Frequency calculations for a dynamic simulation

1

Hello,

I have run a simulation with the *FREQUENCY card, and I am getting the natural frequencies as expected.
I used the following *STEP

*STEP
*FREQUENCY
10

** fix on the lower boundary from x to z.  
*BOUNDARY
Nfix1, 1, 3

*CLOAD
Nsurface, 1, 0.0
Nsurface, 2, 0.0
Nsurface, 3, 0.0

*NODE FILE
 U
*END STEP

I am also able to see the change in the natural frequency when a load in applied in the previous *STATIC step.

*STEP
*STATIC, DIRECT
** fix on the lower boundary from x to z.  
*BOUNDARY
Nfix1, 1, 3

*CLOAD
Nsurface, 1, 10.0
Nsurface, 2, 0.0
Nsurface, 3, 0.0

*END STEP

*STEP, PERTURBATION
*FREQUENCY, STORAGE=YES
2
*END STEP

Now, I want to run a dynamic simulation with the **DYNAMIC, DIRECT card, but the simulation stops within one step.

How can I have the frequencies stored for all the time steps solved in the dynamic simulation?

I use the following:

*STEP
*DYNAMIC, DIRECT
1.E-2, 1.0

** fix on the lower boundary from x to z.  
*BOUNDARY
Nfix1, 1, 3

*CLOAD
Nsurface, 1, 10.0
Nsurface, 2, 0.0
Nsurface, 3, 0.0

*FREQUENCY, STORAGE=YES
2

*NODE FILE
 U
*EL FILE
** S, E
*END STEP
2

I don’t think that you can follow a dynamic analysis with a frequency step. That’s the case in Abaqus (quote from its documentation: A general implicit dynamic analysis cannot be interrupted to perform perturbation analyses: before performing the perturbation analysis, Abaqus/Standard requires that the structure be brought into static equilibrium.) and most likely also in CalculiX.

Apart from that, your last extract from input file is missing *End step keyword for the first step and *Step keyword for the second one.

1 Like
3

@Calc_em Thank you for your reply. :slight_smile: