The absence of sub-grid scale(SGS) motions leads to severe errors in particle pair dynamics, which represents a great challenge to the large eddy simulation of particle-laden turbulent flow. In order to address this i...The absence of sub-grid scale(SGS) motions leads to severe errors in particle pair dynamics, which represents a great challenge to the large eddy simulation of particle-laden turbulent flow. In order to address this issue,data from direct numerical simulation(DNS) of homogenous isotropic turbulence coupled with Lagrangian particle tracking are used as a benchmark to evaluate the corresponding results of filtered DNS(FDNS). It is found that the filtering process in FDNS will lead to a non-monotonic variation of the particle collision statistics, including radial distribution function, radial relative velocity, and the collision kernel. The peak of radial distribution function shifts to the large-inertia region due to the lack of SGS motions, and the analysis of the local flowstructure characteristic variable at particle position indicates that the most effective interaction scale between particles and fluid eddies is increased in FDNS. Moreover,this scale shifting has an obvious effect on the odd-order moments of the probability density function of radial relative velocity, i.e. the skewness, which exhibits a strong correlation to the variance of radial distribution function in FDNS.As a whole, the radial distribution function, together with radial relative velocity, can compensate the SGS effects for the collision kernel in FDNS when the Stokes number based on the Kolmogorov time scale is greater than 3.0. However,it still leaves considerable errors for St< 3.0.展开更多
The particle collision behavior and heat transfer performance are investigated to reveal the heat transfer enhancement and fouling prevention mechanism in a Na_(2)SO_(4) circulating fluidized bed evaporator.The partic...The particle collision behavior and heat transfer performance are investigated to reveal the heat transfer enhancement and fouling prevention mechanism in a Na_(2)SO_(4) circulating fluidized bed evaporator.The particle collision signals are analyzed with standard deviation by varying the amount of added particles ε(1%–3%),circulation flow velocity u(0.37–1.78 m·s^(-1)),and heat flux q(7.29–12.14 kW·m^(-2)).The results show that the enhancement factor reach up to 14.6%by adding polytetrafluoroethylene particles at ε=3%,u=1.78 m·s^(-1),and q=7.29 kW·m^(-2).Both the standard deviation of the particle collision signal and enhancement factor increase with the increase in the amount of added particles.The standard deviation increases with the increase in circulation flow velocity;however,the enhancement factor initially decreases and then increases.The standard deviation slightly decreases with the increase in heat flux at low circulation flow velocity,but initially increases and then decreases at high circulation flow velocity.The enhancement factor decreases with the increase in heat flux.The enhancement factor in Na_(2)SO_(4) solution is superior to that in water at high amount of added particles.The empirical correlation for heat transfer is established,and the model results agree well with the experimental data.展开更多
For investigating efficiently the stagnation kinetic-process of Z-pinch,we develop a novel modified electrostatic implicit particle-in-cell algorithm in radial one-dimension for Z-pinch simulation in which a small-ang...For investigating efficiently the stagnation kinetic-process of Z-pinch,we develop a novel modified electrostatic implicit particle-in-cell algorithm in radial one-dimension for Z-pinch simulation in which a small-angle cumulative binary collision algorithm is used.In our algorithm,the electric field in z-direction is solved by a parallel electrode-plate model,the azimuthal magnetic field is obtained by Ampere’s law,and the term for charged particle gyromotion is approximated by the cross product of the averaged velocity and magnetic field.In simulation results of 2 MA deuterium plasma shell Zpinch,the mass-center implosion trajectory agrees generally with that obtained by one-dimensional MHD simulation,and the plasma current also closely aligns with the external current.The phase space diagrams and radial-velocity probability distributions of ions and electrons are obtained.The main kinetic characteristic of electron motion is thermal equilibrium and oscillation,which should be oscillated around the ions,while that of ion motion is implosion inwards.In the region of stagnation radius,the radial-velocity probability distribution of ions transits from the non-equilibrium to equilibrium state with the current increasing,while of electrons is basically the equilibrium state.When the initial ion density and current peak are not high enough,the ions may not reach their thermal equilibrium state through collisions even in its stagnation phase.展开更多
This paper presents an extension of the lumped particle model in[1]to include the effects of particle collisions.The lumped particle model is a flexible framework for the modeling of particle laden flows,that takes in...This paper presents an extension of the lumped particle model in[1]to include the effects of particle collisions.The lumped particle model is a flexible framework for the modeling of particle laden flows,that takes into account fundamental features,including advection,diffusion and dispersion of the particles.In this paper,we transform a binary collision model and concepts from kinetic theory into a collision procedure for the lumped particle framework.We apply this new collision procedure to investigate numerically the role of particle collisions in the hindered settling effect.The hindered settling effect is characterized by an increase in the effective drag coefficient CD that influences each particle in the flow.This coefficient is given by CD=(1−φ)−nC∗D,whereφis the volume fraction of particles,C∗D is the drag coefficient for a single particle,and n≃4.67 for creeping flow.We obtain an approximation for CD/C∗D by calculating the effective work done by collisions,and comparing that to the work done by the drag force.In our numerical experiments,we observe a minimal value of n=3.0.Moreover,by allowing high energy dissipation,an approximation for the classical value for creeping flow,n=4.7,is reproduced.We also obtain high values for n,up to n=6.5,which is consistent with recent physical experiments on the sedimentation of sand grains.展开更多
The data of charged particles produced in proton-proton collisions extracted from Durham particle data group at energy ranges √s = 6.3 - 17 GeV and at 0.9 - 7 TeV are investigated in the framework of Tsallis thermo-s...The data of charged particles produced in proton-proton collisions extracted from Durham particle data group at energy ranges √s = 6.3 - 17 GeV and at 0.9 - 7 TeV are investigated in the framework of Tsallis thermo-statistics and the Vlasov time dynamics. The analysis can describe the experimental data well all-over the considered energies and rapidity intervals. The variation of the collision parameters (chemical potential, entropy index and the time of evolution) is studied and discussed as a function of the final state temperature. According to the obtained result, a scenario, and a script of the time evolution for the particle production is simulated by the pp collision.展开更多
In the context of unified hydrodynamics, we discuss the pseudorapidity distributions of the charged particles produced in Au-Au and Cu-Cu collisions at the low RHIC energies of √SNN = 19.6 and 22.4 GeV, respectively....In the context of unified hydrodynamics, we discuss the pseudorapidity distributions of the charged particles produced in Au-Au and Cu-Cu collisions at the low RHIC energies of √SNN = 19.6 and 22.4 GeV, respectively. It is found that the unified hydrodynamics alone can give a good description to the experimental measurements. This is different from the collisions at the maximum RHIC energy of √SNN = 200 GeV or at LHC energy of √SNN= 2.76 TeV, in which the leading particles must be taken into account so that we can properly explain the experimental observations.展开更多
Some of the possible decays of pp collisions at LHC experiment are considered. The vector bosons mediating in the electroweak interactions and right-handed leptons except neutrinos are assumed to be the most resultant...Some of the possible decays of pp collisions at LHC experiment are considered. The vector bosons mediating in the electroweak interactions and right-handed leptons except neutrinos are assumed to be the most resultant particles from the pp collisions. Neutrinos and anti-neutrinos will be observed when one-double electron charged vector bosons are the resultant particles. The charge conservation is thought to be the dominant factor of these decays. The amplitude transitions for Feynman diagram of these decays are written.展开更多
The elliptic flow v2, for π±, K±, p and p in Au＋Au collisions at center-of-mass energies √sNN=7.7, 11.5, 14.5 and 19.6 GeV, is analyzed using a multiphase transport model. A significant difference in the ...The elliptic flow v2, for π±, K±, p and p in Au＋Au collisions at center-of-mass energies √sNN=7.7, 11.5, 14.5 and 19.6 GeV, is analyzed using a multiphase transport model. A significant difference in the v2 values for p and p is observed, and the values of v2 splitting are larger compared with π＋ and π-, K＋ and K-. The difference increases with decreasing the center-of-mass energy. The effect of the quark coalescence mechanism in a multi-phase transport model to the value of elliptic difference △v2 between p and p- has been discussed. The simulation of Au＋Au collisions at 14.5 GeV shows that the effect of hadron cascade to △v2 is not obvious, and a larger patton-scattering cross section can lead to a larger △v2.展开更多
In this paper,the power law of particle size distributions (PSDs) in conventional water treatment processes is developed. After measuring the particle size distributions of raw-water,settled water and filtered water,a...In this paper,the power law of particle size distributions (PSDs) in conventional water treatment processes is developed. After measuring the particle size distributions of raw-water,settled water and filtered water,a mathematical model between particle diameter and the amount of particles was studied. The value of collision frequency factor β in the PSDs model can be used to represent the collision behavior of particles ,and can be used as foundation exponent to choose suitable coagulation to accelerate particles aggregation. At the same time,the relationship between the value of parameter K and the total particles volume V was deduced. K is defined as particle volume exponent,which can represent the total volume of particles. The degression degree of K shows the removal efficiency of potable water treatment units.展开更多
The investigation was carried out on the technical problems of finishing the inner surface of elbow parts and the action mechanism of particles in elbow precision machining by abrasive flow.This work was analyzed and ...The investigation was carried out on the technical problems of finishing the inner surface of elbow parts and the action mechanism of particles in elbow precision machining by abrasive flow.This work was analyzed and researched by combining theory,numerical and experimental methods.The direct simulation Monte Carlo(DSMC)method and the finite element analysis method were combined to reveal the random collision of particles during the precision machining of abrasive flow.Under different inlet velocity,volume fraction and abrasive particle size,the dynamic pressure and turbulence flow energy of abrasive flow in elbow were analyzed,and the machining mechanism of particles on the wall and the influence of different machining parameters on the precision machining quality of abrasive flow were obtained.The test results show the order of the influence of different parameters on the quality of abrasive flow precision machining and establish the optimal process parameters.The results of the surface morphology before and after the precision machining of the inner surface of the elbow are discussed,and the surface roughness Ra value is reduced from 1.125μm to 0.295μm after the precision machining of the abrasive flow.The application of DSMC method provides special insights for the development of abrasive flow technology.展开更多
In dielectrics and semiconductors, a plasma model of the generation and slip of dislocations is considered, where under shock loads in a generalized space of rectangular pulses an alternating field forms a distributio...In dielectrics and semiconductors, a plasma model of the generation and slip of dislocations is considered, where under shock loads in a generalized space of rectangular pulses an alternating field forms a distribution of pairs of photoelectrons and cations;these electrons with velocities <em>V<sub>e</sub></em> create <em>δ</em>-collisions with cold plasma from free electrons and holes with masses <em>m<sub>e</sub></em> and <em>m<sub>h</sub></em> (<em>m<sub>h</sub></em> <span style="white-space:normal;"><span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">≫</span></span> </span></span><em>m<sub>e</sub></em>), they emit and absorb longitudinal electron plasma waves whose phase velocities <em>w<sub>pw</sub></em> / <em>k<sub>pw</sub></em> are close to or are equal to the velocities <em>V<sub>e</sub></em>, while the frequencies <em>w<sub>pw</sub></em> and wave numbers <em>k<sub>pw</sub></em> of the wave packet of plasma waves are complex, the short-wave components <img src="Edit_3da65014-7fd8-4799-bcf1-02d90028f4e0.bmp" alt="" /> of this wave packet at <em>k<sub>pw</sub></em> <span style="white-space:normal;"><span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">⋅</span></span></span> </span><em>a<sub>e </sub></em><span style="white-space:nowrap;">≫ </span>1 (<em>a<sub>e</sub></em> -Debye screening radius) decay in the core linear defect, and its long-wavelength components <img src="Edit_4481889b-5097-4d26-9019-b0322f5ff8d0.bmp" alt="" /> propagate in the region of the medium surrounding the core of the defect at <em>k<sub>pw</sub></em> <span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">⋅</span></span></span> <em>a<sub>e</sub></em> <span style="white-space:nowrap;"><<span style="white-space:nowrap;"><span style="white-space:nowrap;">≅</span></span></span> 1. When a defect is generated, the distribution of cations under the influence of the internal Coulomb field shifts to the region of the first peak (protrusion) of the electron plasma wave, thereby forming a vacancy valley. When sliding under the influence of an external electric field, a cationic plasma wave consisting of a vacancy valley and two cationic protrusions moves against the background of an additional potential relief created by an electron plasma wave near the core of the defect. It has been shown that <em>δ</em>-collisions create flows of dynamic large-scale correlations of plasma fluctuations in the form of asymptotics of different-time correlators of density and potential fluctuations as <em>t</em> → +∞.展开更多
We study the collision property of spinning particles near a Banados-Teitelboim-Zanelli(BTZ)black hole.Our results show that although the center-of-mass energy of two ingoing particles diverges if one of the particles...We study the collision property of spinning particles near a Banados-Teitelboim-Zanelli(BTZ)black hole.Our results show that although the center-of-mass energy of two ingoing particles diverges if one of the particles possesses a critical angular momentum,the particle with critical angular momentum cannot exist outside of the horizon due to violation of the timelike constraint.Further detailed investigation indicates that only a particle with a subcritical angular momentum is allowed to exist near an extremal rotating BTZ black hole,and the corresponding collision center-of-mass energy can be arbitrarily large in a critical angular momentum limit.展开更多
Flight simulators can provide a suitable alternative to real flight, mainly to increase safety through the training of crew, and evaluation data from simulator can be used to validation and certification of aircraft s...Flight simulators can provide a suitable alternative to real flight, mainly to increase safety through the training of crew, and evaluation data from simulator can be used to validation and certification of aircraft systems. However, it must convey some degree of realism to the user to be effective. For that reason, it is necessary to calibrate the simulator software. Calibration for flight simulation is parameter identification process. The process is formulated as an optimization problem, and it is solved by using a new approach named Multiple Particle Collision Algorithm （MPCA）. Results show a good performance for the employed approach.展开更多
Sand storm is a serious environmental threat to humans. Sand particles are transported by saltation and suspension, causing soil erosion in one place and deposition in another. In order to prevent and predict sand sto...Sand storm is a serious environmental threat to humans. Sand particles are transported by saltation and suspension, causing soil erosion in one place and deposition in another. In order to prevent and predict sand storms, the causes and the manners of particle motions must he studied in detail. In this paper a standard k-8 model is used for the gas phase simulation and the discrete element method （DEM） is used to predict the movements of particles using an in-house procedure. The data are summarized in an Eulerian-Eulerian regime after simulation to get the statistical particle Reynolds stress and particle collision stress. The results show that for the current case the Reynolds stress and the air shear stress predominate in the region 20-250 mm above the initial sand bed surface. However, in the region below 3 ram, the collision stress must be taken into account in predicting particle movement.展开更多
Researches in the field of low-energy nuclear reactions (LENR) have shown a wide variety of manifestations of these phenomena. They appear in metals with hydrogen dissolved in them, in plasma, in gas discharge, in ele...Researches in the field of low-energy nuclear reactions (LENR) have shown a wide variety of manifestations of these phenomena. They appear in metals with hydrogen dissolved in them, in plasma, in gas discharge, in electrolysis, and even in biological systems. In addition to energy release, which far exceeds the capabilities of chemical reactions, LENR is characterized by a huge variety of emerging chemical elements. This report provides examples of appearance of many initially missing elements in different LENR installations. For example, in the nickel-hydrogen LENR reactor created in our laboratory, which worked for 7 months, Ca, V, Ti, Mn, Fe, Co, Cu, Zn, Ga, Ba, Sr, Yb, Hf were found. Moreover, new elements were found not only in the “fuel” but also in the surrounding matter. The huge variety of chemical elements that arise can be explained by the fact that in the processes of LENR, the interaction covers several atoms at once. The article discusses approaches to explaining the phenomena discovered in the process of LENR researches.展开更多
Elbow wear is a major threat to the multiphase pipeline transportation industry,which has a negative impact on the stable operation of the transportation system.In order to find the wear reduction methods of elbows in...Elbow wear is a major threat to the multiphase pipeline transportation industry,which has a negative impact on the stable operation of the transportation system.In order to find the wear reduction methods of elbows in the fluidization pipeline transportation system for 2000-meter-deep coal resources,the swirler was installed upstream of the elbows,and wear simulations and tests of three kinds of elbows were carried out.The results showed that the maximum wear rate(MWR)of elbows increased and then decreased along the elbow angle.Due to the different directions of gravity,the heavy wear position(HWP)of the horizontal-vertical(H-V)elbow was in front of the vertical-horizontal(V-H)elbow.Because the downstream portion of the horizontal-horizontal(H-H)elbow was still a horizontal pipe,the HWP of the H-H elbow almost covered the whole elbow.The swirler placed upstream of the elbows could make the particles at the elbow move to the intrados of the elbows,resulting in less collision between the particles and the extrados of the elbows,thus reducing the wear of the elbows.The wear reduction effects of swirlers on three different elbows were favorably connected with the guide vane angle(GVA)and negatively correlated with the guide vane length(GVL),decreased first and then increased as the guide vane height(GVH)increased,and were little affected by the guide vane number(GVN)and the guide vane thickness(GVT).The mathematical models between the MWR of the elbows and guide vane parameters were established.By bench tests,the wear reduction effect of three kinds of elbows under the optimal guide vane parameters was 58.4%,76.9%,and 78.6%,respectively.The errors between the bench test results and the simulation results were around 10%.展开更多
The present research focuses on improving the prediction of rotating particle collisions.Current particle-surface collision models do not accurately predict the particle rebound when taking rotation into account.Exper...The present research focuses on improving the prediction of rotating particle collisions.Current particle-surface collision models do not accurately predict the particle rebound when taking rotation into account.Experimental data,such as the studies by Gorham and Kharaz(2000),Buck,Tang,Heinrich,Deen and Kuipers(2017),and Dong and Moys(2006)show that the Tsuji,Oshima and Morikawa(1985)model is inaccurate due to the incorrect tangential coefficient of restitution assumption.Hoomans,Kuipers,Mohd Salleh,Stein,and Seville(2001)introduced a similar model to the work by Tsuji et al.(1985)which includes a tangential coefficient of restitution but is only in two dimensions and does not consider out of plane rebounds.This work re-derives the particle collision model from the impulse equations for binary collisions in 3D while considering rotating particles.The derived equations in this work compares well to experimental particle-surface impact studies.The implications of this model are seen by investigating erosion due to particle collision in a simple pipe bend.It is shown that Tsuji et al.(1985)over predicts the erosion.These small differences in particle trajectories between the present model and the Tsuji et al.(1985)model will grow in complex flows with multiple close range particle impacts leading to inaccurate erosion predictions which will negatively impact the design of turbomachinery and pneumatic pipes.展开更多
We integrate the lattice Boltzmann method(LBM) and immersed boundary method(IBM) to capture the coupling between a rigid boundary surface and the hydrodynamic response of an enclosed particle laden fluid. We focus on ...We integrate the lattice Boltzmann method(LBM) and immersed boundary method(IBM) to capture the coupling between a rigid boundary surface and the hydrodynamic response of an enclosed particle laden fluid. We focus on a rigid box filled with a Newtonian fluid where the drag force based on the slip velocity at the wall and settling particles induces the interaction. We impose an external harmonic oscillation on the system boundary and found interesting results in the sedimentation behavior. Our results reveal that the sedimentation and particle locations are sensitive to the boundary walls oscillation amplitude and the subsequent changes on the enclosed flow field. Two different particle distribution analyses were performed and showed the presence of an agglomerate structure of particles. Despite the increase in the amplitude of wall motion, the turbulence level of the flow field and distribution of particles are found to be less in quantity compared to the stationary walls. The integrated LBM-IBM methodology promised the prospect of an efficient and accurate dynamic coupling between a non-compliant bounding surface and flow field in a wide-range of systems. Understanding the dynamics of the fluid-filled box can be particularly important in a simulation of particle deposition within biological systems and other engineering applications.展开更多
Nano-impact electrochemistry is an efficient way to probe the physical and chemical properties of individual particles.Unfortunately,limited by the weak adsorption between particles and a microelectrode(ME),the partic...Nano-impact electrochemistry is an efficient way to probe the physical and chemical properties of individual particles.Unfortunately,limited by the weak adsorption between particles and a microelectrode(ME),the particle collision events evolve randomly to be elastic or inelastic.These events occur intermittently to produce unmarked transient signal sets that seriously interfere with single particle measurement.Here,we report a nitrogen-skinned carbon nanocone electrode(NS-CNCE) to enhance its adsorption capacity greatly towards metal particles and thus realize non-dynamic(i.e.,inelastic impacts) single particle analysis.The surface of NS-CNCEs characteristic of excellent adhesion,smoothness,and conductivity can effectively capture the landing metal particles to form a stable contact for efficient electronic communication.Using superior NS-CNCEs,we investigated electrochemical oxidation of Ag(or Au) particles and electrocatalytic amplification of Pt particles,respectively,under non-dynamic electrochemistry.The determined particle size is highly consistent with the physical characterization.Statistical analysis of transient signals confirms the strong adhesion of NS-CNCEs to metal particles,which is also in line with the prediction of a particle-electrode adsorption energy model.The proposed strategy has effectively solved the major challenge of general single metal particle collision analysis.展开更多
The collisional Penrose process of massive spinning particles in a rotational Einstein-Gauss-Bonnet(EGB) black hole background is studied. By numerically solving the equations of motion for spinning particles, we find...The collisional Penrose process of massive spinning particles in a rotational Einstein-Gauss-Bonnet(EGB) black hole background is studied. By numerically solving the equations of motion for spinning particles, we find that the energy extraction efficiency increases monotonically with the decrease of the EGB coupling parameterα. Moreover, the efficiency η increases as the particle spin s grows. We also find that the energy extraction efficiency increases with the decrease of the EGB coupling parameter α. When the EGB coupling constant α = 0, our results reduce to the Kerr case, which has been investigated previously.展开更多
基金supported by the National Natural Science Foundation of China (Grants 51390494, 51306065, and 51276076)the Foundation of State Key Laboratory of Coal Combustion (Grant FSKLCCB1702)
文摘The absence of sub-grid scale(SGS) motions leads to severe errors in particle pair dynamics, which represents a great challenge to the large eddy simulation of particle-laden turbulent flow. In order to address this issue,data from direct numerical simulation(DNS) of homogenous isotropic turbulence coupled with Lagrangian particle tracking are used as a benchmark to evaluate the corresponding results of filtered DNS(FDNS). It is found that the filtering process in FDNS will lead to a non-monotonic variation of the particle collision statistics, including radial distribution function, radial relative velocity, and the collision kernel. The peak of radial distribution function shifts to the large-inertia region due to the lack of SGS motions, and the analysis of the local flowstructure characteristic variable at particle position indicates that the most effective interaction scale between particles and fluid eddies is increased in FDNS. Moreover,this scale shifting has an obvious effect on the odd-order moments of the probability density function of radial relative velocity, i.e. the skewness, which exhibits a strong correlation to the variance of radial distribution function in FDNS.As a whole, the radial distribution function, together with radial relative velocity, can compensate the SGS effects for the collision kernel in FDNS when the Stokes number based on the Kolmogorov time scale is greater than 3.0. However,it still leaves considerable errors for St< 3.0.
基金This work is supported by the open foundation of State Key Laboratory of Chemical Engineering(SKL-ChE-18B03)the Municipal Science and Technology Commission of Tianjin,China under Contract No.2009ZCKFGX01900.
文摘The particle collision behavior and heat transfer performance are investigated to reveal the heat transfer enhancement and fouling prevention mechanism in a Na_(2)SO_(4) circulating fluidized bed evaporator.The particle collision signals are analyzed with standard deviation by varying the amount of added particles ε(1%–3%),circulation flow velocity u(0.37–1.78 m·s^(-1)),and heat flux q(7.29–12.14 kW·m^(-2)).The results show that the enhancement factor reach up to 14.6%by adding polytetrafluoroethylene particles at ε=3%,u=1.78 m·s^(-1),and q=7.29 kW·m^(-2).Both the standard deviation of the particle collision signal and enhancement factor increase with the increase in the amount of added particles.The standard deviation increases with the increase in circulation flow velocity;however,the enhancement factor initially decreases and then increases.The standard deviation slightly decreases with the increase in heat flux at low circulation flow velocity,but initially increases and then decreases at high circulation flow velocity.The enhancement factor decreases with the increase in heat flux.The enhancement factor in Na_(2)SO_(4) solution is superior to that in water at high amount of added particles.The empirical correlation for heat transfer is established,and the model results agree well with the experimental data.
基金the graduated students Zhixing Feng,Xiaoqiang Zhang,and Deli Fang for their excellent works to develop the PIC simulation codes of Z-pinch.This research was partly supported by the National Natural Science Foundation of China(Grant Nos.11675025 and 11135007)the Innovation Project of China Academy of Engineering Physics(Grant No.CX2019030).
文摘For investigating efficiently the stagnation kinetic-process of Z-pinch,we develop a novel modified electrostatic implicit particle-in-cell algorithm in radial one-dimension for Z-pinch simulation in which a small-angle cumulative binary collision algorithm is used.In our algorithm,the electric field in z-direction is solved by a parallel electrode-plate model,the azimuthal magnetic field is obtained by Ampere’s law,and the term for charged particle gyromotion is approximated by the cross product of the averaged velocity and magnetic field.In simulation results of 2 MA deuterium plasma shell Zpinch,the mass-center implosion trajectory agrees generally with that obtained by one-dimensional MHD simulation,and the plasma current also closely aligns with the external current.The phase space diagrams and radial-velocity probability distributions of ions and electrons are obtained.The main kinetic characteristic of electron motion is thermal equilibrium and oscillation,which should be oscillated around the ions,while that of ion motion is implosion inwards.In the region of stagnation radius,the radial-velocity probability distribution of ions transits from the non-equilibrium to equilibrium state with the current increasing,while of electrons is basically the equilibrium state.When the initial ion density and current peak are not high enough,the ions may not reach their thermal equilibrium state through collisions even in its stagnation phase.
文摘This paper presents an extension of the lumped particle model in[1]to include the effects of particle collisions.The lumped particle model is a flexible framework for the modeling of particle laden flows,that takes into account fundamental features,including advection,diffusion and dispersion of the particles.In this paper,we transform a binary collision model and concepts from kinetic theory into a collision procedure for the lumped particle framework.We apply this new collision procedure to investigate numerically the role of particle collisions in the hindered settling effect.The hindered settling effect is characterized by an increase in the effective drag coefficient CD that influences each particle in the flow.This coefficient is given by CD=(1−φ)−nC∗D,whereφis the volume fraction of particles,C∗D is the drag coefficient for a single particle,and n≃4.67 for creeping flow.We obtain an approximation for CD/C∗D by calculating the effective work done by collisions,and comparing that to the work done by the drag force.In our numerical experiments,we observe a minimal value of n=3.0.Moreover,by allowing high energy dissipation,an approximation for the classical value for creeping flow,n=4.7,is reproduced.We also obtain high values for n,up to n=6.5,which is consistent with recent physical experiments on the sedimentation of sand grains.
文摘The data of charged particles produced in proton-proton collisions extracted from Durham particle data group at energy ranges √s = 6.3 - 17 GeV and at 0.9 - 7 TeV are investigated in the framework of Tsallis thermo-statistics and the Vlasov time dynamics. The analysis can describe the experimental data well all-over the considered energies and rapidity intervals. The variation of the collision parameters (chemical potential, entropy index and the time of evolution) is studied and discussed as a function of the final state temperature. According to the obtained result, a scenario, and a script of the time evolution for the particle production is simulated by the pp collision.
基金Supported by the Shanghai Key Lab of Modern Optical System
文摘In the context of unified hydrodynamics, we discuss the pseudorapidity distributions of the charged particles produced in Au-Au and Cu-Cu collisions at the low RHIC energies of √SNN = 19.6 and 22.4 GeV, respectively. It is found that the unified hydrodynamics alone can give a good description to the experimental measurements. This is different from the collisions at the maximum RHIC energy of √SNN = 200 GeV or at LHC energy of √SNN= 2.76 TeV, in which the leading particles must be taken into account so that we can properly explain the experimental observations.
文摘Some of the possible decays of pp collisions at LHC experiment are considered. The vector bosons mediating in the electroweak interactions and right-handed leptons except neutrinos are assumed to be the most resultant particles from the pp collisions. Neutrinos and anti-neutrinos will be observed when one-double electron charged vector bosons are the resultant particles. The charge conservation is thought to be the dominant factor of these decays. The amplitude transitions for Feynman diagram of these decays are written.
基金Supported by the National Natural Science Foundation of China under Grant No U1332125the Program for Innovation Research of Science in Harbin Institute of Technology under Grant No B201408
文摘The elliptic flow v2, for π±, K±, p and p in Au＋Au collisions at center-of-mass energies √sNN=7.7, 11.5, 14.5 and 19.6 GeV, is analyzed using a multiphase transport model. A significant difference in the v2 values for p and p is observed, and the values of v2 splitting are larger compared with π＋ and π-, K＋ and K-. The difference increases with decreasing the center-of-mass energy. The effect of the quark coalescence mechanism in a multi-phase transport model to the value of elliptic difference △v2 between p and p- has been discussed. The simulation of Au＋Au collisions at 14.5 GeV shows that the effect of hadron cascade to △v2 is not obvious, and a larger patton-scattering cross section can lead to a larger △v2.
基金Sponsored by the National Basic Research Program of China(973)(Grant No.2004CB41850)the Natural Science Foundation of Heilongjiang Prov-ince(Grant No.E200609)
文摘In this paper,the power law of particle size distributions (PSDs) in conventional water treatment processes is developed. After measuring the particle size distributions of raw-water,settled water and filtered water,a mathematical model between particle diameter and the amount of particles was studied. The value of collision frequency factor β in the PSDs model can be used to represent the collision behavior of particles ,and can be used as foundation exponent to choose suitable coagulation to accelerate particles aggregation. At the same time,the relationship between the value of parameter K and the total particles volume V was deduced. K is defined as particle volume exponent,which can represent the total volume of particles. The degression degree of K shows the removal efficiency of potable water treatment units.
基金Projects(51206011,U1937201)supported by the National Natural Science Foundation of ChinaProject(20200301040RQ)supported by the Science and Technology Development Program of Jilin Province,China+1 种基金Project(JJKH20190541KJ)supported by the Education Department of Jilin Province,ChinaProject(18DY017)supported by Changchun Science and Technology Program of Changchun City,China。
文摘The investigation was carried out on the technical problems of finishing the inner surface of elbow parts and the action mechanism of particles in elbow precision machining by abrasive flow.This work was analyzed and researched by combining theory,numerical and experimental methods.The direct simulation Monte Carlo(DSMC)method and the finite element analysis method were combined to reveal the random collision of particles during the precision machining of abrasive flow.Under different inlet velocity,volume fraction and abrasive particle size,the dynamic pressure and turbulence flow energy of abrasive flow in elbow were analyzed,and the machining mechanism of particles on the wall and the influence of different machining parameters on the precision machining quality of abrasive flow were obtained.The test results show the order of the influence of different parameters on the quality of abrasive flow precision machining and establish the optimal process parameters.The results of the surface morphology before and after the precision machining of the inner surface of the elbow are discussed,and the surface roughness Ra value is reduced from 1.125μm to 0.295μm after the precision machining of the abrasive flow.The application of DSMC method provides special insights for the development of abrasive flow technology.
文摘In dielectrics and semiconductors, a plasma model of the generation and slip of dislocations is considered, where under shock loads in a generalized space of rectangular pulses an alternating field forms a distribution of pairs of photoelectrons and cations;these electrons with velocities <em>V<sub>e</sub></em> create <em>δ</em>-collisions with cold plasma from free electrons and holes with masses <em>m<sub>e</sub></em> and <em>m<sub>h</sub></em> (<em>m<sub>h</sub></em> <span style="white-space:normal;"><span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">≫</span></span> </span></span><em>m<sub>e</sub></em>), they emit and absorb longitudinal electron plasma waves whose phase velocities <em>w<sub>pw</sub></em> / <em>k<sub>pw</sub></em> are close to or are equal to the velocities <em>V<sub>e</sub></em>, while the frequencies <em>w<sub>pw</sub></em> and wave numbers <em>k<sub>pw</sub></em> of the wave packet of plasma waves are complex, the short-wave components <img src="Edit_3da65014-7fd8-4799-bcf1-02d90028f4e0.bmp" alt="" /> of this wave packet at <em>k<sub>pw</sub></em> <span style="white-space:normal;"><span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">⋅</span></span></span> </span><em>a<sub>e </sub></em><span style="white-space:nowrap;">≫ </span>1 (<em>a<sub>e</sub></em> -Debye screening radius) decay in the core linear defect, and its long-wavelength components <img src="Edit_4481889b-5097-4d26-9019-b0322f5ff8d0.bmp" alt="" /> propagate in the region of the medium surrounding the core of the defect at <em>k<sub>pw</sub></em> <span style="white-space:nowrap;"><span style="white-space:nowrap;"><span style="white-space:nowrap;">⋅</span></span></span> <em>a<sub>e</sub></em> <span style="white-space:nowrap;"><<span style="white-space:nowrap;"><span style="white-space:nowrap;">≅</span></span></span> 1. When a defect is generated, the distribution of cations under the influence of the internal Coulomb field shifts to the region of the first peak (protrusion) of the electron plasma wave, thereby forming a vacancy valley. When sliding under the influence of an external electric field, a cationic plasma wave consisting of a vacancy valley and two cationic protrusions moves against the background of an additional potential relief created by an electron plasma wave near the core of the defect. It has been shown that <em>δ</em>-collisions create flows of dynamic large-scale correlations of plasma fluctuations in the form of asymptotics of different-time correlators of density and potential fluctuations as <em>t</em> → +∞.
基金Supported by National Natural Science Foundation of China(11775082)。
文摘We study the collision property of spinning particles near a Banados-Teitelboim-Zanelli(BTZ)black hole.Our results show that although the center-of-mass energy of two ingoing particles diverges if one of the particles possesses a critical angular momentum,the particle with critical angular momentum cannot exist outside of the horizon due to violation of the timelike constraint.Further detailed investigation indicates that only a particle with a subcritical angular momentum is allowed to exist near an extremal rotating BTZ black hole,and the corresponding collision center-of-mass energy can be arbitrarily large in a critical angular momentum limit.
文摘Flight simulators can provide a suitable alternative to real flight, mainly to increase safety through the training of crew, and evaluation data from simulator can be used to validation and certification of aircraft systems. However, it must convey some degree of realism to the user to be effective. For that reason, it is necessary to calibrate the simulator software. Calibration for flight simulation is parameter identification process. The process is formulated as an optimization problem, and it is solved by using a new approach named Multiple Particle Collision Algorithm （MPCA）. Results show a good performance for the employed approach.
基金supported by the National Natural Science Foundation of China(Grant No.10532030)the CAS Innovation Program
文摘Sand storm is a serious environmental threat to humans. Sand particles are transported by saltation and suspension, causing soil erosion in one place and deposition in another. In order to prevent and predict sand storms, the causes and the manners of particle motions must he studied in detail. In this paper a standard k-8 model is used for the gas phase simulation and the discrete element method （DEM） is used to predict the movements of particles using an in-house procedure. The data are summarized in an Eulerian-Eulerian regime after simulation to get the statistical particle Reynolds stress and particle collision stress. The results show that for the current case the Reynolds stress and the air shear stress predominate in the region 20-250 mm above the initial sand bed surface. However, in the region below 3 ram, the collision stress must be taken into account in predicting particle movement.
文摘Researches in the field of low-energy nuclear reactions (LENR) have shown a wide variety of manifestations of these phenomena. They appear in metals with hydrogen dissolved in them, in plasma, in gas discharge, in electrolysis, and even in biological systems. In addition to energy release, which far exceeds the capabilities of chemical reactions, LENR is characterized by a huge variety of emerging chemical elements. This report provides examples of appearance of many initially missing elements in different LENR installations. For example, in the nickel-hydrogen LENR reactor created in our laboratory, which worked for 7 months, Ca, V, Ti, Mn, Fe, Co, Cu, Zn, Ga, Ba, Sr, Yb, Hf were found. Moreover, new elements were found not only in the “fuel” but also in the surrounding matter. The huge variety of chemical elements that arise can be explained by the fact that in the processes of LENR, the interaction covers several atoms at once. The article discusses approaches to explaining the phenomena discovered in the process of LENR researches.
基金the“Double-First Class”Discipline Construction Project of China University of Mining and Technology(Grant No.2019XKPT03)the Graduate Innovation Program of China University of Mining and Technology(Grant No.2022WLKXJ013)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘Elbow wear is a major threat to the multiphase pipeline transportation industry,which has a negative impact on the stable operation of the transportation system.In order to find the wear reduction methods of elbows in the fluidization pipeline transportation system for 2000-meter-deep coal resources,the swirler was installed upstream of the elbows,and wear simulations and tests of three kinds of elbows were carried out.The results showed that the maximum wear rate(MWR)of elbows increased and then decreased along the elbow angle.Due to the different directions of gravity,the heavy wear position(HWP)of the horizontal-vertical(H-V)elbow was in front of the vertical-horizontal(V-H)elbow.Because the downstream portion of the horizontal-horizontal(H-H)elbow was still a horizontal pipe,the HWP of the H-H elbow almost covered the whole elbow.The swirler placed upstream of the elbows could make the particles at the elbow move to the intrados of the elbows,resulting in less collision between the particles and the extrados of the elbows,thus reducing the wear of the elbows.The wear reduction effects of swirlers on three different elbows were favorably connected with the guide vane angle(GVA)and negatively correlated with the guide vane length(GVL),decreased first and then increased as the guide vane height(GVH)increased,and were little affected by the guide vane number(GVN)and the guide vane thickness(GVT).The mathematical models between the MWR of the elbows and guide vane parameters were established.By bench tests,the wear reduction effect of three kinds of elbows under the optimal guide vane parameters was 58.4%,76.9%,and 78.6%,respectively.The errors between the bench test results and the simulation results were around 10%.
基金funded as a Virginia Tech Rolls-Royce Doctoral Fellow.
文摘The present research focuses on improving the prediction of rotating particle collisions.Current particle-surface collision models do not accurately predict the particle rebound when taking rotation into account.Experimental data,such as the studies by Gorham and Kharaz(2000),Buck,Tang,Heinrich,Deen and Kuipers(2017),and Dong and Moys(2006)show that the Tsuji,Oshima and Morikawa(1985)model is inaccurate due to the incorrect tangential coefficient of restitution assumption.Hoomans,Kuipers,Mohd Salleh,Stein,and Seville(2001)introduced a similar model to the work by Tsuji et al.(1985)which includes a tangential coefficient of restitution but is only in two dimensions and does not consider out of plane rebounds.This work re-derives the particle collision model from the impulse equations for binary collisions in 3D while considering rotating particles.The derived equations in this work compares well to experimental particle-surface impact studies.The implications of this model are seen by investigating erosion due to particle collision in a simple pipe bend.It is shown that Tsuji et al.(1985)over predicts the erosion.These small differences in particle trajectories between the present model and the Tsuji et al.(1985)model will grow in complex flows with multiple close range particle impacts leading to inaccurate erosion predictions which will negatively impact the design of turbomachinery and pneumatic pipes.
基金supported by the National Natural Science Foundation of China(Grant No.11372068)the National Key Basic Research and Development Program of China(Grant No.2014CB744104)
文摘We integrate the lattice Boltzmann method(LBM) and immersed boundary method(IBM) to capture the coupling between a rigid boundary surface and the hydrodynamic response of an enclosed particle laden fluid. We focus on a rigid box filled with a Newtonian fluid where the drag force based on the slip velocity at the wall and settling particles induces the interaction. We impose an external harmonic oscillation on the system boundary and found interesting results in the sedimentation behavior. Our results reveal that the sedimentation and particle locations are sensitive to the boundary walls oscillation amplitude and the subsequent changes on the enclosed flow field. Two different particle distribution analyses were performed and showed the presence of an agglomerate structure of particles. Despite the increase in the amplitude of wall motion, the turbulence level of the flow field and distribution of particles are found to be less in quantity compared to the stationary walls. The integrated LBM-IBM methodology promised the prospect of an efficient and accurate dynamic coupling between a non-compliant bounding surface and flow field in a wide-range of systems. Understanding the dynamics of the fluid-filled box can be particularly important in a simulation of particle deposition within biological systems and other engineering applications.
基金supported by the National Natural Science Foundation of China (21721003,21635007)the Instrument Developing Project of the Chinese Academy of Sciences (YJKYYQ20210003)the Natural Science Foundation of Jilin Province(20210101402JC)
文摘Nano-impact electrochemistry is an efficient way to probe the physical and chemical properties of individual particles.Unfortunately,limited by the weak adsorption between particles and a microelectrode(ME),the particle collision events evolve randomly to be elastic or inelastic.These events occur intermittently to produce unmarked transient signal sets that seriously interfere with single particle measurement.Here,we report a nitrogen-skinned carbon nanocone electrode(NS-CNCE) to enhance its adsorption capacity greatly towards metal particles and thus realize non-dynamic(i.e.,inelastic impacts) single particle analysis.The surface of NS-CNCEs characteristic of excellent adhesion,smoothness,and conductivity can effectively capture the landing metal particles to form a stable contact for efficient electronic communication.Using superior NS-CNCEs,we investigated electrochemical oxidation of Ag(or Au) particles and electrocatalytic amplification of Pt particles,respectively,under non-dynamic electrochemistry.The determined particle size is highly consistent with the physical characterization.Statistical analysis of transient signals confirms the strong adhesion of NS-CNCEs to metal particles,which is also in line with the prediction of a particle-electrode adsorption energy model.The proposed strategy has effectively solved the major challenge of general single metal particle collision analysis.
基金the National Natural Science Foundation of China(NSFC)(11775082)。
文摘The collisional Penrose process of massive spinning particles in a rotational Einstein-Gauss-Bonnet(EGB) black hole background is studied. By numerically solving the equations of motion for spinning particles, we find that the energy extraction efficiency increases monotonically with the decrease of the EGB coupling parameterα. Moreover, the efficiency η increases as the particle spin s grows. We also find that the energy extraction efficiency increases with the decrease of the EGB coupling parameter α. When the EGB coupling constant α = 0, our results reduce to the Kerr case, which has been investigated previously.
