Non linear Frequency dependent load in SS dynamic

why it is showing this warning when trying to solve SS dynamic step with frequency dependent loads within the same step!

I created multiple tables with different frequencies and scale of 1 each, I called the each table to apply different load value for each tabular (each frequency).

It’s not a PrePoMax bug so I moved this to General Questions category. The message comes from CalculiX.

Why did you use multiple tables for that and not a single table with frequency vs amplitude data ?

As an example, if you want the load to have the original magnitude (scale 1) at 3 Hz, doubled magnitude at 4 Hz and tripled magnitude at 5 Hz, the definition should look like this:


And the load definition should reference this amplitude.

You can also do this in the opposite way - set the load magnitude to 1 and specify the actual values of the force in amplitude definition.

Hi, thanks for your quick answer, I am a new user of calculix and prepomax facilitates things for me. Actually, I am importing the loads from another software and they are defined versus frequencies, so my loads changes with frequency , should I re-compute the scale for each frequency from the first load data? No other way to import loads and apply them continuously within the same step? (I am modifying manually the inp file generated from Prepomax and run it with calculix launcher)

Yes I tried this way but since it is within the same step, it fails and shows same warning! If I use multiple steps, should I get finally continuous loading process?

It will be continuous if you use a single amplitude and define frequency vs amplitude (scale) data. The solver will interpolate between the specified frequencies. No need to use multiple amplitudes or multiple steps. A single amplitude covers the load variation during the whole step, either in the frequency domain (SSD analysis) or in the time domain (other analysis types).

1 Like

Hi, still facing some issues with this method because sometimes the force could be negative and then the scale value is not accepting a negative value! Wanna try the second choice of multiple steps and for each step will update the CLOAD value with keep using amplitude TABULAR (by assigning 1 scale for each frequency). The problem I used Op=mod /New to update force load from 1 step to another to update load data BUT seems the load are applied continuously during each step (for each step I am defining the frequency rang of SSD as sub-range of the overall frequency range of my problem) : I need a way to control Step or Ramp loading, is there a way for that? an INP example would be helpful. PS: I am trying to get the frequency response of a structure to an harmonic load) for a well defined frequency range

There are no other amplitude types in CalculiX (unlike in Abaqus) but the total time parameter can be helpful:

The total time is the time accumulated until the beginning of the actual step augmented by the local step time. In *STEADY STATE DYNAMICS procedures total time coincides with frequency (in cycles/time).

1 Like