excessive distortion error in Abaqus

[gamertag]

I am simulating a impact scenario in Abaqus Dynamic Explicit.
Abaqus throws up this error of "excessive distortion/ratio of wave speed ....greater than one" after executing certain time increments.
Can anyone pls tell me why this error occurs when we run the simulation and how to remedy it?

 

[GPapazafeiropoulos]

There may be a very large contact acceleration correction that was applied a few increments prior to
termination. Do the following:
(1) Decrease the velocity of impact
(2) Change the density of the material(s) where the error occurs
(3) Change the modulus of elasticity of the material(s) where the error occurs
(4) Change the time incrementation
(5) Change the mesh refinement where impact occurs

Regards,

_______________________________________________
George Papazafeiropoulos
First Lieutenant, Infrastructure Engineer, Hellenic Air Force
Civil Engineer, M.Sc., Ph.D. candidate, NTUA
Email: gpapazafeiropoulos@yahoo.gr
Website:

http://users.ntua.gr/gpapazaf/

 

[gamertag]

Thanks!!!

 

[Mustaine3]

#1-3 are changing the physics of the model and make the simulation useless.
#4 is not possible, since the stable increment size is calculated automatically by Explicit and the user has only limited and indirect influence in that.


- Refine the mesh and use a little bit of mass scaling when the stable increment size goes down too much. Make sure you're not changing the inertia too much with mass scaling.

- Check if you can use adaptive meshing the keep the elements in a good shape.

- Check if you can define a material failure criteria that deactivates also the elements with a failed material.

 

[gamertag]

@ Mustaine3 . I am modelling a hyper-viscoelastic material. Abaqus doesnt allow the use of adaptive meshing for this material type. Is there any way to get around this limitation?

 

[IceBreakerSours]

I can see why Abaqus (or, for that matter, any FE code) will have trouble with certain element types; I can not see why there should be an issue vis a vis the choice of a material law. But its been years since I last played with adaptive remeshing (that too for fun sake) so it is likely that I am wrong.

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[Mustaine3]

There are limitations regarding the possible material models. I think it comes from the decoupling of the material from the elements during the remeshing sweeps.


If none of all the hints are working, the CEL method might be an option. But it would be my last choice...

 

[gamertag]

@ Mustaine3. Correction. Abaqus does allow the use of Adaptive meshing for the viscohyperelastic material, for some modes of hourglass control. I have used Adaptive meshing with hourglass control set to relax stiffness and stiffness modes, but with no sucess. I have one element which getting excessively distorted. Can I deactivate this element from further analysis?

 

[IceBreakerSours]

gamertag:

I strongly suggest taking 'baby steps'; your statements reveal your 'kitchen-sink' strategy. For instance, ".. for some modes of hourglass control.", "Can I deactivate this element from further analysis?".

Have you gone through the Getting Started Guide (Interactive Edition)? If not, take a few days to do so - front to back.

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[gamertag]

When using adaptive meshing, is it necessary that the mesh elements on the boundary and the contact regions be restricted to move along with the material???

 

[gamertag]

Also for modelling the contact scenario more accurately, does improving the smoothness of the analytical rigid surface help? Can the smoothness of semicircular surface be further increased?