#1 2017-03-10 13:57:49

Msegade

Member

Registered: 2017-02-23

Posts: 31

Singular matrix in simple truss

Hi

I'm trying to do a simple 2D truss analysis with a vertical load in one of the nodes. The problem is that I get that the matrix is singular, but I can't find what is wrong with model. I tried making the model with beams instead of articulated bars, and adding more bonudary conditions, but I get the same error.  I suppouse that there is a problem with the mesh, but it seems fine to me.

I attach the comm, med and mess files.

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Attachments:
truss.zip, Size: 8.87 KiB, Downloads: 380

stephaneberger

Member

From: Strasbourg (France)

Registered: 2012-10-15

Posts: 70

Re: Singular matrix in simple truss

Hi

The issue comes from your mesh.
When you use barre element, you must have only one SEG2 element between 2 nodes.
When you mesh your geometry, you have to apply only 1 element per edge.
(see test case ssll110a)

stephane

Msegade

Member

Registered: 2017-02-23

Posts: 31

Re: Singular matrix in simple truss

Thanks for the reply

I tried with the mesh you suggested, but I get the same results: singular matrix. However I managed to get the analysis to run with beam elements, and the deformation give the solution to what was wrong:

The elements wasn't connected at the nodes for some small numeric errors in the geometry!

Merging the nodes in salome solved the problem.