Influence of particle shape and contact parameters on DEM-simulated bulk density of wheat

Authors: PETINGCO, MARVIN - Kansas State University; Casada, Mark; MAGHIRANG, RONALDO - University Of Illinois; CHEN, ZHENGPU - Purdue University; AMBROSE, ROSE P. - Purdue University; FASINA, OLADIRAN - Auburn University

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2020
Publication Date: 8/1/2020
Citation: Petingco, M.C., Casada, M.E., Maghirang, R.G., Chen, Z., Ambrose, R.K., Fasina, O.O. 2020. Influence of particle shape and contact parameters on DEM-simulated bulk density of wheat. Transactions of the ASABE. 63(6):1657-1672. https://doi.org/10.13031/trans.13718.
DOI: https://doi.org/10.13031/trans.13718

Interpretive Summary: Grain bulk density is an important property in the grain industry, used in grading, designing storage systems, and estimating the mass of grain in bins. Bulk density of grain in a storage bin increases with the overbearing pressure of the grain and varies with handling processes such as grain fall height, filling rate, and use of a spreader as compared to spout filling. The widely varying interactions between kernels under compaction create a complex problem that can best be analyzed in computer models by considering the movement and interactions of each individual particle. This computer modeling technique, called the discrete element method (DEM), requires knowledge of how the particle shape and contact parameters (such as coefficients of friction) affect modeling a system such as this wheat bulk density. To improve the modeling and understanding of grain compaction processes, experimental density measurements and DEM modeling simulations were conducted. Results showed that the bulk density is higher for particles having lower length to width ratio and smoother surfaces, indicating that it is important to capture those aspects of the true shape of particles being modeled to accurately predict grain bulk density. The most important contact parameters for modeling were identified as the particle-to-particle coefficient of static friction and particle-to-particle coefficient of rolling friction. Determining these material properties accurately will improve the prediction of grain bulk density as affected by different handling processes. These results contribute to a better understanding of the influence of particle shape and contact parameters on simulating bulk density for wheat and also defined a specific particle model with three size fractions for use in simulating container filling operations using the DEM method.

Technical Abstract: he discrete element method (DEM) has been shown to be an effective tool for simulating behavior of granular material. The accuracy of the simulations depends highly on contact models used, physical parameters of particulate materials, and contact parameters (particle-to-particle and particle-to-wall coefficients of static friction, rolling friction, and restitution). In bins, grain bulk density increases with overburden pressure, grain fall heights, and with the use of grain spreaders. DEM can be used to better understand the behavior of granular material and how different processes affects grain bulk density. However, the effects of particle shape and contact parameters on grain bulk density should be understood first, so we evaluated the effects of particle models, aspect ratio, contact parameters on DEM simulations bulk density measurements. Wheat samples were sieved to obtain three size fractions for experiments. Grain characteristics, including single kernel weight, kernel density, kernel dimensions, aspect ratio, and bulk density, were determined for each size fraction. Contact parameters were evaluated to determine which parameters have the most significant effect on simulated bulk density. Results showed that DEM simulated bulk density of wheat increased with lower aspect ratio, like experimental results. Greater smoothness of ellipsoidal particles (7-sphere versus 5-sphere) produced greater DEM simulated bulk density of wheat larger size fractions, similar to the experiments. However, increasing the number of spheres to approximately 30 for better representation of wheat particles (ASG) did not produce the trend of greater simulated bulk density seen in the experiments. The 5- and 7-sphere pseudo-ellipsoidal particles also require less computational effort than the ASG particles making them preferable for DEM simulations of bulk density. Among the six contact parameters, the wheat-wheat coefficient of static friction and wheat-surface coefficient of rolling friction had the most significant effect on the simulated bulk density. The optimum contact parameter values were also determined for DEM simulation of wheat bulk density.