Simulation of realistic granular agricultural material behavior using a physics-based game engine

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Li, Zhaohui
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Peschel, Joshua
Schaefer, Vernon
Darr, Matthew
Tekeste, Mehari
Li, Beiwen
Committee Member
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Agricultural and Biosystems Engineering
This dissertation introduces the framework and property configuration of simulating direct shear and triaxial test for agricultural materials using physics engine. The first chapter describes a computational approach for simulating direct shear test results for corn kernels using a physics engine. Existing discrete element method (DEM) approaches rely on simplified particle shapes, usually spheres, and do not fully capture the geometry of irregular particles such as corn kernels. The physics engine framework introduced in this work was adapted from Project Chrono and leverages the use of realistic geometries of corn kernels which can significantly improve simulation accuracy. Direct shear simulations of 100, 200, and 300 kPa normal pressure settings were conducted using 750 corn kernels of varying 3D shape. Coincidence force ratio and vertical displacement curves of simulation and experiment results show the physics engine framework satisfactorily simulate the direct shear test for corn. Pearson correlations of corresponding confining pressure curves all greater than 0.98 illustrate suitable correlation between the simulation and experimental data. The results also uniquely show the micro behaviors of the corn kernels including degree of rotation, number of contacts, and contact normal forces, which cannot be readily observed in laboratory experiments. This work will be of interest to researchers and practitioners in the fields of grain science and production systems. The second chapter constructs computational direct shear test simulations of realistic wheat and sunflower seed using a Project Chrono physics engine. The physics engine is capable of importing customer defined realistic geometries which is an evolutional improvement beyond traditional discrete element methods (DEM) simulations. As agricultural simulation studies utilizing physics engine are lacking, is the primary purpose is to validate the accuracy and effectiveness of physics engine simulation of agricultural grains. The simulation results show high Pearson correlation (greater than 0.97) regarding the experimental outcomes which has provided evidence of the physics engine’s effectiveness. The Project Chrono model can discover grain micro-behaviors that are impossible to obtain in traditional experiments, for instance, particle transition, particle rotation, magnitude and direction of contact force. The highly alignment of the simulation and experiment results validates the accuracy of the physics engine in representing agricultural grains. The third chapter represents a new approach for simulating triaxial shear test of realistic corn particles using a physics game engine. The commonly used discrete element method (DEM) is adapted to simplified geometry properties that represents particles using single sphere or cluster of spheres. In order to simulate realistic grain kernels, the physics engine, Project Chrono, is an applicable option as it has evolved to have enough accuracy for academic applications. However, since there are limited applications of Project Chrono in simulating agricultural particles, there is low evidence to support the accuracy of grain simulations. To overcome this issue and build the foundation for simulating complicated systems in the future, the validation of triaxial shear test is selected. The simulation results are compared with the experiment results of the stress-strain behavior of triaxial shear tests. Triaxial shear tests of 4, 10, 20, 30, and 40 kPa settings simulations are performed with 750 corn kernels sample that is formed by realistic 3D models with small variations to increase diversity. The highly alignment of the experiments and simulations results, with Pearson correlation > 95%, validates the high accuracy of the simulations using Project Chrono. The simulation outputs more micro-behaviors of the particles including number of contact, direction, and magnitude of each contact force, that are impossible to obtain from laboratory experiments.