共查询到20条相似文献，搜索用时 15 毫秒
1.
2.
The paper presents a numerical study on the side resistance of a drilled shaft in granular materials. The numerical result is used to develop new design equations for the side resistance of drilled shafts in granular soils. The Discrete Element Method (DEM) is used to model a drilled shaft in granular material. The granular material is represented as assemblies of ellipsoidal particles. Nominal side resistance is represented as the product of a parameter (β) and vertical stress. The numerical result shows that the relationship between β and void ratio can be described by a hyperbolic function for a given vertical stress. DEM result is also compared with three design equations. Although these design equations capture the decrease of β with depth, deviation is observed between the DEM results and the design equations. Finally, new design equations based on state parameter are proposed. 相似文献
3.
Breakage of particles will have greatly influence on mechanical behavior of granular material(GM)under external loads,such as ballast,rockfill and sand.The discrete element method(DEM)is one of the most popular methods for simulating GM as each particle is represented on its own.To study breakage mechanism of particle breakage,a cohesive contact mode is developed based on the GPU accelerated DEM code-Blaze-DEM.A database of the 3D geometry model of rock blocks is established based on the 3D scanning method.And an agglomerate describing the rock block with a series of non-overlapping spherical particles is used to build the DEM numerical model of a railway ballast sample,which is used to the DEM oedometric test to study the particles’breakage characteristics of the sample under external load.Furthermore,to obtain the meso-mechanical parameters used in DEM,a black-analysis method is used based on the laboratory tests of the rock sample.Based on the DEM numerical tests,the particle breakage process and mechanisms of the railway ballast are studied.All results show that the developed code can better used for large scale simulation of the particle breakage analysis of granular material. 相似文献
4.
This paper presents a numerical evaluation on the degradation evolutions in three well-known constitutive models for bonded geomaterials using the Distinct Element Method (DEM). A series of isotropic, constant stress ratio and biaxial compression tests on the bonded geomaterials were carried out by a two-dimensional (2D) DEM code, NS2D, for this purpose. The constitutive models examined are the disturbed state constitutive model (DSC model), the superloading yield surface model and Nova’s model. First, a microscopic interpretation of the degradation variable, which is used to describe the degradation evolution in the models, was presented based on the micromechanics theory to compare the degradation evolutions used by the models with the DEM results. Then, the macromechanical responses of the numerical specimens in the DEM tests were examined in comparison with the experimental data on the artificially bonded sands. Finally, the degradation evolutions observed in the DEM tests were compared with the results predicted by the constitutive models. The study shows that the DEM results are able to capture the main features of the artificially bonded sands. The degradation evolutions used in the three constitutive models are all overally in agreement with the DEM results. In addition, two simple evolution equations for the degradation variable, which can well describe the degradation evolution observed in the DEM tests, were presented and discussed. 相似文献
5.
Gao-Feng Zhao Qiuyue Yin Adrian R. Russell Yingchun Li Wei Wu Qin Li 《国际地质力学数值与分析法杂志》2019,43(1):166-182
The bonded discrete element model (DEM) is a numerical tool that is becoming widely used when studying fracturing, fragmentation, and failure of solids in various disciplines. However, its abilities to solve elastic problems are usually overlooked. In this work, the main features of the 2D bonded DEM which influence Poisson's ratio and Young's modulus, and accuracy when solving elastic boundary value problems, are investigated. Outputs of numerical simulations using the 2D bonded DEM, the finite element method, a hyper elasticity analysis, and the distinct lattice spring model (DLSM) are compared in the investigation. It is shown that a shear interaction (local) factor and a geometric (global) factor are two essential elements for the 2D bonded DEM to reproduce a full range of Poisson's ratios. It is also found that the 2D bonded DEM might be unable to reproduce the correct displacements for elastic boundary value problems when the represented Poisson's ratio is close to 0.5 or the long-range interaction is considered. In addition, an analytical relationship between the shear stiffness ratio and the Poisson's ratio, derived from a hyper elasticity analysis and applicable to discontinuum-based models, provides good agreement with outputs from the 2D bonded DEM and DLSM. Finally, it is shown that the selection of elastic parameters used the 2D bonded DEM has a significant effect on fracturing and fragment patterns of solids. 相似文献
6.
Liu Guang Sun WaiChing Lowinger Steven M. Zhang ZhenHua Huang Ming Peng Jun 《Acta Geotechnica》2019,14(3):843-868
We present a numerical analysis on injection-induced crack propagation and coalescence in brittle rock. The DEM network coupling model in PFC is modified to capture the evolution of fracture geometry. An improved fluid flow model for fractured porous media is proposed and coupled with a bond-based DEM model to simulate the interactions among cracks induced by injecting fluid in two nearby flaws at identical injection rates. The material parameters are calibrated based on the macro-properties of Lac du Bonnet granite and KGD solution. A grain-based model, which generates larger grains from assembles of particles bonded together, is calibrated to identify the microscopic mechanical and hydraulic parameters of Lac du Bonnet granite such that the DEM model yields a ratio between the compressive and tensile strength consistent with experiments. The simulations of fluid injection reveal that the initial flaw direction plays a crucial role in crack interaction and coalescence pattern. When two initial flaws are aligned, cracks generally propagate faster. Some geometrical measures from graph theory are used to analyze the geometry and connectivity of the crack network. The results reveal that initial flaws in the same direction may lead to a well-connected crack network with higher global efficiency.
相似文献7.
在原有有限元/离散元（FEM/DEM）耦合分析方法中,实现了一种新的爆破计算模型。该模型考虑了在爆生气体的作用下,随着裂隙的扩展,气体占据的体积不断增大,气体压力逐渐减小这一问题。同时考虑了气体嵌入与爆腔联通的裂隙对裂隙的作用力。克服了原有FEM/DEM方法中的爆破模型仅仅将压力施加于爆腔四周的岩壁上,无法考虑爆生气体嵌入生成的裂隙对裂隙的作用。提出了一种新颖的贯通裂隙网络形成的递归搜索算法,只需通过编写一个简单的递归函数,即可实现复杂裂隙网络的搜索,采用一种简洁的方法完成了对复杂问题的处理。最后通过一个爆破算例,结果表明FEM/DEM方法可以对爆炸过程中应力波的传播及岩体中裂纹的萌生、扩展进行全程捕捉,展现了该方法用于爆破模拟的潜力。 相似文献
8.
离散单元法适合室内试验和局部小尺度问题的模拟,但在分析隧道开挖等大尺度问题时计算复杂且耗时.为拓展离散元在大尺度问题分析中的适用性,尝试将离散元与理论解分区耦合.针对深埋圆形隧道围岩开挖过程,采用离散元模拟内部近孔口处围岩,外部采用理论解,耦合边界上使用迭代算法,控制收敛以保证力与位移连续条件,在弹性阶段范围内对两区域进行耦合以分析解法的适用性和误差.针对隧洞有、无内压两类算例,采用该分区耦合方法经15步左右迭代收敛,所得边界位移与理论解分别相差1.86%、3.2%;所得离散元结果与理论解对比良好：位移误差随角度有关、最大处在13.5%以内,应力误差除在少量部位为15%左右外,其余各处在8.6%以内.据此表明,该方法具有相当的精度及可行性. 相似文献
9.
This paper presents a numerical investigation into mechanical behavior and strain localization in methane hydrate (MH) bearing sediments using the distinct element method (DEM). Based on the results of a series of laboratory tests on the bonded granules idealized by two glued aluminum rods and the available experimental data of methane hydrate samples, a pressure and temperature dependent bond contact model was proposed and implemented into a two-dimensional (2D) DEM code. This 2D DEM code was then used to numerically carry out a series of biaxial compression tests on the MH samples with different methane hydrate saturations, whose results were then compared with the experimental data obtained by Masui et al. [9]. In addition, stress, strain, void ratio and velocity fields, the distributions of bond breakage and averaged pure rotation rate (APR) as well as the evolution of strain localization were examined to investigate the relationships between micromechanical variables and macromechanical responses in the DEM MH samples. The numerical results show that: (1) the shear strength increases as methane hydrate saturation SMH increases, which is in good agreement with the experimental observation; (2) the strain localization in all the DEM MH samples develops with onset of inhomogeneity of void ratio, velocity, strain, APR, and distortion of stress fields and contact force chains; and (3) the methane hydrate saturation affects the type of strain localization, with one shear band developed in the case of 40.9% and 67.8% methane saturation samples, and two shear bands formed for 50.1% methane saturation sample. 相似文献
10.
颗粒材料数值样本的坐标排序生成技术 总被引：1，自引：0，他引：1
颗粒材料离散颗粒模型的数值模拟结果与颗粒材料的数值样本密切相关,随着离散单元在颗粒材料数值模拟领域的广泛应用,颗粒材料的数值样本生成技术日益受到重视。基于RSA模型研究如何使随机生成的颗粒材料更密实,对均匀颗粒而言亦即如何在指定区域内生成更多的颗粒,讨论了4类修正方案,并建议了一种基于坐标排序的样本生成技术。研究表明,在传统的颗粒体随机生成技术基础上,通过对随机生成的x坐标序列或y坐标序列进行排序,可使生成的颗粒材料数值样本更密实。 相似文献
11.
用数值方法对岩质高边坡进行稳定性分析时,描述岩体结构对的精细程度会影响分析结果,但常见的有限单元法程序仍难以对复杂节理岩体进行精细建模。为解决这一问题,将结构面网络模拟与离散单元法相结合,在UDEC软件中,利用FISH语言编写网络模拟程序,依据结构面统计资料和结构面分级,实现对复杂岩体结构的精细描述。以某大型水电工程边坡为例,在对岩体结构进行精细描述的基础上,采用离散元强度折减法对边坡进行稳定性分析。通过与极限平衡法和一般离散元结果的对比,表明基于复杂岩体结构精细描述确定的边坡潜在滑动面和安全系数是合理的,为复杂岩质边坡破坏模式和稳定性的分析提供了新的途径。 相似文献
12.
大尺度断层往往控制了沉积盆地的形成和油气成藏,而小尺度断层则影响着注水开发效果和剩余油分布.大尺度断层可以通过二维或三维地震资料识别,而小尺度断层的识别则特别困难.本文提出了一种基于断层分形生长模式和三维地质力学模拟相结合来确定小尺度断层的数量、发育位置和方位的方法,并根据油田开发动态资料来确定小尺度断层对注水开发和剩余油分布的影响.将地震上识别的大尺度断层引入到三维数值力学模型中,模拟大尺度断层形成时期断裂带附近的应力扰动作用,然后结合破裂准则来建立最易发生破裂的方位和最大库伦剪切应力网格,以这两套网格和断层尺度的幂律分布确定的小尺度断层数量为约束条件来确定随机模型,对小尺度断层的密度、产状和发育位置进行定量预测.研究表明:利用分形理论和三维地质力学模拟可以对大尺度断层伴生小尺度断层进行有效预测;小尺度断层对注水开发效果和剩余油分布的影响取决于小尺度断层的规模(断距)以及小尺度断层方位和注采方向的关系. 相似文献
13.
Li-Ying Chang 《Geomechanics and Geoengineering》2018,13(3):159-167
The ranges of initial void ratios that can be achieved for numerical samples with the same grading as actual sand under gravity are explored using three-dimensional discrete element method (DEM). A corrected compressible accumulation model is proposed to predict the packing density of sand. Compared with the measured results, the errors of the prediction results are small. For three-dimensional DEM samples, when the ratio of sample size to particle size L/R is equal to or larger than 30, the maximum and the minimum void ratios are minimally affected by the sample size L. The maximum void ratios and the minimum void ratios of numerical samples with spherical particles are much smaller than those of actual sands. The generation method for numerical samples with non-spherical particles is proposed based on the theory of CPM. The variations of void ratios of numerical samples with non-spherical particles are wider than actual sands. So it can meet all the need of DEM simulation on the void ratio of actual sand. 相似文献
14.
The discrete element method (DEM) is frequently used in numerical simulation of the behaviour of discontinuum often encountered in granular flow, soil or rock mechanics or powder compaction. The DEM requires an assemblage of elements that need to fill the domain geometry. Generation of such arrangement of elements, such as disks in 2D DEM simulation is not a trivial task. The available methods to create the arrangements of disks can either take considerable time, have limited control over the final outcome of the disk generation or exhibit difficulty in generating a tight arrangement of disk with varying radii. This paper presents an algorithm employing principles of computational geometry to efficiently generate a tight packing of disks while addressing the common problems of disk generation. The algorithm’s performance is linear with respect to time and scales well. As a demonstration of the algorithm’s capabilities, a DEM model of an ore pass is presented. 相似文献
15.
Sousani Marina Eshiet Kenneth Imo-Imo Ingham Derek Pourkashanian Mohamed Sheng Yong 《Environmental Earth Sciences》2014,72(9):3383-3399
A three-dimensional model is presented and used to reproduce the laboratory hydraulic fracturing test performed on a thick-walled hollow cylinder limestone sample. This work aims to investigate the implications of the fluid flow on the behaviour of the micro-structure of the rock sample, including the material strength, its elastic constants and the initialisation and propagation of fractures. The replication of the laboratory test conditions has been performed based on the coupled Discrete Element Method (DEM) and Computational Fluid Dynamics scheme. The numerical results are in good agreement with the experimental data, both qualitatively and quantitatively. The developed model closely validates the overall behaviour of the laboratory sample, providing a realistic overview of the cracking propagation towards total collapse as well as complying with Lame’s theory for thick-walled cylinders. This research aims to provide some insight into designing an accurate DEM model of a fracturing rock that can be used to predict its geo-mechanical behaviour during Enhanced Oil Recovery applications. 相似文献
16.
David Toe Franck Bourrier Ignacio Olmedo Jean-Matthieu Monnet Frédéric Berger 《Landslides》2017,14(5):1603-1614
The objective of this research was to use numerical models based on mechanical approaches to improve the integration of the protective role of forests against rockfall into block propagation models. A model based on the discrete element method (DEM) was developed to take into account the complex mechanical processes involved during the impact of a block on a tree. This modelling approach requires the definition of many input parameters and cannot be directly integrated into block propagation models. A global sensitivity analysis identified the leading parameters of the block kinematics after impact (i.e. block energy reduction, trajectory changes, and rotational velocity): the impact velocity, the tree diameter, and the impact point horizontal location (i.e. eccentricity). Comparisons with the previous experimental and numerical studies of block impacts on trees demonstrated the applicability of the DEM model and showed some of the limitations of earlier approaches. Our sensitivity analysis highlights the significant influence of the impact velocity on the reduction of the block’s kinetic energy. Previous approaches usually also focus on parameters such as impact height, impact vertical incidence, and tree species, whose importance is only minor according to the present results. This suggests that the integration of forest effects into block propagation models could be both improved and simplified. The DEM model can also be used as an alternative to classical approaches for the integration of forest effects by directly coupling it with block propagation models. This direct coupling only requires the additional definition of the location and the diameter of each tree. Indeed, the input parameters related to the mechanical properties of the stem and the block/stem interaction in the DEM model can be set to average values because they are not leading parameters. The other input parameters are already defined or calculated in the block propagation model. 相似文献
17.
18.
Esperanza Muñoz-Salinas C. S. Renschler D. Palacios L. M. Namikawa 《Natural Hazards》2008,45(2):309-320
In contrast to dramatic flow regime changes by less frequent large-scale volcanic eruptions, those caused by more frequent
small-scale processes in volcanic landscapes may also drastically change the direction and dynamics of flow in a drainage
system formed solely by fluvial processes. During such periods of channel morphology change, it is necessary to frequently
update channel flow parameters to assess preventive measures for civil protection purposes. Often aerial photography is impracticable,
since parts of the channels are covered by dense vegetation, while total station and laser topographic surveys are often too
slow and costly, particularly during a high frequency of events. This article introduces and validates a new methodology for
updating the representation of channel morphology in Digital Elevation Models (DEM) used specifically for assessing the dangers
of frequently occurring lahars along gorges in volcanic landscapes during eruptive and non-eruptive periods. The updating
of channel cross-sections was achieved by inserting more detailed representative profiles of homogeneous channel sectors in
DEMs derived from existing less detailed topographic maps. The channel profiles were surveyed along the thalweg in equidistant
points according to Universal Transverse Mercator (UTM) (x,y) coordinates and elevation derived from the existing DEM. The
proposed technique was applied at Tenenepanco-Huiloac Gorge on Popocatépetl volcano, Mexico, in an area affected by major
lahars during the volcano’s most recent eruptive period from 1994 to 2005. The proposed method can reduce the cost and person-hours
of a regular channel topographic survey dramatically and the enhanced DEM can determine volume parameters and flood zones
associated with the 1 July 1997 and 21 January 2001 lahars, respectively. In addition, the updated DEM with better channel
representation allowed a more realistic fluid flow and lahar simulation with the process-based TITAN2D model. 相似文献
19.
We have developed a new approach for the numerical modeling of deformation processes combining brittle fracture and viscous flow. The new approach is based on the combination of two meshless particle-based methods: the discrete element method (DEM) for the brittle part of the model and smooth particle hydrodynamics (SPH) for the viscous part. Both methods are well established in their respective application domains. The two methods are coupled at the particle scale, with two different coupling mechanisms explored: one is where DEM particles act as virtual SPH particles and one where SPH particles are treated like DEM particles when interacting with other DEM particles. The suitability of the combined approach is demonstrated by applying it to two geological processes, boudinage, and hydrofracturing, which involve the coupled deformation of a brittle solid and a viscous fluid. Initial results for those applications show that the new approach has strong potential for the numerical modeling of coupled brittle–viscous deformation processes. 相似文献
20.
Pirnia Pouyan Duhaime François Ethier Yannic Dubé Jean-Sébastien 《Acta Geotechnica》2020,15(10):2877-2889
This paper presents a coupled finite and discrete-element model (FEM and DEM) to simulate internal erosion. The model is based on ICY, an interface between COMSOL, an FEM engine, and YADE, a DEM code. With this model, smaller DEM subdomains are generated to simulate particle displacements at the grain scale. Particles in these small subdomains are subjected to buoyancy, gravity, drag and contact forces for short time steps (0.1 s). The DEM subdomains provide the macroscale (continuum) model with a particle flux distribution. Through a mass conservation equation, the flux distribution allows changes in porosity, hydraulic conductivity and hydraulic gradient to be evaluated for the same time steps at a larger, continuum scale. The updated hydraulic gradients from the continuum model provide the DEM subdomains with updated hydrodynamic forces based on a coarse-grid method. The number of particles in the DEM subdomains is also updated based on the new porosity distribution. The hierarchical multiscale model (HMM) was validated with the simulation of suffusion. Results for the proposed HMM algorithm are consistent with results based on a DEM model incorporating the full sample and simulation duration. The proposed HMM algorithm could enable the modelling of internal erosion for soil volumes that are too large to be modelled with a single DEM subdomain.
相似文献