For your information cig-long readers, Walter, Louise and I had a conversation around this issue two weeks ago. <div><div><br></div><div>I don't think there are any supporters of Q1Q1 for this particular problem left any more. Underworld defaults to Q1P0 but provides recovered deviatoric stress and pressure quantities which mitigate the checkerboard problem. This can be configured quickly and is at least well-understood and tested.</div>
<div><br></div><div>Q2P1 would be useful to have next. It is implemented in underworld (and therefore gale) but there are some shortcomings / bugs left to iron out with the current integration scheme for PIC and (my guess is that) there are some outstanding issues with multigrid and some of the processing plugins. I am not sure about the implementation of the stress / pressure recovery for these elements although they are likely to be less important.<br>
<div><br></div><div>Walter was very keen to get this particular element working in gale before he steps back from active development.</div><div><br></div><div>Louis</div><div><br><br><div class="gmail_quote">On Sat, Sep 24, 2011 at 20:16, laetitia le pourhiet <span dir="ltr"><<a href="mailto:laetitia.le_pourhiet@upmc.fr">laetitia.le_pourhiet@upmc.fr</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div bgcolor="#FFFFFF" text="#000000">
Hi Brian and the others,<br>
<br>
There is not much you can do about that I gave up trying to do such
models with Gale.<br>
It is now established Q1Q1 elements are not suited for this kind of
problems.<br>
What you can do is to<br>
1) Remove the free surface/sky to work with delta rho instead of rho<br>
2) Increase the resolution.<br>
<br>
Basically you should only use these elements for extended thin shit
problems. <br>
<br>
The old Q1P0 had other problems, but they could be used to model
drip/subduction problems.<br>
<br>
If CIG still wants to spend some time/money on Gale<br>
It would be usefull to have a switch between elements, like in UW so
that depending on the model set up we can choose the best suited
element.<br>
<br>
hope this was helpfull<br>
<br>
Laetitia<div><div></div><div class="h5"><br>
<br>
On 9/24/11 12:44 AM, Brian Wilson wrote:
</div></div><blockquote type="cite"><div><div></div><div class="h5">Hi all,<br>
<br>
I'm working on a model of lithospheric drip and despite having
zero flux on the boundaries, I am getting downward velocities with
no compensating upwelling, which would seem to violate the
divergence free condition. Has anybody else had a similar problem
and/or figured out a solution? I've attached a copy of my input
file if anyone wants to look at it; everything is scaled as
follows: distance: km, mass: 10^15 kg, time: m.y.<br>
<br>
Thanks,<br>
Brian<br>
<br>
<fieldset></fieldset>
<br>
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<br>
<br>
<div>-- <br>
<b>Dr Laetitia Le Pourhiet</b><\n>
MCF - Institut des Sciences de la Terre Paris - UPMC<\n>
tel : <a href="tel:%2B33%201%2044%2027%2058%2083" value="+33144275883" target="_blank">+33 1 44 27 58 83</a><\n>
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