[MBDyn-users] Offset modal body with revolute hinge

Jim, Timothy Timothy.Jim at eads.com
Tue Jun 16 16:05:07 CEST 2015

Issue solved - it was a problem with the CG position in the FEM file,
not MBDyn.


Kind regards. 


From: Jim, Timothy 
Sent: Tuesday, June 16, 2015 1:32 PM
To: 'mbdyn-users at mbdyn.org'
Subject: RE: Offset modal body with revolute hinge


Apologies to double post, just to clarify, if I remove the hinge joint,
the body freefalls normally. Adding the revolute hinge constraint then
causes the body to rotate about the hinge upwards.


Kind regards,



From: Jim, Timothy 
Sent: Tuesday, June 16, 2015 1:16 PM
To: 'mbdyn-users at mbdyn.org'
Subject: Offset modal body with revolute hinge


Dear all,


I am experiencing a strange response using a modal body and a revolute
hinge - I have a nodal body that is offset from its modal node (i.e. the
modal node starts at the origin but the body starts at some location
x,y,z) due to the problem setup. The modal node is not constrained in
any other way. I have a clamped static node at an arbitrary position in
space upon which one end of the revolute hinge is referenced. The other
end of the hinge is attached to the first physical node on the body (an
extracted FEM interface node).


The body starts off parallel to the x-axis and gravity is on (I want to
see the body swing under the influence of gravity) but when I run the
simulation, the body apparently swings 'upwards', away from the ground
and oscillates as if gravity is set upside down. I know that this isn't
the case as when I use a clamp instead of a revolute hinge to constrain
the FEM interface node, I see that the body deflects downwards in a
manner that is consistent with a beam clamped at one end.


Has anyone come across this before? Any ideas on how else to test this
model would be appreciated.


Many thanks and kind regards,


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