Problem (probably) solved.<br><br>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.<br>
<br>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.<br><br>Thanks for the extra brain power,<br>Ian<br><br>
<div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Nov 15, 2012 at 8:27 AM, <span dir="ltr"><<a href="mailto:aspect-devel-request@geodynamics.org" target="_blank">aspect-devel-request@geodynamics.org</a>></span> wrote:<br>
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Today's Topics:<br>
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1. Question regarding heat fluxes (Ian Rose)<br>
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<br>
Message: 1<br>
Date: Thu, 15 Nov 2012 08:27:42 -0800<br>
From: Ian Rose <<a href="mailto:ian.rose@berkeley.edu" target="_blank">ian.rose@berkeley.edu</a>><br>
Subject: [aspect-devel] Question regarding heat fluxes<br>
To: aspect-devel <<a href="mailto:aspect-devel@geodynamics.org" target="_blank">aspect-devel@geodynamics.org</a>><br>
Message-ID:<br>
<CAEm=<a href="mailto:8TRBJix1fbjf_cdNj7U0hK2cXQSjUFBu04WLk%2B5qVJimzg@mail.gmail.com" target="_blank">8TRBJix1fbjf_cdNj7U0hK2cXQSjUFBu04WLk+5qVJimzg@mail.gmail.com</a>><br>
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<br>
Hi all,<br>
<br>
I have been doing some tests with aspect involving heat fluxes out of the<br>
top and bottom boundaries, and am getting some behavior I don't<br>
understand.<br>
<br>
When the convection reaches steady state, the heat fluxes out of the top<br>
and bottom should be equal and opposite, otherwise, of course, it wouldn't<br>
be steady. However, if I look at a simple convection model in with 2d<br>
shells, I find that the flux out the top is considerably lower than the<br>
flux out of the bottom at steady state. I am attaching a prm file and a<br>
plot of heat fluxes as demonstration. The qualitative change at ~10 Gyr is<br>
due to a transition from organized to chaotic convection. The basic heat<br>
flux story is unchanged, though.<br>
<br>
Looking at the code for heat flux statistics, nothing seems obviously<br>
wrong. I should note that doing the same test for a box geometry where the<br>
top and bottom have the same area produces the expected results.<br>
<br>
Am I missing something about how this should work? Any insights as to what<br>
is going on would be appreciated.<br>
Best,<br>
Ian<br>
<br>
PS All calculations are done with r1353<br>
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</blockquote></div><br></div>