Although a series of hypotheses have been proposed,the mechanism underlying coal and gas outburst remains unclear.Given the low-index outbursts encountered in mining practice,we attempt to explore this mechanism using...Although a series of hypotheses have been proposed,the mechanism underlying coal and gas outburst remains unclear.Given the low-index outbursts encountered in mining practice,we attempt to explore this mechanism using a multiphysics coupling model considering the effects of coal strength and gas mass transfer on failure.Based on force analysis of coal ahead of the heading face,a risk identification index C_(m)and a critical criterion(C_(m)≥1)of coal instability are proposed.According to this criterion,the driving force of an outburst consists of stress and gas pressure gradients along the heading direction of the roadway,whereas resistance depends on the shear and tensile strengths of the coal.The results show that outburst risk decreases slightly,followed by a rapid increase,with increasing vertical stress,whereas it decreases with increasing coal strength and increases with gas pressure monotonically.Using the response surface method,a coupled multi-factor model for the risk identification index is developed.The results indicate strong interactions among the controlling factors.Moreover,the critical values of the factors corresponding to outburst change depending on the environment of the coal seams,rather than being constants.As the buried depth of a coal seam increases,the critical values of gas pressure and coal strength decrease slightly,followed by a rapid increase.According to its controlling factors,outburst can be divided into stress-dominated,coal-strength-dominated,gas-pressure-dominated,and multi-factor compound types.Based on this classification,a classified control method is proposed to enable more targeted outburst prevention.展开更多
General reductions in lubricant viscosities and increasing loads in machine components highlight the role of tribofilms in providing surface protection against scuffing.However,the relationship between the scuffing pr...General reductions in lubricant viscosities and increasing loads in machine components highlight the role of tribofilms in providing surface protection against scuffing.However,the relationship between the scuffing process and the growth and removal of tribofilm is not well understood.In this study,a multiphysics coupling model,which includes hydrodynamic lubrication,asperity contact,thermal effect,tribochemistry reaction,friction,and surface wear,was developed to capture the initiation of surface scuffing.Simulations and experiments for a piston ring and cylinder liner contact were conducted following a step-load sequence under different temperature conditions.The results show that high temperature and extreme load could induce the lubricant film collapse,which in turn triggers the breakdown of the tribofilm due to the significantly increased removal process.The failures of both lubricant film and tribofilm progress instantaneously in a coupling way,which finally leads to severe scuffing.展开更多
Differing from traditional pressurized water reactors(PWRs),heat pipe cooled reactors have the unique characteristics of fuel thermal expansion,expansion reactivity feedback,and thermal contact conductance.These react...Differing from traditional pressurized water reactors(PWRs),heat pipe cooled reactors have the unique characteristics of fuel thermal expansion,expansion reactivity feedback,and thermal contact conductance.These reactors require a new multiphysics coupling method.In this paper,a transient coupling method based on OpenFOAM is proposed.The method considers power variation,thermal expansion,heat pipe operation,thermal contact conductance,and gap conductance.In particular,the reactivity feedback caused by working medium redistribution in a heat pipe is also preliminarily considered.A typical heat pipe cooled reactor KRUSTY(Kilowatt Reactor Using Stirling TechnologY)is chosen as the research object.Compared with experimental results of load following,the calculated results are in good agreement and show the validity of the proposed method.To discuss the self-adjusting capability of this type of reactor system,a hypothetical accident is simulated.It is assumed that at the beginning of this accident,loss of the heat sink occurs.After 1500 s of the transient process,the reactor system recovers immediately.During this hypothetical accident,the control rod is always out of the reactor core,and the reactor only relies on the reactivity feedback to regulate the fission power.According to the simulation,the peak temperature is only about 1112 K,which is far below the safety limit.As for system recovery,the reactor needs approximately 2500 s to return to a steady state and can realize effective power regulation by reactivity feedback.This study confirms the availability of this coupling method and that it can be an effective tool for the simulation of heat pipe cooled reactors.展开更多
Aiming at solving problems of low efficiency,low cable capacity in current 300m open-pit mine cable winding truck,a 900 m cable winding plan was proposed.In this paper,the mechanism of the thermal effect of the cable ...Aiming at solving problems of low efficiency,low cable capacity in current 300m open-pit mine cable winding truck,a 900 m cable winding plan was proposed.In this paper,the mechanism of the thermal effect of the cable was described,and a two-dimensional axisymmetric electromagnetic-fluid-temperature multiphysics coupling model of the cable reel was established regarding the 900m cable reel as independent system.Considering the structure of the drum,the number of cable winding layers,the factors of heat conduction,heat radiation and convective heat transfer in the actual working process,the steady state analysis of the multi-physical field coupling was carried out.The sum of the losses of each part of the cable was obtained through the calculation of electromagnetic field,which was used as a heat source to calculate and analyze the temperature distribution of different layers of cable winding,as well as the temperature distribution and heat dissipation characteristics of different structures of the drum.The results show that three layers of cable winding is the best design.The lowest temperature of closed cylindrical drum is 70℃after heat dissipation,which has obvious advantages compared with the lowest temperature of 85℃after heat dissipation of squirrel-cage cylindrical drum.The results provide a reliable theoretical basis for the research and development of a new type of mine cable winding truck with 900 m cable capacity.展开更多
Since the resin-based composite materials are of essential importance in many key engineering fields,the manufacture processes are highly worth studying and optimizing for satisfying quality control at the highest pos...Since the resin-based composite materials are of essential importance in many key engineering fields,the manufacture processes are highly worth studying and optimizing for satisfying quality control at the highest possible production rate.In this paper,combined with the impregnation theory,the flow-thermal-mechanical multiphysics coupling model is built to characterize,investigate and optimize the osmotic flow process of hot-melt resin in fiber fabrics with the uniformity and adequacy of resin impregnation as the evaluation criteria.First,the osmotic flow process is characterized by the osmotic flow front of resin,which is tracked by the phase-field method.Then,the influencing factors of roller clearance,temperature and speed are comprehensively investigated.After that,the simulation data of resin impregnation degree are fitted by polynomial curves,with accuracy up to 96.13%,for further investigation of interaction between influencing factors.Finally,based on the above results,the operation parameter combination for impregnation process is optimized with the response surface method and provided as the guidance for practical application.展开更多
The increasing integration of small-scale structures in engineering,particularly in Micro-Electro-Mechanical Systems(MEMS),necessitates advanced modeling approaches to accurately capture their complex mechanical behav...The increasing integration of small-scale structures in engineering,particularly in Micro-Electro-Mechanical Systems(MEMS),necessitates advanced modeling approaches to accurately capture their complex mechanical behavior.Classical continuum theories are inadequate at micro-and nanoscales,particularly concerning size effects,singularities,and phenomena like strain softening or phase transitions.This limitation follows from their lack of intrinsic length scale parameters,crucial for representingmicrostructural features.Theoretical and experimental findings emphasize the critical role of these parameters on small scales.This review thoroughly examines various strain gradient elasticity(SGE)theories commonly employed in literature to capture these size-dependent effects on the elastic response.Given the complexity arising from numerous SGE frameworks available in the literature,including first-and second-order gradient theories,we conduct a comprehensive and comparative analysis of common SGE models.This analysis highlights their unique physical interpretations and compares their effectiveness in modeling the size-dependent behavior of low-dimensional structures.A brief discussion on estimating additional material constants,such as intrinsic length scales,is also included to improve the practical relevance of SGE.Following this theoretical treatment,the review covers analytical and numerical methods for solving the associated higher-order governing differential equations.Finally,we present a detailed overview of strain gradient applications in multiscale andmultiphysics response of solids.Interesting research on exploring the relevance of SGE for reduced-order modeling of complex macrostructures,a universal multiphysics coupling in low-dimensional structures without being restricted to limited material symmetries(as in the case of microstructures),is also presented here for interested readers.Finally,we briefly discuss alternative nonlocal elasticity approaches(integral and integro-differential)for incorporating size effects,and conclude with some potential areas for future research on strain gradients.This review aims to provide a clear understanding of strain gradient theories and their broad applicability beyond classical elasticity.展开更多
A suitable channel structure can lead to efficient gas distribution and significantly improve the power density of fuel cells.In this study,the influence of two channel design parameters is investigated,namely,the rat...A suitable channel structure can lead to efficient gas distribution and significantly improve the power density of fuel cells.In this study,the influence of two channel design parameters is investigated,namely,the ratio of the channel width to the bipolar plate ridge width(i.e.,the channel ridge ratio)and the channel depth.The impact of these parameters is evaluated with respect to the flow pattern,the gas composition distribution,the temperature field and the fuel cell output capability.The results show that a decrease in the channel ridge ratio and an increase in the channel depth can effectively make the distributions of velocity,temperature and concentration more uniform in each channel and improve the output capability of the fuel cell.An increase in the channel ridge ratio and depth obviously reduces the flow resistance and improves the flow characteristics.展开更多
With the large-scale mining of coal resources,the huge economic losses and environmental problems caused by underground coal fires have become increasingly prominent,and the research on the status quo and response str...With the large-scale mining of coal resources,the huge economic losses and environmental problems caused by underground coal fires have become increasingly prominent,and the research on the status quo and response strategies of underground coal fires is of great significance to accelerate the green prevention and control of coal fires,energy conservation and emission reduction.In this paper,we summarized and sorted out the research status of underground coal fires,focused on the theoretical and technical issues such as underground coal fire combustion mechanism,multiphysics coupling effect of coal fire combustion,fire prevention and extinguishing technology for underground coal fires,and beneficial utilization technology,and described the latest research progress of the prevention and control for underground coal fire hazards.Finally,the key research problems in the field of underground coal fire hazards prevention and control were proposed in the direction of the basic theory,technology research,comprehensive management and utilization,with a view to providing ideas and solutions for the management of underground coal fires.展开更多
The spewing of a screw conveyor easily occurs from the earth pressure balance(called EPB)shield in a water-rich sand stratum.This may lead to the collapse of the tunnel face and even serious subsidence of the ground s...The spewing of a screw conveyor easily occurs from the earth pressure balance(called EPB)shield in a water-rich sand stratum.This may lead to the collapse of the tunnel face and even serious subsidence of the ground surface.To understand the spewing mechanism of the shield screw conveyor and explore the critical hydraulic condition of soil spewing in a shield–soil chamber,a simplified theoretical model for the spewing of the screw conveyor was developed based on the equation of groundwater flow in the screw conveyor under turbulent state.Thus,coupling Darcy's law with Brinkman's equation,this model was implemented within the COMSOL Multiphysics framework.The underground water flow in the shield screw conveyor was simulated so as to obtain its velocity and flow rate.Numerical simulations show that the water pressure distribution is concentrated in the lower part of the soil chamber after the groundwater enters the soil chamber.When the groundwater enters the screw conveyor,its pressure gradually decreases along the direction of the screw conveyor.When the water flow reaches the stratum–shield interface,the flow velocity changes markedly:first increases and concentrates at the entrance of the lower soil chamber,plummets and stabilizes gradually,and increases again at the exit.The soil chamber and screw conveyor are significantly depressurized.It is also found that the soil permeability coefficient can be reduced to k<2.6×10^(−4)cm/s through appropriate soil improvement,which can effectively prevent the occurrence of spewing disasters.展开更多
When a solid rocket engine is ignited,the throat lining of the nozzle is prone to chemical ablation owing to high-temperature gas erosion,resulting in thrust loss.In this paper,a coupled fluid-solid model for thermoch...When a solid rocket engine is ignited,the throat lining of the nozzle is prone to chemical ablation owing to high-temperature gas erosion,resulting in thrust loss.In this paper,a coupled fluid-solid model for thermochemical ablation on the nozzle wall is established based on the multi-component Navier-Stokes equations,SST k-ω turbulence model,finite-rate chemical reaction model on the nozzle wall,variable transport properties of the nozzle material,and the heat conduction equation.Compared with the experimental data,the maximum error of the calculated ablation rate was 4.37%,validating the effectiveness of the model.Subsequently,the effects of different combustion chamber components,pressures,and temperatures on the ablation rate of the carbon-carbon(C/C)throat lining were studied.The results indicate that the temperature at the nozzle throat was the highest,resulting in the maximum ablation rate.As the Al mass fraction at the nozzle inlet increased,the thermochemical ablation rate of the nozzle decreased with a lower oxidizer mass fraction.The inlet pres sure and temperature of the nozzle were positively correlated with the ablation rate,with the temperature having a more significant impact than the pressure.These findings provide theoretical guidance for the thermal protection design of rocket engine nozzles.展开更多
The photothermal self-driving process of Janus microparticles has wide application prospects in the fields of biomedicine.Since silica and gold have good biocompatibility and high photothermal conversion efficiency,th...The photothermal self-driving process of Janus microparticles has wide application prospects in the fields of biomedicine.Since silica and gold have good biocompatibility and high photothermal conversion efficiency,the SiO_(2)@Au Janus microparticles are widely used as drug carriers.Based on the multiphysics coupling method,the photothermal self-driving process of SiO_(2)@Au Janus microparticles was investi-gated,wherein the substrate was SiO_(2)particles and one side of the particles was coated with gold film.Under a continuous wave laser with irradiation of 20 W/cm^(2),the distance covered by the Janus particles was increased by increasing the thickness of the gold film and reducing the size of the SiO_(2)particles;the self-driving characteristics of the Janus particles were controlled substantially by increasing the intensity of the incident laser.Based on the simulation results,the thermophoretic motion and Brownian motion of particles can be measured by comparing the absolute values of the thermophoretic force impulse,Brownian force impulse,and drag force impulse.The Brownian force acting on Janus microparticles under low laser power cannot be ignored.Furthermore,the minimum laser power required for Janus particles to overcome Brownian motion was calculated.The results can effectively guide the design of Janus particles in biomedicine and systematically analyze the mechanism of particle thermophoretic motion during drug delivery.展开更多
Electronic packaging is an essential branch of electronic engineering that aims to protect electronic,microelec-tronic,and nanoelectronic systems from environmental conditions.The design of electronic packaging is hig...Electronic packaging is an essential branch of electronic engineering that aims to protect electronic,microelec-tronic,and nanoelectronic systems from environmental conditions.The design of electronic packaging is highly complex and requires the consideration of multi-physics phenomena,such as thermal transport,electromagnetic fields,and mechanical stress.This review presents a comprehensive overview of the multiphysics coupling of electric,magnetic,thermal,mechanical,and fluid fields,which are crucial for assessing the performance and reliability of electronic devices.The recent advancements in multi-scale simulation techniques are also system-atically summarized,such as finite element methods at the macroscopic scale,molecular dynamics and density functional theory at the microscopic scale,and particularly machine learning methods for bridging different scales.Additionally,we illustrate how these methods can be applied to study various aspects of electronic pack-aging,such as material properties,interfacial failure,thermal management,electromigration,and stress analysis.The challenges and the potential applications of multi-scale simulation techniques in electronic packaging are also highlighted.Further,some future directions for multi-scale simulation techniques in electronic packaging are concluded for further investigation.展开更多
Introducing a magnetic-field gradient into an electrically driven chemical reaction is expected to give rise to intriguing research possibilities.In this work,we elaborate on the modes and mechanisms of electrocatalyt...Introducing a magnetic-field gradient into an electrically driven chemical reaction is expected to give rise to intriguing research possibilities.In this work,we elaborate on the modes and mechanisms of electrocatalytic activity(from the perspective of alignment of magnetic moments)and selectivity(at the molecular level)for the CO_(2)reduction reaction in response to external magnetic fields.We establish a positive correlation between magnetic field strengths and apparent current densities.This correlation can be rationalized by the formation of longer-range ordering ofmagnetic moments and the resulting decrease in the scattering of conduction electrons and charge-transfer resistances as the field strength increases.Furthermore,aided by the magnetic-field-equipped operando infrared spectroscopy,we find that applied magnetic fields are capable of weakening the C–O bond strength of the key intermediate*COOH and elongating the C–O bond length,thereby increasing the faradaic efficiency for the electroreduction of CO_(2)to CO.展开更多
Power-to-hydrogen by electrolysis(PtHE)is a promising technology in the carbon-neutral evolution of energy.PtHE not only contributes to renewable energy integration but also accelerates decarbonization in industrial s...Power-to-hydrogen by electrolysis(PtHE)is a promising technology in the carbon-neutral evolution of energy.PtHE not only contributes to renewable energy integration but also accelerates decarbonization in industrial sectors through green hydrogen production.This paper presents a comprehensive review of PtHE technology.First,technical solutions in PtHE technology are introduced to clarify pros and cons of one another.Besides,the multiphysics coupling and the multi-energy flow are investigated to reveal the insight mechanism during operation of compactly assembled industrial PtHE plants.Then,the development trends of core components in PtHE plants,including electrocatalysts,electrode plates and operation strategy,are reviewed,respectively.Research thrusts needed for PtHE in carbon-neutral transition are also summarized.Finally,three configurations of the PtHE plant in energy system integration are introduced,which can achieve renewable energy integration and efficient energy utilization.Index Terms-Carbon neutrality,power-to-hydrogen nby electrolysis(PtHE),multiphysics coupling,multidisciplinary.展开更多
基金This work was supported by the National Natural Science Foundation of China(52004276)National Postdoctoral Program for Innovative Talents(BX20190369)+1 种基金Natural Science Foundation of Jiangsu Province(BK20200636)China Postdoctoral Science Foundation(2019M661996).
文摘Although a series of hypotheses have been proposed,the mechanism underlying coal and gas outburst remains unclear.Given the low-index outbursts encountered in mining practice,we attempt to explore this mechanism using a multiphysics coupling model considering the effects of coal strength and gas mass transfer on failure.Based on force analysis of coal ahead of the heading face,a risk identification index C_(m)and a critical criterion(C_(m)≥1)of coal instability are proposed.According to this criterion,the driving force of an outburst consists of stress and gas pressure gradients along the heading direction of the roadway,whereas resistance depends on the shear and tensile strengths of the coal.The results show that outburst risk decreases slightly,followed by a rapid increase,with increasing vertical stress,whereas it decreases with increasing coal strength and increases with gas pressure monotonically.Using the response surface method,a coupled multi-factor model for the risk identification index is developed.The results indicate strong interactions among the controlling factors.Moreover,the critical values of the factors corresponding to outburst change depending on the environment of the coal seams,rather than being constants.As the buried depth of a coal seam increases,the critical values of gas pressure and coal strength decrease slightly,followed by a rapid increase.According to its controlling factors,outburst can be divided into stress-dominated,coal-strength-dominated,gas-pressure-dominated,and multi-factor compound types.Based on this classification,a classified control method is proposed to enable more targeted outburst prevention.
基金the National Natural Science Foundation of China(52130502,52171315)the National Key R&D Program of China(2022YFB4201102).
文摘General reductions in lubricant viscosities and increasing loads in machine components highlight the role of tribofilms in providing surface protection against scuffing.However,the relationship between the scuffing process and the growth and removal of tribofilm is not well understood.In this study,a multiphysics coupling model,which includes hydrodynamic lubrication,asperity contact,thermal effect,tribochemistry reaction,friction,and surface wear,was developed to capture the initiation of surface scuffing.Simulations and experiments for a piston ring and cylinder liner contact were conducted following a step-load sequence under different temperature conditions.The results show that high temperature and extreme load could induce the lubricant film collapse,which in turn triggers the breakdown of the tribofilm due to the significantly increased removal process.The failures of both lubricant film and tribofilm progress instantaneously in a coupling way,which finally leads to severe scuffing.
基金supported by the National Key Research and Development Project of China(Grant No.2020YFB1901700)Science Challenge Project(Grant No.TZ2018001)+1 种基金the National Natural Science Foundation of China(Grant Nos.11775126 and 11775127)the Tsinghua University Initiative Scientific Research Program。
文摘Differing from traditional pressurized water reactors(PWRs),heat pipe cooled reactors have the unique characteristics of fuel thermal expansion,expansion reactivity feedback,and thermal contact conductance.These reactors require a new multiphysics coupling method.In this paper,a transient coupling method based on OpenFOAM is proposed.The method considers power variation,thermal expansion,heat pipe operation,thermal contact conductance,and gap conductance.In particular,the reactivity feedback caused by working medium redistribution in a heat pipe is also preliminarily considered.A typical heat pipe cooled reactor KRUSTY(Kilowatt Reactor Using Stirling TechnologY)is chosen as the research object.Compared with experimental results of load following,the calculated results are in good agreement and show the validity of the proposed method.To discuss the self-adjusting capability of this type of reactor system,a hypothetical accident is simulated.It is assumed that at the beginning of this accident,loss of the heat sink occurs.After 1500 s of the transient process,the reactor system recovers immediately.During this hypothetical accident,the control rod is always out of the reactor core,and the reactor only relies on the reactivity feedback to regulate the fission power.According to the simulation,the peak temperature is only about 1112 K,which is far below the safety limit.As for system recovery,the reactor needs approximately 2500 s to return to a steady state and can realize effective power regulation by reactivity feedback.This study confirms the availability of this coupling method and that it can be an effective tool for the simulation of heat pipe cooled reactors.
基金This work was supported in part by 2019 Local Project of Science and Tech nology Research Service of Liaoning Provincial Department of Education(LJ2019FL003)by 2019 Science and Technology Research and Innovation Te am Project of Liaoning Provincial Department of Education(LT2019007)by 2020 Youth Science and Technology Talents"Nursery"Projects of Scient ific Research of Liaoning Province Education Department(LJ2020QNL019).
文摘Aiming at solving problems of low efficiency,low cable capacity in current 300m open-pit mine cable winding truck,a 900 m cable winding plan was proposed.In this paper,the mechanism of the thermal effect of the cable was described,and a two-dimensional axisymmetric electromagnetic-fluid-temperature multiphysics coupling model of the cable reel was established regarding the 900m cable reel as independent system.Considering the structure of the drum,the number of cable winding layers,the factors of heat conduction,heat radiation and convective heat transfer in the actual working process,the steady state analysis of the multi-physical field coupling was carried out.The sum of the losses of each part of the cable was obtained through the calculation of electromagnetic field,which was used as a heat source to calculate and analyze the temperature distribution of different layers of cable winding,as well as the temperature distribution and heat dissipation characteristics of different structures of the drum.The results show that three layers of cable winding is the best design.The lowest temperature of closed cylindrical drum is 70℃after heat dissipation,which has obvious advantages compared with the lowest temperature of 85℃after heat dissipation of squirrel-cage cylindrical drum.The results provide a reliable theoretical basis for the research and development of a new type of mine cable winding truck with 900 m cable capacity.
基金financially supported by the National Natural Science Foundation of China(52176202)。
文摘Since the resin-based composite materials are of essential importance in many key engineering fields,the manufacture processes are highly worth studying and optimizing for satisfying quality control at the highest possible production rate.In this paper,combined with the impregnation theory,the flow-thermal-mechanical multiphysics coupling model is built to characterize,investigate and optimize the osmotic flow process of hot-melt resin in fiber fabrics with the uniformity and adequacy of resin impregnation as the evaluation criteria.First,the osmotic flow process is characterized by the osmotic flow front of resin,which is tracked by the phase-field method.Then,the influencing factors of roller clearance,temperature and speed are comprehensively investigated.After that,the simulation data of resin impregnation degree are fitted by polynomial curves,with accuracy up to 96.13%,for further investigation of interaction between influencing factors.Finally,based on the above results,the operation parameter combination for impregnation process is optimized with the response surface method and provided as the guidance for practical application.
基金support from the Anusandhan National Research Foundation(ANRF),erstwhile Science and Engineering Research Board(SERB),India,under the startup research grant program(SRG/2022/000566).
文摘The increasing integration of small-scale structures in engineering,particularly in Micro-Electro-Mechanical Systems(MEMS),necessitates advanced modeling approaches to accurately capture their complex mechanical behavior.Classical continuum theories are inadequate at micro-and nanoscales,particularly concerning size effects,singularities,and phenomena like strain softening or phase transitions.This limitation follows from their lack of intrinsic length scale parameters,crucial for representingmicrostructural features.Theoretical and experimental findings emphasize the critical role of these parameters on small scales.This review thoroughly examines various strain gradient elasticity(SGE)theories commonly employed in literature to capture these size-dependent effects on the elastic response.Given the complexity arising from numerous SGE frameworks available in the literature,including first-and second-order gradient theories,we conduct a comprehensive and comparative analysis of common SGE models.This analysis highlights their unique physical interpretations and compares their effectiveness in modeling the size-dependent behavior of low-dimensional structures.A brief discussion on estimating additional material constants,such as intrinsic length scales,is also included to improve the practical relevance of SGE.Following this theoretical treatment,the review covers analytical and numerical methods for solving the associated higher-order governing differential equations.Finally,we present a detailed overview of strain gradient applications in multiscale andmultiphysics response of solids.Interesting research on exploring the relevance of SGE for reduced-order modeling of complex macrostructures,a universal multiphysics coupling in low-dimensional structures without being restricted to limited material symmetries(as in the case of microstructures),is also presented here for interested readers.Finally,we briefly discuss alternative nonlocal elasticity approaches(integral and integro-differential)for incorporating size effects,and conclude with some potential areas for future research on strain gradients.This review aims to provide a clear understanding of strain gradient theories and their broad applicability beyond classical elasticity.
基金This work was sponsored by the National Key R&D Program of China[Grant Number 2020YFB0106603]the Key R&D Program of Shandong Province[Grant Number 2020CXGC010404]the Undergraduate School of Shandong University,China[Grant Number 2022Y155].
文摘A suitable channel structure can lead to efficient gas distribution and significantly improve the power density of fuel cells.In this study,the influence of two channel design parameters is investigated,namely,the ratio of the channel width to the bipolar plate ridge width(i.e.,the channel ridge ratio)and the channel depth.The impact of these parameters is evaluated with respect to the flow pattern,the gas composition distribution,the temperature field and the fuel cell output capability.The results show that a decrease in the channel ridge ratio and an increase in the channel depth can effectively make the distributions of velocity,temperature and concentration more uniform in each channel and improve the output capability of the fuel cell.An increase in the channel ridge ratio and depth obviously reduces the flow resistance and improves the flow characteristics.
基金supported by the National Natural Science Foundation of China (52174229)the Natural Science Foundation of Liaoning Province (2021-KF-23-01),for which the authors are very thankful.
文摘With the large-scale mining of coal resources,the huge economic losses and environmental problems caused by underground coal fires have become increasingly prominent,and the research on the status quo and response strategies of underground coal fires is of great significance to accelerate the green prevention and control of coal fires,energy conservation and emission reduction.In this paper,we summarized and sorted out the research status of underground coal fires,focused on the theoretical and technical issues such as underground coal fire combustion mechanism,multiphysics coupling effect of coal fire combustion,fire prevention and extinguishing technology for underground coal fires,and beneficial utilization technology,and described the latest research progress of the prevention and control for underground coal fire hazards.Finally,the key research problems in the field of underground coal fire hazards prevention and control were proposed in the direction of the basic theory,technology research,comprehensive management and utilization,with a view to providing ideas and solutions for the management of underground coal fires.
基金National Natural Science Foundation of China,Grant/Award Number:U1261212。
文摘The spewing of a screw conveyor easily occurs from the earth pressure balance(called EPB)shield in a water-rich sand stratum.This may lead to the collapse of the tunnel face and even serious subsidence of the ground surface.To understand the spewing mechanism of the shield screw conveyor and explore the critical hydraulic condition of soil spewing in a shield–soil chamber,a simplified theoretical model for the spewing of the screw conveyor was developed based on the equation of groundwater flow in the screw conveyor under turbulent state.Thus,coupling Darcy's law with Brinkman's equation,this model was implemented within the COMSOL Multiphysics framework.The underground water flow in the shield screw conveyor was simulated so as to obtain its velocity and flow rate.Numerical simulations show that the water pressure distribution is concentrated in the lower part of the soil chamber after the groundwater enters the soil chamber.When the groundwater enters the screw conveyor,its pressure gradually decreases along the direction of the screw conveyor.When the water flow reaches the stratum–shield interface,the flow velocity changes markedly:first increases and concentrates at the entrance of the lower soil chamber,plummets and stabilizes gradually,and increases again at the exit.The soil chamber and screw conveyor are significantly depressurized.It is also found that the soil permeability coefficient can be reduced to k<2.6×10^(−4)cm/s through appropriate soil improvement,which can effectively prevent the occurrence of spewing disasters.
基金financially supported by Jiangxi Provincial Natural Science Foundation(20224BAB211010,20232BAB201031)。
文摘When a solid rocket engine is ignited,the throat lining of the nozzle is prone to chemical ablation owing to high-temperature gas erosion,resulting in thrust loss.In this paper,a coupled fluid-solid model for thermochemical ablation on the nozzle wall is established based on the multi-component Navier-Stokes equations,SST k-ω turbulence model,finite-rate chemical reaction model on the nozzle wall,variable transport properties of the nozzle material,and the heat conduction equation.Compared with the experimental data,the maximum error of the calculated ablation rate was 4.37%,validating the effectiveness of the model.Subsequently,the effects of different combustion chamber components,pressures,and temperatures on the ablation rate of the carbon-carbon(C/C)throat lining were studied.The results indicate that the temperature at the nozzle throat was the highest,resulting in the maximum ablation rate.As the Al mass fraction at the nozzle inlet increased,the thermochemical ablation rate of the nozzle decreased with a lower oxidizer mass fraction.The inlet pres sure and temperature of the nozzle were positively correlated with the ablation rate,with the temperature having a more significant impact than the pressure.These findings provide theoretical guidance for the thermal protection design of rocket engine nozzles.
基金supported by the Heilongjiang Province Natural Science Foundation(Grant No.LH2019E053)Fundamental Research Funds for Central Universities(Grant No.FRFCU5710051421).
文摘The photothermal self-driving process of Janus microparticles has wide application prospects in the fields of biomedicine.Since silica and gold have good biocompatibility and high photothermal conversion efficiency,the SiO_(2)@Au Janus microparticles are widely used as drug carriers.Based on the multiphysics coupling method,the photothermal self-driving process of SiO_(2)@Au Janus microparticles was investi-gated,wherein the substrate was SiO_(2)particles and one side of the particles was coated with gold film.Under a continuous wave laser with irradiation of 20 W/cm^(2),the distance covered by the Janus particles was increased by increasing the thickness of the gold film and reducing the size of the SiO_(2)particles;the self-driving characteristics of the Janus particles were controlled substantially by increasing the intensity of the incident laser.Based on the simulation results,the thermophoretic motion and Brownian motion of particles can be measured by comparing the absolute values of the thermophoretic force impulse,Brownian force impulse,and drag force impulse.The Brownian force acting on Janus microparticles under low laser power cannot be ignored.Furthermore,the minimum laser power required for Janus particles to overcome Brownian motion was calculated.The results can effectively guide the design of Janus particles in biomedicine and systematically analyze the mechanism of particle thermophoretic motion during drug delivery.
基金supported by the National Natural Science Foundation of China(U2241244).
文摘Electronic packaging is an essential branch of electronic engineering that aims to protect electronic,microelec-tronic,and nanoelectronic systems from environmental conditions.The design of electronic packaging is highly complex and requires the consideration of multi-physics phenomena,such as thermal transport,electromagnetic fields,and mechanical stress.This review presents a comprehensive overview of the multiphysics coupling of electric,magnetic,thermal,mechanical,and fluid fields,which are crucial for assessing the performance and reliability of electronic devices.The recent advancements in multi-scale simulation techniques are also system-atically summarized,such as finite element methods at the macroscopic scale,molecular dynamics and density functional theory at the microscopic scale,and particularly machine learning methods for bridging different scales.Additionally,we illustrate how these methods can be applied to study various aspects of electronic pack-aging,such as material properties,interfacial failure,thermal management,electromigration,and stress analysis.The challenges and the potential applications of multi-scale simulation techniques in electronic packaging are also highlighted.Further,some future directions for multi-scale simulation techniques in electronic packaging are concluded for further investigation.
基金supported by the Fundamental Research Funds for the Central Universities(2023ZDPY04).
文摘Introducing a magnetic-field gradient into an electrically driven chemical reaction is expected to give rise to intriguing research possibilities.In this work,we elaborate on the modes and mechanisms of electrocatalytic activity(from the perspective of alignment of magnetic moments)and selectivity(at the molecular level)for the CO_(2)reduction reaction in response to external magnetic fields.We establish a positive correlation between magnetic field strengths and apparent current densities.This correlation can be rationalized by the formation of longer-range ordering ofmagnetic moments and the resulting decrease in the scattering of conduction electrons and charge-transfer resistances as the field strength increases.Furthermore,aided by the magnetic-field-equipped operando infrared spectroscopy,we find that applied magnetic fields are capable of weakening the C–O bond strength of the key intermediate*COOH and elongating the C–O bond length,thereby increasing the faradaic efficiency for the electroreduction of CO_(2)to CO.
基金supported in part by National Natural Science Foundation of China(No.52177089)ABB Power Grids Research(No.ABB20171127REU-CTR)。
文摘Power-to-hydrogen by electrolysis(PtHE)is a promising technology in the carbon-neutral evolution of energy.PtHE not only contributes to renewable energy integration but also accelerates decarbonization in industrial sectors through green hydrogen production.This paper presents a comprehensive review of PtHE technology.First,technical solutions in PtHE technology are introduced to clarify pros and cons of one another.Besides,the multiphysics coupling and the multi-energy flow are investigated to reveal the insight mechanism during operation of compactly assembled industrial PtHE plants.Then,the development trends of core components in PtHE plants,including electrocatalysts,electrode plates and operation strategy,are reviewed,respectively.Research thrusts needed for PtHE in carbon-neutral transition are also summarized.Finally,three configurations of the PtHE plant in energy system integration are introduced,which can achieve renewable energy integration and efficient energy utilization.Index Terms-Carbon neutrality,power-to-hydrogen nby electrolysis(PtHE),multiphysics coupling,multidisciplinary.
