0 INTRODUCTION Pressure-stress coupling(PSC)refers to the bidirectional mechanical interaction between pore pressure and in-situ stress within subsurface formations(Hillis,2000).Variations in pore pressure redistribut...0 INTRODUCTION Pressure-stress coupling(PSC)refers to the bidirectional mechanical interaction between pore pressure and in-situ stress within subsurface formations(Hillis,2000).Variations in pore pressure redistribute the stress field,while evolving stress states in turn alter pore pressure.This reciprocity,governed by poroelasticity and multiphysics interactions,underlies a wide spectrum of geomechanical processes,including fracture initiation,fluid migration,reservoir evolution,and fault slip or seismicity(Xu et al.,2020).Conventional theories often treat pressure and stress as independent variables.展开更多
Based on the stability theory of linear time-varying continuous system, this paper investigates the synchronization of two linear bidirectionally-coupled systems. Sufficient conditions for asymptotic synchronization a...Based on the stability theory of linear time-varying continuous system, this paper investigates the synchronization of two linear bidirectionally-coupled systems. Sufficient conditions for asymptotic synchronization are obtained for general chaotic system with bidirectional coupling via linear error feedback. Since the trajectory of chaotic system is continuous and bounded, one can choose suitable coupled pararneters to satisfy the proposed criterion. The criterion can also be applied to the global synchronization for chaotic systems with linear unidirectional coupling. The chaotic Chen system and the generalized Lorenz-like system are taken as examples, the simulations verify the effectiveness of the proposed method.展开更多
Rock block removal is the prevalent physical mechanism for rock erosion and could affect the stability of dam foundations and spillways.Despite this,understanding of block removal is still inadequate because of the co...Rock block removal is the prevalent physical mechanism for rock erosion and could affect the stability of dam foundations and spillways.Despite this,understanding of block removal is still inadequate because of the complex interactions among block characteristics,hydraulic forces,and erosive processes acting on the block.Herein,based on a previously conducted physical experiment of erosion of a single rock block,the removal processes of two different protruding blocks are represented by a coupled computational fluid dynamics-discrete element model(CFD-DEM)approach under varied flow conditions.Additionally,the blocks could be rotated with respect to the flow direction to consider the effect of the discontinuity orientation on the block removal process.Simulation results visualize the entire block removal process.The simulations reproduce the effects of the discontinuity orientation on the critical flow velocity inducing block incipient motion and the trajectory of the block motion observed in the physical experiments.The numerical results present a similar tendency of the critical velocities at different discontinuity orientations but have slightly lower values.The trajectory of the block in the simulations fits well with the experimental measurements.The relationship between the dimensionless critical shear stress and discontinuity orientation observed from the simulations shows that the effect of block protrusion becomes more dominant on the block incipient motion with the increase of relative protrusion height.To our knowledge,this present study is the first attempt to use the coupled finite volume method(FVM)-DEM approach for modelling the interaction behavior between the block and the flowing water so that the block removal process can be reproduced and analyzed.展开更多
To mitigate and alleviate low wheel-rail adhesion,a train-borne system is utilised to deposit sand particles into the wheel-rail interface via a jet of compressed air in a process called rail-sanding.Britain Rail Safe...To mitigate and alleviate low wheel-rail adhesion,a train-borne system is utilised to deposit sand particles into the wheel-rail interface via a jet of compressed air in a process called rail-sanding.Britain Rail Safety and Standards Board introduced guidelines on the sand particles’shape,size,and uniformity which needs to be adhered to for rail-sanding.To further inves-tigate these guidelines and help improve them,this research presents a parametric study on the particle characteristics that affect the rail-sanding process including density,size and size distribution,coefficient of uniformity,and shape,utilising a coupled computational fluid dynamics-discrete element method(CFD-DEM)model.The efficiency of rail-sanding is esti-mated for each case study and compared to the benchmark to optimise the sand characteristics for rail-sanding.It is concluded that particle size distribution(within the accepted range)has an insignificant effect on the efficiency while increasing particle size or the coefficient of uniformity decreases the efficiency.Particle shape is shown to highly affect the efficiency for flat,compact and elongated particles compared to the spherical shape.The current numerical model is capable of accurately predicting the trends in the efficiency compared to the actual values obtained from full-scale experiments.展开更多
As the primary functional component of a fusion reactor,the fusion blanket pebble bed,composed of numerous particles,is crucial for tritium breeding,neutron multiplication,and radiation shielding.Particles within trit...As the primary functional component of a fusion reactor,the fusion blanket pebble bed,composed of numerous particles,is crucial for tritium breeding,neutron multiplication,and radiation shielding.Particles within tritium-breeding pebble beds are subjected to prolonged neutron irradiation,high thermal loads,and strong magnetic fields in fusion environments.Such conditions render them susceptible to pulverization and fragmentation.The resulting fragments and powders migrate and are deposited into the gas channel,driven by the purge gas.The reduction in the effective flow area of the gas increases the flow resistance,resulting in tritium retention,degraded heat transfer,and other adverse effects.These conditions impair the thermodynamic properties of the pebble beds and hinder the self-maintenance of tritium.Limited information exists on powder migration and clogging mechanisms in fusion blanket pebble beds,particularly under diverse physical conditions.The aim of this study was to use a computational fluid dynamics model coupled with the discrete element method(CFD-DEM)to numerically explore powder migration and clogging in pebble beds.The model considers factors such as breeder orientation,purge velocity,powder size distribution,and friction coefficient.We propose two migration and clogging mechanisms.One involves powder with a large particle size,and the other does not.The results indicate that the powder migration velocity progresses through three stages:rapid decay,linear decay,and stability.Pebble-bed clogging manifests in two forms:extensive superficial clogging and uniform internal clogging.Two fitted curves were used to depict the migration and clogging tendencies.The powder size distribution significantly influenced the powder migration.The breeder orientation,powder size,and friction coefficient affected the distribution of the clogging powders.However,the impact of the purge velocity on powder migration and clogging in pebble beds was limited,and this effect varied significantly with different particle size ratios.Based on the analysis,a formula is proposed to characterize the behavior of the powder in the pebble beds.The results of this study can aid in analyzing and predicting powder dynamics in pebble beds.展开更多
Traditional power supply method for moving electric railway vehicles is based on contact type power collection technology.This sometimes cannot meet the requirements of modern rail transportation.A new wireless power ...Traditional power supply method for moving electric railway vehicles is based on contact type power collection technology.This sometimes cannot meet the requirements of modern rail transportation.A new wireless power transfer(WPT)technology can offer significant benefits in modern rail transportation particularly in some stringent environments.This paper reviews the status and the development of rail transit power supply technology,and introduces a new challenging technology--inductive power transfer(IPT)technology for rail transit.Tesla established the underpinning of IPT technology and creatively and significantly demonstrated power transfer by using highly resonant tuned coils long time ago.However,only in recent years the IPT technology has been significantly improved including the transfer air-gap length,transfer efficiency,coupling factor,power transfer capability and so on.This is mainly due to innovative semiconductor switches,higher control frequency,better coil designs and high performance material,new track and vehicle construction techniques.Recent advances in IPT for rail transit and major milestones of the developments are summarized in this paper.Some important technical issues such as coupling coil structures,power supply schemes,segmentation switching techniques for long-distance power supply,and bidirectional IPT systems for braking energy feedback are discussed.展开更多
In this paper we study the chaos synchronization and anti-synchronization problems between two hyper-chaotic systems with bidirectional coupling,and present synchronization and anti-synchronization methods of chaotic ...In this paper we study the chaos synchronization and anti-synchronization problems between two hyper-chaotic systems with bidirectional coupling,and present synchronization and anti-synchronization methods of chaotic systems,based on timedelayed feedback.Coupling coefficients between the drive and response systems are different,which are supposed to be nonlinearly coupled.Based on the nonlinear control theory,the synchronization and anti-synchronization between two different time-delay hyper-chaotic systems are investigated.The condition of synchronization is derived according to the error dynamical systems.Numerical simulations show the effectiveness and feasibility of the proposed synchronous conditions.展开更多
掘进机回转台在截割煤岩时承受偏载荷及强冲击作用,其性能影响掘进机的工作效率及安全性。为探究掘进机回转台疲劳寿命的影响因素及最佳服役参数,提出了一种基于Kriging代理模型和DEM-MFBD(discrete element model-multi flexible body ...掘进机回转台在截割煤岩时承受偏载荷及强冲击作用,其性能影响掘进机的工作效率及安全性。为探究掘进机回转台疲劳寿命的影响因素及最佳服役参数,提出了一种基于Kriging代理模型和DEM-MFBD(discrete element model-multi flexible body dynamics,离散单元法-多柔性体动力学)双向耦合技术的回转台疲劳寿命预测方法。首先,建立了掘进机截割部与回转台的空间受力模型,明确了截割部与回转台的受力规律。然后,联合RecurDyn与EDEM软件对回转台进行双向刚柔耦合动力学仿真分析,获得了回转台在工作状态下的应力分布。最后,利用拉丁超立方抽样法选取15组掘进机服役参数作为输入,以回转台疲劳寿命为响应,建立了对应的Kriging代理模型,并利用粒子群优化算法对代理模型进行寻优,得到了回转台在最佳服役参数下的疲劳寿命。结果表明,当掘进机的截割头转速为54 r/min、回转台横摆速度为1.003 m/min、截割臂垂直摆角为7°时,回转台的疲劳寿命最长。结合DEM-MFBD双向耦合技术、Kriging代理模型与粒子群优化算法来探究掘进机的最佳服役参数,可为回转类部件的优化设计提供新思路。展开更多
基金supported by the National Natural Science Foundation of China(Nos.U24B6002,42488101)the Key R&D Program of Shandong Province,China(No.2024CXPT076)the Independent innovation research program of China University of Petroleum(East China)(No.21CX06001A)。
文摘0 INTRODUCTION Pressure-stress coupling(PSC)refers to the bidirectional mechanical interaction between pore pressure and in-situ stress within subsurface formations(Hillis,2000).Variations in pore pressure redistribute the stress field,while evolving stress states in turn alter pore pressure.This reciprocity,governed by poroelasticity and multiphysics interactions,underlies a wide spectrum of geomechanical processes,including fracture initiation,fluid migration,reservoir evolution,and fault slip or seismicity(Xu et al.,2020).Conventional theories often treat pressure and stress as independent variables.
基金This work was supported bythe National Natural Science Foundation (No .60174005) Natural Science Foundation of Jiangsu Province (No .BK2001054) .
文摘Based on the stability theory of linear time-varying continuous system, this paper investigates the synchronization of two linear bidirectionally-coupled systems. Sufficient conditions for asymptotic synchronization are obtained for general chaotic system with bidirectional coupling via linear error feedback. Since the trajectory of chaotic system is continuous and bounded, one can choose suitable coupled pararneters to satisfy the proposed criterion. The criterion can also be applied to the global synchronization for chaotic systems with linear unidirectional coupling. The chaotic Chen system and the generalized Lorenz-like system are taken as examples, the simulations verify the effectiveness of the proposed method.
文摘Rock block removal is the prevalent physical mechanism for rock erosion and could affect the stability of dam foundations and spillways.Despite this,understanding of block removal is still inadequate because of the complex interactions among block characteristics,hydraulic forces,and erosive processes acting on the block.Herein,based on a previously conducted physical experiment of erosion of a single rock block,the removal processes of two different protruding blocks are represented by a coupled computational fluid dynamics-discrete element model(CFD-DEM)approach under varied flow conditions.Additionally,the blocks could be rotated with respect to the flow direction to consider the effect of the discontinuity orientation on the block removal process.Simulation results visualize the entire block removal process.The simulations reproduce the effects of the discontinuity orientation on the critical flow velocity inducing block incipient motion and the trajectory of the block motion observed in the physical experiments.The numerical results present a similar tendency of the critical velocities at different discontinuity orientations but have slightly lower values.The trajectory of the block in the simulations fits well with the experimental measurements.The relationship between the dimensionless critical shear stress and discontinuity orientation observed from the simulations shows that the effect of block protrusion becomes more dominant on the block incipient motion with the increase of relative protrusion height.To our knowledge,this present study is the first attempt to use the coupled finite volume method(FVM)-DEM approach for modelling the interaction behavior between the block and the flowing water so that the block removal process can be reproduced and analyzed.
基金funded by the UK Engineering and Physical Sciences Research Council (EPSRC) grant No. EP/V053655/1 RAILSANDING-Modelling Particle Behaviour in the Wheel–Rail Interface the support received from AltairEngineering and Physical Sciences Research CouncilEP/V053655/1, Sadegh Nadimi
文摘To mitigate and alleviate low wheel-rail adhesion,a train-borne system is utilised to deposit sand particles into the wheel-rail interface via a jet of compressed air in a process called rail-sanding.Britain Rail Safety and Standards Board introduced guidelines on the sand particles’shape,size,and uniformity which needs to be adhered to for rail-sanding.To further inves-tigate these guidelines and help improve them,this research presents a parametric study on the particle characteristics that affect the rail-sanding process including density,size and size distribution,coefficient of uniformity,and shape,utilising a coupled computational fluid dynamics-discrete element method(CFD-DEM)model.The efficiency of rail-sanding is esti-mated for each case study and compared to the benchmark to optimise the sand characteristics for rail-sanding.It is concluded that particle size distribution(within the accepted range)has an insignificant effect on the efficiency while increasing particle size or the coefficient of uniformity decreases the efficiency.Particle shape is shown to highly affect the efficiency for flat,compact and elongated particles compared to the spherical shape.The current numerical model is capable of accurately predicting the trends in the efficiency compared to the actual values obtained from full-scale experiments.
文摘As the primary functional component of a fusion reactor,the fusion blanket pebble bed,composed of numerous particles,is crucial for tritium breeding,neutron multiplication,and radiation shielding.Particles within tritium-breeding pebble beds are subjected to prolonged neutron irradiation,high thermal loads,and strong magnetic fields in fusion environments.Such conditions render them susceptible to pulverization and fragmentation.The resulting fragments and powders migrate and are deposited into the gas channel,driven by the purge gas.The reduction in the effective flow area of the gas increases the flow resistance,resulting in tritium retention,degraded heat transfer,and other adverse effects.These conditions impair the thermodynamic properties of the pebble beds and hinder the self-maintenance of tritium.Limited information exists on powder migration and clogging mechanisms in fusion blanket pebble beds,particularly under diverse physical conditions.The aim of this study was to use a computational fluid dynamics model coupled with the discrete element method(CFD-DEM)to numerically explore powder migration and clogging in pebble beds.The model considers factors such as breeder orientation,purge velocity,powder size distribution,and friction coefficient.We propose two migration and clogging mechanisms.One involves powder with a large particle size,and the other does not.The results indicate that the powder migration velocity progresses through three stages:rapid decay,linear decay,and stability.Pebble-bed clogging manifests in two forms:extensive superficial clogging and uniform internal clogging.Two fitted curves were used to depict the migration and clogging tendencies.The powder size distribution significantly influenced the powder migration.The breeder orientation,powder size,and friction coefficient affected the distribution of the clogging powders.However,the impact of the purge velocity on powder migration and clogging in pebble beds was limited,and this effect varied significantly with different particle size ratios.Based on the analysis,a formula is proposed to characterize the behavior of the powder in the pebble beds.The results of this study can aid in analyzing and predicting powder dynamics in pebble beds.
基金This work was supported in part by the National Key R&D Program of China under Grant 2017YFB1201003.
文摘Traditional power supply method for moving electric railway vehicles is based on contact type power collection technology.This sometimes cannot meet the requirements of modern rail transportation.A new wireless power transfer(WPT)technology can offer significant benefits in modern rail transportation particularly in some stringent environments.This paper reviews the status and the development of rail transit power supply technology,and introduces a new challenging technology--inductive power transfer(IPT)technology for rail transit.Tesla established the underpinning of IPT technology and creatively and significantly demonstrated power transfer by using highly resonant tuned coils long time ago.However,only in recent years the IPT technology has been significantly improved including the transfer air-gap length,transfer efficiency,coupling factor,power transfer capability and so on.This is mainly due to innovative semiconductor switches,higher control frequency,better coil designs and high performance material,new track and vehicle construction techniques.Recent advances in IPT for rail transit and major milestones of the developments are summarized in this paper.Some important technical issues such as coupling coil structures,power supply schemes,segmentation switching techniques for long-distance power supply,and bidirectional IPT systems for braking energy feedback are discussed.
基金Supported by Scientific and Technological Research Project of The Education Department Henan Province(12B110012)
文摘In this paper we study the chaos synchronization and anti-synchronization problems between two hyper-chaotic systems with bidirectional coupling,and present synchronization and anti-synchronization methods of chaotic systems,based on timedelayed feedback.Coupling coefficients between the drive and response systems are different,which are supposed to be nonlinearly coupled.Based on the nonlinear control theory,the synchronization and anti-synchronization between two different time-delay hyper-chaotic systems are investigated.The condition of synchronization is derived according to the error dynamical systems.Numerical simulations show the effectiveness and feasibility of the proposed synchronous conditions.
文摘掘进机回转台在截割煤岩时承受偏载荷及强冲击作用,其性能影响掘进机的工作效率及安全性。为探究掘进机回转台疲劳寿命的影响因素及最佳服役参数,提出了一种基于Kriging代理模型和DEM-MFBD(discrete element model-multi flexible body dynamics,离散单元法-多柔性体动力学)双向耦合技术的回转台疲劳寿命预测方法。首先,建立了掘进机截割部与回转台的空间受力模型,明确了截割部与回转台的受力规律。然后,联合RecurDyn与EDEM软件对回转台进行双向刚柔耦合动力学仿真分析,获得了回转台在工作状态下的应力分布。最后,利用拉丁超立方抽样法选取15组掘进机服役参数作为输入,以回转台疲劳寿命为响应,建立了对应的Kriging代理模型,并利用粒子群优化算法对代理模型进行寻优,得到了回转台在最佳服役参数下的疲劳寿命。结果表明,当掘进机的截割头转速为54 r/min、回转台横摆速度为1.003 m/min、截割臂垂直摆角为7°时,回转台的疲劳寿命最长。结合DEM-MFBD双向耦合技术、Kriging代理模型与粒子群优化算法来探究掘进机的最佳服役参数,可为回转类部件的优化设计提供新思路。
