[Geoqus] Erosion and surface modification with ABAQUS

[Peter Connolly]

Hi Kasper

What I meant by a passive step is one in which ONLY the nodal
displacement was applied i.e. no external drivers to the model are
changed. 

I can envisage 2 ways of doing this (but have only done 1>),

1> the normal kinematic boundary condition way in which only the
*BOUNDARY option is used in the step definition to relocate the nodes,
the step then executes as normal, modifying the system to reflect the
new geometry. For sure this works since many people use it to move model
boundaries.

2> using a user routine to move the nodes to their new positions but
omit solving the model. This is possible but not recommended by HKS
since the modified model would not be stable in the FE solver. If the
node displacements where small viz incremental erosion I don't see why
it wouldn't work, if they were large viz the scale of a mountain I'd
expect a "few" issues to arise!!! For example, when using the *INITIAL
CONDITION options they recommend an initial "stabilisation step" to sort
everything out, so with large position changes the same would probably
apply here. This is not really different to option 1 above! If you tried
this, what happens when you solve the model would need careful
investigation. For example, one question is: "how does the new solution
implicitly solve the state for the moved nodes within the next
solution". 

I think option 1 is the way to go since it's fairly easy to impliment,
and probably happens even if you do option 2!


Take care

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: 17 September 2003 15:40
To: Geoscientific Abaqus User Group
Subject: Re: [Geoqus] Erosion and surface modification with ABAQUS


Hi Peter Connolly,

you wrote that you would include a 'passive' step to minimise the 
influence (on element stress?) when moving nodes with the *BOUNDARY 
option. Can You please explain what you mean with a 'passive' step? I am

very interested how this works, because it seems that this would be a 
more elegant way then the way I went.

Thanks

Kasper

Peter Connolly wrote:

>...
>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 minimise influence, if 
>that’s whats needed. Again, a user routine could handle the 
>identification of which nodes to shuffle.
>
>...
>
-- 
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| Dr. Kasper D. Fischer             <kasper.fischer at ruhr-uni-bochum.de>
|
| Ruhr-Universität Bochum
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| Institut für Geologie, Mineralogie und Geophysik
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| NA 3 / 174                        Tel: +49 234 3227574
|
| D-44780 Bochum                    Fax: +49 234 3214181
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| Germany                           www.geophysik.ruhr-uni-bochum.de
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