[CIG-LONG] GALE: Time dependent loading of an unstable layer

[Walter Landry]

Karen Paczkowski <karen.paczkowski at yale.edu> wrote:
> 1)  How can I create a time dependent forcing function?  Ideally I  
> would like a time dependent normal force on the top of the box that is  
> a combination of the relaxation of the topography (like in the  
> sinusoidal.xml) and the oscillating applied vertical loading.

You will have to write a new StandardConditionFunction.  Section 7.5
has instructions on how to do that.  The function

  StgFEM_StandardConditionFunctions_StepFunction

has an example of how to get the time coordinate.  Then you will use a
StressBC to apply it to the top.

> 2)  Can I track the rate a certain interface/isotherm/etc moves?  For  
> example, in the cookbook there is a topography relaxation example.  I  
> can get the correct images for the strain rate invariant and velocity  
> field, but I'm not sure how to determine the relaxation rate of the  
> top interface.  Is there a simple way to do this?  I would like to  
> track the growth rate of the Rayleigh-Taylor instability.  Will this  
> be possible?

The best way to track a particular point on the surface is to extract
it from the vtk files.  For example, for the sinusoid example, to look
at the top right point, I can use the shell script

  for i in `seq -w 0 10`; do head -n 568 output.sinusoid/fields.0.000$i.vts | tail -n 1; done

The script runs through the field output files.  For each file, it
extracts line 568 by getting the first 568 lines and then extracts the
last line of that output.  That gives me the output

  0.5 0.99 0
  0.5 0.995540234820877 0
  0.5 0.999490364527093 0
  0.5 1.00027465600373 0
  0.5 0.999849941773926 0
  0.5 1.0001336417245 0
  0.5 0.99996050453487 0
  0.5 1.00012179450133 0
  0.5 1.00000901361254 0
  0.5 1.00012299563956 0
  0.5 1.00001791485582 0

If you want to do something more complicated like tracking an
isotherm, then you will want to use Paraview.  Paraview has a lot of
options, so it depends exactly on what you want.

Cheers,
Walter Landry
walter at geodynamics.org