Unconnected Regions

[flyforever85]

I've never had this problem and I spent hours looking for a solution but with no results.

ABAQUS keeps telling me I have 2 unconnected regions in my model and because of the it cannot process an Inertia Relief analysis. I can't share the inp file unfortunately

1. my analysis is linear static;
2. There is no contact region modelled, just couplings (old RBE2 and RBE3s)
3.I run a modal analysis and nothing seems to move
4. I found in the the commando unconnected_regions=yes would give me the region that are unconnected. When I use it though the command line though, I get exaclty the same element and nodes sets I have without this commando on.

Any idea of what other checks I should do?

Thanks

 

[FEA way]

Do you use tie constraints in this simulation ? Are you sure that couplings are correctly defined ? Sometimes unconnected regions are nothing to worry about (especially when modal analysis doesn't show any rigid body motions) but it's always good to check them.

 

[flyforever85]

Unfortunately I have to worry because the analysis aborts due to the unconnected region. It's an helicopter so I don't have boundary conditions clamping the model but just the inertia relief. I do have tie constraints and couplings (both kinematic and structural). The original model worked then some modification were done and now it doesn't converge anymore.

I found it awkward that abaqus doesn't give the possibility to see where this error is.

Also: in the modal analysis the model shows the first 6 rigid modes as expected and then different other modes. In none of them I can see part of the structure moving.

 

[FEA way]

Do you use unconnected_regions command in regular analysis or in datacheck ? Because it’s meant for the latter. If you run datacheck with this command turned on it should return sets indicating problematic region of the model.

 

[flyforever85]

I did use it in datacheck as: abaqus datacheck job=... input=... unconnected_regions=yes cpus=4 interactive

 

[flyforever85]

I found the problem: one of the connector I had was created on reference point that were not connected to any part of the structure.