ERROR : RADIOSS IMPLICIT STOPPED DUE TO TIMESTEP LIMIT ** ISTOP=-2

Karthic_22061

Hi,

I am trying Geom-nonlinear in Optistruct.

 

Please guide me in solving the convergence issue due to geometric non-linearity

RADIOSS IMPLICIT STOPPED DUE TO TIMESTEP LIMIT **

      ISTOP=-2

 

I faced the very same error message in RADIOSS (Implicit). Please have a look at the model for clarification if any..

Unable to find an attachment - read this blog

Altair Forum User

Hi Kathik,

 

 From RADIOSS help, 

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Karthic_22061

Hi Prakash,

I tried all the above, but i couldn't solve the problem with Radioss(implicit)

So trying to solve with Optistruct. I don't want to move to explicit.  How to solve it .....

 

Altair Forum User said:

Hi Karthic,

When the time step is smaller than the input minimum one (see /IMPL/DT/STOP), RADIOSS will stop the run with this message.

The reason is generally due to the convergence issue (DT_min), if DT_min was already small enough or not.

There is no general workaround for convergence issue, as outlined below:

>>Check the model, constraint conditions, materials, contact interface defines and so on.

>>If the fail was due to instability, try /IMPL/DT/3 (Riks method) or /IMPL/QSTAT for general instability case.

>>Switching other convergence criteria (see Itol in /IMPL/NONLIN)

 

Altair Forum User said:

Hi George,

Thank you for the reply..

Riks method can only be used for static analysis.. If so how can i include the geometric nonlinear and at the same time solve for the buckling

Altair Forum User said:

Hi Karthic,

The Riks type arc-length method is suitable for nonlinear static analysis of unstable problems like buckling, snap-through. 

I recommend you to go through /IMPL/DT/3 in Help Menu where this is described.

Altair Forum User said:

Hi George,

I tried using /IMPL/DT/3 (Riks type arc-length method) , but my run doesn't start converging.

 

Please do have a look at the model  attached. Help me to solve the convergence issue due to geometric nonlinear.  

Altair Forum User said:

Hi Karthic,

I doubt with the loading type used. Can you try with /IMPDISP instead of /CLOAD.

Can you try with explicit formulation, as implicit solution is RADIOSS is more to complement the explicit Solution.  So we suggest to use it only for specific cases like Spring Back. 

Unable to find an attachment - read this blog

Altair Forum User

Karthik,

 

I hope you already tried with imposed displacement. Did you see any results?

Karthic_22061

Hi Prakash,

Thank you , Time step error overcame by imposed displacement. I also tried Geo nonlinear (implic dynamic). Now i am trying to match my results. /emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' />