[aspect-devel] Help needed with setting up an EBA benchmark

[Katrina Arredondo]

I guess I was puzzled by your question on how to nondimensionalize the
energy equation because I've planned to test EBA in ASPECT using the
dimensional equations. I didn't word my confusion well. To me ASPECT equals
dimensional terms and equations, but I suppose a nondimensional form could
be good for testing. However, if that becomes an option, users may
consistently choose to use the nondimensional form over the dimensional
form because it's "easier." As is we are being forced to translate
everything into dimensional form.

 If we want to test dimensional vs nondimensional we would probably need to
change the code as written in ASPECT.  The changes will be more extreme if
latent heat is included. Without latent heat we would still need to add the
Dissipation and Raleigh number and extra temperature term multipliers into
the momentum and energy equations.

T0 is defined by the user and is usually the surface temperature or 0
Celsius. The benchmark is giving the nondimensional form of that number.

In my incomplete subduction models, I added T0 to my ASPECT viscosity and
temperature modules because it is a commonly used term. In my ASPECT and
CitcomS input decks, T0 is defined by the user (me).

Here at Davis the ASPECT discussion group has repeatedly asked ourselves
what is the best way to translate the dimensional terms in ASPECT into the
nondimensional Rayleigh and Dissipation numbers during postprocessing. If
that still isn't well defined I can bring it up at the next meeting or ask
Prof. Don Turcotte. Many of the terms used to define those numbers, such as
delta T in the Rayleigh number, are also used elsewhere in the initial
model to define the initial temperature field, etc while other terms like
the thermal expansivity could be chosen as the average throughout the
model.

 We can help you with this.

 - Katrina




On Thu, Sep 4, 2014 at 5:18 PM, Wolfgang Bangerth <bangerth at tamu.edu> wrote:

> On 09/04/2014 07:09 PM, Katrina Arredondo wrote:
>
>> But why does it need to be nondimensionalized? Just to be consistent
>> with the benchmark?
>>
>
> It doesn't have to be. The benchmark is defined in terms of nondimensional
> quantities -- it is what it is. But ASPECT does not take Rayleigh and
> Dissipation numbers as inputs. I have to somehow translate them into the
> physical quantities.
>
>
>
> > I guess I was thinking that this could be a test for how "easy" it is
> > to translate the geodynamics nondimensional terms into dimensional
> > terms in ASPECT. Otherwise why have the dimensional terms at all, if
> > it's too hard.
>
> Because the real world is sufficiently complicated that
> nondimensionalization does not work. (For example, what exactly is the
> Rayleigh number when you have variable gravity, a geometry for which there
> is no obvious lengthscale, and thermal expansion and viscosity depend
> strongly on the temperature?) I think the better question is why we should
> have the nondimensional form if it only describes idealized but
> non-realistic situations :-)
>
> Best
>  Wolfgang
>
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth               email:            bangerth at math.tamu.edu
>                                 www: http://www.math.tamu.edu/~bangerth/
>
> _______________________________________________
> Aspect-devel mailing list
> Aspect-devel at geodynamics.org
> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/aspect-devel
>



-- 

Katrina Arredondo
Ph.D. Candidate
Geodynamics/Subduction Zones
University of California, Davis
Department of Geology
One Shield Avenue, Davis CA 95616
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.geodynamics.org/pipermail/aspect-devel/attachments/20140904/dd57f52f/attachment.html>