# Spatial domain of different compositional fields:
# Quartz sand (qsand) has two layers with 1 cm thickness each.
# Corundum sand (csand) is in the middle of the 2-layer quatz sand and is
# 1 cm thick.
# The boundary 2-mm-thin layers (bound) sit on both the bottom of the domain and
# between the sand and rigid indenter block. The right boundary has a constant
# inflow velocity, which pushes a rigid block that approximates a mobile wall.
# Movement of the rigid block drives deformation in the sand layers.
# The boundary between the rigid block and boundary layers produces a sharp
# velocity discontinuity that localizes brittle deformation.
# The sticky air layer is set on top of the sand layer and approximates a
# free surface.

# Velocity boundary conditions
subsection Boundary velocity model
  set Zero velocity boundary indicators              = bottom    #no slip
  set Tangential velocity boundary indicators        = left      #free slip

  # right - material inflow with a velocity of 2.5 cm/hour at the height of
  # the pushing block. The velocity linearly decreases from the base of the
  # rigid block to 0 cm/hour at the base of the model.
  set Prescribed velocity boundary indicators        = right:function

  subsection Function
    set Variable names                             = x,y
    set Function constants                         = cm=0.01, h=3600, th=0.002
    set Function expression                        = if(y>th, -2.5*cm/h, -(y/th)*2.5*cm/h); 0
  end
end

# The top boundary is open (zero traction), which allows the sticky air to
# flow freely through it as topography develops along the wedge. Additional
# testing revealed that using a true free surface leads to significant mesh
# distortion and associated numerical instabilities.
subsection Boundary traction model
  set Prescribed traction boundary indicators        = top: zero traction
end
