Instantaneous Particle Velocity Research Articles

Hybrid Acoustic Metamaterial Based on Absorption Accumulation Peaks for a Broad Sound Energy Control

Controlling sound energy over a wide spectrum of frequencies through structures with a subwavelength scale is a challenge in acoustics. In this sense, a hybrid acoustic metamaterial model (HAMM) that acts over a wide frequency spectrum is presented. The structure consists of a combination of a porous layer and an acoustic metamaterial (AMM). Two samples are evaluated to establish effective control of sound energy () between 450 and 6400 Hz with the structure reaching a maximum ratio of . Furthermore, the behavior of sound waves in the structure is explored through analysis of the sound pressure field, instantaneous particle velocity, and thermoviscous dissipation. One of the highlights of the HAMM is that it is composed of an AMM that has a low phase velocity. Thus, the ultra‐slow sound in part of the structure allows the low‐frequency resonance frequency to be shifted to lower frequencies. Another characteristic is that because of the accumulation of absorption peaks below the bandgap of the AMM, a low‐frequency broadband absorption is guaranteed. Therefore, this work contributes substantially to advances in the area of sound energy control over a wide spectrum of frequencies through the use of different combined acoustic materials.

Parabolic Cylindrical Description of Velocity and Acceleration Tensor in Bipolar Coordinate Using Tensor Analysis

Instantaneous velocity and acceleration are often studied and expressed in Cartesian, Circular Cylindrical, and Spherical Coordinate systems but it is a well-known fact that some bodies cannot be perfectly described in these coordinate systems, so they required some other curvilinear systems such as oblate spheroidal, parabolic cylindrical, elliptic cylindrical bipolar, and others. It is of important interest in theoretical physics to establish equations of motion in Bipolar Coordinate system, which is essentially suitable to accurately describe the motion of bipolar bodies such as hyperbolas, ellipses and other curves in the universe. In this work, we derived a new expression for the instantaneous velocity and acceleration vector of bodies and test particles in the bipolar coordinate system using tensor analysis. The Laplacian of a scalar field in this bipolar coordinate system was also derived which has applications in mechanics.

Four-way coupled modelling of swirling particle-laden flow in Methane-central coaxial jets

A novelty particle subgrid scale model is established to model the effect of gas flow on particle motion behaviors and a four-way coupling method to describe the particle-particle collisions by granular temperature equation is also developed. Menthane-central jets of particle-laden swirling flow in coaxial chamber are modeled by a multiphase second-order moment model and numerically predicted by the large-eddy simulation. Simulation results of two-phase hydrodynamics are in good agreement with experimental measurement. Evolution of coherent structure, recirculation region, periodic vortices formation, breakup, coalescence and pair, stronger mixing are captured and analyzed successfully. Compared to gas-annular flow, it is benefit for the stabilization of flame due to the strongly radial spread of particle dispersions and mixing momentum exchanges. The core-annular flow structures of particle concentration are observed, and instantaneous particle velocity are complied with the normal distribution. At shear layers of core-jetting regions of X/R=0.56, correlations of axial-tangential gas and particle fluctuation velocities are approximately 3.0 and 6.0 times larger than those of far downstream flows.

Probabilistic description of coarse particle motion above threshold by particle tracking velocimetry method in an experimental study

Sediment motion behavior plays an important role in the sediment and hydraulic engineering, though its physics is still not fully understood. Ignoring the stochastic nature of the sediment transport leads to various equations for bedload transport which are now being challenged due to their results. In this study, the non-suspended particle motion (bedload transport) in different hydraulic conditions was assessed by a particle tracking technique called the Particle Tracking Velocimetry (PTV). The results of the PTV were applied to describe the particle behavior throughout the probability distribution functions. Knowing the particle motion behavior would be a guidance to learn more about the parameter/s governing the particle transport in different sediment transport regimes. After calibrating and validating the frames (resulted from the PTV), the instantaneous particle velocity was measured. Different probability distribution functions were assessed with Kolmogorov-Smirnov criterion to find the best function which fits the collected data (i.e. the particle velocity). It was shown that the probability distribution function is Log-Normal for lower particle Reynolds number and on the other hand, in the higher particle Reynolds number, the Normal distribution is best describing the particle velocity. The results of this research also could be applied in similar hydraulic conditions in eco-hydraulic field, specifically macro-plastic movement as bedload in river courses.

Modelling of the mean electric charge transport equation in a mono-dispersed gas–particle flow

Abstract

Fast random wave generation in numerical tanks

Generating and absorbing random waves in numerical models is a challenging problem, in particular when meaningful wave statistics should be generated to meet design sea-state requirements. The methodology presented herein allows for the generation of random wave fields (free surface elevation and velocities) to be reconstructed in time and in space by using window processing from a reference time series. It is demonstrated that the methodology is efficient in reproducing long non-repeating wave sequences by using only O(101)–O(102) wave components, rather than O(103)–O(104) required by a direct reconstruction from a single spectrum. This reduces the computational times required for the development of wave-train time-series elements by 40 times. Errors in instantaneous surface elevation and particle velocity between windowed and non-windowed reconstruction techniques were less than 0·4 and 0·2%, respectively, in the cases considered. The technique was combined with the relaxation zone method typically used in numerical wave tanks for generating waves. The simulations were performed using Proteus, a rapidly developing CFD−FEM toolkit for modelling fluid−structure interaction cases. The use of windowed reconstruction reduced the overall computational time associated with the simulation of waves in a numerical wave tank by ∼40 and ∼70% for serial and parallel execution. Results of the study show windowed reconstruction to be suitable for the representation of long-duration wave trains. Wave height and peak period are conserved within 2 and 1%, respectively.

Fast magnetic field evolution in neutron stars: The key role of magnetically induced fluid motions in the core

In [Gusakov et al.\ PRD, 96, 103012, (2017)], we proposed a self-consistent method to study the quasistationary evolution of the magnetic field in neutron-star cores. Here we apply it to calculate the instantaneous particle velocities and other parameters of interest, which are fixed by specifying the magnetic field configuration. Interestingly, we found that the magnetic field can lead to generation of a macroscopic fluid motion with the velocity, significantly exceeding the diffusion particle velocities. This result calls into question the standard view on the magnetic field evolution in neutron stars and suggests a new, shorter timescale for such evolution.

Experimental and theoretical study of bed load particle velocity

ABSTRACTThis paper reports an experimental study of sediment particle velocity in the Hydraulic Engineering Laboratory at the University of Arizona. The experiments were performed in a rectangular channel filled with a layer of coarse sand or gravel. The instantaneous particle velocity was measured by using the images captured with a commercial camera. An innovative image processing technique was developed for tracking individual particle motion, which leads to the determination of instantaneous particle velocity vector. Both the mean particle velocity and the distribution of particle velocities were analyzed. It was found that the instantaneous bed shear stress dominated the particle velocity as well as the probability density function of its distribution. This observation is consistent with the theoretically derived equations for particle velocity and its distribution. Furthermore, the Kolmogorov–Smirnov test confirmed the agreement between the distribution of experimental data and that obtained from the theoretical analysis.

In vitro actin motility velocity varies linearly with the number of myosin impellers

Cardiac myosin is the motor powering the heart. It moves actin with 3 step-size varieties generated by torque from the myosin heavy chain lever-arm rotation under the influence of myosin essential light chain whose N-terminal extension binds actin. Proposed mechanisms adapting myosin mechanochemical characteristics on the fly sometimes involve modulation of step-size selection probability via motor strain sensitivity. Strain following the power stroke, hypothetically imposed by the finite actin detachment rate 1/ton, is shown to have no effect on unloaded velocity when multiple myosins are simultaneously strongly actin bound in an in vitro motility assay. Actin filaments slide ∼2 native step-sizes while more than 1 myosin strongly binds actin probably ruling out an actin detachment limited model for imposing strain. It suggests that single myosin estimates for ton are too large, not applicable to the ensemble situation, or both. Parallel motility data quantitation involving instantaneous particle velocities (frame velocity) and actin filament track averaged velocities (track velocity) give an estimate of the random walk step-size, δ. Comparing δ for slow and fast motility components suggests the higher speed component has cardiac myosin upshifting to longer steps. Variable step-size characteristics imply cardiac myosin maintains a velocity dynamic range not involving strain.

Experimental study of bed-load transport using particle motion tracking

A series of experiments were conducted in a flume to study bed-load transport. The motion of bed-load particles was captured by a series of images taken by a high-speed camera.A novelparticle motion tracking method was developed to automatically detect all the moving particles and calculate the instantaneous particle velocities. The instantaneous bed load transport rate was calculated based on particle velocity and the volume of moving particles. To verify this method, bed load transport rate based on the image processing technique was compared to the manually measured ones as well as data from other experiments. Results showed that the new technique made it possible to quantify the spatial and temporal variations of bed load transport rate at the individual particle scale.

Detecting densified zone formation in membrane-assisted fluidized bed reactors through pressure measurements

This work reports the results of an experimental investigation on densified zone formation in a membrane fluidized bed reactor using combined pressure fluctuation and PIV (Particle Image Velocimetry) measurements. A pseudo 2D experimental setup was used, where porous plates on the back plate of column mimicked gas extraction through flat vertically inserted membranes. The maximum in the standard deviation of pressure fluctuations, commonly employed to indicate the transition to turbulent fluidization, shifted to lower fluidization velocities with an increase in the fraction of fluidizing gas being extracted. Flow visualization showed that this result is connected to the onset of stable densified zone formation, which occurred at progressively lower fluidization velocities as the gas extraction fraction was increased. It has also been found that the extent of densified zones quantified using instantaneous particle velocity maps collected by PIV increases with increasing gas extraction rates. This effect became larger for smaller particles. Results have therefore shown that the peak in pressure fluctuations in fluidized beds with gas extraction through flat vertical membranes indicates the onset of densified zones formation rather than turbulent fluidization. Such densified zones can have substantial detrimental effects (such as induced mass transfer limitations, gas bypass etc.) on the reactor performance and can be identified via pressure measurements, as illustrated in this work.

Simulations of dynamic properties of particles in horizontal rotating ellipsoidal drums

Flow behavior of particles in the horizontal rotating ellipsoidal drum (RED) is predicted by means of the discrete element method (DEM). The effect of flattening of the ellipsoidal drum on flow regimes of particles is simulated because of its importance to industrial applications, and because the underlying flow of particles is not fully explained yet. Different flow regimes are produced by varying flattening. The resulting contact forces between the drum wall and particles are predicted in the horizontal RED and horizontal rotating cylinder drum (RCD). The flow of particles in the horizontal RED becomes significantly different to that in the horizontal RCD due to the increase of flattening of the ellipsoidal drum. At high rotation speed, a crescent shaped flow mode is observed at the orientation angle of 90° and a showery raining mode is observed at 120°. The results show that the resulting contact forces between the particles and the drum wall increase with the increase of flattening and rotation speed. The velocity of particles is changed with the orientation angle of the horizontal RED. The translational granular temperature and configurational temperature are calculated from simulated instantaneous translational velocity and displacement of particles, respectively. The simulated translational granular temperature and configurational temperature increase with the increase of flattening and rotation speed. The rate of energy dissipation through collisions and contact interactions of particles is predicted in the horizontal RED and RCD.

Particle Velocity, Solids Hold-Up, and Solids Flux Distributions in Conical Spouted Beds Operating with Heavy Particles

Conical spouted beds operating with high-density particles have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors. To design, scale-up, and manufacture these coaters, detailed investigation of local flow structure is of paramount importance. Therefore, in this study, local instantaneous particle velocity and solids hold-up and flux measurements were carried out in spouted beds having a wide range of cone angles (30°, 45°, 60°) using zirconia particles (dp = 0.5, 1 mm; ρp = 6050 kg/m3). Effects of axial height, particle diameter, conical angle, and static bed height on local flow behavior were investigated. Comparisons were also made with the results of low-density particle studies. It is shown that particle velocity decreases and solids hold-up and flux increase along the bed height in the spout. The solids circulation is augmented as particle diameter and conical angle are decreased and static bed height is increased.

Stochastic Lagrangian model for hydrodynamic acceleration of inertial particles in gas–solid suspensions

The acceleration of an inertial particle in a gas–solid flow arises from the particle’s interaction with the gas and from interparticle interactions such as collisions. Analytical treatments to derive a particle acceleration model are difficult outside the Stokes flow regime, but for moderate Reynolds numbers (based on the mean slip velocity between gas and particles) particle-resolved direct numerical simulation (PR-DNS) is a viable tool for model development. In this study, PR-DNS of freely-evolving gas–solid suspensions are performed using the particle-resolved uncontaminated-fluid reconcilable immersed-boundary method (PUReIBM) that has been extensively validated in previous studies. Analysis of the particle velocity variance (granular temperature) equation in statistically homogeneous gas–solid flow shows that a straightforward extension of a class of mean particle acceleration models (drag laws) to their corresponding instantaneous versions, by replacing the mean particle velocity with the instantaneous particle velocity, predicts a granular temperature that decays to zero, which is at variance with the steady particle granular temperature that is obtained from PR-DNS. Fluctuations in particle velocity and particle acceleration (and their correlation) are important because the particle acceleration–velocity covariance governs the evolution of the particle velocity variance (characterized by the particle granular temperature), which plays an important role in the prediction of the core annular structure in riser flows. The acceleration–velocity covariance arising from hydrodynamic forces can be decomposed into source and dissipation terms that appear in the granular temperature evolution equation, and these have already been quantified in the Stokes flow regime using a combination of kinetic theory closure and multipole expansion simulations. From PR-DNS data we show that the fluctuations in the particle acceleration that are aligned with fluctuations in the particle velocity give rise to a source term in the granular temperature evolution equation. This approach is used to quantify the hydrodynamic source and dissipation terms of granular temperature from PR-DNS results for freely-evolving gas–solid suspensions that are performed over a wide range of solid volume fraction ($0.1\leqslant {\it\phi}\leqslant 0.4$), Reynolds number based on the slip velocity between the solid and the fluid phase ($10\leqslant \mathit{Re}_{m}\leqslant 100$) and solid-to-fluid density ratio ($100\leqslant {\it\rho}_{p}/{\it\rho}_{f}\leqslant 2000$). The straightforward extension of drag law models does not give rise to any source in the granular temperature due to hydrodynamic effects. This motivates the development of better Lagrangian particle acceleration models that can be used in Lagrangian–Eulerian formulations of gas–solid flow. It is found that a Langevin equation for the increment in the particle velocity reproduces PR-DNS results for the stationary particle velocity autocorrelation in freely-evolving suspensions. Based on the data obtained from the simulations, the functional dependence of the Langevin model coefficients on solid volume fraction, Reynolds number and solid-to-fluid density ratio is obtained. This new Lagrangian particle acceleration model reproduces the correct steady granular temperature and can also be adapted to gas–solid flow computations using Eulerian moment equations.

Effect of Domain Size on Fluid–Particle Statistics in Homogeneous, Gravity-Driven, Cluster-Induced Turbulence

Scaling of volume fraction and velocity fluctuations with domain size is investigated for high-mass-loading suspensions of finite-size inertial particles subject to gravity. Results from highly resolved Euler–Lagrange simulations are evaluated via an adaptive spatial filter with an averaging volume that varies with the local particle concentration. This filter enables the instantaneous particle velocity to be decomposed into a spatially correlated contribution used in defining the particle-phase turbulent kinetic energy (TKE), and a spatially uncorrelated contribution used in defining the granular temperature. The total granular energy is found to grow nearly linearly with the domain size, while the balance between the separate contributions remains approximately constant.

Numerical simulation of different flow regimes in a horizontal rotating ellipsoidal drum

Flow regimes of particles are predicted by means of discrete element method (DEM) in a horizontal rotating ellipsoidal drum (RED) at different rotation speeds and flattening. The macroscopic behavior of the particle flow is produced in a horizontal RED at specified rotation speed, and compared to the motion of particles in the horizontal rotating cylinder drums (RCD). Simulations indicate that there are two different flow regimes in one round with the rotating angles of the horizontal RED. The particle bed became more dilated with the increase of rotation speed. The evolution of resulting contact forces between particles and drum walls is predicted in the horizontal RED at different rotation speeds and flattening. Simulated mixing index indicates that the mixing of particles is improved at the low rotation speed and the segregation of particles is enhanced at the high rotation speed in the horizontal RED. The translational granular temperature and con temperature are calculated from simulated instantaneous velocity and displacement of particles. The predicted configurational and translational granular temperatures increase with the increase of rotation speeds and flattening in the horizontal RED. The rate of energy dissipation based on the generalized granular temperature is increased with the increase of rotation speeds in the horizontal RED.

Measurements and modeling of instantaneous particle orientation within abrasive air jets and implications for particle embedding

Previous theoretical studies indicate that the material removal mechanism and the likelihood of particle embedding in solid particle erosion processes strongly depend on instantaneous particle orientation at impact. The present study utilized pulsed laser shadowgraphy to measure the size, shape, and instantaneous orientation distributions of particles within a micro-abrasive jet at various pressures, particle sizes, and nozzle standoff distances. A particle orientation angle was defined as the angle between the particle linear velocity vector (approximately parallel to the jet centerline axis) and the line connecting the center of mass to the furthest downstream particle vertex. Particles were considered to be ‘oriented’, i.e. in a configuration favorable to embedding, if this angle was between 0 and 10°. The measurements revealed that, at all pressures (i) between 24% and 29.5% of the particles were oriented at the nozzle exit; (ii) the percentage of oriented particles increased slowly with standoff distance; (iii) larger particles had a stronger tendency to orient than smaller ones; (iv) particles having larger aspect ratios had a stronger tendency to aerodynamically align with the jet, and (v) although not all particles that were oriented actually embedded, the measured percentage of embedded particles on Al 6061-T6 surfaces nevertheless correlated with the percentage of oriented particles. A model capable of predicting the instantaneous particle orientation and velocity within and downstream of the nozzle was presented and shown to agree well with measurements. To the knowledge of the authors, these are the first measurements of the instantaneous orientation of abrasive particles under conditions that are typical of abrasive air jets. The results may have important implications for optimizing solid particle erosion tests and in abrasive jet machining applications.

Developing a High Speed Fiber-optic Endoscopic Technique for Measuring Particle Phase Characteristics in a Spouted Bed

A novel endoscopic photography technique coupling a high speed CCD camera and an intrusive fiber-optic endoscope has been extended to enable the investigation of particle flow behavior in a 3D spouted bed 1500mm in height and 200mm in diameter. A series of algorithms have been specifically optimized to realize the process of image processing and the calculation of the instantaneous particle velocity data. Then particle phase velocity and granular temperature were obtained respectively by statistical analysis and detailed study of the obtained data. The results showed that instantaneous particle velocities exhibited random complexity in both magnitude and direction. Although little information could be extracted from the raw data directly, the profile of particle phase velocity was able to show the mainstream particle flow patters along bed radius. Also, the computed granular temperature could be used to characterize the local particle fluctuation intensity. All experimental results could be useful to validate the CFD models for gas-solid flow systems.

Erratum to: Turbulent velocity, sediment motion and particle trajectories under breaking tidal bores: simultaneous physical measurements

A tidal bore is a hydrodynamic discontinuity propagating upstream in an estuarine zone with a funnel shape as the tide starts rising under spring tidal conditions. The transient sediment motion beneath tidal bores was investigated in laboratory under controlled flow conditions by measuring simultaneously the fluid and sediment particle velocities. Although no sediment transport was observed in the initially steady flow and in undular bores, a transient sheet flow motion was observed beneath the breaking bores. The sediment transport was initiated during the passage of the bore roller toe by the large longitudinal pressure gradient force, and the sediment particles were subjected to large horizontal accelerations. About 5 % of all particles were accelerated in excess of 1 g. The sediments were advected upstream with an average velocity close to the instantaneous fluid velocity. The time evolution of instantaneous particle velocity for each trajectory was analysed, using the starting point of particle trajectory corresponding to the entrainment point, and the end point to the particle stoppage point. The present data provided some quantitative data in terms of force terms acting on sediment particles beneath a tidal bore and their trajectory characteristics.

Quantifying the Dynamic Evolution of Graded Gravel Beds Using Particle Tracking Velocimetry

AbstractThe motion of graded gravels under steady and spatially uniform turbulent flow is investigated in laboratory conditions using particle tracking velocimetry (PTV). The gravel bed is subjected to flows approaching critical armor velocity, and water worked until static armor is reached. A digital particle tracking (DPT) algorithm, based on image subtraction between subsequent frames, is developed and applied on the particle scale as the graded gravel bed is water-worked. The dynamic evolution of graded gravels is quantified continuously for up to 8 h. Characteristics of particle motion are identified, and movement patterns under complex flow conditions are analyzed. Particle tracking is applied to low-frequency (0.67-fps) and high-frequency (30-fps) data. This study provides a new perspective on gravel particle transport distances, trajectory sinuosity, sediment transport rate, fractional sediment transport rates, particle movement patterns, and instantaneous particle velocities.