[MBDyn-users] Placing the middle node of a 3 node beam

masarati at aero.polimi.it masarati at aero.polimi.it
Tue Feb 22 20:01:05 CET 2011

> Hi,
> just a little question about the 3 node beam element:
> Is it allowed to place the (structual) middle node not exactliy in the
> middle, but e.g. lets say 1/3 of the lenght of the beam?
> I mean not like:
> 1-----2-----3
> But:
> 1---2-------3

It is, but you must be aware of the possible consequences.  In addition to
Romuald's comment, as soon as you move the mid-node you distort the metric
of the beam.  Not only this impacts the location of the point where
constitutive properties are evaluated; it may also yield surprising
results: as in plane and solid isoparametric elements, moving the mid-node
to a quarter-length of the element yields infinite strain at the closest
end node, as used in linear fracture mechanics to model crack tip
conditions.  I strongly recommend to place the mid-node exactly at

> Jens
> BTW: the *.log file patch works fine - thank you very much for that!
> Just the "name" is missing in the headline - but thats realy not that
> critical :)

Yeah, I noticed that after posting the patch.  It is fixed in the
mainstream code, will appear in the official release ;)

Cheers, p.

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