[MBDyn-users] Placing the middle node of a 3 node beam -> for using AeroDyn

Pierangelo Masarati masarati at aero.polimi.it
Wed Feb 23 17:34:43 CET 2011

Jens.vanSchelve at Emerson.com wrote:
> Yes, this should work. Only two little issues: No aerodynamics near the
> hub and
> I would like to have the beam as long as the blade - it might be
> confusing in the
> post-processing and visualisation otherwise.
> Also what came to our mind is that it might be an advantage to have more
> resulution
> near the tip because of tip loss corrections and bigger deformations.
> Therfore we could also place the beam3 elements at Chebyshev collocation
> points.
> In this case only the mid nodes of each element would have an
> aerodynamic
> element applied.
> Meaning only every second node would have an external force. Is this
> still ok?
> Like:
>        ____A____ ___B___ __C__
>  ---  |         |       |     |
> (HUB) 1----2----3---4---5--6--7
>  ---  |_________|_______|_____|
> Aerodynamic element (force) on 2, 4, 6 only

Less than ideal.  If visualization is your driving requirement, you 
should place a dummy node of type "offset" at the end of the blade.  A 
dummy node is a fake node (i.e. no degrees of freedom nor equations 
related to it) that is output like other nodes.  The "offset" type means 
that its output corresponds to the rigid body motion of a point rigidly 
offset from a parent structural node.  So you could have

             ___A___ ___B___ ___C___ ___D___
   ---      |       |       |       |       |
  (HUB) 1-------2-------3-------4-------5---d
   ---      |_______|_______|_______|_______|

where "d" is your dummy node.

You could refine the mesh by using offsets (keyword "position" after 
each node's label in the input to module-aerodyn).  This way, you could have

              ____A____ ___B___ __C__ __D__
   ---       |         |       |     |     |
  (HUB) 1---------2---------3-----4-----5--d
   ---       |    A--------B------C-----D  |

Cheers, p.

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