Relative Kinetic Energy Research Articles

Lagrangian Irreversibility and Energy Exchanges in Rotating-Stratified Turbulent Flows.

Turbulence in stratified and rotating turbulent flows is characterized by an interplay between waves and eddies, resulting in continuous exchanges between potential and kinetic energy. Here, we study how these processes affect the turbulent energy cascade from large to small scales, which manifests itself by an irreversible evolution of the relative kinetic energy between two tracer particles. We find that when r_{0}, the separation between particles, is below a characteristic length ℓ_{t}, potential energy is on average transferred to kinetic energy, reducing time irreversibility, and conversely when r_{0}>ℓ_{t}. Our Letter reveals that the scale ℓ_{t} coincides with the buoyancy length scale L_{B} over a broad range of configurations until a transition to a wave-dominated regime is reached.

Investigation of geometrical hopper and initial packing state on the inter-phase momentum transfer with granular flow in vertical packed bed

Abstract For the specific application of vertical packed bed design, the main task is to optimize and improve the granular flow pattern, since a worse granular flow pattern is detrimental to the performance of heat transfer and flow in vertical packed bed. To improve the uniformity of granular flow profiles, an application of the discrete element method is used to investigate the granular flow pattern in a vertically packed bed under the condition of different tapered hopper angles and initial packing states. The uniformity of granular dramatically decreases with an increase in the fluctuation of granular velocity distribution. The variation of structural parameters has a positive influence on enhancing the stability of the granular layer. Coefficient of variation and relative fluctuation kinetic energy are introduced as criteria to describe the stability of the granular layer. This study numerically reveals the evolution of initial packing states has a slight influence on improving the stability of granular flow.

Effects of electrostatic interaction on clustering and collision of bidispersed inertial particles in homogeneous and isotropic turbulence

In sandstorms and thunderclouds, turbulence-induced collisions between solid particles and ice crystals lead to inevitable triboelectrification. The charge segregation is usually size dependent, with small particles charged negatively and large particles charged positively. In this work, we perform numerical simulations to study the influence of charge segregation on the dynamics of bidispersed inertial particles in turbulence. Direct numerical simulations of homogeneous isotropic turbulence are performed with the Taylor Reynolds number ${Re}_{\lambda }=147.5$ , while particles are subjected to both electrostatic interactions and fluid drag, with Stokes numbers of 1 and 10 for small and large particles, respectively. Coulomb repulsion/attraction is shown to effectively inhibit/enhance particle clustering within a short range. Besides, the mean relative velocity between same-size particles is found to rise as the particle charge increases because of the exclusion of low-velocity pairs, while the relative velocity between different-size particles is almost unaffected, emphasizing the dominant roles of differential inertia. The mean Coulomb-turbulence parameter, ${Ct}_0$ , is then defined to characterize the competition between the Coulomb potential energy and the mean relative kinetic energy. In addition, a model is proposed to quantify the rate at which charged particles approach each other and to capture the transition of the particle relative motion from the turbulence-dominated regime to the electrostatic-dominated regime. Finally, the probability distribution function of the approach rate between particle pairs is examined, and its dependence on the Coulomb force is further discussed using the extended Coulomb-turbulence parameter.

Molecular dynamics study on the thermal conductivity and ballistic resistance of twisted graphene

The twist as a new degree of freedom induces several angle dependent properties in twisted graphene, such as electronic and optical properties. However, the ballistic resistance and thermal conductivity of twisted graphene remain not well understood and experimentally challenging. Therefore, the effect of interlayer twist angle on the thermal conductivity and ballistic resistance of bilayer graphene (BLG) has been explored using molecular dynamics simulation herein. Results show that the thermal conductivity of graphene is very sensitive to the twist angle of the interlayer plane. As the twist angle increases from 0° to 60°, the in-plane thermal conductivity of twisted bilayer graphene (t-BLG) first decreases and then increases with a periodic interval of 30°, exhibiting an asymmetric double V-shaped curve. And the cross-plane thermal conductivity of t-BLG gradually first decreases from 0° to 30° and then increases from 30° to 60°, also showing an asymmetric V-shaped curve. In contrast, the interlayer twist angle has a limited influence on the ballistic resistance of t-BLG. With the change of the twist angle, the ballistic limit velocity does not change much, and the fluctuation range is less than 1.56%; the relative kinetic energy also changes little with the fluctuation less than 4%. Such a slight difference is insufficient to make a significant change in its ballistic resistance and its impact resistance is mainly affected by the number of membrane layers. Each additional layer increases its ballistic limit speed by about 8%. This study will provide some theoretical guidance for the study of heat dissipation in the anti-ballistic process of twisted graphene and the design of advanced protective materials.

Double layer acceleration of ions with differently charged states in a laser induced plasma

The electric field driven acceleration of plasma ions is an intrinsic effect in laser-induced plasma plumes and is responsible for the generation of high-energy ions. At high laser fluences (≥ 2 J/cm2), multiply charged ions are formed and affect the plume expansion dynamics. In this paper, we used kinetic energy-resolved mass spectrometry to investigate the relative abundance and kinetic energy distributions of singly- and doubly-charged ions produced by KrF-laser ablation of nine different oxide targets. The doubly charged metal ions with a lower mass-to-charge (m/z) ratio show narrow energy distributions at high average kinetic energies coinciding with the cutoff energies for the singly-charged ion distributions. The observation suggests that the recombination of higher charged ions plays a prominent role in the formation of the high-energy tail for singly-charged ions. The results are discussed in terms of component volatility and a dynamic double layer, where ions with different m/z values experience different accelerations.

Numerical investigation of hydraulic jump for different stilling basins using FLOW-3D

Abstract Stilling basin of the Tuansa barrage is a modified form of the United States Bureau of Reclamation (USBR) Type-III basin, which includes impact baffle and friction blocks. Soon after the barrage's operation, baffle blocks were found to be uprooted. Additionally, previous studies also highlighted the issues of rectangular baffle blocks, i.e., less drag, smaller wake zone, and flow reattachment. On the contrary, the use of wedge-shaped splitter blocks is found limited downstream of diversion barrages. Therefore, this study focuses on the hydraulic effects of wedge-shaped splitter blocks on hydraulic jump (HJ) and energy dissipation using FLOW-3D and confirms its suitability downstream of the diversion barrage. The study mainly investigated the free surface profiles, roller lengths, relative energy losses, velocity profiles, and turbulent kinetic energies for three different stilling basins. The results of free surface profiles indicated that new basins stabilised the HJ and produced smaller lengths of HJ. The results also showed that as the flow increased, the roller lengths decreased in the new basins. Similarly, with an increase in the flow, the relative energy loss increased in new basins. Furthermore, within HJ, and at the basins' end, the results showed higher decay of velocity and turbulent kinetic energy in the new basins.

Modeling Chondrule Dust Rim Growth with Ellipsoidal Monomers

Fine-grained dust rims (FGRs) surrounding chondrules in carbonaceous chondrites encode important information about early processes in the solar nebula. Here, we investigate the effect of the nebular environment on FGR porosity, dust size distribution, and grain alignment, comparing the results for rims comprised of ellipsoidal and spherical grains. We conduct numerical simulations in which FGRs grow by collisions between dust particles and chondrules in both neutral and ionized turbulent gas. The resultant rim morphology is related to the ratio ϵ of the electrostatic potential energy at the collision point to the relative kinetic energy between colliding particles. In general, large ϵ leads to a large rim porosity, large rim grain size, and low growth rate. Dust rims comprised of ellipsoidal monomers initially grow faster in thickness than rims comprised of spherical monomers, due to their higher porosity. As the rims grow and obtain a greater electrostatic potential, repulsion becomes dominant, and this effect is reversed. Grain size coarsening toward the outer regions of the rims is observed for low- and high-ϵ regimes, and is more pronounced in the ellipsoidal case, while for the medium-ϵ regime, small monomers tend to be captured in the middle of the rims. In neutral environments, ellipsoidal grains have random orientations within the rim, while in charged environments ellipsoidal grains tend to align with maximum axial alignment for ϵ = 0.15. The characterization of these FGR features provides a means to relate laboratory measurements of chondrite samples to the formation environment of the parent bodies.

The Anatomy of a Turbulent Radiative Mixing Layer: Insights from an Analytic Model with Turbulent Conduction and Viscosity

Turbulent radiative mixing layers (TRMLs) form at the interface of cold, dense gas and hot, diffuse gas in motion with each other. TRMLs are ubiquitous in and around galaxies on a variety of scales, including galactic winds and the circumgalactic medium. They host the intermediate-temperature gases that are efficient in radiative cooling, thus playing a crucial role in controlling the cold gas supply, phase structure, and spectral features of galaxies. In this work, we develop an intuitive analytic 1.5-dimensional model for TRMLs that includes a simple parameterization of the effective turbulent conductivity and viscosity and a piecewise power-law cooling curve. Our analytic model reproduces the mass flux, total cooling, and phase structure of 3D simulations of TRMLs at a fraction of the computational cost. It also reveals essential insights into the physics of TRMLs, particularly the importance of the viscous dissipation of relative kinetic energy in balancing radiative cooling as the shear Mach number approaches unity. This dissipation takes place both in the intermediate-temperature phase, which reduces the enthalpy flux from the hot phase, and in the cold phase, which enhances radiative cooling. Additionally, our model provides a fast and easy way of computing the column density and surface brightness of TRMLs, which can be directly linked to observations.

Fog Intermittency and Critical Behavior

The intermittency of fog occurrence (the switching between fog and no-fog) is a key stochastic feature that plays a role in its duration and the amount of moisture available. Here, fog intermittency is studied by using the visibility time series collected during the month of July 2022 on Sable Island, Canada. In addition to the visibility, time series of air relative humidity and turbulent kinetic energy, putative variables akin to the formation and breakup conditions of fog, respectively, are also analyzed in the same framework to establish links between fog intermittency and the underlying atmospheric variables. Intermittency in the time series is quantified with their binary telegraph approximations to isolate clustering behavior from amplitude variations. It is shown that relative humidity and turbulent kinetic energy bound many stochastic features of visibility, including its spectral exponent, clustering exponent, and the growth of its block entropy slope. Although not diagnostic, the visibility time series displays features consistent with Pomeau–Manneville Type-III intermittency in its quiescent phase duration PDF scaling (−3/2), power spectrum scaling (−1/2), and signal amplitude PDF scaling (−2). The binary fog time series exhibits properties of self-organized criticality in the relation between its power spectrum scaling and quiescent phase duration distribution.

Pulsatile Blood Flow Simulation for Subject-Specific Geometry of a Human Aortic Arch

Pulsatile blood flow in a subject-specific human aortic arch and its major branches is studied computationally for a peak Reynolds number of 1553 and a Womersley number of 22.74. The aortic geometry is constructed from the CT-scan images of a subject. The aorta has out-of-plane curvature and significant area variation along the flow direction. A physiologically representative pulsatile velocity waveform is applied as boundary condition at the inlet of the aorta. The primary velocity profiles are skewed towards the inner wall of the ascending aorta during the entire cardiac cycle. In the decelerating phase, reverse flow is noted along the inner wall and the magnitude of maximum velocity is about 50 % of the peak flow condition. Flow separation is observed in the inner wall of the ascending aorta during the decelerating and reverse flow phases of the cardiac cycle. In the accelerating phase, however, flow separation does not occur. The major observation of the present work is the existence of complex and asymmetrical vortical flow structures which are not observed either in simple curved pipes or in idealized aortic arch computational studies. The relative strength of the secondary flow with respect to the primary flow is quantified by means of Relative Secondary Kinetic Energy whose highest value is evaluated to be 1.202 occurring near the entrance of the right carotid artery during the maximum reverse flow condition. High values of wall shear stress is observed at distal of the left and right subclavian arteries, the bifurcation of brachiocephalic artery between right subclavian artery and right carotid artery, and proximal inner wall of descending aorta during the cardiac cycle. The wall shear stress at the bifurcations of the branches are low and oscillatory and generally correlates with the preferential sites for atherosclerosis. The flow structures on the aorta wall are explicitly highlighted by the limiting streamlines. The application of limiting streamlines to clearly elucidate the complex on-wall flow structures is one of the key contributions of the present study. During the decelerating and reverse flow phases several critical points are observed on the aortic wall. These complex flow structures vanish during the accelerating phase. The observations made in the present study will be helpful in creating accurate and clinically useful computational models.

Cross sections of the Rb83(p,γ)Sr84 and Kr84(p,γ)Rb85 reactions at energies characteristic of the astrophysical γ process

We have measured the cross section of the $^{83}\mathrm{Rb}(p,\ensuremath{\gamma})^{84}\mathrm{Sr}$ radiative capture reaction in inverse kinematics using a radioactive beam of $^{83}\mathrm{Rb}$ at incident energies of 2.4 and $2.7\phantom{\rule{0.16em}{0ex}}A$ MeV. Prior to the radioactive beam measurement, the $^{84}\mathrm{Kr}(p,\ensuremath{\gamma})^{85}\mathrm{Rb}$ radiative capture reaction was measured in inverse kinematics using a stable beam of $^{84}\mathrm{Kr}$ at an incident energy of $2.7A$ MeV. The effective relative kinetic energies of these measurements lie within the relevant energy window for the $\ensuremath{\gamma}$ process in supernovae. The central values of the measured partial cross sections of both reactions were found to be $0.17--0.42$ times the predictions of statistical model calculations. Assuming the predicted cross section at other energies is reduced by the same factor leads to a slightly higher calculated abundance of the $p$ nucleus $^{84}\mathrm{Sr}$, caused by the reduced rate of the $^{84}\mathrm{Sr}(\ensuremath{\gamma},p)^{83}\mathrm{Rb}$ reaction derived from the present measurement.

Age- and sex-specific reference values of biventricular flow components and kinetic energy by 4D flow cardiovascular magnetic resonance in healthy subjects

BackgroundAdvances in four-dimensional flow cardiovascular magnetic resonance (4D flow CMR) have allowed quantification of left ventricular (LV) and right ventricular (RV) blood flow. We aimed to (1) investigate age and sex differences of 4D flow CMR-derived LV and RV relative flow components and kinetic energy (KE) parameters indexed to end-diastolic volume (KEiEDV) in healthy subjects; and (2) assess the effects of age and sex on these parameters. MethodsWe performed 4D flow analysis in 163 healthy participants (42% female; mean age 43 ± 13 years) of a prospective registry study (NCT03217240) who were free of cardiovascular diseases. Relative flow components (direct flow, retained inflow, delayed ejection flow, residual volume) and multiple phasic KEiEDV (global, peak systolic, average systolic, average diastolic, peak E-wave, peak A-wave) for both LV and RV were analysed. ResultsCompared with men, women had lower median LV and RV residual volume, and LV peak and average systolic KEiEDV, and higher median values of RV direct flow, RV global KEiEDV, RV average diastolic KEiEDV, and RV peak E-wave KEiEDV. ANOVA analysis found there were no differences in flow components, peak and average systolic, average diastolic and global KEiEDV for both LV and RV across age groups. Peak A-wave KEiEDV increased significantly (r = 0.458 for LV and 0.341 for RV), whereas peak E-wave KEiEDV (r = − 0.355 for LV and − 0.318 for RV), and KEiEDV E/A ratio (r = − 0.475 for LV and − 0.504 for RV) decreased significantly, with age. ConclusionThese data using state-of-the-art 4D flow CMR show that biventricular flow components and kinetic energy parameters vary significantly by age and sex. Age and sex trends should be considered in the interpretation of quantitative measures of biventricular flow.Clinical trial registration https://www.clinicaltrials.gov. Unique identifier: NCT03217240.

Cluster structure of C11 investigated with a breakup reaction

The excitation spectra above the breakup threshold of C11 were measured using the invariant mass method with a 25.0-MeV/nucleon beam bombarding a carbon target for the first time. This measurement was performed with a zero-degree double-sided silicon strip detector together with four CsI(Tl) detectors, which could detect breakup fragments with low relative kinetic energy. Some resonances in C11 were clearly observed in the excitation energy range of 8–14 MeV proceeding through the Be7 + α channel. Among them, a resonance with the largest yield was observed around 8.10 MeV. We assign it as the head of the Kπ=3/2− rotational band, and suggest the 9.38-MeV state as the second member of this band.1 MoreReceived 3 May 2022Revised 16 September 2022Accepted 11 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.014320©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBreakup reactionsNuclear structure & decaysProperties6 ≤ A ≤ 19Nuclear Physics

Three-Dimensional Vibrational Characteristics of Functionally Graded Rotating Microbeams Based on the Higher-Order Refined Shear Deformation Theory

This study establishes a novel three-dimensional dynamic model for functionally graded rotating microbeams simultaneously considering flapwise and chordwise shear effects based on a refined shear deformation theory and the modified couple stress theory. Five kinematic variables are introduced to describe the rotating microbeam’s axial, flapwise, and chordwise motions using a higher-order refined shear deformation theory. The related strain energy and kinetic energy functionals are discretized by the assumed mode method. Applying the Euler–Lagrange variational formulation, the governing equations for the rotating microbeam are obtained. Selective examples are provided to demonstrate the convergence and effectiveness of the proposed model. Finally, the impacts of slenderness ratio, rotation speed, material index, material length scale parameter (MLSP), and Poisson’s effect on the vibrational characteristics of the microbeam are examined. Numerical results indicate that the mode shape transition and frequency loci veering phenomena could easily occur under slight changes in the above factors when dense modes appear in the rotating microbeam; moreover, there is a positive/negative competitive relationship among the effects of rotation speed, MLSP, and shear deformation; Poisson’s effect seriously affects the coupling between axial and non-axial motions of the rotating microbeam. The results obtained are expected to provide data accumulation and methodological basis for the failure analysis and vibration shape determination of micro air vehicles.

Effect of Coating Thickness on the Atomic Oxygen Resistance of Siloxane Coatings Synthesized by Plasma Polymerization Deposition Technique

Atomic oxygen in the low Earth orbit (LEO) environment is highly oxidizing. Due to the high flight speed of spacecraft, the relative kinetic energy of high-flux atomic oxygen bombarding the spacecraft surface can reach up to about 5 eV. Therefore, atomic oxygen is one of the most dangerous space environment factors in LEO, which seriously affects the safe operation and service life of spacecraft in orbit. In order to meet the requirements for the high reliability and long lifetime of spacecraft, effective protection measures must be taken on their sensitive surfaces. Siloxane is a coating with an organic–inorganic hybrid structure. Compared with SiO2 and other inorganic atomic oxygen protective coatings, it has better flexibility and is better at anti-atomic oxygen performance. In this paper, the plasma polymerization deposition technique was used to prepare large-area siloxane coatings on different substrates with different thicknesses for improving atomic oxygen resistance by optimizing the process parameters. The thickness of the coating was measured by different methods, and the results showed that the thickness distribution was consistent. By observing the surface morphology of the coating, it was uniform and compact without obvious defects, so the uniformity of large-area coating was also ideal. The adhesion and heat/humidity resistance of siloxane coatings were examined by pull-off testing and damp-heat testing, respectively. The results showed that the siloxane coatings with a thickness of about 400 nm exhibited better physical properties. At the same time, the ground simulation testing of atomic oxygen confirmed that siloxane coatings with a thickness of 418 nm presented the best performance of atomic oxygen resistance. The atomic oxygen erosion yield of siloxane coatings with a thickness of 418 nm was as low as 5.39 × 10−27 cm3/atoms, which was three orders of magnitude lower than that of the uncoated Kapton substrate and presented a good anti-atomic oxygen performance. Meanwhile, it has also successfully passed the damp-heat test. The coating thickness is only several hundred nanometers and does not increase the weight of the spacecraft, which makes it a relatively ideal LEO atomic oxygen protection material. Furthermore, a possible mechanism was proposed to explicate the physicochemical process of atomic oxygen attacking the coating materials.

Distributed Coordinated Brake Control for Longitudinal Collision Avoidance of Multiple Connected Automated Vehicles

The emerging connected automated vehicle (CAV) technique brings a new opportunity for the development of cooperative collision avoidance systems. This paper proposes a distributed coordinated brake control (DCBC) algorithm for longitudinal collision avoidance of multiple CAVs. Firstly, the studied scenario is defined, within which the communication topology and vehicle dynamics are modeled for a vehicle string and the control objective is designed to minimize the total relative kinetic energy. Next, the control problem is formulated into a centralized model predictive control problem, which is then transformed into a quadratic programming (QP) problem. By separating the QP problem into several sub-problems assigned to each CAV, distributed optimization is introduced to solve the QP problem in a distributed manner. Elaborate numerical simulation comparisons are conducted to demonstrate the advantage of the proposed DCBC algorithm.

Elastic scattering of ruthenium atoms from Si and O atoms in the range of relative kinetic energies of 2-200 eV

Interconnector technologies of a new generation involve the use of ruthenium. The high cost of experimental study of sputtering and etching of trenches in Ru leads to the need to optimize it by modeling that requires knowledge of the cross sections of elementary processes of interaction of plasma particles with Ru. In this work, the binary interatomic potentials of Ru-Ru and Ru-Si pairs tested by the molecular dynamics method, and the Ru-O one calculated by the method of multi-reference configurational interaction MRCI/AV5Z were used to calculate the elastic scattering cross sections of the atomic pairs in the energy range typical of plasma etching chambers. Keywords: ruthenium, elastic scattering, cross sections, sputtering, binary potential.

Experimental and Numerical Characterization of Violent Sloshing Flows Using a Single Degree of Freedom Approach

In this work, the most fundamental aspects of an aeronautical sloshing problem have been studied using an alternative and simplified model. This model consists of a single degree of freedom version of the original problem which keeps the essence of the fluid structure interaction and also the most relevant physical aspects of the industrial case. Two independent methodologies have been used: first an experimental rig has been designed to measure and visualize different magnitudes of the problem and also a smoothed particle hydrodynamics formulation has been adapted to obtain a local representation of the flow interaction. Two very different fluids in terms of viscosity have been tested, and the differences in terms of the characteristics of the sloshing regimes, free surface fragmentation and relative kinetic energy have been described and compared. Apart from the comparison of the results obtained by both methodologies in terms of tank acceleration, sloshing forces and free surface evolution, a deep study of the sloshing force has been performed. This study focuses on a deeper understanding of the different aspects that constitute the sloshing force, such as its synchronization with the tank movement, the relation to the movement of the liquid’s center of mass and the physical projection of the force on the pressure and viscous parts. Additionally, a reconstruction of the sloshing force as a sum of the pressure signal recorded by a finite number of pressure sensors has been also performed.

Drag model from interface-resolved simulations of particle sedimentation in a periodic domain and vertical turbulent channel flows

A drag correlation is established for laminar particle-laden flows, based on data from the interfaced-resolved direct numerical simulations (IR-DNS) of particle sedimentation in a periodic domain at density ratio ranging from 2 to 1000, particle concentration ranging from 0.59 % to 14.16 %, and particle Reynolds number below 132. Our drag decreases slightly with increasing density ratio when the other parameters are fixed. The drag correlation is then corrected to account for the turbulence effect by introducing the relative turbulent kinetic energy, from the IR-DNS data of the upward turbulent channel flows laden with the particles larger than the Kolmogorov length scale at relatively low particle volume fractions. A drift velocity model is developed to obtain the effective slip velocity from the interphase mean velocity difference for the vertical turbulent channel flow by considering the effects of particle inertia, particle concentration distribution and large-scale streamwise vortices.

Particle Sorting in Scree Slopes: Characterization and Interpretation From the Micromechanical Perspective

AbstractParticle sorting is one of the most interesting phenomena observed in the formation of scree slopes. We present a study of this phenomenon through physical model tests and numerical simulations at the grain scale, with a focus on the link between the degree of sorting and particle attributes, as well as the underlying mechanisms. By characterizing the degree of sorting with the graphic segregation index, we show that the degree of sorting increases as the difference in particle size and shape between the component materials of the deposited mixture increases. We propose two factors, the relative size factor (SFr) and relative shape factor (ORr), and show that the degree of sorting increases with the absolute values of these two factors (|SFr| and |ORr|). By monitoring the motions of tracer particles in the numerical simulations, we found that particle migration proceeds in a periodical mode of "collision/friction ⇌ regaining ⇌ collision/friction." Also, we performed energy analyses, revealing that relatively large and rounded particles tend to have a lower rate of kinetic energy dissipation, migrate at a higher velocity over a longer period of time, and have a larger migration distance. In addition, we define a relative kinetic energy dissipation rate |Dk_r| and find that it is positively correlated with |SFr| and |ORr|; the discrepancy in particle size and shape between the component materials is responsible for the difference in their kinetic energy dissipation rates, and it is the latter that determines their migration distance difference and sorting features.