The active case with reactions.#
This section was contributed by Juliane Dannberg and René Gaßmöller.
In addition, there are setups where one wants the compositional fields to
interact with each other. One example would be material upwelling at a
mid-ocean ridge and changing the composition to that of oceanic crust when it
reaches a certain depth. In this cookbook, we will describe how this kind of
behavior can be achieved by using the composition reaction
function of the
material model.
We will consider the exact same setup as in the previous paragraphs, except for the initial conditions and properties of the two compositional fields. There is one material that initially fills the bottom half of the domain and is less dense than the material above. In addition, there is another material that only gets created when the first material reaches the uppermost 20% of the domain, and that has a higher density. This should cause the first material to move upwards, get partially converted to the second material, which then sinks down again. This means we want to change the initial conditions for the compositional fields:
subsection Initial composition model
set Model name = function
subsection Function
set Variable names = x,z
set Function expression = if(z<0.5, 1, 0); 0
end
end
Moreover, instead of the simple
material model, we will use the
composition reaction
material model, which basically behaves in the same
way, but can handle two active compositional field and a reaction between
those two fields. In the input file, the user defines a depth and above this
reaction depth
the first compositional fields is converted to the second
field. This can be done by changing the following section (the complete input
file can be found in
cookbooks/composition-reaction/composition-reaction.prm).
subsection Material model
set Model name = composition reaction
subsection Composition reaction model
set Thermal conductivity = 1e-6
set Thermal expansion coefficient = 0.01
set Viscosity = 1
set Density differential for compositional field 1 = -5
set Density differential for compositional field 2 = 5
set Reaction depth = 0.2
end
end
Results of this model are visualized in Fig. 45 – Fig. 50. What is visible is that over the course of the simulation, the material that starts at the bottom of the domain ascends, reaches the reaction depth and gets converted to the second material, which starts to sink down.