MASS and STIFFNESS matrices in ABAQUS

[ridbay]

Hi, everybody

is there anybody who knows how to get the MASS and STIFFNESS matrices from the ABAQUS and, maybe let them write down to a file?

Thanks in advance,

ridbay

 

[Drej]

Look in the keyword manual under *ELEMENT MATRIX OUTPUT

Cheers,

-- drej --

 

[ridbay]

Thanks Drej,

but i have already rewieved the *ELEMENT MATRIX OUTPUT and implemented the keywords therein... unfortunately i could not get the matrices up to now...

Should i write the keywords on "EDIT KEYWORDS" (which can be reached by clicking: Model -> Edit Keywords -> Model_Name)under the History output line?

and under which Procedure can i use it? General procedures such as Static, linear perturbation such as Frequency ?

or can you provide anymore explanation?

thanks

 

[Drej]

All structural analyses apart from static will involve calculation and manipulation of the mass matrix.

In the static case:

kx = f (f = nodal forces, k = stiffness matrix, x = nodal displacements hence no mass matrix needed).

Eigenvalue (modal or free vibration):

kx + ma = 0 (m = mass matrix, a = nodal acceleration)

Dynamic (transient):

kx + ma + cv = f(t) (c = damping constant (Ns/m), v = nodal velocity, m = mass matrix)

I don't know the preprocessor you're using, but why not write out the deck manually and add the *ELEMENT MATRIX OUTPUT manually into the applicable part of the deck. Check in the manual for the correct position of this keyword in the deck, but I believe it should be located within the *STEP module. The matrices will then appear in your chosen file (or .dat if none) file.


E.g.


*STEP
etc
etc.
*ELEMENT MATRIX OUTPUT, OUTPUT FILE=FILENAME.EXT, MASS=YES, STIFFNESS=YES, ELSET=ELSET_NAME
*END STEP



Cheers,

-- drej --