Mean Kinetic Energy Research Articles

Inhomogeneity of Structural and Dynamical Characteristics of Dusty Plasma in a Gas Discharge

Dusty plasma crystals are commonly considered as spatially homogeneous structures with equal values of their structural and thermodynamic parameters in various regions of the system. Inhomogeneity of the interparticle distance, the amplitude of thermal particle oscillations, the Lindemann parameter, and the coupling parameter is shown to arise even in a system of particles with a simplified interaction model including a screened Coulomb potential and a parabolic trap. The kinetic energy distribution for particles in an inhomogeneous dusty plasma monolayer is investigated: it is shown that the mean kinetic energy of particles in the central part of the structure can differ significantly from the mean kinetic energy of particles on its periphery due to the inhomogeneity of structural parameters. The detected effects are verified using analytical methods and numerical simulations and by comparison with a dusty plasma experiment in a dc glow discharge. The results obtained are of great importance for investigating finite systems of like charges in a trap and studying the mechanism of phase transitions in dusty plasma systems.

ZnO thin films grown at different plasma energies by the laser ablation of metallic Zn with a 532 nm wavelength

In this work, structural, optical and electrical properties of ZnO thin films grown by laser ablation of a Zn metallic target on oxygen atmosphere using the 532 nm emission of the second harmonic of a Nd:YAG laser, are studied. Different mean kinetic energies of the plasma (Ek) at fixed ion density (Np) were used as control parameters. X-ray diffraction profiles show the presence of a width (002) peak together with a peak associated with the (101) reflection. Changes in Ek affect the crystallinity of the samples. An intense PL emission in the visible range of the spectra associated with a majority intrinsic donor defects can be observed. The films showed an unusual low electrical resistivity as compared to the commonly reported values for undoped ZnO thin films.

Seasonal and interannual variability of vertical turbulent exchange coefficient in the Black Sea pycnocline in 2013–2016 and its relation to variability of mean kinetic energy of surface currents

In this paper, we analyze seasonal and interannual variability of vertical turbulent diffusion coefficient (Kt). Our calculations are based on the time series from 2013 to 2016, obtained in the north-eastern Black Sea within the depth range of 30–220 m by using an Aqualog profiler. The synchronized measurements included vertical profiles of sea temperature, conductivity, density, and current velocity. The calculations were performed according to a well-known parameterization of vertical turbulent exchange coefficient based on the Richardson number, originally proposed by Munk and Anderson (1948). We found that strongest vertical mixing occurred from October to March and was located above the isopycnals of 14.0–14.2, reaching the maximum of 8.8 × 10−4 m2/s in December. In this period, Kt values exceeding 10−4 m2/s were observed in the water column down to the isopycnal of 15.0 and even below. Mixing intensity during the cold seasons of the year grew to 1.2 × 10−4 m2/s in average, which was twice as high as that in the warm seasons. Analysis of temporal variability of the mean surface kinetic energy (MKE), derived from altimetry data, showed a high correlation between the MKE and column-averaged Kt values on both seasonal and interannual time scales. The Kt variations lagged those of MKE by about a month, probably owing to a gradual deepening of current jets and an increase of mixed layer depth from October to January.

Microscopic Study of Proton Kinetic Energy Anomaly for Nanoconfined Water.

The reported anomalies of the proton mean kinetic energy, Ke(H), in nanoconfined water, as measured by deep inelastic neutron scattering (DINS), constitute a longstanding problem related to proton dynamics in hydrogen-bonded systems. A considerable number of theoretical attempts to explain these anomalies have failed. The mean vibrational density of states (VDOS) of protons in water nanoconfined inside single wall carbon nanotubes (SWCNTs) is calculated as a function of temperature and SWCNT diameter, DCNT, by classical molecular dynamics (MD) simulation using the TIP4P-2005f water model. The calculated VDOS are utilized for deducing the mean kinetic energy of the water protons, Ke(H), by treating each phonon state as a harmonic oscillator. The calculation depicts a strong confinement effect as reflected in the drop of the value of Ke(H) at 5 K for DCNT < ∼12 Å, while absent for larger diameters. The results also reveal very significant blue and red shifts of the stretching and bending modes, respectively, compared to those in bulk ice, in agreement with experiment.

Bose-Einstein condensation of correlated atoms in a trap

The Bose-Einstein condensation of correlated atoms in a trap is studied by examining the effect of inter-particle correlations to one-body properties of atomic systems at zero temperature using a simplified formula for the correlated two body density distribution. Analytical expressions for the density distribution and rms radius of the atomic systems are derived using four different expressions of Jastrow type correlation function. In one case, in addition, the one-body density matrix, momentum distribution and kinetic energy are calculated analytically, while the natural orbitals and natural occupation numbers are also predicted in this case. Simple approximate expressions for the mean square radius and kinetic energy are also given.

Kinetic Bohm criterion in the Tonks-Langmuir model: Assumption or theorem?

New first integral is found in the collision-free Tonks-Langmuir model. The integral has a clear physical interpretation: the weighted mean inverse kinetic energy of ions, evaluated in the quasineutral approximation, equals (kTe/2)−1 at all points in space. This feature is also present in the full (not relying on the assumption of quasineutrality) model: for small values of the Debye length, the weighted mean inverse kinetic energy is with good accuracy equal to (kTe/2)−1 in the entire region of quasineutral plasma, including in the vicinity of the space-charge sheath. These results constitute a mathematical proof of the kinetic Bohm criterion and provide a new look at the problem, which has been discussed for several decades. In particular, these results show that the much-debated problem of divergence for slow ions stems from a misinterpretation. Moreover, these results explain why no unique form of kinetic Bohm criterion, modified with the account of ionization and/or collisional and/or geometrical effects in the sheath, has emerged: it cannot be postulated in a nonarbitrary way since there is simply no definite value of the inverse mean kinetic energy with which the ions enter the sheath, if these effects are non-negligible.

The development of a 3D computational mesh to improve the representation of dynamic processes: The Black Sea test case

The Black Sea is one of the largest land-locked basins in the world. Due to the vulnerability of its unique marine ecosystem, accurate long-term modelling of its hydrodynamics is needed. In this study, we first compare the skills of four NEMO based Black Sea models in a free-run which use different discretization schemes. We find that the most accurate results are obtained with the model (named CUR-MEs) which has a 3D mesh optimized for the prevailing dynamics. This new model uses a curvilinear horizontal grid with increased resolution (≈950m) over the shelf-break and lower resolution (≈6km) in areas where the scale of relevant processes is larger (≈20km). In the vertical, CUR-MEs uses Multi-Envelope curved s-levels designed to optimize the representation of the Cold Intermediate Layer (CIL). Second, we compare CUR-MEs in free-run with the data-assimilative CMEMS reanalysis. Validation against independent observations shows that the two models have similar skills - e.g., the difference between the mean BIAS and RMSE of the two models is ≈0.15°C for temperature and ≈0.07 for salinity. The CUR-MEs model, even without data assimilation, is able to correctly reproduce the details of the variability of the Mean Kinetic Energy and the CIL.

Effect of external magnetic field on wakefield generation in underdense plasma slab using backward semi-Lagrangian Vlasov code

Laser wakefield excitation in the interaction of femtosecond laser pulse with an underdense thin magnetized plasma slab is studied by one dimensional relativistic Vlasov-Maxwell system of equations. The interaction is modeled by relativistic Vlasov equation in propagation direction of laser pulse and fluid equations in transverse direction. Backward semi-Lagrangian method (BSL) is used for numerical solution of Vlasov equation. Generation of wakefields by a right and left handed circularly polarized (RCP) and (LCP) laser pulses in the interaction with nonmagnetized and magnetized plasma slab are examined and compared. Two directions are considered for external magnetic field, parallel and antiparallel to direction of laser pulse propagation. The results show that applying magnetic field along (opposite to) the propagation direction of RCP (LCP) laser pulse increases amplitude of density steepening and consequently wakefields amplitude, and mean kinetic energy of electrons compared with nonmagnetized plasma. The results are in complete agreement with previous analytical and numerical reports.

Mean kinetic energy distribution in finite-size wind farms: A function of turbines’ arrangement

In this work the redistribution and recovery of mean kinetic energy in a realistic, finite size wind farm is studied for neutral atmospheric boundary layer conditions. Five different wind farm configurations, with different wind turbine arrangements, are considered, with four different inter-turbine spacings. By means of a localized control volume analysis, this work quantifies the mean kinetic energy recovery mechanisms as a function of downstream distance from the wind farm leading edge. Results illustrate the dependence of the mean kinetic energy distribution on the turbines’ arrangement and the spatial evolution of the dominant transport mechanisms (advection and vertical flux). In the first rows of turbines, advection dominates the wake recovery, while for the last rows of turbines vertical flux of mean kinetic energy is the dominant transport mechanism. In between, a smooth transition exists between both mechanisms. From the results a low-order power output predictor model for a finite size wind farm is developed. This model allows estimating the harvested power at each wind turbine row with only the geometrical wind farm layout as an input. The low-order model is compared with other published models and validated using published experimental measurements. The new model performs very well, with errors smaller than 5%.

Flow kinematics and air entrainment under laboratory spilling breaking waves

Laboratory measurements of velocity fields and void fraction under spilling breaking waves are presented. Modified particle image velocimetry was used to quantify the flow kinematics and turbulence while fibre optic reflectometry was used to quantify the breaking-induced air entrainment inside the aerated region of the spilling breakers. The measurements confirmed that the ratio of the local energy flux and the local energy density sharply increases and exceeds the threshold value of 0.85 near the onset of breaking. Based on the measured velocity fields, the maximum horizontal velocity reached at the onset of breaking, with being the phase speed of the primary breaking wave. The maximum horizontal velocity then reached at approximately one-quarter of a wave period after the onset of breaking. The results also confirmed that the wavelet-educed turbulence length scale estimates are comparable to the previously reported values with different wave parameters, suggesting that the dependence of the size of energy-containing eddies on the physical scales of the breaking waves is insignificant. The measured void fraction showed a similarity profile although the measurement locations span one wavelength. The mean kinetic energy, turbulent kinetic energy, potential energy and total energy were quantified with and without the void fraction being accounted for. Results show near 60 % and 40 % overestimates of the kinetic energy and the potential energy if the void fraction is not considered. After correcting the density variation due to air entrainment, the total energy dissipated following an exponential decay, with 43 % and 65 % energy being dissipated at one and two wavelengths downstream from the breaking point, respectively. The equipartition assumption was found to be applicable before and during the entire breaking process in the present spilling breakers.

Fluid carving

We present a method for intelligently resizing fluid simulation data using seam carving methods. While advances in post-processing techniques have allowed artists greater control over content late in the production process, this technology has largely remained confined to image processing. Our fluid carving system allows fluid simulation post-processing by performing content-aware non-uniform scaling on baked-out fluid simulation data. Specifically, we extend video seam carving techniques to 4-dimensional animated fluid volume data with a graph cut energy function based on mean curvature and kinetic energy. To reduce the complexity of performing graph cuts on 4D data, we provide a new graph construction formulation that greatly reduces the run-time and memory consumption, which are otherwise prohibitively expensive. We demonstrate that our system is useful for post-production fluid simulation changes and editable fluid FX libraries.

A comparison of entrainment in turbulent line plumes adjacent to and distant from a vertical wall

We present simultaneous two-dimensional measurements of the velocity and buoyancy fields on a central vertical plane in two-dimensional line plumes: a free plume distant from vertical boundaries and a wall plume, adjacent to a vertical wall. Data are presented in both an Eulerian and a plume coordinate system that follow the instantaneous turbulent/non-turbulent interface (TNTI) of the plume. We present measurements in both coordinate systems and compare the entrainment in the two flows. We find that the value of the entrainment coefficient in the wall plume is greater than half that of the free plume. The reduction in entrainment is investigated by considering a decomposition of the entrainment coefficient based on the mean kinetic energy where the relative contributions of turbulent production, buoyancy and viscous terms are calculated. The reduced entrainment is also investigated by considering the statistics of the TNTI and the conditional vertical transport of the ambient and engulfed fluid. We show that the wall shear stress is non-negligible and that the free plume exhibits significant meandering. The effect of the meandering on the entrainment process is quantified in terms of the stretching of the TNTI where it is shown that the length of the TNTI is greater in the free plume and, further, the relative vertical transport of the engulfed ambient fluid is observed to be 15 % greater in the free plume. Finally, the turbulent velocity and buoyancy fluctuations, Reynolds stresses and the turbulent buoyancy fluxes are presented in both coordinate systems.

The Cooling Effect of Beam Self-Fields on the Photocathode Surface in High Gradient RF Injectors

The intrinsic slice emittance of the emitted electrons on the photocathode surface at each moment during the transient photoemission process depends on the transverse size of the slice and the mean kinetic energy of the electrons within the slice. The latter relies on the surface barrier potentials of the cathode material at a fixed wavelength of the incident light, and is thus significantly influenced by the presence of strong rf and beam self-fields at /close to the cathode surface. This is, in particular, the case in high brightness injectors for modern free electron lasers. In this article, the beam self-fields are determined in a self-consistent approach, based on which improved transverse and temporal emission distributions are obtained. The nonlinear correlations of the intrinsic surface slice emittance within the bunch are shown for multiple bunch charges. A peak to peak variation of the intrinsic surface emittance is estimated as 30% for the highest charge-density case considered in this paper. An overall reduction of the average intrinsic emittance is computed as 10% accordingly. The cooling effect on the cathode surface is enhanced as the local space-charge density rises. The impacts of the cooling effect on downstream beam qualities are demonstrated through particle tracking simulations based on the injector setup at the Photo Injector Test Facility at DESY in Zeuthen (PITZ).

Ventricular vortex loss analysis due to various tricuspid valve repair techniques: an ex vivo study.

The deteriorating nature of severe functional tricuspid regurgitation (FTR) has led to the heightened interest in this pathology. However, therapies are heterogeneous and an ideal technique is uncertain. The hemodynamic impact on the cardiac chamber following therapeutic repairs has not been well studied, while its analysis could be used to predict the treatment success. In this study, the hemodynamics of the right ventricle (RV) after 1) clover edge-to-edge tricuspid repair, and 2) double orifice tricuspid repair was evaluated in three right heart models using an ex vivo pulsatile platform emulating severe FTR with the aid of stereoscopic particle image velocimetry. Although all repairs substantially reduced tricuspid regurgitant area, they resulted in a more than 50% reduction in diastolic tricuspid valve (TV) opening area. Splitting the TV orifice into multiple smaller orifices by both repairs eliminated the ring-shaped vortical structure inside the RV observed in FTR cases. Postrepair RV domain was mostly occupied with irregular vortical features and isolated vortex residuals. Moreover, vortical features varied among repair samples, indicating enhanced sensitivity of RV flow to postrepair TV morphology. Compared with clover repair, double orifice subjected the RV to enhanced swirling motions and exposed more regions to vortical motions, potentially indicating better rinsing and lower risk of mural thrombus formation. Double orifice repair increased the levels of RV mean kinetic energy and viscous energy loss than those observed in clover repair, although the impact of these on the cardiac efficiency remains unclear. These preliminary insights could be used to improve future treatment design and planning.NEW & NOTEWORTHY While clover and double orifice tricuspid repairs markedly improved leaflet coaptation, they substantially reduced diastolic tricuspid opening area. Postrepair right ventricle (RV) exhibited specific hemodynamic traits, including the loss of ring-shaped vortical structure and the enhanced sensitivity of RV flow to postrepair tricuspid valve morphology. Compared with clover technique, double orifice repair led to higher swirling motions in the RV domain, which could indicate lower risk of mural thrombus formation.

Dynamical Origin of the Total and Zero-Point Kinetic Energy in a Quantum Fluid.

By applying an exponential mode analysis to ring polymer molecular dynamics simulations of dense fluid parahydrogen, we find that the dynamical processes establishing the time behavior of the Kubo velocity autocorrelation function display the same nature as those already observed in high-density classical fluids. This result permits us to demonstrate that the exponential mode decomposition is a unique tool to identify which dynamical processes lead to one of the most notable properties of quantum fluids: the large value of the mean kinetic energy per particle and the importance of the zero-temperature quantum effects in determining it.

Solids flow pattern in cold flow mockup of fluidized bed gasifier

We report solids flow pattern in a laboratory-scale fluidized bed of coal and ash mixtures. Suitable tracers were designed and deployed to determine the solids flow path of a typical particle through Radioactive Particle Tracking (RPT). Experiments were conducted in a cylindrical bed of 0.1 m in i.d. with two inventory compositions, namely, 70% Coal + 30% Bottom Ash (Composition I) and 20% Coal + 80% Bottom Ash (Composition II). Comparative analysis of RPT measurements yielded overall bed behavior, which was quantified in terms of time-averaged mean velocity, solids flux, RMS velocity, and kinetic energy per unit volume of the coal – bottom ash mixture. The mean axial velocity and solids flux profile indicated the influence of strong slugs on the solids flow patterns.

Turbulence characteristics in a rough open channel under unsteady flow conditions

ABSTRACT Most open channel flows are generally unsteady in nature. Very few studies have been carried out in the past to investigate the turbulence characteristics in unsteady open channel flows over a rough bed at different test reaches. In the present study, experiments are conducted for two different flow depths over a rough bed and hydrographs are passed at the inlet of a rectangular flume. With consideration of laboratory constraints, the present study characterizes the unsteady flow as high catchment with long duration flood. The behavior of velocities in both the rising limb and falling limb for same flow depth is observed. Classical hysteresis effect of stage-discharge (h ~ Q) rating curve is illustrated. The present study investigates the turbulent intensities and Reynolds stresses under unsteady flow conditions. The turbulence intensities and Reynolds stresses in the rising limb are higher than that of the falling limb at same flow depth. Turbulence characteristics, i.e. turbulent kinetic energy (TKE), mean kinetic energy (MKE) and turbulent kinetic dissipation rate are also analyzed. It is found that the turbulence intensities, Reynolds stresses, and Turbulence characteristics are gradually decreased towards the downstream reaches.

Analysis of flow at the vicinity of vegetation stems in the floodplain of a compound open channel

ABSTRACT An analysis of flow was carried out in this study to find the effects of trees on the flow structure in a straight compound open channel. To resemble the vegetation stem, two rows of vertical rods were installed on the floodplain of an asymmetrical compound channel. Two-dimensional flow velocity was measured using Particle Image Velocimetry. The results showed a decreasing trend in turbulent kinetic energy and turbulent intensity along the floodplain. At low flow depth, a significant decrease was observed in mean velocity and kinetic energy. Similar reduction was observed at the intersection of floodplain and main channel and around the stems. Under this condition, the direction of velocity vectors changed from floodplain to the main channel. However, this trend was reversed at higher flow depths. This reversal was due to the changes in momentum transfer and shear stress at the intersection of floodplain and main channel. Additionally, a numerical analysis showed that vortices are formed at the junction of the floodplain and main channel.

LES of the Gas-Exchange Process Inside an Internal Combustion Engine Using a High-Order Method

High-order, wall-resolved large eddy simulations (LES) using the spectral element method (SEM) were performed to investigate the gas-exchange process inside a laboratory-scale internal combustion engine (ICE) and study the in-cylinder flow evolution. Using a stabilizing filter, over 30 engine cycles were simulated to generate data for statistical analysis, which demonstrated good agreement in the mean and root mean-squared (rms) phase-averaged velocity fields across three different filter parameter/resolution combinations. The large scale flow motion was characterized during each stage of the engine cycle. Tumble ratio profiles indicate peak values during the intake stroke which decay during compression and are almost non-existent thereafter. The tumble breakdown process is quantified by investigating the evolution of the mean and turbulent kinetic energy over the full cycle, and its effect on the evolution of the momentum and thermal boundary layers is discussed. Algorithmic advances to the computational fluid dynamics (CFD) solver Nek5000, employed in the current study, resulted in significant reduction in the wall-time needed for the simulation of each cycle for mesh resolutions of at least an order of magnitude higher than the current state-of-the-art.

Characteristics and evolution of a coastal mesoscale eddy in the Western Bay of Bengal monitored by high-frequency radars

Evolution of a coastal cyclonic eddy has been investigated using surface current observations from high-frequency radar (HFR) along the western Bay of Bengal (BoB) near Andhra Pradesh coast during October-December 2015. The HFRs tracked the genesis of the cyclonic eddy from early October, which persisted throughout November and dissipated after mid-December within the shelf-slope regions of HFR domain along the western boundary of BoB. A vector-based technique has been adapted to detect and track the mesoscale cyclonic eddy. The eddy is observed to propagate with a mean speed of ∼0.27 m s−1 (23.36 km day−1). It is asymmetric in nature with an average radius of ∼90 (80) km along the eastern and western (northern and southern) sides of the cyclonic eddy aligned along-shelf. The eddy has been characterized based on the Eulerian parameters; normalized vorticity (∼0.75), divergence (∼0.20), strain (∼0.25), and Okubu-Weiss (OW) parameter (−0.7 × 10−9 s−2). Positive vorticity and divergence, along with lower strain at the eddy center, justify the cyclonic eddy. The negative values of OW parameter show good agreement with the eddy-cores detected. Kinematics show that the Rossby number (R0) varies in the range 0.6–1.2, depicting that the cyclonic eddy is associated with mesoscale dynamical features and matches perfectly with the geostrophic balance. The eddy-induced upwelling signatures are observed from the subsurface temperature and salinity structures. The upwelling is well supported by positive (∼11 × 10−7 N m−3) wind stress curl during November. The sea surface temperature (SST), surface chlorophyll-a concentration as well as sea surface salinity (SSS) associated with the cyclonic eddy, show the advection of warm waters from the open ocean and low saline cold waters from the coastline. This study reveals that the eddy evolved due to baroclinic instability, well indicated by positive values of T2 (rate of conversion of mean potential energy to eddy potential energy) and lower values of Brunt–Väisälä Frequency (N2), whereas growth and intensification of the eddy are attributed to barotropic instability, supported by the positive values of T4 (the conversion of mean kinetic energy to eddy kinetic energy).