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Livio Mariano

Frequency analyses using Altair Activate

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With the last Activate version 2019.2, under Model we have the new “Finalization” tab

where we can type an oml script that is executed at the end of the simulation.

I’ve found this capability extremely useful for frequency analyses...


I’ve created a simple model where we run a co-simulation between Activate & Motion

(the approach works also using Activate in standalone mode but with the Motion integration is definitely more interesting).

All the related files and the video are enclosed.


In the example, we have a system of 2 masses: mass1 and mass2. The input to the Multi-body System is the force on mass2 while the output is the displacement of mass1.


Force and displacement are respectively passed as Input1 and Input2 to the FrequencyWorld superblock in the Activate diagram.


When you run the Activate model a dialog box appears.

Here you can set the sampling frequency (be careful to aliasing issues since the value will affect the Nyquist frequency)

and the type of analysis:

Turn 0 to 1 the options if you want to analyse in frequency input 1, input 2 and/or the Transfer Function input1/input2.

When you turn 1 the last option, the file TF.mat with the transfer function information is generated in the same model folder to be used for further analyses in Compose (e.g. LTI ROM generation…).


For each input, the model calculates the fft together with the PSD.

The calculation is made in Model-Finalization where we also handle the various options.

The script is a bit articulated to properly handle every scenario (even/odd number of the sampling data, leakage, normalization…)


Scripts and FrequencyWorld superblock can obviously be re-used for other applications (and easily improved e.g adding filters ...).









robertavarela and stmaster like this

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