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Dr. Ayush Nuwal, Ajay Kumar, and Professor John Economou
Modern militaries are exploring the teaming of military vehicles with smaller uninhabited ground vehicles (UGVs), to improve the success of operations in the off-road terrains. The UGVs can be used to perform initial mobility testing on soft soils, to predict the go/no-go performance of vehicles. Because of the variation in the sizes of the UGV and military vehicle, it is imperative whether the scalability of tyre-soil interaction exists or not. The scalability assumes that similar systems behave in a similar manner at different dimensional scales. Dimensional analysis is carried out to determine similarity between the systems and identify design parameters affecting scalability. In this study, the lightweight vehicles (FED Alpha) are considered as the full-scale systems (as upper boundary) and UGVs (Husky or Warthog) as scaled system. The 335/65R22.5 tyre with operational range of loading for full scale vehicle is considered. The smaller UGV tyres (0.7, 0.5 and 0.25 scale) represent scaled system. The 2NS and fine-grain sands were modelled using the DEM (EpAM contact model). The direct shear and pressure-sinkage tests were simulated to calibrate the soil model (cone index from 14.79-149 kPa). Validated simulations of tyre-soil interaction, show that 'drawbar-pull vs slip' and 'tractive-efficiency vs slip' are scalable, within given size and loading conditions. However, the prediction is dependent on soil parameters and size of the scaled systems (0.7 and 0.5 scale demonstrated the scalability clearly). The prediction was better in 2NS sand due to higher cone index. Up to 0.5 scale-system can predict the full- scale system’s mobility performance on sandy soils. This finding can be used to develop lighter UGVs to support full-scale vehicles in the off-road terrains.
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