducted in circular cross-section CFBs, but industrial preference is for a square cross-section CFBs, but industrial preference is for a square cross-section boiler, and hence they have adopted this configuration in their present work. Their measurements, while confirming the core-annulus flow structure for CFBs, also provide a more comprehensive microscopic detail of particle velocities in the two regions, in addition to providing a basis for particle aggregation.« less

Holographic particle image velocimetry (HPIV)

There are several well-known difficulties in forming and analysing holographic particle data in the micrometre and sub-micrometre size range. This paper suggests that these problems can be overcome by using a combination of research techniques. Firstly, it has been found that it is possible to record images of sub-micrometre particles using conventional photographic materials. Essentially, a diffraction limited optical component has been used to provide aberration free particle images. Secondly, the sensitivity of the holographic material has been increased with the use of specialized holographic processing chemicals. Thirdly, it has been found that it is possible to encode holoraphically double, slightly displaced, particle images using a pulse laser. Thus, Young's fringes can be obtained directly from the stored holographic data and the particle velocity can be measured directly from the hologram. Fourthly, the holographic particle data can be automatically analysed using a software programme. Finally, since the data is stored holographically, it is possible to obtain instantaneous three-dimensional particle velocity. This paper demonstrates that it is possible to perform holographic particle image velocimetry automatically, with only a small amount of pre-processing.

Verification of linear theory for particle velocities in wind waves based on field measurements

Analyses are presented of field measurements of spectral transfer functions between surface elevation and subsurface three-dimensional particle velocity in wind-generated waves, in conditions ranging from young seas to old swells. The results are in agreement with the linear theory predictions to within the measurement error margin, which is estimated to be ± 5% for the gain functions and ± 4° in phase as far as the possible systemic errors are concerned. No correlation is found of the degree of agreement between measurements and linear theory with wave age or wave sleepness.