[OpenFOAM] Integrating a custom variable over a line

babakflame · November 29, 2016, 12:57

Dear Fellows

I have defined a custom variable as $\rho_e U_x$ , where

is the component of velocity in x direction and $\rho_e$ is the bulk charge density. My domain is a simple 2D rectangle.

Now I want to calculate the integral $\int^L_0 (\rho_e U_x) \, dy$ ,where L is the height of the channel, on different x positions. I read previous threads. Some of them were mentioning patchIntegrate, However this utility calculates the integration on outlet and inlet, whereas I need this integral on different x positions in my domain.

Attached, please take a look at my domain and coordinates alongwith a distribution of the custom variable $\rho_e U_x$ .

Regards

Persia · November 29, 2016, 15:08

Have you tried the "Integrate Variables" filter in ParaView? You can slice your domain at different locations and then find the integral over each slice with this filter.

babakflame · November 29, 2016, 15:43

Hey Maryam,

Thanks for your reply. Actually I had seen integrate variable filter and had used it. It gives me just a value that I assume its over the surface of the slice i.e. it gives me

$\int^H_0 \int^L_0 (\rho_e U_x) \, dy dx$ .

However, what I want is the integral over vertical lines not on whole surface of a slice.

I have attached a screen shot of my paraview with using integrateVariable Filter. Any further hint is appreciated.

Regards

babakflame · November 29, 2016, 16:09

I am thinking of two consecutive slices one in Z normal and the second one in X normal direction, the result can be a line in the desired x position and then using integrateVariables on custom variable $(\rho_e U_X)$ . It gives me a value.

However, is that value the result of following integral??
$\int^L_0 (\rho_e U_x) \, dy$

Regards

Tobi · November 30, 2016, 17:30

Hi bobi,

The app is not showing the equations correct but your steps should lead to what you need. Using slices to generate a line an then integrate this one, should lead to the required integral. Maybe a simple test case should give you the proof. However, keep in mind that you introduce interpolation errors.

Cheers

babakflame · November 30, 2016, 20:43

Thanks Tobi

Do you know any other filter that can be used for integration along one line?

I am thinking of a snippet for doing it inside the code. I will add that snippet soon.

Regards

babakflame · December 1, 2016, 22:51

Dear Fellows

I will put this information here, It might be useful for others in future about integrateVariable filter.

If you want to use integrateVariable filter for integrating over a line, construct that line through consecutive slices, and then use integrateVariable filter. I compared the values from integrateVariable filter with a custom method. I think this filter performs well.

@Tobi: I compared values from plot_over_line (with sufficient numbers) against integrateVariable filter. They were comparable.

Regards

samar · October 11, 2017, 08:41

how to use integrate variable filter in paraview?

Tobi · October 11, 2017, 08:57

The easiest way is just to apply it on your domain but it depend what you would like to do. I suggest you to have a look here: https://www.paraview.org/paraview-guide/

Bdew8556 · May 19, 2019, 19:45

Hey guys.

Im a bit confused on the maths behind integrate variables.
If I just have a simple duct, flow from left to right, and I put a slice perpendicular to the flow, then apply integrate variables am I getting:

Integral over surface (U.dA)/A. So the area weighted average velocity essentially?

November 29, 2016, 15:08	Integrate Variables filter in ParaView	#2
Persia New Member Maryam Join Date: Dec 2015 Posts: 13 Rep Power: 10	Have you tried the "Integrate Variables" filter in ParaView? You can slice your domain at different locations and then find the integral over each slice with this filter.

November 30, 2016, 17:30		#5
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,708 Blog Entries: 6 Rep Power: 51	Hi bobi, The app is not showing the equations correct but your steps should lead to what you need. Using slices to generate a line an then integrate this one, should lead to the required integral. Maybe a simple test case should give you the proof. However, keep in mind that you introduce interpolation errors. Cheers babakflame likes this. __________________ Keep foaming, Tobias Holzmann

December 1, 2016, 22:51		#7
babakflame Senior Member Bobby Join Date: Oct 2012 Location: Michigan Posts: 454 Rep Power: 15	Dear Fellows I will put this information here, It might be useful for others in future about integrateVariable filter. If you want to use integrateVariable filter for integrating over a line, construct that line through consecutive slices, and then use integrateVariable filter. I compared the values from integrateVariable filter with a custom method. I think this filter performs well. @Tobi: I compared values from plot_over_line (with sufficient numbers) against integrateVariable filter. They were comparable. Regards Tobi and Persia like this.

October 11, 2017, 08:57		#9
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,708 Blog Entries: 6 Rep Power: 51	The easiest way is just to apply it on your domain but it depend what you would like to do. I suggest you to have a look here: https://www.paraview.org/paraview-guide/ __________________ Keep foaming, Tobias Holzmann

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November 29, 2016, 16:09		#4
babakflame Senior Member Bobby Join Date: Oct 2012 Location: Michigan Posts: 454 Rep Power: 15	I am thinking of two consecutive slices one in Z normal and the second one in X normal direction, the result can be a line in the desired x position and then using integrateVariables on custom variable $(\rho_e U_X)$ . It gives me a value. However, is that value the result of following integral?? $\int^L_0 (\rho_e U_x) \, dy$ Regards

November 30, 2016, 20:43		#6
babakflame Senior Member Bobby Join Date: Oct 2012 Location: Michigan Posts: 454 Rep Power: 15	Thanks Tobi Do you know any other filter that can be used for integration along one line? I am thinking of a snippet for doing it inside the code. I will add that snippet soon. Regards

October 11, 2017, 08:41		#8
samar New Member Samarendra Panda Join Date: Jun 2017 Posts: 8 Rep Power: 8	how to use integrate variable filter in paraview?

May 19, 2019, 19:45		#10
Bdew8556 Senior Member Brett Join Date: May 2013 Posts: 212 Rep Power: 13	Hey guys. Im a bit confused on the maths behind integrate variables. If I just have a simple duct, flow from left to right, and I put a slice perpendicular to the flow, then apply integrate variables am I getting: Integral over surface (U.dA)/A. So the area weighted average velocity essentially?