Draft force prediction for a high-speed disc implement using discrete element modelling

Abstract

Draft force is an important dynamic parameter for agricultural soil-engaging tools and implements. Soil-disc interaction dynamics has changed enormously in modern tillage practice because of the use of larger machines, faster speeds, and different tool arrangements. Most existing studies on draft force prediction are for conventional tillage. In this study, a discrete element model (DEM) was developed to predict draft forces for high-speed (12 km h−1 or higher) tillage. Draft forces were measured for an individually mounted disc using soil bin tests at low speeds in a sandy loam soil. Results were compared for the accuracy with the predicted values from the ASABE standard equation. Results showed that relative error ranged from 8% to 14%. Due to the limitations of the testing facility, the DEM model was calibrated using 6 km h−1 tillage speed and verified with other test speed measurement. The calibrated model was able to predict draft force with a minimum relative error of 1%. The calibrated particle stiffness, was found to be 20 kN m−1. The calibrated model was then used to examine the effects of operating parameters including gang angle, tilt angle, operating speed, disc diameter and tillage depth on draft forces at 16 km h−1. From these simulations, it was shown that draft increased with an increase in gang angle, tillage depth, and speed. The draft force was reduced with an increase in tilt angle and remained relatively constant with the change of disc diameter. Finally, the simulated data were used to develop a multivariate regression equation to predict the draft for a high-speed tillage operation. This equation is suitable for the soil conditions studied and further validation is required to verify this equation.