The perform_POD application is used to perform POD on a standard OpenFOAM case.

Introduction

In this tutorial the POD is applied on a simple lid-driven cavity example.

The case is solved using icoFoam and then the modes are extracted using the perform_POD utility. Run the code using the standard icoFoam solver from OpenFOAM

icoFoam

Once the solution is performed you can the ITHACA-FV utility to extract the modes running:

perform_POD

The modes, together with the eigenvalues and the cumulative eigenvalues are stored inside the ITHACAoutput/POD. folder.

You can eventually use also the Allrun file to perform both operation together. For more details see also the perform_POD.C file and check the system/ITHACAPODdict file in the system folder to understand how this file should be prepared.

The ITHACAPODdict file

The ITHACAPODdict file located in the system folder is used to define the characteristics of the fields on which you want to perform the POD and how many modes you want to extract. Let's have a detailed look to it.

With the following lines you decide on which fields you want to perform the POD, put the name of the field followed by the _pod string:

Then for each field we have to specify the exact file name of the field, how many modes we want to extract and the type of the field (vector or scalar). In this case we have 10 modes for both velocity and pressure field:

Then you have to select the initialTime from which you want to start acquiring the snapshots and the FinalTime

Eventually, instead of the finalTime you could define the number of snapshots

The plain ITHACAPODdict dictionary

 
// a fake class just to print out the doxygen documentation
class fake