SOL 106 - Export Stiffness Matrix in nonlinear case

Hi,

to export the stiffness matrix of a purely linear FE model I've successfully referred to the MALTER command explained in simcompanion.hexagon.com/.../how-to-export-mass-and-stiffness-matrices-of-a-large-model so far.

But in addition to that now I'd like to compute a nonlinear static load case and export the linearized stiffness matrix around the static equilibrium point.

How can I do this in an elegant way?

Best regards,

Johannes

0 Don.Graff over 4 years ago

Hi Johannes, I'm not sure this is exactly what you want, but if you are just looking for the differential stiffness you can use the alter in the following article:

simcompanion.mscsoftware.com/.../index

Here it is:

$ Alter used to export the differential stiffness in a SOL106

$ run... it can be printed, output4'd and punched as a DMIG.

$

$ NOTE: This is developed for MSC Nastran and is use-at-your-own-risk.

$      Do your own validation before using for production work.

$

$

compile nlstatic list noref $

$

ALTER 'END $ NLSTATIC'(1,-3) $

message //'' $

message //'Matrix kdggx (gset differential stiffness) follows'

matprn kdggxx// $

message //'' $

OUTPUT4 KDGGXX//-1/31/2  $ differential stiffness

TYPE PARM,,I,N,PUNCHFLG=1 $ GENERATE DMIG PUNCHED OUTPUT

TYPE PARM,,I,N,SORTFLG=1 $ INPUT MATRICES ARE IN INTERNAL SORT

MATMOD KDGGXX,EQEXIN,USET,,,/,

      /16/PUNCHFLG/SORTFLG//////////'KDDEXT'/'G' $

In SOL106, I think the different stiffnesses are kept in separate matrices (linear, differential, material), though at some point I'm sure they get combined.
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0 JohLut over 4 years ago

Hi Don, thank you. Is it possible to print only the components of the differential stiffness matrix belonging to the ASet?
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0 Don.Graff over 4 years ago

Try adding this and then using the resulting matrix instead of the original:

UPARTN USETNL,KDGGXX/KDAAXX,,,/'G'/'A' $

Please do extensive testing to make sure it is doing what you expect! I did not test it extensively...
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0 Don.Graff over 4 years ago

If you do not want the GSET info at all, just put it after this:

compile nlstatic list noref $

$

ALTER 'END $ NLSTATIC'(1,-3) $

And then edit the remaining statements to use KDAAXX instead of KDGGXX. The MATMOD that punches the DMIG would need to be changed to:

MATMOD KDAAXX,EQEXIN,USETNL,,,/,

/16/PUNCHFLG/SORTFLG//////////'KAAEXT'/'A' $
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0 JohLut over 4 years ago

Thank you so much!
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