R. Lal Kushwaha

CFD Simulation of Soil Forces on a Flat Tillage Tool

Soil forces on a tillage tool are of interest for several reasons, including the draft and power requirement to pull the implement. Pressure exerted by soil on the tillage tool and its distribution on tool surface with respect to tool wear is an important parameter for tool design with respect to the tool size and shape. The stress experienced by soil due to the tool motion is very important in identifying the soil mechanical behavior. The objective of this research was to gain an insight into soil forces and the pressure distribution on a simple tool considering the dynamics of soiltool interaction from fluid flow approach. Pressure distribution over the surface of a flat tillage tool, soil failure due to tool movement and draft requirement were investigated using computational fluid dynamics (CFD) for high speed tillage using a commercial CFD software CFX4.4. Soil was characterized as a Bingham material in its rheological behavior. Three dimensional simulations were conducted by control volume method with structured mesh. Results obtained from the simulations were compared with published data. Soil pressure on the tool surface increased with the tool operating speed. Pressure concentration was the highest at the tool tip; it decreased towards the soil surface and extended over greater area on the tool surface with increase in tool speed. Draft was related as a square function of speed. The longitudinal distance of the pressure bulb from the tool face(further most yield surface or conventionally, rupture distance) on the horizontal plane initially increased with speed and after a critical speed range of 4-6 m s-1, it did not increase with speed.

Soil Viscosity and Yield Stress measurement using a Motorized Rheometer

A motorised soil rheometer was developed at the Department of Agricultural and Bioresource Engineering, University of Saskatchewan to determine soil viscosity and yield stress. The device works on the principle of torsional shear applied to a standard vane with controlled strain rate following ASTM standards. Rheological measurements were carried out for a clay loam soil at different soil moisture contents (10, 13, 17 and 20% d.b.) and soil compaction levels (100, 150, 200, 300 and 400 kPa) to find their effects on soil viscosity and yield strength. The values of viscosity of a clay loam soil were found to spread in the range of 53x103 to 283x103 Pa.s, while the yield stress variation had a range of 4 to 28 kPa. Viscosity was highly affected by the compaction levels for the moisture contents tested. Increase in soil compaction was accompanied by a sharp increase in soil viscosity. Yield stress also increased with soil compaction for all the levels of moisture content with a steep increase when the compaction level was increased from 300 kPa to 400 kPa. The moisture content of 17% (d.b) was found to have a reduced viscosity and yield stress.

Simulation of Soil Deformation around a Tillage Tool using Computational Fluid Dynamics

Tillage tool modeling concerns primarily soil deformation patterns and force requirement as the tool interacts with soil. Though there is much literature available on soil forces and energy consumption with respect to the soil mechanical behavior considering soil as a solid or elasto-plastic material, large soil deformations resulting from the tool action have not been studied. This paper deals with preliminary modeling of soil flow around a tool using the computational fluid dynamics (CFD) approach. Main objective of this modeling was to characterize soil as a Bingham fluid to determine soil flow pattern around the tool. Simulations were based on the governing equations of non-Newtonian fluid flow with the viscoplastic constitutive relationship. Simulations were carried out using commercial software CFX 4.4. Initial results look promising in identifying soil deformation patterns, quantifying soil failure front and analyzing effect of speed on the failure front propagation. Further studies with this fluid flow approach are expected to reveal details of soil behavior around a tillage tool.

Propagation of Soil Failure Front Associated with various Agricultural Tillage Tools

Current North American soil tillage practices loosen soil to depths of 75 to 150 mm (3 to 6 inches). As the soil is tilled, the failure path precedes the motion of the tillage tool. Previous research has examined the forces within the soil to predict the soil failure. This paper experimentally quantifies the rate and the path of the failure front through the soil. From high speed digital film analysis, the failure front was analysed for three tillage tools operating at 4 km/h speed. The tillage tools included sweep, knife opener and an elliptical tool. The depth of operation was either 75 mm or 100mm. Soil conditions, namely its moisture content and the level of compactness were recorded. For the sweep tillage tool, temporal profiles of the failure or crack growth were quantified from the high speed videography. If the tool operational speed can be increased to overcome the speed of the failure front, the soil disturbances will be minimal to non existent.

Tillage force prediction from terrain characterization with the bevameter

Abstract The relationship between the soil parameters measured during soil testing using the bevameter system and horizontal forces acting on a simple tillage tool were investigated. Field experiments were conducted on untilled, compacted and recently tilled soil. On both soils, five sites were randomly chosen where bevameter and draft measurements were performed. The parameters measured were modulus of soil deformation, wet and dry bulk density, soil moisture content, tool operating depth, tool operating speed and horizontal draft. A statistical analysis of data indicated that a mathematical model for predicting draft should include operating depth, dry bulk density and modulus of deformation.