Evaluating damped natural frequencies using Readmac function in Hyperstudy

Simon Križnik

Hi,

I am trying to calibrate stiffness and damping parameters in a complex eigenvalue analysis with Hyperstudy. However, there is a warning message when evaluating the damped natural frequency using readmac function (similar to tutorial HS-4410):

"The Datatype "Eigen Mode (Grids)" does not have all components "Time,X,Y,Z,MAG".
Please check if you are using correct datatype"

It works with normal modes analysis, but is complex eigenvalue analysis also supported with this function? It is possible to extract undamped natural frequency from the out file, but not damped natural frequency. Is there any workaround? 

The relevant files are attached if someone would kindly look into it.

Olcay Met_22435

Hi Simon,

 

Readmac function in HyperWorks returns a vector of 3 outputs: eigenvalue, MAC value and ID of the best matched mode. In Normal Modes, the eigenvalue is a single value which is real output. However, In Complex Eigenvalue Analysis, the returned eigenvalue is real+imaginary. Hence, it errors out. If you make a comparison via punch file, you will see that in Normal Modes each node has 6 components and in Complex Eigen, there are 12 (real+imaginary)

$LABEL = Normal Mode
$EIGENVECTOR
$REAL OUTPUT
$SUBCASE ID = 3
$EIGENVALUE = 1.1001696E+04 MODE = 1
1 G 0.000000E+00 0.000000E+00 0.000000E+00
-CONT- 0.000000E+00 0.000000E+00 0.000000E+00

 

$LABEL = Complex EIGENVALUE
$EIGENVECTOR
$REAL-IMAGINARY OUTPUT
$SUBCASE ID = 1
$EIGENVALUE = ( -5.2379214E+00, 1.0501967E+02) MODE = 1
1 G 0.000000E+00 0.000000E+00 0.000000E+00
-CONT- 0.000000E+00 0.000000E+00 0.000000E+00
-CONT- 0.000000E+00 0.000000E+00 0.000000E+00
-CONT- 0.000000E+00 0.000000E+00 0.000000E+00

 

Simon Križnik

Hi Olcay,

 

Thanks for your reply. However, I already figured out why it does not work but I would like to know how to make it work.

 

If there are no modal assurance criteria function currently available in HS for evaluating complex eigenfrequencies, is there a workaround to extract just the damped eigenfrequencies (with the drawback that without MAC mode order may change during optimization)? 

Olcay Met_22435

Unless you can, somehow, manage to output eigenvalues in the same fashion of Normal Modes from OptiStruct (I am not sure if it is possible), there is currently no workaround. 

Simon Križnik

I was hoping for a solution, but thanks anyway.