Current Velocity Distribution Research Articles

Observation of radial velocity along the Yangtze River based on sentinel-1A

ABSTRACT Estuaries and coasts runoff plays a crucial role in the dynamics of the ocean system. However, the current emphasis on synthetic aperture radar (SAR) retrieved current velocities has been on studying strong boundary currents and large-scale ocean circulation, resulting in relatively limited observational research on estuarine current velocities. This study aims to observe the current velocities in the Yangtze River estuary area using Sentinel-1A SAR data. The findings indicate a high agreement between the current velocities retrieved by Sentinel-1A and those observed at hydrographic stations, showcasing the characteristics of current velocity distribution associated with seafloor topography. This highlights the significant potential of SAR in observing estuarine current velocities, contributing to the analysis of benthic topography and the statistics of river runoff.

Influence of the permeability of submerged breakwaters on surrounding wave and current fields

ABSTRACT While a submerged breakwater has become one of the preferred options of shore protection structures because of its lower impact on the coastal landscape and environment, it causes complicated hydrodynamic characteristics and sometimes fails to meet the expected coastal protection functions. Accurate prediction of wave and current around the structure is therefore essential for appropriate design of a submerged breakwater. This study focused on the influence of the permeability of the submerged breakwater and newly conducted laboratory experiments using permeable and impermeable breakwaters. The model, Simulate WAves till SHore (SWASH), was then applied to these laboratory experiments and the difference of measured and computed wave and current field around the structure was investigated. It was found that the model qualitatively well represented the horizontal distribution of wave heights and phase-averaged current velocities although it overestimated the shoreward volume flux over the impermeable breakwater, but not over the permeable breakwater. Comparison of these contrasting results between permeable and impermeable breakwaters revealed that the phase-averaged bottom shear stress was underestimated on the crest of the impermeable breakwater. This feature highlighted the importance of the bottom friction forces accounting for the wave current coexisting field for better predictions of wave-induced current field around the submerged breakwaters.

Performance Analysis of Geometric Properties of Fuel Cell Components

Due to factors including low emission values, great energy efficiency, and reduced environmental contamination, fuel cells have gained popularity recently. Fuel cells using polymer electrolyte membranes can distribute reactant gases through gas flow channels and remove water that forms during the reaction from the fuel cell. This study looked at how different channel sizes and channel cross-section geometries (rectangular, triangular, and semicircular) affected the distribution of current density, oxygen concentration, velocity, and temperature parameters on the cathode catalyst in the flow channels of a single-channel PEM fuel cell at 0.75 V cell voltage. The model with the highest current density and consequently the best fuel cell performance was determined to be 9 x 10-5 A/cm2 in a channel with a height and breadth of 0.1 cm and A = 1 cm2, according to the data obtained. The flow channel length was assessed at 0.2 in the analysis results for all models because it did not alter with the oxygen concentration distribution. In varied channel designs with the same area, it has been found that the velocity distribution varies inversely with the current density. The maximum velocity value recorded at this location was 33.1 m/s in a semicircular canal with a R of 0.34 mm. It has been discovered that fuel cells from more places operate better as a result.

Experimental and numerical analysis of a novel reverse-polarity plasma torch with transferred arc hot-wall nozzle for atmospheric plasma spraying of YSZ coatings

A novel reverse-polarity plasma torch (RPT) with transferred arc (TA) hot-wall nozzle was proposed to enhance the energy of the plasma jet and improve the heating and acceleration performance of the refractory ceramic particles during atmospheric plasma spraying, and was applied to prepare high-performance YSZ coatings. First of all, the two RPTs either with TA hot-wall nozzle or with non-transferred arc (NTA) hot-wall nozzle were designed carefully, and their electro-thermal characteristics were tested through experiments to analyze and compare their performance. Results showed that the RPT with TA hot-wall nozzle (TA-RPT) presented higher arc voltage, thermal efficiency and plasma jet mean enthalpy than those of the RPT with NTA hot-wall nozzle (NTA-RPT) and the conventional normal-polarity plasma torches. Subsequently, numerical simulation models of the TA-RPT and NTA-RPT were established to study the influence of the TA hot-wall nozzle on the current density, temperature and velocity distributions of the plasma jet. Results showed that the use of the TA hot-wall nozzle can significantly enhance the energy of the plasma jet, while maintain the temperature and velocity of the plasma jet at downstream region of the RPT exit at a higher level. Finally, YSZ coatings were prepared by the TA-RPT and NTA-RPT respectively at the same spraying parameters. Results showed that the TA-RPT sprayed coatings exhibited denser and more uniform microstructures, fewer defects such as large-scale pores and inter-laminar cracks, and higher deposition rate than those of the NTA-RPT sprayed coatings. Moreover, the porosity, surface roughness, microhardness, crack extension forces and stability of the mechanical properties of the TA-RPT sprayed coatings were superior to those of the NTA-RPT sprayed coatings.

Convergence of the Malvinas Current branches near 44°S

Field measurements of the Malvinas Current (MC) velocity distribution were performed at the western slope of the Argentine Basin in the South Atlantic Ocean between 47° and 43°S including several sections across the current. The data were collected in January and March 2020 using a Shipborne Acoustic Current Doppler Profiler (SADCP) and allowed us to study circulation patterns in the upper 700 m of the ocean. The observations reveal substantial differences in the current structures at each location; the SADCP data suggest that two distinct current branches at 46°S converge downstream near 44°S making it difficult to distinguish the high-velocity cores farther north. A detailed comparison between the velocity structures indicates that the branches converge due to the change in the orientation and width of the continental slope, and is consistent with potential vorticity conservation. At the same time, satellite altimetry shows that the branches merge to a single high-velocity jet, suggesting that satellite altimetry does not reproduce all features of the MC internal structure and indicates the importance of further direct velocity observations in this region. Despite the above-mentioned limitations of altimetry, the satellite-derived geostrophic velocities suggest that the pathways of the MC high-velocity jets are quite stable. In addition, both satellite altimetry and direct measurements indicate that the branches tend to converge downstream near 44°S.

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.

Mass segregation and dynamics of primordial binaries in star clusters with a radially anisotropic velocity distribution

ABSTRACT This paper is the third in a series investigating, by means of N-body simulations, the implications of an initial radially anisotropic velocity distribution on the dynamics of star clusters. Such a velocity distribution may be imprinted during a cluster’s early evolutionary stages and several observational studies have found examples of old globular clusters in which radial anisotropy is still present in the current velocity distribution. Here we focus on its influence on mass segregation and the dynamics of primordial binary stars (disruptions, ejections, and component exchanges). The larger fraction of stars on radial/highly eccentric orbits in the outer regions of anisotropic clusters lead to an enhancement in the dynamical interactions between inner and outer stars that affects both the process of mass segregation and the evolution of primordial binaries. The results of our simulations show that the time-scale of mass segregation of the initially anisotropic cluster is longer in the core and shorter in the outer regions, when compared to the initially isotropic system. The evolution of primordial binaries is also significantly affected by the initial velocity distribution and we find that the rate of disruptions, ejections, and exchange events affecting the primordial binaries in the anisotropic clusters is higher than in the isotropic ones.

Numerical study on the flow environment for a novel design of net cage with a shielding device

As aquaculture moves from inshore to the deep sea, developing a comfortable swimming environment for the farmed fish to cope with the strong current in the open sea becomes vitally imperative. This study designs a novel net cage with a shielding device to provide a sheltered area for the farmed fish at extreme ambient current speeds. Considering the time-consuming and substantial economic loss caused by the destruction of the net cage in situ measurements, a numerical method based on computational fluid dynamics (CFD) modeling is employed to evaluate the flow field of the net cage. Three characterized parameters, namely the height of the middle plane nets, the inclined angle of plane nets, and the net solidity, are used to estimate their influences on the flow field of a net cage and the drag force loaded on it. The results highlight that the height variation of the middle-plane nets has little effect on the flow field and the drag force. Nevertheless, the increased inclined angle of plane nets and net solidity leads to a dramatic fluctuation regarding the current velocity distribution and the drag force. In particular, the increase of the inclined angle for the plane nets causes a noticeable increase in the cage volume. With this understanding, further aquaculture net cages can potentially be designed to better withstand the ocean's rigors and maintain the aquaculture industry's sustainability.

Dynamic Optimization Method for Broadband ADCP Waveform with Environment Constraints.

Broadband acoustic Doppler current profiler (ADCP) is widely used in agricultural water resource explorations, such as river discharge monitoring and flood warning. Improving the velocity estimation accuracy of broadband ADCP by adjusting the waveform parameters of a phase-encoded signal will reduce the velocity measurement range and water stratification accuracy, while the promotion of stratification accuracy will degrade the velocity estimation accuracy. In order to minimize the impact of these two problems on the measurement results, the ADCP waveform optimization problem that satisfies the environment constraints while keeping high velocity estimation accuracy or stratification accuracy is studied. Firstly, the relationship between velocity or distance estimation accuracy and signal waveform parameters is studied by using an ambiguity function. Secondly, the constraints of current velocity range, velocity distribution and other environmental characteristics on the waveform parameters are studied. For two common measurement applications, two dynamic configuration methods of waveform parameters with environmental adaptability and optimal velocity estimation accuracy or stratification accuracy are proposed based on the nonlinear programming principle. Experimental results show that compared with the existing methods, the velocity estimation accuracy of the proposed method is improved by more than 50%, and the stratification accuracy is improved by more than 22%.

Analysis on The Effect of Groyne Type Impermeable Placement on Sediment Distribution in Lariang River Bend

Sedimentation and erosion caused by differences in discharge is a problem that often occurs at river bends. One of the functions of placing the groyne is to reduce the river flow velocity along the riverbank, accelerate sedimentation, and ensure the embankment or river bank's safety against scouring. This study aimed to determine the distribution of current velocity, distribution of riverbed shear stress, and sediment distribution to the effect of groyne placement. There are 7 (seven) simulation models used to get the most effective groyne placement. From the model simulation results by adding a groyne building on the river's outer bend for the simulation model scenario 2 to scenario 7, the largest sedimentation production is in scenario 3, namely the height of riverbed sediment deposits 230 hours of 1.094 m. Furthermore, the groyne building's effective placement is determined based on a maximum change in the riverbed scenario. In scenario 3, the placement and dimensions of the groyne length of 17.5 m; distance between groyne 24.4 m; the groyne is inclined upstream in the direction of flow 10°

A magnetic reconnection model for hot explosions in the cool atmosphere of the Sun

Context. Ultraviolet (UV) bursts and Ellerman bombs (EBs) are transient brightenings observed in the low solar atmospheres of emerging flux regions. Magnetic reconnection is believed to be the main mechanism leading to formation of the two activities, which are usually formed far apart from each other. However, observations also led to the discovery of co-spatial and co-temporal EBs and UV bursts, and their formation mechanisms are still not clear. The multi-thermal components in these events, which span a large temperature range, challenge our understanding of magnetic reconnection and heating mechanisms in the partially ionized lower solar atmosphere. Aims. We studied magnetic reconnection between the emerging magnetic flux and back ground magnetic fields in the partially ionized and highly stratificated low solar atmosphere. We aim to explain the multi-thermal characteristics of UV bursts, and to find out whether EBs and UV bursts can be generated in the same reconnection process and how they are related with each other. We also aim to unearth the important small-scale physics in these events. Methods. We used the single-fluid magnetohydrodynamic (MHD) code NIRVANA to perform simulations. The background magnetic fields and emerging fields at the solar surface are reasonably strong. The initial plasma parameters are based on the C7 atmosphere model. We simulated cases with different resolutions, and included the effects of ambipolar diffusion, radiative cooling, and heat conduction. We analyzed the current density, plasma density, temperature, and velocity distributions in the main current sheet region, and synthesized the Si IV emission spectrum. Results. After the current sheet with dense photosphere plasma emerges and reaches 0.5 Mm above the solar surface, plasmoid instability appears. The plasmoids collide and coalesce with each other, which causes the plasmas with different densities and temperatures to be mixed up in the turbulent reconnection region. Therefore, the hot plasmas corresponding to the UV emissions and colder plasmas corresponding to the emissions from other wavelengths can move together and occur at about the same height. In the meantime, the hot turbulent structures concentrate above 0.4 Mm, whereas the cool plasmas extend to much lower heights to the bottom of the current sheet. These phenomena are consistent with published observations in which UV bursts have a tendency to be located at greater heights close to corresponding EBs and all the EBs have partial overlap with corresponding UV bursts in space. The synthesized Si IV line profiles are similar to that observed in UV bursts; the enhanced wing of the line profiles can extend to about 100 km s−1. The differences are significant among the numerical results with different resolutions, indicating that the realistic magnetic diffusivity is crucial to revealing the fine structures and realistic plasmas heating in these reconnection events. Our results also show that the reconnection heating contributed by ambipolar diffusion in the low chromosphere around the temperature minimum region is not efficient.

Quasi-Ballistic Drift-Diffusion Simulation of SiGe Nanowire MOSFETs Using the Kinetic Velocity Model

This paper presents the calibration of the novel kinetic velocity model (KVM) in the drift-diffusion (DD) transport approach, which can account for the ballistic effect in short-channel devices. The KVM considers a thermionic emission limit and a free carrier acceleration limit for the mobility. We develop a methodology to extract the parameters for the KVM and for the high-field saturation velocity model for SiGe nanowires over the whole mole fraction range. The calibrated DD simulations with KVM show good agreement with Boltzmann transport equation results in terms of on-state current and carrier-weighted velocity distribution over a wide range of gate lengths for both linear and saturation regimes.

WAVE-CURRENT INTERACTION AT A RIGHT ANGLE OVER ROUGH BEDS: TURBULENCE ANALYSIS

In the present work, an investigation on the hydrodynamics of wave-current orthogonal combined flow has been carried out. The work focuses on the effects of the oscillatory flow superposed on the current steady boundary layer, and on how the oscillatory flow affects the current velocity distribution. A laboratory experimental campaign of wave-current orthogonal interaction has been carried out in a shallow water basin at DHI Water and Environment (Horsholm, Denmark), in order to investigate the orthogonal combined flow in the presence of different roughness beds. Mean flow has been investigated by computing time- and space-averaged velocity profiles. Friction velocity and equivalent roughness have been inferred from the velocity profiles by best fit technique, in order to quantify the shear stress experienced by the current mean flow. Tests in the presence of only current, only waves and combined flow have been performed. Instantaneous velocities have been Reynolds-averaged in order to obtain turbulent fluctuations time series and compute turbulence related quantities, such as Reynolds stresses. The mean current velocity profiles have been also compared with a selection of analytical models in order to assess their validity for the case of wave-current orthogonal flow for the considered wave and current condition ranges. The analysis of the mean flow revealed a complex interaction of the waves and currents combined flow. Depending on the relative strength of the current with respect to the waves, the superposition of the oscillatory flow may determine an increase or a decrease of the bottom friction experienced by the current. Such a behavior is also strictly related to the bed physical roughness. Analysis of the turbulence Reynolds stresses seems to confirm the results of the mean flow investigation.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/GbtOgeLlVTU

Act in contravention: a non-planar coupled electrode design utilizing “tip effect” for ultra-high areal capacity, long cycle life zinc-based batteries

Aqueous zinc-based batteries (ZBBs) have great potential as commercial energy storage devices. However, the poor cycling stability of zinc anode under high areal capacity limits their further application. Herein, a coupled non-planar electrode design achieved by the tailored flat-top pyramid carbon felt (TCF) is proposed for ZBBs, which can effectively increase the zinc deposition sites, adjust the deposition morphology, optimize the current and electrolyte flow velocity distribution and provide necessary space for zinc plating. Interestingly, by utilizing “tip effect”, the coupled TCFs enable precise control of the zinc dendrite growth position, effectively reducing the risk of short circuit. Based on such coupled TCFs, zinc-iodine flow batteries can deliver an ultra-high areal capacity of 240 mAh cm−2 and a superb cycling stability over 300 cycles (areal capacity of 160 mAh cm−2) at a high current density of 40 mA cm−2. Therefore, we provide an effective strategy for high areal capacity zinc anode design, which may promote the development of high energy density and long cycle life ZBBs.

Impact of Sea Ice on the Hydrodynamics and Suspended Sediment Concentration in the Coastal Waters of Qinhuangdao, China

The influence of sea ice on the hydrodynamics, sediment resuspension, and suspended sediment concentration (SSC) in the coastal area of Qinhuangdao was systematically investigated using 45-day in situ measurements at two stations (with ice at station M1 and without ice at station M2) in the Bohai Sea in the winter of 2018. It was found that the daily fluctuations of temperature and salinity at M1 are more significant than those at M2. During a typical seawater icing event on January 28, the temperature and salinity of the bottom water at M1 were decreased by 1.77 °C and increased by 0.4 psu, respectively. Moreover, due to the shielding effect of the sea ice, the residual current was much less affected by the wind at M1 than at M2. For the vertical distribution of current velocity, it changed from a traditional logarithmic type under ice-free conditions to parabolic type under ice-covered conditions due to the larger drag coefficient of the water body on the solid ice surface. For the SSC and turbidity at the bottom layer, the average values were 4.9 μL/L and 8.6 NTU at M1, respectively, approximately half of those at M2. The smaller SSC and turbidity at M1 can be attributed to the lower near-bottom turbulent kinetic energy (TKE). At M2, however, the larger SSC is closely related to the strong wind forcing, which could induce higher TKE without sea ice cover, and hence stronger turbulent resuspension. The seabed sediment analysis results showed that in the study area, fine sand is most likely to resuspend, while cohesive particles would resuspend only under strong hydrodynamic conditions.

Observations of Near-Surface Mixing Behind a Headland

Field observations were collected near the mouth of the Bagaduce River, Maine, in order to understand how complex features affect the intratidal and lateral variability of turbulence and vertical mixing. The Bagaduce River is a low-inflow, macrotidal estuary that features tidal islands, tidal flats and sharp channel bends. Profiles of salinity, temperature, and turbulent kinetic energy dissipation (ε) were collected for a tidal cycle across the estuary with a microstructure profiler. Lateral distributions of current velocities were obtained with an acoustic doppler current profiler. Results showed intratidal asymmetries in bottom-generated vertical eddy diffusivity and viscosity, with larger values occurring on ebb (Kz: 10−2 m2; Az: 10−2 m2/s) compared to flood (Kz: 10−5 m2/s; Az: 10−4 m2/s). Bottom-generated mixing was moderated by the intrusion of stratified water on flood, which suppressed mixing. Elevated mixing (Kz: 10−3 m2; Az: 10−2.5 m2/s) occurred in the upper water column in the lee of a small island and was decoupled from the bottom layer. The near-surface mixing was a product of an eddy formed downstream of a headland, which tended to reinforce vertical shear by laterally straining streamwise velocities. These results are the first to show near-surface mixing caused by vertical vorticity induced by an eddy, rather than previously reported streamwise vorticity associated with lateral circulation.

The Curve Fit Analysis of Mean Longshore Current Velocity Distribution Under Different Mild Slope Conditions

Studying the distribution of longshore current velocity has important practical significance for coastal sediment transport and nearshore material transport and diffusion. Based on the experimental results of 1:100 slope and 1:40 slope mild slope longshore current, this essay adopts MATLAB software and uses different functions to fit and analyze the mean longshore current velocity distribution under mild slope in two cases. The results show that the maximum value of 1:100 mean longshore current velocity have a concave trend on the nearshore side, three kinds of functions can properly fit the mean longshore current velocity distribution. In the case of 1:40, three kinds of functions cannot appropriately show the mean longshore current velocity distribution. Therefore, the distribution characteristics that the convex trend is on the coastal side of the 1:40 mild slope can be better described by proposing a custom piecewise function and relevant constraints.

Integrated marine monitoring for drilling discharges under mesotidal forcing

There is a range of hydrocarbon exploration and extraction industrial project activities taking place on the North West Shelf of the Australian Continent. The shelf is a diverse and important marine ecosystem, with a number of globally significant shallow coral reefs and marine protected areas, which are vital for survival of threatened and protected species. Some of the mentioned exploration and extraction activities, such as offshore drilling, may be permitted within few kilometres away from sensitive habitats extant near a project resource extraction area. The habitats may in some cases be presented by submerged shoal ecosystems of high biodiversity and thus high environmental/ecological value, due to the presence of either or both benthic biota and fish assemblages. As part of an environmental assessment program for the industrial activities, some of the offshore exploration operators examine the effects of drilling discharges on the marine ambience. This study describes such an assessment. For the assessment, a novel integrated marine monitoring approach was conceptually designed; the program was then executed in the field using bottom-mounted equipment and a remotely operated underwater vehicle with sensors mounted on it. This study focuses on assessing the wind conditions in the project area, sea level and current velocities, in situ water temperature, salinity, turbidity and acoustic echo intensity, over several stages of the drilling operations while the drilling cuttings and muds were discharged into the water column. The collected during the austral autumn months of April and May winds showed prevailing east-southeaserlies, which is aligned well with the general understanding of wind climatology of the area. Importantly, stronger than usual winds may have a defining impact on current speeds and directions, with the current speeds enhanced by such winds. On these occasions the water transporting a discharge material may pushed towards the sensitive habitat present in the area. Normally though the hydrodynamics in the project area are dominated by semi-diurnal tides. Both vertical current velocity and water temperature distributions indicated the presence of three layers within the water column over the project site. The vertical distribution of water salinity was rather homogenous throughout the entire water column. The monitored by an optical instrument turbidity and acoustic echo intensity from an ADCP (acoustic Doppler current profiler) showed that tracing discharge plumes with a remotely operated underwater vehicle is a viable technique, which could be implemented at other locations. Such independent parameters though need a thorough cross-calibration and inter-validation for the results to be fully understood.

Experimental and numerical study of current-induced artificial upwelling

The aim of the current paper is to investigate hydrodynamic characteristics of the artificial upwelling induced by ocean currents. Experiments were performed in a flume at different density difference heads, horizontal current velocities and upwelling pipe diameters. A three-dimensional computational fluid dynamics (CFD) model was employed on wider range of parameters for further analysis. The performance of the numerical model has been confirmed by the experimental findings. The present results show that the volume flow rate of current-induced artificial upwelling is influenced by geometrical parameters and inclination angle of the pipe, the horizontal current velocity and vertical distribution of water density. In ideal two-layer density stratified water, the critical current velocity to generate upwelling linearly increases with the increase of the density difference, and the maximum rising height for upwelling is inversely proportional to the density difference. Feasibility analysis was taken by using current and density profiles of the East China Sea near Dongji Islands, which provides an useful reference for engineering practice.

Numerical investigation of coupled arc and electrode for GTAW with a longitudinal electromagnetic field

Due to the good conductivity of ions and free electrons in the arc column, arc plasma possesses a remarkable magnetic controllability. Thus, a new technique of electromagnetic stirring has been developed which is of great interest during welding process by applying superimposed external magnetic field. However, few researches have focused on arc behavior with a coupled electrode under a magnetic field. In this paper, a three-dimensional plasma arc model coupled cathode was developed, and the distributions of current density, electric potential, magnetic field, pressure, velocity and temperature of plasma arc were obtained by solving the conservation equations of momentum, mass and energy coupled Maxwell’s equations. By applying finite volume method, when the intensity of applied electromagnetic field exceeded a threshold value, it reveals that arc contraction near cathode and arc divergence near anode are induced resulting in mutation phenomenon. The distributions of arc temperature and pressure deviate from the axis of tungsten and exhibit a bimodal shape. This is distinctly different from that of the free arc under natural combustion condition. In addition, the maximum velocity of the plasma flow appears on both sides of the arc symmetry axis. Moreover, arc plasma presents a behavior of heavy reflow and eddy, and a low-temperature area and a negative pressure zone appear in the central axis of arc plasma.