[Geoqus] Erosion and surface modification with ABAQUS

[Vincent Godard]

 Thank you very much for your answers,

So it seems that the simpliest way to deal with erosion is to remove elements. 
I was a bit reluctant to do this that way, but as you can make density 
dependant of user defined fields it may be possible to "smooth" the process. 
I'm thinking of using my erosion routine to modify the density of the 
elements (via user subroutine) just below the surface, from initial density 
down to zero, before removal.
At that point, I'm trying to figure out how to identify and handle the nodes 
and elements concerned by this removal. Do you think it is possible to do 
this automaticaly with user subroutines or do I need to stop the analysis and 
then restart after removal?

 I am an absolute begginer with ABAQUS so if anybody has a simple input file 
related to a geodynamic problem to send to me that would help me to get 
started (in particular to deal with isostasy, contact surfaces ans things 
like that).

Thanks in advance

Vincent.


Le Mardi 16 Septembre 2003 15:30, Peter Connolly a écrit :
> Dear Vincent
>
> I'm a little unsure excactly what you are trying to do here. My guess is
> that you want to add or remove an arbitaty  set of elements (say ones
> that exceed 1000m above sea level) and then remesh the top 2000m so that
> you have a fine mesh near the surface for high density data extraction?
> This should be doable, but unlike Kasper, I would suggest doing this
> inside the FE run as a user subroutine. For the example above this would
> handle the check for your "failure criterion (in my example Z>1000m) and
> then remove the offending elements, then all the remeshing subrutines.
> All doable, but will require a bit of work in fortran and C.
>
> With regards to Kasper's comment on moving nodes. As long as you know
> which, where and how then I think the way to do this would be to move
> the nodes (if necessary defined via a user routine) using the *BOUNDARY
> option with the step definition. You could always make a dedicate
> "passive" step with the nodal displacements to mimimise influence, if
> that’s whats needed. Again, a user routine could handle the
> identification of which nodes to shuffle.
>
> If you know how your topography evolved and you all want to do is add
> and remove elements in a predetermined order then yes, this should be
> straightforward. You would have to collect the appropriate elements into
> sets that are turned "on or off" in each analysis step. This would be
> simple, and if you could use a really fine mesh for the near surface (ie
> lots of RAM available or simple rheologies) then remeshing wouldn't be
> necessary.
>
> Hope that helps
>
>
> Peter
>
>
> -----Original Message-----
> From:
> geoqus-bounces+peter.connolly=gpi.uni-karlsruhe.de at lists.ruhr-uni-bochum
> .de
> [mailto:geoqus-bounces+peter.connolly=gpi.uni-karlsruhe.de at lists.ruhr-un
> i-bochum.de] On Behalf Of Kasper Fischer
> Sent: 16 September 2003 16:37
> To: geoqus at lists.ruhr-uni-bochum.de
> Subject: Re: [Geoqus] Erosion and surface modification with ABAQUS
>
>
> Hi Vincent Godard,
>
> first of all I want to welcome You to the Geoqus User Group. You
> will
> find more about Geoqus on
> http://www.ruhr-uni-bochum.de/geoqus
>
> I am working with Abaqus for many years. During my Ph.D I have
> worked on
> the same topic as You. The interaction of tectonic and surface
> processes. It is possible to do the task You want to do, but it is a
> little bit tricky. I used a feature of Abaqus to add or delete
> elements
> during the calculation. This can be done very easily but one has to
> figure out which element is affected. The main disadventage is
> that the
> topography is very coarse since the size of the elements can't be
> too
> small for a good performance. I have done this with the old
> version of
> Abaqus (v. 5.8) and an IDL interface which read in the results of
> the
> program to calculate the erosion and sedimentation (Golem by Greg
> Tucker) and deciding on the results where to add or remove
> elements. The
> current version of Abaqus (v. 6.3) has a scripting interface
> (python)
> which might make things easier. If You want I can send You the
> IDL scripts.
>
> A other choice would be to move only the surface nodes of the
> elements.
> But I was not sure how this can be done in Abaqus and if it is
> possible
> what happens to internal stress and strain values of the affected
> element. Maybe somebody else has an idea or done this?
>
> I hope that I could help You and I am looking forward to
> discussing this
> topic here.
>
> Kasper Fischer

-- 
Vincent Godard
Equipe de géodynamique
Laboratoire de Géologie
Ecole Normale Supérieure
24, Rue Lhomond
75231 Paris Cedex 05, France
Tel: +33 1 44 32 22 63  Fax +33 1 44 32 22 00
email: godard at geologie.ens.fr