generalized/effective mass

[jhml]

Can anybody give me the physical meaning of 'generalized' and 'effective' mass in a modal analysis? I'm not looking for formulae, only for the meaning of it.

Thanks for your help.

Jan

 

[Spirit]

Generalized mass has not really got a physical meaning, it is only what you have on the diagonal of the mass matrix once you write the equation of motion in modal space. Effective mass is a value that gives you an idea of the fraction of mass that participates in a specific direction to a specific mode (i. e. if you have some 75% of the total mass as effective mass of a mode in Z direction, then you are dealing with a mainly Z direction mode). Very rough, but I hope it helps. Cheers.
'Ability is 10% inspiration and 90% perspiration.'

 

[jhml]

Thanks for the explanation, Spirit.
We work with Samcef (FEA software) and after a modal analysis calculation they always give three tables: one with frequencies and generalized mass, one with effective mass, and one with the total effective mass in the directions of the coordinate system. So, I always wandered why they also give generalised mass. But now, I've got a confirmation that it doesn't have a real physical meaning.

Thanks again.

Jan