Comparison Of DEM and Traditional Modeling Methods For Simulating Steady-State Wheel-Terrain Interaction For Small Vehicle.

A simulation study was conducted to evaluate three terramechanics methods used for predicting single wheel performance of small vehicles on granular terrain.  Traditional Bekker-type terramechanics methods do not consider the soil profile, the soil dynamics, or the transient wheel dynamics, which can be important factors in vehicle performance.  The ‘dynamic Bekker’ method used to overcome these limitations treats the wheel a free body, which allows for multibody dynamics simulations, and discretizes the soil into grid regions, which allows for more complex soil profiles.  Another option is to use the discrete element method, 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 operation.  Single-wheel experiments were performed on Mojave Martian Simulant to evaluate performance at various slip ratios.  Similar tests were simulated using three terramechanics methods: traditional Bekker, dynamic Bekker, and the discrete element method.  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 will help determine the accuracy of each method during steady-state, and whether the computation cost of the discrete element method is warranted for steady-state conditions.