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FDR (Force Distributing Rigid) element of RecurDyn is similar to RBE of other FE software.

(In this article, FDR and RBE will be used as the same meaning)


1. RBE2 = FDR (Rigid Type)

2. RBE3 = FDR (Interpolation Type)



RBE is usually used when a joint or a force is applied to a flexible body (FFlex body) in RecurDyn. 



For example, when you create a joint at the center of the hole in the below body, you need to create an RBE to connect the nodes around the hole, and create the joint at the master node (center).





Next, you need to select the type of the RBE between RBE2 and RBE3.

There is no perfect rule, but here are some guides to help you choose the type of RBE.


1. RBE2

  • Master node and the slave nodes are connected rigidly.
  • The slave nodes have no deformation. (The relative displacements among the nodes don't change)
  • The relative displacement of the master node doesn't change.
  • Generally, faster and more stable than RBE3 when simulating



2. RBE3

  • The relative displacements among the slave nodes can change (deformable)
  • The relative displacement of the master node can change as well.
  • Generally, slower than RBE2 but more practical because it can be deformed.


3. Guide to select between RBE2 and RBE3.

  • The real connections cannot be 'perfectly rigid', so that RBE3 is more feasible element
  • But if the connection can be assumed that it is rigid enough, then RBE2 is recommended.
  • in summary, 
    • Firstly, you can use RBE2, if there is no special reason to use RBE3
    • Especially, if the connection is the bolting or welding, it is rigid enough so that RBE2 can be reasonable choice.
    • If you are more interested in the behavior of other part of the body rather than the connection area where RBE is used, then you can use RBE2.
    • If you want a faster and more stable simulation, RBE2 is a good choice.
    • If the connection should be flexible and you are interested in the detailed behavior of the connection area, RBE3 needs to be used firstly.





* Multi-Body Dynamics Software, RecurDyn

* MFBD (Multi Flexible Body Dynamics)