Calibration Of DEM Model Parameters For Coal Particles And Research On Relationships Between Macro And Micro Parameters

The method of numerical simulation has been used widely in these studies of mechanized coal mining process and transportation,especially the discrete element method(DEM),which can take discrete characteristics of coal into account,has been used to study the interaction between coal mine machinery and coal rock.Simulation results can provide technical guidance for the structure design of coal mining machinery and the selection of matching equipment.However,the accuracy of simulation results depends on the DEM parameters of particle model.At present,there are few studies on the calibration of simulation parameters for coal particles.In order to simulate actual working conditions more accurately,this paper studied the calibration of DEM model parameters for coal particles and relationships between macro and micro parameters.From the perspective of coal bulk fluidity,taking accumulation angle as evaluation index,designs of Plackett-Burman(PB)test and single factor tests were carried out for contact parameters of coal particle model.The significance and significance ranking of each contact parameter on accumulation characteristics were obtained by analyzing factor variance and single factor sensitivity.Results showed that significance order of each factor on accumulation angle is as follows: coal-coal static friction coefficient > coal-coal rolling friction coefficient > coal-steel static friction coefficient > coal-coal surface energy,while other contact parameters have little effect on accumulation angle,with the influence rate is less than 1%;moreover,the influence of coal-coal static friction coefficient is more significant than that of other parameters.These contact parameters for particle model of dry and wet coal(including two kinds of water content,10% and 15% respectively)were calibrated and verified based on DEM.The specific process was as follows: considering irregular shapes of coal particles,according to the classification of shapes of actual coal particles,three typical models were established using the method of filling spherical particles in EDEM.A series of experiments were carried out to measure the size of coal particles,shear modulus of coal,the density of coal particle,coalcoal recovery coefficient,coal-steel recovery coefficient,coal-steel static friction coefficient and accumulation angle of coal bulk.While parameters that couldn't be measured directly by experiments were calibrated virtually by comparing simulation result with experiment one,first,taking accumulation angle as response index,the regression model between accumulation angle and parameters to be calibrated was established based on Box-Behnken Design(BBD),and variance analysis and optimization of regression model were carried out;then,taking the actual accumulation angle as response value,the optimal parameter combination was obtained by solving the optimized model;finally,from two aspects of the fitting degree of stacking profile curves and the numerical difference of accumulation angles obtained by funnel test and skateboard test,the optimal parameter combination was validated by comparing simulation result with experiment one.Results showed that stacking profile curves conform very well,the numerical difference of accumulation angles of experiment and simulation is less than 4.7%,which shows that those parameters obtained by above calibration method have high reliability.It can provide suitable parameters for follow-up discrete element simulations of the interaction between coal bulk and coal mine machinery.Through experiments,those variations of parameters with water content were studied;through simulations,based on those calibrated parameters of coal particle models with 10% moisture content,the variation of surface energy which is a simulated parameter to characterize the water content,with particle size was obtained as follows,the ratio of surface energy among particles was equal to the inverse ratio of particle size,and the hypothesis of setting surface energy between coal particles under the mixing of different particle sizes was put forward as follows: the surface energy was superposed linearly with the surface energy of each mixed particle size in proportion of particle mass of each size.