Node types and how to implement the associated force in FEA?


When using the class "AnyMechOutputFileForceExport" to export all forces associated with a specific segment for further FEA, there are many types of nodes in the exported results file.
For example in the case of the Pelvis Segment:

  1. Normal Ins. Node (Ins on the bone landmark)
  2. Via Node (could be on the bone or the space)
    4.PressureNode > Eg: AbdominalPressureMuscle

How to implement "Via Node" or "WrapSurf" in FEA considering that these forces act on an imaginary point in the space and not on the bone itself?!

In case of the same muscle link is attached to Via Node and Ins Node, should I sum these two forces together? or adopt only the force associated with Ins Node?

Another question,
In AnyBody there is a pelvis segment and sacrum segment; however,
many sacrum nodes are defined on the pelvis segment (check the InsNodes of the pelvis segment tree) instead of the sacrum segment!! why?!!


Hi Ahmed,

It depends on the question at hand. In some cases you can simplify your model and just apply these forces as we suggest (concentrated force at the node + node-surface constraints), i.e. in case of analysis of joint articulation. But in other case, where you need very detailed loads on the boney surface close to the via point - it's trickier. I would analyze individual muscles and see whether it has any connection to the surface or not. Also you could check the value of the muscle force - if it is 0.1-2 N - maybe it matters less. Could you describe your particular problem?

Sacrum/Pelvis node sharing - yes, that was an issue, but it should be resolved in the newer versions of AMMR. The logic there was that for the musculoskeletal analysis it does not matter - since the 2 segments were rigidly connected, but it does matter for the FEA. One way would be to use the latest AMMR with corrections, the other to select particular muscles and apply to sacrum instead of pelvis or vice versa.

Kind regards,

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