Prediction of tractive force model for disc harrowing using sensitivity analysis

Abstract

In this study, a comparative evaluation of tractive force models for disc harrowing, at different tillage speeds was carried out in order to determine optimal tillage speeds.  The predictive models were developed using dimensional analysis.  The tillage operation in a loamy sand soil, at tillage speeds of 1.94 m s^-1, 2.22 m s^-1 and 2.5 m s^-1 respectively was conducted, using trace tractor techniques.  Parameters such as drawbar pull, rolling resistance, wheel slip, moisture content, cone index, wheel numeric, contact pressure, speed, width of harrow, depth of harrow, and tractive force were measured.  The developed mathematical models describing the tractors tyre-soil interactions parameters were evaluated using sensitivity analysis of the measured parameters.  The wheel tractors tractive force models depicted highest sensitivity coefficients of 0.2405, 0.2331 and 0.3041 for drawbar pull during harrowing with tillage speeds at 1.94 m s^-1, 2.22 m s^-1 and 2.50 m s^-1 respectively.  The results obtained showed that 10%, 50% and 100% changes of independent variables (U1) would cause dependent variables (N) negligible changes.  These indicate that the sensitivity of developed predicted models to changes in the constituent independent variables are negligible and insignificant.  This result also indicates that at tillage speed of 2.22 m s^-1 the lowest sensitivity coefficient of 0.2331 was obtained among others, which is an indication of the best tillage speed for harrowing operation.

Keywords: predictive, tractive force, disc harrowing, modelling, sensitivity measurement, soil moisture