Nastran Punch Files for Stiffness Matrix 1

[feajob]

Hi,

I am would like to know how can I get the stiffness matrix at some specific nodes of a Nastran Finite Element Model?

I believe that I should prepare a punch file with contents similar to the following lines:

DMIG KAAX 0 6 2 0 363
DMIG* KAAX 815 1
* 815 1 2.094630203D+05
DMIG* KAAX 815 2
* 815 1 5.452199544D+01
* 815 2 7.202035606D+04
DMIG* KAAX 815 3
* 815 1-1.187792338D+04
* 815 2-8.340854301D+01
* 815 3 7.054812146D+03
DMIG* KAAX 815 4
* 815 1 5.956672400D+03
* 815 2 1.614047795D+06
* 815 3-9.830448080D+03
* 815 4 8.008238936D+07
DMIG* KAAX 815 5
* 815 1-3.302141465D+06
* 815 2 4.679375985D+03
* 815 3-6.878970667D+05
* 815 4 6.516078489D+05
* 815 5 2.395260092D+08
DMIG* KAAX 815 6
* 815 1 2.197964123D+03
* 815 2 9.450145395D+05
* 815 3-5.384814661D+03
* 815 4 4.320186476D+07
* 815 5 4.148338821D+05
* 815 6 2.530261259D+08



Thanks,
A.A.Y.

 

[Spirit]

Hello feajob,

what you should do is run a file where the GRIDs for which you require the stiffness values are defined via the ASET card:

ASET1 123456 GRID1 GRID2 ... GRIDn

and add in the parameter section of the same file the line

PARAM,EXTOUT,DMIGPCH

It should give what you are asking for.

Regards,

Spirit



'Ability is 10% inspiration and 90% perspiration.'

 

[feajob]

Hi Spirit,

Thank you for your response. I put the following lines in a model.

aset1,123,3245
PARAM,EXTOUT,DMIGPCH

And, I got a punch file as follows:

DMIG KAAX 0 6 2 0 155520
DMIG* KAAX 3245 1
* 3245 1 1.169233642D+02
DMIG* KAAX 3245 2
* 3245 1-5.191796938D+00
* 3245 2 1.489866977D+02
DMIG* KAAX 3245 3
* 3245 1 4.308966685D+01
* 3245 2 6.827149784D+00
* 3245 3 2.929045851D+02
DMIG PAX 0 9 2 0 4
DMIG* PAX 1 0
* 3245 1 8.973292961D-01
* 3245 2-2.682531133D-02
* 3245 3-2.384527642D-01
DMIG* PAX 2 0
* 3245 1 8.254319696D-01
* 3245 2-2.436249156D-02
* 3245 3-2.537991949D-01
DMIG* PAX 3 0
* 3245 1 8.194554349D-01
* 3245 2-2.450994401D-02
* 3245 3-2.631562907D-01
DMIG* PAX 4 0
* 3245 1 4.426057545D-01
* 3245 2-3.810084949D-02
* 3245 3-2.589523757D-01
DMIG VAX 0 9 2 0 1
DMIG* VAX 1 0
* 3245 1 1.000000000D+00
* 3245 2 1.000000000D+00
* 3245 3 1.000000000D+00

Actually, I was looking only for KAAX. Please let me know if you know anything about PAX and VAX. I guess that PAX is related to load matrix, but I don't know any thing about VAX.

Thanks,
A.A.Y.

 

[Spirit]

Hello feajob,

the PAX matrix indeed refers to the reduced matrix of loads. I don't know the exact meaning of the VAX part, I read somewhere that it should be related to the rigid mody motion of your model (not sure though).
I usually erase it happily from my reduced structures files anyway.

Regards,

Spirit



'Ability is 10% inspiration and 90% perspiration.'