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Estimates sediment transport in Iraqi Rivers are essential for effective rivers management, particularly when delivery rates is potential threat to environment and ecological systems. Therefore, this research was performed for estimating sediment transport rates in a certain reach from Euphrates River downstream Al Hindiyah Barrage and examine the stat of Entrainment Rate Esi of bed sediments under a unsteady stream flow. In spite of complexity and the difficulty of conducting measurements, the sediment load were measured with satisfactory perfection to achieve acceptable results for monitoring this river reach. The acoustic Doppler current profiler (ADCP) technique were used to measure velocity distribution, cross section profiles, and using (Helley-Smith) sampler to collect bed load samples from twenty cross sections downstream Al Hindiya Barrage. The investigation of suspended sediment concentration in vertical profiles has consisted of using an Entrainment rate relation (Esi), also for evaluating materials concentration near the bed and the upward, the vertical distribution of material particles was examine in the water column. The measurement results are clarified that there are many regions of river covered with high sedimentation, but the suspended load is prevalent mode of transport with average value 97.313%. The observed suspended sediment yield in the river reach was ranged from 386.645 ton/day to 6588.58 ton/day during the drought condition and low level of water discharge and may change with discharge change. While bed load yield ranged between 0.270 ton/day to 5.394 ton/day. The investigation is represented a non-equilibrium condition in sediment transport is prevalent circumstance in channel system. It is tested the relation of Ei against limited grainsizes data and skin shear velocity U*skin then analyzed the regression. The result is shown that near-bed entrainment, evaluated at 15% of the flow depth, decreases with the ratio of settling velocity to skin-friction shear velocity due to its role in determining bed load-layer concentrations. The fit relation for R2 = 0.48 and correlation r = -0.55 are shown that outstanding an association between maximal flow resistance and sediment diffusivities, this is probably because bed-form prompt by turbulence flow which caused nonlinear dependence. [ABSTRACT FROM AUTHOR]

Centrifugal fans are widely used in applications for the ventilation of air to induce pressure and drive the flow medium. The centrifugal fans are applied not only to produce fresh air but also to absorb toxic gases from the environment. Complex flow patterns are present in the centrifugal fan's impeller and volute casing. The flow patterns of a backward curved centrifugal fan are the main topic of this study. The flow in the impeller blade channels needs to be better understood to optimize the design and performance of any turbomachine. This work uses numerical analysis to examine the flow patterns inside a backward curved centrifugal fan employed in the ventilation system. Computational fluid dynamic code serves as the foundation for numerical analysis, ANSYS-CFX 21.2. The fan under investigation in this study has an operational speed of 1500 rpm, a pressure head of 4 m, and a volume flow rate of 3 m3min-1. A change in mass flow rates has a direct impact on the pressure and velocity distributions in the centrifugal fan's impeller passageways. By varying the mass flow rates, the numerical results have demonstrated the three-dimensional properties of the flow, particularly in the impeller blade passageways and the casing. The fan casing contains the highpressure region, while the impeller intake is the low-pressure area. The area within the volute tongue in which flow recirculation occurs. The backward curved centrifugal fan has a static efficiency of 93% and a total efficiency of 96% at the specified volume flow rate. This suggested methodology can be used to identify fluid flow constraints in the volute casing, comprehend internal flow patterns in the backward curved centrifugal fan, and enhance centrifugal fan performance. [ABSTRACT FROM AUTHOR]

This investigation aims to analyze the effects of heat transport characteristics in the unsteady flow of nanofluids over a moving plate caused by a moving slot factor. The BRS variable is utilized for the purpose of analyzing these characteristics. The process of mathematical computation involves converting the governing partial differential equations into ordinary differential equations that have suitable similarity components. The Keller-Box technique is employed to solve the ordinary differential equations (ODEs) and derive the corresponding mathematical outcomes. Figures and tables present the relationship between growth characteristics and various parameters such as temperature, velocity, skin friction coefficient, concentration, Sherwood number, and Nusselt number. The results are assessed by comparing them to previous findings. The observation reveals that higher dimensionless reference temperature and variable values of the moving slot parameter have a suppressing effect on the velocity and temperature patterns of nanofluids. Higher values of the dimensionless reference temperature and moving slot parameter lead to enhancements in the Sherwood number, skin friction coefficient, and Nusselt number. The conductivity of the nanofluid is ultimately affected by these enhancements. [ABSTRACT FROM AUTHOR]

In the current research, a thorough examination unfolds concerning the attributes of magnetohydrodynamic (MHD) boundary layer flow and heat transfer inherent to nanoliquids derived from Sisko Al2O3-Eg and TiO2- Eg compositions. Such nanoliquids are subjected to an extending surface. Consideration is duly given to slip boundary conditions, as well as the effects stemming from variable viscosity and variable thermal conductivity. The analytical approach applied involves the application of suitable similarity transformations. These conversions serve to transform the initial set of complex nonlinear partial differential equations into a more manageable assembly of ordinary differential equations. Through the utilization of the FEM, these reformulated equations are solved, considering the specified boundary conditions. The outcomes attained are graphically depicted by means of plots and tables. These visual aids facilitate a comprehensive exploration of how diverse parameters exert influence over the distributions of velocity, temperature, and concentration. Furthermore, detailed scrutiny is directed towards the fluctuations characterizing pivotal parameters, viz., Nusselt number, skin-friction coefficient, and Sherwood number. It is identified that the Nusselt number showcases a diminishing trend coinciding with increasing values of the volume fraction parameter (φ). This trend remains consistent regardless of whether the nanoliquid under consideration is Al2O3-Eg or TiO2-Eg based. In contrast, both the skin-friction coefficient and Sherwood number assume lower values as the volume fraction parameter (φ) escalates. This pattern remains congruent across both classifications of nanoliquids. The findings of the study impart valuable insights into the complex interplay governing the characteristics of HMT pertaining to Sisko Al2O3-Eg and TiO2-Eg nanoliquids along an extending surface. [ABSTRACT FROM AUTHOR]

The natural convection from a vertical hot plate with radiation and constant flux is studied numerically to know the velocity and temperature distribution characteristics over a vertical hot plate. The governing equations of the natural convection in two-dimension are solved with the implicit finite difference method, whereas the discretized equations are solved with the iterative relaxation method. The results show that the velocity and the temperature increase along the vertical wall. The influence of the radiation parameter in the boundary layer is significant in increasing the velocity and temperature profiles. The velocity profiles increase with the increase of the radiation parameter. The temperature profiles near the wall plate parallel each other due to the constant heat flux applied to the wall. The influence of the radiation parameter is significant either in velocity or temperature characteristics. At the same time, the effect of the Prandtl number greater than 0.71 is not sensitive to the velocity and temperature variations elsewhere. [ABSTRACT FROM AUTHOR]

The plenum chamber of a heat setting machine is a key structure for distributing hot air to different air channels. Its outlet velocity uniformity directly determines the heating uniformity of textiles, significantly affecting the heat setting performance. In a traditional heat setting machine, the outlet airflow maldistribution of the plenum chamber still exists. In this study, a novel plenum chamber with an airfoil baffle was established to improve the uniformity of the velocity distribution at the outlet in a heat setting machine. The structural influence of the plenum chamber on the velocity distribution was investigated using a computational fluid dynamics program. It was found that a chamber with a smaller outlet partition thickness had a better outlet velocity uniformity. The structural optimization of the plenum chamber was conducted using the particle swarm optimization algorithm. The outlet partition thickness, the transverse distance and the longitudinal distance of the optimized plenum chamber were 20, 686. 2 and 274. 6 mm, respectively. Experiments were carried out. The experimental and simulated results showed that the optimized plenum chamber with an airfoil baffle could improve the outlet velocity uniformity. The air outlet velocity uniformity index of the optimized plenum chamber with an airfoil baffle was 4. 75% higher than that of the plenum chamber without an airfoil baffle and 5. 98% higher than that of the conventional chamber with a square baffle in a commercial heat setting machine. [ABSTRACT FROM AUTHOR]

Research on the expansion and fracture of explosively driven metal shells has been a key issue in weapon development and structural protection. It is important to study and predict the failure mode, fracture mechanism, and fragment distribution characteristics of explosively driven metal shells. In this study, we used the finite element-smoothed particle hydrodynamics (FE-SPH) adaptive method and the fluid-structure interaction method to perform a three-dimensional numerical simulation of the expansion and fracture of a metal cylindrical shell. Our method combined the advantages of the FEM and SPH, avoiding system mass loss, energy loss, and element distortion; in addition, the proposed method had a good simulation effect on the interaction between detonation waves and the cylindrical shell. The simulated detonation wave propagation, shell damage morphology, and fragment velocity distribution were in good agreement with theoretical and experimental results. We divided the fragments into three regions based on their shape characteristics. We analyzed the failure mode and formation process of fragments in different regions. The numerical results reproduced the phenomenon in which cracks initiated from the inner surface and extended to the outer surface of the cylindrical shell along the 45° or 135° shear direction. In addition, fragments composed of elements are identified, and the mass and characteristic lengths of typical fragments at a stable time are provided. Furthermore, the mass and size distribution characteristics of the fragments were explored, and the variation in the fitting results of the classical distribution function under different explosion pressures was examined. Finally, based on mathematical derivation, the distribution formula of fragment velocity was improved. The improved formula provided higher accuracy and could be used to analyze any metal cylindrical shells with different length-to-diameter ratios. [ABSTRACT FROM AUTHOR]

Casting is a manufacturing process in which molten metal is poured through the gating system to fill the mould cavity where it solidifies. Variations in casting parameters by different researchers have led to significant variations in casting guidelines, which have forced Foundry Engineers to carry out a number of trial-and-error runs to create guidelines based on their own experience. These variations in guidelines have led to defects occurring in casting during the mould filling process. This work aimed at determining the critical drop height and critical flow velocity of a certain molten aluminum alloy as it flow down the mould sprue in gravity sand casting. The continuity equation was used to describe the velocity distribution of the aluminum alloy as it flows down the sprue. The mathematical tool used in this research is the finite element method. It involves the discretization of the domain of interest into smaller finite elements. The weak form of the governing equation was obtained and integrated over the domain of interest. The results obtained, established the critical flow velocity of aluminum alloy, down the sprue, as 2.565 × 10³ mm/s and the critical drop height as 377mm. Results obtained were compared with literature and were also used to produce various casts, it was observed that casts produced, using sprue height below the critical drop height obtained prevented casting defects, while at sprue height above the critical drop height, the danger of casting defects could not be avoided. [ABSTRACT FROM AUTHOR]

Pressure drops and velocity distributions of liquid metal MHD flow in pipes are closely related to the geometry of the cross-section. Liquid metal flows in two types of electrically conducting circular pipes under a uniform magnetic field applied transversely to the flow are investigated numerically using large eddy simulation with a coherent structure model developed in the Open-FOAM environment. One pipe has a typical circular cross-section (N-pipe), whereas the other has four V-shaped strips at the wall parallel and perpendicular to the magnetic field (F-pipe). The increasing transverse magnetic field causes a turbulent MHD flow evolves into a single-sided turbulent flow and a laminar flow in the N-pipe. The V-shaped strips on the Hartmann wall generate a low-velocity belt along the magnetic field direction in the center of the pipe and weak high-velocity jets near the V-shaped strips. Furthermore, the inflection points in the velocity profile improve instability and turbulence. The root mean square of the velocity fluctuation, in particular, the transverse components increase with the Hartmann number increasing along the magnetic field direction in the F-pipe. The V-shaped strips delay the MHD turbulent-laminar transition. However, the skin friction coefficient is slightly higher in the F-pipe than in the N-pipe, with the same dimensionless parameters. The research results can be applied to the turbulence promoter in the MHD pipe flow. [ABSTRACT FROM AUTHOR]

The unsteady flow behaviour of two side-by-side rotors in ground proximity is experimentally investigated. The rotors induce a velocity distribution interacting with the ground causing the radial expansion of the rotor wakes. In between the rotors, an interaction of the two wakes takes place, resulting in an upward flow similar to a fountain. Two types of flow topologies are examined and correspond to two different stand-off heights between the rotors and the ground: the first one where the height of the fountain remains below the rotor disks, and a second one where it emerges above, being re-ingested. The fountain unsteadiness is shown to increase when re-ingestion takes place, determining a location switch from one rotor disk to the other, multiple times during acquisition. Consequently, variable inflow conditions are imposed on each of the two rotors. The fountain dynamics is observed at a frequency that is about two orders of magnitude lower than the blade passing frequency. The dominant characteristic time scale is linked to the flow recirculation path, relating this to system parameters of thrust and ground stand-off height. The flow field is analysed using proper orthogonal decomposition, in which coupled modes are identified. Results from the modal analysis are used to formulate a simple dynamic flow model of the re-ingestion switching cycle. [ABSTRACT FROM AUTHOR]

In 1984 Shuichi Nosé invented an isothermal mechanics designed to generate Gibbs' canonical distribution for the coordinates {q} and momenta {p} of classical N-body systems [1, 2]. His approach introduced an additional timescaling variable s that could speed up or slow down the {q, p} motion in such a way as to generate the Gaussian velocity distribution ∝ e-p2/2mkT and the corresponding potential distribution, ∝ e-F(q)/kT. (For convenience here we choose Boltzmann's constant k and the particle massmboth equal to unity.) SoonWilliam Hoover pointed out that Nosé's approach fails for the simple harmonic oscillator [3]. Rather than generating the entire Gaussian canonical oscillator distribution, the Nosé-Hoover approach, which includes an additional friction coefficient ζ with distribution e-ζ2/2/v 2p, generates only a modest fractal chaotic sea, filling a small percentage of the canonical (q, p, ζ) distribution. In the decade that followed this thermostatted work a handful of ergodic algorithms were developed in both three- and four-dimensional phase spaces. These new approaches generated the entire canonical distribution, without holes. The 2024 Snook Prize problem is to study the efficiency of several such algorithms, such as the five ergodic examples described here, so as to assess their relative usefulness in attaining the canonical steady state for the harmonic oscillator. The 2024 Prize rewarding the best assessment is United States $1000, half of it a gift from ourselves with the balance from the Pozna'n Supercomputing and Networking Center. [ABSTRACT FROM AUTHOR]

In this paper, the derivation of a formula is presented to determine the time taken for the discharge of an open tank through a vertical, rectangular orifice. This formula allows a simpler and more accurate determination of the discharge time. The formula obtained by the integration of velocity distribution was checked using a numerical model. It is shown the great correspondence between the derived formula and a formula for small orifices, regardles of whether the orifice is small or not, except in the cases where the height of orifice is much greater than the height of water level from the upper edge of the orifice. The presented formula takes into account the velocity distribution down the orifice and can be treated as a formula for all rectangular orifices. [ABSTRACT FROM AUTHOR]

This study attempts to provide a more precise and comprehensive model for stream-wise velocities in turbulent smooth-wall open channel flows. Velocity profiles are obtained from the resolution of two ordinary differential equations. The first is derived from the Reynolds-averaged Navier-Stokes (RANS) equation while the second is from the equilibrium between turbulent kinetic energy (TKE) production and dissipation. We assessed different analytical models for eddy viscosity, TKE and mixing length. Computation results for velocity profiles were assessed and compared to experimental data for different flow conditions and the well-known linear, log and log-wake laws. Our results show that the model based on the RANS equation provides more accurate velocity profiles. In the viscous sublayer and buffer layer, the method based on Prandtl's eddy viscosity model and Van Driest mixing length gives more precise results. For the log layer and outer region, a mixing length equation derived from Von Karman's similarity hypothesis, provides the best agreement with measured data except near the free surface where we used an additional correction based on a damping function for eddy viscosity. This method allows more accurate velocity profiles with the same value of the damping coefficient that is valid under different flow conditions. [ABSTRACT FROM AUTHOR]

We consider the problem of recovering the physical parameters of ejecta from data of photon Doppler velocimetry (PDV). The results of PDV measurements of ejecta production from shock-loaded Pb samples are presented. Shockwaves in the samples were generated by an accelerated flyer-plate. Depending on the sample thickness, the shock-breakout pressure varied from 27.5 to 43 GPa. The ejecta transport occurred in the air. The spectral profile J ( ω ) of heterodyne beats underlies our analysis of the experiments. The noise-free component of | J ( ω ) | 2 is shown to obey the transport equation which accounts for multiple scattering and absorption of the probing beam in the cloud of moving particles. This provides a means for theoretical modeling of PDV data. Varying the values of the free-surface velocity and the parameters of the velocity distribution of ejecta, we fit the calculated spectrum to the PDV-measured one. We apply this method to time-resolved PDV spectra and, based on the ejecta optical model, recover the values of the free-surface velocity, the areal density, and the density-velocity distribution of ejecta. [ABSTRACT FROM AUTHOR]

Lateral inhomogeneity in Earth's mantle affects the tidal response. In this study, the analytical method for determining the effect of lateral inhomogeneity on tidal gravity, presented by Molodenskiy (1980), is introduced. Moreover, the current study reformulates the expressions for estimating the lateral inhomogeneity effects with respect to the unperturbed Earth and supplements some critical derivation process to enhance the method. The effects of lateral inhomogeneity are calculated using several real Earth models. By considering the collective contributions of seismic wave velocity disturbance and density disturbance, the global theoretical changes of semidiurnal gravimetric factor are obtained, which vary from −0.22 % to 0.17 % compared with those in a layered Earth model, no more than 1/3 of the ellipticity's effect. The gravity changes caused by laterally-inhomogeneous disturbance are also computed, and turn out to be up to 0.16 % compared with the changes caused by tide-generating potential. The current study tests the importance of lateral inhomogeneity and other factors. The results indicate that the rotation, ellipticity, and inelasticity on tidal gravity are the most dominant factors, the ocean tide loading is the moderate one, and the lateral inhomogeneity is the least but not negligible factor, because the three-dimensional effect is comparable with ocean tide loading at some locations. Moreover, the amplitude of tidal gravity caused by lateral inhomogeneity is noticeable larger than the precision of superconducting gravimeters. [ABSTRACT FROM AUTHOR]

A phenomenological continuum model is developed using systematic molecular dynamics (MD) simulations of force-driven liquid argon flows confined in gold nano-channels at a fixed thermodynamic state. Well known density layering near the walls leads to the definition of an effective channel height and a density deficit parameter. While the former defines the slip-plane, the latter parameter relates channel averaged density with the desired thermodynamic state value. Definitions of these new parameters require a single MD simulation performed for a specific liquid-solid pair at the desired thermodynamic state and used for calibration of model parameters. Combined with our observations of constant slip-length and kinematic viscosity, the model accurately predicts the velocity distribution and volumetric and mass flow rates for force-driven liquid flows in different height nano-channels. Model is verified for liquid argon flow at distinct thermodynamic states and using various argon-gold interaction strengths. Further verification is performed forwater flowin silica and gold nano-channels, exhibiting slip lengths of 1.2 nm and 15.5 nm, respectively. Excellent agreements between the model and the MD simulations are reported for channel heights as small as 3 nm for various liquid-solid pairs. [ABSTRACT FROM AUTHOR]

We measured the fully resolved 3-dimensional velocity distributions of nitric oxide photodesorbed from a gold single crystal. These experiments combine time-of-flight measurements and the velocity map imaging technique to yield velocity distributions resolved in three dimensions for a prototypical surface-adsorbate system. Nitric oxide adsorbed on Au(100) was photodesorbed using a 355 nm laser beam. The desorbed NO molecules were ionised in the gas-phase by resonance-enhanced multi-photon ionisation within a set of velocity map imaging optics. The NO molecules preferentially leave the surface along the surface normal with a very narrow angular distribution, indicating a non-thermal desorption process. [ABSTRACT FROM AUTHOR]

In this study, the analytical solution of steady hydromagnetic double exothermic combustible reaction fluid flow in a porous medium with convective cooling wall is presented. The viscous heating reactive liquid is totaling exothermic without consumption of material. The combustion reaction of the fluid takes place in a Poiseuille device, and it is been propelled by pressure gradient and pre-exponential bimolecular kinetics. The device is exposed to convective cooling to keep the reactive hydromagnetic fluid from distortion. The weighted residual method (WRM) is analytically used to get the numerical values for the dimensionless nonlinear governing equations. The solution to temperature and velocity distribution is carried out and the result is graphically depicted. The Nusselt number and skin friction coeffcient is also showed for some significant parameters engrained in the flow and the solution obtained is compared with numerical method. As obtained in the study, the second exothermic reaction term increases the combustion process; hence the term will assist in reducing toxic discharge from the engines that pollute the environment. The Frank-Kamenetskii parameter contributes highly to system thermo-fluid destruction; as such it must be monitored. [ABSTRACT FROM AUTHOR]

Contactless inductive flow tomography (CIFT) can reconstruct the complex 3-dimensional flow structure of the large-scale circulation in liquid metal filled Rayleigh-Bénard (RB) convection cells. The method relies on the precise measurement of weak magnetic fields induced by currents in the conducting liquid arising from the fluid motion in combination with primary excitation fields. The velocity distribution is reconstructed from the magnetic field measurements by solving a linear inverse problem using the Tikhonov regularization and L-curve method. A number of technical challenges have to be overcome to reach the desired accuracy of the measurement signals. In this paper we will describe our design of a new CIFT set-up for a large RB vessel with a diameter of 320mm and a height of 640 mm. We outline the major factors perturbing the measurement signal of several tens of nanoteslas and describe solutions to decrease mechanical drifts by thermal expansion to a sub-critical level to enable CIFT measurements for high-Rayleigh number flows. [ABSTRACT FROM AUTHOR]

This paper identifies laminar separation bubbles at the root or span-wise midsection of a rectangular wing using direct surface pressure measurements in the wind tunnel and analyses their behavior at different Reynolds numbers and angles of attack. The separation, transition, and reattachment locations are determined as functions of the angles of attack and the Reynolds number. The transition structure and turbulence characteristics in the separated shear layer are studied using laser Doppler velocimetry. Surface pressure data and simultaneously acquired velocity signals are correlated to show the pattern of growing disturbances in the shear layer. Surface oil flow visualizations clarified the wingtip and separation bubble's interactions near the leading edge of the wing at the higher angles of attack. Turbulence statistics are also calculated from the streamwise velocity distributions, and an apparent deviation is observed for the skewness and flatness values from the normal distributions in the near-wall region. The separation bubble effect on aerodynamic coefficients of a 3D rectangular wing root section is studied and reported. [ABSTRACT FROM AUTHOR]

The creation of an opening in a broad-crested weir body increases the discharge coefficient and reduces the water elevation behind the weir. In this study, three-dimensional numerical modeling is applied to investigate the water behavior, free-surface profiles, and velocity distributions over a broad-crested weir with one opening, two vertically arranged openings, and two horizontally arranged openings. The present study is limited to the above-described weir-opening arrangements. To determinate the most accurate turbulence model, results from the numerical simulation were compared with experimental data. Based on this comparison, the RNG turbulence model was chosen. The behavior of two horizontally arranged openings and the no-opening model were similar and critical flow occurred in two other models (one opening and two vertically arranged openings), downstream of the weir. Also, the maximum velocity in the models without openings was higher than in the other cases. [ABSTRACT FROM AUTHOR]

The sputtering of hexagonal boron nitride (h-BN) by impacts of energetic xenon ions is investigated using a molecular dynamics (MD) model. The model is implemented within an open-source MD framework that utilizes graphics processing units to accelerate its calculations, allowing the sputtering process to be studied in much greater detail than has been feasible in the past. Integrated sputter yields are computed over a range of ion energies from 20eV to 300eV, and incidence angles from 0° to 75°. Sputtering of boron is shown to occur at energies as low as 40eV at normal incidence, and sputtering of nitrogen at as low as 30eV at normal incidence, suggesting a threshold energy between 20eV and 40eV. The sputter yields at 0° incidence are compared to existing experimental data and are shown to agree well over the range of ion energies investigated. The semi-empirical Bohdansky curve and an empirical exponential function are fit to the data at normal incidence, and the threshold energy for sputtering is calculated from the Bohdansky curve fit as 35±2eV. These results are shown to compare well with experimental observations that the threshold energy lies between 20eV and 40eV. It is demonstrated that h-BN sputters predominantly as atomic boron and diatomic nitrogen, and the velocity distribution function (VDF) of sputtered boron atoms is investigated. The calculated VDFs are found to reproduce the Sigmund-Thompson distribution predicted by Sigmund's linear cascade theory of sputtering. The average surface binding energy computed from Sigmund-Thompson curve fits is found to be 4.5eV for ion energies of 100eV and greater. This compares well to the value of 4.8eV determined from independent experiments. [ABSTRACT FROM AUTHOR]

Experiments, analytic modeling, and numerical simulations are presented to characterize carbon plasmas produced by high-intensity (109 - 1013 W cm-2) lasers relevant to experimental laboratory astrophysics. In the large-scale limit, the results agree well with a self-similar isentropic, adiabatic fluid model. Laser-target simulations, however, show small-scale structure in the velocity distribution of different ion species, which is also seen in experiments. These distributions indicate that most of the plasma energy resides in moderate charge states (C+3-C+4), most of the mass resides in the lowest charge states, and the highest charge states move fastest. [ABSTRACT FROM AUTHOR]

Charge exchange from doubly charged rare gas cations to simple diatomics proceeds with a large cross section and results in populations of many vibrational and electronic product states. The charge exchange between Xe2+ and N2, in particular, is known to create N+2 in both the A and B electronic states. In this work, we present integral charge exchange cross section measurements of the Xe2+ + N2 reaction as well as axial recoil velocity distributions of the Xe+ and N+2 product ions for collision energies between 0.3 and 100 eV in the center-of-mass (COM) frame. Total charge-exchange cross sections decrease from 70 Ų to about 40 Ų with increasing collision energy through this range. Analysis of the axial velocity distributions indicates that a Xe2+ - N2 complex exists at low collision energies but is absent by 17.6 eV COM. Analysis of the axial velocity distributions reveals evidence for complexes with lifetimes comparable to the rotational period at low collision energies. The velocity distributions are consistent with quasi-resonant single charge transfer at high collision energies. [ABSTRACT FROM AUTHOR]

The study establishes different analytical model for velocity distribution, boundary shear stress, stage–discharge curves and their application to the trapezoidal compound channel. The analytical solution to the depth-integrated Navier–Stokes equations is used for the same, and their results are validated using experimental data and numerical solution. The parameters used to predict the three-dimensional characteristics of the flow field over compound channel in the analytical solution require modelling of friction factor, eddy viscosity coefficient and secondary current term. The Shiono and Knight model (SKM), which is an analytical solution for RANS equation through empiricism, is compared with two similar analytical-based models, viz. K-method and extended SKM, and with one numerical method, i.e. K–ε model through simulation based modelling. The results obtained in the analyses show that the secondary flow parameter plays a vital role and its significance proliferates near side slope where momentum transfers takes place from the main channel to the flood plain. The contrast in the results is shown with the help of variation in percentage error over the cross section, root mean square error and Nash–Sutcliffe efficiency (E). [ABSTRACT FROM AUTHOR]

A time-dependent 3D numerical model considering anode evaporation is developed for the high current vacuum arc (VA) under a realistic spatial magnetic field. The simulation work contains steady state 3D numerical simulation of high current VA considering anode evaporation at nine discrete moments of first half wave of 50 Hz AC current, transient numerical simulation of anode activity, and realistic spatial magnetic field calculation of commercial cup-shaped electrodes. In the simulation, contact opening and arc diffusion processes are also considered. Due to the effect of electrode slots, the simulation results of magnetic field and temperature of anode plate exhibit six leaves shape (SLS). During 6-8 ms, the strong evaporation of anode surface seriously influence the parameter distributions of VA. Ions emitted from anode penetrate into arc column and the axial velocity distribution on the anode side exhibits SLS. The ions emitted from anode surface have the same temperature with anode surface, which cool the arc plasma and lead to a relative low temperature area formed. The seriously evaporation of anode leads to the accumulation of ions near the anode, and then the current density is more uniform. [ABSTRACT FROM AUTHOR]

An improved nanosecond time-resolved Raman spectroscopy is performed to observe laser-driven shock propagation in the anthracene/epoxy glue layer. The digital delay instead of optical delay line is introduced for sake of unlimited time range of detection, which enables the ability to observe both shock loading and shock unloading that always lasts several hundred nanoseconds. In this experiment, the peak pressure of shock wave, the pressure distribution, and the position of shock front in gauge layer were determined by fitting Raman spectra of anthracene using the Raman peak shift simulation. And, the velocity of shock wave was calculated by the time-dependent position of shock front. [ABSTRACT FROM AUTHOR]

Particle image velocimetry (PIV) is a powerful image correlation method for measuring bulk velocity fields of flowing media. It typically uses optical images, representing quasi-two-dimensional experimental slices, to measure a single velocity value at each in-plane position. However, projection-based imaging methods, such as x-ray radiography or shadowgraph imaging, encode additional out-of-plane information that regular PIV is unable to capture. Here, we introduce a new image analysis method, named deep velocimetry, that goes beyond established PIV methods and is capable of extracting full velocity distributions from projected images. The method involves solving a deconvolution inverse problem to recover the distribution at each in-plane position, and is validated using artificial data as well as controlled laboratory x-ray experiments. The additional velocity information delivered by deep velocimetry could provide new insight into a range of fluid and granular flows where out-of-plane variation is significant. [ABSTRACT FROM AUTHOR]

An experimental method for determination of aerodynamic loads is presented. It is based on velocity vector field results obtained with Particle Image Velocimetry (PIV). As PIV is an optical measurement technique, the developed method for load determination can be defined as noninvasive. It is shown that the only information needed to estimate the lift and drag forces exerted on a body placed in the flow is a velocity distribution measured around the investigated object. Therefore, PIV results provide sufficient input experimental data to be used. Fundamental fluid mechanics theories were employed to develop algorithms for load estimation. Determination of the lift force is based on velocity circulation calculations. It is obtained by integrating the velocity field along a closed-loop encircling the body. An essential achievement made is the development of a procedure for finding an optimal size of the integration curve used for lift calculations. In the case of the drag force estimation, an analysis of fluid momentum changes has been used. The momentum deficit, within a given control volume containing the analysed aerofoil, is determined and related to the reaction drag force exerted on the body. Additionally, pressure field reconstruction based on velocity data, which enabled an application of small control surfaces and kept the drag estimation error at a satisfactorily low level, was introduced. The developed method was tested and verified with the reference computational fluid dynamics simulation results and applied further to the wind tunnel experimental data. A flow around the standard NACA0012 aerofoil at two flow regimes was investigated (Re= 0.7 × 10 5 and Re= 1.4 × 10 5 ). Lift and drag coefficient characteristics as a function of the angle of attack were obtained. An exceptional agreement between the experimental and reference numerical lift characteristics was attained (relative differences no larger than 5%). In the case of drag estimation, an acceptable level of similarity was observed (max. discrepancies below 20%). [ABSTRACT FROM AUTHOR]

In this paper, we extend the unified gas-kinetic wave-particle (UGKWP) methods to the multi-species gas mixture and multiscale plasma transport. The construction of the scheme is based on the direct modeling on the mesh size and time step scales, and the local cell's Knudsen number determines the flow physics. The proposed scheme has the multiscale and asymptotic complexity diminishing properties. The multiscale property means that according to the cell's Knudsen number the scheme can capture the non-equilibrium flow physics when the cell size is on the kinetic mean free path scale, and preserve the asymptotic Euler, Navier-Stokes, and magnetohydrodynamics (MHD) when the cell size is on the hydrodynamic scale and is much larger than the particle mean free path. The asymptotic complexity diminishing property means that the total degrees of freedom of the scheme reduce automatically with the decreasing of the cell's Knudsen number. In the continuum regime, the scheme automatically degenerates from a kinetic solver to a hydrodynamic solver. In the UGKWP, the evolution of microscopic velocity distribution is coupled with the evolution of macroscopic variables, and the particle evolution as well as the macroscopic fluxes is modeled from a time accumulating solution of kinetic scale particle transport and collision up to a time step scale. For plasma transport, the current scheme provides a smooth transition from particle-in-cell (PIC) method in the rarefied regime to the magnetohydrodynamic solver in the continuum regime. In the continuum limit, the cell size and time step of the UGKWP method are not restricted by the particle mean free path and mean collision time. In the highly magnetized regime, the cell size and time step are not restricted by the Debye length and plasma cyclotron period. The multiscale and asymptotic complexity diminishing properties of the scheme are verified by numerical tests in multiple flow regimes. [ABSTRACT FROM AUTHOR]

The present article provides a detailed analysis of entropy generation on the unsteady three-dimensional incompressible and electrically conducting magnetohydrodynamic flow of a Casson nanofluid under the influence of mixed convection, radiation, viscous dissipation, Brownian motion, Ohmic heating, thermophoresis and heat generation. At first, similarity transformation is used to transform the governing nonlinear coupled partial differential equations into nonlinear coupled ordinary differential equations, and then the resulting highly nonlinear coupled ordinary differential equations are numerically solved by the utilization of spectral quasi-linearization method. Moreover, the effects of pertinent flow parameters on velocity distribution, temperature distribution, concentration distribution, entropy generation and Bejan number are depicted prominently through various graphs and tables. It can be analyzed from the graphs that the Casson parameter acts as an assisting parameter towards the temperature distribution in the absence of viscous and Joule dissipations, while it has an adverse effect on temperature under the impacts of viscous and Joule dissipations. On the contrary, entropy generation increases significantly for larger Brinkman number, diffusive variable and concentration ratio parameter, whereas the reverse effects of these parameters on Bejan number are examined. Apart from this, the numerical values of some physical quantities such as skin friction coefficients in x and z directions, local Nusselt number and Sherwood number for the variation of the values of pertinent parameters are displayed in tabular forms. A quadratic multiple regression analysis for these physical quantities has also been carried out to improve the present model's effectiveness in various industrial and engineering areas. Furthermore, an appropriate agreement is obtained on comparing the present results with previously published results. [ABSTRACT FROM AUTHOR]

Hybrid simulations of Venus have produced nightside structure. It is believed these are the first simulations to produce the structure reported by spacecraft such as the Pioneer Venus Orbiter (PVO). The simulations reveal that the structure is created by the ∇ Pe ambipolar electric field when it aligns with local IMF (interplanetary magnetic field) direction. Thus, the orientation of the IMF in and near the ionosphere controls where on the nightside the tail structure will occur. The structure size and density is found to agree well with that measured by the PVO spacecraft. Further, comparisons with ion energy and velocity distributions also agree well with the summary conclusions from a variety of PVO papers and with some nightside observations by Venus Express. The agreement between the data and simulations lends confidence that the simulation results have merit. [ABSTRACT FROM AUTHOR]

Significance of different effects is studied when a travelling magnetic field interacts with an electrically conducting flow. Numerical experiment is carried out by using the open source softwares OpenFOAM, Elmer and EOF-library. The influence of individual electromagnetic effects on the flow behavior depending on the Stuart number is considered and the evolution of the fluid flow profile in a duct is discussed. It is shown that the shape of the Hartmann velocity distribution and velocity profile in the duct depends on the spatial distribution of the travelling magnetic field. The obtained results indicate that the longitudinal end effect influences the velocity distribution along the duct, and the transverse end effect does not change qualitatively the behavior of flows, but affects the flow velocity magnitude. A relationship between the occurrence of reverse flows and the calculated similarity criteria is demonstrated. [ABSTRACT FROM AUTHOR]

The geometry of a duct cross-section has a significant influence on the velocity distribution and pressure drop of liquid metal flow subjected to a transverse magnetic field. In this paper, liquid metal flows in an electrically conducting circular pipe and in a pipe with V-shaped strips at the inner wall are numerically analyzed using a laminar model by an in-house MHD solver developed in the OpenFOAM environment. Distributions of velocity, induced electric current and pressure drop in three kinds of pipes have been analyzed. The effect of the position and depth of V-shaped strips on the velocity distribution and on the pressure drop have been studied. Numerical results show that V-shaped strips in Roberts layers can change the electric current direction from perpendicular to oblique to the magnetic field. This decreases the Lorentz force in Roberts layers and enhances the intensity of the jets. Velocity jets are observed at the bottom of the V-shaped strips attached to Hartmann layers. Moreover, a low-velocity belt forms in the central region of the fluid. The MHD pressure drop in pipes with V-shaped strips is a little higher than that in a normal circular pipe. The increase of the number and depth of V-shaped strips will increase the MHD pressure drop. The relative difference of the pressure drop coefficient decreases with increasing Hartmann number. The duct cross-section geometry can be used to control MHD flow, and the obtained results can be referenced in the design of the liquid metal blanket. [ABSTRACT FROM AUTHOR]

Modeling and computational framework are carried out to explore the influence of irregular heat source/sink and viscous dissipation on magnetohydrodynamic flow of Newtonian/non-Newtonian liquid due to a curved stretching sheet. An appropriate similarity conversion is implemented to convert the basic flow equations into dimensionless ODE's and they being solved by means of Runge-Kutta method with shooting scheme. Numerical outcomes of drive, thermal and concentration distributions, also wall friction, thermal and mass transport rates are explored through graphical trends and tabular values. Simultaneous solutions are drawn for Newtonian and non-Newtonian liquids. The major findings of this study are rising the curvature parameter values inflates the momentum boundary layer, ergo develops the velocity distributions. Also, the heat transfer rate under the influence of irregular heat generation/absorption and dissipation effects is remarkably large for non-Newtonian liquid as compared with Newtonian liquid. [ABSTRACT FROM AUTHOR]

In this study, we present a novel procedure to simulate the velocity distribution of a narrow sewer channel using a combination of a simple and accurate machine learning tool, namely, extreme learning machine (ELM). We also examined the uncertainty associated with the model in simulating the more complex velocity–depth profiles in narrow sewer channels using the 95 percent predicted uncertainties (95PPU%) and d-factor indices. The data for estimating the velocity distribution were measured at a municipal sewer pipe in France. We measured the velocity distribution in a cross section for 10 different depths with width-to-depth ratios ranging from 1.75 to 2.44. The new ELM model has the 95PPU% and the d-factor of 53.25% and 0.36, respectively, in the training dataset and 84.93% and 1.9 in the test dataset. The error analysis confirmed that ELM model outperforms all existing models for predicting velocity profile in narrow sewers. The proposed method is compared with existing methods, and it appears that in addition to being simpler and having no limitations, this model exhibits better performance as well (root mean square error (RMSE) = 0.04 and mean absolute percentage error (MAPE) = 3.56%). [ABSTRACT FROM AUTHOR]

Breaching flow slides are accompanied by the generation of turbidity currents. Measurements of these currents are critical for understanding the interaction between the turbidity current and the slope surface, as well as for the validation of numerical models. However, there are insufficient data available detailing the velocity distribution or sediment concentration in these currents. This paper presents experimental results of unique large‐scale physical model experiments on breaching flow slides conducted at the water lab of Delft University of Technology, The Netherlands. The model tests were carried out in a tank with a subaqueous sandy slope steeper than the internal friction angle for that sand. We performed a series of novel experiments in which various nonvertical initial slope angles were tested, providing the first quantitative data for such initial conditions. Measurements of flow thickness, velocities, and sediment concentrations are obtained, providing the spatial and temporal evolution of the turbidity currents and the resulting underwater slope morphology. The experimental results reveal that the breaching‐generated turbidity currents are self‐accelerating and that they dominate the problem of breaching flow slides. We evaluated the theoretical expression for the erosion velocity in the case of pure beaching—where the turbidity current has no influence on the erosion—and it overestimated the observed erosion. The analysis of the failure evolution showed that the sand erosion rate increases due to the acceleration of the turbidity currents downslope, until a certain threshold, leading to the steepening of the breach face and thus the occurrence of surficial slides. Key Points: We conducted novel experiments where nonvertical initial breach faces were tested, providing the first quantitative data for such conditionsWe provide direct measurements visualizing the structures of velocity and sediment concentration for breaching‐generated turbidity currentsBreaching‐generated turbidity currents are self‐accelerating; sediment entrainment and flow velocity enhance each other [ABSTRACT FROM AUTHOR]

Reservoir sedimentation usually occurs in rivers that carry heavy amounts of silt. Setting reasonable schedules for drainage hole operations can balance the reservoir sediment levels and downstream river morphology. China's Yellow River is well known for its abundant sediment supply. The Xiaolangdi Reservoir is the key control project for the main stem of the Yellow River, and its sediment accumulation is especially serious. Preventing sedimentation before the gates is an important issue. The characteristics of the flow and sediment before the intake towers under scheduled drainage hole operations should be thoroughly researched. In this study, a three-dimensional numerical model was established based on MIKE 3. Variations of the flow structure, sediment concentration, and sedimentation elevation were the parameters studied under the scheduled operations. The results showed that the features of the bend flow are developed during the model phase. The velocity distribution in the vertical direction does not follow the general logarithmic distribution law of open channels. Scouring funnels appear during the development of the sedimentation surface before the intake towers. The sedimentation elevation is lower than the permissible value and has no influence on gate operations. This paper can provide a reference for similar research. [ABSTRACT FROM AUTHOR]

Gasoline direct injection engines are highly dependent on the spray performance and associated combustion quality. The spray formation depends on many factors, namely internal flow characteristics, injection conditions, ambient conditions and fuel properties. There have been many studies performed to obtain a better understanding of these factors in recent years. In contrast to the others, studies on the internal flow characteristics are often performed numerically, as such, relevant experimental data is still lacking. Experimental investigations of the internal flow, such as flow turbulence, velocity distribution and cavitation are especially challenging under realistic conditions. Therefore, these conditions are generally simplified to diminish the demand for specialized experimental equipment and facilitate the measurements. In this regard, experimental data under relevant conditions are of high interest in the spray community. This work is focused on the internal flow study of multi-hole transparent nozzles under transient conditions at 1:1 geometrical scale. Injection pressure up to 100 bar is applied. The formation and development of string cavitation inside the nozzle hole are observed and presented in detail. For that, a novel ultra high-speed imaging technique at 5 MHz is applied. This technique in combination with the micro particle image velocimetry method, is then able to help to produce the velocity distribution of the internal flow. The velocity data is used further to reconstruct the pressure inside the nozzle by applying the Reynolds-averaged Navier–Stokes equations. Thus, the unique experimental data for the pressure distribution of the liquid fuel is obtained. [ABSTRACT FROM AUTHOR]

This paper presents a µPIV measurement of the 3D2C velocity distribution of Taylor droplets moving in a square horizontal microchannel at Ca c = 0.005 and Re c = 0.051 . We reconstruct the third velocity component and present an accuracy assessment of the reconstruction based on a volume flow balance of the 3D3C velocity field. The velocity field allows the investigation of the 3D flow features such as stagnation regions and the shear rate distribution. The maximum shear rate is located at the entrances and exits of the wall films and at the corner flow (gutter) bypassing the Taylor droplet. The regions of high strain correspond to the cap positions of the Taylor droplets. An experimental data set allows visualization of the streamlines of the velocity distribution on the interface of a Taylor droplet and to directly relate it to the main and secondary vortices of the droplet phase velocity field. The measurement data are provided as a digital resource for the validation of numerical simulation or further assessment. [ABSTRACT FROM AUTHOR]

The Hayabusa2 spacecraft investigated the small asteroid Ryugu, which has a rubble-pile structure. We describe an impact experiment on Ryugu using Hayabusa2's Small Carry-on Impactor. The impact produced an artificial crater with a diameter >10 meters, which has a semicircular shape, an elevated rim, and a central pit. Images of the impact and resulting ejecta were recorded by the Deployable CAMera 3 for >8 minutes, showing the growth of an ejecta curtain (the outer edge of the ejecta) and deposition of ejecta onto the surface. The ejecta curtain was asymmetric and heterogeneous and it never fully detached from the surface. The crater formed in the gravity-dominated regime; in other words, crater growth was limited by gravity not surface strength. We discuss implications for Ryugu's surface age. [ABSTRACT FROM AUTHOR]

In traditional surface wave tomography based on seismic noise, 2D phase or group velocity distribution is obtained by performing pure‐path inversion after extracting interstation velocities based on the noise cross‐correlation function. In this paper, we show that 2D surface wave phase velocity maps of adequate quality can be obtained directly, without interferometry, by beamforming the ambient noise recorded at array of stations. This method does not require a good azimuthal distribution of the noise sources. The 2D surface wave phase velocity map is obtained by moving the subarrays within a larger dense network of stations. The method is illustrated with seismic noise recorded by over 600 stations of the ChinArray (Phase II). We obtain 2D Rayleigh wave phase velocity maps between 7 and 35 s in Northeastern (NE) Tibetan Plateau and adjacent regions that compare well with results obtained with other methods. The shear wave velocity model is then derived by inverting the phase velocity with depth. The model correlates well with geology and tectonics in NE Tibet. Two clear mid‐to‐low crustal low‐velocity zones are observed at 15‐ to 35‐km depth beneath the Songpan‐Ganzi terrane and Northwestern Qilian Orogen, possibly facilitating lower crustal flow in this key region for the tectonic evolution of NE Tibet. Key Points: We present a beamforming method to extract the phase velocity of the Rayleigh wave directly from the ambient noise, without interferometryA 3D Vs model of NE Tibet is established by inverting the obtained Rayleigh wave velocity mapsMid crustal low velocity zones are observed in the Songpan‐Ganzi Terrane and in NW Qilian Orogen [ABSTRACT FROM AUTHOR]

We present a statistical study of the ion upflow associated with subauroral polarization streams (SAPS) in the ionospheric subauroral region at different substorm times using three Defense Meteorological Satellite Program satellite (F16–F18) data for five years (2010–2014) in the Northern Hemisphere. The results show similarities between SAPS and the ion upflow at different intensity of substorms both in occurrence rate distribution and velocity distribution. In comparison to SAPS, the distribution of the ion upflow shows the smaller occurrence region and lower velocity. We also find that frictional heating plays an important role in ion upflow from the SAPS region. The intense substorms can trigger strong SAPS channels, enhanced frictional heating, and large ion upflow. In addition, there is a moderate linear correlation between SAPS velocity and field‐aligned velocity that is consistent with some previous findings. Our results also show that frictional heating can gradually dominate the ion upflow process in intense substorms, while it may not be the only factor to affect the whole upflow process. Key Points: Ion upflow is frequently observed near the SAPS flow channel, with similar distributions in the occurrence and velocity as SAPSStatistical analysis shows that field‐aligned (ion upflow) velocity has moderate linear correlation with SAPS velocity indeedFrictional heating can gradually dominate the ion upflow process, while it may not be the only factor to affect such process [ABSTRACT FROM AUTHOR]