Effect of Milling Parameters on DEM Modeling of a Planetary Ball Mill

The effects of the milling parameters involving shape of powder particles, rotation speed, and ball-to-powder diameter (BPDR) on DEM modeling in the planetary ball mill were investigated. BPDR was varied from 1 to 10. The results revealed that the size and shape of the powder particles do not give a significant change in simulation results when BPDR attains maximum value of 10. The increasing of BPDR leads to the increase of simulation time and size. Hence, the effect of change of the powder particle shape on the calculated data size is not significant. The results also revealed that the increasing rotation speed increases impact energy between powder particles.

Composite wedge failure using photogrammetric measurements and DFN-DEM modelling

Analysis and prediction of structural instabilities in open pit mines are an important design and operational consideration for ensuring safety and productivity of the operation. Unstable wedges and blocks occurring at the surface of the pit walls may be identified through three-dimensional(3D) image analysis combined with the discrete fracture network(DFN) approach. Kinematic analysis based on polyhedral modelling can be used for first pass analysis but cannot capture composite failure mechanisms involving both structurally controlled and rock mass progressive failures. A methodology is proposed in this paper to overcome such limitations by coupling DFN models with geomechanical simulations based on the discrete element method(DEM). Further, high resolution photogrammetric data are used to identify valid model scenarios. An identified wedge failure that occurred in an Australian coal mine is used to validate the methodology. In this particular case, the failure surface was induced as a result of the rock mass progressive failure that developed from the toe of the structure inside the intact rock matrix. Analysis has been undertaken to determine in what scenarios the measured and predicted failure surfaces can be used to calibrate strength parameters in the model.

基于CFD-DEM的流-固耦合数值建模方法研究进展

随着土体渗流侵蚀研究的逐渐深入,对土颗粒流失和变形破坏机理的研究方法呈现出多尺度的特点。其中,计算流体力学-离散元耦合方法(CFD-DEM)为在细观尺度上研究流-固耦合相互作用对土体宏观力学特性的影响提供了一种行之有效的方法。针对CFD-DEM耦合方法在岩土工程领域应用现状,本文系统总结现有流-固耦合计算方法的优缺点,重点论述CFD-DEM耦合方法的建模策略,包括固相颗粒形状建模与粒间接触模型、流体相控制方程及参数计算方法,以及CFD-DEM耦合计算,并就相关问题进行深入探讨,最后提出了CFD-DEM耦合方法未来的发展方向。

基于倾斜三维模型与机载LiDAR点云的DEM快速更新

随着倾斜摄影技术的发展和实景三维建设的不断推进,地形级实景三维地理场景对DEM现势性要求日益提高。为了解决传统方法更新DEM成本高、工作量大的问题,本文提出了利用倾斜三维模型成果转换点云,融合两期DSM和DOM进行变化检测,替换已有机载LiDAR点云,快速更新DEM的方法,并通过项目验证了该方法的可行性,极大地节约了生产成本,为DEM更新提供了思路。

基于高分7号卫星DEM的坡度坡长计算精度评价

[目的]坡度和坡长作为重要的地形因子,其计算的准确性直接影响坡面土壤侵蚀模型的评价精度。高分7号卫星的高精度高程测量能力在地形因子的准确提取上具有较大潜力,期望能将其利用到坡度和坡长提取之中,实现对地形的准确表达。这需要对利用高分7号卫星DEM提取坡度坡长的结果进行精度评价。[方法]利用地形因子(LS)计算工具,对陕西省吴堡县4个小流域高分7号卫星、1∶10000地形图、激光雷达影像生成的DEM进行坡度、坡长的提取。采用相关系数(r)、相对偏差和绝对偏差作为评价指标,评价高分7号提取地形因子的精度。[结果]与激光雷达和1∶10000地形图的坡度和坡长相比,高分7号提取的流域平均坡度偏低7.50%~9.02%,坡长偏大1.83%~19.35%,但坡长和坡度分级的面积比例并不存在显著差异;高分7号提取的坡度结果偏差(16.46%~44.26%)明显小于坡长的偏差(75.25%~140.87%);高分7号所提取的坡度坡长在沟间地上的相对偏差(坡度15.48%~56.63%,坡长50.02%~130.79%)明显低于沟谷地(坡度21.28%~63.61%,坡长93.01%~192.51%)。[结论]利用高分7号DEM提取坡度坡长时,对于获取坡长坡度面积分级和对指定点的坡度提取时是可行的,而对于指定点的坡长提取时则结果不够可靠,在研究流域中坡长坡度的空间分布上具有较大优势,而提取具体某一位置处的坡长坡度时的优势则不明显。

基于DEM-SPH流固耦合的冰区船舶快速性预报

船舶在冰区海域中航行会受到冰水环境阻力的影响,是冰区船舶快速性研究中的重要影响因素。为合理分析冰区船舶的快速性能,该文采用基于离散元(discrete element method,DEM)和光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法的流固耦合模型模拟船舶冰区航行过程,获得不同航速下的船舶阻力和推进力,进一步计算出螺旋桨的推力、扭矩以及定速航行所需的螺旋桨转速等参数。为研究船体结构、海冰与海水之间的流固耦合作用,文中通过SPH粒子与固定粒子边界相对运动的拟合项直接计算固体与流体之间的相互作用力,建立船体结构、海冰与海水耦合的DEM-SPH模型,并基于该模型分别对船舶在冰区的航行阻力和推进力进行模拟,通过拟合的方式匹配航行阻力和推进力,并考虑尾部流场导致的船体阻力增额,从而预报船舶在特定航速下实现自航所需的螺旋桨转速。此外,文中还模拟了DTMB 5415船模在浮冰区和层冰区中航行的阻力和不同螺旋桨转速下的推力,对船模在不同工况下实现特定航速航行所需的螺旋桨转速进行了预报。计算结果表明:DEM-SPH耦合模型对船-冰、桨-冰作用中的流固耦合过程模拟效果出色,可完整描述船体及尾部伴流场对海冰的拖曳作用;通过文中所述阻力-推力模拟算例及强制力的拟合分析,所形成的基于数值模拟方法的船舶自航下螺旋桨转速预报,可为进一步的试验验证和工程应用推广奠定基础。

基于DEM的高山峡谷水库库容模型研究

库容是水库的一项重要指标,但在高山峡谷中的水库库容与水位高程呈现非确定关系性。本文对此类水库的库容与水位高程建立了水位-库容函数模型,首先,利用机载激光雷达和多波束水深测量系统采集的库区数字高程模型(DEM)数据和获取的水库各高程面面积,计算对应的库容;其次,使用Matlab工具将水位-库容函数模型根据实际情况分高程段进行多项式拟合建模、筛选和分析等,获得具有较高精度的水位-库容函数模型,对水库的安全运行管理具有一定的实用意义。

基于多尺度DEM一体化融合技术构建水利枢纽三维地形技术研究与应用

本文通过研究多尺度DEM一体化融合技术,构建了水利枢纽的三维地形模型,并深入研究了该技术在数字孪生乌鲁瓦提水利工程汛期模拟、汛期预演、汛期预警中的应用。首先对不同尺度DEM数据进行预处理,如数据清洗和去噪,以提高数据质量,然后采用多尺度分析方法,将不同尺度的DEM数据进行一体化融合,得到更准确、全面的地形信息。该技术的核心是基于多分辨率频域融合方法,将高分辨率DEM数据与低分辨率的DEM数据结合起来。通过分析不同尺度上的地形特征,可以提取出更丰富的地貌信息,为水利工程的规划和设计提供了重要的参考依据。

Flow-Induced Clogging in Microfiltration Membranes: Numerical Modeling and Parametric Study

Microfiltration membrane technology has been widely used in various industries for solid-liquid separation. However, pore clogging remains a persistent challenge. This study employs (CFD) and discrete element method (DEM) models to enhance our understanding of microfiltration membrane clogging. The models were validated by comparing them to experimental data, demonstrating reasonable consistency. Subsequently, a parametric study was conducted on a cross-flow model, exploring the influence of key parameters on clogging. Findings show that clogging is a complex phenomenon affected by various factors. The mean inlet velocity and transmembrane flux were found to directly impact clogging, while the confinement ratio and cosine of the membrane pore entrance angle had an inverse relationship with it. Two clog types were identified: internal (inside the pore) and external (arching at the pore entrance), with the confinement ratio determining the type. This study introduced a dimensionless number as a quantitative clogging indicator based on transmembrane flux, Reynolds number, filtration time, entrance angle cosine, and confinement ratio. While this hypothesis held true in simulations, future studies should explore variations in clogging indicators, and improved modeling of clogging characteristics. Calibration between numerical and physical times and consideration of particle volume fraction will enhance understanding.

融合自注意力机制与生成对抗网络的DEM空洞填充

针对现有数字高程模型(digital elevation model, DEM)数据空洞填充算法存在修复效果不连续、适用空值范围狭小以及细节重构丢失等问题,提出了一种融合自注意力机制的生成式对抗网络的DEM空洞填充方法。首先,构造自注意力机制提取DEM数据特征信息,改善DEM空洞填充结果高程值不连续和纹理细节缺失的问题。其次,在生成器中使用对称结构的卷积与反卷积网络结构,保证生成可靠度较高的数据以实现空洞区域填充,并利用判别器实现空洞填充结果的预分类。最后,结合重构损失函数进行训练,提升DEM空洞填充结果对异常值的鲁棒性,增强模型的回归能力。采用不同分辨率DEM数据进行空洞填充并与现有方法进行对比,结果表明:所提方法能够大幅提升填充精度,有效解决原始数据中存在的空洞问题。

猴子岩水库色玉滑坡涌浪灾害链CFD–DEM耦合数值模拟

滑坡涌浪是一种常见的地质灾害现象,由于滑坡体与水体之间存在复杂的流固耦合作用,使得传统的单一介质模型无法进行准确求解。为此,介绍一种基于计算流体力学方法(CFD)与离散单元法(DEM)的流固耦合模型CFD–DEM,采用计算流体力学方法(CFD)求解水体流动,采用离散单元法(DEM)模拟散粒体滑坡运动,充分利用不同计算模型的优势,对滑坡及涌浪演进过程进行数值模拟分析。首先,利用该耦合模型对Robbe–Saule开展的颗粒堆积体坍塌–涌浪试验进行了相同工况下的数值计算,从颗粒坍塌运动过程、涌浪高度演化过程等方面进行对比,结果表明模拟结果与试验结果吻合很好,验证了CFD–DEM流固耦合模型的有效性。然后,将该方法应用于四川省猴子岩水库色玉滑坡–涌浪灾害的演进过程分析,重现了该事件滑坡失稳运动、涌浪产生及传播、涌浪爬升、涌浪回流的全过程,计算结果显示:计算得到的电站进水口处涌浪高度与实测数据较为接近;色玉滑坡从失稳运动至静止堆积的持续时间约为20 s,颗粒平均速度最大达到16.12 m/s;滑坡引起的涌浪约在滑坡失稳10 s后传播到对岸,之后开始沿坡面向上爬升,最大爬升高度达到27.32 m。研究表明CFD–DEM流固耦合模型能够很好地应用于模拟山区河谷大规模滑坡涌浪灾害,可为库区防灾减灾提供高效的技术支持。

Snake Model for the Extraction of Loess Shoulder-line from DEMs

Shoulder lines are the most important landform demarcations for geographical analysis,soil erosion modeling and land use planning in the Loess Plateau area of China.This paper proposes an automatic,effective and accurate method of determining loess shoulder line from DEMs by integrating a hydrological D8 algorithm and a snake model.The watershed boundary line is adopted as the initial contour which evolves to identify the exact position of loess shoulder-line by the guidance of an external force of snake model from DEMs.Experiments show that the method overcomes the difficulties in both threshold selection for edge detection and the disconnecting issues in former extraction approaches.The accuracy evaluation of shoulder-line maps from the two test sites of the loess plateau area show obvious improvements in the extraction.The average contour matching distance of the new method is 12.0 m on 5 m resolution DEM,and shows improvement in the accuracy and continuity.The comparisons of accuracy evaluations of the two test sites show that the snake model method performs better in the loess plain area than in the area with high gully density.

基于Model Builder DEM的明暗等高线绘制

以重庆市缙云山DEM为数据源,首先利用ArcGIS的Model Builder生成明暗等高线模型,然后导入重庆市缙云山DEM数据得到明暗等高线,最后根据明暗等高线属性字段设置受光面和背光面等高线颜色得到具有三维立体效果的明暗等高线地图。实验结果表明,根据DEM绘制得到的明暗等高线与缙云山实际地貌形态较符合,能真实反映缙云山的三维地貌形态,弥补了传统等高线表示地形立体感不强的缺点,同时空间建模也大大提高了等高线绘制工作的效率。

Modelling of piping collapses and gully headcut landforms: Evaluating topographic variables from different types of DEM

The geomorphic studies are extremely dependent on the quality and spatial resolution of digital elevation model(DEM)data.The unique terrain characteristics of a particular landscape are derived from DEM,which are responsible for initiation and development of ephemeral gullies.As the topographic features of an area significantly influences on the erosive power of the water flow,it is an important task the extraction of terrain features from DEM to properly research gully erosion.Alongside,topography is highly correlated with other geo-environmental factors i.e.geology,climate,soil types,vegetation density and floristic composition,runoff generation,which ultimately influences on gully occurrences.Therefore,terrain morphometric attributes derived from DEM data are used in spatial prediction of gully erosion susceptibility(GES)mapping.In this study,remote sensing-Geographic information system(GIS)techniques coupled with machine learning(ML)methods has been used for GES mapping in the parts of Semnan province,Iran.Current research focuses on the comparison of predicted GES result by using three types of DEM i.e.Advanced Land Observation satellite(ALOS),ALOS World 3D-30 m(AW3D30)and Advanced Space borne Thermal Emission and Reflection Radiometer(ASTER)in different resolutions.For further progress of our research work,here we have used thirteen suitable geo-environmental gully erosion conditioning factors(GECFs)based on the multi-collinearity analysis.ML methods of conditional inference forests(Cforest),Cubist model and Elastic net model have been chosen for modelling GES accordingly.Variable’s importance of GECFs was measured through sensitivity analysis and result show that elevation is the most important factor for occurrences of gullies in the three aforementioned ML methods(Cforest=21.4,Cubist=19.65 and Elastic net=17.08),followed by lithology and slope.Validation of the model’s result was performed through area under curve(AUC)and other statistical indices.The validation result of AUC has shown that Cforest is the most appropriate model for predicting the GES assessment in three different DEMs(AUC value of Cforest in ALOS DEM is 0.994,AW3D30 DEM is 0.989 and ASTER DEM is 0.982)used in this study,followed by elastic net and cubist model.The output result of GES maps will be used by decision-makers for sustainable development of degraded land in this study area.

Coupled hydro-thermo-mechanical modeling of hydraulic fracturing in quasi-brittle rocks using BPM-DEM

This paper presents an improved understanding of coupled hydro-thermo-mechanical(HTM) hydraulic fracturing of quasi-brittle rock using the bonded particle model(BPM) within the discrete element method(DEM). BPM has been recently extended by the authors to account for coupled convective econductive heat flow and transport, and to enable full hydro-thermal fluidesolid coupled modeling.The application of the work is on enhanced geothermal systems(EGSs), and hydraulic fracturing of hot dry rock(HDR) is studied in terms of the impact of temperature difference between rock and a flowing fracturing fluid. Micro-mechanical investigation of temperature and fracturing fluid effects on hydraulic fracturing damage in rocks is presented. It was found that fracture is shorter with pronounced secondary microcracking along the main fracture for the case when the convectiveeconductive thermal heat exchange is considered. First, the convection heat exchange during low-viscosity fluid infiltration in permeable rock around the wellbore causes significant rock cooling, where a finger-like fluid infiltration was observed. Second, fluid infiltration inhibits pressure rise during pumping and delays fracture initiation and propagation. Additionally, thermal damage occurs in the whole area around the wellbore due to rock cooling and cold fluid infiltration. The size of a damaged area around the wellbore increases with decreasing fluid dynamic viscosity. Fluid and rock compressibility ratio was found to have significant effect on the fracture propagation velocity.

多源数据城区精细DEM建模方法

城区因建筑物密集、植被覆盖、交通流量大等,难以构建精度统一的DEM,本文基于大比例尺数字地形图、DOM、无人机摄影测量生成的DEM或基于激光雷达点云生成的DSM等数据,探讨构建精细DEM的方法。该方法首先从大比例尺数字地形图中提取等高线、高程点等用于直接构建DEM;然后提取道路边线、建筑物轮廓线、广场边界、隔离带、陡坎、湖泊边线等二维特征线要素,分别采用不同的方法融合DEM和DSM获得正确的高程信息,并结合实际情况加工处理后生成三维特征线;最后以此为基础应用具有约束的方法构建TIN模型。本文结合现有的数据源特点,分析了不同区域的模型精度。试验结果表明,构建的DEM与地形图吻合度高,可满足城区洪涝分析、精细管理、实景三维建设的需要。

基于FEM–DEM的空心稳定杆内壁喷丸仿真分析

目的建立有限元–离散元耦合的喷丸模型,研究喷丸参数对空心稳定杆内壁残余应力场的影响规律。方法基于ABAQUS有限元分析软件和“先整体后局部”的建模方法,建立26MnB5钢空心稳定杆全段和局部FEM–DEM喷丸模型,并对模型进行残余应力验证。通过局部喷丸模型研究弹丸撞击角度、速度、表面覆盖率和喷丸流量对稳定杆第4弯折处内壁残余应力场分布的影响规律。结果残余应力场分布的实验值与仿真值的误差在7%以内,验证了模型的准确性。随着弹丸撞击角度的增大,最大残余应力和残余压应力层深也会随之增大,并在60°后达到饱和;当弹丸速度为80m/s和100m/s且弹丸数量为1∶1时,表面残余应力和最大残余应力分别约为-926 MPa和-1309 MPa;随着弹丸覆盖率的增大,表面残余应力和最大残余应力均增大,但增幅变缓,在覆盖率为200%后基本达到饱和;随着喷丸流量的增大,表面残余应力和最大残余应力先增大后减小,在1.2kg/min时达到最大值,分别约为-649MPa和-1049MPa。结论基于FEM–DEM的空心稳定杆内壁喷丸模型能够很好地预测残余应力场的分布,该研究为空心稳定杆内壁喷丸工艺的数值模拟提供了研究思路和理论支持。

基于DEM数据和遗传算法的对海雷达部署优化研究

针对当前雷达组网部署优化问题缺少对海探测研究,以及基于实际地形数据的遗传算法(GA)求解复杂度高的问题,开展了基于数字高程模型(DEM)数据和遗传算法的对海探测部署优化研究。基于预先阵地和对海探测雷达威力模型,所提的算法可有效减少遗传算法寻优空间,极大提高优化求解速度。仿真表明,该算法可获得和遍历法近似的最优结果,随着部署规模的增大,具有明显的速度优势。

不同森林覆盖类型对LiDAR生成DEM的精度影响分析

运用机载激光雷达(LiDAR)获取的高精度数字高程模型(DEM)是目前地学分析应用满足精细化要求的基础数据。目前对森林覆盖下DEM产品的精度影响分析依然有所欠缺。以实时动态载波相位差分技术(RTK)结合全站仪实测的高程碎部点与机载LiDAR数据生成的高精度DEM产品数值做差,进行单因素方差分析(ANOVA)检验以及独立样本T-检验。经多重比较分析(LSD)可知,以马尾松为代表的针叶林和以桉树、茶树、黄连木、荔枝、阔叶混合林为代表的阔叶林之间差值相差较大,说明针叶林和阔叶林两种不同森林覆盖类型的绝对精度存在差异。但Robust检验结果显示阔叶林地表DEM的精度均值相等性为1,说明阔叶林(以桉树、茶树、黄连木、荔枝、阔叶混合林林地为代表)地表DEM精度不受树种的影响。综上,阔叶林与针叶林的地表DEM精度差异显著,说明阔叶林和针叶林对机载LiDAR生成森林区域地表DEM存在一定的影响。