A combined experimental and numerical approach is proposed in this study for the characterisation of the mechanical behaviour of foamed geopolymer concretes. Advanced experimental techniques ...employing X-Ray CT give both microstructures and mechanical responses of a range of geopolymer concretes with varying densities. In parallel with this, a numerical modelling technique based on the discrete element method (DEM) is developed for explicit descriptions of air-void distribution, while the mortar binder is described at the micro/meso scale with cohesive behaviour. The calibrated and validated DEM model is then used to systematically study the effects of air-void content, air-void distribution and microstructural parameters, including particle size and porosity on the compressive strength of foamed concretes. A non-linear relationship between the compressive strength and porosity of foamed concretes is found from DEM simulations, which are consistent with our experimental findings and existing strength-porosity models. Furthermore, it is found that the air-void distribution has a significant influence on the compressive strength of foamed concretes, while the micro-void structure has less effect on the loading bearing capacity of the material. The proposed combined approach demonstrates the tight correlations between experimental and numerical techniques in characterising the mechanical behaviour of foamed concretes for practical design purposes.
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•A combined experimental-numerical approach can further the characterisation of foamed concretes with varying densities.•Porosity and types of air voids in a foamed concrete can have a profound effect on its mechanical properties.•DEM analyses indicate that local pore collapse and macro shear failure compete to govern the response of foamed concrete.•DEM simulations could provide consistent numerical data for the development of a better strength-porosity model.
Hydraulic fracturing has proven to be an efficient technique to enhance production in unconventional reservoirs. Since heterogeneity is commonplace in reservoir rocks, it is vital to investigate the ...influence of rock heterogeneity on hydraulic fracture propagation. Here, based on the combined finite-discrete element method (FDEM) and cohesive zone model, two series of numerical models with uniformly distributed and Weibull-distributed elastic modulus of rock are assembled, respectively. The comparison with the theoretical solution demonstrates the reliability of the simulation models in both the toughness-dominated regime (TDR) and viscosity-dominated regime (VDR). The parameter analysis demonstrates the rationality of parameters for cohesive elements. The results show that the previous theoretical equations can be used as a preliminary evaluation of simulation parameters. The effects of different parameters such as element size, Weibull distribution type, and far-field stress on hydraulic fracture length, fluid pressure, maximum fracture aperture, and the final fracture morphology are evaluated. The results demonstrate that the distribution type of rock elastic modulus has a significant impact on the hydraulic fracture propagation in both TDR and VDR. The “jump” phenomena have been observed in TDR caused by high fracture toughness. The displacement of fracture location and asymmetrically dynamic propagation are affected by the distribution of rock elastic modulus. Besides, the hydraulic fracture propagation in TDR is more susceptible to element size, the distribution of rock elastic modulus, and far-field stress than that in VDR. This research may shed light on the development of hydraulic fracturing technology in tight reservoirs.
This paper presents a novel implementation of a hydro-mechanically coupled, finite-discrete element method (FDEM) optimized to exploit the computing parallelism of graphics processing units (GPUs). A ...co-processing approach is adopted with the control loop of FDEM executed serially on the CPU and compute-intensive tasks off-loaded to the GPU. A benchmarking study indicates speedups of up to 100× compared to sequential CPU execution. The implementation is validated by comparing 3D laboratory-scale rock fracturing simulations with experimental results. The effectiveness of the approach for practical rock engineering applications is demonstrated through the back analysis of a slope in a fractured rock mass.
This paper describes the implementation and advantages of grain based modelling (GBM) in the combined finite-discrete element method (FDEM) to study the mechanical behaviour of crystalline rocks. GBM ...in FDEM honours grain petrological properties and explicitly models grain boundaries. The simulation results demonstrated that GBM in FDEM predicted more realistic microscopic and macroscopic response of rocks than conventional FDEM models. The explicit modelling of crack boundaries captured microscopic failure transition from along grain boundaries to coalescence along the shear band, dominated by intraphase cracks. This novel framework presents a gateway into further understanding the behaviour of crystalline rocks and granular minerals.
The coupling between fluid and granular materials is commonly encountered in nature and engineering practice. Moreover, the shape of granular materials in practical applications is normally ...non-spherical. Therefore, investigating the particle-fluid systems containing non-spherical particles for a deeper understanding of their underlying mechanisms and then for improving the performance of the related industrial processes should be an urgent necessity for practical needs. For investigating the intricate flow behaviors of particle-fluid systems, the numerical simulation method of coupling DEM (Discrete Element Method) with CFD (Computational Fluid Dynamics) has been widely recognized as a promising tool, and many efforts have been devoted to the CFD-DEM investigations of non-spherical particles in recent years. This paper aims to review development of the CFD-DEM investigations for non-spherical particles from theoretical models to applications in recent six years. It primarily represents three principal aspects: the theoretical foundations of DEM for modeling non-spherical particles, the coupling methodologies between CFD and DEM and the use of the non-spherical CFD-DEM coupling model in different applications involving particle-fluid flows. In the end, the conclusions and the outlooks for future investigations are given.
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Discrete element method (DEM) is widely used in industrial and environmental applications for numerical modelling of mixing and transport of lumpy materials. However, it is computationally expensive ...for a large number of particles. To reduce this cost, we have implemented a revision approach for traditional coarse graining as proposed by Bierwisch et al. J. Mech. Phys. and Solids, 57, 31, 2009. We introduce the use of variable coarse grain ratio instead of the uniform one to provide faster computation compare to the traditional coarse graining giving more flexibility to reduce the number of particles. To overcome the problem of violation of geometrical similarity derived from this method, we implement a correction parameter to measure overlap distance between parcels containing small and large particles. The results show fairly good agreement between the revision model, reference DEM simulations and the experimental data of W. Sui et al. Nature Sci. Reports, 7, 8, 2017.
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•Introducing a faster alternative tool for poly disperse granular flow simulation.•The simulation results are validated with respect to experimental data.•Better accuracy in particle distribution compare to traditional coarse graining.•Providing a prediction method for the revision parameter.
This paper proposes a new 2D continuous-discontinuous heat conduction model to simulate heat transfer and thermal cracking in fractured quasi-brittle materials by combining with mechanical ...calculations of the Finite-Discrete Element Method. By updating the sharing relationship of the nodes at the cracks, the model can accurately predict the temperature evolution, crack propagation and considers the effect of cracking on heat conduction. We verified the correctness of the continuous-discontinuous heat conduction model using examples of heat conduction in a continuum, media with single or multiple cracks, thermal deformation problems, and cracking induced by temperature gradient and thermal mismatch. The numerical results indicate that the continuous-discontinuous heat conduction model well reflects the effect of crack propagation on heat conduction and the discontinuity of temperature across the cracks. It provides a powerful tool for studying the whole process and mechanism analysis of thermal cracking of quasi-brittle materials.
Rock slope failure is particularly detrimental to the safety of human life and engineering infrastructure. The pre-existing discontinuities in the jointed rock slopes play a key role in the slope ...stability, and the destabilization process often related to the complex interaction between the discontinuities and the intact rock bridge. Understanding the failure mechanism and accurately predicting the failure process are essential for the safety of jointed rock slopes. In this paper, a jointed rock slope analysis model (Y-slopeJ) is developed to evaluate the stability state and simulate the progressive failure process of jointed rock slopes based on the combined finite-discrete element method (FDEM). The accuracy and robustness of the proposed model are validated by numerical tests. Then this Y-slopeJ is applied to investigate the failure mechanism and failure process of rock slopes with various types of discontinuities, with an emphasis on crack initiation, propagation and coalescence. This work proposed a promising tool in understanding and predicting the progressive failure process of jointed rock slopes.
In the current study, the mixing of bi-disperse particles in a horizontal paddle mixer was investigated through the sampling experimental technique and discrete element method (DEM). LIGGGHTS ...software was employed as the DEM solver. A close agreement between the simulation and experimental data was observed. Using the calibrated DEM model, the influence of some operating parameters such as impeller rotational speed, vessel fill level, particle number ratio (rn) and particle loading arrangement on the mixing quality was analyzed. A detailed analysis of this specific type of mixer comprising bi-disperse particles has not been reported in literature. It was found that rn had the most significant effect on the mixing performance. It was also found that the diffusion mechanism was dominant over the convection mechanism and in the cases in which the values of the diffusion coefficients of 5 mm and 3 mm particles were close, the best mixing performance was achieved.
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•The performance of a paddle blender comprising bi-disperse particles was studied.•The particle number ratio had the most decisive effect on mixing quality.•The particle loading arrangement did not play a significant role on mixing quality.•The diffusion mechanism was the dominant mechanism in the mixing system.•The mixing system has a low segregation tendency for the operating conditions used.
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