Vertical Particle Velocity Research Articles

Bed symmetry in the fountain confined conical spouted beds with open-sided draft tubes

Bed symmetry has been analysed in fountain confined conical spouted beds operating with fine particles. Thus, vertical particle velocities and the spout shape have been determined in a wide range of spouting air velocities and bed configurations. Bed symmetry is widely accepted in the spouted beds without draft tubes or with nonporous ones, but this is not the case when open-sided draft tubes are used. Thus, radial particle velocity profiles differ depending on the cross-sectional angular plane considered in the open-sided draft tubes. The spout expands preferentially along the tube opened surface, and is wider as spouting air velocity and aperture ratio are increased. The literature correlations proposed for the average spout diameter have been analysed and no one is valid for estimating this parameter in the whole range of spouting air velocities and configurations analysed in these systems operating with fine particles.

Mechanisms governing the settling velocities and spatial distributions of inertial particles in wall-bounded turbulence

We use theory and Direct Numerical Simulations (DNS) to explore the average vertical velocities and spatial distributions of inertial particles settling in a wall-bounded turbulent flow. The theory is based on the exact phase-space equation for the Probability Density Function describing particle positions and velocities. This allowed us to identify the distinct physical mechanisms governing the particle transport. We then examined the asymptotic behavior of the particle motion near the wall, revealing the fundamental differences to the near wall behavior that is produced when incorporating gravitational settling. When the average vertical particle mass flux is zero, the averaged vertical particle velocity is zero away from the wall due to the particles preferentially sampling regions where the fluid velocity is positive, which balances with the downward Stokes settling velocity. When the average mass flux is negative, the combined effects of turbulence and particle inertia lead to average vertical particle velocities that can significantly exceed the Stokes settling velocity, by as much as ten times. Sufficiently far from the wall, the enhanced vertical velocities are due to the preferential sweeping mechanism. However, as the particles approach the wall, the contribution from the preferential sweeping mechanism becomes small, and a downward contribution from the turbophoretic velocity dominates the behavior. Close to the wall, the particle concentration grows as a power-law, but the nature of this power law depends on the particle Stokes number. Finally, our results highlight how the Rouse model of particle concentration is to be modified for particles with finite inertia.

Noise types and their attenuation in towed marine seismic: A tutorial

The presence of noise in towed marine seismic data is a long-standing problem. The various types of noise present in marine seismic records are never truly random. Instead, seismic noise is more complex and often challenging to attenuate in seismic data processing. Therefore, we have examined a wide range of real data examples contaminated by different types of noise including swell noise, seismic interference noise, strumming noise, passing vessel noise, vertical particle velocity noise, streamer hit and fishing gear noise, snapping shrimp noise, spike-like noise, cross-feed noise, and streamer-mounted device noise. The noise examples investigated focus only on data acquired with analog group forming. Each noise type is classified based on its origin, coherency, and frequency content. We then determine how the noise component can be effectively attenuated through industry-standard seismic processing techniques. In this tutorial, we avoid presenting the finest details of either the physics of the different types of noise themselves or the noise attenuation algorithms applied. Rather, we focus on presenting the noise problems themselves and find out how well the community is able to address such noise. Our aim is that, based on the provided insights, the geophysical community will be able to gain an appreciation of some of the most common types of noise encountered in marine towed seismic, in the hope to inspire more researchers to focus their attention on noise problems with greater potential industry impact.

Fine particle flow pattern and region delimitation in fountain confined conical spouted beds

A novel borescopic technique together with the monitoring of pressure fluctuation signals (power spectral distribution, PSD) has been used to track fine particles and characterize solid flow dynamics in fountain confined conical spouted beds. Radial and axial particle velocity profiles have been obtained for different configurations, and spout-annulus and fountain core-periphery interfaces have been delineated. The downward particle velocities in the annulus peak at intermediate positions in this zone, whereas the upward velocities in the dilute zones (spout and fountain core) peak at the axis or close to this position. Among the different configurations analysed in this work, the system without draft tube shows the greatest vertical particle velocities in almost all the different radial and axial positions. The evolution of the spout size along the bed depends on the configuration used, but all of them differ from those commonly reported in the literature. Thus, the spout expands from the bed bottom to the surface, without any neck at an intermediate bed level. Furthermore, the cross-sectional spout shape has been delineated in the systems with open-sided draft tube, and significant spout expansion is observed due to air percolation from the spout into the annulus through the opened faces. Finally, the average spout diameters of the systems without draft tube and with open-sided draft tubes have been compared with those predicted by literature correlations. Those proposed by San José et al. and Volpicelli et al. provide the best fit for the configurations without draft tube and with open-sided draft tube, with their relative errors being 9.83% and 8.88%, respectively.

CFD-DEM simulation of Small-Scale Challenge Problem 1 with EMMS bubble-based structure-dependent drag coefficient

In this study, the energy minimization multi-scale (EMMS)/Bubbling model is coupled with the computational fluid dynamics/discrete element method (CFD-DEM) model via a structure-dependent drag coefficient to simulate the National Energy Technology Laboratory (NETL) small-scale challenge problem using the open-source multiphase flow code MFIX. The numerical predictions are compared against particle velocity measurements obtained from high-speed particle image velocimetry (HSPIV) and differential pressure measurements. The drag-reduction effect of the EMMS bubble-based drag coefficient is observed to significantly improve predictions of the horizontal particle velocity and granular temperature when compared to several other drag coefficients tested; however, the vertical particle velocity and pressure fluctuation characteristic predictions are degraded. The drag-reduction effect is characterized by a reduction in the sizes of slugs or voids, as identified through spectral decomposition of the pressure fluctuations. Overall, this study shows great promise in employing drag coefficients, developed via multi-scale approaches (such as the EMMS paradigm), in CFD-DEM models.

Vector sensor beam steering for underwater acoustic communications

Acoustic Vector Sensors(VS) have been widely used for direction-of-arrival estimation in the past, while the employment of VS for underwater communications is a recent topic. Due to its compact size, VS may be used as a receiver in applications such as on board of Unmanned Underwater Vehicles (UUV), providing higher maneuverability and operational capabilities. Thus, in this study, the communication performance of a VS beam-steering technique is quantified. The performance analysis is made comparing the VS beam-steering with the versus time-reversal method in a shallow water simulation. The underwater channel is given by the seismo-acoustic propagation model, OASES. A Phase Shift Keying(PSK) modulation is adopted and the receiver includes a Decision Feedback Equalizer. An individual analysis of horizontal and vertical particle velocity is made to show the steering effects in the error performance. Moreover, as the steering angle is range-dependent, a comparison between methods is performed varying the range. The result indicates that the optimum steering angle, which brings less error, may not be related to the source direction. Furthermore, the proposed receiver shows the outperformance comparing to the time-reversal in both SNR and range, demonstrating the spatial filter advantage provided by this co-located sensor.

Measurement and control of seismic effects in large scale dragline bench blasts – An approach

Large scale dragline bench blasting is prevalent in many surface mines in India. Blasting in benches as high as 30–50 m to obtain a dragline cut measuring, typically, 80 m in width and 200 m in length requires 250–300 tonnes of explosives. Such a large amount of explosive induces severe seismic effects on the highwall. Backbreak is one such undesirable seismic effect, generally observed in these blasts, which reduces blasting efficiency, fragmentation and dragline utilization leading to lower productivity. An attempt has been made in this research to understand the mechanism of backbreak in relevance to dragline bench blasting. Seismic tomography using 24-channels was used to characterize the rockmass. Near-field vibration measurement was conducted to record ground vibrations using two Triaxial Borehole Geophones placed within a distance of 40 m from the last row of the blast. Vibration levels upto 1026 mm/s and backbreak extending upto 10.6 m were recorded. For modeling ground vibration in near-field, the Holmberg and Persson (1979) model was examined against the square root scaled distance model and was modified to incorporate a rockmass parameter. High values of vertical peak particle velocity (PPV) and strain were recorded indicating that long column charges and large diameter holes are responsible for massive cratering and resultant seismic impacts. The plots of PPV against frequency and geometrical attributes of backbreak showed that release of load damage mechanism was most prevalent in high benches. Backbreak was reduced using pre-splitting method of controlled blasting and increasing the effective delay in successive firings. A backbreak mitigation programme is proposed, which can be useful when integrated with dragline bench blasts.

Impact of vertical water particle motions on focused SAR altimetry

Abstract New in this work is a new analytical derivation of a Delay-Doppler map model for Fully-Focused SAR, which includes the vertical wave particle motion and a more general surface representation. It was indeed already noticed in Egido and Smith (2017) that the open ocean surfaces decorrelate within the integration time interval, which is used in the FF-SAR processing to form the synthetic antenna. However, this was not further discussed. The impact of surface motion is expected to be larger on FF-SAR than for unfocused SAR, since a longer integration time is used in the first processing. We introduce vertical wave particle velocities and accelerations as random variables in the analytical formulation, and relate this variables to ocean-wave spectral parameters, such as the mean zero up-crossing and crest period. Further on, we show and discuss for the first time that the flat sea surface response and the probability density function of the height of scattering surface elements are not the same as in unfocused SAR. Moreover, the response of a point target differs significantly and depends on the location of a scattering surface element, the satellite orbit parameters and the tracking range. This work provides the analytical expressions and a thorough discussion of these issues, including numerical results using CryoSat-2 mission parameters.

In Situ Experiment and Analysis of the Attenuation Characteristics of Environmental Vibrations Based on Frequency Sweep Method

Analysis of the attenuation characteristics of environmental vibrations with different frequencies is of great benefit for preventing many vibration-related problems. This study carried out an in situ experimental study on the attenuation characteristics of a series of single frequency ground vibrations caused by harmonic excitations. An electromagnetic vibration excitation system was adopted to generate harmonic excitations at frequencies varying from 10 Hz to 80 Hz with steps 5 Hz. 5 low frequency, 1 component, 991B vibration sensors fastened on the ground surface were used for the measurement of the vertical velocity time histories of ground vibrations at 5 test points with different distances from the vibration source. The vibration level in terms of the vertical peak particle velocity of single frequency ground vibrations in general decayed monotonically but nonlinearly with distance, however, the attenuations of 15 Hz, 45 Hz, 65 Hz and 75 Hz ground vibrations were oscillatory due to vibration interference on the ground surface. The attenuation of single frequency ground vibrations was more rapid in the zone close to the vibration source than that in the zone far away. This study demonstrates that comparison of the attenuation characteristics of high and low frequency ground vibrations should take into account the difference in the amplitudes of the corresponding ground vibrations.

An experimental study on a horizontal-vertical pneumatic conveying system using oscillatory flow

To reduce the power consumption of a horizontal-vertical pneumatic conveying system, an oscillator is mounted with a 45° oblique plane through the pipe axis in this study. This experimental study focuses on the effect of oscillatory flow using the oscillator on the horizontal-vertical pneumatic conveying system in terms of the overall pressure drop of the system, power consumption, local pressure drop, and particle velocity. Compared with conventional pneumatic conveying (axial-flow), the pressure drop and power consumption can be reduced using the oscillatory flow in a lower air velocity range. Meanwhile, the particle axial velocity of the oscillatory flow is higher than that of the axial-flow near the bottom of pipe. This outcome indicates that the accelerating effect of oscillatory flow is obvious near the bottom of the pipe, and the particle vertical velocity of the oscillatory flow is positive, whereas the particle vertical velocity of the axial-flow is almost negative. This result shows that the particles of the oscillatory flow are suspended sufficiently, but the particles of the axial-flow have a tendency of deposition. Furthermore, the fluctuation intensity of the particle velocity of the oscillatory flow is higher than that of the axial-flow, especially near the bottom of the pipe.

Estimation of seabed properties and range from vector acoustic observations of underwater ship noise.

The Intensity Vector Autonomous Recorder (IVAR) simultaneously measures acoustic particle velocity and pressure. IVAR was deployed during the 2017 Seabed Characterization Experiment (SBCEX) with the primary objective to study sound propagation in fine-grained, muddy sediments. In this study a Bayesian inversion framework is applied to ship underwater noise recorded by IVAR. The data are relative phase of pressure and vertical particle velocity, a quantity that is independent of the ship noise source spectrum. Inversion estimates for the sediment layer and underlying basement properties are in agreement with other reports from SBCEX.

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.

Comparison of Euler-Euler and Euler-Lagrange Approaches for Simulating Gas-Solid Flows in a Multiple-Spouted Bed

Abstract In this work, a comparative study of Euler-Euler and Euler-Lagrange approaches for modeling gas-solid flows in the multiple-spouted bed has been carried out to investigate the hydrodynamics of gas-solid flows. The influence of inlet gas velocity on the hydrodynamics of gas-solid flows in the multiple-spouted bed is investigated as well. Hydrodynamic characteristics of gas-solid flows such as flow behaviors, solid volume fraction, particle velocity and particle trajectory are analyzed and discussed in detail, providing some basic mechanism analysis of the gas-solids in the multiple-spouted bed. It is found that the central spout gas jet is a little confined by the auxiliary gas jets, and the hole-to-hole synergy is quite obvious when the auxiliary spout gas velocity is higher than the central spout gas velocity. When central/auxiliary gas velocity is 10/20 m/s, the maximum vertical particle velocities predicted by Euler-Euler and Euler-Lagrange approaches are 452 mm/s and 721 mm/s at the height of 10 mm respectively. A typical cycle period of a single particle is about 1.25 s, and the residence time in the spout regions is about 0.14 s in one cycle period in auxiliary dominant pattern. The curves of bed expansion height versus time calculated by Euler-Lagrange approach rise and fall periodically, while the curves calculated by Euler-Euler approach keep steady with little change. It is much easier for particles to be blew in the multiple-spouted bed using the Euler-Lagrange approach. The simulation results obtained from two models can provide some guidance for modifying the multiple-spouted bed to optimize physical operations such as drying and coating in the multiple-spouted bed.

Source-independent time-domain vector-acoustic full-waveform inversion

Dual-sensor seismic acquisition systems that record the pressure and particle velocity allow the recording of the full-vector-acoustic (VA) wavefields. Most previous studies have focused on data-domain processing methods based on VA seismic data; whereas, few studies focused on using full-VA seismic data in full-waveform inversion (FWI). Conventional acoustic FWI only takes advantage of the pressure recordings to estimate the medium’s velocity model. Some artifact events will appear in the adjoint-state wavefields based on the conventional acoustic FWI method. These artifact events further reduce the accuracy of acoustic FWI. To simultaneously use pressure and vertical particle velocity recordings, we introduced a new time-domain VA FWI method. The VA FWI method can take advantage of directivity information contained in the VA seismic data. Thus, the adjoint-state wavefields based on VA FWI are more accurate than those from the conventional acoustic FWI method. In addition, we applied a convolution-based objective function to eliminate the effects of the source wavelet and implement a time-domain multiscale strategy in VA FWI. Synthetic examples are presented to demonstrate that VA FWI can improve the accuracy of acoustic FWI in the presence and absence of a free surface in the acoustic case. In addition, VA FWI does not significantly increase the computation and memory costs, but it has better convergence when compared with conventional acoustic FWI.

Sensitivity analysis and validation of a Two Fluid Method (TFM) model for a spouted bed

A spouted bed has been simulated through a Computational Fluid Dynamic model using the Two Fluid Method and validated against experimental data. A sensitivity analysis has assessed the influence of the characteristic parameters on the solution. Among them, the accurate selection of the drag law seems to have the strongest influence on the results. In order to extend the capabilities of Ansys Fluent, Di Felice’s drag law was also considered through a User Defined Function. The assessment of the granular phase and its kinetic, collisional and frictional forces, is highly relevant to achieve a correct prediction of the particle velocity profile. The specularity coefficient appears to be more influencing than the restitution coefficient, but both parameters are useful to optimise the model. Overall, the prediction of the particle vertical velocity is accurate whereas the height of the fountain is slightly over-predicted.

Particle Filtering for Localization of Broadband Sound Source Using an Ocean-Bottom Seismometer Sensor.

Passive source localization is a challenging task for one receiver, and the pressure sensor provides relatively simple information. An ocean-bottom seismometer (OBS) sensor placed on the seafloor surface can provide more information—not only pressure information, but also three-axis (x-, y-, and z-axis) velocity information at the seafloor interface. In this paper, an OBS sensor was used to estimate the position of the broadband sound source in a Pekeris shallow water waveguide with elastic bottom. As the dynamics that characterize ocean acoustic applications are inherently nonlinear, non-Gaussian, and non-stationary processes that quickly vary with space and time, sequential Bayesian filtering, such as particle filtering (PF), is able to adapt to these environmental changes. Simulation results show that the PF method with the vertical wave impedance (the ratio of the pressure and vertical particle velocity) in the frequency domain as a measurement vector is not affected by source depth and source spectrum information, making it more tolerant and more robust than that with pressure in positioning. Experimental data results verified the effectiveness of the PF method with the vertical wave impedance for the localization of the explosive source.

Tracking of Particles in Froth Using Neutron Imaging

AbstractThe movement of hydrophobic particles in a rising froth column is investigated. Gadolinium particles are hydrophobized and floated by means of small air bubbles. The generated froth is investigated by neutron imaging. Particles are identified by correlating the resulting radiographs with an artificial template of a typical particle and subsequent scanning for local maxima. The movement of the particles in the froth was analyzed for different froth stabilities, which resulted from various concentrations of the frother sodium oleate. Decreasing froth stability leads to lower superficial vertical particle velocity and to higher horizontal diffusion of particles due to bubble rupture.

Tunnel millisecond-delay controlled blasting based on the delay time calculation method and digital electronic detonators to reduce structure vibration effects.

The reasonable delay time of millisecond-delay blasting using digital electronic detonators can significantly reduce the vibration effects induced by tunnel blasting. This study proposes a method for calculating the delay time for cut holes, easer holes and periphery holes, considering the rocks breaking effect as well as wave superposition theory. And then according to the actual layout diagram of the tunnel holes, the delay time calculation formulas of different holes are put forward. Then the delay times were calculated according to the formulas and applied in the field tests. The velocities, rocks breaking and wave superposition cancellation of the vibration using different delay times are analyzed with digital electronic detonators. Then the optimum delay times of different holes were obtained and applied to New Hongyan tunnel project. The velocity and frequency of the vibration with digital electronic detonators are analyzed, compared with non-electronic detonators. The effects of charge and delay time on the velocity and principal frequency of a blasting seismic wave are discussed. The results indicate that the delay time for the holes must be prioritized to achieve breaking effects in the rock with the simultaneous formation of a new free surface, next considering the wave superposition cancellation. When the delay time of cut holes was 5 ms, the rocks breaking effect and wave superposition cancellation effect both worked well. The velocity of the vibration induced by the cut holes blasting was about only 0.46–0.51 cm/s. When the delay time was 6 ms or much longer, the rocks breaking effect would fail. With regard to the easer holes and periphery holes, the optimum delay time of them were all 5ms. The vertical peak particle velocity was reduced from 2.974 cm/s to 0.901 cm/s with digital electronic detonators. Therefore, the velocity had decreased by 69.70% than non-electronic detonators, which was caused by reducing the single simultaneous explosive charge and setting optimum delay time. The proposed delay time calculation method is demonstrated to be sufficiently accurate and can thus be used as a guideline to reduce tunnel blasting vibrations.

Time reversal communication using vertical particle velocity and pressure signals in shallow water

Acoustic communication in shallow water is characterized by multipath channels, which cause significant delay spreading, leading to inter-symbol interference. This inter-symbol interference necessarily causes a significant degradation in communication performance. Although a time reversal technique has been reported to produce satisfactory performance in multipath dominant environments, this technique requires a large receiver array covering the water column to achieve reliable communication performance. In this paper, a time reversal single-input multiple-output system using the pressure signal and the vertical component of the particle velocity is presented. The vertical component of the particle velocity was estimated using the finite difference in gradient between pressures measured by two vertically adjacent receivers. The experiment was conducted in shallow water off the south coast of Korea, where the water depth is 59 m and the bottom consists of silty clay. The results showed that the time reversal communication system based on vector quantities performed better than systems where only the pressure signals were used.

Acoustic Pressure and Particle Velocity for Spatial Filtering of Bottom Arrivals

This paper discusses the advantages of using a combination of acoustic pressure and particle velocity motion for filtering bottom arrivals. A possible area of application is reflection seismology where, traditionally, the seismic image is extracted from the bottom-reflected broadband acoustic signals received on hydrophones. Since hydrophones are omnidirectional in nature, the received bottom returns are often contaminated by waterborne signals, sea surface reflections, and noise. A substantial part of the processing of the data is dedicated to filtering out these unwanted signals. Today, vector sensors allow us to measure both acoustic pressure and particle velocity motion in a single and compact sensor. The combination of pressure and particle velocity measured at a single location or particle velocity and particle velocity gradient at closely spaced locations allows for spatial beam steering to predetermined directions and filter out unwanted replicas from other directions. Moreover, this can be done at the sensor level, dramatically decreasing the offline processing. The spatial filtering capabilities of various pressure-pressure, particle velocity-particle velocity, and pressure-particle velocity combinations are analyzed in view of filtering the bottom arrivals. It is shown that the combination of pressure and vertical particle velocity and, particularly, the combination of vertical particle velocity and particle velocity gradient enhance bottom arrivals. Moreover, a simple steering procedure combining pressure and particle velocity components of a triaxial sensor allows us to determine the tridimensional structure of the acoustic field and the separation of the bottom reflections. The spatial selectivity of the various sensor combinations is shown with simulations and verified with experimental data acquired with 10 cm separated vector sensors in the 800-1250-Hz band, during the Makai 2005 sea trial, off Kauai Island, HI, USA.