滑坡涌浪链生灾害的演化过程涉及滑坡体-河流之间复杂的相互作用,流固耦合方法在颗粒尺度下的应用正日益凸显。为了深入研究这一问题,研究采用颗粒尺度的CFD(Computational Fluid Dynamics)-DEM(Discrete Element Method)流固耦合方法...滑坡涌浪链生灾害的演化过程涉及滑坡体-河流之间复杂的相互作用,流固耦合方法在颗粒尺度下的应用正日益凸显。为了深入研究这一问题,研究采用颗粒尺度的CFD(Computational Fluid Dynamics)-DEM(Discrete Element Method)流固耦合方法。通过编写UDF,以改进计算流体力学软件FLUENT中离散相模型只能进行动量交换而无法考虑排水效应的缺点。这不仅改善了滑坡体与流体间的体积置换问题,而且克服了网格颗粒临界尺寸比的限制。在颗粒堆积体坍塌-涌浪试验模拟中,数值模拟计算得到的最大涌浪高度为8.67 cm,与物理试验结果较为一致,证明了改进后的CFD-DEM流固耦合模型能有效还原颗粒运动状态及涌浪的波动变化,能够满足滑坡涌浪过程模拟中滑坡体粗颗粒材料建模和高分辨率真实地形网格的需求。展开更多
砂土液化是常见的地震灾害,目前应用于研究砂土液化动力特性的室内试验以及模型试验还不能全面反映土体液化全过程。计算流体动力学(computational fluid dynamics,CFD)与离散元法(discrete element method,DEM)耦合模拟方法能够准确地...砂土液化是常见的地震灾害,目前应用于研究砂土液化动力特性的室内试验以及模型试验还不能全面反映土体液化全过程。计算流体动力学(computational fluid dynamics,CFD)与离散元法(discrete element method,DEM)耦合模拟方法能够准确地模拟各类水土耦合问题。通过二次开发的CFD-DEM流固耦合模块实现离散元软件PFC3D与计算流体力学软件OpenFOAM之间的力学信息交互,利用颗粒水下自由沉降验证该方法的可行性。利用PFC3D软件模拟室内循环三轴试验标定出具有真实饱和砂土动力特性的数值砂样。根据已有的参数信息以及耦合模拟方法建立了饱和砂土的场地液化模型。模拟结果表明,离散元法能够复现室内砂土液化试验,标定参数可应用于场地液化模拟;单颗粒沉降速度与理论解一致验证了CFD-DEM耦合方法的准确性;峰值加速度0.25g下不同深度处土体均会发生液化,液化时超孔压比无法达到1,超孔压累计值由浅层往深层递增;液化后土体强度自下而上逐渐恢复,再固结的场地土体结构呈现均匀化发展趋势。展开更多
为研究混凝土运输车搅拌筒内的混凝土与骨料颗粒的真实运动情况,采用CFD-DEM耦合的方法,考虑混凝土的非牛顿流体特性及骨料颗粒间的相互作用,对混凝土进料、搅拌、出料过程的混凝土及颗粒运动规律进行数值模拟。通过将出料时间和出料速...为研究混凝土运输车搅拌筒内的混凝土与骨料颗粒的真实运动情况,采用CFD-DEM耦合的方法,考虑混凝土的非牛顿流体特性及骨料颗粒间的相互作用,对混凝土进料、搅拌、出料过程的混凝土及颗粒运动规律进行数值模拟。通过将出料时间和出料速率数值仿真结果与实验对比,验证了CFD-DEM耦合方法的可行性。将计算流体动力学(Computational Fluid Dynamics,CFD)和离散元(Discrete Element Method,DEM)仿真结果导入ABAQUS中对叶片结构强度进行了分析,结果表明:叶片所受应力远小于材料的许用应力,最大节点位移满足刚度设计要求。最后对叶片的磨损情况进行了分析。展开更多
The rapid discharge of cuttings from the air cushion chamber is crucial for the construction safety and excavation efficiency of the slurry shield.Previous studies have mainly focused on the transport characteristics ...The rapid discharge of cuttings from the air cushion chamber is crucial for the construction safety and excavation efficiency of the slurry shield.Previous studies have mainly focused on the transport characteristics of cuttings in the slurry discharge pipe,while the complete process of cuttings entering the slurry discharge pipe from the air cushion chamber until they are discharged was often overlooked.Based on the CFD-DEM coupling method and combined with actual engineering,this paper established a numerical model that can more completely reflect the cuttings discharge process during slurry shield tunneling,and the effects of the slurry velocity at slurry gate and scouring pipes,inclination angle of slurry discharge pipe,cuttings diameter and shape coefficient were investigated by analyzing the variation in the mass flow rate,mass of discharged cuttings,and discharged ratio.The results revealed that increasing the slurry velocity can promote the discharge of cuttings.To keep the discharged rate at a high level,it is recommended that the slurry velocity at the slurry gate should be greater than 0.15 m/s.Reducing the inclination angle of the discharge pipe is conducive to the rapid discharge of cuttings.Cuttings with large diameter or small shape coefficient are more prone to accumulate in the air cushion chamber and cause clogging risk.The research results not only help to improve engineers'understanding of cuttings discharge in slurry shield,but also provide practical guidance for formulating relevant construction measures.展开更多
我国西南山区极易发生滑坡、泥石流等地质灾害,从而导致大量泥沙进入河道,河床发生冲淤变形,使原有的水沙运动状态发生改变。通过计算流体力学（Computational Fluid Dynamics,CFD）与离散元（Discrete Element Method,DEM）耦合的方法...我国西南山区极易发生滑坡、泥石流等地质灾害,从而导致大量泥沙进入河道,河床发生冲淤变形,使原有的水沙运动状态发生改变。通过计算流体力学（Computational Fluid Dynamics,CFD）与离散元（Discrete Element Method,DEM）耦合的方法对水沙变化条件下典型山区河道内的三维水沙运动及河床冲淤变形过程进行了数值模拟,并将三维数值模拟结果与实验结果进行了比对。计算结果表明：上游强输沙水流进入变比降河道后,河道内会发生溯源淤积,且流量越小、加沙强度越大,泥沙溯源淤积发展的速度越快;淤积锋面到达处的水位会迅速升高,随着淤积前锋的继续发展,该位置处的水位会趋于稳定;泥沙大量淤积后,会导致河床比降减小,洪水水位增加,严重威胁河道防洪安全。展开更多
A large amount of loose debris materials were deposited on the slope of mountainous areas after the 2008 Ms 8.0 Wenchuan earthquake. During and after the earthquake, these loose debris deposits collapsed and slide int...A large amount of loose debris materials were deposited on the slope of mountainous areas after the 2008 Ms 8.0 Wenchuan earthquake. During and after the earthquake, these loose debris deposits collapsed and slide into valleys or rivers, changing river sediment supply condition and channel morphology. To investigate the mechanisms of granular flow and deposition, the dynamics of slope failure and sediment transportation in typical mountainous rivers of different intersection angles were analyzed with a coupling model of Computational Fluid Dynamics and Discrete Element Method(CFD-DEM). The numerical results show that the change of intersection angle between the granular flow flume and the river channel can affect the deposit geometry and the fluid flow field significantly. As the intersection angle increases, the granular velocity perpendicular to the river channel increases, while the granular velocity parallel to the river channel decreases gradually. Compared to the test of dry granular flow, the CFD-DEM coupling tests show much higher granular velocity and larger volume of sediments entrained in the river. Due to the river flow, particles located at the edge of the deposition will move downstream gradually and the main section of sediments deposition moves from the center to the edge of the river channel. As a result, sediment supply in the downstream river will distribute unevenly. Under the erosion of fluid flow, the proportion of fine particles increases, while the proportion of coarse particles decreases gradually in the sediment deposition. The build-up of accumulated sediment mass will cause a significant increase in water level in the river channel, thus creating serious flooding hazard in mountainous rivers.展开更多
本文采用CFD-DEM耦合法(Computational Fluid Dynamics and Discrete Element Method)对三维移动床中多粒径高炉渣颗粒的余热回收过程进行了数值模拟与分析。研究了三种不同粒径分布系统:均一粒径系统,二元混合粒径系统和正态分布粒径...本文采用CFD-DEM耦合法(Computational Fluid Dynamics and Discrete Element Method)对三维移动床中多粒径高炉渣颗粒的余热回收过程进行了数值模拟与分析。研究了三种不同粒径分布系统:均一粒径系统,二元混合粒径系统和正态分布粒径系统的气-固换热特性。通过应用程序编程接口Api控制高炉渣颗粒的质量流率,使得移动床内颗粒流动达到动态平衡。进一步分析了颗粒相和流体相的温度场、对流和辐射换热率、颗粒和气体的出口温度以及移动床的余热回收率,获得了不同粒径分布颗粒系统的气固换热规律。研究发现:在相同工况下,二元混合粒径系统的颗粒出口温度最低,气体出口温度最高,换热效果最好,余热回收率相较于其余两种粒径系统也最高。展开更多
We investigate the effect of particle shape on the transportation mechanism in well-drilling using a three-dimensional model that couples computational fluid dynamics （CFD） with the discrete element method （DEM）. ...We investigate the effect of particle shape on the transportation mechanism in well-drilling using a three-dimensional model that couples computational fluid dynamics （CFD） with the discrete element method （DEM）. This numerical method allows us to incorporate the fluid-particle interactions （drag force, contact force, Saffman lift force, Magnus lift force, buoyancy force） using momentum exchange and the non-Newtonian behavior of the fluid. The interactions of particle-particle, particle-wall, and particle-drill pipe are taken into account with the Hertz-Mindlin model. We compare the transport of spheres with non-spherical particles （non-smooth sphere, disc, and cubic） constructed via the multi- sphere method for a range of fluid inlet velocities and drill pipe inclination angles. The simulations are carried out for laboratory-scale drilling configurations. Our results demonstrate good agreement with published experimental data. We evaluate the fluid-particle flow patterns, the particle velocities, and the particle concentration profiles. The results reveal that particle sphericity plays a major role in the fluid-solid interaction. The traditional assumption of an ideal spherical particle may cause inaccurate results.展开更多
文摘砂土液化是常见的地震灾害,目前应用于研究砂土液化动力特性的室内试验以及模型试验还不能全面反映土体液化全过程。计算流体动力学(computational fluid dynamics,CFD)与离散元法(discrete element method,DEM)耦合模拟方法能够准确地模拟各类水土耦合问题。通过二次开发的CFD-DEM流固耦合模块实现离散元软件PFC3D与计算流体力学软件OpenFOAM之间的力学信息交互,利用颗粒水下自由沉降验证该方法的可行性。利用PFC3D软件模拟室内循环三轴试验标定出具有真实饱和砂土动力特性的数值砂样。根据已有的参数信息以及耦合模拟方法建立了饱和砂土的场地液化模型。模拟结果表明,离散元法能够复现室内砂土液化试验,标定参数可应用于场地液化模拟;单颗粒沉降速度与理论解一致验证了CFD-DEM耦合方法的准确性;峰值加速度0.25g下不同深度处土体均会发生液化,液化时超孔压比无法达到1,超孔压累计值由浅层往深层递增;液化后土体强度自下而上逐渐恢复,再固结的场地土体结构呈现均匀化发展趋势。
文摘为研究混凝土运输车搅拌筒内的混凝土与骨料颗粒的真实运动情况,采用CFD-DEM耦合的方法,考虑混凝土的非牛顿流体特性及骨料颗粒间的相互作用,对混凝土进料、搅拌、出料过程的混凝土及颗粒运动规律进行数值模拟。通过将出料时间和出料速率数值仿真结果与实验对比,验证了CFD-DEM耦合方法的可行性。将计算流体动力学(Computational Fluid Dynamics,CFD)和离散元(Discrete Element Method,DEM)仿真结果导入ABAQUS中对叶片结构强度进行了分析,结果表明:叶片所受应力远小于材料的许用应力,最大节点位移满足刚度设计要求。最后对叶片的磨损情况进行了分析。
基金support from the National Natural Science Foundation of China(grant number 52278403)the Natural Science Foundation of Shandong Province(grant number ZR2021ME135).
文摘The rapid discharge of cuttings from the air cushion chamber is crucial for the construction safety and excavation efficiency of the slurry shield.Previous studies have mainly focused on the transport characteristics of cuttings in the slurry discharge pipe,while the complete process of cuttings entering the slurry discharge pipe from the air cushion chamber until they are discharged was often overlooked.Based on the CFD-DEM coupling method and combined with actual engineering,this paper established a numerical model that can more completely reflect the cuttings discharge process during slurry shield tunneling,and the effects of the slurry velocity at slurry gate and scouring pipes,inclination angle of slurry discharge pipe,cuttings diameter and shape coefficient were investigated by analyzing the variation in the mass flow rate,mass of discharged cuttings,and discharged ratio.The results revealed that increasing the slurry velocity can promote the discharge of cuttings.To keep the discharged rate at a high level,it is recommended that the slurry velocity at the slurry gate should be greater than 0.15 m/s.Reducing the inclination angle of the discharge pipe is conducive to the rapid discharge of cuttings.Cuttings with large diameter or small shape coefficient are more prone to accumulate in the air cushion chamber and cause clogging risk.The research results not only help to improve engineers'understanding of cuttings discharge in slurry shield,but also provide practical guidance for formulating relevant construction measures.
文摘我国西南山区极易发生滑坡、泥石流等地质灾害,从而导致大量泥沙进入河道,河床发生冲淤变形,使原有的水沙运动状态发生改变。通过计算流体力学（Computational Fluid Dynamics,CFD）与离散元（Discrete Element Method,DEM）耦合的方法对水沙变化条件下典型山区河道内的三维水沙运动及河床冲淤变形过程进行了数值模拟,并将三维数值模拟结果与实验结果进行了比对。计算结果表明：上游强输沙水流进入变比降河道后,河道内会发生溯源淤积,且流量越小、加沙强度越大,泥沙溯源淤积发展的速度越快;淤积锋面到达处的水位会迅速升高,随着淤积前锋的继续发展,该位置处的水位会趋于稳定;泥沙大量淤积后,会导致河床比降减小,洪水水位增加,严重威胁河道防洪安全。
基金supported by the National Natural Science Foundation of China (51579163 and 51639007)the National Key R&D Program of China (2017YFC1502504 and 2016YFC0402304)
文摘A large amount of loose debris materials were deposited on the slope of mountainous areas after the 2008 Ms 8.0 Wenchuan earthquake. During and after the earthquake, these loose debris deposits collapsed and slide into valleys or rivers, changing river sediment supply condition and channel morphology. To investigate the mechanisms of granular flow and deposition, the dynamics of slope failure and sediment transportation in typical mountainous rivers of different intersection angles were analyzed with a coupling model of Computational Fluid Dynamics and Discrete Element Method(CFD-DEM). The numerical results show that the change of intersection angle between the granular flow flume and the river channel can affect the deposit geometry and the fluid flow field significantly. As the intersection angle increases, the granular velocity perpendicular to the river channel increases, while the granular velocity parallel to the river channel decreases gradually. Compared to the test of dry granular flow, the CFD-DEM coupling tests show much higher granular velocity and larger volume of sediments entrained in the river. Due to the river flow, particles located at the edge of the deposition will move downstream gradually and the main section of sediments deposition moves from the center to the edge of the river channel. As a result, sediment supply in the downstream river will distribute unevenly. Under the erosion of fluid flow, the proportion of fine particles increases, while the proportion of coarse particles decreases gradually in the sediment deposition. The build-up of accumulated sediment mass will cause a significant increase in water level in the river channel, thus creating serious flooding hazard in mountainous rivers.
文摘本文采用CFD-DEM耦合法(Computational Fluid Dynamics and Discrete Element Method)对三维移动床中多粒径高炉渣颗粒的余热回收过程进行了数值模拟与分析。研究了三种不同粒径分布系统:均一粒径系统,二元混合粒径系统和正态分布粒径系统的气-固换热特性。通过应用程序编程接口Api控制高炉渣颗粒的质量流率,使得移动床内颗粒流动达到动态平衡。进一步分析了颗粒相和流体相的温度场、对流和辐射换热率、颗粒和气体的出口温度以及移动床的余热回收率,获得了不同粒径分布颗粒系统的气固换热规律。研究发现:在相同工况下,二元混合粒径系统的颗粒出口温度最低,气体出口温度最高,换热效果最好,余热回收率相较于其余两种粒径系统也最高。
文摘We investigate the effect of particle shape on the transportation mechanism in well-drilling using a three-dimensional model that couples computational fluid dynamics （CFD） with the discrete element method （DEM）. This numerical method allows us to incorporate the fluid-particle interactions （drag force, contact force, Saffman lift force, Magnus lift force, buoyancy force） using momentum exchange and the non-Newtonian behavior of the fluid. The interactions of particle-particle, particle-wall, and particle-drill pipe are taken into account with the Hertz-Mindlin model. We compare the transport of spheres with non-spherical particles （non-smooth sphere, disc, and cubic） constructed via the multi- sphere method for a range of fluid inlet velocities and drill pipe inclination angles. The simulations are carried out for laboratory-scale drilling configurations. Our results demonstrate good agreement with published experimental data. We evaluate the fluid-particle flow patterns, the particle velocities, and the particle concentration profiles. The results reveal that particle sphericity plays a major role in the fluid-solid interaction. The traditional assumption of an ideal spherical particle may cause inaccurate results.
