hello,

For a same model and after one modal analysis, I should compare Abaqus effective mass and Caesar 4.5 effective mass. But in Caesar output listing, there is nothing like in Abaqus. I’ve seen the “participation factor” but I only run a modal analysis and not an harmonic analysis.

I currently use the “modes mass normalized” because it’s a kind of movement ratio and “mass model” because it’s the mass per nodes .In an excel datasheet I multiply for each node mass model and the absolute value of modes mass normalized. The trend is almost good but there is a big difference in mass effective value. How can I do to have more accurate result?

If anybody already met this problem and solves it…

Thank in advance.

How does Abaqus define "effective mass"?

The table of effective mass indicates the amount of mass active in each degree of freedom for any one mode.
In my case below the results indicate that the first mode with significant mass in the y-direction is mode 1 in the x-direction is mode 2 and in the z-direction is mode 3.
The effective mass is here in tons and the sum of effective mass on each direction converges to the total mass model when the mode amount increases.

E I G E N V A L U E O U T P U T
MODE NO EIGENVALUE FREQUENCY GENERALIZED MASS
(RAD/TIME) (CYCLES/TIME)
1 2360.9 48.590 7.7333 0.51854
2 3069.7 55.405 8.8179 0.33414
3 3092.9 55.614 8.8513 0.27380

P A R T I C I P A T I O N F A C T O R S
MODE NO X-COMPONENT Y-COMPONENT Z-COMPONENT
1 2.69662E-02 1.0108 -1.57870E-02
2 0.53091 0.31442 0.15180
3 1.76382E-02 0.18330 1.0361

E F F E C T I V E M A S S
MODE NO X-COMPONENT Y-COMPONENT Z-COMPONENT
1 3.77068E-04 0.52983 1.29234E-04
2 9.41836E-02 3.30330E-02 7.70005E-03
3 8.51818E-05 9.19936E-03 0.29391


With:
Generalized mass (GM)
Participation factor (PF)
Effective mass (EM)

EM=GM*PF^2 for each mode i, in each direction x y z
calculated in red

Else there is here a link to the Abaqus modal variables theory:

https://hpcsg.esc.rl.ac.uk/Columbus/service/abaqus_no/docs/V6.3_HTMLdocs/books/stm/ch02s05ath24.html

The value that CAESAR II reports for the "Participation Factor" is actually the "Mode Coefficient", where

"mode coefficient[i]" = "participation factor[i]" * "acceleration[i]" / "natural frequency[i]^2"


This is a more useful value because it shows the relative importance of the load-mode combination to the overall response.

The downside of this idea is that you can't match the participation factors against values from any other software.

I only do a modal analysis and I can't find the "mode coefficient" values in the dynamic outputs.

You can't get this for a "Modal" only analysis, since there are no loads.