Finite Element-discrete Element Method Research Articles

A coupled finite element-discrete element method for the modelling of brake squeal instabilities

The work presented here proposes a contribution on the analysis of brake squeal phenomenon using a transient coupled finite element-discrete element method (FEM-DEM) simulation with pad surface topography evolution. To build the coupled FEM-DEM model, a non-overlapping strong coupling is first employed between the FEM and DEM subdomains. Second, a new calibration methodology of the DEM microscopic properties is proposed based on the eigenvalue analysis of the full model. The results of the coupled FEM-DEM model show a good agreement in terms of unstable frequencies and the evolution of the pad contact state history when compared to full FEM models, both for new and worn pad topographies. The evolution of the pad surface topography during the transient analysis results in a complex frequency behaviour, with abrupt shifts of instabilities and new operating deflection shapes, in agreement with reported experimental results. The proposed coupled FEM-DEM model thus seems to be a valuable tool for a better understanding of the squeal triggering due to the evolution of the pad surface topography. This contribution paves the way to advanced numerical analyses of brake squeal phenomenon, which triggering conditions are still under investigation.

Dynamic propagation of tensile and shear fractures induced by impact load in rock based on the dual bilinear cohesive zone model

PurposeThe purpose of this study is to simulate the tensile and shear types of fractures using the mixed fracture criteria considering the energy evolution based on the dual bilinear cohesive zone model and investigate the dynamic propagation of tensile and shear fractures induced by an impact load in rock. The propagation of tension and shear at different scales induced by the impact load is also an important aspect of this study.Design/methodology/approachIn this study, based on the well-developed dual bilinear cohesive zone model and combined finite element-discrete element method, the dynamic propagation of tensile and shear fractures induced by the impact load in rock is investigated. Some key technologies, such as the governing partial differential equations, fracture criteria, numerical discretisation and detection and separation, are introduced to form the global algorithm and procedure. By comparing with the tensile and shear fractures induced by the impact load in rock disc in typical experiments, the effectiveness and reliability of the proposed method are well verified.FindingsThe dynamic propagation of tensile and shear fractures in the laboratory- and engineering-scale rock disc and rock strata are derived. The influence of mesh sensitivity, impact load velocities and load positions are investigated. The larger load velocities may induce larger fracture width and entire failure. When the impact load is applied near the left support constraint boundary, concentrated shear fractures appear around the loading region, as well as induced shear fracture band, which may induce local instability. The proposed method shows good applicability in studying the propagation of tensile and shear fractures under impact loads.Originality/valueThe proposed method can identify fracture propagation via the stress and energy evolution of rock masses under the impact load, which has potential to be extended into the investigation of the mixed fractures and disturbance of in-situ stresses during dynamic strata mining in deep energy development.

Mechanisms of rainfall-induced landslides and interception dynamic response: a case study of the Ni changgou landslide in Shimian, China

Geological hazards, especially landslides and mudslides, are frequent in Caoke County, Sichuan Province, China. In September 2022, the mechanical parameters of the soil were obtained through a basic investigation of the landslide characteristics of Ni changgou. Upon that, the finite element-discrete element method was used to reconstruct the three-dimensional numerical model of the landslide on the right bank of Ni changgou, and the initiation mechanism of rainfall on landslide and the formation of debris flow impact dam process were simulated. Furthermore, the pore pressure, stability coefficient as well as displacement of the landslide body were analyzed. It turned out that with the increase of rainfall intensity, the pore water pressure value also increases, where pore water pressure rises rapidly. the slope is close to the unstable edge, Eventually, it tends to one under rainfall conditions, and due to gravity, the slide of the landslide is induced. The duration of landslide movement is about 200 s, the maximum average velocity of the landslide reaches 4.85 m/s, and the average movement distance is close to 500 m. In addition, this method is applied to the Chutougou debris flow, and the corresponding hazard analysis is added which could better show the treatment and application of debris flow in actual engineering.

Coupled finite element-discrete element method (FEM/DEM) for modelling hypervelocity impacts

Coupled finite element-discrete element method (FEM/DEM) for modelling hypervelocity impacts

Human-Autonomous Devices for Finite Element Discrete Element Analysis of Geo Material Based on Digital Image Technology

Based on the theory of digital image processing, geometric vector transformation and the principle of automatic generation of finite element meshes, a finite element-discrete element analysis method for digital image of geotechnical engineering materials is proposed. Combining the digital image technology with the finite element-discrete element method (FDEM) coupling analysis method proposed by Munjiza, a FDEM analysis system is developed to characterize the real heterogeneity of rock mass, which provides a new way to model rock mass and study the fracture mechanism of rock mass from a meso-scopic point of view. With the help of digital image technology, the system obtains the real meso-structure of rock material from the image of rock section. With the help of mature mesh generation technology, it maps it to the FDEM computational grid, thus overcoming the shortcomings of the original FDEM in considering material heterogeneity. Using this system, the Brazilian disk splitting test is simulated numerically, and the real fracture process of granite under load is reproduced. And we examined how transparency and task type influence trustfulness, perceived quality of work during human-autonomous system interaction. The numerical simulation results show that the stress distribution of rock samples considering heterogeneity is asymmetric, and the micro-structure of rock has an important influence on the crack propagation and stress distribution in rock.

Numerical Analysis for Dynamic Propagation and Intersection of Hydraulic Fractures and Pre-existing Natural Fractures Involving the Sensitivity Factors: Orientation, Spacing, Length, and Persistence

Pre-existing natural fractures in a fractured reservoir will intersect with the hydraulic fractures and propagate dynamically during the hydrofracturing process, which has a significant impact on the morphology of the fracture network and subsequent gas production. If the representative properties of the natural fractures cannot be accurately extracted and appropriate numerical models are not established to describe the propagation and intersection behaviors of the fractures, it is difficult to determine the fracturing scheme for naturally fractured reservoirs and to obtain the expected fracture network and gas production. In this study, the combined finite element-discrete element method and discrete fracture network model were used to simulate the hydrofracturing process of naturally fractured reservoirs by controlling different sensitivity factors (orientation, spacing, length, and persistence) of natural fractures. To investigate the sensitivity factors, typical numerical cases were carefully designed and established, and the results of the dynamic propagation and intersection of hydraulic fractures and pre-existing natural fractures were derived. Two typical types of fracture network morphologies are detected when hydraulic fractures intersect the natural fractures: center-type (intersection of hydraulic fractures and the crossed cluster of the natural fractures) and edge-type (intersection of hydraulic fractures and the edge of the natural fractures). The quantitative results of the length and volume of the fracture networks and gas production in enhanced permeability fractured reservoirs were analyzed. The mechanisms by which the sensitivities of natural fractures affect and control the optimal fracturing behaviors are well understood; the conditions of small fracture spacing, large fracture length, or small fracture persistence of natural fractures are conducive for hydraulic fractures to intersect with the natural fractures and form a complex center-type fracture network and improve gas production.

A Hybrid FEM/DEM Approach to Estimating Rock Block Breakage due to Gravity Free-Fall

An understanding of the fragmentation of rock blocks from gravity free-fall has applications to rock fall analysis as well as block cave mining. In the case of a rock fall, blocks splitting mechanics can reduce the overall block energy and therefore reduce the travel distance of the blocks. Conversely, splitting may result in a larger number of smaller fragments that may still pose a risk despite their reduced dimensions. In the case of block caving, splitting of blocks it is believed to aid the flow of the ore column, to reduce the potential of hang-ups, and to allow for easier extraction and processing of the ore. Traditional methods for block fragmentation analysis use empirical relationships and rule-based approaches that heavily rely on the block geometry, rather than block-to-block interactions. In this paper we present a study of fragmentation processes using a hybrid finite-element/discrete-element method (FEM/DEM). The approach is capable to account for the numerical instability generally associated with the simulation of high velocity surface interactions and subsequent fracturing. To date the analysis has focused on the simulation of free-falling blocks onto a fixed surface. The initial and final block breakage has been compared against parameters including the roughness and curvature of the impacted surface, and the rock block orientation in space during free fall. We believe the results could provide useful insight into designing catchments for rock fall, as well as an increased understanding of the complexities of secondary fragmentation estimates and the range of fragmentation that could be expected in block caving.

Simulation of Tractive Performance of Off-road Tire on Gravel Road by Combined Finite Element-discrete ElementMethod and Experimental Validation

Simulation of Tractive Performance of Off-road Tire on Gravel Road by Combined Finite Element-discrete ElementMethod and Experimental Validation

Excavation unloading‐induced fracturing of hard rock containing different shapes of central holes affected by unloading rates and in situ stresses

AbstractSlabbing failure and strain rock burst are the main failure patterns during the excavation and construction phases of deep tunnels in hard and brittle rock, which cause unexpected equipment damage and casualties. This study presents a numerical simulation with an unloading central hole within a hard rock specimen in the laboratory scale. A combined finite element/discrete element method (FEM/DEM) reproduces the crack initiation, propagation, and coalescence around the central hole during the entire failure process. The influence of sectional shapes, unloading rates of holes, and in situ stresses on the failure characteristics and mechanical response of typical hard and brittle rocks were investigated by analysis of the failure pattern, displacement distribution (average velocity) of monitoring elements, and released strain energy value. The numerical results indicate that the sectional shapes, unloading rates, and in situ stresses have a significant impact on the severity of destruction and failure range in hard rock under the excavation unloading conditions. Slabbing failure (stable failure) is always the dominant failure pattern around a circular hole, which shows higher bearing capacities and self‐stabilization. With the increase in unloading rates, more visible cracks are generated around the holes, and the displacement and average velocity of discrete blocks are further raised. This is particularly evident in rock specimens with holes having vertical walls, leading to intense unstable failure (strain rock burst) accompanied by a large amount of strain energy released. In situ stresses affect considerably the stability of the surrounding rock during the excavation unloading process. With constant in situ stress, the order of destruction severity around the central hole according to its sectional shape is cube > trapezoid > U‐shape > ellipse > circle. The destruction intensity is further aggravated with the increase in lateral pressure coefficient, and the failure regions are always observed in the roof and floor of the central hole. This study confirms that strain rock burst tends to be induced in hard and brittle rock tunnels with polygonal roadway section under high unloading rates and lateral pressure coefficients.

A free, square, point-loaded ice sheet: A finite element-discrete element approach

Deflection of a free, thin, square, elastic, point-loaded ice sheet is studied. A three-dimensional, combined finite element-discrete element method (FEM-DEM) is applied. Examined is a set of square, self-similar (plan view) ice sheet samples with the side lengths of L=20, 40, 80, and 160 m; thicknesses of h=0.5, 1.0, and 1.5 m; and the average discrete element sizes of l=2h and 3h. The samples are generated and meshed via a centroidal Voronoi tessellation procedure. Each mesh is unstructured and consists of convex polyhedra as the discrete elements and a Delaunay-triangulated, in-plane beam lattice of co-rotational, viscously damped Timoshenko beam finite elements. Two load cases are considered: a sheet sample subjected to i) a vertical, centrally applied point load; and ii) a vertical point load on an edge. In both load cases, a good agreement is found between the deflections computed with the FEM-DEM approach and with FEM. Maximum, non-dimensionalized deflections w¯max (w¯max=q/Fz, where q=q(wmax) is an approximate, resultant reaction force due to the buoyancy, wmax the computed maximum deflection, and Fz the applied point load) scale, in each load case, either by a power-law, w¯max∝hm1(L), or exponentially, w¯max∝10m2(h)L, depending on whether computed over h (for each L) or vice versa. The exponents m1 and m2 are not constants, but functions of L and h, respectively, and approximately equal in either load case. In-plane size estimates are sought for an FEM-DEM sheet sample to represent either a) an infinite, elastic, point-loaded ice sheet; or b) a semi-infinite, elastic, point-loaded (with the load on the free edge) ice sheet with a free edge. A free, square, point-loaded FEM-DEM sheet sample well approximates both a) and b), if L/2>≈5lch, where lch denotes a characteristic length.

Numerical analysis of the effects of bedded interfaces on hydraulic fracture propagation in tight multilayered reservoirs considering hydro-mechanical coupling

Tight multilayered hydrocarbon reservoirs are typical in unconventional oil and gas extraction, in which widespread bedded interfaces have crucial effects on hydraulic fracturing propagation behavior. However, because of the complex natural properties of bedded interfaces in natural layers, such as geometric structure, distribution, strength, and contact conditions, their effects on fracture propagation and governing mechanisms are not well understood. In particular, traditional theoretical models are not suitable for characterizing the propagation behavior of hydraulic fractures in multilayered reservoirs and conventional numerical methods cannot effectively simulate the interactions between hydraulic fractures and bedded interfaces. In this study, the adaptive finite element-discrete element method was introduced to probe the effects of bedded interfaces on hydraulic fracture propagation. Different numerical models of five deviation angles of representative bedded interfaces were established based on the geometric and physical parameters of natural multilayered reservoir rocks. Some novel techniques (local remeshing near the fracture tips to guarantee accurate fracture propagation path, mesh coarsening to improve the computation efficiency, characterization technology for bedded interfaces and contacts between layers, and hydro-mechanical coupling between fluid flow in fracture network and porous rock matrix in the fracturing process) were comprehensively utilized. Furthermore, the fracturing-induced microseismic damaged and contact slip events were identified based on the computed moment tensors to detect the interactions between the hydraulic fractures and bedded interfaces. The results of the cases with single and multiple perforations in horizontal wells show that the bedded interfaces disturb the stress continuity, reselect propagation direction of hydraulic fractures in multiple perforations, induce hydraulic fracture growth, and promote the occurrences of fracturing-induced damaged and contact slip events. The offset and deflection of hydraulic fractures increase with increasing deviation angles between hydraulic fractures and bedded interfaces and the offset vanishes when the deviation angle is 0°.

FE-DEM with interchangeable modeling for off-road tire traction analysis

This study examines a new finite element/discrete element method (FE-DEM) with interchangeable modeling between FEM and DEM for tire traction analysis. In the method, named iFE-DEM, the soil in a soil bin is modeled initially by FEM except for the region under or near the tire, which is modeled using DEM. When the FEM tire model starts to travel over DEM soil elements, the updated tire location will activate new conversion of modeling from FEM to DEM so that the zone of influence around the contact interface between tire and soil can be analyzed continuously using DEM. Those mobilized DEM elements rearward of the tire might be converted again to FEM elements by assuming that the effect of the stress state in DEM generated by tire travel might be negligible. The computational time for two-dimensional iFE-DEM analysis of a slip of 40% using the smallest region of initial DEM under the tire could be reduced to 23% of that obtained using DEM only soil modeling.

Adaptive finite element-discrete element method for numerical analysis of the multistage hydrofracturing of horizontal wells in tight reservoirs considering pre-existing fractures, hydromechanical coupling, and leak-off effects

Multistage fracturing is widely used to improve gas production in tight hydrocarbon reservoirs. As a sequential process that interacts with pre-existing fractures, multistage fracturing must be properly addressed in numerical simulations, which are important in evaluating and optimising fracturing technology. The challenges of accurately representing the complex fracture structures and physical properties of naturally fractured reservoirs cause that the interaction between hydraulic and pre-existing fractures has not yet been resolved satisfactorily. In this study, we adopt an adaptive finite element-discrete element method to simulate the multistage fracturing of a naturally fractured reservoir by improving the mesh auto-refinement and identification of multiple fracture propagation. The numerical model considers interactions among hydraulic fractures, pre-existing fractures, and microscale pores, and integrates the nonlinear Carter leak-off criterion to describe fluid leak-off and hydromechanical coupling effects during multistage fracturing. The proppant transport equation for idealised parallel plate flow in fractures is introduced, and Darcy's law is adopted to analyse the seepage flow in the fracture network and determine the gas recovery. The fracture network and consequent fluid flow induced by the hydrofracturing of unfractured and naturally fractured models are compared to assess the influence of pre-existing fractures on multistage fracturing behaviour and gas production.

Fretting damage modeling of liner-bearing interaction by combined finite element – discrete element method

This paper presents a methodology to study the fretting damage behavior by combined finite element-discrete element method based on FFD method and cut boundary displacement method. A discrete element modeling technique is developed. An inter-element contact constitutive model and its microscopic parameters are determined and calibrated to reproduce continuous and discontinuous behaviors of material in DEM. A crack visualization technique is developed to display cracks according to their failure mode and time dependency. The effect of fretting condition on crack initiation and propagation as well as fretting damage is studied. The mechanism of fretting wear is investigated.

Analysis of Elastic Wheel Performance for Off-road Mobile Robots using FE—DEM

For this study, we applied a finite element-discrete element method (FE-DEM) to predict the tractive performance of an elastic iron wheel for mobile robots running on sand. We developed our program, where FEM is applied to a wheel and a subsurface soil layer, and where DEM is applied to the surface soil layer where the contact interaction between the tire and soil is greatest. The developed FE-DEM tool was found to have sufficient accuracy to predict the performance of an elastic wheel running on deformable soil. Moreover, parametric analysis was applied for those parameters of the rigidity of the tread part of the wheel, the surface soil layer thickness, and the lug height. The effect of rigidity of the tread part was negligible for 1-5 MPa. The surface soil layer thickness was found to have no significant effect on tractive performance. The lug height showed a strong effect on the tractive performance of the wheel, but the effect on net traction seemed to be degraded concomitantly with the increase in lug height.

FE-DEM Analysis of the Effect of Tread Pattern on the Tractive Performance of Tires Operating on Sand

Soil-tire system interaction is a fundamental and important research topic in terramechanics. In this paper, the authors applied a 2-D finite element, discrete element method (FE-DEM), using FEM for the tire and the bottom soil layer and DEM for the surface soil layer. Satisfactory performance analysis was achieved. In this study, to clarify the capabilities and limitations of the method for soil-tire interaction analysis, the tractive performance of real automobile tires with 2 different tread patterns—smooth and grooved—was analyzed by FE-DEM, and the numerical results compared with the experimental results obtained using an indoor traction measurement system. The analysis of tractive performance could be performed with sufficient accuracy by the proposed 2-D dynamic FE-DEM. FE-DEM obtained larger drawbar pull for a tire with a grooved tread pattern, which was verified by the experimental results. Moreover, the result for the grooved tire showed almost the same gross tractive effort and similar running resistance as in experiments. However, for a tire with smooth tread pattern, the analyzed gross tractive effort and running resistance behaved differently than experimental results, largely due to a difference in tire sinkage in FE-DEM.