Prediction of Single Disc Seeding System Forces, Using a Semi-Analytical and Discrete Element Method (DEM)

Abstract

There is a rising interest amongst Australian farmers to use disc seeders due to their ability to operate in high residue conditions and at higher speeds, commonly in the range of 12 to 15 km h−1. This paper reports on developing an analytical and discrete element method (DEM) force prediction model suited to a rotating flat disc blade operating at different sweep and tilt angles. To validate the models, field experiments were carried out with a flat disc blade at two tilt angles of 0 and 20° and four sweep angles of 6, 26, 45 and 90° in sandy soil. An analytical approach was developed following an experimental investigation that showed that only the forward portion of the disc blade is actively involved in generating soil failure, while the magnitude of this active portion of the soil-disc interface varied with sweep angle. The predicted active proportions correlated well with the experimental observations. As applying different sweep angles affects the direction of soil movement relative to the disc face, the directions of the friction and resultant forces at different sweep and tilt angles were determined. The equation of soil acceleration force was adapted to account for different sweep angles. Results showed that the predicted force fits relatively well with the measured data at 90, 45 and 26° sweep angle, while the low correlation between predicted and measured force at 6° sweep angle was due to the scrubbing reaction force not accounted for in the model. Results also showed that a better coefficient of determination (R2 = 0.93) was obtained between DEM vs. test results compared to the analytical model predictions (R2 = 0.86), particularly for predicting side forces. It was found from the study that both the developed analytical approach and DEM model enabled the prediction of soil forces at different sweep and tilt angles acting on a flat disc blade, which can assist in optimising disc design to lower the specific resistance.