error: Solver problem. Numerical singularity when processing D.O.F 1

[cdeepakroy]

I recently(last week) started using abaqus with the motive of modelling the gravitational response of the following model:

> a solid hemisphere with a layer of a hemisperical shell over it.

I successfully created the model with two part instances, then i applied a contact constraint from (0,0,0)->(0,0,-1).

Then i applied an interaction between the curved surface of the solid hemispehere and the hemispherical shell with the solid hemisphere's curved surface as the master surface and the hemispherical shell's inner surface as the slave.

Then i applied a boundary condition that comletely fixes the flat face of the solid hemisphere.

Then i applied a downward body force on both the part instances.

But when i submit the job and monitor its prograss i get a lot of warning messages and finally an error message saying "Too many attempts made in this increment". The warning i get are as follows:

>> 18 nodes may have incorrect normal definitions. The nodes have been identified in node set warnnodeincorrectnormal.

There are 2 unconnected regions in the model.

The system matrix has 3 negative eigenvalues.

Solver problem. Numerical singularity when processing D.O.F. 6 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_6_1_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 5 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_5_1_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 4 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_4_1_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 3 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_3_1_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 2 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_2_1_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 1 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_1_1_1_1_1.

The system matrix has 3 negative eigenvalues.

Solver problem. Numerical singularity when processing D.O.F. 6 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_6_2_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 5 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_5_2_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 4 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_4_2_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 3 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_3_2_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 2 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_2_2_1_1_1.

Solver problem. Numerical singularity when processing D.O.F. 1 of 1 nodes. The nodes have been identified in node set warnnodesolvprobnumsing_1_2_1_1_1.

The system matrix has 3 negative eigenvalues.

......
......
...... and so on many errors like this.


Can anyone tell me what these errors mean and how can i resolve this. I am a newbie to abaqus and finite element analysis, which is the reason i am having a hard time figuring out the cause of these errors.

Please help me......

Thanks in advance.

Deepak

 

[corus]

Use Viewer to view the normals on your model. You may find that the normals don't point in the right directions, particularly with shell elements.
2 unconnected regions implies that the regions haven't made contact. Try imposing a fixed displacement to impose contact before removing that displacement in a 2nd step.
The fact that all 6 dofs have numerical singularities implies that your shell part has decided to float off. This is due to the fact that the regions are unconnected. Resolving the contact problem should remove this error.

If the solid hemisphere and the shell are to remain in contact throughout then there is no need have them as separate parts in contact. Abaqus allows you to apply shell elements to the surface of a solid as a single part, I think.

corus

 

[cdeepakroy]

Re-adjusting the contact, boundary conditions and interaction lead to a successful job completion.

Thanks to corus for it.

But the incorrect normals warning is still prevailing. Can anyone tell me how to get rid of the incorrect normals warning.

 

[corus]

You can flip the normals in CAE if they are pointing in the wrong direction.

corus