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In recent decades, growing efforts have been devoted to coupling the Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM), i.e., CFD-DEM coupling methods, to account for particle–fluid interactions. However, it remains a challenging task for the well-known Immersed Boundary Method (IBM) belonging to the resolved CFD-DEM methods to improve the computational efficiency of large particles occupying several fluid cells and to simulate the interactions between irregularly shaped particles and fluids. In this paper, we present a novel unresolved CFD-DEM method to achieve the end. The main idea of the presented method is to split a large particle into multiple small spherical particles without overlapping using the Bonded-Particle Method (BPM), and simulate the particle–fluid interactions based on each small particle in the context of an unresolved CFD-DEM method. We validate the accuracy and efficiency of the novel method by comparing our numerical results of spherical particles in viscous fluids with those calculated using the IBM and existing experimental data. The presented method is further applied to the irregular large particle–fluid interaction problems, and the numerical results demonstrate the capacity of our method in simulating the motions of nonspherical large particles in the fluid. [ABSTRACT FROM AUTHOR]

A driving technical concern for the automobile industry is their assurance that developed windshield products meet Federal safety standards. Besides conducting innumerable glass breakage experiments, product developers also have the option of utilizing numerical approaches that can provide further insight into glass impact breakage, fracture, and fragmentation. The combined finite-discrete element method (FDEM) is one such tool and was used in this study to investigate 3D impact glass fracture processes. To enable this analysis, a generalized traction-separation model, which defines the constitutive relationship between the traction and separation in FDEM cohesive zone models, was introduced. The mechanical responses of a laminated glass and a glass plate under impact were then analyzed. For laminated glass, an impact fracture process was investigated and results were compared against corresponding experiments. Correspondingly, two glass plate impact fracture patterns, i.e., concentric fractures and radial fractures, were simulated. The results show that for both cases, FDEM simulated fracture processes and fracture patterns are in good agreement with the experimental observations. The work demonstrates that FDEM is an effective tool for modeling of fracture and fragmentation in glass. [ABSTRACT FROM AUTHOR]

The interaction between off-road tires and granular terrain has a great influence on the tractive performance of off-road vehicles. However, the finite element method or the discrete element method cannot effectively study the interaction between off-road tires and granular terrain. The three-dimensional combined finite element and discrete element method is applied to handle this problem. In this study, a calibrated finite element method–discrete element method model is established, in which the finite element model of off-road tire is validated by stiffness tests, while the discrete element model of gravel particles is validated by triaxial compression tests. The calibrated finite element method–discrete element method model can describe the structural mechanics of the off-road tire and the macroscopic mechanical properties of the gravel road. Tractive performance simulations of the off-road tire on gravel road under different slip conditions are performed with the commercial software LS-DYNA. The simulation results are basically corresponded with the soil-bin test results in terms of granular terrain deformation and tractive performance parameters versus the slip rates. Finally, the effects of tread pattern, wheel load, and tire inflation pressure on tractive performance of off-road tire on granular terrain are investigated. It indicates that the calibrated finite element method–discrete element method can be an effective tool for studying the tire–granular terrain interaction and predicting the tractive performance of off-road tire on granular terrain. [ABSTRACT FROM AUTHOR]

Laminated glass has been wildly employed in automobile windshields, modern buildings, etc. thanks to its security and durability performance. A novel 3D adaptive combined DE/FE algorithm is proposed to research its impact fracture mechanical properties if the fracture region is small relative to a specimen while the cracks are propagating at a random position. The proposed method can automatically convert the distorted finite elements into the spherical discrete elements during simulating the impact fracture of laminated glass. In this method a system is completely discretized into the finite elements at the initial moment without any discrete element existing until part of the finite elements becoming severely deformed. Subsequently each finite element, whose maximum tensile stress exceeds a user-specified conversion criterion, is converted into eight spherical discrete elements. At the same time the system is fragmented into two subdomains, the finite element (FE) and the discrete element (DE) subdomains. An extrinsic cohesive fracture model is adaptively adopted only in the DE subregion to capture the crack propagation when the normal stress between the DEs equals or exceeds the cohesive strength. The impact fracture of a glass beam is simulated by the adaptive algorithm and the discrete element method, respectively. Beside of the micro-cracks and cohesive zone, almost the same crack patterns are captured by both the numerical methods. Fortunately, the efficiency of the proposed method is much higher (10 times in this case) than that of the pure DEM. A satisfactory agreement of the simulation results certified the feasibility and effectiveness of such an adaptive algorithm. Finally, the impact fracture simulation is performed by the adaptive algorithm on a laminated glass beam which has the same size as the experimental specimens. Besides of the differences on the cracks occurrence and propagation angle, a similar agreement of the fracture patterns is observed as the experimental results. The common conclusions on the role of PVB interlayer can be obviously obtained by analyzing the simulation results, the same by analyzing the experimental ones. The proposed method is hopeful to be employed to analyze the impact fracture of an automobile windshield subjects to the head impact for the protection of pedestrians safety, the traffic accident reconstruction and the structural optimization of windshield. [ABSTRACT FROM AUTHOR]

The interaction simulations between particles and structures are often performed in the context of the combined discrete-finite element (DEM-FEM) method, where an efficient, robust and accurate contact algorithm for challenging contact problems is essential. A three-dimensional (3D) discrete and finite element contact algorithm, named ZGL here, has been proposed in our research group (Zang, M.Y. et al., 2011. A contact algorithm for 3D discrete and finite element contact problems based on penalty function method. Comput. Mech. 48, 541–550.). Despite being quite well-established, ZGL algorithm may lack efficiency, robustness and accuracy in certain situations, e.g., when special mesh pattern is applied. However, since such cases are readily to appear in practice engineering application, an algorithm named DZCell is developed to resolve these issues and thus significantly applicable to challenging contact problems. The proposed DZCell algorithm includes an improved global phase to directly find the potential segments rather than the nearest node for discrete elements as contact counterparts. Furthermore, both the memory cost and time consumption of this algorithm are linear, and the algorithm is readily to extend to parallel computing. Several numerical examples demonstrate the achievable improvements in terms of efficiency, robustness and accuracy for 3D contact analysis and validate the capability of the DZCell algorithm in the granular science and mechanical engineering. [ABSTRACT FROM AUTHOR]

The combined finite-discrete element method takes the advantages of both the finite element (FE) method and the discrete element (DE) method, but a coupling approach is required for effective combination of the two methods. In this paper, a novel coupling approach is proposed by means of ghost particles. The entire domain is decomposed into a FE- and a DE-subdomain, and ghost particles are constructed inside the interface FE domain to connect with the DE domain in a consistent interaction manner as the DE method. A novel one-step back strategy is proposed to overcome the incompatibility of degree of freedoms between FE nodes and DE particles from a numerical sense. The coupling approach is very simple to implement and its effectiveness is validated by numerical examples. [ABSTRACT FROM AUTHOR]

The mixed mode (I/II) fracture of concrete is investigated by using a four-point combined discrete and finite elements method. The potential fracture zone is simulated by the discrete elements (DEs) and the other zone by the finite elements (FEs). A cohesive fracture model is employed to simulate the brittle fracture only in the DE subregion. Mesh-size independency of the cohesive fracture model subjected to the DE is carefully investigated with a simple case. Subsequently, the mixed mode fracture behaviors of two simple concrete specimens are simulated and the simulation results achieve good agreements with the other simulations and experimental results. [ABSTRACT FROM AUTHOR]

When applying the combined finite-discrete element method for analysis of dynamic problems, contact is often encountered between the finite elements and discrete elements, and thus an effective contact treatment is essential. In this paper, an accurate and robust contact detection algorithm is proposed to resolve contact problems between spherical particles, which represent rigid discrete elements, and convex quadrilateral mesh facets, which represent finite element boundaries of structural components. Different contact scenarios between particles and mesh facets, or edges, or vertices have been taken into account. For each potential contact pair, the contact search is performed in an hierarchical way starting from mesh facets, possibly going to edges and even further to vertices. The invalid contact pairs can be removed by means of two reasonable priorities defined in terms of geometric primitives and facet identifications. This hierarchical contact searching scheme is effective, and its implementation is straightforward. Numerical examples demonstrated the accuracy and robustness of the proposed algorithm. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: A four-point combined DE/FE algorithm is proposed to constrain the rotation of a discrete element about its linked point and analyze the cracks propagation of laminated glass. In this approach, four linked points on a discrete element are combined with four nodes of the corresponding surface of a finite element. The penalty method is implemented to calculate the interface force between the two subdomains, the finite element (FE) and the discrete element (DE) subdomains. The sequential procedure of brittle fracture is described by an extrinsic cohesive fracture model only in the DE subdomain. An averaged stress tensor for granular media, which is automatically symmetrical and invariant by translations, is used to an accurate calculation of the averaged stress of the DE. Two simple cases in the elastic range are given to certify the effectiveness of the combined algorithm and the averaged stress tensor by comparing with the finite element method and the mesh-size dependency of the combined algorithm and the cohesive model is also investigated. Finally, the impact fracture behavior of a laminated glass beam is simulated, and the cracks propagation is compared with experimental results showing that the theory in this work can be used to predict some fracture characteristics of laminated glass. [Copyright &y& Elsevier]

A freely combined three-dimensional (3D) discrete and finite element (FE) algorithm is developed. The algorithm, which is based on the method combining the discrete element (DE) and the corresponding node of the FE proposed by Lei and Zang, treats each combined point on the facet of the FE as the corresponding node of the method. This new algorithm includes global search, local search and the combined force calculation processes. The combined force between the DE and FE is processed by using a penalty function method. Following that, the corresponding numerical code is implemented into the in-house developed code, a dynamic explicit DE/FE code named CDFP. To test the accuracy of the proposed algorithm and the corresponding numerical code, the vibration process of two beams under dynamic force and the vibration process of two glass plates under impact of rigid sphere are simulated in elastic range. By comparing the results with those calculated by using LS-DYNA, it is shown that they agree with each other very well. [ABSTRACT FROM AUTHOR]

A new contact search algorithm named virtual-surface contact algorithm is developed for dealing with the interaction between spherical discrete elements (DEs) and finite elements (FEs). The basic idea of the contact algorithm is forming a virtual surface above the FE surface. Therefore, the contact problem between DE and FE surface is treated as that between the DE mass center and the virtual surface. Then, the projection of the DE mass center on the virtual surface is determined using spatial area coordinates without solving nonlinear equations and the contact force is processed by using a penalty function method. So, the quick contact searching and accurate evaluation of penetration have been achieved. Finally, the accuracy of this algorithm is investigated via four numerical examples. [ABSTRACT FROM AUTHOR]