[aspect-devel] Aspect-devel Digest, Vol 12, Issue 3

[Ian Rose]

Problem (probably) solved.

The lower boundary, having a smaller surface area, requires a thinner
boundary layer to keep up with the heat flux out of the top boundary.  If
you run at too low a resolution (as I was), then the temperature gradient
at the bottom is too shallow due to numerical diffusion and you
significantly underestimate the lower  heat flux.

With the box geometry you can also leave the boundary layer underresolved,
but at least the error is the same in the top and bottom, so they match
well.

Thanks for the extra brain power,
Ian



On Thu, Nov 15, 2012 at 8:27 AM, <aspect-devel-request at geodynamics.org>wrote:

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>    1. Question regarding heat fluxes (Ian Rose)
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> Message: 1
> Date: Thu, 15 Nov 2012 08:27:42 -0800
> From: Ian Rose <ian.rose at berkeley.edu>
> Subject: [aspect-devel] Question regarding heat fluxes
> To: aspect-devel <aspect-devel at geodynamics.org>
> Message-ID:
>         <CAEm=
> 8TRBJix1fbjf_cdNj7U0hK2cXQSjUFBu04WLk+5qVJimzg at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi all,
>
> I have been doing some tests with aspect involving heat fluxes out of the
> top and bottom boundaries, and am getting some behavior I don't
> understand.
>
> When the convection reaches steady state, the heat fluxes out of the top
> and bottom should be equal and opposite, otherwise, of course, it wouldn't
> be steady.  However, if I look at a simple convection model in with 2d
> shells, I find that the flux out the top is considerably lower than the
> flux out of the bottom at steady state.  I am attaching a prm file and a
> plot of heat fluxes as demonstration.  The qualitative change at ~10 Gyr is
> due to a transition from organized to chaotic convection.  The basic heat
> flux story is unchanged, though.
>
> Looking at the code for heat flux statistics, nothing seems obviously
> wrong.  I should note that doing the same test for a box geometry where the
> top and bottom have the same area produces the expected results.
>
> Am I missing something about how this should work?  Any insights as to what
> is going on would be appreciated.
> Best,
> Ian
>
> PS All calculations are done with r1353
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