Discrete Element Model Parameters Research Articles

Modelling mineral slurries using coupled discrete element method and smoothed particle hydrodynamics

Slurry in wet grinding mills is critical for transporting fine progenies out of the system to downstream floatation process. It is commonly modelled as Newtonian fluids when simulating grinding mills with numerical tools. However, rheology of the slurry exhibits shear thinning non-Newtonian behaviours. This study aims to investigate the non-Newtonian characteristics of mineral slurries both experimentally and numerically. Non-Newtonian smoothed particle hydrodynamics (SPH) and its coupling to discrete element modelling (DEM) framework was initially described. Non-Newtonian rheology of a copper slurry with various solids concentrations was determined experimentally by a rotary viscometer. SPH-DEM modelling of the viscometry test was conducted with both Newtonian and Power-law non-Newtonian settings in fluid phase, and comparisons were performed. Results suggested that the non-Newtonian SPH based method better reflects actual rheological behaviours of the slurry. In addition, DEM parameters exhibited limited impacts on rheology of the solids-liquid mixture, particularly at low solids concertation and high shear rate states. The findings suggested that the non-Newtonian based SPH-DEM method should be used to more accurately model the slurry flows within grinding mills.

An Effective Inverse Procedure for Identifying DEMParameters of Rock-Like Materials

This study aims to identify discrete element model parameters of rock-like materials. An inverse procedure is developed to determine the discrete element model parameters from experimental measurements. This involves the solution of an inverse problem through minimizing the misfit function which describes the error between numerical computation and experiment by an optimization procedure. In this procedure, the discrete element method is adopted as the numerical calculation method of the forward problem. The orthogonal experimental design is used for parameter sensitivity analysis. Besides, the approximation model with radial basis function is adopted instead of the actual calculation model to reduce the time of forward calculation. The ant-colony optimization algorithm is employed as the inverse operator. Therefore, the parameters of the discrete element model are optimized by this procedure. The three-point bending experiment with discrete element simulation is provided to verify the validity and accuracy of the inversion results. The results indicate that it can rapidly obtain the available and reliable model parameters just through a few sets of experimental data. As a result, this inverse procedure can be applied more widely to parameter identification of the discrete element model for brittle materials.

Discrete element modeling of cultivator sweep-to-soil interaction: Worn and hardened edges effects on soil-tool forces and soil flow

Simulation of tool-to-soil interaction provides opportunities to accelerate new equipment design and evaluate performance of tillage tools. Simulation based evaluation of worn tillage tools performance on soil flow has not been done. Discrete Element Modelling (DEM) has a potential to simulate worn tool to soil interaction problems, where worn tools CAD can be generated using 3D scanning. The DEM parameters of Hertz-Mindlin with Parallel Bond model were calibrated to match draft force and soil failure zone measured from a tool bar moving at 0.22 m/s and 38 mm cutting depth. The draft force and soil forward failure zone were predicted at 7% and 24% relative errors compared to measured values, respectively. Using the optimized DEM soil model, the interaction of three 3D reconstructed sweeps (new sweep, carbide treated-worn, untreated-worn) with soil were simulated to compare their geometric wear dimensional loss, performance on soil forces and soil flow. Results showed that the carbide treated-worn sweep had similar soil draft force and soil forward failure distance as the new sweep. The untreated-worn sweep showed lower vertical force (less suction) and its wing induced soil failure zone (front and lateral) showed poor soil tilth quality compared with the carbide treated-worn sweep and the new sweep.

Studying On The Parameters Of Bond-model In DEM For Asphalt Mixture

The discrete element method used to simulate asphalt mixture’s performance can fully consider the effect of interaction between particles, but the key to use discrete element method is to select reasonable parameters of contact constitutive model. Using 2D and 3D discrete element method to establish asphalt mixture splitting test model which adopting contact-bond method between particles, the influence of particle stiffness and bond strength on the simulation results are analyzed. It is found that the straight slope of the load-deformation curve is mainly determined by the stiffness parameter and the peak load is determined by the bond strength. Asphalt mixture laboratory splitting test of AC-20 and AC-13 at -10°C, 0°C, 10°C and 20°C are accomplished, then according to the load-deformation curve’s initial slope and peak load, discrete element model parameters are determined. The relationship between load-deformation curve’s initial straight slope and stiffness, peak load and bond strength are concluded on the basis of splitting test results curve.

Calibration of discrete element model parameters: soybeans

Discrete element method (DEM) simulations are broadly used to get an insight of flow characteristics of granular materials in complex particulate systems. DEM input parameters for a model are the critical prerequisite for an efficient simulation. Thus, the present investigation aims to determine DEM input parameters for Hertz–Mindlin model using soybeans as a granular material. To achieve this aim, widely acceptable calibration approach was used having standard box-type apparatus. Further, qualitative and quantitative findings such as particle profile, height of kernels retaining the acrylic wall, and angle of repose of experiments and numerical simulations were compared to get the parameters. The calibrated set of DEM input parameters includes the following (a) material properties: particle geometric mean diameter (6.24 mm); spherical shape; particle density ( $$1220~\hbox {kg m}^{-3}$$ ), and (b) interaction parameters such as particle–particle: coefficient of restitution (0.17); coefficient of static friction (0.26); coefficient of rolling friction (0.08), and particle–wall: coefficient of restitution (0.35); coefficient of static friction (0.30); coefficient of rolling friction (0.08). The results may adequately be used to simulate particle scale mechanics (grain commingling, flow/motion, forces, etc) of soybeans in post-harvest machinery and devices.

Defining the effect of sweep tillage tool cutting edge geometry on tillage forces using 3D discrete element modelling

The energy required for tillage processes accounts for a significant proportion of total energy used in crop production. In many tillage processes decreasing the draft and upward vertical forces is often desired for reduced fuel use and improved penetration, respectively. Recent studies have proved that the discrete element modelling (DEM) can effectively be used to model the soil–tool interaction. In his study, Fielke (1994) [1] examined the effect of the various tool cutting edge geometries, namely; cutting edge height, length of underside rub, angle of underside clearance, on draft and vertical forces. In this paper the experimental parameters of Fielke (1994) [1] were simulated using 3D discrete element modelling techniques. In the simulations a hysteretic spring contact model integrated with a linear cohesion model that considers the plastic deformation behaviour of the soil hence provides better vertical force prediction was employed. DEM parameters were determined by comparing the experimental and simulation results of angle of repose and penetration tests. The results of the study showed that the simulation results of the soil-various tool cutting edge geometries agreed well with the experimental results of Fielke (1994) [1]. The modelling was then used to simulate a further range of cutting edge geometries to better define the effect of sweep tool cutting edge geometry parameters on tillage forces. The extra simulations were able to show that by using a sharper cutting edge with zero vertical cutting edge height the draft and upward vertical force were further reduced indicating there is benefit from having a really sharp cutting edge. The extra simulations also confirmed that the interpolated trends for angle of underside clearance as suggested by Fielke (1994) [1] where correct with a linear reduction in draft and upward vertical force for angle of underside clearance between the ranges of −25 and −5°, and between −5 and 0°. The good correlations give confidence to recommend further investigation of the use of DEM to model the different types of tillage tools.

Discrete element modeling of vibrating tillage tools

Purpose – The analysis of the effect of tool vibrations on the measured and simulated draught forces of cultivator tools. This paper aims to discuss this issue. Design/methodology/approach – Soil bin measurements and discrete element method (DEM)-based simulations. Findings – The soil-tool interaction induced free vibrations of cultivator tools have significant impact on the measured draught force, and the simulations made by using vibrating tools give similar results. Research limitations/implications – Accurate calibration of discrete element model parameters can be done based on the reproduction of the whole Mohr-Coulomb failure line. Draught force ratio – velocity ratio values seem to be independent of tool geometry and soil conditions in case of velocity ratio higher than 2. Practical implications – DEM-based numerical simulations can be used for modeling the effect of tool vibration on the draught force values. During discrete element simulations of soil-tool interaction, the effect of tool vibration may not be neglected. Originality/value – The paper demonstrates that during the discrete element modelling of the soil-tool interaction, the tool vibration phenomenon should not be neglected.

Three-dimensional discrete element modelling (DEM) of tillage: Accounting for soil cohesion and adhesion

Recent studies have shown that the discrete element modelling (DEM) can effectively be used to model the soil-tool interaction if both an appropriate contact model and DEM parameters are used. Ucgul, M., Fielke J.M and Saunders, C. (2014a) Biosystems Engineering. 121: 105–117 showed that hysteretic spring contact model (HSCM) can give accurate predictions of draft and vertical forces for a range of sweep tillage tool geometries operating in a cohesionless soil. In this study a linear adhesion/cohesion model was integrated with the HSCM to model the cohesive behaviour of soil and its interaction with a tillage tool. The proposed contact model was validated with the direct shear tests performed and further validation was achieved via DEM simulation of the interaction between soil and tillage tool tests. The results showed that the suggested contact model can be used to predict both tillage draft and vertical tillage forces for varying speed, operating depth, moisture content and compaction levels. The results also showed that the DEM parameters determined in our earlier paper can be directly used in the suggested model without further re-calibration. It was observed that the soil bulk density has a significant effect on the predicted tillage forces and when the measured wet bulk density was used in the simulations a good correlation with measured forces was able to be achieved. Thus, the method presented has good potential to accurately model tillage forces in a range of soil and operating conditions.

Three-dimensional discrete element modelling of tillage: Determination of a suitable contact model and parameters for a cohesionless soil

Accurate modelling of soil–implement interaction is vital to optimise the design of tillage implements. Discrete element modelling (DEM) is a numerical method used for modelling the mechanical behaviour of granular materials. When DEM is used for tillage the soil is assumed to consist of distinct particles with the interactions between the particles controlled by contact models that are governed by physical laws. In previous three-dimensional (3D) DEM tillage studies the soil particles were assumed as having elastic contacts and the plastic deformation behaviour of the soil particles was not taken into account. Using EDEM software, a non-linear elastic contact model was compared with a linear hysteretic spring contact model that considers the plasticity of the soil. The DEM parameters required to run the simulations were determined from angle of repose and penetration tests, matching the simulation results to test results using a modelled spherical particle with radii of 10 mm. The simulation results of both the non-linear elastic and linear hysteretic spring (plastic) contact models were compared with experimental results from a sweep tillage tool. An improved correlation was obtained between the measured draft and vertical force results using the linear hysteretic spring (plastic) contact model. Further simulations using the linear hysteretic spring (plastic) model showed there was a quadratically increasing trend with particle size from 4 to 10 mm for the parameters of coefficient of restitution of soil–soil, friction of soil–soil and integration time step.

3D DEM tillage simulation: Validation of a hysteretic spring (plastic) contact model for a sweep tool operating in a cohesionless soil

Discrete element modelling (DEM) is a numerical method for examining the dynamic behaviour of granular media. To enable an accurate DEM simulation to be run appropriate determination of the DEM parameters is essential. Ucgul et al. (2014) proposed using a hysteretic spring (linear plastic) contact model and a method of an angle of repose test and penetration tests using a disc and cone to determine appropriate DEM parameters for modelling of soil-tool interactions in a cohesion less soil. In this paper the draft and vertical forces, and the furrow profile for a sweep tool were predicted for varying geometries and speeds. The simulation results were compared to Fielke (1988)’s experimental sweep results for varying width and rake angles. A good correlation was obtained between the predicted and measured tillage forces for both draft and vertical forces (R2=0.95–0.99) with using 10mm radii particles. The DEM simulations were able to be run in under 2h. Whilst the use of 10mm radius particles gave a timely solution and good force predictions the soil flow and resulting furrow profile were less than those measured. Simulations with a 20mm thick layer of 1.5mm radii particles over a base of 10mm radii particles provided a more accurate representation of soil flow and furrow profile but doubled the computation time. The effect of particle size was found to be a result of differences in response by the soil flow to the impact with the tine onto which the sweep blades were mounted. The work also highlighted how multiple tool geometries can be created and simulated to hone in on a critical tool geometry parameter such as rake angle so as to achieve a desired result such as minimum draft force or maximum vertical down force.

Investigation into calibration of discrete element model parameters for scale-up and validation of particle–structure interactions under impact conditions

Discrete element method (DEM) is a popular numerical method used to understand the discontinuous flow of granular materials and optimise the design and operation of equipment. The impingement of granular material on to flat surfaces can involve complex flow dynamics and can be difficult to model using analytical techniques. There are a vast number of industrial applications where particle-to-structure interactions occur such as belt conveyor impact plate transfer stations consisting of a large number of particles and complex particulate behaviour. Classical analytical methods can be used to provide a quantitative description of the flow of granular material through a transfer point in regards to trajectory and velocity distribution but are generally limited to 2-D analysis. DEM methodology has been well established but there is a lack of detailed validation of DEM models to experimental data and methods to calibrate and scale-up DEM models to attain accurate predictions and results. This paper presents a detailed comparative analysis between classical analytical methods and DEM to predict the flow mechanisms associated with the deformation of granular material impacting a flat plate. Results from DEM simulations and analytical models are compared with experimental results from a variable-geometry conveyor transfer facility to validate and evaluate the numerical methods to solve granular flow problems. The study has focused on evaluating the ability to accurately model material discharge trajectories, the velocity of impact from the inflowing stream, the velocity of the material stream after impingement and the resultant forces on the impact plate. Methods to effectively calibrate the DEM material interaction parameters are also presented and evaluated to quantify the calibration methodology. A sensitivity analysis has been conducted to investigate the variation of DEM parameters and contact models on the impact reaction forces and examine effective techniques to scale parameters to reduce computational time and resources.

Parameter Determination of Discrete Element Model of Conditioned Soil by Genetic Neural Network

The inversion method combining the genetic neural network and the discrete element simulation of triaxial tests is firstly described for determining the discrete element model parameters of the conditioned soil. The purpose is to make the error of the simulation curves and the laboratory curves of the triaxial test minimum. The solve approach is the parameters identification based on the genetic neural network. The network training sample is provided by the discrete element simulation. The input sample is the simulation curves of triaxial test, and the output sample is the model parameters. The laboratory triaxial test curves of the conditioned soil are used to determine its model parameters. The simulation curves calculated with the inversed parameters match the laboratory curves well, which illustrate that the discrete element model can accurately predict the deformation characteristics and flow patterns of conditioned soils.