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Relationship between complete matrixes('K','E','D',L') and the elliminated ones ('Kc','Ec','Dc',Lc')

Posted 7 sept. 2011, 14:50 UTC−4 Version 4.0, Version 4.0a, Version 4.1, Version 4.2 2 Replies

Masoud Ghorbani Moghaddam
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Hi,

I know that the elliminated matrix is the matix after removing those DOF of the model that have pre-valued and they do not contribute into these matrixes. Even in the Help Document, it has told same definition as any other FEM books. But in practice, when I get the complete matrixes('K','E','D',L') and also the elliminated ones ('Kc','Ec','Dc',Lc'), I see totally different numbers. For example, one of them is that:

1) Damping matrix (D) is Zero, but the Elliminated Damping Matirx (Dc) is Nonzero(Complex number).
or
2) Some part of the Stiffness Matrix (24*24) and the elliminated stiffness matrix with reduced 12 DOF (12*12) is:

>> MA.K----------------------------------------MA.Kc

1.0e+010 *----------------------------------1.0e+011 *

(1,1) 1.8291--------------------------- (1,1) 1.0091
(2,1) 0.3205----------------------------(2,1) 0.1062
(3,1) 0.3205----------------------------(3,1) 0.1062
(4,1) -0.3675---------------------------(4,1) -0.2064
(5,1) 0.1603----------------------------(5,1) 0.0531

I appreciate if someone tells me what is the right way for interpreting the Elliminated Matrixes?

Best Regards,
Masoud
2 Replies Last Post 1 nov. 2011, 14:05 UTC−4
COMSOL Moderator

Hello Masoud Ghorbani Moghaddam

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Marios Karaoulis
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Posted: 1 decade ago 15 oct. 2011, 19:17 UTC−4
It seems that a lot of people keeps asking the same question, but noone gets an answer.

Even if you exctact ('K','E','D',L') ,
why I can't go back to the solution using K\L

How can we use those matrices?

The connection between these matrices can be found here
www.kxcad.net/Altair/HyperWorks/oshelp/direct_matrix_approach.htm
It seems that a lot of people keeps asking the same question, but noone gets an answer. Even if you exctact ('K','E','D',L') , why I can't go back to the solution using K\L How can we use those matrices? The connection between these matrices can be found here http://www.kxcad.net/Altair/HyperWorks/oshelp/direct_matrix_approach.htm
Masoud Ghorbani Moghaddam
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Posted: 1 decade ago 1 nov. 2011, 14:05 UTC−4
Marios,

Hi. Could you figure out how they should be interpreted?
Marios, Hi. Could you figure out how they should be interpreted?

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