Effect of rock mass structure and block size on the slope stability--Physical modeling and discrete element simulation

This paper studies the stability of jointed rock slopes by using our improved three-dimensional discrete element methods (DEM) and physical modeling. Results show that the DEM can simulate all failure modes of rock slopes with different joint configurations. The stress in each rock block is not homogeneous and blocks rotate in failure development. Failure modes depend on the configuration of joints. Toppling failure is observed for the slope with straight joints and sliding failure is observed for the slope with staged joints. The DEM results are also compared with those of limit equilibrium method (LEM). Without considering the joints in rock masses, the LEM predicts much higher factor of safety than physical modeling and DEM. The failure mode and factor of safety predicted by the DEM are in good agreement with laboratory tests for any jointed rock slope.     

地形三维可视化的实现与应用

文中讨论了地形三维可视化的原理，详细介绍了高级编程语言与OpenGL结合开发环境下的地形三维可视化的计算机实现过程。在此基础之上，讨论了基于GRID DEM的应用分析功能的实现,包括等高线、坡度图、通视分析以及淹没分析。为三维地形可视化的实施提出了有效的方案。     

大规模三维场景可视化的数据组织方法研究

针对大规模三维场景的可视化问题，文章提出了以数据分割和动态调度为主要思想的解决方案，并重点对空间数据组织方法进行了研究和实践，提出通过数据的预处理和编码机制将空间数据组织成金字塔形的数据库结构，以支持动态的数据调度和绘制。文中通过具体应用的实例证明了该数据组织方法的有效性。     

NASA EOS Terra ASTER: Volcanic topographic mapping and capability

Up-to-date, accurate topographic data are a crucial resource for volcanic research and risk mitigation efforts, in particular, for modeling volcanic flow processes at a detailed spatial resolution. In this paper, we examine the utility of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument currently operating on the NASA Terra satellite, which provides near infrared (VNIR) stereo imaging from which topography can be derived. We wrote software to generate digital elevation models (DEMs) from the ASTER level 1A product, which employs an automated stereo matching technique to calculate the parallax offsets between the images acquired by the nadir- and aft-looking sensors. Comparison of ASTER DEMs with DEMs derived from other sources (digitized 1:50 K topographic maps and aerial interferometric radar) at Ruapehu volcano reveal an RMS error of about 10 m for the ASTER DEM, in the absence of significant atmospheric water vapor. A qualitative assessment of surface features showed that the ASTER DEM is superior to the interpolated 1:50 K map product but falls short of the detail provided by aerial interferometric radar, especially in terms of stream channel preservation. A second ASTER DEM was generated for Taranaki volcano, where previously only 1:50 K topographic map data were available. Although the 2000 Space Shuttle radar topography mission (SRTM) will largely remedy the previous global paucity of adequate topographic data at volcanoes, such as Taranaki, we anticipate the problem that at active volcanoes, the topography may change significantly following activity, rendering the SRTM data inaccurate. With the high temporal coverage of the dataset, ASTER not only provides a means to update significant (>10 m) topographic measurements at active volcanoes via a time-series of DEMs, but also provides a simultaneous means to map surface cover and localized land-use via the near infrared sensors. Thus we demonstrate the potential for up-to-date volcanic economic risk assessment using geographic information systems (GIS) analysis.     

An analytical solution for geotextile-wrapped soil based on insights from DEM analysis

This paper presents a novel analytical solution for geotextile-wrapped soil based on a comprehensive numerical analysis conducted using the discrete element method (DEM). By examining the soil–geotextile interface friction, principal stress distribution, and stress–strain relations of the constituent soil and geotextile in the DEM analysis, a complete picture of the mechanical characterization of geotextile-wrapped soil under uniaxial compression is first provided. With these new insights, key assumptions are verified and developed for the proposed analytical solution. In the DEM analysis, a near-failure state line that predicts stress ratios relative to the maximums at failure with respect to deviatoric strain is uniquely identified; dilation rates are found to be related to stress ratios via a single linear correlation regardless of the tensile stiffness of the geotextile. From these new findings, the assumptions on the stress-state evolution and the stress–dilatancy relation are developed accordingly, and the wrapped granular soil can therefore be modeled as a Mohr–Coulomb elastoplastic solid with evolving stress ratio and dilation rate. The development of the proposed analytical model also demonstrates an innovative approach to take advantage of multiscale insights for the analytical modeling of complex geomaterials. The analytical model is validated with the DEM simulation results of geotextile-wrapped soil under uniaxial compression, considering a wide range of geotextile tensile stiffnesses. To further examine the predictive capacity of the analytical model, the stress–strain response under triaxial compression conditions is solved analytically, taking both different confining pressures and geotextile tensile stiffnesses into account. Good agreement is obtained between the analytical and DEM solutions, which suggests that the key assumptions developed in the uniaxial compression conditions also remain valid for triaxial compression conditions.     

Effect of port configuration on discharge from a HICOM® mill

The discharge behaviour of different port configurations in a HICOM mill is investigated using DEM simulation. The charge in the mill is strongly sheared and circulates rapidly but has a free surface shape that is constant and which rotates with the mill rotation. The horizontal cross-sectional area of the charge decreases with increasing height. Particles within the mill discharge when the rotating charge flows over and is pushed towards the discharge ports. DEM enables the prediction of transient and steady state mass flow rates from each of the individual discharge ports. Twelve discharge ports at different locations in the mill are used here to explore the optimality of the various size and location options and to explore if there is any interaction in the discharge between adjacent ports. This provides information relevant to the operation of this type of mill, guidance for port selection and provides a general demonstration of how DEM can be used to predict transport and discharge behaviour of mills.     

基于离散单元法的群楼拆除爆破仿真模拟

基于青岛开发区一商场爆破工程,利用颗粒离散元法建立离散元网格实体模型,用多面体离散元法模拟分析拆除爆破中建筑物的倒塌过程。研发的网格实体模型详细模拟了建筑物从结构局部失稳到整体完全倒塌的整个过程,确定了爆堆轮廓线和爆堆尺寸,直观给出了爆破设计的效果。触地振动、冲击力变化分析结果表明:所给出的爆破方案可达到预期拆除爆破的效果,触地振动符合《爆破安全规程》要求;该模型可优化爆破设计,指导爆破施工,为建筑物拆除爆破的灾害预测与安全评估提供理论依据。     

Comparison of solid particle erosion predictions using the dense discrete phase and discrete element models

A numerical procedure involving the dense discrete phase model (DDPM) is used to calculate solid particle erosion. DDPM works in two mechanisms. First, the discrete particles are treated as a pseudofluid, and the interaction among particles is evaluated by solving the governing equations of the pseudofluid. Second, the equivalent pressure of the pseudofluid is applied to a single particle to reflect the blocking effect of high-concentration particles. The numerical procedure is well verified by comparison with the experimental data picked from a direct impact test. In addition, the DDPM predictions are compared with the discrete element model (DEM) predictions in detail. Both methods show that the predicted mass loss caused by sand per unit mass decreases with an increase in sand concentration. DDPM indirectly considers the influence of particle interactions on solid particle erosion, and the predicted erosion contours are more uniform and smoother than the DEM-predicted contours.     

Anchor plate bearing capacity in flexible mesh facings

This work addresses the problem of the loading capacity of an anchor plate coupled with a steel wire mesh in soil retaining applications. The interaction mechanism between the flexible mesh facing, the underlying soil layer and the plate is studied starting from the results of several laboratory punch tests involving both the plate and the mesh only, and the whole soil-mesh-plate system. The experimental tests have been reproduced by adopting a 3D discrete element model where also the wire mesh is discretized as an assembly of interconnected nodal particles. The interaction between these particles is ruled by elasto-plastic tensile force–displacement laws in which a distortion is introduced in a stochastic manner to account for the wires’ geometrical irregularities. The mesh model is then validated with reference to a set of punch tests in which the shape and size of the punching element as well as the nominal wire diameter were varied. Subsequently, the model is extended to a punch against soil test configuration permitting an insight into the nontrivial local mechanism between the mesh facing and the underlying granular layer. The good agreement between the numerical predictions and the experimental observations at the laboratory scale allowed us to extend the model towards more realistic field conditions for which the role of the mesh panel boundary conditions, the mesh mechanical properties, the soil mechanical properties and the anchor plate geometry is investigated.     

DEM在风电场风机点位优化设计中的应用

本文基于DEM,通过Arc GIS10.0软件,采用空间分析工具提取出风电场测区内风机点位的坡度图,通过对坡度图进行分级统计分析,设计出风电场中风机点位的最优位置,从而提高工程项目的质量和效率。