辣椒籽的物性参数是离散元仿真中重要的输入,为提高其数值模拟的可靠性与准确度,对辣椒籽的物性参数进行试验测量,主要包括三轴尺寸、密度、泊松比、摩擦系数、恢复系数等。结合EDEM中“Hertz-Mindlin with JKR”粘力模型,引入表面能参...辣椒籽的物性参数是离散元仿真中重要的输入,为提高其数值模拟的可靠性与准确度,对辣椒籽的物性参数进行试验测量,主要包括三轴尺寸、密度、泊松比、摩擦系数、恢复系数等。结合EDEM中“Hertz-Mindlin with JKR”粘力模型,引入表面能参数,进行休止角试验。通过Plackett-Burman试验在各影响因子中筛选出最具显著性的3个影响参数(辣椒籽—籽滚动摩擦系数、辣椒籽表面能、辣椒籽—钢板滚动摩擦系数),建立3个显著影响参数与休止角的回归模型,研究显著因子在交互作用下对休止角的影响。将显著参数的区间按梯度平均分为5个水平进行爬坡试验得到最佳取值范围,运用响应面法(Box-Behnken)分析回归模型的二次多项式在休止角、相对误差和三个重要参数之间的方差,以相对误差最小值对模型进行优化,得到最优组合:辣椒籽间的滚动摩擦系数为0.75、JKR表面能为0.31 J/m^(2)、辣椒籽与钢板间滚动摩擦系数为0.60。用通过标定试验得到的最优参数组合进行模拟堆积试验,平均休止角为26.71°,相对误差为4.61%。展开更多
目的确定湿式滚抛磨块在接触过程中各相关物理性能参数的取值。方法基于EDEM离散元仿真模拟,选取系统中"Hertz-Mindlin with JKR"接触模型,以休止角为评价指标,对湿式滚抛磨块离散元模拟的最优参数组合进行标定。首先运用Plac...目的确定湿式滚抛磨块在接触过程中各相关物理性能参数的取值。方法基于EDEM离散元仿真模拟,选取系统中"Hertz-Mindlin with JKR"接触模型,以休止角为评价指标,对湿式滚抛磨块离散元模拟的最优参数组合进行标定。首先运用Plackett-Burman试验选取对湿式滚抛磨块有显著影响的3个参数项(湿式滚抛磨块间的滚动摩擦系数、碰撞恢复系数和JKR表面能),然后用最陡爬坡试验确定出显著性参数的最优区间,最后通过响应曲面法(Box-Behnken)分别对休止角和相对误差与3个显著性参数的回归模型二次多项式进行方差分析,并寻找最优参数组合。结果得到了最优参数组合解:磨块间滚动摩擦系数为0.0597,碰撞恢复系数为0.7444,JKR表面能为0.1J/m2。运用最佳参数组合进行仿真分析,得到休止角的均值为27.17?,与实验的休止角相对误差为0.6%。结论使用该方法进行湿式滚抛磨块离散元物理性能参数的标定具有可行性,不仅可以为实现仿真模拟的参数确定提供依据,同时可为其他非规则形状散体的参数测定提供参考。展开更多
海底滑坡是海洋中常见的一种灾害地质现象,一旦发生将会对水下基础设施造成破坏,而目前很少有有关海底黏性滑坡体运动演化行为方面的模拟研究。采用计算流体动力学(computational fluid dynamics,简称CFD)和离散元法(discrete element m...海底滑坡是海洋中常见的一种灾害地质现象,一旦发生将会对水下基础设施造成破坏,而目前很少有有关海底黏性滑坡体运动演化行为方面的模拟研究。采用计算流体动力学(computational fluid dynamics,简称CFD)和离散元法(discrete element method,简称DEM)建立了描述水与颗粒相互作用的流固耦合模型,通过引入颗粒间黏聚力模型,发展海底黏性滑体运动演化过程的CFD-DEM耦合分析方法,并开展了多个典型算例的验证分析。在此基础上,考虑滑体黏性作用和初始速度,系统地模拟了海底滑坡体的运动学特征(运动速度和距离)和形态特征(滑体长度、宽度、形状等),并深入探究了滑体运动及演化过程的影响机制。结果表明:该耦合方法可以较好地模拟再现海底滑坡体的小尺度运动行为,滑坡体的黏性作用对其运动学特征和形态特征具有显著影响,初始速度也明显影响了滑体各部位在运动过程中的颗粒流场演化及分布特征。这一成果可为真实海底滑坡的运动演化过程模拟和有效预测提供重要的科学依据。展开更多
为了解决双卧轴搅拌机的搅拌低效区问题,可旋转搅拌臂与叶片重合,利用搅拌臂来搅拌低效区物料,增强其物料流动性。通过对建立的单搅拌叶片模型进行非线性规划计算,得出其叶片最优参数。为证明该优化结构的准确性,同时建立普通叶片、双...为了解决双卧轴搅拌机的搅拌低效区问题,可旋转搅拌臂与叶片重合,利用搅拌臂来搅拌低效区物料,增强其物料流动性。通过对建立的单搅拌叶片模型进行非线性规划计算,得出其叶片最优参数。为证明该优化结构的准确性,同时建立普通叶片、双排叶片与该优化叶片进行对比,将三种叶片分别装配在同一搅拌筒内导入EDEM模拟搅拌过程。颗粒接触模型采用为Hertz-Mindlin with JKR Cohesion,相关参数通过塌落度数值模拟进行校核。结果发现新型叶片可增大低效区物料速度,改善低效区物料流动性;两轴速度差较小,筒端物料堆积较少从而使物料运转更流畅;可从宏观上增加物料剪切对流运动,微观上增大颗粒动能,使颗粒碰撞更剧烈,物料能够快速达到均匀状态,提高整盘物料搅拌效率。展开更多
This paper continues our recent work on the relationship between discrete contact interactions at the microscopic scale and continuum contact interactions at the macroscopic scale (Hulikal et al., J. Mech. Phys. Solid...This paper continues our recent work on the relationship between discrete contact interactions at the microscopic scale and continuum contact interactions at the macroscopic scale (Hulikal et al., J. Mech. Phys. Solids 76, 144-161, 2015). The focus of this work is on adhesion. We show that a collection of a large number of discrete elements governed by a threshold-force based model at the microscopic scale collectively gives rise to continuum fracture mechanics at the macroscopic scale. A key step is the introduction of an efficient numerical method that enables the computation of a large number of discrete contacts. Finally, while this work focuses on scaling laws, the methodology introduced in this paper can also be used to study rough-surface adhesion.展开更多
The adhesion failure has become one dominant factor in determining the reliability and service life of miniaturized devices subject to loadings with arbitrary orientations.This article establishes an adhesive full sti...The adhesion failure has become one dominant factor in determining the reliability and service life of miniaturized devices subject to loadings with arbitrary orientations.This article establishes an adhesive full stick contact model between an elastic half-space and a rigid cylinder loaded in any direction.Using the Papkovich-Neuber functions,the Fourier integral transform,and the asymmetric bipolar coordinates,the exact solution is obtained.Unlike the Johnson-Kendall-Roberts(JKR)model,the present adhesive contact model takes into account the effects of the load direction as well as the coupling of the normal and tangential contact stresses.Besides,it considers the full stick contact which has large values of the friction coefficient between contacting surfaces,contrary to the frictionless contact supposed in the JKR model.The result shows that suitable angles can be found,which makes the contact surfaces difficult to be peeled off or easy to be pressed into.展开更多
文摘辣椒籽的物性参数是离散元仿真中重要的输入,为提高其数值模拟的可靠性与准确度,对辣椒籽的物性参数进行试验测量,主要包括三轴尺寸、密度、泊松比、摩擦系数、恢复系数等。结合EDEM中“Hertz-Mindlin with JKR”粘力模型,引入表面能参数,进行休止角试验。通过Plackett-Burman试验在各影响因子中筛选出最具显著性的3个影响参数(辣椒籽—籽滚动摩擦系数、辣椒籽表面能、辣椒籽—钢板滚动摩擦系数),建立3个显著影响参数与休止角的回归模型,研究显著因子在交互作用下对休止角的影响。将显著参数的区间按梯度平均分为5个水平进行爬坡试验得到最佳取值范围,运用响应面法(Box-Behnken)分析回归模型的二次多项式在休止角、相对误差和三个重要参数之间的方差,以相对误差最小值对模型进行优化,得到最优组合:辣椒籽间的滚动摩擦系数为0.75、JKR表面能为0.31 J/m^(2)、辣椒籽与钢板间滚动摩擦系数为0.60。用通过标定试验得到的最优参数组合进行模拟堆积试验,平均休止角为26.71°,相对误差为4.61%。
文摘目的确定湿式滚抛磨块在接触过程中各相关物理性能参数的取值。方法基于EDEM离散元仿真模拟,选取系统中"Hertz-Mindlin with JKR"接触模型,以休止角为评价指标,对湿式滚抛磨块离散元模拟的最优参数组合进行标定。首先运用Plackett-Burman试验选取对湿式滚抛磨块有显著影响的3个参数项(湿式滚抛磨块间的滚动摩擦系数、碰撞恢复系数和JKR表面能),然后用最陡爬坡试验确定出显著性参数的最优区间,最后通过响应曲面法(Box-Behnken)分别对休止角和相对误差与3个显著性参数的回归模型二次多项式进行方差分析,并寻找最优参数组合。结果得到了最优参数组合解:磨块间滚动摩擦系数为0.0597,碰撞恢复系数为0.7444,JKR表面能为0.1J/m2。运用最佳参数组合进行仿真分析,得到休止角的均值为27.17?,与实验的休止角相对误差为0.6%。结论使用该方法进行湿式滚抛磨块离散元物理性能参数的标定具有可行性,不仅可以为实现仿真模拟的参数确定提供依据,同时可为其他非规则形状散体的参数测定提供参考。
文摘海底滑坡是海洋中常见的一种灾害地质现象,一旦发生将会对水下基础设施造成破坏,而目前很少有有关海底黏性滑坡体运动演化行为方面的模拟研究。采用计算流体动力学(computational fluid dynamics,简称CFD)和离散元法(discrete element method,简称DEM)建立了描述水与颗粒相互作用的流固耦合模型,通过引入颗粒间黏聚力模型,发展海底黏性滑体运动演化过程的CFD-DEM耦合分析方法,并开展了多个典型算例的验证分析。在此基础上,考虑滑体黏性作用和初始速度,系统地模拟了海底滑坡体的运动学特征(运动速度和距离)和形态特征(滑体长度、宽度、形状等),并深入探究了滑体运动及演化过程的影响机制。结果表明:该耦合方法可以较好地模拟再现海底滑坡体的小尺度运动行为,滑坡体的黏性作用对其运动学特征和形态特征具有显著影响,初始速度也明显影响了滑体各部位在运动过程中的颗粒流场演化及分布特征。这一成果可为真实海底滑坡的运动演化过程模拟和有效预测提供重要的科学依据。
文摘为了解决双卧轴搅拌机的搅拌低效区问题,可旋转搅拌臂与叶片重合,利用搅拌臂来搅拌低效区物料,增强其物料流动性。通过对建立的单搅拌叶片模型进行非线性规划计算,得出其叶片最优参数。为证明该优化结构的准确性,同时建立普通叶片、双排叶片与该优化叶片进行对比,将三种叶片分别装配在同一搅拌筒内导入EDEM模拟搅拌过程。颗粒接触模型采用为Hertz-Mindlin with JKR Cohesion,相关参数通过塌落度数值模拟进行校核。结果发现新型叶片可增大低效区物料速度,改善低效区物料流动性;两轴速度差较小,筒端物料堆积较少从而使物料运转更流畅;可从宏观上增加物料剪切对流运动,微观上增大颗粒动能,使颗粒碰撞更剧烈,物料能够快速达到均匀状态,提高整盘物料搅拌效率。
基金Project(12072309)supported by the National Natural Science Foundation of ChinaProject(19B546)supported by the Education Department Foundation of Hunan Province,ChinaProject(2019RS1059)supported by the Hunan Innovative Province Construction Project,China。
基金support for this study from the National Science Foundation of the United States (Grant EAR 1142183)the Terrestrial Hazards Observations and Reporting Center (THOR) at the California Institute of Technology
文摘This paper continues our recent work on the relationship between discrete contact interactions at the microscopic scale and continuum contact interactions at the macroscopic scale (Hulikal et al., J. Mech. Phys. Solids 76, 144-161, 2015). The focus of this work is on adhesion. We show that a collection of a large number of discrete elements governed by a threshold-force based model at the microscopic scale collectively gives rise to continuum fracture mechanics at the macroscopic scale. A key step is the introduction of an efficient numerical method that enables the computation of a large number of discrete contacts. Finally, while this work focuses on scaling laws, the methodology introduced in this paper can also be used to study rough-surface adhesion.
基金supported by the National Natural Science Foundation of China(Nos.11972257,11832014,and 11472193)the China Scholarship Council(CSC)the Fundamental Research Funds for the Central Universities(No.22120180223)。
文摘The adhesion failure has become one dominant factor in determining the reliability and service life of miniaturized devices subject to loadings with arbitrary orientations.This article establishes an adhesive full stick contact model between an elastic half-space and a rigid cylinder loaded in any direction.Using the Papkovich-Neuber functions,the Fourier integral transform,and the asymmetric bipolar coordinates,the exact solution is obtained.Unlike the Johnson-Kendall-Roberts(JKR)model,the present adhesive contact model takes into account the effects of the load direction as well as the coupling of the normal and tangential contact stresses.Besides,it considers the full stick contact which has large values of the friction coefficient between contacting surfaces,contrary to the frictionless contact supposed in the JKR model.The result shows that suitable angles can be found,which makes the contact surfaces difficult to be peeled off or easy to be pressed into.
