  A multiscale model for real-time simulation of terrain dynamics is explored.
To represent the dynamics on different scales the model combines the
description of soil as a continuous solid, as distinct particles and as rigid
multibodies. The models are dynamically coupled to each other and to the
earthmoving equipment. Agitated soil is represented by a hybrid of contacting
particles and continuum solid, with the moving equipment and resting soil as
geometric boundaries. Each zone of active soil is aggregated into distinct
bodies, with the proper mass, momentum and frictional-cohesive properties,
which constrain the equipment's multibody dynamics. The particle model
parameters are pre-calibrated to the bulk mechanical parameters for a wide
range of different soils. The result is a computationally efficient model for
earthmoving operations that resolve the motion of the soil, using a fast
iterative solver, and provide realistic forces and dynamic for the equipment,
using a direct solver for high numerical precision. Numerical simulations of
excavation and bulldozing operations are performed to validate the model and
measure the computational performance. Reference data is produced using coupled
discrete element and multibody dynamics simulations at relatively high
resolution. The digging resistance and soil displacements with the real-time
multiscale model agree with the reference model up to 10-25%, and run more than
three orders of magnitude faster.
