Effect of granular ruler in discrete element model of sandy loam fluidity in Ma yam planting field

This study aims to significantly improve the computational efficiency of discrete element method (DEM) in the agricultural field, particularly in the simplified model for harvesting the yam-sandy loam soil complex. Taking the sandy loam soil as the research object, the dual-target parameter calibration experiments were used to construct non-spherical particles in the discrete element software, together with enlarging the size of a single particle. The dynamic accumulation angle, flow quality, and flow rate were determined in the drum and collapse tests, and thereby to explore the influence of particle ruler effect on the flow characteristics in the particle group. The maximum scale factor of particles in the model was set as S=4, and the rotating speed of drum was set as4rpm, 40rpm, and 80rpm, respectively. The dynamic angles of repose in the particle group were measured in the actual and simulation test. Subsequently, a collapse test was carried out to monitor the discharge outlet flow during the collapse of particle groups' indifferent sizes. The test results show that the average static accumulation angle of 2mm sandy loam matrix after drying treatment was 32.16°, and the average dynamic accumulation angle was 35.02°. The simulation parameters obtained from the dual-target calibration test were more accurate than that from the independent calibration test. The dynamic accumulation angle that formed by the real sandy loam particles in the drum decreased with the increase of particle size and rotation speed, while, the non-spherical particle group only changed the particle size in the simulation test. There was a relatively small difference in the dynamic angle of repose that produced in the case of diameter. In the collapse test, the changing trend of flow quality representing by the particle groups of different diameters in the flow process was basically the same as that of average flow velocity. The error was also increasing with the continuous increase of diameter. The amount of particles in the same calculation domain decreased by 87.24% (S=2) and 98.92% (S=4), respectively, indicating that the simulation time significantly reduced. Especially, when S=2, the calculation efficiency was significantly improved, compared with that of the non-stretched particles. The FT4 rheological test showed that when the scaling factor S was 2, the fitting curve of resistance FV and its torque T with the time changes was about twice that of the unfolding factor. When the scaling factor S was 4, the slopes of two fitted curves were totally different, indicating that the correlation was significantly reduced, compared with the original ruler. The findings can provide a sound theoretical basis on the construction of discrete element scaling model for the sandy loam soil, and the simulation calculation in agricultural engineering.