Monitor Derivatives
 

Hi Everyone
Is it possible to calculate in STAR-CCM the derivatives of a monitor and display them on a plot ?

Thanks

What kind of monitor are you talking about? Field Monitor or Report monitor? Spatial or temporal derivative?

Im talking about report monitor. Id like to calculate the derivatives of the Pressure.Vs.Time during the simulation

In this case you can do it like that:
Your Report for the Monitor has a Field Function like "ReportPressure". Use this FF for a Field Sum Monitor with a sliding window of 2 and a trigger of "TimeStep". In that way you sum the value of your Report of the current timestep and the previous one. This value exists in each cell but obviously has the same value everywhere. The adjacent Field Function has the name "SumOfReportPressure". To get the derivative you have to create another FF "DerivativePressure" with the Syntax "(2*$ReportPressure-$SumOfReportPressure)/$TimeStep".
This will deliver the derivative between the current and the previous timestep of your pressure Report. Again, it is presented in each and every cell with the same value. To get it into a plot you can simply create a Maximum Report with a derived Monitor that can be added to a plot.

Hope this helps.

Thank you. Ill try it

Its working ! Thanks

That is a very good answer. I wish, there was an embedded field function or operator, which would enable you to calculate the rate of change of a variable. Nice trick!

Said to be implemented in new version.

Is implemented in the latest version as "Field History" Monitor. You can give the tool a sliding window of 2 to have the latest 2 timestep values of a certain field function. They can then be used to calculate the time derivative.

Is implemented in the latest version as "Field History" Monitor. You can give the tool a sliding window of 2 to have the latest 2 timestep values of a certain field function. They can then be used to calculate the time derivative.