Negetive Eign Value

[san07gita]

My beam model worked fine for a small load. However, whenever I was trying to give a large load, its giving me an warning massege "2 negative eign values" and followed by an error message. I am sure the load is not too much for the model. Any one have any idea whats going on and how I can avoid that problem.

 

[johnsmith2]

did u try to re-fine the mesh?

 

[Yoman228]

If it is a very long beam, change the element type to hybride beam element may help.
Or you would like to try using stabilization in the step to check is if there is an error in the model such as material.

 

[bassmanjax]

Hi

What is the error message that you get?

Regards

Martin

 

[xerf]

Did you set NLGEOM to ON ?

 

[san07gita]

The Error Message is "Too many attempts...."

Yes, I Set Nlgeom to on.I think that is why the beam is distorting too much.

 

[Yoman228]

have you tried the method I suggested?
And turning The NLGEOM On is a must in large deformation analysis in order to get the correct result.

 

[bassmanjax]

Try reducing the minimum time step size.

Regards

Martin

 

[mizzjoey]

or you could try changing the displacement tolerance to 100%. This relaxes the controls so the solver won't crash when it senses that the deformation is too big compared to the default spec.

try adding *controls after your *step. It helps with my solution sometimes.

*Controls, parameters=field, field=displacement
, 100.0

 

[brep]

This type of negative eigenvalue warning is often caused by the structure starting to buckle. Have you done a buckling analysis to see if you indeed are loading it in such a way as to induce buckling?