# How to plot pressure and force of single (or multiple) points on a patch over all time steps?

Hi

I have a multiphase case (VOF) and simulated it using interFoam. Using ExtractBlock filter I have selected a patch I need and I have got the patch normals using GenerateSurfaceNormals filter.

My first question is how to define the force on the patch using the calculator filter. Does “p*Normals” work and give the force vector in Newton? I understand that the force is pressure times area, but I cannot see how to multiply pressure by the patch cell area and integrate it over the patch to get Fx and Fy.

Moreover for a single point on the patch, I need to plot the force x and y components and pressure over all time steps. How can I use filters to do it? Any help is greatly appreciated.
Cheer

Hi @A_E

Does “p*Normals” work and give the force vector in Newton?

ParaView doesn’t know anything about your units, it is just doing the math computation that you are asking for.

I need to plot the force x and y components and pressure over all time steps

Plot data over time

Hi Mathieu

Thanks very much for your response.
So I need to calculate the force making sure about the units which is fine but could you please let me know how I can get the patch cells area to integrate my calculations over the patch?
Re plot data over time, my problem is that I cannot select the points I need so that I can plot the point data over time. I have clipped and sliced my patch to get a line and I would like to select a point on the line and plot the results for that point over time but I couldn’t get it to work.

Create the geometry of the point you want to extract, then use ResampleWithDataSet.

Thanks, so you mean to use Point Source filter on the line I have got and then Resample With Dataset filter and then Plot Data Over Time?

That is one way to do it, yes. It would be easier to read a line from a file if it is already defined somewhere. A simple .csv + TableToPoints would do the trick.

Okay thanks. I’ll give them a go. My patch is a bit complex so a bit hard to get the point coordinates but I guess the way you said is good if I can define points in a .csv file somehow.
Cheers Mathieu

And I assume there is no way we can use patch cell areas in our calculations?

You should be able to compute the cell areas first, then use that in a calculator or python calculator.

How can I do the cell area? Could you demonstrate please? Do I need to use a code?

Use CellSize filter.

Awesome, thank you! I’ll check all what you told to get a result