基于GIS技术的淹没区确定方法及虚拟现实表达

给出了基于数字高程模型的GRID结构,适合两种不同类型淹没区的计算方法,尤其是第2种"洪水淹没" 类型方法较有特色.对于采用本方法计算淹没区,准确性受地形图等高距大小、数字化采集精度、数字地面模型(DEM)高程精度以及格网间隔大小、像素探测分辨率等因素的影响.等高距越小,数字化跟踪误差越小,数字地面模型内插越密,格网跨度越短,探测分辨率越高,淹没区计算精度也就越好.空间数据总量及探测分辨率决定了整个算法模型的效率.最后,介绍了将淹没区范围采用OpenGL工具进行虚拟现实三维可视化所涉及的关键技术和方法.该方法在已完成的九五国家地方重大攻关项目所开发的<大型网络级水利防汛及流域规划动态管理信息系统>中得到实现.     

Micromechanics of breakage in sharp-edge particles using combined DEM and FEM

By combining DEM （Discrete Element Method） and FEM （Finite Element Method）, a model is established to simulate the breakage of twodimensional sharp-edge particles, in which the simulated particles are assumed to have no cracks. Particles can, however, crush during different stages of the numerical analysis, if stress-based breakage criteria are fulfilled inside the particles. With this model, it is possible to study the influence of particle breakage on macro- and micro-mechanical behavior of simulated angular materials. Two series of tests, with and without breakable particles, are simulated under different confining pressures based on conditions of biaxial tests. The results, presented in terms of micromechanical behavior for different confining pressures, are compared with macroparameters. The influence of particle breakage on microstructure of sharp-edge materials is discussed and the related confining pressure effects are investigated. Breakage of particles in rockfill materials are shown to reduce the anisotropy coefficients of the samples and therefore their strength and dilation behaviors.     

Micromechanics of breakage in sharp-edge particles using combined DEM and FEM

By combining DEM (Discrete Element Method) and FEM (Finite Element Method),a model is established to simulate the breakage of two-dimensional sharp-edge particles,in which the simulated particles are assumed to have no cracks.Particles can,however,crush during different stages of the numerical analysis,if stress-based breakage criteria are fulfilled inside the particles.With this model,it is possible to study the influence of particle breakage on macro- and micro-mechanical behavior of simulated angular materials.Two series of tests,with and without breakable particles,are simulated under different confining pressures based on conditions of biaxial tests.The results,presented in terms of micromechanical behavior for different confining pressures,are compared with macroparameters.The influence of particle breakage on microstructure of sharp-edge materials is discussed and the related confining pressure effects are investigated.Breakage of particles in rockfill materials are shown to reduce the anisotropy coefficients of the samples and therefore their strength and dilation behaviors.     

外力冲击二级隔离系统参数设计DEM研究

提出了外力冲击的二级隔离系统的ＤＥＭ模型。计算机仿真研究了冲击持续时间及具体波形与隔离系统的动态特性的关系,同时也研究了系统的非线性对系统动态性能的影响。为外力冲击的二级隔离系统的参数设计提供了一种新方法。     

船-冰作用中海冰典型破坏模式的离散元数值模拟

在破冰船破冰过程中,冰排主要表现为挤压与弯曲两种破坏模式.本文基于黏结离散单元法对船-冰作用中的这两种典型破坏模式进行数值模拟.海冰离散元数值试样采用随机排布方式生成,采用单轴压缩试验与三点弯曲试验相结合的方式标定模型中的细观参数.将船-冰碰撞中的挤压和弯曲作用方式简化为直立或倾斜 平板与海冰的作用模式,构建挤压与弯曲...     

Investigation of the effect of filling level on the wear and vibration of a SAG mill by DEM

Semi-autogenous grinding (SAG) mill is widely used in the grinding process of coal and ores because of its strong applicability, large capacity and low consumption of grinding media. Therefore, the research of SAG mill is still of great important practical significance. Among those parameters of the SAG mill, the filling level is very important for it is not only directly related to the processing capacity of the mill, but also affects the operation cost and stability of mill. In this paper, combined with shear impact energy model (SIEM) and discrete element method (DEM), the particle collision energy spectrum was applied to analyze the influence of ore filling level and media filling level on the power draw of the mill, the impact energy on ore, and the wear of liner and media in a slice of an industrial SAG mill. It was found that increasing the ore filling level would increase energy consumption and reduce the energy efficiency and the wear of liner and grinding media. Furthermore, the vibration of mill was explored from the collision energy on liner. The results showed that the low frequency but high energy collision between grinding media and liner was the main reason for liner wear and mill vibration.     

Comparison of near-infrared spectroscopy and DEM simulations for tracing spatial dispersion of water during mixing

The aim of this work was to validate a wet mixing process, in which a liquid spray is used to impregnate particles during mixing. The experimental results obtained using a bladed-mixer with a near-infrared sensor were compared with the results obtained using a 1:1 discrete element method simulation. The porous particles used in both cases absorbed the sprayed liquid for a process time of about 18 min. Multiple sensors attached to the mixer wall continuously monitored the liquid contents of passing particles. The sensors were modeled in the simulation and the resulting signals were analyzed and compared with the experimental results. We show that the algorithms used for spray and liquid absorption can be used to predict the moisture distribution inside granular materials in chemical and pharmaceutical processes. Such simulations can help to save money, e.g., in resource-intensive experimental plans and equipment design studies, and by varying material parameters.     

DEM simulation of small particles clogging in the packing of large beads

The percolation of small particles through a periodic random loose packing of large beads is studied numerically with the Distinct Element Method. The representativity of periodic mono-sized sphere packing of varying system size was first studied by comparing their pore size distributions and tortuosities with those of a larger system, considered as an infinite medium. The results show that a periodic packing of size as low as 4-grain diameters gives a reasonable representation of the porous medium and allows reducing considerably the number of particles that has to be used in the simulations. The flow and clogging of small particles of varying concentrations and friction coefficients flowing through the former packing are then studied numerically. Results show that a steady state is rapidly reached where the mean velocity and mean vertical velocity of small particles are both constant. These mean velocities decrease with an increase in friction coefficient and in small particle concentration. The influence of the friction coefficient μ is much less marked for values of μ larger than or equal to 0.5. The distribution of small particles throughout the crossed packing becomes rapidly heterogeneous. Small particles concentrate in some pores where their velocity vanishes and where the density can reach values larger than the density of the random loose packing. The proportion of particles blocked in these pores varies linearly with concentration. Finally, the narrow throats of the porous medium responsible for blocking are identified and characterized for different values of the friction coefficient.     

A parametric study of cohesive particle agglomeration in a shear flow—numerical simulations by the discrete element method

In this study, we investigate numerically the shear-induced agglomeration of cohesive inertial particles in a simple shear flow. We conduct a series of numerical simulations by implementing a soft-sphere collision model. Post-processing tools are developed in-house to analyze the results of the simulations in terms of transient and terminal numbers of primary particles and agglomerates, magnitudes and distributions of agglomerate size, and fractal dimension as functions of the salient physical parameters. The obtained numerical results compared with existing transient models suggest that, as the system transitions from formation of duplets to larger agglomerates, in most cases the number of agglomerates in the system reveals clear maxima. The results also show evidence of agglomerate densification, as weaker agglomerates with lower fractal dimensions are broken up and stronger ones with higher fractal dimensions are formed. Furthermore, we found that a simple theoretical model proposed by, among others, Chimmili et al. is able to predict the temporal development of the agglomerate size properly.