Modeling the interaction between rover's wheel and soft terrain is of great importance in predicting or evaluating wheel performance for lunar and planetary rovers. The current wheel-soil interaction models predict or evaluate wheel performance under certain conditions. However, most of them do not consider the soil flow and deformation, and thus, they cannot capture the physical phenomena of wheel-soil interaction. Developing a new model that includes such physical phenomena contributes to the improvement of prediction accuracy. To develop such a model, it is necessary to analyze soil flow and deformation beneath the wheel. This study analyzes the stress distributions in the soil and soil flow fields beneath the grouser wheel by performing experiments using the discrete element method (DEM) with the particle simulation tool "Sir partsival". In addition to the single wheel simulation, two simple test simulations - an angle of repose test and a shear test - are performed to confirm the soil flow fields and stress distributions in the soil. In the field of fluid dynamics, (shear) stress generally exists along high gradients of flow velocity. These two tests confirm if the soil stress shows the same trend. The wheel simulations are performed under several slip conditions to investigate their influences on soil flow characteristics. The shape of the soil flow region - the shape of the slip line - can be divided into two patterns depending on the slip conditions. The stress increases along the slip line in all simulations. The findings of this study contribute to understanding the relationship between soil velocity field and stress distribution in the soil.
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