Wide Range Of Velocities Research Articles

Quadrupole radiation and e+e− pair production in the collision of nonrelativistic nuclei

We analyze the one-photon mechanism of e+e− pair production in the collision of nonrelativistic nuclei. The contribution of electric quadrupole radiation of virtual photon to the corresponding cross section is found. The effect of the finite nuclear size is considered in detail. A comparison is made with the contribution of electric dipole radiation of virtual photon and with the contribution of the two-photon pair production mechanism. It is shown that the contribution of electric quadrupole radiation is dominant in a wide range of relative velocities. The cross section for the production of e+e− pair with the capture of an electron by one of the nuclei is also analyzed.

Ballistic performance of quasi-isotropic CFRP laminates under low velocity impact

The perforation characteristics of fiber reinforced laminates is crucial for the design of protective civil and military structures. This paper investigates the perforation characteristics (ballistic limit velocity, residual velocity, perforation energy) of cross ply and quasi-isotropic (QI) carbon fiber reinforced polymer (CFRP) laminates under the impact of a rigid conical steel bullet. The influence of thickness and ply orientation on these characteristics is also studied for a wide range of velocities. The perforation characteristics of these laminates were determined, numerically as well as experimentally. A numerical model is developed by using Hashin damage model to understand the behavior of laminates under high velocity impact. The accuracy of the model is assessed by comparing its prediction with experimental results of cross ply laminates. Then, impact perforation study of different possible configurations made of quasi-isotropic (QI) CFRP laminates, oriented at 0°, 90°, 45° and −45° directions are carried out with the help of validated numerical model. The perforation characteristics predicted with the help of numerical model is in good agreement with the experimental results. Optimal configuration is achieved in terms of energy absorption and damage resistance for better performance under impact loading.

Optimum design of heat exchanging device for efficient heat absorption using high porosity metal foams

The present research provides a numerical assessment of waste heat recovery system which contains high porosity metal foam that absorbs heat from the hot flue gases. Top wall of the heat exchanging device is designed as a sinusoidal corrugated/wavy wall. Three different wavelengths (Lw) of 39, 24.375 and 17.728 mm and three different wave amplitudes (a) of 0.5, 1.0 and 1.5 mm along with various heights of metallic foam of 0.25H, 0.5H and 0.75H are considered. Two different pore density of 20 and 40 with constant porosity of 0.937 are accomplished for the numerical investigation over wide range of fluid velocities. Local thermal equilibrium (LTE) and Darcy extended Forchheimer (DEF) models are employed at the metallic foam region; k-ε turbulence model is accomplished at free flow region of the channel. The heat dissipation rate at the cold wall increases significantly to a maximum height of 0.5H and increases with increasing wave amplitudes of the channel at the expense of pressure drop. On account of smaller wavelength and higher wave amplitude, the heat absorption rate is found to be 26.25% - 32% more than the straight channel with 25% filling rate of metallic foams in the range of fluid velocity considered.

Numerical simulation of bubble columns: LES turbulence model and interphase forces blending approach

In this study the large eddy simulation (LES) turbulence approach was adopted to simulate bubble columns in a wide range of gas velocity and operating conditions, in order to obtain a general model capable of simulating with satisfactory accuracy and moderate computational resources most industrial cases.The model used to carry out the numerical simulations stems on the Eulerian–Eulerian two-fluid model. A particular feature of the model is the implementation of a blending approach, which is adopted to describe the phase inversion at the surface of the gas–liquid mixture.An extended investigation of the main LES turbulence models was conducted at high gas velocity to find the most suitable one for the investigated test cases: the Smagorinsky model accounting also for the bubble induced turbulence provided the most notable results in a wide range of operating conditions. The validity of the model was also confirmed at lower gas velocity. A comparison with the standard k–ε RANS model showed that the LES methods produced significantly more accurate results, in particular for systems with non-symmetrical gas feed, even though the computational time required is marginally higher.

Flow resistance of floodplain vegetation mixtures for modelling river flows

River flows are greatly influenced by floodplain vegetation with implications on hydrological and hydraulic conditions from cross-sectional to river reach scales. Flow models need to reliably reflect changes in the riverine environment, such as vegetation growth associated with altered flow regimes, increased sediment loads and eutrophication. Leaf area index (LAI) based approaches are increasingly used as tools to predict the flow resistance caused by natural vegetation. However, current LAI-based modelling involves uncertainty at low and high vegetation densities and flow velocities due to a lack of research and validation at the outer ranges. The aim of this paper is to investigate the flow resistance for a mixture of flexible floodplain vegetation consisting of woody plants and understory grasses of low to high densities (LAI = 1–5) over a wide range of mean flow velocities (0.05–1.2 m/s) at low relative submergences of 1–2. A novel flume setup was designed by using high-accuracy pressure sensors to measure flow resistance and force sensors to measure plant drag forces. Flow resistance decreased by 35–90% when the submergence H/hv increased from 1 to 2, which is a highly relevant range for floodplain flows. The results provided new evidence that LAI-based modelling of vegetative friction factors can be reliably extended from low to high LAI values for non-submerged vegetation. However, adjustments to existing LAI-based approaches are required for water stages higher than the vegetation height. Furthermore, the friction by the understory grasses cannot be neglected as often assumed in literature especially for cases of low plant densities and low relative submergences.

Flow regime recognition in a long pipeline-riser system based on signals at the top of the riser

To identify conveniently multiphase flow regimes in subsea pipeline-risers, we study in this paper experimentally two-phase flows in a 1657 m long pipeline with an S-shaped riser to simulate field experiment, within a wide range of gas and liquid velocities. Three flow regimes, namely severe slugging, transitional flows, and stable flows, are analyzed based on three differential pressure and one pressure signals at the top of the riser; comparatively speaking, the positions of these signals in the experimental system are similar to those of the sea level signals in industrial fields, which are easy and less expensive to obtain. The obtained signals are decomposed into six scales via a multi-scale wavelet analysis, and further four statistical parameters on each scale are extracted, including mean values, standard deviations, ranges, and mean values of absolute. We compared the effects of six SVM classifiers with different kernel functions on the recognition rate of flow regimes, and it is found the recognition rates of SVM classifier with quadratic and cubic kernel functions are the highest. Further, the principal component analysis is employed to reduce the dimension of statistical parameters and it indicates that the recognition rate tends to increase with the rising number of principal components from 1 to 6, and it remains constant if the principal component number is further increased. Moreover, The results suggest that the recognition rate obtained from the pressure difference between the top of the riser and the separator peaks, and then it comes that from the pressure signal at the top of the riser, and that for the pressure difference signal at the top of the riser is the least satisfying one. As for the optimal differential pressure signals between the top of the riser and the separator, the results show that the recognition rate increases rapidly from 70.2% to 90.4% when the sample duration rising from 2.3 s to 18.6 s, and when the sample duration exceeds 74.4 s, the recognition rate exceeds 92.9% and remains unchanged.

Pore-scale modeling on supercritical CO2 invasion in 3D micromodel with randomly arranged spherical cross-sections

In this study the delicate invasion nature of pure supercritical carbon dioxide sCO2, alongside the determination of the main boundaries for sCO2 flow-pattern transitions inside the nanopores of treated 3D-porous matrix are investigated numerically. Sensitivity parameters under various sCO2 injection rates and flow regimes are discussed. The numerical outcomes are relied on MRT-Lattice Boltzmann method utilized in this study, while unyielded zones and inactive pores are identified by 3D voxels. The structural complexity of near-spherical porous matrices is addressed to study the flow behaviors of sCO2. This micrometer media followed a spherical approach with a studied random arrangement. The lengths of the computational domain in transverse directions were set to be five times as long as the highest diameter dp of the solid matrix, (highest dp= 50 nm), while the longitudinal direction was set to be 40 times dp. The simulations are carried out for a wide range of initial sCO2 velocities, which adimensionally denoted by Reynolds values. As well, unsteady-state flow regimes are adopted for precise interpretations of complex flow patterns and interactions in the nanopores. This numerical methodology allowed the study of the injection boundaries toward each flow regime of sCO2 inside the complex porous structure. Based on the above analysis, a primary flow-pattern chart is established for the invasion of sCO2.

A double-ratio method to measure fast, slow and reverse sap flows.

Sap velocity measurements are useful in fields ranging from plant water relations to hydrology at a variety of scales. Techniques based on pulses of heat are among the most common methods to measure sap velocity, but most lack ability to measure velocities across a wide range, including very high, very low and negative velocities (reverse flow). We propose a new method, the double-ratio method (DRM), which is robust across an unprecedented range of sap velocities and provides real-time estimates of the thermal diffusivity of wood. The DRM employs one temperature sensor upstream (proximal) and two sensors downstream (distal) to the source of heat. This facilitates several theoretical, heat-based approaches to quantifying sap velocity. We tested the DRM using whole-tree lysimetry in Eucalyptus cypellocarpa L.A.S. Johnson and found strong agreement across a wide range of velocities.

Probing the He ii re-Ionization ERa via Absorbing C iv Historical Yield (HIERACHY) I: A strong outflow from a z ∼ 4.7 quasar

ABSTRACT Outflows from supermassive black holes (SMBHs) play an important role in the co-evolution of themselves, their host galaxies, and the larger scale environments. Such outflows are often characterized by emission and absorption lines in various bands and in a wide velocity range blueshifted from the systematic redshift of the host quasar. In this paper, we report a strong broad line region (BLR) outflow from the z ≈ 4.7 quasar BR 1202-0725 based on the high-resolution optical spectrum taken with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph installed on the 6.5 m Magellan/Clay telescope, obtained from the ‘Probing the He ii re-Ionization ERa via Absorbing C iv Historical Yield’ (HIERACHY) project. This rest-frame ultraviolet (UV) spectrum is characterized by a few significantly blueshifted broad emission lines from high ions; the most significant one is the C iv line at a velocity of $\sim -6500$ km s−1 relative to the H α emission line, which is among the highest velocity BLR outflows in observed quasars at z > 4. The measured properties of UV emission lines from different ions, except for O i and Ly α, also follow a clear trend that higher ions tend to be broader and outflow at higher average velocities. There are multiple C iv and Si iv absorbing components identified on the blue wings of the corresponding emission lines, which may be produced by either the outflow or the intervening absorbers.

Estimation of shear‐wave velocities in unconventional shale reservoirs

ABSTRACTAnalysis of compressional and shear‐wave sonic logs in seven organic‐rich shale reservoirs exhibiting a wide range of velocities, total organic content, thermal maturity, fluid compressibility and mineral composition indicates that compressional‐wave velocity is a strong predictor of shear‐wave velocity as is the case for conventional reservoirs. Excluding data with high water saturations, a simple linear relationship is found between the compressional and shear‐wave velocities in shale reservoirs in accordance with laboratory measurements. The relationship can be further refined for prediction purposes by local calibration or with a linear correction for total organic content. Correcting for compositional variation and fluid effects requires more complex treatment. An empirical rock physics model that explicitly incorporates these effects results in high accuracy (0.2% average mean error) in shear‐wave velocity estimation for the entire data set. The model also exhibits good precision with mean absolute error of 2%. This is significantly better than what is achieved by rock physics models that do not explicitly consider fluid properties. These results are obtained without local calibration and without requiring correction for thermal maturity, degree of lithification or the shape or distribution of the solid organic matter. Explicit consideration of mineral composition, fluid substitution effects and amount of solid organic matter was necessary in this formulation to achieve this high average prediction accuracy with near zero bias as well as good precision across all formations and without local calibration. The successful use of Gassmann's equations in this algorithm suggests that errors in shear‐wave velocity prediction in shale reservoirs due to violation of the assumptions underlying these equations are either small or self‐compensating.

Validity of Force-Velocity Profiling Assessed With a Pneumatic Leg Press Device.

The aim of this study was to examine the concurrent validity of force-velocity (FV) variables assessed across 5 Keiser leg press devices. A linear encoder and 2 independent force plates (MuscleLab devices) were mounted on each of the 5 leg press devices. A total of 997 leg press executions, covering a wide range of forces and velocities, were performed by 14 participants (29 [7]y, 181 [5]cm, 82 [8]kg) across the 5 devices. Average and peak force, velocity, and power values were collected simultaneously from the Keiser and MuscleLab devices for each repetition. Individual FV profiles were fitted to each participant from peak and average force and velocity measurements. Theoretical maximal force, velocity, and power were deduced from the FV relationship. Average and peak force and velocity had a coefficient of variation of 1.5% to 8.6%, near-perfect correlations (.994-.999), and a systematic bias of 0.7% to 7.1% when compared with reference measurements. Average and peak power showed larger coefficient of variations (11.6% and 17.2%), despite excellent correlations (.977 and .952), and trivial to small biases (3.9% and 8.4%). Extrapolated FV variables showed near-perfect correlations (.983-.997) with trivial to small biases (1.4%-11.2%) and a coefficient of variation of 1.4% to 5.9%. The Keiser leg press device can obtain valid measurements over a wide range of forces and velocities across different devices. To accurately measure power, theoretical maximal power calculated from the FV profile is recommended over average and peak power values from single repetitions, due to the lower random error observed for theoretical maximal power.

Experimental investigation of gas-liquid flow in a vertical venturi installed downstream of a horizontal blind tee flow conditioner and the flow regime transition

A venturi device is commonly used as an integral part of a multiphase flowmeter (MPFM) in real-time oil-gas production monitoring. Partial flow mixing is required by installing the venturi device vertically downstream of a blind tee pipework that conditions the incoming horizontal gas-liquid flow (for an accurate determination of individual phase fraction and flow rate). To study the flow-mixing effect of the blind tee, high-speed video flow visualization of gas-liquid flows has been performed at blind tee and venturi sections by using a purpose-built transparent test rig over a wide range of superficial liquid velocities (0.3–2.4 m/s) and gas volume fractions (10–95%). There is little ‘homogenization’ effect of the blind tee on the incoming intermittent horizontal flow regimes across the tested flow conditions, with the flow remaining intermittent but becoming more axis-symmetric and predictable in the venturi measurement section. A horizontal (blind tee) to vertical (venturi) flow-pattern transition map is proposed based on gas and liquid mass fluxes (weighted by the Baker parameters). Flow patterns can be identified from the mean and variance of a fast electrical capacitance holdup measured at the venturi throat.

Effect of solid loading and particle size on the phase holdup distribution and bubble behaviour in a pilot-scale slurry bubble column

Complexities in the hydrodynamics of slurry bubble columns lead to noticeable uncertainty in the design and scale-up of these multiphase reactors. Knowledge of local hydrodynamics can alleviate this problem. The effect of solids properties on the local hydrodynamic parameters is a critical subject where the lack of knowledge is undeniable. In the present study, optical fiber probes were used to study the effect of particle size and concentration on the solids and gas distribution inside the bubble column. A pilot-scale cylindrical bubble column 270 cm in height and 29.2 cm in diameter was employed. Glass beads with various mean diameters (35, 71, 156 µm) and 1, 3 and 5 vol% were added to tap water in order to make the slurry phase. Air with a wide range of superficial gas velocities (up to 20 cm/s) was injected into the slurry phase. The results demonstrated that the solid particles' radial and axial distributions were not uniform in the column. Solids concentration showed a local maximum in the near-wall region. Gas holdup had a parabolic shape except for large particles at high solids concentration in which the maximum of the gas holdup was observed at the sides rather than the centerline. The variations in the pressure fluctuations revealed that the particle size decrease led to an increase in the bubble size; however, the initial bubble size was independent of the particle size. Moreover, the increase in the solids concentration resulted in an increase in the gas holdup in the homogeneous flow regime; and a decrease in the heterogeneous one. Finally, a predictive model that can estimate the radial and axial solids distributions in the slurry bubble column is presented.

Validation studies to assist in the development of scale and system independent CFD models for industrial bubble columns

Due to their widespread application there is substantial academic and industrial interest in modelling the hydrodynamics of bubble columns. To this end there is a need to develop and validate modelling approaches which are capable of being applied to industrial systems. In this paper we describe a model which is in good agreement with experimental data across a wide range of scales (columns from 0.19 to 3 m in diameter) and superficial velocities (0.03 to 0.25 m s–1). We have also developed an approach to account for the presence of surface-active compounds, which are frequently present in the liquid phase of industrial processes (e.g., water treatment or fermentation). Using this approach, it is possible to obtain computational predictions in good agreement with experimental measurements of hydrodynamic parameters (e.g., the overall hold-up) and oxygen transfer rates. Finally, to enable the validation work of others a substantial experimental dataset has been included with this work, and areas in need of further investigation have been highlighted.

Experimental and on-site investigation of the in-line vertical axis water turbines for water pipelines

Health monitoring devices are critical for the safe and reliable operation of water supply systems, but their chemical batteries are easily depleted. Thus, this paper developed a micro-vertical axis water turbine that converts part of the water head into electrical energy and supplies power for the monitoring device. The performance of four groups of micro-turbines was investigated in detail through experimental testing. Different from our previous study, the entire performance curves of micro-turbines at different rotation speeds and flow velocities were obtained in order to consider the wide range of flow velocities inside the real water pipeline. The feasibility of the designed turbines in the power supply system was verified by on-site testing. The experimental results show that different types and opening sizes of blocks have a distinct influence on the output power of micro-turbines. Each type of block has the corresponding optimal opening size to gain the highest performance. Within a certain range, the maximum output power varies linearly with the increase in flow velocity. In a specific flow velocity, the optimal rotational speed of the micro-turbine generated the maximum output power can be predicted by the power curve. In addition, through the experimental data, it is found that among all the measured turbines, the 12-blade hollow shaft turbine with a 90% eye-shaped block is the best one, with an output power of 88.2 W and an efficiency of 15.76%. Finally, the results of an on-site test are consistent with that of the experiment properly, which verifies the reliability of the measured data in the laboratory.

Investigation on the Gas Jet Flow Performance Confined in Round Pipe

In this study, the round jet flow behavior arose by the confinement was investigated experimentally and numerically. The confinement characteristics based on multi-scale characterizations in the atmospheric gas jet flow, which generated from a circular symmetrical subsonic nozzle and flowed into a confined round pipe, was used to studied. The studied region near the nozzle possess really short axial length (within 12d), providing initial conditions and boundaries that affected the flow behaviors in this region. A wide range of inlet velocities (0.98 m/s~84.72 m/s) and confined space sizes (1~20) were involved for simulated and quantitative discussions. The velocity profile evolution was recorded by simulations and characterized by a laser Doppler anemometer (LDA) with a resolution of 0.01 m/s. The confinement characteristics were systematically presented to elucidate the performance under the studied confined conditions with different metrics, such as centerline velocity decay (VR), entrainment rate (MR), pressure coefficient (Cp) and length of recirculation region (LR). The results indicated that the recirculation fluid action mainly contributed to the promoted initial velocity profile evolution with the introduction of the confined space. Theoretically, the confined space could reduce the maximum absolute entrainment mass flux, initiating a peak at the center of the recirculation region, which was controlled by the inlet velocity and the confined space size collectively. The remarkable effect of confined space size further contributes to the confinement characteristics of gas jet flow, representing a shortened flow distance despite similar process as that by reducing the diameter ratio (dR). In some cases, because of the miniaturization of confined space size, the dispersion of initial velocity profile evolution was not significant displayed throughout the variable inlet velocity range, especially when the dR was less than 2. This study gives a new insight in the performance of jet flow confined in round pipe, and such knowledge will be helpful to provide great potential and reference to applied fluid mechanics.

Upgrading the Field-Imaging Far-Infrared Line Spectrometer for the Stratospheric Observatory for Infrared Astronomy with kinetic inductance detectors: enabling large sample (extragalactic) surveys

We present the initial design, performance improvements, and science opportunities for an upgrade to the Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS). FIFI-LS efficiently measures fine structure cooling lines, delivering critical constraints of the interstellar medium and star-forming environments. The Stratospheric Observatory for Infrared Astronomy (SOFIA) provides the only far-infrared (FIR) observational capability in the world, making FIFI-LS a workhorse for FIR lines, combining optimal spectral resolution and a wide velocity range. Its continuous coverage of 51 to 203 μm makes FIFI-LS a versatile tool to investigate a multitude of diagnostic lines within our galaxy and in extragalactic environments. The sensitivity and field of view (FOV) of FIFI-LS are limited by its 90s-era photoconductor arrays. These limits can be overcome by upgrading the instrument using the latest developments in kinetic inductance detectors (KIDs). KIDs provide sensitivity gains in excess of 1.4 and allow larger arrays, enabling an increase in pixel count by an order of magnitude. This increase allows a wider FOV and instantaneous velocity coverage. The upgrade provides gains in point source observation speed by a factor >2 and in mapping speed by a factor >3.5, enabled by the improved sensitivity and pixel count. This upgrade has been proposed to NASA in response to the 2018 SOFIA Next Generation Instrumentation call.

A new characteristic peaks group judgement method for the accurate measurement of time‐of‐flight in the ultrasonic gas flowmeter

As a typical method for calculating time-of-flight (TOF), the double-threshold method is widely applied in many time-difference-based ultrasonic gas flowmeters. However, the cycle-skip phenomenon caused by noises and various flowrate often affects the accuracy and reliability of flowmeters. Based on traditional double-threshold method and other improved double-threshold methods, a new characteristic peaks group judgement method is proposed for calculating TOF in this work. In this method, the peak's characteristics of the received signal are used to find the feature point which is stable in different flowrates. Then, based on the feature point, zero-crossing detection is executed for calculating TOF. In order to evaluate the new method, it is compared with traditional double-threshold method and the similarity judgment-based double-threshold method through offline tests on both simulated signals and real-flow signals. Results show that the proposed method can effectively eliminate the cycle-skip phenomenon and has higher precision and reliability than other methods. Furthermore, a digital signal-processing-based ultrasonic gas flowmeter with this method was implemented. Three calibration experiments were carried out on a gas flow standard device. The calibration results show that the flowmeter can achieve accuracy of class 1 in a wide velocity range from 1 to 35 m/s.

High-velocity impact on composite sandwich structures: A theoretical model

A theoretical energy-based model to capture the ballistic response of sandwich structures made of composite material peels and a crushable foam core was developed. The model was based on the wave propagation theory and it was split in six stages with their corresponding energy-absorption mechanisms. The division of the stages was based on the physical interpretation of the perforation process involving reasonable hypotheses and simplifications. The energy-absorption was analysed at velocities below, near and above the ballistic limit within all the stages showing the general trends in terms of their relative importance. The time and velocity at each stage was separately analysed within a wide range of velocities in order to see the stage contribution to the energy-absorption. The model was validated against experimental results obtained in the literature showing a good agreement in terms of the impact-residual velocity curve.

A finite element-guided mathematical surrogate modeling approach for assessing occupant injury trends across variations in simplified vehicular impact conditions.

A finite element (FE)-guided mathematical surrogate modeling methodology is presented for evaluating relative injury trends across varied vehicular impact conditions. The prevalence of crash-induced injuries necessitates the quantification of the human body's response to impacts. FE modeling is often used for crash analyses but requires time and computational cost. However, surrogate modeling can predict injury trends between the FE data, requiring fewer FE simulations to evaluate the complete testing range. To determine the viability of this methodology for injury assessment, crash-induced occupant headinjury criterion (HIC15)trends were predicted from Kriging models across varied impact velocities (10-45 mph; 16.1-72.4 km/h), locations (near side, far side, front, and rear), and angles (-45 to 45°) and compared to previously published data. These response trends were analyzed to locate high-risk target regions. Impact velocity and location were the most influential factors, with HIC15 increasing alongside the velocity and proximity to the driver. The impact angle was dependent on the location andwas minimally influential, often producing greater HIC15 under oblique angles. These model-based head injury trends were consistent with previously published data, demonstrating great promise for the proposed methodology, which provides effective and efficient quantification of human response across a wide variety of car crash scenarios, simultaneously. This study presents a finite element-guided mathematical surrogate modeling methodology to evaluate occupant injury response trends for a wide range of impact velocities (10-45 mph), locations, and angles (-45 to 45°). Head injury response trends were predicted and compared to previously published data to assess the efficacy of the methodology for assessing occupant response to variations in impact conditions. Velocity and location were the most influential factors on the head injury response, with the risk increasing alongside greater impact velocity and locational proximity to the driver. Additionally, the angle of impact variable was dependent on the location and, thus, had minimal independent influence on the head injury risk.