Simulating the effect of rake angle on narrow opener performance with the discrete element method

Abstract

Narrow openers are widely used in Australia to place seed and fertiliser into furrows under no-tillage seeding operations, but excessive soil disturbance often limits their performance. The discrete element method (DEM) and a hysteretic spring contact model can be used to model soil-tool interactions, although previous work has been limited in its evaluation of soil disturbance. A new approach was used to evaluate soil disturbance in DEM simulations using a voidage grid binning technique to identify loosened soil after tillage and therefore paralleling soil bin and field testing methodologies. The effect of opener rake angle (35–90°) was simulated and compared to previous soil bin studies in a sandy loam soil predicting furrow profile parameters loosened area, ridge height, dip area, furrow backfill and lateral soil throw with relative errors of 9%, 16%, 14%, 0.8%, and 9%, respectively. Soil layer mixing trends also followed those measured in soil bin experiments-low rake angle openers moving deep soil up the furrow profile and maximising the furrow mixing effect. Additionally, predicted soil failure (critical depth and forward rupture ratio m) and tillage force rake trends followed those expected from classic empirical based soil mechanics studies. DEM predicted approximately a twofold draught penalty with increasing rake angle as well as a vertical force transition at 71°–closely matching trends consistently reported in literature. The approach followed demonstrated an improved potential for DEM simulations to optimise the performance of narrow openers.