Negative Eigenvalues in Implicit Dynamics

Ameen Topa

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Feb 4, 2022, 8:47:58 PM2/4/22

to LS-DYNA2

Dear all,

I am running the simulations of a quasi-static cyclic load on RC column with implicit dynamics, and I am facing the "MF2 Initialization error 0" when running the implicit dynamic analysis, as shown below:

*** Warning 60124 (IMP+124)
1 negative eigenvalues detected

*** Error 60109 (IMP+109)
terminating : MF2 Initialization error 0

This error occurs towards the end of the simulation. During the first two-thirds of the analysis, everything works fine and convergence happens only after a few iterations in each timestep. There are no element erosions so the model I don't think there are any unconstrained edges. My question: what is the cause of this error and what actions should be taken to resolve it?

Sincerely,
Ameen

The messag file is attached for reference and the implicit keywords used are as follows:
*CONTROL_ACCURACY
$# osu inn pidosu iacc
1 4 0 1
*CONTROL_IMPLICIT_AUTO
$# iauto iteopt itewin dtmin dtmax dtexp kfail kcycle
1 30 10 0.001 0.0 0.0 0 0
*CONTROL_IMPLICIT_DYNAMICS
$GAMMA=0.60 BETA=0.38 Dynamic Results are not of interest
$# imass gamma beta tdybir tdydth tdybur irate alpha
1 0.6 0.38 0.01.00000E281.00000E28 0 0.0
*CONTROL_IMPLICIT_GENERAL
$# imflag dt0 imform nsbs igs cnstn form zero_v
4 0.001 2 1 1 0 0 0
*CONTROL_IMPLICIT_SOLUTION
$# nsolvr ilimit maxref dctol ectol rctol lstol abstol
12 6 15 0.001 0.011.00000E10 0.91.0000E-10
$# dnorm diverg istif nlprint nlnorm d3itctl cpchk
1 1 1 0 0 0 0
$# arcctl arcdir arclen arcmth arcdmp arcpsi arcalf arctim
0 0 0.0 1 2 0 0 0
$# lsmtd lsdir irad srad awgt sred
4 2 0.0 0.0 0.0 0.0
*CONTROL_IMPLICIT_SOLVER
$# lsolvr lprint negev order drcm drcprm autospc autotol
2 0 1 0 4 0.0 1 0.0
$# lcpack mtxdmp iparm1 rparm1 rparm2
2 0 5001.00000E-9 0.001
$# emxdmp rdcmem
0 0.85
*CONTROL_TERMINATION
$# endtim endcyc dtmin endeng endmas nosol
21.0 0 0.0 0.01.000000E8 0

messag

James M. Kennedy

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Feb 7, 2022, 5:35:48 PM2/7/22

to Ameen Topa, LS-DYNA2

Dear Ameen,

Some additional details regarding message:

Error occurred during initialization or factorization process with MF2 direct sparse solver.

You might consider using a different solver.

Sincerely,

James M. Kennedy

KBS2 Inc.

February 7, 2022

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Ameen Topa

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Feb 7, 2022, 10:06:13 PM2/7/22

to James M. Kennedy, LS-DYNA2

Dear Dr. Kennedy

Noted with many thanks! I will check it out and revert back if it still didn't work.

One thing to note: when I run the same model with MAT Plastic Kinematics, I managed to get a Normal Termination. However, the error occurs whenever I used MAT024 with a stress-strain curve (imported from Varmint al's engineering website).

Sincerely,
Ameen

James M. Kennedy

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Feb 8, 2022, 11:13:15 AM2/8/22

to Ameen Topa, LS-DYNA2

Dear Ameen,

I suggest converting your *mat_003 data (eg. etan=1000) to a simple *mat_024 data

(two points entry)

*MAT_PIECEWISE_LINEAR_PLASTICITY

$ Material Type 24

$ MID RO E PR SIGY ETAN FAIL TDEL

2401 0.000010 100000.0 0.0 500.0 1.00 0.0

$ C P LCSS LCSR VP

2401 0.0

$ EPS1 EPS2 EPS3 EPS4 EPS5 EPS6 EPS7 EPS8

$ ES1 ES2 ES3 ES4 ES5 ES6 ES7 ES8

*DEFINE_CURVE

2401

$ STRAIN STRESS

0.000000000 500.0

0.100000000 600.0

Please check for a correct conversion from etan to two point stress-strain input.

I did not check.

Sincerely,

James M. Kennedy

KBS2 Inc.

February 8, 2021

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