Spatial Velocity Distribution Research Articles

Acquisition of Spatial and Temporal Characteristics of Shallow Groundwater Movement Based on Long-Term Temperature Time Series in the Kangding Area, Eastern Tibetan Plateau

Heat has been widely used as a groundwater tracer to determine groundwater flow direction and velocity in a way that is ubiquitous, low-cost, environmentally friendly, and easy to use. However, temperature observations are generally short-term and small-scale, meaning they may not be able to reflect long-term changes in the characteristics of groundwater movement. In this study, we utilize 515 days of temperature data, collected from four measurement points in the Kangding area of the eastern Tibetan Plateau, in order to determine the spatial and temporal distribution of groundwater flow velocities using different analytical heat tracing methods. An analysis is conducted to evaluate the impact of thermal parameter uncertainties on the calculation of flow velocity, and a comparison is undertaken between the results of the phase, amplitude, and combined amplitude-phase methods. We subsequently discuss the relationship between flow velocity changes and precipitation. The results show that the estimated flow velocity is more susceptible to the volumetric heat capacity of the saturated sediment than it is to thermal conductivity. The phase method is more suitable for use in calculations in the study area, indicating that precipitation significantly impacts the flow velocity and that this impact is more pronounced in areas with flat terrain compared to areas with significant variation in elevation. Our research provides a comparative study of the heat tracing methods in areas with varied terrains and offers new evidence for the impact of precipitation and topography on groundwater infiltration.

Improvement of SiC deposition uniformity in CVD reactor by showerhead with baffle

The growth uniformity of silicon carbide (SiC) by halide chemical vapour deposition (HCVD) is influenced by equipment configuration, and a uniform film can be obtained by optimising the chamber structure. An SiC deposition kinetics model is studied in this work, and a detailed chemical reaction mechanism is incorporated into a model reaction chamber to verify the deposition kinetics model. We studied the influence of hole size of showerhead, baffle size, and baffle positioning on the growth uniformity. Further, we then optimised the process parameters using an orthogonal experimental method. Reducing the hole size of showerhead led to a “double peak” in the deposition rate across the substrate from the edge to both sides, which first increased and then decreased. The “double peak” disappeared upon reduction of hole size. With an increase in baffle size, the growth uniformity first increased and then decreased. Moreover, the baffle displacement had little effect on the deposition rate when the baffle-to-showerhead distance was at least 45 mm. Meanwhile, the growth uniformity gradually worsened when the baffle distance was reduced. The showerhead and baffle reduced the extreme difference in deposition rate across the effective deposition area by improving the spatial velocity distribution within the reaction chamber. A uniform SiC film could be obtained using the proposed optimisation method. Furthermore, the results of the orthogonal experimental method showed that the deposition rate increased by 57.8%, and the uniformity of growth standard deviation decreased by 18% compared with the ground state. This study provides theoretical guidance for future optimisations of CVD chambers.

Manipulating nanoparticles based on a laser photothermal trap.

A method of efficient directional optical manipulation of nanoparticles based on a laser photothermal trap is proposed, and the influence mechanism of external conditions on the photothermal trap is clarified. Through optical manipulation experiments and finite-element simulations, it is determined that the main cause of gold nanoparticle directional motion depends on the drag force. The laser power, boundary temperature, and thermal conductivity of the substrate at the bottom of the solution and liquid level essentially affect the intensity of the laser photothermal trap in the solution and then affect the directional movement and deposition speed of gold particles. The result shows the origin of the laser photothermal trap and the three-dimensional spatial velocity distribution of gold particles. It also clarifies the height boundary of photothermal effect onset, which clarifies the boundary between light force and photothermal effect. In addition, nanoplastics are manipulated successfully based on this theoretical study. In this study, the movement law of gold nanoparticles based on the photothermal effect is deeply analyzed through experiments and simulations, which is of significance to the theoretical study of the optical manipulation of nanoparticles using the photothermal effect.

Study on the dust migration law and a spray dust suppression scheme in transportation roadway

To solve the problem of excessive dust concentration in the belt transportation roadway of the mine. Numerical simulations were used to study the dust migration in the belt transportation roadway under 1.5m/s ventilation conditions. The simulation results show the process of dust ejection from the inflow chute to contamination of the whole belt transportation roadway, and the spatial distribution of dust velocity. A comprehensive dust reduction scheme of "central suppression and bilateral splitting" was designed according to the dust distribution, with simultaneous control of the infeed chute and the roadway. In practical application, pneumatic spraying greatly reduces the amount of dust in the guide chute. The misting screen has a significant effect on dust collection and segregation. The solution effectively controls the dust in the space of 20m on both sides of the transfer point, and the dust removal efficiency reaches more than 90%.

Modeling Tool for Estimating Carbon Dioxide Fluxes over a Non-Uniform Boreal Peatland

We present a modeling tool capable of computing carbon dioxide (CO2) fluxes over a non-uniform boreal peatland. The three-dimensional (3D) hydrodynamic model is based on the “one-and-a-half” closure scheme of the system of the Reynolds-Averaged Navier–Stokes and continuity equations. Despite simplifications used in the turbulence description, the model allowed obtaining the spatial steady-state distribution of the averaged wind velocities and coefficients of turbulent exchange within the atmospheric surface layer, taking into account the surface heterogeneity. The spatial pattern of CO2 fluxes within and above a plant canopy is derived using the “diffusion–reaction–advection” equation. The model was applied to estimate the spatial heterogeneity of CO2 fluxes over a non-uniform boreal ombrotrophic peatland, Staroselsky Moch, in the Tver region of European Russia. The modeling results showed a significant effect of vegetation heterogeneity on the spatial pattern of vertical and horizontal wind components and on vertical and horizontal CO2 flux distributions. Maximal airflow disturbances were detected in the near-surface layer at the windward and leeward forest edges. The forest edges were also characterized by maximum rates of horizontal CO2 fluxes. Modeled turbulent CO2 fluxes were compared with the mid-day eddy covariance flux measurements in the southern part of the peatland. A very good agreement of modeled and measured fluxes (R2 = 0.86, p < 0.05) was found. Comparisons of the vertical profiles of CO2 fluxes over the entire peatland area and at the flux tower location showed significant differences between these fluxes, depending on the prevailing wind direction and the height above the ground.

Simultaneous measurement of velocity profile and liquid film thickness in horizontal gas–liquid slug flow by using ultrasonic Doppler method

Horizontal gas–liquid two-phase flows widely exist in chemical engineering, oil/gas production and other important industrial processes. Slug flow pattern is the main form of horizontal gas–liquid flows and characterized by intermittent motion of film region and slug region. This work aims to develop the ultrasonic Doppler method to realize the simultaneous measurement of the velocity profile and liquid film thickness of slug flow. A single-frequency single-channel transducer is adopted in the design of the field-programmable gate array based ultrasonic Doppler system. A multiple echo repetition technology is used to improve the temporal–spatial resolution for the velocity profile. An experiment of horizontal gas–liquid two-phase flow is implemented in an acrylic pipe with an inner diameter of 20 mm. Considering the aerated characteristics of the liquid slug, slug flow is divided into low-aerated slug flow, high-aerated slug flow and pseudo slug flow. The temporal–spatial velocity distributions of the three kinds of slug flows are reconstructed by using the ultrasonic velocity profile measurement. The evolution characteristics of the average velocity profile in slug flows are investigated. A novel method is proposed to derive the liquid film thickness based on the instantaneous velocity profile. The liquid film thickness can be effectively measured by detecting the position and the size of the bubbles nearly below the elongated gas bubble. Compared with the time of flight method, the film thickness measured by the Doppler system shows a higher accuracy as a bubble layer occurs in the film region. The effect of the gas distribution on the film thickness is uncovered in three kinds of slug flows.

The Acceleration Phenomenon of Shock Wave Induced by Nanosecond Laser Irradiating Silicon Assisted by Millisecond Laser

The propagating evolution of shock waves induced by a nanosecond pulse laser (ns laser) irradiating silicon assisted by a millisecond pulse laser (ms laser) is investigated experimentally. A numerical model of 2D axisymmetric two-phase flow is established to obtain the spatial distribution of shock wave velocity. Two types of shock wave acceleration phenomenon are found. The mechanism of the shock wave acceleration phenomenon is discussed. The experimental and numerical results show that the initial stage of ms laser-induced plasma can provide the initial ions to increase probability of collision ionization between free electrons and vapor atoms. The velocity of the ns laser-induced shock wave is accelerated. Furthermore, the ms laser-induced plasma as the propagation medium can also accelerate the ns laser-induced shock wave. The shock wave acceleration methods obtained in this paper can promote the development of laser propulsion technology.

RivQNet: Deep Learning Based River Discharge Estimation Using Close‐Range Water Surface Imagery

AbstractStreamflow data is often the most critical input for hydrologic and hydraulic research, modeling, and design studies. Streamflow measurement using close range non‐contact sensing such as image velocimetry is a new technique that is yet far from maturity. Most current image‐based surface velocimetry techniques use correlation approaches that require user input to run the algorithms. This input can bias results if the operator is inexperienced. The main goal of this study is to develop a novel, accurate and fast river velocimetry scheme called RivQNet that does not require subjective user input. RivQNet processes close‐range non‐contact water surface images using artificial intelligence techniques. The algorithm is a deep‐learning optical flow estimation using a preferred available convolutional neural network architecture (i.e., FlowNet architecture). In this study the presented method is validated with common standard measurement methods and compared with conventional optical flow methodologies. The results indicate that the presented method yields accurate and dense spatial distributions of surface velocities.

Localized transverse flow measurement with dynamic light scattering line-scan OCT.

A novel decorrelation-based approach for measuring localized transverse flow velocity using line-scan (LS) optical coherence tomography (OCT) is proposed. The new approach allows for separation of the flow velocity component along the line-illumination direction of the imaging beam from other orthogonal velocity components, from particle diffusion motion, and from noise-induced distortion in the OCT signal's temporal autocorrelation. The new method was verified by imaging flow in a glass capillary and a microfluidic device and mapping the spatial distribution of the flow velocity within the beam's illumination plane. This method can be extended in the future to map the three-dimensional flow velocity fields for both ex-vivo and in-vivo applications.

A novel Lagrangian formulation to construct relativistic rotating stars: towards its application to their evolution calculations

ABSTRACT We present a new formulation to construct numerically equilibrium configurations of rotating stars in general relativity. Having in mind the application to their quasi-static evolutions on a secular time-scale, we adopt a Lagrangian formulation of our own devising, in which we solve force-balance equations to seek for the positions of fluid elements corresponding to the grid points, instead of the ordinary Eulerian formulation. Unlike previous works in the literature, we do not employ the first integral of the Euler equation, which is not obtained analytically in general. We assign a mass, specific angular momentum and entropy to each fluid element in contrast to the previous Eulerian methods, in which the spatial distribution of the angular velocity or angular momentum is specified. These distributions are determined after the positions of all fluid elements (or grid points) are derived in our formulation. We solve the large system of algebraic non-linear equations that are obtained by discretizing the time-independent Euler and Einstein equations in the finite-element method by using our new multidimensional root-finding scheme, named the W4 method. To demonstrate the capability of our new formulation, we construct some rotational configurations, both barotropic and baroclinic. As toy models, we also solve three evolutionary sequences that mimic the cooling, mass-loss, and mass-accretion.

INFLUENCE MECHANISM OF STAGNATION-POINT FLOW ON LIQUID-PHASE SPRAY PENETRATION LENGTH UNDER ENGINE-LIKE CONDITIONS

Formulation of liquid-phase spray penetration length (LPL) is one of the basic research works of direct injection (DI) engines. To predict the spray evolution and LPL in the limited space more accurately, the diffused background-illumination extinction imaging (DBI) technology and highspeed schlieren method were employed to detect the liquid- and vapor-phase spray development in a constant volume combustion chamber (CVCC). The experimental results show that the LPL of the impinging spray is significantly smaller than that of the free spray when the LPL is close to the impinging distance. When the LPL is much smaller than the impinging distance, the LPL of impinging spray is the same as that of free spray. Furthermore, based on the CFD simulation and the stagnation-point flow theory, the spatial distribution of velocity, pressure, and density at the near-wall surface was analyzed in detail. Due to part of the spray kinetic energy was converted into potential energy, creating a sharp increase in pressure and density near the stagnation point, which suppressed the movement of fuel droplets, resulting in a significantly smaller LPL. Moreover, a novel LPL prediction model is introduced, which considering the inhibiting effect of wall on spray penetration and demonstrates enhanced predictive capability of experimental results.

Time-resolved particle-scale dynamics of a particle-laden jet

Particle-laden jet flow is important to both jet-related industry applications and transmission of the virus through violent expiratory events, such as coughing and sneezing. To help understand its dynamics from the particle level, we develop a time-resolved, three-dimensional (3D), particle tracking velocimetry method, coupled with particle image velocimetry measurement of gas flow, and perform experiments on a dilute particle-laden gas jet. The spatial distributions of velocity and fluctuating velocity of the gas and particles are obtained. It is found that the presence of particles significantly changes the gas turbulence and stretch the gas flow field to the downstream. The probability density function of axial particle velocity shows non-Gaussian distribution and deviates much from those of the spanwise velocities, indicating strong non-equilibrium and anisotropic states. A new drag model is derived based on the reconstructed particle trajectories and gas flow field near the ejector exit with particle Reynolds numbers between 30 and 300. It is found in better agreement with the experimental data than the standard single-particle drag model. A simple model relating the particle volume fraction with particle displacement is developed based on the self-similarity theory of jet, showing good agreement with the experimental measurement.

Cough Aerosol Cloud Parameters

This work is a further development of the authors' COVID-19 pandemic consequences research. The dynamics of the cough aerosol cloud was studied. An experimental setup for fixing spatial and temporal distributions of aerosol cloud velocities was used. Flags were placed on the threads of the experimental setup. On the first and second frames, the area and shape of the flags were different. The process of air passing through the frames was recorded by photographic equipment. The footage was compared by a computer program to identify differences.The results of an experiment with five adults (18–22 years, men), volunteered for study participation, are presented. The method of aerosol cloud visualization is applied. The dynamic parameters of the aerosol cloud are estimated. The velocity of the air flow arising from coughing was measured. The shape of the flow was determined depending on the time. It was found that the flow front moves with acceleration at the initial stage of propagation and with a constant velocity at the final stage. A nonlinear dependence of the change in the volume of cough air flow aerosol on time was established.

Air velocity spatial variability in open Compost-Bedded Pack Barn system with positive pressure ventilation.

In Compost-Bedded Pack Barn (CBP) systems, air velocity is linked with the thermal comfort of housed dairy cattle and bedding quality and, therefore, assessing ventilation efficiency is essential. In this context, the objective of this study was to evaluate and characterize dependence and spatial distribution of air velocity at the 1.5 m height (vair,M) and at bedding level (vair,B) in an open CBP system with positive pressure ventilation. The study was conducted in 2021, in a facility located in the Zona da Mata region, Minas Gerais, Brazil. The facility area was divided into a mesh composed of 55 equidistant points, where vair,M and vair,B data were collected in the morning (09:00 a.m.) and afternoon (03:00 p.m.) periods, during three weeks in Brazilian winter. Geostatistics techniques were used to assess dependence and spatial distribution. In both periods evaluated, there were a strong occurrence of spatial dependence and non-uniform vair,M and vair,B distributions. The vair,M and vair,B values were lower than recommended (1.8 m∙s-1) in more than 65.0% of the area. Adequate ventilation levels were observed only in the first 20.0 m of the facility, from Southeast to Northwest, because of the fan lines present.

Ambient noise tomography in the upper crust of North Harrat Rahat, Saudi Arabia

Images of Rayleigh-wave group velocity were derived for the 1–15 s period range that is sensitive to shear wave velocities in the crust of north Harat Rahat, Saudi Arabia. We used a continuous dataset of ambient noise that was processed by applying the technique depending on the Rayleigh-wave group velocity tomography. The dataset comprises six months of recordings extracted from 12 broadband seismic stations in north Harrat Rahat, Saudi Arabia. Using a cross-correlation technique, the Rayleigh waves have been generated and stacked along the whole time series. Dispersion curves representing fundamental mode Rayleigh waves were derived by a multiple filter technique. Dispersion curves for each station pair were inverted to obtain the one-dimensional model of corresponding shear wave velocities. The spatial distribution of shear wave velocities was depicted from the inverted one-dimensional models at 138 nodes and a reliable resolution was spatially resolved using grid cells of 0.2° expanded over both latitude and longitude. Images obtained from this study improve our understanding of the tectonic development as influenced by magma upwelling beneath the Arabian Shield. Results obtained from this study revealed two low-velocity zones in the upper crust at depths of 15 km west and shallow 10 km east, respectively. This suggests that high conductivity is present as a result of upwelling magma that flows into the upper crust of Arabian Shield coming from plausible deep sources such as the Red Sea Rift or the Afar plume, which are located to the west of the studied area.

RESEARCH OF THE INDIUM ARSENIDE IMPULSE PROPERTIES

Indium arsenide is a promising material for creation of high-performance electronic and optoelectronic devices. A high level of knowledge of indium arsenide properties will make it possible to predict the potential possibilities of its application, as well as multicomponent semiconductors based on it. The problem of studying the properties of InAs in the regime of a strong electric field is relevant.
 In scientific and technical sources, data on the impulse properties of indium arsenide in the regime of a strong electric field are poorly presented. The purpose of the work is to study the field-velocity dependence in the pulsed mode of a strong electric field and to analyze the response to changes in its amplitude, pulse duration, and leading edge duration.
 The method of relaxation equations was used to analyze the field-velocity characteristic in the regime of a strong electric field. In the electric field static regime, the highest value of the drift velocity was 3·105 m/s (with a field amplitude of 2 kV/cm), in the saturation section it was 0.9·105 m/s.
 An analysis of the field-velocity dependence in the pulsed mode of a strong electric field showed that with an increase in the field amplitude, the maximum value of the drift velocity increases, and the duration of the "overshoot" shortens. Fields of 5–30 kV/cm correspond to an increase in the highest velocity value by a factor of 2.7–8. The spatial distribution of the drift velocity gave an estimate of the average velocity and distance traveled by charge carriers at different field values.
 An increase in the duration of the leading edge duration of the field pulse caused a delay in transient processes. At 12 kV/cm < E, the peak value of the drift velocity additionally decreases. The duration of a strong electric field pulse has a significant effect only at values less than the formation time of the drift velocity maximum. Such values of the pulse duration lead to a decrease in the rate of drift and relaxation processes.
 Comparison of the field-velocity dependences in the high-field pulsed mode showed that the maximum value of the drift velocity of InAs electrons exceeds the corresponding values: GaAs, InP – by several times; GaN - an order of magnitude. The duration of the “ overshoot ” of the drift velocity for InAs is somewhat longer than for GaAs, InP, GaN.

EXPERIMENTAL STUDY OF CURRENT-SHEET-LIKE STRUCTURE IN PINCHING PLASMA FLOW WITH ELECTRIC AND MAGNETIC PROBES

The formation of the current-sheet-like structure under the influence of the external magnetic field in pinching plasma flows generated by the magnetoplasma compressor has been studied. A set of magnetic and electric probes were used to measure the self-generated magnetic field, electron temperature, and electric field locally with sufficiently high temporal and spatial resolution. The data obtained from the probe measurements were used to plot the spatial distributions of electric current and drift velocity in the plasma stream to identify the patterns of plasma flow. In the presence of external magnetic field, the current density, electron temperature, and the ion saturation current reach a peak in close proximity to the sheet. Measurements indicate the outflow of two electron jets of different temperatures from the layer.

Patient-specific 0D–3D modeling of blood flow in newborns to predict risks of complications after surgery

Abnormal developments of the cardiovascular system are common congenital malformations. Computational fluid dynamics and mathematical modeling can be used to perform quantitative predictive assessments of hemodynamic properties in varied conditions. This article addresses the development of a coupled 0D–3D model of blood flow in newborns to predict risks of complications after surgery. The 0D-model of systemic circulations is created by using the analogy between the blood flow in vessels and the flow of current through an electric circuit. A shunted section of the aorta and pulmonary artery is replaced with a 3D-model with two-way fluid-solid interaction (FSI).A section in a vessel with the aortic valve is examined in a separate 3D-model. Three-dimensional geometry is based on real CT-scans of a patient. The algorithm for coupling models of different levels relies on meeting the condition that pressures and volumetric blood flows are equal at the interaction boundary. We have developed an algorithm for identifying personal parameters from the results obtained by solving an optimization problem. Computational experiments with different individual geometry of the aorta and aortic valve made it possible to analyze blood flow velocities, near-wall stresses, flows, and valve deformations. Observable near-wall stresses can be considered risk factors that could cause calcification on valve leaflets and other valve diseases. Computational solutions in the “aorta – shunt – pulmonary artery” 3D-system allowed obtaining spatial distributions of velocities, pressures, near-wall stresses and other parameters that are significant in respect to probable pathology development. The developed approaches are primarily relevant for decision-making in surgical practice to predict risks of postoperative complications. In future, our plans are to develop the model so that it covers also saturation and oxygen exchange. This is necessary for assessing whether oxygen supply to the lungs is adequate.

Персонализированное 0d–3d-моделирование течения крови у новорожденных для прогнозирования рисков осложнений после оперативного лечения

Abnormal developments of the cardiovascular system are common congenital malformations. Computational fluid dynamics and mathematical modeling can be used to perform quantitative predictive assessments of hemodynamic properties in varied conditions. This article addresses the development of a coupled 0D–3D model of blood flow in newborns to predict risks of complications after surgery. The 0D-model of systemic circulations is created by using the analogy between the blood flow in vessels and the flow of current through an electric circuit. A shunted section of the aorta and pulmonary artery is replaced with a 3D-model with two-way fluid-solid interaction (FSI).A section in a vessel with the aortic valve is examined in a separate 3D-model. Three-dimensional geometry is based on real CT-scans of a patient. The algorithm for coupling models of different levels relies on meeting the condition that pressures and volumetric blood flows are equal at the interaction boundary. We have developed an algorithm for identifying personal parameters from the results obtained by solving an optimization problem. Computational experiments with different individual geometry of the aorta and aortic valve made it possible to analyze blood flow velocities, near-wall stresses, flows, and valve deformations. Observable near-wall stresses can be considered risk factors that could cause calcification on valve leaflets and other valve diseases. Computational solutions in the “aorta – shunt – pulmonary artery” 3D-system allowed obtaining spatial distributions of velocities, pressures, near-wall stresses and other parameters that are significant in respect to probable pathology development. The developed approaches are primarily relevant for decision-making in surgical practice to predict risks of postoperative complications. In future, our plans are to develop the model so that it covers also saturation and oxygen exchange. This is necessary for assessing whether oxygen supply to the lungs is adequate.

Experimental study of the spray characteristics of twin-fluid atomization: Focusing on the annular flow regime

The characteristics of twin-fluid atomization operating in the annular flow regime were studied experimentally under various gas-to-liquid ratios (GLRs) and injection pressures. The macroscopic morphology of the spray was obtained by shadowgraph, while the droplet size and velocity were measured using a phase-Doppler particle analyzer technique. It was found that the spray cone angle increases almost linearly with the GLR, and the axial distance required for droplet coalescence to outweigh the breakup decreases with increasing GLR. The Sauter mean diameter (SMD) first decreases and then increases along the axial direction due to the competition between turbulent breakup and droplet coalescence. The droplet size follows a lognormal distribution; the droplet velocity distribution is closer to a lognormal distribution under large GLRs, while it follows normal distribution with GLR = 3%. Regarding the radial distribution, low GLRs (3% and 5%) lead to a bimodal spatial velocity distribution, while for large GLRs, the droplet velocity decreases monotonically toward the far field. The spray tends to become more stable with increasing GLR and injection pressure Pinj, whereas the SMD increases with increasing Pinj. The underlying atomization mechanism in a twin-fluid injector in the annular flow state can be regarded as the disintegration of the initial liquid sheet by longitudinal Kelvin–Helmholtz instability followed by transverse Rayleigh–Taylor instability, which yields a direct proportionality of the droplet size to the initial liquid sheet thickness ΔL. Subsequently, for high Pinj, the gas core shrinks and ΔL increases, which results in an increased SMD but enhanced atomization efficiency ΔL/SMD.