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
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
在对离心泵输送不同浓度纤维悬浮液进行外特性实验时,发现0.2%浓度纤维悬浮液对泵效率提升更具有普适性,在各个流量工况下,泵的效率均有所提升,而0.6%浓度纤维悬浮液仅在高流量工况下对泵的效率有提高的效果,对此情况从微观角度进行分析...在对离心泵输送不同浓度纤维悬浮液进行外特性实验时,发现0.2%浓度纤维悬浮液对泵效率提升更具有普适性,在各个流量工况下,泵的效率均有所提升,而0.6%浓度纤维悬浮液仅在高流量工况下对泵的效率有提高的效果,对此情况从微观角度进行分析,运用Matlab图像识别技术对CFD-DEM(computational fluid dynamics-discrete element method)耦合后的流场中的纤维粒子进行取向角度统计分析,发现纤维在流场中的分布呈现出一定的取向角度趋势,低浓度纤维悬浮液中的纤维粒子分布更加趋近于流体流动方向且更稳定,取向角度变化小且高速粒子群占比更大。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
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supported by the Fundamental Research Funds for the Central Universities(Grant No.2023YJS053)the National Natural Science Foundation of China(Grant No.52278386).
文摘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.
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).
文摘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.
文摘在对离心泵输送不同浓度纤维悬浮液进行外特性实验时,发现0.2%浓度纤维悬浮液对泵效率提升更具有普适性,在各个流量工况下,泵的效率均有所提升,而0.6%浓度纤维悬浮液仅在高流量工况下对泵的效率有提高的效果,对此情况从微观角度进行分析,运用Matlab图像识别技术对CFD-DEM(computational fluid dynamics-discrete element method)耦合后的流场中的纤维粒子进行取向角度统计分析,发现纤维在流场中的分布呈现出一定的取向角度趋势,低浓度纤维悬浮液中的纤维粒子分布更加趋近于流体流动方向且更稳定,取向角度变化小且高速粒子群占比更大。
文摘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.
文摘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。
