Changing Total Time changes the result?
Changing Total Time changes the result?
(OP)
I am simulating a ball bouncing using Abaqus/Explicit. I have noticed that if the total time of the simulation is changed theresults also change, which I think does not make sense as the whole setup is the same except the total time.
Here is the plot of Kinetic Energy vs Time for 3 different total times.

After I zoomin, I would expect the plots to overlap, but I find that the plot do not overlap.

I am using automatic timesteping for the simulation. Also the 'Initial time increment' is the same for all the cases.
Can anyone explain why this happens?
Thanks
Here is the plot of Kinetic Energy vs Time for 3 different total times.

After I zoomin, I would expect the plots to overlap, but I find that the plot do not overlap.

I am using automatic timesteping for the simulation. Also the 'Initial time increment' is the same for all the cases.
Can anyone explain why this happens?
Thanks





RE: Changing Total Time changes the result?
This convergence process makes non-linear problems and dynamics problems much more time consuming than your basic linear static analysis, but it's work that needs to be done nonetheless if you want accurate results. It's usually when this process doesn't take place that you start to get people that say FEA can't accurately predict real world values. In nearly all cases it can, however that doesn't mean that it is always worth the effort. Sometimes doing so means spending more money and time than a physical test would take.
I got a little off topic there, but hopefully you understand what I'm saying.
RE: Changing Total Time changes the result?
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RE: Changing Total Time changes the result?
RE: Changing Total Time changes the result?
Okay, I understand that the automatic time step might result to different time increments for different total times based on various factors with the ultimate aim to reach convergence.
Do a similar optimization also take place when a user-defined time increment is used? I guessed in this case a constant time increment would be used throughout the simulation. I tried it with fixed time increments and got a similar graph.
Or can I just assume it as some numreical error?
@Mustaine3 -- I am a little unclear about your point. How do I apply the filter? Can I apply it using Abaqus post processing? or using python, MATLAB?
RE: Changing Total Time changes the result?
TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Changing Total Time changes the result?
Numerical errors are always there, but usually the error/difference is quite small. So it depends on the scale you are looking at. Very small differences can also come from different versions, OS, domain decomposition, ...
Filters are available during the generation of output and also in postprocessing, when you operate on xy data.
@IRstuff
I think I know what you mean, but the step time should have no influence in the stable time increment.
At longer runtime the round off errors might become an issue. Running the job in double precision can help here.
RE: Changing Total Time changes the result?
There are no convergence checks in Abaqus/Explicit.
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