Particle Motion Research Articles

The transformation of the rotational energy of a Kerr black hole

This paper analyzes the feedback of the rotational energy extraction from a Kerr black hole (BH) by the ‘ballistic method’, i.e. the test particle decay in the BH ergosphere pioneered by Roger Penrose. The focus is on the negative energy counterrotating particles (which can be massive or massless) going in towards the horizon, and the feedback on the BH irreducible mass is assessed. Generally, the change in irreducible mass is a function of the conserved quantities of the particle. For an extreme Kerr BH and in the limit μ1/M→0 , all the reduced transformable energy goes into the irreducible mass (i.e. ΔMirr/|E1|→∞ ), resulting in high irreversibility. The amount of extracted energy from the BH using test particles is much lower than the change of transformable energy. For non-extreme Kerr BHs, the effective potential of particle motion on the equatorial plane in Kerr spacetime is analyzed, and it is demonstrated that the Penrose process can only be undergone by BHs with a dimensionless spin a^>1/2 if the decay point coincides with the turning point. Based on that, the lower limit of the change in irreducible mass is provided as a function of the dimensionless spin of the BH. The significance of the increase in the irreducible mass of the BH during the energy extraction process is generally and concisely illustrated by introducing the concept of transformable energy of the BH. The feedback from the Penrose process on the irreducible mass demonstrates the irreversibility of energy extraction and highlights that the total amount of energy that can be extracted from a BH is less than previously anticipated.

Diffusiophoresis in Polymer and Nanoparticle Gradients.

Diffusiophoresis is the movement of the colloidal particles in response to a concentration gradient and can be observed for both electrolyte (e.g., salt) and nonelectrolyte (e.g., glucose) solutes. Here, we investigated the diffusiophoretic behavior of polystyrene (PS-carboxylate surface) microparticles in nonadsorbing charged and uncharged solute gradients [sodium polystyrenesulfonate (NaPSS), polyethylene glycol (PEG), and nanoscale colloidal silica (SiO2)] using a dead-end channel setup. We compared the diffusiophoretic motion in these gradient types with each other and to the case of using a monovalent salt gradient. In each of the nonadsorbing gradient systems (NaPSS, PEG, and SiO2 nanoparticles), the PS particles migrated toward the lower solute concentration. The exclusion distance values (from the initial position) of particles were recorded within the dead-end channel, and it was found that an increase in solute concentration increases exclusion from the main channel. In the polyelectrolyte case, the motion of PS microparticles was reduced by the addition of a background salt due to reduced electrostatic interaction, whereas it remained constant when using the neutral polymer. Particle diffusiophoresis in gradients of polyelectrolytes (charged macromolecules) is quite similar to the behavior when using a PEG gradient (uncharged macromolecule) in the presence of a background electrolyte. Moreover, we observed PS microparticles under different concentrations and molecular weights of PEG gradients. By combining the simulations, we estimated the exclusion length, which was previously proposed to be the order of the polymer radius. Furthermore, the movement of PS microparticles was analyzed in the gradient of silica nanoparticles. The exclusion distance was higher in silica nanoparticle gradients compared to similar-size PEG gradients because silica nanoparticles are charged. The diffusiophoretic transport of the PS microparticles could be simulated by considering the interaction between the PS microparticles and silica nanoparticles.

Correlating ballast resilient modulus with particle movement through SmartRock sensing

The resilient modulus of ballast is a key parameter in assessing track quality and is influenced by various loading conditions, such as deviator stress, bulk stress, loading frequency, and confining pressure. These factors, when incorporated into different models, can sometimes complicate their application in track maintenance planning. Therefore, a simplified model that collectively considers these factors would be beneficial in practical applications for estimating the ballast resilient modulus. This study utilizes smart sensing technology, SmartRock, to track particle movement during large-scale triaxial cyclic loading tests, exploring the potential correlation between ballast resilient modulus and particle motion. The findings indicate that the settling acceleration of ballast particles significantly impacts the ballast resilient modulus. This effect is dependent on the applied cyclic loading pulses, an aspect previously overlooked in research. Consequently, an index termed the Cyclic Loading and Acceleration Index (CLAI) has been introduced. CLAI integrates the effects of deviator stress, loading frequency, loading pulses, and settling acceleration. Based on CLAI, a simplified model for ballast resilient modulus has been developed and validated.

Simulation of particle-laden flows and erosion in an axial fan stage considering the relative position of the blades

Abstract Axial fans are vital accessories in aircraft ventilation systems, but, they may experience erosion from particulate flows, causing a decline in effectiveness over time. This study investigated the trajectories of two types of sand particles and erosion in an axial fan stage, considering the relative position of the blades facing the inlet guide vanes. The movement of particles was simulated using an in-house code that implements a Lagrangian approach along with a stochastic particle-eddy interaction model. The flow field was solved separately and the flow data was transferred to the particle trajectory code. The finite element method allowed for the tracking of particles through the computational cells and accurate determination of their impact positions. A semi-empirical erosion correlation was used to evaluate the local erosion rates, mass removal, and geometry deterioration. As a result, the rotor exhibits a high frequency of impacts and significant erosion on the leading edge of the blade, extending to the upper corner of the pressure side and blade tip, as well as the front of the suction side. In the inlet guide vane, the erosion is spread out along the entire pressure side but at lower erosion rates compared to the rotor blade. The erosion patterns obtained at different pitch-wise positions were cumulated to get better representation of erosion patterns. After being exposed to MIL-E5007E sand (0–1000 $\unicode{x03BC}$ m) at the highest concentration for 10 hours, the blade experienced a reduction of a 0.29% in mass, a 0.45% decrease in tip chord, and a 0.23% increase in tip clearance. On the other hand, AC-coarse sand (0–200 μm) resulted in a 0.23% decrease in blade mass, a 0.4% reduction in tip chord, and a 0.16% increase in tip clearance. The data that is available can be used to monitor the lifespan of axial fans of similar design and select appropriate coatings to protect against erosion.

Effect of Thermal Convection and Mass Transfer on Particle Motion during Sedimentation: A Numerical Study

Effect of Thermal Convection and Mass Transfer on Particle Motion during Sedimentation: A Numerical Study

Stable Motions of High Energy Particles Interacting via a Repelling Potential

The motion of N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$N$$\\end{document} particles interacting by a smooth repelling potential and confined to a compact d\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d$$\\end{document}-dimensional region is proved to be, under mild conditions, non-ergodic for all sufficiently large energies. Specifically, choreographic solutions, for which all particles follow approximately the same path close to an elliptic periodic orbit of the single-particle system, are proved to be KAM stable in the high energy limit. Finally, it is proved that the motion of N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$N$$\\end{document} repelling particles in a rectangular box is non-ergodic at high energies for a generic choice of interacting potential: there exists a KAM-stable periodic motion by which the particles move fast only in one direction, each on its own path, yet in synchrony with all the other parallel moving particles.

A Numerical Study of Smoke Concentration Distribution near Low-Intensity Fires: Sensitivity to Vertical Canopy Structure and Fire Heat Source Strength

Abstract Broadly speaking, prediction of the negative impacts of prescribed fire on air quality is limited by gaps in our understanding of the underlying fire, fuels, and atmospheric processes. These knowledge gaps hinder our ability to accurately predict smoke concentration distributions, leading to unintended smoke intrusions into nearby communities and subsequent threats to public health and safety. In this study, numerical simulations are performed using the Flexible Particle Weather Research and Forecasting (FLEXPART-WRF) Model, a Lagrangian particle dispersion model, with particle motion driven by output from a full-physics atmospheric model with a forest canopy submodel and 10-m horizontal grid spacing [Advanced Regional Prediction System (ARPS)-CANOPY], to address two research questions. First, what is the relationship between near-fire (within ∼50–150 m of fire) smoke concentration distribution and (i) vertical canopy structure and (ii) fire heat source strength? Second, what roles do mean transport (i.e., transport by the mean wind) and turbulent diffusion play in shaping the near-fire smoke concentration distribution? To address these questions, simulations are run with 25 combinations of plant area density profile and fire sensible heat flux magnitude, and smoke is represented by particles with diameters ≤ 2.5 μm (PM2.5). Results show that near-fire PM2.5 concentration distribution is primarily controlled by vertical canopy structure, with fire heat source strength primarily controlling the PM2.5 concentration magnitude. Analysis of the underlying ARPS-CANOPY variables driving the FLEXPART-WRF particle dispersion helps elucidate the roles of mean transport and turbulent diffusion. In total, the study findings suggest that the vertical distribution of canopy vegetation and fire heat source strength are important factors influencing PM2.5 dispersion and concentration distribution near low-intensity fires.

GPU-accelerated approach for 2D fracture analysis of structures combining finite particle method and cohesive zone model

The fracture analysis of structures typically involves strong discontinuity and nonlinear behaviors, and it requires fine meshing and small time steps, making it time-consuming. This study proposes an approach accelerated by graphics processing units (GPU) for two-dimensional (2D) fracture analysis of structures combining finite particle method (FPM) and cohesive zone model (CZM). Specifically, the equations of motion of particles are presented, and the internal forces of planar triangular elements are derived based on FPM. Subsequently, the internal forces of four-particle cohesive element are derived to describe the CZM, and the linear elastic stage, softening stage, and failure stage are depicted according to the traction-separation criteria. An explicit GPU-based FPM analysis strategy for structural fracture analysis is then developed, and the parallel solvers for particles, triangular elements, and cohesive elements are implemented. A quasi-static fracture analysis of a concrete beam and a dynamic fracture analysis of the Kalthoff problem is conducted to verify the effectiveness of the proposed approach. The obtained crack propagation path, load vs. displacement curves, and crack propagation speed are in good agreement with the experimental results and the results in the literature. The efficiency of the proposed approach is also investigated. The achieved maximum speedup ratio of the GPU-accelerated approach to the central processing unit (CPU)-based approach reaches around 24, and the achieved speedup ratio relative to the commercial finite element software Abaqus/Explicit reaches around 11.5, demonstrating the computational efficiency of the proposed approach.

Impact of coated and non-coated magnetic nanoparticles on oil-water separation in green surfactant-based emulsions

This study investigates the efficacy of magnetite nanoparticles as a means of demulsifying surfactant-based emulsions, focusing on light and medium crude oil emulsions. The demulsification capabilities of bare, amine-coated, and oleic acid-coated magnetite nanoparticles were tested. Nanoparticle concentrations ranged from 0.25 % to 8 %. The emulsions used Alpha Olefin Sulfonate and two environmentally friendly surfactants, Coco Glucoside and Greenzyme with sodium and potassium formate as eco-friendly alternatives and sodium chloride as the standard brine. Magnetic demulsification efficacy is highly dependent on the interplay between the nanoparticle surface charge and surfactant, thereby affecting surfactant adsorption onto the particle surface. While gravimetric separation alone has partial effectiveness, the magnetic field enhances particle movement, promoting greater instability. The nanoparticles play a key role in adsorbing surfactant species from the interfacial region, thus facilitating demulsification. Notably, magnetic demulsification is more effective with environmentally friendly surfactants, achieving 100 % separation in most cases. Demulsification of emulsions containing synthetic surfactants is most successful with light crude oil emulsions, and in select cases, achieves 100 % separation with medium crude oil emulsions.

Capillary wave tweezer

Precise control of microparticle movement is crucial in high throughput processing for various applications in scalable manufacturing, such as particle monolayer assembly and 3D bio-printing. Current techniques using acoustic, electrical and optical methods offer precise manipulation advantages, but their scalability is restricted due to issues such as, high input powers and complex fabrication and operation processes. In this work, we introduce the concept of capillary wave tweezers, where mm-scale capillary wave fields are dynamically manipulated to control the position of microparticles in a liquid volume. Capillary waves are generated in an open liquid volume using low frequency vibrations (in the range of 10–100 Hz) to trap particles underneath the nodes of the capillary waves. By shifting the displacement nodes of the waves, the trapped particles are precisely displaced. Using analytical and numerical models, we identify conditions under which a stable control over particle motion is achieved. By showcasing the ability to dynamically control the movement of microparticles, our concept offers a simple and high throughput method to manipulate particles in open systems.

Resistance characteristics and particle movement behavior of a petroleum coke particle packed bed in a vertical shaft calciner under different burden distribution methods

AbstractBecause of the increasingly deteriorating quality of petroleum coke raw materials, abnormal furnace conditions, such as “firing and blasting”, frequently arise during the calcination of petroleum coke with a high powder/coke ratio in a vertical shaft calciner. This poses an urgent technical challenge that needs to be addressed. In iron and steel metallurgy, the burden distribution system is an important way to regulate blast furnace conditions and improve the permeability of a particle packed bed. In this work, advanced burden distribution concepts were introduced into the calcination process of petroleum coke in a vertical shaft calciner. Experimental devices were established to determine the resistance characteristics of a petroleum coke particle packed bed, along with a cold physical model of a 1/8 scale vertical shaft calciner. The influence of particle size and burden distribution methods on the resistance characteristics and particle motion behavior of the petroleum coke particle packed bed was systematically studied. The research findings indicate that both particle size and burden distribution methods significantly impact the resistance characteristics of petroleum coke particle packed beds. The smaller the particle size, the poorer the permeability of the bed. The layered burden distribution, symmetrical burden distribution, and dual‐particle mixed conventional burden distribution all contribute to improving the permeability of the petroleum coke particle packed bed in the vertical shaft calciner. Furthermore, employing symmetrical burden distribution in Bed‐3, which is packed with petroleum coke particles of diameters −3.2 + 2.5 mm and −1.0 + 0.8 mm, results in the smallest unit pressure drop, at only 1.7% of that of the conventional burden distribution of unscreened raw materials. This is the most effective means of improving the permeability of the bed. During the discharging process, particle size and symmetrical burden distribution have no significant impact on the motion characteristics of petroleum coke particles in the vertical shaft calciner. In general, in the calciner area, particles primarily move in a plug flow pattern and gradually transform into funnel flow in the cooling water jacket area. These research results provide the theoretical basis for addressing the technical challenges associated with powder coke calcination in vertical shaft calciners through reasonable burden distribution methods for fine and coarse particles.

Using Brownian model to study the effect of temperature on diffusion coefficient

This study employs molecular simulation techniques, particularly the Brownian motion model, to investigate the influence of temperature on diffusion coefficients. Leveraging Einsteins relationship for calculating diffusion coefficients and a one-dimensional random walk model, we systematically explore the impact of simulation direction, particle quantity, and simulation duration on diffusion behavior. The research extends its scope to three-dimensional Brownian motion simulations, offering insights into the stochastic motion of particles in a fluid. The primary objective is to analyze the relationship between temperature and diffusion coefficients. Through rigorous linear regression analysis, a significant and strong linear association is identified, demonstrating that an increase in temperature correlates with an increase in the diffusion coefficient. The research not only contributes to the fundamental understanding of molecular motion but also provides practical recommendations for simulation parameters, especially in resource-constrained computational environments. The study acknowledges certain limitations in the current Brownian motion algorithm and proposes avenues for future research to enhance computational efficiency and precision. This abstract encapsulates the key methodologies, findings, and implications of the research, laying the foundation for a comprehensive exploration of temperature-dependent diffusion coefficients in molecular systems.

Active particle manipulation with valley vortex phononic crystal

The valley vortex state presents an emerging domain in condensed matter physics. As a new information carrier with orbital angular momentum, it demonstrates remarkable ability for reliable, non-contact particle manipulation. In this paper, an acoustic system is constructed to exhibit the acoustic valley state, and traps particles using acoustic radiation force generated by the acoustic valley. Considering temperature effect on the acoustic system, the band structures for temperature fluctuations are discussed. An active controlled method for manipulating particle movement is proposed. Numerical simulations confirm that the particles can be captured by acoustic valley state, and can be repositioned through alterations in temperature, while maintaining a constant excitation frequency.

Melting thermal process in buoyancy driven radiated flow of (MoS2-SiO2-Au)/H2O near the stagnant point under mixed convection

The study of melting thermal process in ternary nanofluidic system (MoS2-SiO2-Au)/H2O near the point of separation is a fascinating research area. The potential applications of SPFs frequently occurs in analytical chemistry, life sciences, and in mechanical engineering etc. Therefore, the current attempt is made towards the development of new ternary SPFM by considering the thermal radiations, Joule heating, combined convection and magnetic field that act normally to the working domain. Further, using transformation functions and the ternary nanofluid characteristics, the new third order SPFM is developed and implemented RK as mathematical tool. It is examined that the particles movement enlarges for γ1=0.1,0.3,0.5,0.7 and γ2=0.1,0.2,0.3,0.4. The ternary nanofluids velocity increased slowly due to stronger internal viscous forces. Further, the temperature of ternary fluidic system (TFS) increased rapidly for assisting case and γ3=1.0,2.0,3.0,4.0 keeping the nanoparticles concentration 0.06. Moreover, thermal conductivity of nanofluid enhanced by increasing the amount of nanoparticles (MoS2-SiO2-Au) which directly influenced the model dynamics.

Mechanical effects of nanomaterials on the residual shear strength of dry sandy mixtures: Implication for the high mobility of rock avalanches

Nanoparticles found in rock avalanches and natural faults were inferred to be the reason for the ultra-low shear resistance of the materials along the shear surface. Nevertheless, this inference has not been physically verified yet. To investigate the role of nanoparticles in the shear behavior of granular materials, we conducted a series of ring shear tests on silicon dioxide nanoparticles (SN), silica sand (S8), and mixtures of the S8 with different contents of SN, under varying normal stresses (σ) and shear velocities (V). Our results showed that the shear strength (μ) of SN is high when σ is small (≤ 215 kPa at our test range), even though the maximum shear velocity is about 210 cm/s, but shows a great decrease under higher σ (≥ 619 kPa). The shear strength of mixtures varied with SN content. For S8 (M0) and the mixture of 10% SN (M10), when sheared under small σ, μ first decreased slightly with increasing V when V is smaller than 1 cm/s, after that it increased slightly with further increase of V. Nevertheless, this kind of shear-rate dependent behavior was not observed in the tests under higher σ. When the content of SN in the mixture was <20%, μ increased with the increase of SN content. However, with further increase of SN content, μ decreased. Under high normal stress conditions, distinctive powder rolls were observed on the shear surface formed on the tests. When the mixtures with lower SN content (≤50%), the powder rolls were not observed. We inferred that powder rolls can be produced under high SN content and high normal stress conditions, and this structure altered the particle movement mode from sliding friction to rolling resistance, resulting in a significant decrease in the shear strength. These findings provide valuable insights into the shear behavior of granular materials with nanoparticles and then provide evidence for a better understanding of the high mobility of rock avalanches.

Motion of massive particles and geodetic precession in the spacetime of a Galilean rotating observer in the Schwarzschild background

Motion of massive particles and geodetic precession in the spacetime of a Galilean rotating observer in the Schwarzschild background

Applicability Study of Euler–Lagrange Integration Scheme in Constructing Small-Scale Atmospheric Dynamics Models

The atmospheric flow field and weather processes exhibit complex and variable characteristics at small scales, involving interactions between terrain features and atmospheric physics. To investigate the mechanisms of these process further, this study employs a Lagrangian particle motion model combined with a Euler background field approach to construct a small-scale atmospheric flow field model. The model streamlines the modeling process by combining the benefits of the Lagrangian dynamics model and the Eulerian integration scheme. To verify the effectiveness of the Euler–Lagrange hybrid model, experiments using the Fluent wind field model were conducted for comparison. The results show that both models have their advantages in handling terrain-induced wind fields. The Fluent model excels in simulating the general characteristics of wind fields under specific terrain, while the Euler–Lagrange hybrid model is better at capturing the upstream and downstream disturbances of the terrain on the atmospheric flow field. These findings provide powerful tools for in-depth diagnostic analysis of atmospheric flow simulation and convective precipitation processes. Notably, the Euler–Lagrange hybrid model demonstrates excellent computational efficiency, with an average computation time of approximately 2 s per time step in a Python environment, enabling rapid simulation of 40 time steps within approximately 90 s.

Self-interacting scalar field in (2+1) dimensions Einstein gravity with torsion

We study a massless real self-interacting scalar field φ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varphi $$\\end{document} non-minimally coupled to Einstein gravity with torsion in (2+1) space-time dimensions in the presence of a cosmological constant. The field equations with a self-interaction potential V(φ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V(\\varphi )$$\\end{document} including φn\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varphi ^{n}$$\\end{document} terms are derived by a variational principle. By numerically solving these field equations with the 4th Runge–Kutta method, the circularly symmetric rotating solutions for (2+1) dimensions Einstein gravity with torsion are obtained. Exact analytical solutions to the field equations are derived for the proposed metric in the absence of both torsion and angular momentum. We find that the self-interacting potential only exists for n=6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n=6$$\\end{document}, as requested by conformal symmetry. We also study the motion of massive and massless particles in (2+1) Einstein gravity with torsion coupled to a self-interacting scalar field. The effect of torsion on the behavior of the effective potentials of the particles is analyzed numerically.

Precessing and periodic timelike orbits and their potential applications in Einsteinian cubic gravity

Einsteinian cubic gravity (ECG) is the most general theory up to cubic order in curvature, which has the same graviton spectrum as the Einstein theory. In this paper, we investigate the geodesic motions of timelike particles around the four dimensional asymptotically flat black holes in ECG, and discuss their potential applications when connecting them with recent observational results. We first explore the effects of the cubic couplings on the marginally bound orbits (MBO), innermost stable circular orbits (ISCO) and on the periodic orbits around the Einsteinian cubic black hole. We find that comparing to Schwarzschild black hole in general relativity, the cubic coupling enhances the energy as well as the angular momentum for all the bound orbits of the particles. Then, we derive the relativistic periastron precessions of the particles and give a preliminary bound on the cubic coupling employing the observational result of the S2 star’s pericenter precession in SgrA*. Finally, after calculating the periodic orbits’ configurations, we preliminarily evaluate the gravitational waveform radiated from several periodic orbits in one complete period of a test object which orbits a supermassive Einsteinian cubic black hole. Our studies could be helpful for us to better understand the gravitational structure of the theory with high curvatures.

On the Passage of a Relativistic Spinless Particle through a Potential Barrier

Contradictory descriptions of the passage of a relativistic particle through a high potential barrier are investigated. The conventional energy-momentum relation yields a real momentum for the particle within the barrier, suggesting classical particle motion. However, this contradicts the law of conservation of energy, which necessitates that the particle's momentum be imaginary, thereby rendering classical motion impossible. This paradox is resolved through the adoption of a novel energy-momentum relation.