visco_plastic_yield_strain_weakening.prm

# Global parameters
set Dimension                              = 2
set Start time                             = 0
set End time                               = 1
set Use years in output instead of seconds = true
set Nonlinear solver scheme                = single Advection, iterated Stokes
set Max nonlinear iterations               = 1
set Output directory                       = visco_plastic_yield_strain_weakening
set Timing output frequency                = 1

# Model geometry (100x100 km, 10 km spacing)
subsection Geometry model
  set Model name = box

  subsection Box
    set X repetitions = 10
    set Y repetitions = 10
    set X extent      = 100e3
    set Y extent      = 100e3
  end
end

# Mesh refinement specifications
subsection Mesh refinement
  set Initial adaptive refinement        = 0
  set Initial global refinement          = 0
  set Time steps between mesh refinement = 0
end

# Boundary classifications (fixed T boundaries, prescribed velocity)

# Temperature boundary and initial conditions
subsection Boundary temperature model
  set Fixed temperature boundary indicators   = bottom, top, left, right
  set List of model names = box

  subsection Box
    set Bottom temperature = 273
    set Left temperature   = 273
    set Right temperature  = 273
    set Top temperature    = 273
  end
end

# Velocity on boundaries characterized by functions
subsection Boundary velocity model
  set Prescribed velocity boundary indicators = bottom y: function, top y: function, left x: function, right x: function

  subsection Function
    set Variable names      = x,y
    set Function constants  = m=0.0005, year=1
    set Function expression = if (x<50e3 , -1*m/year, 1*m/year); if (y<50e3 , 1*m/year, -1*m/year);
  end
end

subsection Initial temperature model
  set Model name = function

  subsection Function
    set Function expression = 273
  end
end

# Compositional fields used to track finite strain invariant
subsection Compositional fields
  set Number of fields = 1
  set Names of fields = total_strain
end

# We prescribe some initial strain at the center of the domain
subsection Initial composition model
  set Model name = function

  subsection Function
    set Variable names      = x,y
    set Function expression = if(x>=45e3&x<=55e3&y>=45.3e3&y<=55.e3,0.2,0);
  end
end

# Boundary composition specification
subsection Boundary composition model
  set List of model names = initial composition
end

# Material model (values for background material)
subsection Material model
  set Model name = visco plastic

  subsection Visco Plastic
    set Reference strain rate = 1.e-16
    set Viscous flow law = dislocation
    set Prefactors for dislocation creep = 5.e-23
    set Stress exponents for dislocation creep = 1.0
    set Activation energies for dislocation creep = 0.
    set Activation volumes for dislocation creep = 0.
    set Yield mechanism = drucker
    set Angles of internal friction = 0.
    set Cohesions = 1.e6
    set Strain weakening mechanism = plastic weakening with total strain only
    set Start plasticity strain weakening intervals = 0.
    set End plasticity strain weakening intervals = 1.0
    set Cohesion strain weakening factors = 0.5
    set Friction strain weakening factors = 0.5
  end
end

# Gravity model
subsection Gravity model
  set Model name = vertical

  subsection Vertical
    set Magnitude = 10.0
  end
end

# Post processing
# named additional outputs includes the weakened cohesions and friction angles
subsection Postprocess
  set List of postprocessors = velocity statistics, mass flux statistics, visualization

  subsection Visualization
    set Interpolate output = false
    set List of output variables = viscosity, strain rate, named additional outputs
    set Output format            = gnuplot
  end
end

subsection Solver parameters
  subsection Stokes solver parameters
    set Number of cheap Stokes solver steps = 0
  end
end