Particle Motion Research Articles

Energetic neutral atom imaging reveals nearly 11-year cycle of the ring current of Saturn

The drift motion of energetic charged particles can generate an azimuthal electric current around the planet known as the ring current, which regulates the field configuration of the magnetosphere. However, limited coverage of in-situ measurements makes it challenging to investigate the long-term variations of the global ring current. Taking advantage of the energetic neutral atom (ENA) imaging onboard the Cassini mission, we present a nearly 11-year cycle of the suprathermal ring current populations in Saturn’s magnetosphere. We find that the peak location of the suprathermal ring current in local time oscillates between post-midnight and pre-midnight sectors, and its intensity minimizes during the solar maximum. These results indicate that the modulation of the suprathermal ring current is closely related to the solar cycle. Our analysis also offers a preview of the ring current at other giant planets, such as Jupiter, which will be imaged by ENA cameras onboard the JUICE mission.

Novel vibratory compaction quality indices developed from particle migration and distribution characteristics for unbound aggregate materials

Unbound aggregate materials (UAM) with large air voids are increasingly used to construct pavement base and subbase layers as part of the initiative to create sponge cities and improve drainage performance. However, the motion of particles and the spatial distribution of kinetic energy during the particle rearrangement process induced by vibratory loading remain unclear. This study presents the results of laboratory vibratory plate compaction tests conducted on UAM specimens under various combinations of vibratory parameters and different levels of Gravel to Sand ratio (G/S). SmartRock (SR) sensors were placed within the specimens to monitor particle motion in real-time while kinematic energy and its spatial distribution were analyzed from the acceleration time-history signals collected by the SR sensors. Based on high-precision industrial X-ray computed tomography (XCT) and 3D reconstruction technology, this study analyzed the motion and migration rules of the UAM particles. A new compaction index was proposed based on particle motion and kinematic energy to evaluate the compaction quality of the specimens.The findings of this study reveal that vibratory compaction can be divided into two distinct stages. During the first stage, coarse particles primarily move vertically while energy dissipation occurs mainly through compression of air voids but does not form a dense skeleton structure. In the second stage, coarse particles translate horizontally while rotating vertically, resulting in a tendency of the particles to lie flat with their long axes oriented horizontally. During this stage, most of the energy is used to fill air voids, leading to the formation of a densely packed skeleton structure. Kinematic energy indices and particle movement in the middle of the specimen can be used to evaluate the compaction stage and quality. Additionally, the lateral particle motion in the specimen transitions from continuous ascent to gradual descent to almost no kinematic energy, indicating a relatively dense state of compaction. Reducing the void ratio and increasing the contact area between particles in these size ranges of 4.75-9.5mm and 2.36-4.75mm can significantly increase the compaction density and improve the stability and deformation resistance of the subgrade bed.The results of this study provide valuable insights into the mechanisms of vibratory compaction and can be used to optimize compaction methods and improve pavement performance.

Numerical study on heat and mass transfer mechanism of dissolved particles in porous media with corroded skeletons

Heat and mass transfer mechanisms of dissolved particles in porous media with corroded skeletons are investigated by the coupled smoothed profile method and lattice Boltzmann method. Migration and dissolution process of particles in fluids are studied by integrating the source term which is obtained by time-split method. The particle surface temperature variation with time is considered for dynamic convection effect on particle motion. The dissolution rate is the same on the particle surface with the same radius. The solid morphology evolution of porous media is based on the volume of pixel method. The effects of the Damkohler number, Peclet number, Reynolds number, particle size, particle quantity, particle initial distribution and porosity gradient on the permeability evolution with time are investigated. The moving particle blockage effect, small pore throat suction effect, and jet effect are revealed. The porosity, permeability, porous skeleton corrosion degree and the particle migration velocity in the porous zone increase with an increase in the Damkohler number and Reynolds number, or a decrease in the Peclet number. The particle initial distribution and porosity gradient affect the porous skeleton corrosion degree.

Investigating the Effect of Dilatancy Angle and Cohesion on Particle Motion Characteristics Using the SPH Method

Investigating the Effect of Dilatancy Angle and Cohesion on Particle Motion Characteristics Using the SPH Method

An Investigation of Silty Sediment Erodibility Considering the Effects of Upward Seepage and Slope Gradient

The phenomenon of extensive erosion of silty submarine slopes in the Yellow River delta has been well documented in numerous studies. Due to poor drainage and high compressibility, silty sediments are particularly prone to pore pressure buildup and accumulated seepage under wave and current action, which can influence sediment erodibility (e.g., the critical bed shear stress and the erosion rate under various bed shear stresses). To date, there remains a lack of parametric formulation to quantitatively characterize the erodibility of silty sediments with the coupled effects of the hydraulic gradient of upward seepage and the slope gradient. In this study, a series of laboratory experiments were conducted to explore the erodibility of silt sediments from the Yellow River delta under varying hydraulic gradients of upward seepage and slope gradients. The results reveal that both upward seepage and increased slope gradients can enhance the erodibility of silty sediments. Specifically, as the seepage gradient increases from 0.1 to 0.8, the critical Shields parameter required for initiating silty particle motion decreases linearly, with a reduction rate of 0.01 per 0.1 increase in the seepage gradient, independently of changes in slope gradient. Additionally, the erosion coefficient of silty sediments grows exponentially with rising seepage gradients, with its average growth rate accelerating with increasing slope inclination. For flat sediment beds, the erosion coefficient influenced by upward seepage can be up to five times that in the absence of seepage. An empirical formula for calculating the critical Shields parameter and an erosion model incorporating upward seepage gradient and slope effects were developed through multiple regression analysis, providing an experimental basis for numerical simulations of scour in silty submarine slopes under combined waves and currents.

Effect of the Vortex on the Movement Law of Sand Particles in the Hump Region of Pump-Turbine

The pump turbine, as the core equipment of a pumped storage power plant, is most likely to operate in the hump zone between condition changes, which has a great impact on the stable operation of the power plant, and the high sedimentation of a natural river will lead to wear and tear in the overflow components of the equipment. Therefore, this paper is based on the Euler–Lagrange model, and seeks to investigate the distribution of vortices in the hump zone of the pump turbine and its effect on the movement of sand particles. The study shows that as the flow rate increases, the strip vortex in the straight cone section of the draft tube becomes elongated, and the cluster vortex in the elbow tube section gradually decreases. The strip vortex encourages the sand particles to move along its surface, while the cluster vortex hinders the movement of the sand particles. The accumulation areas of the sand particles in the straight cone section and the elbow tube section increase axially and laterally, respectively. The blade vortex in the runner gradually occupies the flow channel as the flow rate increases, and the blade vortex near the pressure surface encourages the sand particles to move towards the suction surface, resulting in the serious accumulation of sand particles on the suction surface. As the flow rate increases, the number of blades where sand particles accumulate increases and the accumulation area moves towards the cover plate and the outlet. The flow separation vortex in the double-row cascade decreases as the flow rate increases, which drives the sand movement in the middle and lower sections of the vanes. The area of sand accumulation in the stay vane decreases with increasing flow rate, but the area of sand accumulation between the guide vanes increases and then decreases. The vortex on the wall surface of the volute gradually decreases with the flow rate, and the vortex zone at the outlet first decreases, then disappears, and finally reappears. The vortex at the wall surface suppresses the sand movement, and its sand accumulation area changes from elongated to lumpy and finally to elongated due to the increase in flow. The results of the study provide an important theoretical reference for reducing the wear of pump turbine overflow components.

Motion of a charge in a constant and uniform field: a description based on the eigenvalues

The motion of a charged particle in a constant and uniform electromagnetic field is investigated. This problem, on its own, has been extensively studied. The novelty is in using an argument based on eigenvalues to arrive at a description of the motion, specifically the way that the velocity behaves at large times.

Truncated Coulomb potential for planar channeling

It is shown that if the atomic screening function is described in the Thomas-Fermi approximation, the corresponding continuous potential for planar channeling to a good accuracy reduces to a truncated Coulomb potential. The sum of two displaced Coulomb potentials also accurately approximates interplanar static continuous potentials for Si, Ge, W crystals in orientation (110), as well as the thermal potential of a Ge crystal in orientation (111), not too close to atomic planes. Such a possibility can be used to facilitate the description of channeled and quasichanneled particle motions. We illustrate this by calculating classical particle channeling periods, quantum energy levels, and the probability of tunneling of a negatively charged particle through a single atomic plane. Simple scaling laws in dependencies of those quantities on the atomic number Z result this case. Published by the American Physical Society 2024

Theory of bunched beam transverse Schottky signals with stationary rf system and high-order chromaticity

Theory of bunched beam transverse Schottky signals with stationary rf system and high-order chromaticity

Editorial for the Micro/Nanoscale Electrokinetics Section

Electrokinetics is the study of fluid flow and particle motion driven by electricity [...]

Features of hydrocarbon liquid-based nanofluid under augmentation of parametric ranges in non-Darcy media

Transport properties of hydrocarbon liquid-based nanofluids in non-Darcy media have key significance in chemical, thermal and mechanical engineering. Therefore, the key focus of this research is to investigate the transport mechanism in nanofluid using Koo–Kleinstreuer–Li (KKL) thermal conductivity model in non-Darcy media under squeezing and permeable effects. The functional fluid is a homogenous mixture of Cu and kerosene. The problem formation is carried out via nanofluid-enhanced properties and similarity rules. Then numerical scheme was endorsed for the results analysis under increasing physical ranges. It is observed that the velocity [Formula: see text] increased when the values of [Formula: see text] vary from 1.0 to 4.0. However, quick particles movement is noticed for [Formula: see text] for 1.0–4.0 and [Formula: see text]1.0 to [Formula: see text]4.0. Further, the thermal process in Cu/kerosene depreciates for [Formula: see text], 1.0, 1.5, 2.0, [Formula: see text], 4, 6, 8 and [Formula: see text], [Formula: see text]4.0, [Formula: see text]6.0, [Formula: see text]8.0, respectively. The stronger permeability of the lower plate highly reduced the fluid movement and depreciation in the movement can be optimized when the fluid sucks from the channel through the lower plate.

Experimental study on the motion characteristics of non-spherical biomass particulate systems in a fluidization tube

This study experimentally investigated the transport characteristics of flaky, fibrous and streaky biomass particles in a fluidization tube. The movement and distribution of these non-spherical biomass particles in different sections of the fluidization tube were visualized and analyzed by using a Particle Tracking Velocimetry measuring approach. The method for calculating the solidity rate distribution of particles in the fluidization tube was also developed. Furthermore, the distribution patterns of non-spherical biomass particles with three different morphologies in the near-wall region of the fluidization tube were significantly analyzed. It could be observed that the area of the non-spherical biomass particles in the near-wall region exhibited an ’M’ shape. Three empirical formulas for predicting the maximum area of non-spherical biomass particle clusters in the fluidization tube were firstly proposed. Among the three prediction formulas, the correlation coefficients are 0.7142, 0.8797, and 0.9567, respectively.

ECVT imaging and CFD simulation of particle flow in a 90° bend

Gas-solid two-phase flow characteristics in a 90° bend within a pneumatic conveying system are critical for design and performance optimization, impacting conveying efficiency and system safety. Electrical Capacitance Volumetric Tomography (ECVT) and Computational Fluid Dynamics (CFD) simulations were employed in this study to investigate the flow characteristics in the bend. The ECVT system for bends was validated through static tests. A setup with a 36 mm inner diameter was constructed for high-speed 3D imaging of 0.9 mm quartz particles. Flow patterns, solid-phase concentration, particle velocity spectra, and mass flow rate were analyzed under various gas velocities. The Euler-Lagrange method and SST K-ω model were used to simulate particle flow and pipe wall erosion numerically. Results indicate diverse flow patterns across different gas velocities, where moderate turbulence enhances efficiency and limits erosion. This study offers an experimental basis for predicting and controlling particle motion, providing scientific guidance for optimizing pneumatic systems.

Simulation of Small-Break Loss-of-Coolant Accident Using the RELAP5 Code with an Improved Wall Drag Partition Model for Bubbly Flow

The RELAP5 code is a computational tool designed for transient simulations of light water reactor coolant systems under hypothesized accident conditions. The original wall drag partition model in the RELAP5 code has a problem in that the bubble velocity is predicted to be faster than the water velocity in the fully developed flow in a constant-area channel. The wall drag partition model, based on the wetted perimeter concept, proves insufficient for accurately modeling bubbly flows. In this study, the wall drag partition model was modified to account for the physical motion of fluid particles. After that, the modified RELAP5 code was applied to predict the SBLOCA of a full-scale nuclear power plant. Considering the SBLOCA scenario, the behavior change in the loop seal clearing phenomenon was clearly shown in the analysis by the model change. Upon the termination of natural circulation, the loop seals were cleared, allowing the steam trapped within the system to discharge through the break. The modified model was confirmed to have an impact at this time. It mainly affected the timing and shape of the loop seal clearing and delayed the overall progress of the accident. It was observed that the flow rate of the bubbly phase decreased as the modified model accounted for wall friction during dispersed flow in the horizontal section, impacting the two-phase flow behavior at the conclusion of the natural circulation phase.

Grain-size distribution in suspension through open channel turbulent flow using space-fractional ADE

The main aim of the present study is to develop a mathematical formulation that can describe the grain-size distribution (GSD) of non-uniform sediments in suspension over erodible sediment beds in a wide open channel under non-equilibrium conditions. The two important characteristics of sediment particles, such as non-local mixing and the hiding-hindering effect during settling, has been considered in the current study. The traditional advection–diffusion equation (ADE) is taken in the modified form as fractional ADE which is capable of capturing non-local movement of particles unlike the traditional diffusion theory where particles jump within a restricted distance along the vertical direction over a small time interval. The equation is further modified for any kth class of non-uniform sediment and the effect of non-local movement is included in the expression of depth averaged sediment diffusivity also. The settling velocity of a particle is taken in a form that contains the effect of hiding and hindering due to the presence of non-uniform particles in the flow. The space-fractional derivative is taken in the Caputo sense where the order α of the fractional derivative varies from 1<α≤2. The non-local effect is considered in the bottom and top boundary conditions also and the governing equation with boundary and initial condition have been solved by Chebyshev collocation method along with Euler’s backward method. The temporal variation of concentration profiles for different size particles is studied by varying α and it is observed that the magnitude of concentration decreases for each size as α increases. Non-local effect on bottom concentration for different size particle is also studied and it is seen that overshooting of bottom concentration gradually decreases as α increases for a particular size. Sensitivity analysis of α on GSD at different heights also has been done. The model has been validated for GSD under equilibrium conditions with available experimental data and it is found that the model aligns well when the non-local mixing effect is taken into account. At the end, an error analysis has been conducted to confirm the accuracy of the presented model.

Dynamics of massive and massless particles in the spacetime of a wiggly cosmic dislocation

In this paper, we investigate the spacetime containing both small-scale structures (wiggles) and spatial dislocation, forming a wiggly cosmic dislocation. We study the combined effects of these features on the dynamics of massive and massless particles. Our results show that while wiggles alone lead to bound states and dislocation introduces angular momentum corrections, their coupling produces more complex effects, influencing both particle motion and wave propagation. Notably, this coupling significantly modifies radial solutions and eigenvalues, with the direction of motion or propagation becoming a critical factor in determining the outcomes. Numerical solutions reveal detailed aspects of particle dynamics as functions of dislocation and string parameters, including plots of trajectories, probability densities, and energy levels. These findings deepen our understanding of how a wiggly cosmic dislocation shapes particle dynamics, suggesting new directions for theoretical exploration in cosmological models.

Particle motion and thermal fluctuations of charged AdS black holes surrounded by exotic fluid with modified Chaplygin equation of state

This study explores the intricate relationships between thermodynamic properties and particle dynamics of charged AdS black holes, emphasizing the impacts of charge Q and higher-order corrections, particularly the parameter β, which is a modified Chaplygin gas parameter. Our analysis of entropy reveals that smaller black holes exhibit decreasing entropy variations with increased β, while larger black holes display a complex behavior characterized by initial entropy increases followed by decreases as the horizon radius expands. The Helmholtz free energy analysis suggests that higher-order corrections significantly modify energy behavior, indicating potential phase transitions influenced by gravitational forces, with increasing β values counteracting instability linked to larger charges. Internal energy assessments show an evolving stability of black holes, transitioning from negative to positive values as entropy increases, while also highlighting the destabilizing effects of electric charge. The specific heat analysis illustrates a complex thermal stability regime, where a rise in specific heat with increasing Q correlates with greater stability. However, critical points of instability arise with higher B values, where B is the BH model parameter. Moreover, the trajectories of particles around non-rotating charged black holes reveal that lower parameters result in unbounded motion. In contrast, higher parameters tend to restrict particles closer to the event horizon. Collectively, these findings underscore the complex interplay among charge, higher-order corrections, and stability in black hole thermodynamics, shedding light on the fundamental mechanisms governing black hole behavior and paving the way for future explorations using advanced models and simulations.

Orbital motion and QPOs testing around rotating Hairy black holes in Horndeski gravity

We investigate the orbital and oscillatory motion of test particles around a rotating hairy black hole in the context of Horndeski gravity. This black hole consists of three parameters, namely, the mass M of the black hole, spin parameter a of the black hole, and the hairy parameter q that results from the Horndeski theory of gravity. Analytical solutions are obtained for the radial profiles of specific energy and angular momentum corresponding to equatorial stable circular orbits, in terms of the model parameters. Using the effective potential method, we also examine the stability of these orbits. Additionally, we derive the analytical expressions for frequencies of radial and latitudinal harmonic oscillations, as a function of the black hole’s mass, charge, and spin of the black hole, for both local and distant observers. The key characteristics of quasi-periodic oscillations near stable circular orbits in the equatorial plane are explored. Furthermore, we analyze the precession of periastron and the Lense-Thirring effect. Our findings reveal that the particle motion around the black hole is significantly shaped by the parameters of the model.

Lyapunov exponents and phase transition of Hayward AdS black hole

In this paper, we study the relationship between the phase transition and Lyapunov exponents for 4D Hayward anti-de Sitter (AdS) black hole. We consider the motion of massless and massive particles around an unstable circular orbit of the Hayward AdS black hole in the equatorial plane and calculate the corresponding Lyapunov exponents. The phase transition is found to be well described by the multivaled Lyapunov exponents. It is also found that different phases of Hayward AdS black hole coincide with different branches of the Lyapunov exponents. We also study the discontinuous change in the Lyapunov exponents and find that it can serve as an order parameter near the critical point. The critical exponent of change in Lyapunov exponent near the critical point is found to be 1/2.

Compressional rheology model for vacuum filtration-consolidation of sludge in geotextile tubes

Recently, the disposal of high-water-content dredged sludge through geotextile tubes with vacuum-assisted prefabricated horizontal drains (PHD) has gained growing popularity for its convenience and efficiency. However, existing simulations for this typical coupled filtration-consolidation process using conventional consolidation models exhibit deficiencies due to the absence of effective stress and invalidity of Darcy’s law in the particle-wandering filtration phase. In this study, based on the compressional rheology theory, a two-dimensional coupled filtration-consolidation model constituted by the compressive yield stress Py(ϕ) and hindered setting factor r(ϕ) is developed to elucidate the solid-solid and solid-fluid interactions during slurry dewatering. A novel approach for measuring consistent Py(ϕ) and r(ϕ) relationships is proposed. The numerical solution is derived utilizing the alternating direction implicit (ADI) difference method and verified against a classical one-dimensional compressional rheology model and a field trial. Further analysis suggests that constitutive parameters, e.g., gel point, affect the dewatering efficiency by determining the relative degree of soil disorder, obstruction to particle movement, and vacuum transmission effect, while design parameters, e.g., PHD spacing and tube height, impact the magnitude and radiation range of vacuum pressure to influence the overall efficiency.