Discrete Element Method Finite Element Method Research Articles

Radial Expansion Favors the Burrowing Behavior of Urechis unicinctus.

Urechis unicinctus can utilize the ability of large deformation to advance in sands by radial expansion, just using a small force. However, the large deformation of U. unicinctus skin and the discrete nature of the sands make it hard to analyze this process quantitatively. In this study, we aim to uncover the burrowing mechanism of U. unicinctus in granular sediments by combining discrete and finite elements. We observe that U. unicinctus will expand radially at the head, and then the head will shrink to move forward. The radial expansion will collapse the sands and let them flow, making it easy to advance. U. unicinctus mainly relies on the skin's large deformation and sufficient pressure to achieve radial expansion. Thus, we first establish the large deformation constitutive model of the skin. The stress-strain relationship can be expressed by the Yeoh model. Meanwhile, the pressure required for radial expansion is indirectly measured by the balloon experiment. To study the effect of radial expansion on the burrowing behavior, we use the finite element method-discrete element method (FEM-DEM) coupling model to simulate the expansion process of burrowing. The simulated pressure for radial expansion is very close to the experimental data, verifying the reliability of the simulation. The results show that the expansion can drastically reduce the pressure of sand particles on the head front face by 97.1% ± 0.6%, significantly decreasing the difficulty of burrowing. This unique underwater burrow method of U. unicinctus can provide new ideas for engineering burrowing devices in soft soil, especially for granular sediments.

Application of a Combined FEM/DEM Approach for Teaching a Deep Rock Mass Mechanics Course

Deep rock mass mechanics is a professional course which is offered to undergraduate and postgraduate students in some mining universities. This course mainly includes the following topics: the geological structure of deep rock mass, the mechanical properties of deep rocks, the strength theory of deep rock masses, stability analysis and control of deep surrounding rock classification of engineering rock masses, and the application of deep rock mechanics in underground mining engineering The purpose of this course is to present students with a basic theoretical knowledge of deep rock mass engineering. Analyzing the limitations of traditional deep rock mass mechanics teaching methods, here, we propose integrating a combined FEM/DEM (Finite Element Method/Discrete Element Method) approach into the teaching of a course on deep rock mass mechanics. The mechanical behaviors and failure instability process of rock at laboratory and engineering scales were analyzed using ELFEN software (a finite/discrete element code). The results show that a combined FEM/DEM approach as a deep rock mass mechanics teaching method is completely feasible and reasonable; this approach has the advantages of strong intuition, high reliability, time and labor savings, and low cost, which can offset the shortcomings of traditional teaching methods. Moreover, the proposed approach can stimulate students’ interests in a mining course on deep rock mass mechanics, deepen students’ understanding of the course curriculum, and cultivate students’ innovative abilities and subjective initiatives.

Numerical simulation of impact and entrainment behaviors of debris flow by using SPH–DEM–FEM coupling method

Abstract Increasing rain levels can easily destabilize and destroy particulate matter in mountainous areas, which can cause natural disasters, such as debris flow and landslides. Constitutive equations and numerical simulation are the theoretical bases for understanding the behavior of these disasters. Thus, this study aimed to investigate the impact of the debris flow and its entrainment behavior on gully bed sediments. We adopted a coupled analysis method based on elastic–plastic constitutive equations by considering the elasto-plasticity of slurry and the elastic characteristics of debris materials. The coupled method consisted of smooth particle hydrodynamic (SPH), discrete element method (DEM), and finite element method (FEM) (SPH–DEM–FEM). SPH particles represented fluid, DEM particles denoted solid immersed in fluid, and FEM elements represented the terrain and structures. The coupling analysis model was used to simulate the coupling contact of solid, liquid, and structures and to describe the entrainment behavior between solid and liquid phases. The model feasibility was verified by comparing the basic simulation results with experimental values of the dam break model and the rotating cylindrical tank model. The coupled model was then combined with the data management and modeling of geographic information system to simulate the 2010 Yohutagawa debris flow event. Finally, we explored the influence of debris shape-related parameters on the debris flow erosion entrainment process.

Influence of weld seam on the compaction characteristics of steel bridge deck pavement asphalt mixture

• The influence of weld seam on the compaction characteristics of SBDP was clarified. • The simulation results were verified with the field compaction results. • Optimization suggestions for SBDP compaction quality monitoring were given. • The findings contribute to the lean construction of SBDP. Many weld seams are generated to connect the orthotropic steel bridge decks (OSBDs), which poses a potential threat to the compaction quality of steel bridge deck pavement (SBDP) asphalt mixture. To clarify the influence of weld seam on the compaction characteristics of SBDP asphalt mixture, the coupled finite element method- discrete element method (FEM-DEM) model with weld seam was established to simulate the SBDP asphalt mixture compaction process, and the simulation results were verified with the field compaction ones. Then, the influence of different weld seam heights on the compaction quality was analyzed and the coupling effect under different compaction speeds was also investigated. Moreover, the impact of weld seam on the particle bonding failure mechanism was further examined. Results show that the weld seam height has little effect on the SBDP asphalt mixture compaction quality under low compaction speed, while large compaction speed would reduce the SBDP asphalt mixture compaction quality, and the existence of weld seam would exacerbate this adverse effect and prompt the particle bonging failures. The SBDP crack propagation process above the weld seam is divided into the initiation, propagation, acceleration and stagnation stages. Furthermore, optimization suggestions for SBDP asphalt mixture compaction quality monitoring were given: for the 25 mm and 30 mm thick SBDP lower layer, the weld seam height is recommended not more than 2 mm and 3 mm, respectively; the compaction speed is recommended not more than 3 km/h and 4 km/h, respectively. The findings contribute to proving the theoretical guidance and technical support for the lean construction of SBDP.

Collapse of dry and immersed polydisperse granular columns: A unified runout description

We study granular flows with grains of different sizes (i.e., polydispersity) in the granular column collapse configuration, in both dry and immersed systems with a Discrete Element Method - Finite Element Method (DEM-FEM) model. We show that polydispersity has an stronger effect on immersed cases than in dry cases, and propose a unified model that links the runout with the column collapse energy. Our results contribute a novel perspective in the study of immersed polydisperse flows.

Numerical study and multi-objective optimization of flexible screening process of flip-flow screen: A DEM-FEM approach

Vibrating flip-flow screens are widely used in deep screening processes. However, in-depth studies on flexible screening processes and the optimization of their operating parameters are limited. This study combines the discrete element method (DEM) and finite element method (FEM) to establish a coupled DEM–FEM model for simulating flexible screening processes. The reliability of the model was experimentally verified. Single-factor and central composite experiments were conducted to analyze the effects of y-direction amplitude, relative amplitude, installation angle, and frequency on particle speed, screening efficiency, and sieve plate stress. Finally, multi-objective optimization was implemented. The results revealed the dynamic response of the amplitude and stress on the flexible screen surface under the impact of materials. Moreover, a mathematical fitting model was derived to describe the relationship between the evaluation index and vibration parameters. Accordingly, a foundation for effectively improving the performance and reliability of flexible screening was established.

Multiscale analysis of tire and asphalt pavement interaction via coupling FEM–DEM simulation

With the aging of roads and the lack of resources for maintenance, a thorough understanding of the interaction between tires and asphalt pavements is crucial to optimize asphalt pavement surface design. Currently, most research on this interaction system is conducted using mesh-based methods in the frame of continuum mechanics, which are insufficient to model the discontinuity behavior of asphalt mixtures during their lifespan. In this study, the Contact Dynamics method is introduced to investigate this interaction system by coupling the finite element method (FEM) and the discrete element method (DEM). FEM is utilized to model the tire and capture the resulting contact stresses on the pavement surface, while DEM is used to model the heterogeneous structure of an asphalt mixture and examine internal mixture responses at the particle scale. Analysis of contact stress distributions for free-rolling and full-braking conditions proves the tire model’s effectiveness. According to particle displacement and force distributions, particles tend to flow along the longitudinal direction and undergo a high tangential contact force under full-braking compared with those under free-rolling, resulting in mixture instability and damage initiation. This study offers an enriching supplement and expansion to mesh-based methods for analyzing pavement surface degradation under tire loads, which can provide insight into pavement surface design.

Coordinated Time-Stepping Method for Coupled DEM–FEM–MBD Algorithm

The coordination of time steps directly affects the accuracy and efficiency of the calculation results in the simulation of the interaction between particles and structures. In this paper, a coordinated time-stepping method for coupling is proposed. The discrete element method (DEM) is used to establish the particle model, and the finite element method (FEM) and multibody dynamics (FEM-MBD) are applied to establish the structural model. The time step of the coupling algorithm between particles and a structure is discussed. The calculation efficiency and accuracy of the above methods are verified by an impact model, particle free falling model and electric pendulum model. Finally, the factors affecting the calculation efficiency of the coupling algorithm are discussed. The results show the following: compared with the theoretical solution, the calculation results of the coordinated time-stepping method are accurate. The multiple relationships of time steps between DEM and FEM-MBD are defined as communication coefficients, and the selection of a communication coefficient of 10 or 50 can effectively improve the calculation efficiency. When the communication coefficient continues to increase, the improvement of the calculation efficiency is not obvious. The number of structural elements has a great impact on the calculation efficiency, the number of particles in a certain range has a small impact on the calculation efficiency, and the time step of the DEM has a great influence on the calculation efficiency. The coordination time step method can improve the efficiency of the calculation while ensuring the accuracy of the calculation.

Combination of the finite element method and particle-based methods for predicting the failure of reinforced concrete structures under extreme water forces

We present a combination of the Finite Element Method (FEM), the Particle Finite Element Method (PFEM), and the Discrete Element Method (DEM) for modeling and analyzing the failure of reinforced concrete structures under impulsive wave forces originating from free-surface flows in critical water hazards. The free-surface water flow is modeled with the PFEM, while the structural behavior and the fractures induced by the water forces in the structure are modeled with a coupled FEM–DEM technique. The concrete material behavior is simulated with a standard isotropic damage model. The reinforcing bars are modeled by a rule of mixtures procedure, for simplicity. The possibilities of the new integrated PDFEM approach for predicting the evolution of free-surface tsunami-type waves and their devastating effect on constructions are validated with experiments on the failure of reinforced concrete plates under large impacting waves, performed in a laboratory facility in Japan.

Coupled Numerical Method for Modeling Propped Fracture Behavior

Hydraulic fracturing is a well-known production intensification technique in the petroleum industry that aims to enhance the productivity of a well drilled mostly in less permeable reservoirs. The process’s effectiveness depends on the achieved fracture conductivity, the product of fracture width, and the permeability of the proppant pack placed within the fracture. This article presents an innovative method developed by our research activity that incorporates the benefit of the Discrete—and Finite Element Method to describe the in situ behavior of hydraulic fractures with a particular emphasis on fracture conductivity. DEM (Discrete Element Method) provided the application of random particle generation and non-uniform proppant placement. We also used FEM (Finite Element Method) Static Structural module to simulate the elastic behavior of solid materials: proppant and formation, while CFD (Computational Fluid Dynamics) module was applied to represent fluid dynamics within the propped fracture. The results of our numerical model were compared to data of API RP-19D and API RP-61 laboratory measurements and findings gained by publishers dealing with propped fracture conductivity. The match of the outcomes verified the method and encouraged us to describe proppant deformation and embedment and their effect as precisely as possible. Based on the results, we performed sensitivity analysis which pointed out the impact of several factors affecting proppant embedment, deformation, and fracture conductivity and let one be aware of a reasonable interpretation of propped hydraulic fracture operation. However, DEM–CFD coupled models were introduced regarding fracturing before, to the best of our knowledge, the developed workflow of coupling DEM–FEM–CFD for modeling proppant-supported fracture behavior has not been applied yet, thus arising new perspectives for explorers and engineers.

Dynamic characteristics of LIWELL flip-flow screen panel and particle movement

Flip-flow screen is an effective solution for screening high-viscosity and fine-grained materials, because of the large vibration intensity of the screen panel. Therefore, investigating the dynamic characteristics of the screen panel is the key to improving the flip-flow screen. In this paper, a new dynamic model is proposed to do dynamic analysis of screen panel. The vibration of the screen panel is simplified into a string vibration model, and the energy equation is established. Then, the Hamilton principle and the Galerkin method are employed to transform the energy equations into ordinary differential equations, with the numerical solutions obtained using MATLAB. The vibration model is established by ABAQUS to obtain the displacement data of each point on the screen panel. To verify the correctness and accuracy of the theory, the simulation results are compared with the theoretical calculation results, and the dynamic characteristics of the vibration of the screen panel are analyzed. Besides, displacement and velocity equations of particle on the screen panel based on the screen panel vibration theory are proposed. A new FEM-DEM (Finite Element Method-Discrete Element Method) coupling simulation model is established in ABAQUS, which is used to investigate the trajectory of one particle and the effect of screen panel’s acceleration on particles’ movement and screening percentage.

A new discrete element-embedded finite element method for transient deformation, movement and heat transfer in packed bed

A new discrete element-embedded finite element method (DEFEM) scheme is proposed here, which solves the contact force and heat conduction of particles with embedded discrete elements (EDE), employs the finite element method (FEM) to get the deformation and internal temperature change of particles with heat and stress on the boundary and employs the discrete element method (DEM) to obtain the movement of particles. The DEFEM is characterized by coupling the deformation, motion and heat conduction of particles .Compared to either merely DEM or pure FEM, DEFEM combines the solution ideas of the FEM and DEM, and avoids the problem of overlapping and penetration of mesh elements in FEM. DEFEM also supports parallel computing, which is about three times faster than a pure FEM solution. As a demonstration, we developed an in-house code to perform DEFEM to simulate the extrusion and heat conduction of packed pebble bed, in comparison with a pure FEM solution for reference. Based on the numerical results, the characteristics of particle deformation and heat transfer in different extrusion speeds and layers are discussed.

Partitioned Strong Coupling of Discrete Elements with Large Deformation Structural Finite Elements to Model Impact on Highly Flexible Tension Structures

This article presents a staggered approach to couple the interaction of very flexible tension structures with large deformations, described with the finite element method (FEM), and objects undergoing large, complex, and arbitrary motions discretized with particle methods, in this case the discrete element method (DEM). The quantitative solution quality and convergence rate of this partitioned approach is highly time step dependent. Thus, the strong coupling approach is presented here, where the convergence is achieved in an iterative manner within each time step. This approach helps increase the time step size significantly, decreases the overall computational costs, and improves the numerical stability. Moreover, the proposed algorithm enables the application of two independent, standalone codes for simulating DEM and structural FEM as blackbox solvers. Systematic evaluations of the newly proposed iterative coupling scheme with respect to accuracy, robustness, and efficiency as well as cross comparisons between strong and weak FEM-DEM coupling approaches are performed. Additionally, the approach is validated against the rest position of an impacting object, and further examples with objects impacting highly flexible protection structures are presented. Here, the protection nets are described with nonlinear structural finite elements and the impacting objects as DEM elements. To allow the interested reader to independently reproduce the results, detailed code and algorithm descriptions are included in the appendix.

开挖卸荷条件下含多条结构面硬岩巷道的破坏特性

Natural geological structures in rock (e.g., joints, weakness planes, defects) play a vital role in the stability of tunnels and underground operations during construction. We investigated the failure characteristics of a deep circular tunnel in a rock mass with multiple weakness planes using a 2D combined finite element method/discrete element method (FEM/DEM). Conventional triaxial compression tests were performed on typical hard rock (marble) specimens under a range of confinement stress conditions to validate the rationale and accuracy of the proposed numerical approach. Parametric analysis was subsequently conducted to investigate the influence of inclination angle, and length on the crack propagation behavior, failure mode, energy evolution, and displacement distribution of the surrounding rock. The results show that the inclination angle strongly affects tunnel stability, and the failure intensity and damage range increase with increasing inclination angle and then decrease. The dynamic disasters are more likely with increasing weak plane length. Shearing and sliding along multiple weak planes are also consistently accompanied by kinetic energy fluctuations and surges after unloading, which implies a potentially violent dynamic response around a deeply-buried tunnel. Interactions between slabbing and shearing near the excavation boundaries are also discussed. The results presented here provide important insight into deep tunnel failure in hard rock influenced by both unloading disturbance and tectonic activation.

Consideration of maximum impact force design for a rock shed against dry granular flow

This paper focuses on the estimation of the maximum impact force of dry granular flow upon a rock shed using a coupled discrete element method (DEM) and finite element method (FEM). The dry granular flow is modeled as an assembly of discrete particles, and the rock shed is modeled by applying the FEM. The coupled DEM–FEM approach calibrated with a small-scale physical experiment is used to simulate the movement of a dry granular flow impacting the rock shed. Full-scale numerical modeling based on the field model is constructed to estimate the maximum impact force of dry granular flow on a rock shed. Based on the numerical results, three key stages of the impact process are identified: startup streams slippery, impact, and pile-up. The sensitivities of bulk density, impact height, slope angle, cushion thickness, and friction coefficient to the maximum impact force are 1, 0.63, 2.68, 0.09, and 0.73, respectively, in the benchmark model, and the parameters with high sensitivities should be given priority in the design of rock sheds. Moreover, an evaluation formula of maximum impact force is obtained and based on the numerical results and Buckingham’s principle.

Simulation model of loading bin bottom by bulk material

The trend of modern times is to use the increasingly more advanced technology of design, research and validation of transport, handling, storage and treatment processes using simulation methods. Programs used take advantage of computational algorithms that determine a large variety of different parameters. To extend the applicability of these programs, collaborative plug-ins (systems) are created that allow two or more simulations, analytical programs and methods to work together. In this study the cooperative plug-ins are utilised in an application dealing with the issues caused by Janssen forces/pressures of bulk material and deformation effects acting on the bottom of a bin. An examination of such issues includes observing a change in the position of a measuring plate due to the deformation of a force sensor placed at an outlet of an innovative prototype for measuring deformation effects. The experiment was evaluated and validation of discrete element method (DEM) simulation created; the force effects acting on the bottom of the bin were then transferred to a finite element method (FEM) analysis. This was followed by strength analysis of the force sensor deformation located under the outlet of the bin. A comparison was made between a real experiment and simulations that consisted of filling the bin with bulk material. Force reactions occurring at the bottom of the bin and the change of the position of the measuring plate due to the deformation of the force sensor were observed. The results show a low percentage deviation of the simulation from the real experiment. The maximum percentage deviation of the simulation from the real measurement expressed by the change of the measuring plate position due to the deformation of the force sensor is 3.70% and 0.23% when the forces acting on the measuring plate are compared using DEM. The results confirmed the assumption that the coupled DEM and FEM simulation is suitable for this type of engineering tasks. Application of the above mentioned DEM simulation and FEM analysis appears to be a universal tool for designing, modifying or upgrading of equipment for transporting, treatment and storing bulk material and includes equipment where the active member comes into contact with bulk material.

Combination of an adaptive remeshing technique with a coupled FEM–DEM approach for analysis of crack propagation problems

This paper presents an enhanced coupled approach between the finite element method (FEM) and the discrete element method (DEM) in which an adaptive remeshing technique has been implemented. The remeshing technique is based on the computation of the Hessian of a selected nodal variable, i.e. the mesh is refined where the curvature of the variable field is greater. Once the Hessian is known, a metric tensor is defined node-wise that serves as input data for the remesher (MmgTools) that creates a new mesh. After remeshing, the mapping of the internal variables and the nodal values is performed and a regeneration of the discrete elements on the crack faces of the new mesh is carried out. Several examples of fracturing problems using the enhanced FEM–DEM formulation are presented. Accurate results in comparison with analytical and experimental solutions are obtained.

An adaptively coupled DEM–FEM algorithm for geometrical large deformation analysis of member structures

An adaptively coupled discrete element method (DEM)–finite element method (FEM) algorithm is proposed to utilize the respective DEM and FEM advantages. The key problems of the algorithm, such as meeting consistency requirements, determining the adaptive criterion, transferring information between the DEM and FEM and dynamic coupled interface processing, are examined in detail. The adaptively coupled algorithm scheme is formulated. The proposed algorithm is subsequently verified by examples. In the algorithm, the identification of large deformation regions is an automatic process, and the DEM and FEM calculation domains can be changed interactively in every load step in real time according to the structural response. When the response of an arbitrary element in the FEM domain exceeds the predetermined adaptive criterion, the element will be moved to the DEM domain and analysed using the DEM. Similarly, when the response of an arbitrary element in the DEM domain is smaller than the predetermined adaptive criterion, the element will be moved to the FEM domain and analysed using the FEM. The transition of elements between the two domains achieves the objective of using the DEM for large deformation regions and the FEM for small deformation regions.

Elastic properties of particle-reinforced composites containing nonspherical particles of high packing density and interphase: DEM–FEM simulation and micromechanical theory

The physical and morphological properties of particles and interfaces can seriously impact the whole mechanical behavior of particle-reinforced composites. In this work, we devise a robust coupling model of the discrete element method (DEM) and the finite element method (FEM) to numerically investigate the effective elastic moduli of particle-reinforced composites consisting of elliptical particles of high packing density, compliant interfaces and homogeneous matrix. In the numerical model, a novel parametric equation for the topological geometry of an interface that is treated as an interphase model is formulated to realize a compliant (penetrable) layer with a constant finite thickness coated surrounding each elliptical particle. Additionally, a convenient strategy is implemented to cope with periodic boundary conditions containing numerous particles. On the other hand, we also propose a micromechanical theoretical framework to derive the effective elastic properties of such three-phase composites by incorporating the fraction of compliant interfaces that is theoretically computed by using the statistical geometry of composites. It is shown that our numerical and theoretical models lead to the prediction of elastic moduli of particle-reinforced composites with nonspherical particles of high packing density to a reasonable accuracy by comparing with available experimental data. Moreover, utilizing the proposed models, we systematically investigate the influence of the characteristics of particles and interphase such as the high packing density and geometries of elliptical particles, and interphase fraction, thickness and stiffness on the elastic moduli of particle-reinforced composites. We find that these physical characteristics play significant roles in determining the mechanical behavior of composites, suggesting that the properties of such materials can be tailored via proper composites engineering and design.

DEM–FEM analysis of soil failure process via the separate edge coupling method

SummaryThe concurrent multiscale method, which couples the discrete element method (DEM) for predicting the local micro‐scale evolution of the soil particle skeleton with the finite element method (FEM) for estimating the remaining macro‐scale continuum deformation, is a versatile tool for modeling the failure process of soil masses. This paper presents the separate edge coupling method, which is degenerated from the generalized bridging domain method and is good at eliminating spurious reflections that are induced by coupling models of different scales, to capture the granular behavior in the domain of interest and to coarsen the mesh to save computational cost in the remaining domain. Cundall non‐viscous damping was used as numerical damping to dissipate the kinetic energy for simulating static failure problems. The proposed coupled DEM–FEM scheme was adopted to model the wave propagation in a 1D steel bar, a soil slope because of the effect of a shallow foundation and a plane‐strain cone penetration test (CPT). The numerical results show that the separate edge coupling method is effective when it is adopted for a problem with Cundall non‐viscous damping; it qualitatively reproduces the failure process of the soil masses and is consistent with the full micro‐scale discrete element model. Stress discontinuity is found in the coupling domain. Copyright © 2017 John Wiley & Sons, Ltd.