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Shrinaath

Time Step

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hi 

 

i having problem in time step.

i checked the minimum time step in the model that comes around 1.934e-03. 

when i run the model in radioss with out mass scaling it takes the DT= 0.1448E-02.

but usually the minimum time step * 0.9 will be taken in radioss as initial time step, when we calculate that 0.001934 * 0.9 = 0.0017406

what is reason behind this

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thanks ivan 

 

i tried with time step DT/NODA/CST 0.144E-02 i am having mass error and energy error as follow 

 

 

RESTART FILES: 2D_SHELL_0001_[0001-0001].rst WRITTEN
 NC=  605000 T= 8.7604E+02 DT= 1.4481E-03 ERR=-60.0% DM/M= 3.2230E-02
 ELAPSED TIME=       1579.40 s  REMAINING TIME=     304910.89 s
 NC=  605500 T= 8.7676E+02 DT= 1.4481E-03 ERR=-60.0% DM/M= 3.2230E-02
 ELAPSED TIME=       1580.85 s  REMAINING TIME=     304938.64 s
 NC=  606000 T= 8.7749E+02 DT= 1.4481E-03 ERR=-60.2% DM/M= 3.2230E-02
 ELAPSED TIME=       1582.20 s  REMAINING TIME=     304945.54 s
 NC=  606500 T= 8.7821E+02 DT= 1.4481E-03 ERR=-60.3% DM/M= 3.2230E-02
 ELAPSED TIME=       1583.49 s  REMAINING TIME=     304941.06 s
 NC=  607000 T= 8.7894E+02 DT= 1.4481E-03 ERR=-60.4% DM/M= 3.2230E-02
 ELAPSED TIME=       1584.80 s  REMAINING TIME=     304941.00 s
 NC=  607500 T= 8.7966E+02 DT= 1.4481E-03 ERR=-60.5% DM/M= 3.2230E-02
 ELAPSED TIME=       1586.16 s  REMAINING TIME=     304950.37 s
     ANIMATION FILE: 2D_SHELLA045 WRITTEN
 NC=  608000 T= 8.8038E+02 DT= 1.4481E-03 ERR=-60.6% DM/M= 3.2230E-02
 ELAPSED TIME=       1587.61 s  REMAINING TIME=     304976.63 s
 NC=  608500 T= 8.8111E+02 DT= 1.4481E-03 ERR=-60.7% DM/M= 3.2230E-02
 ELAPSED TIME=       1588.93 s  REMAINING TIME=     304978.07 s
 NC=  609000 T= 8.8183E+02 DT= 1.4481E-03 ERR=-60.8% DM/M= 3.2230E-02
 ELAPSED TIME=       1590.30 s  REMAINING TIME=     304988.53 s

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It looks like there is some problem with contact after 500 time units. Can you share the h3d file?

 

As mentioned before, step loading functions are not recommended.

energy.jpg

timestep.jpg

mass.jpg

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Large contact energies relative to total energy can cause large negative Energy Errors because contact energy is not part of the Energy Error equation. If the simulation has friction and a lot of sliding contact, then the large contact energy and resulting energy error can be considered acceptable.

 

Your model without friction had reasonable energy error.

shri_edit_0001.out

shri_editT01

 

Step loading functions can cause divergence in implicit or dynamic effects in explicit.

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The input deck is attached.

 

Note the AMS settings used (0.67 scale factor and 2e-3 timestep) are not ideal. First, run with DT/NODA mass scaling until you get reasonable negative energy without friction (15%) and mass error (2%) throughout the simulation. Then set up the AMS run trying to hit the energy error % of DT/NODA run (as well as stress and displacements). 

shri_edit_0000.rad

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