Particle Kinetic Energy Research Articles

A discrete element method with spherical harmonics for irregular granular materials based on the level set contact algorithm

<p indent=0mm>To calculate the mechanical properties of irregular granular materials in natural or industrial fields, a discrete element model based on spherical harmonics that can describe arbitrarily shaped particles is developed. Considering the uneven surfaces and multiple contact points of the spherical harmonic elements, a contact model of arbitrary shapes based on the level set algorithm is developed to calculate the contact direction and overlap between the elements. In this model, spherical harmonic elements with different shapes are discretized into a zero level set function and a discrete spatial-level set function composed of a series of points. In addition, the contact detection between elements is transformed into a solution of two level set functions. All zero level set points are brought into the spatial-level set function of the neighboring element, and the multiple contact points and forces between the two neighboring elements are determined via trilinear interpolation. The elastic collision of a single particle with a wall, the free fall of a particle, and the packing process of multiple particles are simulated using the discrete element method, and the evolution of the translational and rotational kinetic energy of particles over time is studied to validate the discrete element model of the spherical harmonic function based on the level set method. The results show that the discrete element model of spherical harmonic functions based on the level set method can be used to calculate the contact forces between elements. Meanwhile, the energy of the granular system remains constant during the elastic collision, and the system energy decays during the inelastic collision until the kinetic energy approaches zero. Based on the aforementioned method, the influence of uneven surfaces on the packing fraction and average coordination number of granular materials is analyzed, and an effective discrete element model is provided for the numerical simulation of irregular granular materials.

Comparative case study of two methods to assess the eruptive potential of selected active regions

Solar eruptive events, like flares and coronal mass ejections, are characterized by the rapid release of energy that can give rise to emission of radiation across the entire electromagnetic spectrum and to an abrupt significant increase in the kinetic energy of particles. These energetic phenomena can have important effects on the space weather conditions and therefore it is necessary to understand their origin, in particular, what is the eruptive potential of an active region (AR). In these case studies, we compare two distinct methods that were used in previous works to investigate the variations of some characteristic physical parameters during the pre-flare states of flaring ARs. These methods consider: i) the magnetic flux evolution and magnetic helicity accumulation, and ii) the fractal and multi-fractal properties of flux concentrations in ARs. Our comparative analysisis based on time series of photospheric data obtained bythe Solar Dynamics Observatory between March 2011 and June 2013. We selected two distinct samples of ARs: one is distinguished by the occurrence of more energetic M- and X-class flare events, that may have a rapid effect on not just the near-Earth space, but also on the terrestrial environment; the second is characterized by no-flares or having just a few C- and B-class flares. We foundthat the two tested methods complement each other in their ability to assess the eruptive potentials of ARs and could be employed to identify ARs prone to flaring activity. Based on the presented case study, we suggest that using a combination of different methods may aid to identify more reliably the eruptive potentials of ARs and help to better understand the pre-flare states.

Complexity of Magnetic-field Turbulence at Reconnection Exhausts in the Solar Wind at 1 au

Abstract Magnetic reconnection is a complex mechanism that converts magnetic energy into particle kinetic energy and plasma thermal energy in space and astrophysical plasmas. In addition, magnetic reconnection and turbulence appear to be intimately related in plasmas. We analyze the magnetic-field turbulence at the exhaust of four reconnection events detected in the solar wind using the Jensen–Shannon complexity-entropy index. The interplanetary magnetic field is decomposed into the LMN coordinates using the hybrid minimum variance technique. The first event is characterized by an extended exhaust period that allows us to obtain the scaling exponents of higher-order structure functions of magnetic-field fluctuations. By computing the complexity-entropy index we demonstrate that a higher degree of intermittency is related to lower entropy and higher complexity in the inertial subrange. We also compute the complexity-entropy index of three other reconnection exhaust events. For all four events, the B L component of the magnetic field displays a lower degree of entropy and higher degree of complexity than the B M and B N components. Our results show that coherent structures can be responsible for decreasing entropy and increasing complexity within reconnection exhausts in magnetic-field turbulence.

Reconnection and particle acceleration in three-dimensional current sheet evolution in moderately magnetized astrophysical pair plasma

Magnetic reconnection, a plasma process converting magnetic energy to particle kinetic energy, is often invoked to explain magnetic energy releases powering high-energy flares in astrophysical sources including pulsar wind nebulae and black hole jets. Reconnection is usually seen as the (essentially two-dimensional) nonlinear evolution of the tearing instability disrupting a thin current sheet. To test how this process operates in three dimensions, we conduct a comprehensive particle-in-cell simulation study comparing two- and three-dimensional evolution of long, thin current sheets in moderately magnetized, collisionless, relativistically hot electron–positron plasma, and find dramatic differences. We first systematically characterize this process in two dimensions, where classic, hierarchical plasmoid-chain reconnection determines energy release, and explore a wide range of initial configurations, guide magnetic field strengths and system sizes. We then show that three-dimensional (3-D) simulations of similar configurations exhibit a diversity of behaviours, including some where energy release is determined by the nonlinear relativistic drift-kink instability. Thus, 3-D current sheet evolution is not always fundamentally classical reconnection with perturbing 3-D effects but, rather, a complex interplay of multiple linear and nonlinear instabilities whose relative importance depends sensitively on the ambient plasma, minor configuration details and even stochastic events. It often yields slower but longer-lasting and ultimately greater magnetic energy release than in two dimensions. Intriguingly, non-thermal particle acceleration is astonishingly robust, depending on the upstream magnetization and guide field, but otherwise yielding similar particle energy spectra in two and three dimensions. Although the variety of underlying current sheet behaviours is interesting, the similarities in overall energy release and particle spectra may be more remarkable.

Energy Mechanisms of Free Vibrations and Resonance in Elastic Bodies

The scientific novelty of this work is determined by the rationale for the participation in transformations, along with the kinetic energy of particles, of four types of elastic energy, identified by the peculiarities of their phase changes in the oscillation process. Two types are converted into kinetic energy, while the other two types change the deformed state of particles in accordance with the equations of motion due to internal sources. The result is obtained based on the use of the superposition principle in the space of Lagrange variables with the imposition of forced and free oscillations, as well as a new model of mechanics based on the concepts of space, time, and energy with a new scale of average stresses that takes into account the energy of particles in the initial state. In such a model of mechanics, a generalized measure of the elastic energy of particles is a quadratic invariant of asymmetric tensor whose components are partial derivatives of Euler variables with respect to Lagrange variables. The concept of kinematic energy parameters is introduced, which differ from the corresponding volumetric energy densities by a multiplier equal to the modulus of elasticity, which is directly proportional to the density and heat capacity of the material, and inversely proportional to the volumetric compression coefficient. Comparison of the values of kinematic parameters shows that most of the energy required for oscillations is associated with the deformation of particles and comes from internal sources. The mechanisms of transformation of forced vibrations into their own for transverse, torsional, and longitudinal vibrations are considered, as well as the occurrence of resonance when free and forced vibrations are superimposed with the same or a similar frequency. The formation of a new free wave after each cycle of external influences with an increase in amplitude, which occurs mainly due to internal, and not external, energy sources is justified.

Dynamics of a single bubble rising in a quiescent medium

In the present work, an experimental analysis was performed to characterise the flow field around a single bubble of different diameters ∼ 2.77–3.53 mm) rising in a quiescent medium aiming to determine the effect of bubble size on kinetic energy distribution. The velocity field was measured using a non-intrusive particle image velocimetry (PIV) technique and kinetic energy spectrum was determined in both transverse and longitudinal directions applying a Fast Fourier Transformation (FFT). Both small- and large-scale motions of the flow field were identified and separated using a discreate wavelet transformation (DWT) method. It was found that the energy spectrum of the large-scale motions depended on the bubble size while the small-scale energy spectrum was nearly independent of it. The slopes of the energy spectrum were found to be close to -5/3 and -3 for the large- and small-scale regimes, respectively and the transition of slope was observed to occur at the wavenumber corresponding to the bubble diameter. Using the measured velocity field data, a turbulence kinetic energy (TKE) budget analysis was performed involving five components namely kinetic energy production, turbulent transport, pressure diffusion, viscous diffusion, and energy dissipation. Overall, it was observed that in the vicinity of bubble surface, turbulence production term was not entirely balanced by the dissipation term; and turbulent transport and pressure diffusion term also had significant contributions.

Impact of High Inertia Particles on the Shock Layer and Heat Transfer in a Heterogeneous Supersonic Flow around a Blunt Body

One of the most important and complex effects associated with the presence of particles in the flow is the gas-dynamic interaction of particles with the shock layer. Of particular interest is the intensification of heat transfer by high inertia particles rebounding from the surface or by the products of erosion destruction, which reach the front of the bow shock wave and violate the gas-dynamic structure of the flow. In this case, according to experimental data, the increase in heat fluxes is much greater than it could be predicted based on the combined action of the kinetic energy of particles and a high-speed flow. The problem is related to the destruction of the flow structure. In this paper, the problem is studied with numerical simulation. We show that the key role in the intensification of heat transfer is played by the formation of an impact jet flowing onto the surface. An area of increased pressure and heat flux is formed in the zone of action of the impact jet. This effect is maintained over time by the successive action of particles.

Coarse Particle Motion Characteristics in a Double-Stage Slurry Pump Considering Leakage Flow

Along with the pressing demand for the long-distance transportation of coarse particles in the deep-sea mining industry, evaluating the slurry pump’s passing through and erosive wear by studying the particle motion characteristics and the slurry behavior is becoming increasingly important. Research on the influence of leakage flow through the clearance and balancing devices on the motion characteristic of granular grain flow is of great significance but has been seldom studied. This study coupled the discrete element method with the CFD method to investigate the comprehensive effect of a double-stage slurry pump’s main flow and leakage flow on the motion characteristics of particles with a 10 mm diameter. Results show that the leakage flow occupation in main flow falls from 26%–27% to 8%–9% for the two stages, with the flow rate increasing from 80 m3/h to 200 m3/h. In the first stage with leakage, accumulation of coarse particles was observed at the impeller eye, which should be paid much attention to slurry pumps’ operation to eliminate the chance of blockage. In the nonleak situation, although the increment of the average kinetic energy of particles through the impeller is more significant than in the leak case, most of them dissipate primarily by more than 10% collision in the bowl diffuser. In the leak or nonleak case, the average kinetic energy of particles was more than twice through the first stage but only 1.1 times through the second stage. The selection of stages in the slurry pump design should consider the limitation of particle velocity improvement.

EXCITATION OF MAGNETOPLASMA OSCILLATIONS IN SEMICONDUCTOR STRUCTURES BY FLUXES OF CHARGED PARTICLES

The subject of the papers is the processes of analysis and physical model of excitation (amplification) of magnetoplasma oscillations (helicons) by fluxes of charged particles (electrons) in the presence of a constant magnetic field. This model is based on the Cherenkov mechanism for converting kinetic energy of particles into the energy of natural electromagnetic oscillations of solid-state (semiconductor) structures under resonance conditions when the particle velocities coincide with phase velocities of oscillations. The aim here is to justify the formulation of theoretical studies basing on the proposed physical model of generation (amplification) of electromagnetic oscillations (emergence of oscillation instabilities, i.e., exponential growth of their amplitude). We define parameters intervals for the external magnetic field, particle fluxes and types of semiconductor structures which this physical model is applied to. We perform theoretical study of the influence charged particle fluxes have on waveguide characteristics of semiconductor structures. The study justifies the possibility of generation and amplification of magnetoplasma oscillations in the submillimeter range. Our objectives are theoretical studies of the interaction of moving charges with electromagnetic oscillations of a semiconductor structure under conditions of Cherenkov radiation. The methods used are the method of successive approximations for solving the dispersion equations for a system of charged particle flux - semiconductor structure within the framework of hydrodynamic approach. The following results are obtained: Theoretical studies of the functioning of semiconductor components of electrical radio equipment in the presence of charged particle fluxes have been carried out. It is shown that the effect of the particle flux is characterized by the emergence of oscillation instabilities in the semiconductor structure. We have determined one of the mechanisms for the excitation of magnetoplasma oscillations based on the interaction of moving charges with the intrinsic fields of the structures that constitute a semiconductor unit. Such equipment failures occur under conditions of Cherenkov radiation. We have shown that this interaction leads to appearance of a mode of oscillation generation. The results of a comparative analysis of the data obtained in this work make it possible to use the proposed physical model to determine the criteria for the occurrence and development of instabilities of magnetoplasma oscillations. Conclusions. The results obtained in this work can be used in the development of active microwave range devices (amplifiers, generators and transducers of electromagnetic oscillations of the millimeter and submillimeter bands). The comparative analysis of quantitative estimates of the growth rates of oscillation instabilities, depending on the spatial configuration of the acting field (when induced current is parallel to the structure boundary), carried out in this work, provides a solution to the problem of optimizing the operating characteristics of active microwave devices.

A model to simulate large angle Rutherford backscattering spectra in GEANT4

A model was developed to simulate RBS spectra of H, He and Li ions based on the GEANT4 simulation toolkit. The simulation consists of tracking particles inside the medium and collecting kinetic energy and momentum direction at each step of the particle track. With this information, a backscattering spectrum is simulated based on Rutherford and non-Rutherford cross sections, detection angle and energy loss in the sample and the detector. The simulation of impinging particles is governed by GEANT4 physics processes, while the backscattered particle kinetic energy at the detector is evaluated manually. The developed GEANT4 model supports up to five layers, includes evaluation of energy loss straggling and multiple scattering induced energy straggling, evaluation of detector energy resolution of heavier ions. The RBS spectra obtained by our GEANT4 model were compared with the most widely used tools, specifically, IBA Data Furnace WinDF and SIMNRA, and showed a good agreement. The current model lacks evaluation of plural scattering, surface roughness, material porosity influence, etc., however, as it is open source, the users and developers can add the lacking functions.

Numerical Simulation of Granular Column Collapse with Fractal Particle Size Distribution Using Discrete Element Method

This study conducts numerical simulations of the granular column collapse with Fractal Particle Size Distributions (FPSDs) via the Discrete Element Method (DEM) and investigated kinetic behaviours of dry granular flows. The aim of this paper is to explore the effects of the fractal dimension of FPSD on the kinetics of dry granular flows. When the fractal dimension of the flows consisting of granular materials increases, the horizontal particle translational velocities become greater and the mobility improves, whereas the particle rotational velocities decrease. Meanwhile, the change in the potential energy increases, and the particle kinetic energy in the rotational form reduces; thus, the particle kinetic energy in the translational form increases. The reducing particle rotational movement may be related to the reducing particle shearing behaviours because only the contact shearing can affect particle rotational motion. In conclusion, a larger fractal dimension of FPSD of a dry granular flow leads to a longer spreading distance and a smaller rotational velocity.

Numerical simulation of particle velocity and coordination number under the slumping regime in a rotating drum

In this paper, a numerical simulation is applied to statistic the particle velocity and coordination number of the surface layer under the slumping regime in a rotating drum. We find that the particle velocity distribution under different coordination numbers in the avalanche always satisfies Maxwell distribution and exponential distribution. This indicated that the distribution of coordination number is the main factor causing uneven avalanche. Furthermore, the mathematical model of particle velocity and coordination number is established, and a novel method for calculating the kinetic energy of particle system is proposed. It is observed that the maximum kinetic energy of particles in different regions during the uneven avalanche is positively correlated with the avalanche duration. These results reveal the particle flow regular in the rotating drum, which provides reference data for improving the control technology of particle material flow and the heat transfer in industry.

Energy Flux Densities at Dipolarization Fronts

AbstractDipolarization fronts (DFs) have been suggested as crucial energy conversion sites contributing significantly to global energy transfer in the magnetosphere. However, energy partitioning of DF‐driven energy transfer remains hitherto elusive. Using high‐cadence data from MMS spacecraft, we present a detailed investigation of energy flux densities at two DFs with/without surface ripples. We find that during both DF intervals, electron enthalpy flux increases dramatically, carries the greatest energy, and well correlates with local energy conversion. Poynting flux also increases but contributes to a relatively smaller portion. Ion enthalpy flux which in magnitude is slightly smaller than electron enthalpy flux barely changes. Particle kinetic energy and heat fluxes are negligible. Strong difference in energy fluxes observed by different spacecraft is found at the rippled DF, indicating three‐dimensional energy transport. These results indicate that energy budgets at the DFs are dominated by electron physics, rather than ion dynamics suggested by previous studies.

Influence of particle non-dilute effects on its dispersion in particle-laden blast wave systems

Even though the interaction of blast waves with dense particle distributions is ubiquitous in nature and in industry, the underlying physics of the multiphase system evolution is not clearly understood. A canonical multiphase system composed of an embedded monodisperse distribution of spherical particles in a spherical, high-energy gaseous charge is studied numerically using an Eulerian–Lagrangian approach to elucidate the role of non-dilute particle effects on the dynamics of the two-phase flow system. The direct simulation Monte Carlo method is modified to model inelastic particle–particle collisions and to model the gaseous flow inter-leaving through complex structures of monodisperse dense distributions of spherical particles to obtain parameters that are fit to semi-empirical particle cloud drag laws that account for aerodynamic interactions. The study reveals that inter-particle collisions decrease the total particle kinetic energy at early stages of the particle-laden blast wave system evolution, but near-particle interaction increases the particle kinetic energy at this stage. In contrast, at later stages of evolution, collisions tend to retain more kinetic energy, while the aerodynamic interactions tend to dissipate particle kinetic energy.

Investigation of Particle Kinetic Energy for EKF-CMP Process

The particle kinetic energy (PKE) in a slurry film between the pad and wafer during chemical-mechanical polishing (CMP) under the assistance of electro-kinetic force (EKF) was investigated. Novel simulation results of a three-dimensional electro-osmosis flow (3D-EOF) model have been well-verified by velocity fields of particle image velocimetry analysis. The velocity magnitudes of EOF under various simulation conditions have been compared with both experimental and theoretical results. Analysis results for PKE indicate that the PKE value at the top layer is smaller compared to that at the bottom layer due to dissipating PKE in the interactions between the abrasive nanoparticles and the wafer surface. Effective nanoparticle kinetic energy contacting the wafer surface increased with increased electrode voltage and achieved an optimal value at an electrode gap of 2000 μm. Compared with our previous study at a down pressure of 1.5 psi, the optimized polishing performance for a Cu blanket wafer at a loading pressure of 2.5 psi improved 0.32 % for material removal rate, 10.8 % for non-uniformity, and 2.14 %, 3.87 %, 8.1 %, and 8.32 % of surface roughness for Sa, Sq, Ra, and Rq, respectively. The results explain the significant role of kinetic energy affecting abrasive nanoparticles’s motion speed contacting the wafer to achieve an ultra-smooth surface for IC fabrication.

INVESTIGATION OF THE 16O(γ, p)3H3α REACTION AT THE ENERGIES BELOW THE MESON PRODUCTION THRESHOLD

The reaction 16O(γ, p)3H3 induced by bremsstrahlung photons of endpoint energy Emaxγ = 150 MeV has been studied by the method of a diffusion chamber in a magnetic field. The energy dependence of the total cross section has been measured in the energy range from the threshold and has been founded a broad resonance centered at 55 MeV. The rate of decrease in the cross section undergoes a change in the region around 55 MeV. A comparison was made with the cross section for reactions 4He(γ, p)3H and 12С(γ, р)3H2. The agreement between the shapes of distributions for the (γ, p)3H reactions is evident and was concluded that the mechanism of interaction of the γ-quantum with the nucleus is similar. The dependence of average kinetic energy of particles on the total kinetic energy was determined. In the whole energy interval, the distribution for a proton is more than the statistical distribution. Distribution of relative energy of the proton and 3H nucleus in their c.m.s. does not agree with the predictions of the mechanism of photon absorption by an α-particle cluster, but at energies above the maximum, it agrees with calculations within the framework of the quasi-deuteron model of photoabsorption.

Memory effects in a gas of viscoelastic particles

We study a granular gas of viscoelastic particles (kinetic energy loss upon collision is a function of the particles' relative velocities at impact) subject to a stochastic thermostat. We show that the system displays anomalous cooling and heating rates during thermal relaxation processes, this causing the emergence of thermal memory. In particular, a significant Mpemba effect is present, i.e., an initially hotter/cooler granular gas can cool down/heat up faster than an in comparison cooler/hotter granular gas. Moreover, a Kovacs effect is also observed, i.e., a nonmonotonic relaxation of the granular temperature—if the gas undergoes certain sudden temperature changes before fixing its value. Our results show that both memory effects have distinct features, very different and eventually opposed to those reported in theory for granular fluids under simpler collisional models. We study our system via three independent methods: approximate solution of the kinetic equation time evolution and computer simulations (both molecular dynamics simulations and direct simulation Monte Carlo method), finding good agreement between them.

Solid particle erosion of a plasma spray – physical vapor deposition environmental barrier coating in a combustion environment

Environmental barrier coatings (EBCs) were developed to reduce the susceptibility of SiC-based composites to the rapid volatilization and surface recession that occurs in the presence of water vapor. Extensive research and development has been performed on EBCs, and their corresponding failure mechanisms under different environmental conditions. However, one key failure mechanism, solid particle erosion (SPE), has not been thoroughly investigated. As a result, the present work investigates the SPE behavior of a ytterbium disilicate (Yb2Si2O7) environmental barrier coating (EBC) deposited via plasma spray-physical vapor deposition (PS-PVD). Erosion testing was performed at elevated temperature (1200 °C) in a simulated combustion environment at the NASA Glenn Research Center Erosion Burner Rig Facility. Alumina (Al2O3) particles were used as the eroding media. A range of particle kinetic energies and impingement angles were investigated along with the effect of coating surface roughness. The post-erosion damage morphology was characterized using scanning electron microscopy (SEM). The SPE behavior of the PS-PVD EBC was shown to be comparable to other EBC systems reported in the literature.

Optimum silver contact sputtering parameters for efficient perovskite solar cell fabrication

The use of magnetron sputtering for deposition of the metal electrode in perovskite solar cells has been limited because of the damage to the organic hole transport layer by high kinetic energy particles during the sputtering process. In this paper, a systematic investigation into the effect of sputtering power, argon flow rate, sputtering duration, and argon pressure on the performance of the perovskite cells was conducted. The results of this work show that high power conversion efficiency of 18.35% was obtained for solution-processed, air-fabricated perovskite solar cells with Ag contact prepared using magnetron sputtering. The devices also exhibit an excellent short-current density of 22.56 mA/cm2, an open-circuit voltage of 1.10 V and a fill factor of 73.7%. The investigation reveals that sputtering power is the most critical factor that needs to be carefully controlled to minimise the damage to the hole transport layer. This study demonstrates that highly efficient perovskite solar cells can be fabricated using magnetron sputtering if the sputtering parameters are optimised.

Collision-adhesion mechanism of particles and dust deposition simulation on solar PV modules

Dust accumulation has a significant influence on the performance of solar photovoltaic (PV) modules. Investigating the particle collision-adhesion mechanism helps to understand dust accumulation characteristics of PV modules and provide theoretical support for dust removal work, and hence, improve PV efficiency. This study established a collision-adhesion model between particles and PV modules. Then, the mechanical equilibrium-based and energy-based particle adhesion mechanisms were explored and particle deposition condition was proposed. Furthermore, a dust accumulation experiment was created to verify the rationality of simulation model, which was constructed using energy-based particle adhesion mechanism. Based on this, a simulation was performed on the impact of various factors on particle deposition. The results showed the particle kinetic energy loss with a magnitude of 10−13 J in the collision was positively correlated with humidity and particle size, while negatively correlated with wind speed and tilt angle. The particle deposition amount first decreases and then increases with increasing wind speed and particle size. However, it increases with increasing humidity and decreases with increasing tilt angle. Additionally, when the tilt angle increases from 15° to 60°, the particle deposition amount reduced from 4.28 g/m2 to 1.81 g/m2 under 7 m/s. In the future construction of PV power plants, for the area where particle size and average annual wind speed are less than 30 μm and 7 m/s, increasing the tilt angle appropriately can reduce dust accumulation.