Negative stiffness node error

Hi,
I am getting a negative stiffness node error in the radioss run after adding constant time step :
/DT/NODA/CST
0.9 6E-8
Initial time step was 5.84 e-07
There are no contacts at these nodes.


Please change the Stfac to 1 in interface and try running the analysis.
Dear George ,
Same error occurs again after changing the STfac to 1 in interface.
ROOT: ssc93 RESTART: 0001
NUMBER OF HMPP PROCESSES 2
12/07/2016
**ERROR : NEGATIVE STIFFNESS NODE 1068085
**ERROR : NEGATIVE STIFFNESS NODE 1068085
NC= 0 T= 0.0000E+00 DT= 1.0368E-07 ERR= 0.0% DM/M= 8.3687E+01
ANIMATION FILE: ssc93A001 WRITTEN
RESTART FILES: ssc93_0001_[0001-0001].rst WRITTEN
** CPU USER TIME **
#PROC CONT.SORT CONT. F ELEMENT KIN.COND. INTEGR. I/O TASK0 ASSEMB. RESOL
1 .1016E+01 .0000E+00 .1359E+01 .3125E-01 .9375E-01 .1797E+01 .1250E+00 .3125E-01 .2169E+02
** CUMULATIVE CPU TIME SUMMARY **
CONTACT SORTING............: .1016E+01 4.68 %
CONTACT FORCES.............: .0000E+00 0.00 %
ELEMENT FORCES.............: .1359E+01 6.27 %
KINEMATIC COND.............: .3125E-01 0.14 %
regards
RAM


Can you share the model files (starter and engine) to my dropbox link?


Ram,
It is running in HW 14.0 version. Please upgrade your HW version and try running it.
Please clear the penetrations in the model and also impose a fair time step. In the current file mass error is too high and it will terminate the run quickly. So impose a good time step in the model.


Ram,
The time step now imposed is much higher and so the mass added is is also higher. Try with a smaller value which will not add too much mass to the model.
When you impose /AMS (Advanced Mass Scaling) in the model a non physical mass is added to a structure in order to achieve a larger explicit time step. And so. no mass is actually added to the system while solving. Choose a minimum time step, Tmin, from 10 to 20 times than the one used in /DT/NODA/CST. Tsca used is 0.67 for /AMS.
When /DT/AMS is present in RADIOSS Engine Input, option /AMS is mandatory in RADIOSS Starter Input file
The format for input is /DT/AMS
Tsca Tmin
In Help Menu, please see the Example 44- Blow Molding with AMS.
For more info on time step control without compromising the accuracy, please visit the link below:
http://www.altairhyperworks.com/html/en-US/rl/RADIOSS_Simulation_91212.htm
.


Ram,
There is no standard rule but as a fair practice we can tell,
Any targeted model for AMS application should run first in /DT/NODA/CST with a reasonable energy error and acceptable added mass along its simulation time.Computational convergence and accurate results can be obtained by choosing a minimum time step, Tmin, from 10 to 20 times than the one used in /DT/NODA/CST.
If the Tmin input is more the AMS job may either fail or diverge, most likely with an error message.
Dear George,
In my model i have given initial velocity about y axis , but in the result in hyperview it shows zero.
since gravity also comes into the account ,it is difficult to find whether the solver took the velocity or not.
How can we check whether the solver takes that initial velocity or not?
Thanks
RAM


Ram,
I dont think we have such an option available. But the solver will take the loads applied by the user, if there are no kinematic constraints.


Ram,
Ensure you have applied the loads correctly to the model. If any rigid bodies are there, ensure the load is applied in the master node also.
Make sure that the kinematic constraints also does not violate the loads applied.


Dear Ram,
Make IDROT=1 in /IOFLAG and try running the analysis.Please check the results then.
Analysis>>Control Cards>>IOFlagCard
Hi,
Please let us know what type of contact interface you have in your model,