Simulation of Bionic Anti-Drag Subsoiler with Exponential Curve Feature Using Discrete Element Method

Abstract

Subsoiling, as an important mode of conservation tillage, can break plowpan and increase permeability and water retention ability of soil which increase the crop yield. Subsoiler, as a key component of subsoiling, significantly effects on the tillage resistance. Reduction of working resistance of subsoiler can decrease output power of tractor and then further reduce the cost of subsoiling operation. The existing subsoilers have problem of overlarge subsoiling resistance. The conventional methods to resolve such problem include optimal design of the structural parameters of subsoiler and application of oscillation subsoiling device, but those methods not only make the structure of subsoiler more complex, but also increase the cost of agricultural production. Based on biomimetics principles, the upper surface outline of the claw of the house mouse (mus musculus), which has exponential function curve feature, was applied to the structural design of cutting soil edge of subsoiler shaft. Accordingly, the bionic subsoiler which has exponential function curve feature was designed and manufactured. The comparative experiments were conducted using the two types of subsoilers which have exponential function curve shape and parabola type in tillage depth at 300mm and 350mm with the forward velocitys of 0.5m/s and 1.0m/s in the indoor soil bin. The horizontal tillage resistances of the two types of subsoilers were measured using remote-measuring system of agricultural machinery dynamic parameters under different experimental conditions. The results showed that the horizontal tillage resistances increased with the increase of tillage depth and forward velocity. The horizontal tillage resistances of bionic anti-drag subsoiler (BAS) were obviously less than those of parabola type subsoiler (PTS) under same experimental conditions and the reduction was in the range of 8.5-38.2%. It indicated that the cutting soil edge of shaft with exponential function curve structure has remarkable anti-drag property. The simulations of tillage processes of the two types of subsoilers were conducted using discrete element method (DEM), the stress fields and velocity fields were obtained under different simulation conditions. The results showed that the directions of stress fields and velocity fields of the two types of subsoilers have forward and upward variation trend, but the directionality of contact stress of PTS was nonuniform compared with BAS, and such results lead to an increase in soil disturbance. The intensities of stress field and velocity field of BAS were obviously less than those of PTS under same experimental conditions, The results of simulation were consistent with the results of tillage experiments, indicating that the bionic subsoiler with exponential function curve feature has significant anti-drag property. The exponential function curve can be applied to the structural design of cutting soil edge of subsoiler aiming to reduce tillage resistance.