Calibration of DEM simulation: unconfined compressive test and Brazilian tensile test

We simulate rock fracture using ESyS-Particle, which is a 3-D Discrete Element Model developed for modeling geological materials. Two types of simulations are carried out: Unconfined Compressive Test (UCT) and Brazilian Tensile Test (BTT). The results are compared to laboratory tests. Model parameters are determined on the basis of theoretical studies on the elastic properties of regular lattices and dimensionless analysis. The fracture patterns and realistic macroscopic strength are well reproduced. Also the ratio of the macroscopic strength of compression to the tensile strength is obtained numericall

A new algorithm to model the dynamics of 3-D bonded rigid bodies with rotations

In this paper we propose a new algorithm to simulate the dynamics of 3-D interacting rigid bodies. Six degrees of freedom are introduced to describe a single 3-D body or particle, and six relative motions and interactions are permitted between bonded bodies. We develop a new decomposition technique for 3-D rotation and pay particular attention to the fact that an arbitrary relative rotation between two coordinate systems or two rigid bodies can not be decomposed into three mutually independent rotations around three orthogonal axes. However, it can be decomposed into two rotations, one pure axial rotation around the line between the centers of two bodies, and another rotation on a specified plane controlled by another parameter. These two rotations, corresponding to the relative axial twisting and bending in our model, are sequence-independent. Therefore all interactions due to the relative translational and rotational motions between linked bodies can be uniquely determined using such a two-step decomposition technique. A complete algorithm for one such simulation is presented. Compared with existing methods, this algorithm is physically more reliable and has greater numerical accuracy

A numerical simulator of outbursts of coal and gas

An outburst of coal and gas in underground coal mines may occur when stress condition and coal failure combine with rapid gas desorption. A mechanical and fluid coupled numerical simulator, SimBurst, has been developed to simulate the initiation process of the outburst, as a first step to model the whole process of the outburst. This paper describes the simulator and a simple model set up with the simulator to model the initiation of an outburst in roadway excavation to illustrate the methodology and approach with the SimBurst. The model simulated the basic features of an outburst initiation process, including coal deformation, pore pressure and principal stress vector redistribution, and yield and tensile failure zone of coal

A fully coupled solid and fluid model for simulating coal and gas outburst with DEM and LBM

Tyt. z nagł.Bibliogr. s. 383-[384].W niniejszej publikacji prezentujemy w pełni zintegrowany kod oddziaływania pomiędzy cieczą a ciałem stałym, opracowany do modelowania całego procesu wyrzutów węgla i gazu. Metoda elementów dyskretnych stosowana jest do modelowania deformacji i pęknięcia ciała stałego, podczas gdy metoda siatkowa Boltzmanna - do modelowania przepływu cieczy, w tym przepływu swobodnego i przepływu zgodnie z prawem Darcy'ego. Te dwie metody połączone są w procesie dwukierunkowym: część stała zapewnia warunki ruchomej granicy rozdziału, przenosząc pęd do cieczy, a ciecz wywiera opór na ciele stałym. Desorpcja gazu występuje na granicy oddziaływania pomiędzy cieczą a ciałem stałym, a do rozproszenia gazu dochodzi w kodzie ciała stałego, gdzie cząsteczki traktowane są jako materiał porowaty. Prowadzone są wstępne symulacje w celu sprawdzenia poprawności kodu.In this paper, we present a fully coupled solid-fluid code which is developed to model the whole process of coal and gas outbursts. The Discrete Element Method is used to model the deformation and fracture of solid, while Lattice Boltzmann Method models fluid flow, including free flow and Darcy flow. These two methods are coupled in a two-way process: the solid part provides a moving boundary condition and transfers momentum to the fluid, and the fluid exerts a dragging force to the solid. Gas desorption occurs at solid-fluid boundary, and gas diffusion is implemented in the solid code where particles are assumed as porous material. Some preliminary simulations are carried out to validate the code.Dostępny również w formie drukowanej.SŁOWA KLUCZOWE: wyrzut węgla i gazu, oddziaływanie ciecz-ciało stałe, metoda elementów dyskretnych, metoda siatkowa Boltzmanna. KEYWORDS: coal and gas outbursts, solid-fluid coupling, Discrete Element Method, Lattice Boltzmann Method

Modeling wing crack extension: Implications for the ingredients of discrete element model

In this study, we investigate what basic mechanisms a Discrete Element Model should have in order to reproduce the realistic wing crack extension, a widely observed phenomenon in uni-axial compression of brittle material with pre-existed crack. Using our Discrete Element Model—the Lattice Solid Model, we study how cracks propagate when different force-displacement laws are emplyed. Our results suggest that the basic features of crack propagation observed in laboratories cannot be reproduced under the following circumstances: 1) When only normal forces between two bonded particles exist and particle rotation is prohibited; 2) normal and shear stiffnesses are present and particle rotation is prohibited; 3) normal, shear stiffnesses and particle rotation are present and bending (rolling) stiffness is absent. Only when normal, shear and bending stiffness exist and particle rotation is permitted, is it possible to reproduce laboratory tests. We conclude that particle rotations and rolling resistance play a significant role and cannot be neglected while modeling such phenomenon. The effects of friction in the crack plane and confining pressure on extension of the cracks are also discussed

Macroscopic elastic properties of regular lattices

In this paper we study analytically the elastic properties of the 2-D and 3-D regular lattices consisting of bonded particles. The particle-scale stiffnesses are derived from the given macroscopic elastic constants (i.e. Young's modulus and Poisson's ratio). Firstly a bonded lattice model is presented. This model permits six kinds of relative motion and corresponding forces between each bonded particle pair. By comparing the strain energy distributions between the discrete lattices and the continuum, the explicit relationship between the microscopic and macroscopic elastic parameters can be obtained for the 2-D hexagonal lattice and the 3-D hexagonal close-packed and face-centered cubic structures. The results suggest that the normal stiffness is determined by Young's modulus and the particle size (in 3-D), and that the ratio of the shear to normal stiffness is related to Poisson's ratio. Rotational stiffness depends on the normal stiffness, shear stiffness and particle sizes. Numerical tests are carried out to validate the analytical results. The results in this paper have theoretical implications for the calibration of the spring stiffnesses in the Discrete Element Method

The ESys_Particle: A new 3D discrete element model with single particle rotation

In this paper, the Discrete Element Model (DEM) is reviewed, and the ESyS_Particle, our new version of DEM, is introduced. We particularly highlight some of the major physical concerns about DEMs and major differences between our model and most current DEMs. In the new model, single particle rotation is introduced and represented by a unit quaternion. For each 3-D particle, six degrees of freedom are employed: three for translational motion, and three for orientation. Six kinds of relative motions are permitted between two neighboring particles, and six interactions are transferred, i.e., radial, two shearing forces, twisting and two bending torques. The relative rotation between two particles is decomposed into two sequence-independent rotations such that all interactions due to the relative motions between interactive rigid bodies can be uniquely determined. This algorithm can give more accurate results because physical principles are obeyed. A theoretical analysis about how to choose the model parameters is presented. Several numerical tests have been carried out, the results indicate that most laboratory tests can be well reproduced using our model

A finite deformation method for discrete modeling: particle rotation and parameter calibration

We present a finite deformation method for 3-D discrete element modeling. In this method particle rotation is explicitly represented using quaternion and a complete set of interactions is permitted between two bonded particles, i.e., normal and tangent forces, rolling and torsional torques. Relative rotation between two particles is decomposed into two sequence-independent rotations, such that an overall torsional and rolling angle can be distinguished and torques caused by relative rotations are uniquely determined. Forces and torques are calculated in a finite deformation fashion, rather than incrementally. Compared with the incremental methods our algorithm is numerically more stable while it is consistent with the non-commutativity of finite rotations. We study the macroscopic elastic properties of a regularly arranged 2-D and 3-D lattice. Using a micro-to-macro approach based on the existence of a homogeneous displacement field, we study the problem of how to choose the particle-scale parameters (normal, tangent, rolling and torsional stiffness) given the macroscopic elastic parameters and geometry of lattice arrangement. The method is validated by reproducing the wing crack propagation and the fracture patterns under uniaxial compression. This study will provide a theoretical basis for the calibration of the DEM parameters required in engineering applications