[MBDyn-users] Finite element coupling

Romuald NORET romuald.noret at cdr.hutchinson.fr
Wed May 5 16:58:05 CEST 2010


I took a little bit of time to make sure to understand what I need.
Solution #2 : it requires lots of iterations without to be sure to 
converge. So even if I am still curious about how it could work, I don't 
think  it will be the best way to solve large analysis.
Solution #3 : do you have documentation about it? I tried without success, 
I hope it is the best way for my analysis.

I can summarize my analysis by this schema :

  +---+---+ /
 /   /   /|/
+---+---+ o
|   |   |/

Of course real studis are a little bit more complex, but it is the same 
with more elements. So I would like to make a coupling between :
- the first part (at the left) : some finites elements with a finite 
element software
- the second part (at the right) : sprigns with MBDyn (with total joint)

Thanks in advance.

Best regards,
Romuald Noret

Pierangelo Masarati <masarati at aero.polimi.it> 
05/02/2010 16:58

Romuald NORET <romuald.noret at cdr.hutchinson.fr>
mbdyn-users at mbdyn.org
Re: [MBDyn-users]  Finite element coupling

Romuald NORET wrote:
> Hello,
> I am wonderdering if it is possible to make a coupling between MBDyn and 
> finite element software, for structural analysis.
> It is possible and if it is this case, do you have an example?

Not sure what you exactly mean, by coupling.  Right now, you have many 
options, at different levels.

1) you can import Component Mode Synthesis elements (the "modal" joint)

2) you can have MBDyn talk to an external solver by sending "measures" 
(using the stream output element) and reading "controls" (using the 
stream driver), provided the other solver talks MBDyn's protocol (which 
is pretty simple).  Somebody did it in Python to talk to Code Aster (I 
don't have the code, but we can ask, or redo it from scratch; the whole 
thing is similar to what Doug Baldwin used animate models in Blender 
run-time).  This implements a "loose coupling" scheme, where MBDyn and 
the external solver independently solve the respective problems and 
communicate each other's results.  In some cases, this may result in 
unstable couplings, much like you would have when using explicit 
integration schemes.

3) in 1.3.11 there are provisions for "tight" couplings in a scheme 
where MBDyn outputs motion to and read loads from an external solver; 
the two solvers can iterate in a staggered manner, in order to guarantee 
that they converge simultaneously.  This is now working for sure in case 
of CMS models; it should also work for node sets, although it's not 
thoroughly tested.  Of course, the other codes need to be able to read 
and write data according to MBDyn's format.  We provide an open format 
for data exchange via ASCII files and library calls for inter-process 
communication using UNIX sockets.  Adding built-in supports for 
different formats should be straightforward.  We did it to communicate 
with FOI's EDGE using EDGE's built-in file format.

Does this help?

Cheers, p.

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