[aspect-devel] Questions on Boundary temperature model/Function

[Magali Billen]

Hello Timo,

Thanks for your response to Tim about setting the boundary indicators. I'm still confused about a couple things with different input options,
so I'll try to explain more clearly what we are trying to do.

We have a box (3000 x 3000 km). At the top (z=3000) we want the temperature to be constant (Ttop=273 K) and fixed for the whole run.
At the bottom (z=0), we want the temperature to be function of position ( Tbot (x,0)). For the initial condition, the temperature will be linear
with depth, but varies as a function of x, because the bottom boundary temperature changes T(x,z) = (Tbot(x,0) - Ttop)*(L-z)/L + Ttop.

So, to implement this, I define the initial temperature with:
subsection Initial conditions
  set Model name = function
  subsection Function
    set Variable names      = x,z
    set Function constants  = Tcon=1673, xstep=0.5, dT=100, L=3000, sm=0.02, Ttop=273
    set Function expression = (((Tcon - (1-xstep)*dT) + dT*(0.5 + (1/pi)*atan( (x - xstep*L)./(sm*L) ))) - Ttop)*(L-z)/L + Ttop;
  end 
end

Then I tell Aspect that the top and bottom boundaries have fixed temperature (sides are insulating be default):

subsection Model settings
  set Fixed temperature boundary indicators   = bottom, top
end

So, where I get confused is how do I assigned the constant temperature to the top and the functional temperature to the bottom?

I feel like I can either enter the function for the bottom or the constant for the top, but not both. If I enter the same function as
the initial conditions (as below), does it just evaluate this function on each of the boundaries?  OR, do I need to use two separate 
functions (one that is just T=273) with an if statement (if z=0 T=T(x,0), if z=3000 T=273? If I need to use an if statement, can you 
give me an example of what this looks like?

subsection Boundary temperature model
  set Model name = Function
  
  subsection Function
    set Variable names      = x,z
    set Function constants  = Tcon=1673, xstep=0.5, dT=100, L=3000, sm=0.02, Ttop=273
    set Function expression = (((Tcon - (1-xstep)*dT) + dT*(0.5 + (1/pi)*atan( (x - xstep*L)./(sm*L) ))) - Ttop)*(L-z)/L + Ttop;
  end
  
end


Thanks in advance for any help you (or anyone else on the list) can give.
Magali


On Feb 21, 2015, at 6:13 AM, Timo Heister <timo.heister at gmail.com> wrote:

> Hey Tim,
> 
>> I am trying to figure out how to assign the function to a specific boundary.
>> Below is the current function. I would like to have it only pertain to the
>> bottom boundary. Thank you!
> 
> subsection Model settings
>  set Fixed temperature boundary indicators   = bottom
> end
> 
> causes your boundary condition for the temperature to be applied to
> the bottom only (the others will be insulating).
> 
> For your initial condition you have to supply a value everywhere. Do
> you want it to be zero except at the bottom boundary?
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> Aspect-devel mailing list
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Earth & Planetary Sciences Dept., UC Davis
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Office Phone: (530) 752-4169
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