Constraint – Rigid link

[akshay somkuwar]

Hi NextFEM community,

I have recently started exploring NextFEM Designer. I am working on a simple brace model using quad elements and wanted to constrain the perimeter nodes to a central node using rigid links, while applying a pinned boundary condition to the central node.
However, when I try to use the rigid link option, it seems that the constraints are not being applied properly – it feels like I am missing a step. On the other hand, when I use the rigid diaphragm option between the nodes, it works as expected.
Any help or guidance on how to correctly apply rigid links would be greatly appreciated.
P.S. I have attached a screenshot showing the model with the rigid diaphragm applied.
Thank you!

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[NextFEM Admin]

Dear Akshay,
to clarify about internal constraints:
– rigid links bounds all degrees of freedom (DoFs), while
– rigid floor involves only x,y and rz.
Looking at your screenshot, the issue you encounter is not clear enough; I believe you should try to directly draw the rigid links by selecting the “Draw link” option in the same mask.

[akshay somkuwar]

Hi,

– The issue I am encountering is that whether I select the nodes or draw the link, it is not creating a rigid link between the nodes. However, the rigid diaphragm option seems to be working fine.
– I do understand the constraints applied on the degrees of freedom (DOF). I just wanted to show that while the rigid diaphragm option is working fine, the rigid link option is encountering an issue — or perhaps I am missing something (In some trials it was saying waiting for spring2 element).

[NextFEM Admin]

Can you share your file telling between which nodes you created the link? Can you descrive the operations you do in detail?

[akshay somkuwar]

Sure,
Please find the attached file.
Following operations are performed
1. For Rigid diaphragm-
1. selection of nodes (node 1 and 2)
2. Assign > Constrains > Preset > Rigid diaphragm > specify master node > apply

2 Rigid link
1. selection of nodes (node 3 and 4)
2. same procedure as above
but the constraint neither shown in constraints list or shown when tried to view.

Additionally I would appreciate if you could also provide guidance on how to set 1st mode as initial condition to account for initial imperfection.

Thank you very much

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[NextFEM Admin]

Thanks for it, we’ll solve in the next minor patch (File / Update / Check for minor updates…).
Currently we don’t support initial imperfection as per 1st mode.

[akshay somkuwar]

Thank you very much.

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