increasing LS-DYNA run time abnormally

FREIDOUN KAMRANIMEHR

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Jan 30, 2022, 4:50:23 AM1/30/22

to LS-DYNA2

Dear All

I have made a car chassis crash model with 50 mSec termination time. At the beginning of LS_DYNA running, estimation of run time is 15 hr that is normal I guess. After a while (approximately after one hour and at 1.6 mSec of solving time) the run speed decreases abnormally. after Ctrl-c and SW2. I see 277777 hr for run time estimation, that means continuing the run is really impossible although the software is still running. Of course this problem is Simultaneous with a huge buckling of a angle section part in the model and breaking some of it's elements due to it's impact to rigid wall. However I'm not sure to be relation between these two phenomenon because even before of time 1.6 mSec such sophisticated impact and breaking was happen for another portions of the model.

please help me to solve the problem.

l...@schwer.net

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Jan 30, 2022, 10:04:41 AM1/30/22

to FREIDOUN KAMRANIMEHR, LS-DYNA2

The timestep in LS-DYNA is selected by computing the shortest element elastic wave transient time, i.e. how long it takes for a wave to cross each element.

Typically as 2D and 3D elements deform this time decreases and hence the stable timestep in LS-DYNA decreases.

The only way to progress a simulation like yours with an extremely small timestep is to eliminate (erode) the troubling small timestep element. This is the reason element erosion was first introduced into explicit finite elements.

--len

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