Multi-scale Modeling Method Of Ellipsoidal Particles Based On Discrete Element Method

Particle shape is an important parameter in bulk materials.In recent years,the use of discrete element numerical methods to model non-spherical particles at different scales has attracted extensive attention of researchers.At the micro-scale,in order to obtain micro-mechanical information such as contact and expansion between particles,it is necessary to accurately describe the shape of non-spherical particles.At the macro-scale,due to the limitation of simulation calculation,the accuracy of non-spherical particle model must be neglected as the non-main index to realize the physical phenomena in the massive particle system.Therefore,it is of great engineering and scientific significance to study the discrete element model of non-spherical particles at micro scale and macro scale.In this paper,the non-spherical particulate matter(approximate ellipsoidal particles)after hulling of rice is taken as the research object,and the particle shape of brown rice is modeled on the micro-scale and macro-scale respectively by the multi-sphere filling method and the coarsening method.The feasibility and validity of the ellipsoidal particle modeling method proposed in this study are verified by comparing the numerical simulation and experimental results of static and dynamic accumulation of ellipsoidal particles and shear box experiments.The contents and conclusions of this paper are as follows:(1)Micro-scale modeling method for brown rice particle.First,the brown rice grain is regarded as an ellipsoid,and the lengths of the long axis and the short axis are determined,and geometric modeling is performed by the multi-ball filling method.Secondly,the geometric model of the ellipsoid particles with the filling numbers of 5,7,9,11,13,15 and 17 is obtained by theoretical calculation of the geometrical contour of the particles.Finally,the angle factor of the ellipsoidal particle model with different filling numbers is calculated by numerical simulation.(2)Brown rice particle micro-scale model test.The brown rice particle accumulation test was carried out based on the bottomless cylinder method and the drum method,the static accumulation angle and the dynamic accumulation angle of the brown rice particle were measured.Through the analysis of the accumulation process of brown rice particle,the results show that the grain filling number of brown rice can not predict the simulation precision,and the angle of filling ball can be determined by applying the angle factor,and the particle geometry sampling interval of 9o is suitable for the angle factor.Numeral Calculations.Finally,through the comparison of experiments and simulation results,the micro-particle discrete particle model has the highest precision when the number of brown rice seeds is 15 balls at the micro-scale scale.(3)Macro-scale modeling method for brown rice particle.Firstly,1000 grain of brown rice particles were randomly selected for dimensional measurement,and the particle size distribution of brown rice particles was obtained.The actual average particle size of brown rice particles was calculated to be 2.84 mm.Secondly,the coarse-graining method was used to model the discrete element geometry of brown rice particles,and the geometric model of brown rice particles with magnification factors of 1,1.5,5 and 12.5 was established.(4)Macro-scale model test of brown rice particle.The brown rice seed unloading test was carried out based on the shear box,and the tilt angle of the brown rice grain unloading was measured by an image method.At the same time,a consistent method was used to simulate the unloading of the brown rice kernel shear box.Finally,through the comparison of experiments and simulation results,the results show that the friction parameter set can be used as the calibration parameter for the discrete element modeling of brown rice.When the inter-particle sliding friction and rolling friction coefficient is 0.31,the obtained discrete element numerical study results are applicable to reveal the physical test phenomenon of brown rice grain group under quasi-static and high dynamic flow.The research results in this paper can provide a methodological basis for the numerical modeling of ellipsoidal particles,and also provide a reference for the modeling of other non-spherical particles.