modal mass and modal stiffness, effective mass and effective stiffness 1

[richard98]

Dear all,
I want to obtain the modal mass and modal stiffness, effective mass and effective stiffness for some modes from my modal analysis in ANSYS.
By default, the modal mass is normallized in ANSYS, then the modal stiffness is equal to the square of natural frequency for a mode. Right?

Could anaybody help me?
Thanks in advance.

Richard

 

[Drej]

Not sure how you are differentiating between effective/modal mass/stiffness. However, the modal stiffness, as you've called it, is the root of the eigenvalues for that mode, i.e.:

[k] = [omega]^2 . . . (1)

where [omega]^2 is the eigenvalue for mode .


also:

[k] = [omega]^2*[M] . . . (2)

where [M] is the modal mass matrix. In ANSYS, the eigenvectors are normalised to the mass matrix by default, such that [M]=1, hence there is a direct relationship between stiffness(es) and eigenvalue(s) given in (1). The modal mass is ported to the output file (jobname.out) post-solution as well as participation factors &c (being the root of the effective mass).

Hope this helps,

-- drej --