WTMASS and Eigenvalue in FEMAP/NASTRAN

[JohnSmith54545]

Hi

I want to get the eigenvalues of an Objekt with FEMAP/NASTRAN. In FEMAP I can choose to change the WTMASS. Is it necessary? What is it exactly for?
I have tested it with an easy spring-mass-system and I only get to a right answer, if i haven't picked it.

Thanks for your help

 

[brad]

WTMASS is a parameter used to adjust for inconsistent units. An example--if one uses mm as a length basis and N as a force, then the appropriate mass basis for consistency is Mg (1000 Kg). Often people prefer to use Kg as their mass basis. A way to resolve this inconsistency is to use WTMASS (in this case the value of 0.001 is used).

WTMASS adjusts every term in the mass matrix by this factor, thereby correcting the inconsistency. If an analyst uses a consistent set of units (Mg in the above example), WTMASS is unnecessary (by default, it is 1.0--no adjustment made).

Brad