Impossible to set more than one thermal viscosity exponent in ASPECT

ASPECT
1

Dear developers. In CITCOM is possible to use more than one thermal viscosity exponent, for example:

num_mat=4 # number of material group with possibly different rheology
	visc0=1.0,1.0,1.0,50.0 	# pre-exponential constant
 	viscE=9.21,9.21,9.21,11.51	#activation energy
	viscZ=0.0,0.0,0.0,0.0

I checked the aspect manual and in ASPECT you can set only one thermal viscosity coefficient for your planet, it would be fantastic if, in future update, i could set more than one value, for example:

set Thermal viscosity exponents = 9.21,9.21,9.21,11.51
set Viscosity prefactors = 1.0, 1.0, 1.0, 50.0

I mean, i can use 10 as a value, i don’t ithink that my simulation will change a lot
Thank you for your help and your work
Francesco

2

Francyrad:
all of this depends on what material model you are using. Can you explain which model you use? Separately, what would these multiple exponents correspond to? The viscosities of different phases? Different compositions?
Best
W.

3

Thank you Bangerth for your answer. Actually i’m using a multicomponent model. So i’m doing a mix between Steinberger, ASCII and simple:

   subsection Compositing
      set Viscosity = ascii reference profile
      set Density = Steinberger
      set Thermal expansion coefficient = Steinberger
      set Specific heat = Steinberger
      set Thermal conductivity = Steinberger
      set Compressibility = Steinberger
      set Entropy derivative pressure = Steinberger
      set Entropy derivative temperature = Steinberger
      set Reaction terms = Steinberger
  end

According to the paper that i want to emulate, the thermal viscosity exponent, called also “Activation energy”, correspond the the term A of this equation:

Screenshot 2023-06-20 alle 12.43.26
Screenshot 2023-06-20 alle 12.43.262246Ă—258 37.7 KB

The ASPECT’s manual refer to it as the thermal viscosity exponent:

Screenshot 2023-06-20 alle 12.44.32
Screenshot 2023-06-20 alle 12.44.321848Ă—228 61.4 KB

The point is that in CITCOM you can choose as many thermal viscosity exponent as many viscosity prefactors you have, in ASPECT you can only choose one. So, going back to my post, i was asking if in a future update will be possible to set up more than one thermal viscosity exponent like in Citcom.
Best regards
Francesco

4

Francesco,
I’m still not clear what the multiple exponents would correspond to. If you provide multiple exponents, how does CITCOM define the overall viscosity?

The longer answer of course is that, as in most volunteer projects, functionality appears if someone implements it. In your case, if there is no material model that does what you want to do, you can always implement your own material model that does what you want it to do.

Best
W.

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