Modelling and simulation of the straw-grain separation process based on a discrete element model with flexible hollow cylindrical bonds

The grain separation process in a combine harvester is nonlinear and full of uncertainty. To study the process of separating grains from straw-grain mixtures (SGMs) in a combine harvester, a bonded-particle straw model (BSM) with flexible hollow cylindrical bonds was proposed. The mechanical properties of the BSM were simulated and compared with analytical predictions and experimental results. The maximum relative error between the BSM cantilever deflections and bending analytical predictions was 4.04%, and that between the normal displacements and stretching analytical predictions was 0.28%. Similarly, the maximum relative errors of the BSM cantilever deflections from bending test results and the normal displacements from stretching test results were 12.87% and 4.78%, respectively. Then, separation experiments with different straw area densities (SADs) were simulated using the BSM, and the simulation results were compared with experimental data. The coefficients of determination of the separation curve over time exceeded 0.995 for SADs of 2 and 3 kg/m(2). Good agreement was achieved with maximum relative errors of 6.69% and 7.06% for the separation fraction results with SADs of 2 and 3 kg/m(2), respectively. The BSM could accurately describe the separation process of grain from straw and quantify the interference of the straw and equipment.