Using /explicit for a dynamic step

[cgbridges]

Hello -

I have a model that is loaded almost entirely with static loads. The critical step, however, is best done dynamically, and will result in the failure of certain elements.

I'm having numerical problems in this final step when using /standard, but have been told that /explicit would handle the problem much better. From what I've read in the manuals and online, it appears that I can just apply /explicit to this one step, but I am not clear on how I would do that.

Am I incorrect in thinking this? And if not, where would it be put into consideration?

Thank you!

 

[RGX124]

Hi,
I think you just have to create your "explicit" step by putting the keyword *DYNAMIC instead of *STATIC.
*DYNAMIC is still used with Abaqus standard for direct integration.

Regards

RK

 

[cgbridges]

This may seem simple or obvious, but:

Do *dynamic steps default to /explicit?

If so: wow, I did not know that.

 

[bassmanjax]

No, they do not default to explicit. *DYNAMIC invokes the impicit dynamic solver.

You have to use the *DYNAMIC, EXPLICIT card.

There are advantages to using Explicit over Standard, like the general contact algorithm in 3D models - very handy!

Be aware that there are subtle differences between running ABAQUS/Explicit vs ABAQUS/Standard, as they have evolved as two seperate solvers.

- Contact. In Standard, defined as part of the model. In Explicit, defined as history (step) data.
- Structural loads & BC's specified in Explicit generally need to have amplitude curves associated with them.
- Time step is critical, you ideally need to run with small (>100ms) timesteps to get 'sensible' run times. Look up 'quasi-static' analyses....

Basically, it's not just as simple as changing *STATIC to *DYNAMIC, EXPLICIT.

In your case, you may be better running the *STATIC steps in one input deck, then importing the results of this analysis to a new analysis using *IMPORT and *INSTANCE - the documentation is pretty good on this (look up 'Restarting an analysis'). I don't have access to the docs at the mo, otherwise I'd point you to the right places!

Martin

 

[cgbridges]

Thanks Martin.

If you don't mind me picking your brain a bit more... I've been playing around with *restart, and it doesn't seem right for what I'm doing (a lot of the keywords I'm using aren't supported with /explicit). However, it would be good to have an /explicit step that imports the response (stresses, deflections, etc) from the previous /standard (*static) steps.

Is this how *import is used? If so, what else do I need to include in that new input file? Nodes, materials, element definitions, and the *dynamic load step I want to run?

Thanks again.