[sap_92]

I have a question related to controlling the frequency at which the solution field is written in the folder. I can control the frequency of solution writing in controlDict using below parameters

writeControl timeStep;

writeInterval 200;

Basically, this will write a solution after every 200 time steps.

Now, I would like to create a custom function which computes the magnitude of velocity over the whole domain (sum of square of velocity u at every grid point) and write this variable to a text file or csv file at every time step while the simulation is running. How can I do it? I wont to keep the frequency of writing the entire solution (u,v,k,...) at 200 time steps only. Can someone please point me to resources that guides on how to create a custom function to compute some quantity at every time step in OpenFoam?