Hi,

I’m running a *FREQUENCY analysis after preloading the system with some centrifugal force.

*STEP,NLGEOM=YES,INC=100

*STATIC

1,1,0,0

*DLOAD

Model,CENTRIF,296526.7811172,0,0,0,0,0,1

*END STEP

*STEP,PERTURBATION

*FREQUENCY

12

*SELECT CYCLIC SYMMETRY MODES,NMIN=0,NMAX=1

*NODE FILE,GLOBAL=YES

U

*END STEP

First step is using NLGEOM=YES

What I do not understand is this message in the console when the second step starts.

STEP 2

Frequency analysis was selected

Perturbation parameter is active

Nonlinear geometric effects are taken into account

Decascading the MPC’s

…

¿What does Nonlinear geometric effects are taken into account in a *Frequency calculation mean?

If I set *STEP,PERTURBATION,NLGEOM=NO the message disappear.

If I set *STEP,PERTURBATION the message is shown but the calculation works and completes.

If I set *STEP,PERTURBATION,NLGEOM=YES Frequency stops and there is a new message:

*ERROR reading *STEP: PERTURBATION and NLGEOM are mutually exclusive.

*ERROR reading *STEP. Card image: *STEP,PERTURBATION,NLGEOM=YES

*ERROR in calinput: at least one fatal error message while reading the input deck: CalculiX stops.

¿Which would be the correct parameters to take my Centrifugal NLGEOM effects computed in the previous STEP into consideration for the Frequency analysis.?

Thanks