Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal ...Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal in the desired direction,thus it provides supplementary links for wireless networks.Most of prior works on RIS-aided wireless communication systems consider continuous phase shifts,but phase shifts of RIS are discrete in practical hardware.Thus we focus on the actual discrete phase shifts on RIS in this paper.Using the advanced deep reinforcement learning(DRL),we jointly optimize the transmit beamforming matrix from the discrete Fourier transform(DFT)codebook at the base station(BS)and the discrete phase shifts at the RIS to maximize the received signal-to-interference plus noise ratio(SINR).Unlike the traditional schemes usually using alternate optimization methods to solve the transmit beamforming and phase shifts,the DRL algorithm proposed in the paper can jointly design the transmit beamforming and phase shifts as the output of the DRL neural network.Numerical results indicate that the DRL proposed can dispose the complicated optimization problem with low computational complexity.展开更多
Distributed precision jamming(DPJ)is a novel blanket jamming concept in electronic warfare,which delivers the jamming resource to the opponent equipment precisely and ensures that friendly devices are not affected.Rob...Distributed precision jamming(DPJ)is a novel blanket jamming concept in electronic warfare,which delivers the jamming resource to the opponent equipment precisely and ensures that friendly devices are not affected.Robust jamming performance and low hardware burden on the jammers are crucial for practical DPJ implementation.To achieve these goals,we study the robust design of wideband constant modulus(CM)discrete phase waveform for DPJ,where the worst-case combined power spectrum(CPS)of both the opponent and friendly devices is considered in the objective function,and the CM discrete phase constraints are used to design the wideband waveform.Specifically,the resultant mathematical model is a large-scale minimax multi-objective optimization problem(MOP)with CM and discrete phase constraints.To tackle the challenging MOP,we transform it into a single-objective minimization problem using the Lp-norm and Pareto framework.For the approximation problem,we propose the Riemannian conjugate gradient for CM discrete phase constraints(RCG-CMDPC)algorithm with low computational complexity,which leverages the complex circle manifold and a projection method to satisfy the CM discrete phase constraints within the RCG framework.Numerical examples demonstrate the superior robust DPJ effectiveness and computational efficiency compared to other competing algorithms.展开更多
This study aims to conduct a sensitivity analysis of closure models and modeling parameters for the Dense Discrete Phase Modeling(DDPM)approach in order to investigate the hydrodynamics of a 3D lab-scale Tapered Fluid...This study aims to conduct a sensitivity analysis of closure models and modeling parameters for the Dense Discrete Phase Modeling(DDPM)approach in order to investigate the hydrodynamics of a 3D lab-scale Tapered Fluidized Bed(TFB).The closure models and model parameters under investigation include the gas-solid drag force,viscous models,particle-particle interaction models,restitution coefficient,specularity coefficient,and rebound coefficient.The primary objective of this sensitivity analysis is to optimize the numerical model's performance.The numerical results,in terms of axial and lateral Solid Volume Fraction(SVF)profiles obtained from the sensitivity analysis,indicate that the drag force and restitution coefficient significantly influence the hydrodynamics of the TFB.Properly selecting these parameters could result in the improved performance of the numerical model.However,the sensitivity of turbulence models,particle-particle interaction models,specularity coefficient,and rebound coefficient has a lesser impact on the hydrodynamics results.This work concludes with the recommendation of a set of closure models and modeling parameters that offer the most accurate prediction of the hydrodynamics of the TFB.展开更多
The vapor diffusion and transport resulting from steam generator tube rupture(SGTR)accidents are a major concern threatening lead-based reactor core safety.In this study,a high-parameter SGTR experimental platform and...The vapor diffusion and transport resulting from steam generator tube rupture(SGTR)accidents are a major concern threatening lead-based reactor core safety.In this study,a high-parameter SGTR experimental platform and the multi-phase multi-physics processes numerical simulation were developed to investigate the phase behavior and interaction mechanisms.This study revealed the interaction mechanisms of lead-bismuth liquid metal and water driven by flash vaporization,jet impingement boiling,and moderate boiling.The migration and evolution of the discrete phases(vapor-water mixture)were inferred from the temperature transient laws and a numerical simulation.The results revealed that the evolution of the discrete phases consists of three stages:cavity formation,flanking diffusion,and stable up-floating.The jet pressure significantly extended the disturbance period.Variations in the water temperature mainly affected the depressurization boiling process,altering the diffusion region of the discrete phases.The temperature of the liquid metal and the duration of the jet had a minimal impact on the behavior of the discrete phases.This study provides a crucial reference for constructing a complete picture of accident evolution.展开更多
Acoustic holograms can recover wavefront stored acoustic field information and produce high-fidelity complex acoustic fields. Benefiting from the huge spatial information that traditional acoustic elements cannot matc...Acoustic holograms can recover wavefront stored acoustic field information and produce high-fidelity complex acoustic fields. Benefiting from the huge spatial information that traditional acoustic elements cannot match, acoustic holograms pursue the realization of high-resolution complex acoustic fields and gradually tend to high-frequency ultrasound applications. However, conventional continuous phase holograms are limited by three-dimensional(3D) printing size, and the presence of unavoidable small printing errors makes it difficult to achieve acoustic field reconstruction at high frequency accuracy. Here, we present an optimized discrete multi-step phase hologram. It can ensure the reconstruction quality of image with high robustness, and properly lower the requirement for the 3D printing accuracy. Meanwhile, the concept of reconstruction similarity is proposed to refine a measure of acoustic field quality. In addition, the realized complex acoustic field at 20 MHz promotes the application of acoustic holograms at high frequencies and provides a new way to generate high-fidelity acoustic fields.展开更多
Computational fluid dynamics(CFD)has become a valuable tool to study the complex gas-solid hydrodynamics in the circulating fluidized bed(CFB).Based on the two fluid model(TFM)under the Eulerian-Eulerian framework and...Computational fluid dynamics(CFD)has become a valuable tool to study the complex gas-solid hydrodynamics in the circulating fluidized bed(CFB).Based on the two fluid model(TFM)under the Eulerian-Eulerian framework and the dense discrete phase model(DDPM)under the Eulerian-Lagrangian framework,this work conducts the comparative study of the gas-solid hydrodynamics in a CFB riser by these two different models.Results show that DDPM could be used to predict gas-solid hydrodynamics in the circulating fluidized bed,and there are differences between TFM and DDPM,especially in the radial distribution profiles of solid phase.Sensitivity analysis results show that the gas-solid drag model exhibits significant effects on the results for both the two models.The specularity coefficient and the restitution coefficient in the TFM,as well as the reflection coefficient and the parcel number in the DDPM,exhibit less impact on the simulated results.展开更多
A dense discrete phase model combined with the kinetic theory of granular flows was used to study the bubbling characteristics and segregation of poly-dispersed particle mixtures in a thin fluidized bed.Our simulation...A dense discrete phase model combined with the kinetic theory of granular flows was used to study the bubbling characteristics and segregation of poly-dispersed particle mixtures in a thin fluidized bed.Our simulations showed that in using the hybrid Eulerian-Lagrangian method,the common use of one computational cell in the thickness direction of the thin bed does not predict wall friction correctly.Instead,a three-cell discretization of the thickness direction does predict the wall friction well but six cells were needed to prevent overprediction of the bed expansion.The change in specularity factor(SF)of the model not only affected the predictions of the velocity of particles,but also had a considerable impact on their flow pattern.A decrease in SF,which decreases wall friction,showed an over-prediction in the size of bubbles,particle velocities,and void fraction of the bed,and led to a shift in the circulation center toward the bottom of the bed.The segregation of the Geldart B particles was studied in the narrow range from 400 to 600μm with a standard deviation less than 10%of the average diameter.Simulations showed that large particles accumulated close to the distributor at the bottom of the bed and the center of the bed,but small particles moved towards the wall and top surface.The decrease in the mean particle size and spread in shape of the distribution improves mixing by up to 30%at a superficial gas velocity of around 2.5 times the minimum fluidization velocity.Log-normal mixtures with a small proportion of large particles had the most uniform distribution with a thin layer of jetsam forming at the bottom of the bed.Finally,experimental verification of the segregation and mixing of polydisperse particles with narrow size distribution is suggested.展开更多
Liquid-solid binary fluidized beds are widely used in many industries. However, the flow behavior of such beds is not well understood due to the lack of accurate experimental and numerical data. In the current study, ...Liquid-solid binary fluidized beds are widely used in many industries. However, the flow behavior of such beds is not well understood due to the lack of accurate experimental and numerical data. In the current study, the behavior of monodisperse and binary liquid-solid fluidized beds of the same density but dif- ferent sizes is investigated using radioactive particle tracking （RPT） technique and a dense discrete phase model （DDPM）. Experiments and simulations are performed in monodisperse fluidized beds containing two different sizes of glass beads （0.6 and I mm） and a binary fluidized bed of the same particles for vari- ous bed compositions. The results show that both RPT and DDPM can predict the mixing and segregation pattern in liquid-solid binary fluidized beds. The mean velocity predictions of DDPM are in good agree- ment with the experimental findings for both monodisperse and binary fluidized beds. However, the axial root mean square velocity predictions are only reasonable for bigger particles. Particle-particle interac- tions are found to be critical for predicting the flow behavior of solids in liquid-solid binary fluidized beds.展开更多
This paper takes further insight into the sparse geometry which offers a larger array aperture than uniform linear array(ULA)with the same number of physical sensors.An efficient method based on closed-form robust Chi...This paper takes further insight into the sparse geometry which offers a larger array aperture than uniform linear array(ULA)with the same number of physical sensors.An efficient method based on closed-form robust Chinese remainder theorem(CFRCRT)is presented to estimate the direction of arrival(DOA)from their wrapped phase with permissible errors.The proposed algorithm has significantly less computational complexity than the searching method while maintaining similar estimation precision.Furthermore,we combine all phase discrete Fourier transfer(APDFT)and the CFRCRT algorithm to achieve a considerably high DOA estimation precision.Both the theoretical analysis and simulation results demonstrate that the proposed algorithm has a higher estimation precision as well as lower computation complexity.展开更多
To investigate the influence of snow particle rotational motion on the accumulation of snow in the bogie region of high-speed trains,an Euler‒Lagrange numerical approach is adopted.The study examines the effects of sn...To investigate the influence of snow particle rotational motion on the accumulation of snow in the bogie region of high-speed trains,an Euler‒Lagrange numerical approach is adopted.The study examines the effects of snow particle diameter and train speed on the ensuing dynamics.It is shown that considering snow particle rotational motion causes significant deviation in the particle trajectories with respect to non-rotating particles.Such a deviation increases with larger snow particle diameters and higher train speeds.The snow accumulation on the overall surface of the bogie increases,and the amount of snow on the vibration reduction device varies greatly.In certain conditions,the amount of accumulated snow can increase by several orders of magnitudes.展开更多
To investigate the deposition distribution of snow particles in the bogie surfaces of a high-speed train,a snow particle deposition model,based on the critical capture velocity and the critical shear velocity,was elab...To investigate the deposition distribution of snow particles in the bogie surfaces of a high-speed train,a snow particle deposition model,based on the critical capture velocity and the critical shear velocity,was elaborated.Simulations based on the unsteady Reynolds-Averaged Navier-Stokes(RANS)approach coupled with Discrete Phase Model(DPM)were used to analyze the motion of snow particles.The results show that the cross beam of the bogie frame,the anti-snake damper,the intermediate brake clamps in the rear wheels,the traction rod and the anti-rolling torsion bar are prone to accumulate snow.The accumulation mass relating to the vertical surface in the rear region,horizontal surface in the front region and the corner area of the bogie is high.The average snow accumulation mass for each component ordered from high to low is as follow:traction rod,frame,bolster,brake clamp 2,anti-rolling torsion bar,brake clamp 1,transverse damper,axle box 2,axle box 1,air spring,anti-snake damper,tread cleaning device.The snow accumulation mass on the front components of the bogie is more significant than that relating to the rear components.Particularly,the average snow accumulation mass of rear brake clamp 2 and axle box 2 is about twice as high as that of the front brake clamp 1 and axle box 1.展开更多
Ice particles could form under the continuous impingement of incoming supercooled droplets in icing conditions,which will change the surface roughness to enhance the further heat and mass transfer during icing process...Ice particles could form under the continuous impingement of incoming supercooled droplets in icing conditions,which will change the surface roughness to enhance the further heat and mass transfer during icing process.A fixed-grid porous enthalpy method based on the improved Discrete Phase Model(DPM)and Volume of Fluid(VOF)integrated algorithm is developed to solve the multiphase heat transfer problem to give more detailed demonstration of the formation of initial ice roughness.The algorithms to determine the criterion of transformation from DPM to VOF and the allocation of source items during transformation are improved to the general DPM-VOF algorithm.Two verification cases,namely two glycerine-solution droplets impact and single droplet freeze,are conducted to verify the accuracy and reliability of the enthalpy-DPMVOF method,where the simulation results match well with experiment phenomena.Ice roughness on a NACA0012 airfoil is precisely captured and the effects on convective heat transfer characteristics are preliminarily revealed.The results illustrate that the enthalpy-DPM-VOF method could successfully capture the characteristics of motion and the phase change process of droplet,as well as balance the calculation accuracy and efficiency.展开更多
The diesel particulate matter(DPM) emission from diesel powered equipment in underground mines can cause health hazards including cancer to the miners. The understanding of the DPM propagation pattern under realistic ...The diesel particulate matter(DPM) emission from diesel powered equipment in underground mines can cause health hazards including cancer to the miners. The understanding of the DPM propagation pattern under realistic mining condition is required for selecting proper DPM control strategies and to improve working practices in underground mines. In this paper, three dimensional simulations of DPM emission from the exhaust tail pipe of a load-haul-dump(LHD) vehicle and its subsequent distribution inside an isolated zone in the typical underground mine are carried out using two different solution models available in Ansys Fluent. The incoming fresh air into the isolated zone is treated as a continuous phase and DPM is treated either as a continuous phase(gas) or as a secondary discrete phase(particle). Species transport model is used when DPM is treated as gas and discrete phase model is used when DPM is assumed to behave like a particle. The distributions of DPM concentration inside the isolated zone obtained from each method are presented and compared. From the comparison results, an accurate and economical solution technique for DPM evaluation can be selected.展开更多
A resident time model is proposed to evaluate the performance of agitated extraction columns. In this model, the resident time of dispersed drops is simulated with the discrete phase modeling, where the continuous pha...A resident time model is proposed to evaluate the performance of agitated extraction columns. In this model, the resident time of dispersed drops is simulated with the discrete phase modeling, where the continuous phase and the dispersed phase （drops） are described by the single-phase Navier-Stokes （turbulence） model and Lagrangian model, respectively. The interaction of dispersed phase and continuous phase is neglected for the low concentration of drop in the cases studied. The statistical parameters of drops （the average resident time and standard deviation） under different operation conditions are computed for four columns. The relation of the above statistical parameters with the performance of columns is discussed and the criterions for an optimal compartment are outlined. Our results indicate that the resident time model is useful to evaluate the performance and optimize the design of extraction columns.展开更多
In order to reveal the influence of forced ventilation on the dispersion of droplets ejected from roadheader-mounted external sprayer,the paper studies the air-flowing field and the droplet distribution under the cond...In order to reveal the influence of forced ventilation on the dispersion of droplets ejected from roadheader-mounted external sprayer,the paper studies the air-flowing field and the droplet distribution under the condition of gentle breeze and normal forced ventilation in heading face using the particle tracking technology of computational fluid dynamics(CFD).The results show that air-flowing tendency in the same section presents great comparability in the period of gentle breeze and forced ventilation,and the difference mainly embodies in the different wind velocity.The influence of ventilation on the dispersion of droplets is faint under the gentle breeze condition.The droplet can be evenly distributed around the cutting head.However,under the normal forced ventilation,a large number of droplets will drift to the return air side.At the same time,droplet clusters are predominantly presented in the lower part of windward side and the middle of the leeward side around the cutting head.In contrast,the droplet concentration in other parts around cutting head decreases a lot and the droplets are unable to form close-grained mist curtain.So the dust escape channel is formed.In addition,the simulation results also reveal that the disturbance of air flow on the droplet distribution can be effectively relieved when using ventilation duct with Coanda effect(VDCE).Field experiment results show that the dust suppression efficiency of total dust and respirable dust increases respectively by 10.5%and 9.3%when using VDCE,which proves that it can weaken the influence of airflow on droplet dispersion.展开更多
Based on computational fluid dynamics method,the effect of atomization gas pressure on the atomization efficiency of Laval nozzle was studied,and then a discrete phase model was established and combined with industria...Based on computational fluid dynamics method,the effect of atomization gas pressure on the atomization efficiency of Laval nozzle was studied,and then a discrete phase model was established and combined with industrial trials to study the effect of a new type of assisted gas nozzles(AGNs)on powder size distribution and amorphous powder yield.The results show that increasing the atomization pressure can effectively improve the gas velocity for the Laval nozzle;however,it will decrease the aspiration pressure,and the optimal atomization pressure is 2.0 MPa.Compared with this,after the application of AGNs with the inlet velocity of 200 m s^(-1),assisted gas jet can increase the velocity of overall droplets in the break-up and solidification area by 40 m s^(-1) and the maximum cooling rate is increased from 1.9×10^(4) to 2.3×10^(4) K s^(-1).The predicted particle behavior is demonstrated by the industrial trails,that is,after the application of AGNs,the median diameter of powders d50 is decreased from 28.42 to 25.56 lm,the sphericity is increased from 0.874 to 0.927,the fraction of amorphous powders is increased from 90.4% to 99.4%,and only the coercivity is increased slightly due to the accumulation of internal stress.It is illustrated that the AGNs can improve the yield of fine amorphous powders,which is beneficial to providing high-performance raw powders for additive manufacturing technology.展开更多
Nutrients supply especially like nutrients and oxygen play vital role in tissue engineering process.It is found that tissue could not grow very well in the middle of the scaffold because few nutrients could transport ...Nutrients supply especially like nutrients and oxygen play vital role in tissue engineering process.It is found that tissue could not grow very well in the middle of the scaffold because few nutrients could transport to the middle.Nutrient limitations would reduce cell proliferation and differentiation.In that case,there is urgent need to understand the nutrient distribution for both in vitro and in vivo study,as no technology is able for researchers to observe the nutrients transport during those process.In this paper,a numerical model coupling with VOF(volume of fluid)model and species transport model together for predicting the distribution of oxygen and glucose in the scaffold after implantation in to the site is developed.Comparing with our previous in vivo tests,the regenerated tissue distribution has a similar trend as oxygen distribution rather than glucose.The reported scaffold manufactured by additive manufacturing provided a good interconnected structure which facilitated the nutrient transportation in the scaffold.Considering nutrient transportation,this numerical model could be used in better understanding the nutrients transportation in the scaffold,and leading to a better understanding of tissue formation in the scaffold.展开更多
The standard k-ε turbulence model and discrete phase model (DPM) were used to simulate the heat and mass transfer in a liquid-desiccant evaporator driven by a heat pump using FLUENT software, and the temperature fiel...The standard k-ε turbulence model and discrete phase model (DPM) were used to simulate the heat and mass transfer in a liquid-desiccant evaporator driven by a heat pump using FLUENT software, and the temperature field and velocity field in the device were obtained. The performance of the liquid-desiccant evaporator was studied as the concentration of the inlet solution varied between 21% and 30% and the pipe wall temperature between 30 and 50 ℃. Results show that the humidification rate and the humidification efficiency increased with the inlet air temperature, the solution flow rate, the solution temperature, and the pipe wall temperature. The humidification rate and humidification efficiency decreased with increasing moisture content in inlet air and the concentration of inlet solution. The humidification rate increased substantially but the humidification efficiency decreased as the inlet air flow rate increased. The error between the simulations and experimental results is acceptable, meaning that our model can provide a theoretical basis for optimizing the performance of a humidifying evaporator.展开更多
To avoid the volume expansion of basic oxygen furnace (BOF) slag for use in building materials, a hot slag modification process was proposed to reduce free CaO (f-CaO) in the molten slag. A transient 3D numerical mode...To avoid the volume expansion of basic oxygen furnace (BOF) slag for use in building materials, a hot slag modification process was proposed to reduce free CaO (f-CaO) in the molten slag. A transient 3D numerical model of BOF molten slag modification by SiO_(2) particles was established. The flow and heat transfer of molten slag, movement and dissolution of the modifier, and concentration distribution of f-CaO in slag during the modification of BOF were studied. The distribution of f-CaO concentration is inhomogeneous all over the molten slag. The mixing effect at the slag surface is weaker than that at the half-height plane of the slag. To consume the f-CaO below 2.0 wt.% in the slag, the optimum quantity of the SiO_(2) modifier is 10.0% of the mass of the slag. The fine SiO_(2) particles help attain a lower final mass fraction of f-CaO and a higher SiO_(2) utilization ratio.展开更多
Transmission of airborne bacteria is the main factor causing surgical site infection(SSI),which is harmful to patients′health and even lives.Numerical study is conducted on the effect of the operating table protected...Transmission of airborne bacteria is the main factor causing surgical site infection(SSI),which is harmful to patients′health and even lives.Numerical study is conducted on the effect of the operating table protected by horizontal laminar flow screen.Discrete phase model(DPM)is used.Numerical simulation is carried out to evaluate particle trajectories with the Lagrange approach.As a result,the protecting effect of horizontal laminar flow screen is established,and the protecting parameters of the air velocity supplied by the screen and the protecting distance are optimized.The optimized air velocity supplied by the screen should be at 0.4—0.6 m/s.And the protecting distance should be less than 1.3 m.This work provides references for the study on the depuration of operating table or room.展开更多
文摘Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal in the desired direction,thus it provides supplementary links for wireless networks.Most of prior works on RIS-aided wireless communication systems consider continuous phase shifts,but phase shifts of RIS are discrete in practical hardware.Thus we focus on the actual discrete phase shifts on RIS in this paper.Using the advanced deep reinforcement learning(DRL),we jointly optimize the transmit beamforming matrix from the discrete Fourier transform(DFT)codebook at the base station(BS)and the discrete phase shifts at the RIS to maximize the received signal-to-interference plus noise ratio(SINR).Unlike the traditional schemes usually using alternate optimization methods to solve the transmit beamforming and phase shifts,the DRL algorithm proposed in the paper can jointly design the transmit beamforming and phase shifts as the output of the DRL neural network.Numerical results indicate that the DRL proposed can dispose the complicated optimization problem with low computational complexity.
基金supported by the National Natural Science Foundation of China(No.62301581)the Postgraduate Scientific Research Innovation Project of Hunan Province,China(No.CX20230045)。
文摘Distributed precision jamming(DPJ)is a novel blanket jamming concept in electronic warfare,which delivers the jamming resource to the opponent equipment precisely and ensures that friendly devices are not affected.Robust jamming performance and low hardware burden on the jammers are crucial for practical DPJ implementation.To achieve these goals,we study the robust design of wideband constant modulus(CM)discrete phase waveform for DPJ,where the worst-case combined power spectrum(CPS)of both the opponent and friendly devices is considered in the objective function,and the CM discrete phase constraints are used to design the wideband waveform.Specifically,the resultant mathematical model is a large-scale minimax multi-objective optimization problem(MOP)with CM and discrete phase constraints.To tackle the challenging MOP,we transform it into a single-objective minimization problem using the Lp-norm and Pareto framework.For the approximation problem,we propose the Riemannian conjugate gradient for CM discrete phase constraints(RCG-CMDPC)algorithm with low computational complexity,which leverages the complex circle manifold and a projection method to satisfy the CM discrete phase constraints within the RCG framework.Numerical examples demonstrate the superior robust DPJ effectiveness and computational efficiency compared to other competing algorithms.
基金supported by the Ratchadapisek Somphot Fund for Postdoctoral Fellowship,Chulalongkorn Universitythe Research Grant from the National Research Council of Thailand(N42A660438)Thailand Science Research and Innovation Fund Chulalongkorn University.
文摘This study aims to conduct a sensitivity analysis of closure models and modeling parameters for the Dense Discrete Phase Modeling(DDPM)approach in order to investigate the hydrodynamics of a 3D lab-scale Tapered Fluidized Bed(TFB).The closure models and model parameters under investigation include the gas-solid drag force,viscous models,particle-particle interaction models,restitution coefficient,specularity coefficient,and rebound coefficient.The primary objective of this sensitivity analysis is to optimize the numerical model's performance.The numerical results,in terms of axial and lateral Solid Volume Fraction(SVF)profiles obtained from the sensitivity analysis,indicate that the drag force and restitution coefficient significantly influence the hydrodynamics of the TFB.Properly selecting these parameters could result in the improved performance of the numerical model.However,the sensitivity of turbulence models,particle-particle interaction models,specularity coefficient,and rebound coefficient has a lesser impact on the hydrodynamics results.This work concludes with the recommendation of a set of closure models and modeling parameters that offer the most accurate prediction of the hydrodynamics of the TFB.
基金supported by the National Natural Science Foundation of China(Nos.U20B2011 and 123B2086)。
文摘The vapor diffusion and transport resulting from steam generator tube rupture(SGTR)accidents are a major concern threatening lead-based reactor core safety.In this study,a high-parameter SGTR experimental platform and the multi-phase multi-physics processes numerical simulation were developed to investigate the phase behavior and interaction mechanisms.This study revealed the interaction mechanisms of lead-bismuth liquid metal and water driven by flash vaporization,jet impingement boiling,and moderate boiling.The migration and evolution of the discrete phases(vapor-water mixture)were inferred from the temperature transient laws and a numerical simulation.The results revealed that the evolution of the discrete phases consists of three stages:cavity formation,flanking diffusion,and stable up-floating.The jet pressure significantly extended the disturbance period.Variations in the water temperature mainly affected the depressurization boiling process,altering the diffusion region of the discrete phases.The temperature of the liquid metal and the duration of the jet had a minimal impact on the behavior of the discrete phases.This study provides a crucial reference for constructing a complete picture of accident evolution.
基金Project supported by the China Postdoctoral Science Foundation (Grant No.2023M732745)the National Natural Science Foundations of China (Grant Nos.61974110 and 62104177)+1 种基金the Fundamental Research Funds for the Central Universities,China (Grant Nos.QTZX23022 and JBF211103)the Cooperation Program of XDU– Chongqing IC Innovation Research Institute (Grant No.CQ IRI-2022CXY-Z07)。
文摘Acoustic holograms can recover wavefront stored acoustic field information and produce high-fidelity complex acoustic fields. Benefiting from the huge spatial information that traditional acoustic elements cannot match, acoustic holograms pursue the realization of high-resolution complex acoustic fields and gradually tend to high-frequency ultrasound applications. However, conventional continuous phase holograms are limited by three-dimensional(3D) printing size, and the presence of unavoidable small printing errors makes it difficult to achieve acoustic field reconstruction at high frequency accuracy. Here, we present an optimized discrete multi-step phase hologram. It can ensure the reconstruction quality of image with high robustness, and properly lower the requirement for the 3D printing accuracy. Meanwhile, the concept of reconstruction similarity is proposed to refine a measure of acoustic field quality. In addition, the realized complex acoustic field at 20 MHz promotes the application of acoustic holograms at high frequencies and provides a new way to generate high-fidelity acoustic fields.
基金Financial support by National Natural Foundation Fund of China(No.J1770040,Nu.J1070042)is gldtefully dcklluwledged.
文摘Computational fluid dynamics(CFD)has become a valuable tool to study the complex gas-solid hydrodynamics in the circulating fluidized bed(CFB).Based on the two fluid model(TFM)under the Eulerian-Eulerian framework and the dense discrete phase model(DDPM)under the Eulerian-Lagrangian framework,this work conducts the comparative study of the gas-solid hydrodynamics in a CFB riser by these two different models.Results show that DDPM could be used to predict gas-solid hydrodynamics in the circulating fluidized bed,and there are differences between TFM and DDPM,especially in the radial distribution profiles of solid phase.Sensitivity analysis results show that the gas-solid drag model exhibits significant effects on the results for both the two models.The specularity coefficient and the restitution coefficient in the TFM,as well as the reflection coefficient and the parcel number in the DDPM,exhibit less impact on the simulated results.
基金We thank Dr.David Dayton at RTI International for his help and valuable comments.We acknowledge a contribution from North Carolina Agricultural and Technical State University,supported by funds partially provided by U.S.Department of Energy(Grant#:EE0003138)U.S.National Scientific Foundation(Grant#:HRD-1242152).Mention of a trade name,proprietary products or company name is for presentation clarity and does not imply endorsement by the authors or the university.
文摘A dense discrete phase model combined with the kinetic theory of granular flows was used to study the bubbling characteristics and segregation of poly-dispersed particle mixtures in a thin fluidized bed.Our simulations showed that in using the hybrid Eulerian-Lagrangian method,the common use of one computational cell in the thickness direction of the thin bed does not predict wall friction correctly.Instead,a three-cell discretization of the thickness direction does predict the wall friction well but six cells were needed to prevent overprediction of the bed expansion.The change in specularity factor(SF)of the model not only affected the predictions of the velocity of particles,but also had a considerable impact on their flow pattern.A decrease in SF,which decreases wall friction,showed an over-prediction in the size of bubbles,particle velocities,and void fraction of the bed,and led to a shift in the circulation center toward the bottom of the bed.The segregation of the Geldart B particles was studied in the narrow range from 400 to 600μm with a standard deviation less than 10%of the average diameter.Simulations showed that large particles accumulated close to the distributor at the bottom of the bed and the center of the bed,but small particles moved towards the wall and top surface.The decrease in the mean particle size and spread in shape of the distribution improves mixing by up to 30%at a superficial gas velocity of around 2.5 times the minimum fluidization velocity.Log-normal mixtures with a small proportion of large particles had the most uniform distribution with a thin layer of jetsam forming at the bottom of the bed.Finally,experimental verification of the segregation and mixing of polydisperse particles with narrow size distribution is suggested.
文摘Liquid-solid binary fluidized beds are widely used in many industries. However, the flow behavior of such beds is not well understood due to the lack of accurate experimental and numerical data. In the current study, the behavior of monodisperse and binary liquid-solid fluidized beds of the same density but dif- ferent sizes is investigated using radioactive particle tracking （RPT） technique and a dense discrete phase model （DDPM）. Experiments and simulations are performed in monodisperse fluidized beds containing two different sizes of glass beads （0.6 and I mm） and a binary fluidized bed of the same particles for vari- ous bed compositions. The results show that both RPT and DDPM can predict the mixing and segregation pattern in liquid-solid binary fluidized beds. The mean velocity predictions of DDPM are in good agree- ment with the experimental findings for both monodisperse and binary fluidized beds. However, the axial root mean square velocity predictions are only reasonable for bigger particles. Particle-particle interac- tions are found to be critical for predicting the flow behavior of solids in liquid-solid binary fluidized beds.
基金supported by the Fund for Foreign Scholars in University Research and Teaching Programs(the 111 Project)(B18039)
文摘This paper takes further insight into the sparse geometry which offers a larger array aperture than uniform linear array(ULA)with the same number of physical sensors.An efficient method based on closed-form robust Chinese remainder theorem(CFRCRT)is presented to estimate the direction of arrival(DOA)from their wrapped phase with permissible errors.The proposed algorithm has significantly less computational complexity than the searching method while maintaining similar estimation precision.Furthermore,we combine all phase discrete Fourier transfer(APDFT)and the CFRCRT algorithm to achieve a considerably high DOA estimation precision.Both the theoretical analysis and simulation results demonstrate that the proposed algorithm has a higher estimation precision as well as lower computation complexity.
基金funded by The National Natural Science Foundation of China(Grant No.12172308)the Provincial Natural Science Foundation of Hunan(Grant No.2023JJ40260).
文摘To investigate the influence of snow particle rotational motion on the accumulation of snow in the bogie region of high-speed trains,an Euler‒Lagrange numerical approach is adopted.The study examines the effects of snow particle diameter and train speed on the ensuing dynamics.It is shown that considering snow particle rotational motion causes significant deviation in the particle trajectories with respect to non-rotating particles.Such a deviation increases with larger snow particle diameters and higher train speeds.The snow accumulation on the overall surface of the bogie increases,and the amount of snow on the vibration reduction device varies greatly.In certain conditions,the amount of accumulated snow can increase by several orders of magnitudes.
基金supported by the National Key Research and Development Program of China[Grant No.2016YFB1200402].
文摘To investigate the deposition distribution of snow particles in the bogie surfaces of a high-speed train,a snow particle deposition model,based on the critical capture velocity and the critical shear velocity,was elaborated.Simulations based on the unsteady Reynolds-Averaged Navier-Stokes(RANS)approach coupled with Discrete Phase Model(DPM)were used to analyze the motion of snow particles.The results show that the cross beam of the bogie frame,the anti-snake damper,the intermediate brake clamps in the rear wheels,the traction rod and the anti-rolling torsion bar are prone to accumulate snow.The accumulation mass relating to the vertical surface in the rear region,horizontal surface in the front region and the corner area of the bogie is high.The average snow accumulation mass for each component ordered from high to low is as follow:traction rod,frame,bolster,brake clamp 2,anti-rolling torsion bar,brake clamp 1,transverse damper,axle box 2,axle box 1,air spring,anti-snake damper,tread cleaning device.The snow accumulation mass on the front components of the bogie is more significant than that relating to the rear components.Particularly,the average snow accumulation mass of rear brake clamp 2 and axle box 2 is about twice as high as that of the front brake clamp 1 and axle box 1.
基金supported by the National Natural Science Foundation of China(No.51706244)National Science and Technology Major Projects of China(No.2017-VIII-0003-0114)。
文摘Ice particles could form under the continuous impingement of incoming supercooled droplets in icing conditions,which will change the surface roughness to enhance the further heat and mass transfer during icing process.A fixed-grid porous enthalpy method based on the improved Discrete Phase Model(DPM)and Volume of Fluid(VOF)integrated algorithm is developed to solve the multiphase heat transfer problem to give more detailed demonstration of the formation of initial ice roughness.The algorithms to determine the criterion of transformation from DPM to VOF and the allocation of source items during transformation are improved to the general DPM-VOF algorithm.Two verification cases,namely two glycerine-solution droplets impact and single droplet freeze,are conducted to verify the accuracy and reliability of the enthalpy-DPMVOF method,where the simulation results match well with experiment phenomena.Ice roughness on a NACA0012 airfoil is precisely captured and the effects on convective heat transfer characteristics are preliminarily revealed.The results illustrate that the enthalpy-DPM-VOF method could successfully capture the characteristics of motion and the phase change process of droplet,as well as balance the calculation accuracy and efficiency.
基金financial support provided by the Western US Mining Safety and Health Training&Translation Center by the National Institute for Occupational Safety and Health(NIOSH)
文摘The diesel particulate matter(DPM) emission from diesel powered equipment in underground mines can cause health hazards including cancer to the miners. The understanding of the DPM propagation pattern under realistic mining condition is required for selecting proper DPM control strategies and to improve working practices in underground mines. In this paper, three dimensional simulations of DPM emission from the exhaust tail pipe of a load-haul-dump(LHD) vehicle and its subsequent distribution inside an isolated zone in the typical underground mine are carried out using two different solution models available in Ansys Fluent. The incoming fresh air into the isolated zone is treated as a continuous phase and DPM is treated either as a continuous phase(gas) or as a secondary discrete phase(particle). Species transport model is used when DPM is treated as gas and discrete phase model is used when DPM is assumed to behave like a particle. The distributions of DPM concentration inside the isolated zone obtained from each method are presented and compared. From the comparison results, an accurate and economical solution technique for DPM evaluation can be selected.
基金Supported by the National Natural Science Foundation of China (No. 20376053).
文摘A resident time model is proposed to evaluate the performance of agitated extraction columns. In this model, the resident time of dispersed drops is simulated with the discrete phase modeling, where the continuous phase and the dispersed phase （drops） are described by the single-phase Navier-Stokes （turbulence） model and Lagrangian model, respectively. The interaction of dispersed phase and continuous phase is neglected for the low concentration of drop in the cases studied. The statistical parameters of drops （the average resident time and standard deviation） under different operation conditions are computed for four columns. The relation of the above statistical parameters with the performance of columns is discussed and the criterions for an optimal compartment are outlined. Our results indicate that the resident time model is useful to evaluate the performance and optimize the design of extraction columns.
基金supported by the Program for Postgraduates Research Innovation in University of Jiangsu Province of China (No.CXLX13_955)the National Natural Science Foundation of China (No.51104153)
文摘In order to reveal the influence of forced ventilation on the dispersion of droplets ejected from roadheader-mounted external sprayer,the paper studies the air-flowing field and the droplet distribution under the condition of gentle breeze and normal forced ventilation in heading face using the particle tracking technology of computational fluid dynamics(CFD).The results show that air-flowing tendency in the same section presents great comparability in the period of gentle breeze and forced ventilation,and the difference mainly embodies in the different wind velocity.The influence of ventilation on the dispersion of droplets is faint under the gentle breeze condition.The droplet can be evenly distributed around the cutting head.However,under the normal forced ventilation,a large number of droplets will drift to the return air side.At the same time,droplet clusters are predominantly presented in the lower part of windward side and the middle of the leeward side around the cutting head.In contrast,the droplet concentration in other parts around cutting head decreases a lot and the droplets are unable to form close-grained mist curtain.So the dust escape channel is formed.In addition,the simulation results also reveal that the disturbance of air flow on the droplet distribution can be effectively relieved when using ventilation duct with Coanda effect(VDCE).Field experiment results show that the dust suppression efficiency of total dust and respirable dust increases respectively by 10.5%and 9.3%when using VDCE,which proves that it can weaken the influence of airflow on droplet dispersion.
基金funded by Key research and development project of Shandong province in China(Grant Number 2018TSCYCX-10).
文摘Based on computational fluid dynamics method,the effect of atomization gas pressure on the atomization efficiency of Laval nozzle was studied,and then a discrete phase model was established and combined with industrial trials to study the effect of a new type of assisted gas nozzles(AGNs)on powder size distribution and amorphous powder yield.The results show that increasing the atomization pressure can effectively improve the gas velocity for the Laval nozzle;however,it will decrease the aspiration pressure,and the optimal atomization pressure is 2.0 MPa.Compared with this,after the application of AGNs with the inlet velocity of 200 m s^(-1),assisted gas jet can increase the velocity of overall droplets in the break-up and solidification area by 40 m s^(-1) and the maximum cooling rate is increased from 1.9×10^(4) to 2.3×10^(4) K s^(-1).The predicted particle behavior is demonstrated by the industrial trails,that is,after the application of AGNs,the median diameter of powders d50 is decreased from 28.42 to 25.56 lm,the sphericity is increased from 0.874 to 0.927,the fraction of amorphous powders is increased from 90.4% to 99.4%,and only the coercivity is increased slightly due to the accumulation of internal stress.It is illustrated that the AGNs can improve the yield of fine amorphous powders,which is beneficial to providing high-performance raw powders for additive manufacturing technology.
基金supported by Versus Arthritis UK(Grant no:21977)European Commission via a H2020-MSCA-RISE programme(BAMOS,Grant no:734156)+1 种基金Innovative UK via Newton Fund(Grant no:102872)Engineering and Physical Science Research Council(EPSRC)via DTP CASE programme(Grant no:EP/T517793/1).
文摘Nutrients supply especially like nutrients and oxygen play vital role in tissue engineering process.It is found that tissue could not grow very well in the middle of the scaffold because few nutrients could transport to the middle.Nutrient limitations would reduce cell proliferation and differentiation.In that case,there is urgent need to understand the nutrient distribution for both in vitro and in vivo study,as no technology is able for researchers to observe the nutrients transport during those process.In this paper,a numerical model coupling with VOF(volume of fluid)model and species transport model together for predicting the distribution of oxygen and glucose in the scaffold after implantation in to the site is developed.Comparing with our previous in vivo tests,the regenerated tissue distribution has a similar trend as oxygen distribution rather than glucose.The reported scaffold manufactured by additive manufacturing provided a good interconnected structure which facilitated the nutrient transportation in the scaffold.Considering nutrient transportation,this numerical model could be used in better understanding the nutrients transportation in the scaffold,and leading to a better understanding of tissue formation in the scaffold.
基金Project(2016YFC0700100) supported by the National Key R&D Program of ChinaProject(JDJQ20160103) supported by Promotion of the Connotation Development Quota Project of Colleges and Universities-Outstanding Youth of Architectural University,China
文摘The standard k-ε turbulence model and discrete phase model (DPM) were used to simulate the heat and mass transfer in a liquid-desiccant evaporator driven by a heat pump using FLUENT software, and the temperature field and velocity field in the device were obtained. The performance of the liquid-desiccant evaporator was studied as the concentration of the inlet solution varied between 21% and 30% and the pipe wall temperature between 30 and 50 ℃. Results show that the humidification rate and the humidification efficiency increased with the inlet air temperature, the solution flow rate, the solution temperature, and the pipe wall temperature. The humidification rate and humidification efficiency decreased with increasing moisture content in inlet air and the concentration of inlet solution. The humidification rate increased substantially but the humidification efficiency decreased as the inlet air flow rate increased. The error between the simulations and experimental results is acceptable, meaning that our model can provide a theoretical basis for optimizing the performance of a humidifying evaporator.
基金the National Natural Science Foundation of China(Grant Nos.U1860205 and 52204352)Young Elite Scientist Sponsorship Program by China Association for Science and Technology(Grant No.YESS20200210)Youth Project of Hubei Natural Science Foundation(Grant No.2022CFB593).
文摘To avoid the volume expansion of basic oxygen furnace (BOF) slag for use in building materials, a hot slag modification process was proposed to reduce free CaO (f-CaO) in the molten slag. A transient 3D numerical model of BOF molten slag modification by SiO_(2) particles was established. The flow and heat transfer of molten slag, movement and dissolution of the modifier, and concentration distribution of f-CaO in slag during the modification of BOF were studied. The distribution of f-CaO concentration is inhomogeneous all over the molten slag. The mixing effect at the slag surface is weaker than that at the half-height plane of the slag. To consume the f-CaO below 2.0 wt.% in the slag, the optimum quantity of the SiO_(2) modifier is 10.0% of the mass of the slag. The fine SiO_(2) particles help attain a lower final mass fraction of f-CaO and a higher SiO_(2) utilization ratio.
基金Supported by the National Natural Science Foundation of China(51106074)
文摘Transmission of airborne bacteria is the main factor causing surgical site infection(SSI),which is harmful to patients′health and even lives.Numerical study is conducted on the effect of the operating table protected by horizontal laminar flow screen.Discrete phase model(DPM)is used.Numerical simulation is carried out to evaluate particle trajectories with the Lagrange approach.As a result,the protecting effect of horizontal laminar flow screen is established,and the protecting parameters of the air velocity supplied by the screen and the protecting distance are optimized.The optimized air velocity supplied by the screen should be at 0.4—0.6 m/s.And the protecting distance should be less than 1.3 m.This work provides references for the study on the depuration of operating table or room.
