Tidal waves,intermittent rainfall,and fluctuations in water levels,which create cyclic hydraulic gradients,can exacerbate the migration of fine particles within soils and lead to deterioration in stability.However,mac...Tidal waves,intermittent rainfall,and fluctuations in water levels,which create cyclic hydraulic gradients,can exacerbate the migration of fine particles within soils and lead to deterioration in stability.However,macroscale experimental methods struggle to capture the microscopic deformations that occur during seepage-induced erosion.Therefore,this study,which is based on the coupled computational fluid dynamics–discrete element method(CFD–DEM)coupling method,investigates the contact mechanical mechanisms that induce macroscopic deformation under cyclic hydraulic gradients by considering the effects of different amplitudes and frequencies.The results show that the erosion mass of fine particles increases in a stepwise manner,with a multipeak variation in the erosion rate,and both the erosion amount and intensity are greater under constant gradient conditions.Fine particles erode primarily near the contact surface and,after migration,accumulate mainly in the coarse particle layers close to the contact surface.Increasing the amplitude and frequency of the cyclic hydraulic gradient leads to more fine particle blockages within the coarse particle layer.The cyclic hydraulic gradient causes the contact force chain network to repeatedly break and reorganize,reducing the shear strengths of the soil and resulting in more pronounced anisotropy in the contact force distribution.展开更多
To fundamentally alleviate the excavation chamber clogging during slurry tunnel boring machine(TBM)advancing in hard rock,large-diameter short screw conveyor was adopted to slurry TBM of Qingdao Jiaozhou Bay Second Un...To fundamentally alleviate the excavation chamber clogging during slurry tunnel boring machine(TBM)advancing in hard rock,large-diameter short screw conveyor was adopted to slurry TBM of Qingdao Jiaozhou Bay Second Undersea Tunnel.To evaluate the discharging performance of short screw conveyor in different cases,the full-scale transient slurry-rock two-phase model for a short screw conveyor actively discharging rocks was established using computational fluid dynamics-discrete element method(CFD-DEM)coupling approach.In the fluid domain of coupling model,the sliding mesh technology was utilized to describe the rotations of the atmospheric composite cutterhead and the short screw conveyor.In the particle domain of coupling model,the dynamic particle factories were established to produce rock particles with the rotation of the cutterhead.And the accuracy and reliability of the CFD-DEM simulation results were validated via the field test and model test.Furthermore,a comprehensive parameter analysis was conducted to examine the effects of TBM operating parameters,the geometric design of screw conveyor and the size of rocks on the discharging performance of short screw conveyor.Accordingly,a reasonable rotational speed of screw conveyor was suggested and applied to Jiaozhou Bay Second Undersea Tunnel project.The findings in this paper could provide valuable references for addressing the excavation chamber clogging during ultra-large-diameter slurry TBM tunneling in hard rock for similar future.展开更多
基于计算流体力学-离散元耦合方法(computational fluid dynamics-discrete element method,CFD-DEM),运用STAR-CCM+软件,对船舶在浮冰区航行过程中的冰阻力特性与破冰机理开展了系统的数值模拟分析。为保证模拟结果的数值可靠性,首先...基于计算流体力学-离散元耦合方法(computational fluid dynamics-discrete element method,CFD-DEM),运用STAR-CCM+软件,对船舶在浮冰区航行过程中的冰阻力特性与破冰机理开展了系统的数值模拟分析。为保证模拟结果的数值可靠性,首先完成了网格收敛性验证,并通过多尺度网格加密及敏感性分析,确定了兼顾计算效率与模拟精度的最优数值模型。研究重点考察了船舶航速与浮冰厚度两个关键参数对冰阻力的非线性影响规律,揭示了船-冰相互作用中冰阻力变化与破碎能量耗散的内在机制。进一步从应力波传播、断裂模式、动能转化等角度,对不同工况下浮冰的破碎程度、裂纹扩展路径及碎冰堆积形态进行了定量评估与定性分析。该研究深化了对船-冰-水多相耦合动力学行为的理解,并为极地船舶冰区航行性能优化与抗冰结构设计提供了可靠的数值分析方法与工程参考。展开更多
The extended discrete element method (XDEM) multi-physics and multi-scale simulation platform is being developed at the Institute of Computational Engineering, the University of Luxembourg. The platform is an advanced...The extended discrete element method (XDEM) multi-physics and multi-scale simulation platform is being developed at the Institute of Computational Engineering, the University of Luxembourg. The platform is an advanced multi-physics simulation technology that combines flexibility and versatility to establish the next generation of multi-physics and multi-scale simulation tools. For this purpose, the simulation framework relies on coupling various predictive tools based on an Eulerian and Lagrangian approach. The Euleria n approach represents the wide field of con tinuum models;the Lagra ngian approach is perfect for characterising discrete phases. Continuum models thus include classical simulation tools, such as computational fluid dynamics simulation and finite element analysis, while an extended configuration of the classical discrete element method addresses the discrete (e.g., particulate) phase. Apart from predicting the trajectories of in dividual particles, XDEM-suite extends the application of the XDEM to estimating the thermodynamic state of each particle using advanced and optimised algorithms. The thermodynamic state may include temperature and species distributions due to chemical reaction and external heat sources. Hence, coupling these extended features with either computational fluid dynamics simulation or finite element analysis opens a wide range of applications as diverse as pharmaceuticals, agriculture, food processing, mining, construction and agricultural machinery, metals manufacturing, energy production and systems biology.展开更多
Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards.Previous studies of it have mainly focused on suffusion in homogeneous soil specimens.In this study,the coupled ...Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards.Previous studies of it have mainly focused on suffusion in homogeneous soil specimens.In this study,the coupled discrete element method(DEM)and computational fluid dynamics(CFD)approach is adopted to model suffusion in multi-layered soils with different fines contents,and soils with one or more impermeable zones.The parameters of the CFD-DEM model are first calibrated with the classic Ergun test and a good match with experiment is obtained.Then suffusion in multi-layered soils with different fines contents and impermeable zones is simulated and discussed.The simulation results show that,for soils with multiple layers,the cumulative eroded mass is mainly determined by the fines content of the bottom layer.In general,the higher the fines content of the bottom soil layer,the higher the cumulative eroded mass.In addition,suffusion is more severe if the fines content of the layer above is decreased.Impermeable zones inside soil specimens can increase the flow velocity around those zones,facilitating the migration of fine particles and intensifying suffusion.展开更多
【目的】棒销式砂磨机的工作过程存在复杂的气体、液体和固体的三相耦合现象,为了使仿真工况更接近实际工况,构建气-液-固三相耦合仿真模型,提高棒销式砂磨机仿真设计的准确性。【方法】采用离散单元法(discrete element method,DEM)和...【目的】棒销式砂磨机的工作过程存在复杂的气体、液体和固体的三相耦合现象,为了使仿真工况更接近实际工况,构建气-液-固三相耦合仿真模型,提高棒销式砂磨机仿真设计的准确性。【方法】采用离散单元法(discrete element method,DEM)和计算流体动力学(computational fluid dynamics,CFD)分别研究固体相和流体相,并引入流体体积模型(volume of fluid model,VOF)区分流体相所包含的液体相和气体相,分析固体相运动方程、流体相控制方程,确定气-液界面的识别方法和耦合计算方法,制定仿真流程;通过单球落水仿真、颗粒群落水仿真试验分析CFD-DEM-VOF三相耦合模型仿真计算的精度,并进行准确性验证;在设置仿真参数、进行网格划分及其无关性分析基础上,针对棒销式砂磨机的CFD-DEM-VOF三相耦合模型进行仿真试验;对流体速度、颗粒总能量和颗粒的速度的仿真结果进行分析,并通过实验验证仿真结果。【结果】在单球落水仿真试验中,根据CFD-DEM-VOF三相耦合模型的仿真结果与根据Stokes定律的理论计算结果基本吻合;在颗粒群落水仿真过程中,液面上升高度的仿真值与理论值之间的相对误差为1.37%,VOF模型的体积守恒性较好;棒销四面体网格边长小于2 mm、研磨桶四面体网格边长小于2.5 mm时,满足网格独立性的精度要求,同时计算量也较少;随着棒销转速的增大,流体速度、颗粒总能量、颗粒平均速度也逐渐增大;当棒销转速为1400~2000 r/min时,CFD-DEM-VOF三相耦合模型流体速度的仿真与实验结果最为接近;当棒销转速为1400~2200 r/min时,CFD-DEM-VOF三相耦合模型的颗粒总能量仿真值与实验值的最大相对误差为1%。【结论】与仅仅采用流体相、固体相单相模型或固-液两相模型相比,采用CFD-DEM-VOF三相耦合模型设计棒销式砂磨机的计算精度和准确性较高,仿真性能好。展开更多
Surface modification for micro-nanoparticles at the atomic and close-to-atomic scales is of great importance to enhance their performance in various applications,including high-volume battery,persistent luminescence,e...Surface modification for micro-nanoparticles at the atomic and close-to-atomic scales is of great importance to enhance their performance in various applications,including high-volume battery,persistent luminescence,etc.Fluidized bed atomic layer deposition(FB-ALD)is a promising atomic-scale manufacturing technology that offers ultrathin films on large amounts of particulate materials.Nevertheless,nanoparticles tend to agglomerate due to the strong cohesive forces,which is much unfavorable to the film conformality and also hinders their real applications.In this paper,the particle fluidization process in an ultrasonic vibration-assisted FB-ALD reactor is numerically investigated from micro-scale to macro-scale through the multiscale computational fluid dynamics and discrete element method(CFD-DEM)modeling with experimental verification.Various vibration amplitudes and frequencies are investigated in terms of their effects on the fluid dynamics,distribution of particle velocity and solid volume fraction,as well as the size of agglomerates.Results show that the fluid turbulent kinetic energy,which is the key power source for the particles to obtain the kinetic energy for overcoming the interparticle agglomeration forces,can be strengthened obviously by the ultrasonic vibration.Besides,the application of ultrasonic vibration is found to reduce the mean agglomerate size in the FB.This is bound to facilitate the heat transfer and precursor diffusion in the entire FB-ALD reactor and the agglomerates,which can largely shorten the coating time and improve the film conformality as well as precursor utilization.The simulation results also agree well with our battery experimental results,verifying the validity of the multiscale CFD-DEM model.This work has provided momentous guidance to the mass manufacturing of atomic-scale particle coating from lab-scale to industrial applications.展开更多
针对深水网箱自动投饵系统颗粒饲料气力输送时易阻塞与破损的问题,为揭示自动投饵系统中颗粒饲料的气力输送运动特性,开展了管道颗粒饲料气固两相流的数值模拟研究。基于气固两相流理论,分别建立了计算流体模型与离散元模型,通过计算流...针对深水网箱自动投饵系统颗粒饲料气力输送时易阻塞与破损的问题,为揭示自动投饵系统中颗粒饲料的气力输送运动特性,开展了管道颗粒饲料气固两相流的数值模拟研究。基于气固两相流理论,分别建立了计算流体模型与离散元模型,通过计算流体力学与离散单元法(computational fluid dynamics-discrete element method,CFD-EDM)耦合求解,对饲料颗粒从气力输送管道初始阶段到稳定阶段的运动过程进行了分析,得到颗粒从初始状态到运动稳定阶段的颗粒位置分布情况。对不同位置管道内压力进行了分析对比,得到从管道入口到颗粒运动稳定状态时刻的压降。模拟仿真结果为自动投饵装备的模拟仿真与优化设计提供了参考,使其可以对饲料颗粒运动有更好的导向性,更好地降低弯管处颗粒碰撞的能量损失。展开更多
基金financially supported by the Natural Science Foundation of China(Grant Nos.52425805 and U2569208)Development Fund of Tunnel and Underground Engineering Research Center of Jiangsu Province(Grant No.2021-SDJJ-04).
摘要Tidal waves,intermittent rainfall,and fluctuations in water levels,which create cyclic hydraulic gradients,can exacerbate the migration of fine particles within soils and lead to deterioration in stability.However,macroscale experimental methods struggle to capture the microscopic deformations that occur during seepage-induced erosion.Therefore,this study,which is based on the coupled computational fluid dynamics–discrete element method(CFD–DEM)coupling method,investigates the contact mechanical mechanisms that induce macroscopic deformation under cyclic hydraulic gradients by considering the effects of different amplitudes and frequencies.The results show that the erosion mass of fine particles increases in a stepwise manner,with a multipeak variation in the erosion rate,and both the erosion amount and intensity are greater under constant gradient conditions.Fine particles erode primarily near the contact surface and,after migration,accumulate mainly in the coarse particle layers close to the contact surface.Increasing the amplitude and frequency of the cyclic hydraulic gradient leads to more fine particle blockages within the coarse particle layer.The cyclic hydraulic gradient causes the contact force chain network to repeatedly break and reorganize,reducing the shear strengths of the soil and resulting in more pronounced anisotropy in the contact force distribution.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.2023YJS053)the National Natural Science Foundation of China(Grant No.52278386).
摘要To fundamentally alleviate the excavation chamber clogging during slurry tunnel boring machine(TBM)advancing in hard rock,large-diameter short screw conveyor was adopted to slurry TBM of Qingdao Jiaozhou Bay Second Undersea Tunnel.To evaluate the discharging performance of short screw conveyor in different cases,the full-scale transient slurry-rock two-phase model for a short screw conveyor actively discharging rocks was established using computational fluid dynamics-discrete element method(CFD-DEM)coupling approach.In the fluid domain of coupling model,the sliding mesh technology was utilized to describe the rotations of the atmospheric composite cutterhead and the short screw conveyor.In the particle domain of coupling model,the dynamic particle factories were established to produce rock particles with the rotation of the cutterhead.And the accuracy and reliability of the CFD-DEM simulation results were validated via the field test and model test.Furthermore,a comprehensive parameter analysis was conducted to examine the effects of TBM operating parameters,the geometric design of screw conveyor and the size of rocks on the discharging performance of short screw conveyor.Accordingly,a reasonable rotational speed of screw conveyor was suggested and applied to Jiaozhou Bay Second Undersea Tunnel project.The findings in this paper could provide valuable references for addressing the excavation chamber clogging during ultra-large-diameter slurry TBM tunneling in hard rock for similar future.
摘要基于计算流体力学-离散元耦合方法(computational fluid dynamics-discrete element method,CFD-DEM),运用STAR-CCM+软件,对船舶在浮冰区航行过程中的冰阻力特性与破冰机理开展了系统的数值模拟分析。为保证模拟结果的数值可靠性,首先完成了网格收敛性验证,并通过多尺度网格加密及敏感性分析,确定了兼顾计算效率与模拟精度的最优数值模型。研究重点考察了船舶航速与浮冰厚度两个关键参数对冰阻力的非线性影响规律,揭示了船-冰相互作用中冰阻力变化与破碎能量耗散的内在机制。进一步从应力波传播、断裂模式、动能转化等角度,对不同工况下浮冰的破碎程度、裂纹扩展路径及碎冰堆积形态进行了定量评估与定性分析。该研究深化了对船-冰-水多相耦合动力学行为的理解,并为极地船舶冰区航行性能优化与抗冰结构设计提供了可靠的数值分析方法与工程参考。
摘要The extended discrete element method (XDEM) multi-physics and multi-scale simulation platform is being developed at the Institute of Computational Engineering, the University of Luxembourg. The platform is an advanced multi-physics simulation technology that combines flexibility and versatility to establish the next generation of multi-physics and multi-scale simulation tools. For this purpose, the simulation framework relies on coupling various predictive tools based on an Eulerian and Lagrangian approach. The Euleria n approach represents the wide field of con tinuum models;the Lagra ngian approach is perfect for characterising discrete phases. Continuum models thus include classical simulation tools, such as computational fluid dynamics simulation and finite element analysis, while an extended configuration of the classical discrete element method addresses the discrete (e.g., particulate) phase. Apart from predicting the trajectories of in dividual particles, XDEM-suite extends the application of the XDEM to estimating the thermodynamic state of each particle using advanced and optimised algorithms. The thermodynamic state may include temperature and species distributions due to chemical reaction and external heat sources. Hence, coupling these extended features with either computational fluid dynamics simulation or finite element analysis opens a wide range of applications as diverse as pharmaceuticals, agriculture, food processing, mining, construction and agricultural machinery, metals manufacturing, energy production and systems biology.
基金This work is supported by the Research Grants Council(RGC)of Hong Kong(No.15226322)the National Natu‐ral Science Foundation of China(No.42207210).
摘要Suffusion in broadly graded granular soils is caused by fluid flow and is a typical cause of geo-hazards.Previous studies of it have mainly focused on suffusion in homogeneous soil specimens.In this study,the coupled discrete element method(DEM)and computational fluid dynamics(CFD)approach is adopted to model suffusion in multi-layered soils with different fines contents,and soils with one or more impermeable zones.The parameters of the CFD-DEM model are first calibrated with the classic Ergun test and a good match with experiment is obtained.Then suffusion in multi-layered soils with different fines contents and impermeable zones is simulated and discussed.The simulation results show that,for soils with multiple layers,the cumulative eroded mass is mainly determined by the fines content of the bottom layer.In general,the higher the fines content of the bottom soil layer,the higher the cumulative eroded mass.In addition,suffusion is more severe if the fines content of the layer above is decreased.Impermeable zones inside soil specimens can increase the flow velocity around those zones,facilitating the migration of fine particles and intensifying suffusion.
基金supported by the National Natural Science Foundation of China(51835005 and 51911540476)National Key Research and Development Program of China(2020YFB2010401)+3 种基金Hubei Province Natural Science Foundation for innovative research groups(2020CFA030)Independent Innovation Research Fund of HUST(2019kfyXMBZ025)Tencent Foundationthe Engineering and Physical Sciences Research Council project(EP/T019085/1).
摘要Surface modification for micro-nanoparticles at the atomic and close-to-atomic scales is of great importance to enhance their performance in various applications,including high-volume battery,persistent luminescence,etc.Fluidized bed atomic layer deposition(FB-ALD)is a promising atomic-scale manufacturing technology that offers ultrathin films on large amounts of particulate materials.Nevertheless,nanoparticles tend to agglomerate due to the strong cohesive forces,which is much unfavorable to the film conformality and also hinders their real applications.In this paper,the particle fluidization process in an ultrasonic vibration-assisted FB-ALD reactor is numerically investigated from micro-scale to macro-scale through the multiscale computational fluid dynamics and discrete element method(CFD-DEM)modeling with experimental verification.Various vibration amplitudes and frequencies are investigated in terms of their effects on the fluid dynamics,distribution of particle velocity and solid volume fraction,as well as the size of agglomerates.Results show that the fluid turbulent kinetic energy,which is the key power source for the particles to obtain the kinetic energy for overcoming the interparticle agglomeration forces,can be strengthened obviously by the ultrasonic vibration.Besides,the application of ultrasonic vibration is found to reduce the mean agglomerate size in the FB.This is bound to facilitate the heat transfer and precursor diffusion in the entire FB-ALD reactor and the agglomerates,which can largely shorten the coating time and improve the film conformality as well as precursor utilization.The simulation results also agree well with our battery experimental results,verifying the validity of the multiscale CFD-DEM model.This work has provided momentous guidance to the mass manufacturing of atomic-scale particle coating from lab-scale to industrial applications.
摘要针对深水网箱自动投饵系统颗粒饲料气力输送时易阻塞与破损的问题,为揭示自动投饵系统中颗粒饲料的气力输送运动特性,开展了管道颗粒饲料气固两相流的数值模拟研究。基于气固两相流理论,分别建立了计算流体模型与离散元模型,通过计算流体力学与离散单元法(computational fluid dynamics-discrete element method,CFD-EDM)耦合求解,对饲料颗粒从气力输送管道初始阶段到稳定阶段的运动过程进行了分析,得到颗粒从初始状态到运动稳定阶段的颗粒位置分布情况。对不同位置管道内压力进行了分析对比,得到从管道入口到颗粒运动稳定状态时刻的压降。模拟仿真结果为自动投饵装备的模拟仿真与优化设计提供了参考,使其可以对饲料颗粒运动有更好的导向性,更好地降低弯管处颗粒碰撞的能量损失。