Summing two volScalarFields

kilimanjaro2 · January 14, 2023, 13:16

Hi,

I would like to know what OpenFOAM does to the boundaryField when summing two volScalarFields.

Say :

Code:

volScalarField f1 = p1 + p2;

The internalField gets summed up element-wise. That is clear.

Now, let us say that p1 only has fixedValue boundary conditions and p2 only has fixedGradient.

What ends up in f1?

Does openfoam take the fixedGradient values from p2, estimates the value on the face and sums it up it with the fixedValue of p1?

If so, where is this made in the code?

dlahaye · January 14, 2023, 14:48

Boundary conditions are typically applied *after* summing up contributions in the eon. Details are in eg the book by Moukalled, see https://link.springer.com/book/10.10...-3-319-16874-6.

Edit: eon => eqn or equation

kilimanjaro2 · January 15, 2023, 07:10

Quote:

Originally Posted by dlahaye

Boundary conditions are typically applied *after* summing up contributions in the eon. Details are in eg the book by Moukalled, see https://link.springer.com/book/10.10...-3-319-16874-6.

Hello,
Thanks for the comment.

What does "eon" mean?
Would you be so kind as to tell me where this information is located in the book? So far, I was not able to find this information.

dlahaye · January 15, 2023, 11:28

Section 15.6 "Boundary Conditions".

kilimanjaro2 · January 17, 2023, 13:58

Quote:

Originally Posted by dlahaye

Section 15.6 "Boundary Conditions".

This section is on boundary conditions for incompressible NS.
I would believe that the relevant part is :
"The unknown boundary pressure pb is extrapolated from the interior solution
using either a truncated Taylor series expansion around point C such that pressure is found from:"
$p_b = p_C + \nabla p_C \cdot \vec{d}_{Cb}$

So, when I sum two `volScalarField`s, the values that exist in the boundary with the `calculated` type are a reflection of this.

dlahaye · January 18, 2023, 04:29

First perform summation of two volScallarFields.

Once summmation is performed, apply boundary conditions on the resulting sum.

Same procedure for incompressible and compressible.

January 14, 2023, 13:16	Summing two volScalarFields	#1
kilimanjaro2 New Member Join Date: Dec 2022 Posts: 14 Rep Power: 3	Hi, I would like to know what OpenFOAM does to the boundaryField when summing two volScalarFields. Say : Code: volScalarField f1 = p1 + p2; The internalField gets summed up element-wise. That is clear. Now, let us say that p1 only has fixedValue boundary conditions and p2 only has fixedGradient. What ends up in f1? Does openfoam take the fixedGradient values from p2, estimates the value on the face and sums it up it with the fixedValue of p1? If so, where is this made in the code?

January 14, 2023, 14:48		#2
dlahaye Senior Member Domenico Lahaye Join Date: Dec 2013 Posts: 730 Blog Entries: 1 Rep Power: 17	Boundary conditions are typically applied after summing up contributions in the eon. Details are in eg the book by Moukalled, see https://link.springer.com/book/10.10...-3-319-16874-6. Edit: eon => eqn or equation Last edited by dlahaye; January 15, 2023 at 11:26.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Postprocess: sampleDict works but creates no output folder	shock77	OpenFOAM Post-Processing	14	November 15, 2021 08:27
volVectorField from 3 volScalarFields without for loop	Houthuys	OpenFOAM Programming & Development	2	June 6, 2017 05:43
Multiple volScalarFields using List<volScalarField>	vbchris	OpenFOAM Programming & Development	6	September 14, 2014 06:38
foamToEnsight does not convert all volScalarFields	stevenbeale	OpenFOAM Post-Processing	2	February 14, 2014 04:20
a reconstructPar issue	immortality	OpenFOAM Post-Processing	8	June 16, 2013 11:25

January 15, 2023, 11:28		#4
dlahaye Senior Member Domenico Lahaye Join Date: Dec 2013 Posts: 730 Blog Entries: 1 Rep Power: 17	Section 15.6 "Boundary Conditions".

January 18, 2023, 04:29		#6
dlahaye Senior Member Domenico Lahaye Join Date: Dec 2013 Posts: 730 Blog Entries: 1 Rep Power: 17	First perform summation of two volScallarFields. Once summmation is performed, apply boundary conditions on the resulting sum. Same procedure for incompressible and compressible.