How to run a dynamic load step

[lucas_bueno]

I’m currently trying to apply a load from a demolition hammer on a scaffold, which has a cyclic load of about 8Hz and plan to study its effect on the structure. However, PrePoMax still does not support this kind of analysis. Do you guys know how can I achieve this? Is there a way to change keywords on input file and run on CalculiX standalone? I appreciate if someone has an enlightment. I tried to apply this on a simple model of cantilever beam with tabular amplitude on load, but have no idea on how to do this and found nothing on PrePoMax and Calculix discourse groups. I attached the files below.

dynamic_attempt.pmx (4.9 MB)
Analysis-1.inp (2.4 MB)

Thanks in advance.

[FEAnalyst]

Check this thread:

Random and harmonic vibration analysis

Dear All, Is there any plan to add dynamic analysis to prepomax? I normally use FEA for modal analysis and propose structure modification to avoid resonance vibration problem. However, it would be nice if we could predict dynamic stress from measured vibration data as well in some cases which natural frequency could not be shifted away from excitation sources with sufficient margin. With predicted dynamic stress, it can be compared against S-N curve of material for fatigue failure analysis. Als…

There I showed how to modify keywords to run steady-state dynamic analysis. However, as I’ve mentioned in that post, the results can’t be visualized in PrePoMax and you will have to use GraphiX which is CalculiX’s native postprocessor.

[lucas_bueno]

Thank you very much, @FEAnalyst . I did a research today on steady state dynamic analysis, it’s exactly what I need to do. I don’t have much trouble running on CalculiX standalone because I installed it on my Ubuntu virtual machine (had too many errors when trying to install on Windows).

As it looks like, you have good experience on the subject, so can you check if my logic makes sense?

1. Make a model on PrePoMax with the appropriate boundary conditions to run Frequency step with storage

2. Make a second step with the load I want to apply, with the amplitude tool as follows
   
   because my load is of 8 Hz

3. With this, I generate the *.inp file and manually change the second step header keywords to:
   *STEP, PERTUBATION
   *STEADY STATE DYNAMICS
   1.,20.,20,3.
   So I run from 1 to 20 Hz using 20 data points and more points on resonant frequencies (if any)

4. Then, I run the input file on CalculiX standalone and post-process on GraphiX

Does it make sense? Anyway, thanks for the help!

[FEAnalyst]

@lucas_bueno

I don’t have much trouble running on CalculiX standalone because I installed it on my Ubuntu virtual machine (had too many errors when trying to install on Windows).

You don’t have to install CalculiX on Windows to run analyses with this solver. You can download the files, place them in the same folder as the input file and run the simulation from the command line.

@lucas_bueno

Does it make sense?

Yes, that’s correct approach. I’ll just add that amplitude is not necessary.

[lucas_bueno]

Hello @FEAnalyst , I managed to run my analysis using your tips from here and from the other post you made. Thank you for the patience to instruct me.

I’ve managed to find the displacements for my structure under harmonic load (the plot is from displacement versus frequency of the load in a structure with 93Hz of natural vibration). This is not the original problem to 8Hz demolition hammer, but is analogous and helped me to understand how to conduct the analysis. Thank you very much.