ASET1 card in NASTRAN

[Giang123]

Hi all,

I have a question about the ASET1 card in NASTRAN. When it is added to a BDF file, what does it mean? I read the manual, and it specifies the DOFs of a node that you want. However, in the case of a node within a shell element, theoretically, a shell element always has 6 DOFs. But in some problems, I encountered the requirement to set the ASET1 card for a shell element with 3 DOFs to perform normal mode SOL 103. Is that correct?

Best,

Giang

 

[sdm919]

In computing vibration or buckling eigenvalues using Nastran SOL 103 or 105, an ASET is used to reduce the computational effort. Often, the translational DOFs are sufficient to describe the desired modes. Of course there are exceptions, so it is not a blanket statement.

For example, a straight cantilever beam modeled with say 10 elements, with the x-axis along the beam and the y-axis vertical, and the z-axis out-of-plane. If you only want the in-plane vibration modes, you would only need to put DOF 2 for all the nodes in the ASET. Similarly, for a simply-supported square flat plate in the x-y plane, say with a 10x10 element mesh, you would only need to put DOF 3 (normal to plate) for each node in the ASET.

To convince yourself, I strongly advise you to run a few simple cases like those mentioned above, both with a full ASET and with an ASET limited as I've described. You should find the differences to be small.

 

[Giang123]

Hi sdm919,

I have tested, and ASET is used to reduce the computational effort; however, it seems that ASET1 is different from the constraint. For example:
- With format: ASET1 123 1 34 mean node 1, node 34 has DOFs (Degrees of Freedom) in the translational x, y, z directions but no rotation.
So, is it equivalent to not using ASET1 and instead constraint the rotation in the x, y, z directions?
(I have tested both cases using ASET1 and constraint the rotation in x, y, z, and the results are different)
Do you know why they differ like that? I am currently trying to convert ASET1 from MSC NASTRAN to another software, for example, ABAQUS, and I do not know how ASET1 functions at the moment.