No-rotation constraint imposed on a surface not working.

[naibaf_omsare]

As entitled, in a model, a no-rotation constraint was imposed on a surface, but it does not work according to the shapes of the resonant modes. I'm using Autodesk Inventor Nastran version 2024.2.0.62. The type of analysis is "Normal Modes". Example of mode shapes are these:

The arrows point to the surface which is supposed to remain horizontal. The next screenshot shows how the constraint is defined:

The little cube on top of the cylindrical head is just another component.

Any help would be appreciated.

Regards,

Fabián

[John_Holtz · Accepted solution]

Hi Fabian,

Rotation of nodes on solid elements are not calculated. Therefore, it is not possible to restrain only the rotation on a solid.

What motion are you really trying to prevent? What I see in the image is the piece is translating in the Z direction. To prevent that, apply a Tz constraint. The alternative is to apply a rigid body connector to the model and constrain the center point of the connector. The rotation constraint creates X,Y,Z reaction forces where the rigid connector attaches to the model. The X,Y,Z reaction forces essentially creates a moment which prevents "rotation".

John

[naibaf_omsare]

Hello John,

Thank you very much for your reply and the suggestion.

Following your suggestion, I used a rigid connector attached to the surface I want to constrain, and then applied the no-rotation constraint to the centre point of the connector. It seems to be working as desired.

Regards,

Fabián