Comparison of discrete element method and traditional modeling methods for steady-state wheel-terrain interaction of small vehicles

A simulation study was conducted to evaluate three terramechanics methods for predicting single wheel performance of small vehicles on granular terrain. Traditional Bekker-type terramechanics methods do not consider the soil profile, soil dynamics, or transient wheel dynamics, which can be important factors in vehicle performance. The ‘dynamic Bekker’ method treats the wheel as a free body and discretizes the soil into grid regions, which allows for multibody dynamics simulations on more complex soil profiles. Another option is to use the discrete element method (DEM), which makes fewer assumptions but requires significantly more computation time. Before these methods can be evaluated in dynamic conditions, they must first be tested in steady-state conditions. Single-wheel experiments were performed on Mojave Martian Simulant to evaluate performance at various slip ratios. Similar tests were simulated using traditional Bekker, dynamic Bekker, and DEM. Each method was tuned to match direct shear and pressure-sinkage tests performed on the same soil. While Bekker-type methods only require curve-fitting to determine soil parameters, the discrete element method was tuned by simulating the soil tests with varying parameters. The results from this study show DEM can better predict wheel performance both qualitatively and quantitatively, though at a considerably higher computation cost.