PARAM, EFFMAS

Bulk Data Entry Outputs modal participation factors and effective mass for normal modes analyses.

Parameter Values Description
EFFMAS <YES, NO, Integer>

Default = NO
≤ 0 or NO
The modal participation factors, modal participation factor ratio, modal effective mass and modal effective mass fraction are not output for normal modes analysis.
> 0 or YES
The modal participation factors, modal participation factor ratio, modal effective mass, and modal effective mass fraction will be computed and output to the .out and .pch files (OUTPUT,PUNCH should be active for .pch file output) for normal modes analysis. They are computed as:
Modal Participation Factor = M P F = A T M V M modal
The Modal Participation Factor is a measure of how close each mode is to a rigid body mode.
The Modal Participation Factor Ratio is the Modal Participation Factor for each rotational and translational direction divided by the maximum Modal Participation Factor of all the modes for that direction. So, each of the six directions will have a value of 1.0 for the mode that has the maximum Modal Participation Factor and the other modes will have a value less than 1.0.
Modal Effective Mass = E F F M A S = M P F × [ A T M V ]
The Modal Effective Mass is a measure of how much mass is associated with each mode.
Modal Effective Mass Fraction = E F F M F R = E F F M A S / R B M
The Modal Effective Mass fraction is a ratio of Modal Effective mass and the Rigid Body mass.
Where,
A
Matrix of eigenvectors.
M
System mass matrix.
V
Objective function matrix.
Six rigid body modes are used as objective function in normal modes analysis to obtain M P F and E F F M A S .
M modal
Diagonal modal mass matrix.
R B M
Rigid body mass.

Comments

  1. PARAM,EFFMAS,YES outputs the specified matrices above for Normal Modes Analysis.
  2. The MEFFMASS I/O Entry provides additional control over the normal modes analysis mass output, and can be used in place of PARAM,EFFMAS,YES, if the output is to be fine-tuned or if these matrices are to be output only for particular grids.
  3. If OUTPUT,PUNCH is also specified along with PARAM,EFFMAS,YES, then the Modal Participation Factors, Modal Participation Factor Ratios, and the Modal Effective Mass matrices are printed to the Punch file, as well.