  The Material Point Method (MPM) is a hybrid Eulerian-Lagrangian approach
capable of simulating large deformation problems of history-dependent
materials. While the MPM can represent complex and evolving material domains by
using Lagrangian points, boundary conditions are often applied to the Eulerian
nodes of the background mesh nodes. Hence, the use of a structured mesh may
become prohibitively restrictive for modeling complex boundaries such as a
landslide topography. We study the suitability of unstructured background mesh
with isoparametric elements to model irregular boundaries in the MPM. An
inverse mapping algorithm is used to transform the material points from the
global coordinates to the local natural coordinates. Dirichlet velocity and
frictional boundary conditions are applied in the local coordinate system at
each boundary node. This approach of modeling complex boundary conditions is
validated by modeling the dynamics of a gravity-driven rigid block sliding on
an inclined plane. This method is later applied to a flume test of controlled
debris flow on an inclined plane conducted by the United States Geological
Survey (USGS).
