exponential_decay.base.prm

#########################################################
# This is a benchmark case that tests the operator split
# solver scheme, which can use a different time step to
# compute reactions between compositional fields than
# the time step used for advection.
# In this test case, there is no advection, and we start
# from a composition (and temperature) that is 1 everywhere
# in the domain and then decays over time, following the
# equations for exponential decay.

# We use a plugin that implements the reactions for exponential
# decay.
set Additional shared libraries = ./libexponential_decay.so
set Dimension                              = 2
set Start time                             = 0
set End time                               = 100
set Use years instead of seconds           = false

# We use a new solver scheme option that enables the operator split.
set Nonlinear solver scheme                = single Advection, single Stokes
set Use operator splitting                 = true
set Maximum time step                      = 10

# As we split the time-stepping of advection and reactions,
# there are now two different time steps in the model:
# We control the advection time step using the 'Maximum time step'
# parameter (as this benchmark has no driving force, and hence very
# low velocities, we can not use the CFL number), and the reaction
# time step using the 'Reaction time step' parameter.
# We will vary both parameters in different model runs.
subsection Solver parameters
  subsection Operator splitting parameters
    set Reaction time step                 = 0.0005
  end
end

subsection Geometry model
  set Model name = box

  subsection Box
    set X extent = 1
    set Y extent = 1
  end
end

subsection Boundary velocity model
  set Tangential velocity boundary indicators = 0, 1, 2, 3
end

subsection Compositional fields
  set Number of fields = 1
end

subsection Gravity model
  set Model name = vertical
end

# Both initial temperature and composition are set to 1,
# and will decay starting from this value.
subsection Initial temperature model
  set Model name = function

  subsection Function
    set Variable names      = x,z
    set Function expression = 1.0
  end
end

subsection Initial composition model
  set Model name = function

  subsection Function
    set Variable names      = x,z
    set Function expression = 1.0
  end
end

# We choose material and heating models that let temperature
# and composition decay over time, and that is implemented in
# a plugin.
subsection Heating model
  set List of model names = exponential decay heating

  subsection Exponential decay heating
    set Half life = 10
  end
end

subsection Material model
  set Model name = exponential decay

  subsection Exponential decay
    set Half life = 10
  end

  subsection Composition reaction model
    set Thermal conductivity          = 0
    set Thermal expansion coefficient = 1e-4
    set Viscosity                     = 1e5
    set Density differential for compositional field 1 = 0
  end
end

# As composition and temperature do not depend on x or y,
# we can use a coarse resolution.
subsection Mesh refinement
  set Initial adaptive refinement        = 0
  set Initial global refinement          = 3
  set Time steps between mesh refinement = 0
end

# We output some statistics about the composition, and make
# use of a postprocessor that computes errors compared to the
# analytical solution for exponential decay.
subsection Postprocess
  set List of postprocessors = composition statistics, visualization, ExponentialDecayPostprocessor

  subsection Visualization
    set Time between graphical output = 0
  end
end