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Old   May 21, 2011, 02:29
Default Shallow water + VOF
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MIT
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Mitsuru Nishikawa
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I am new to this forum and beginner as a developper of CFD. Please help me in the development of openfoam solver.

I am intended to merge the codes of shallow water equation and of VOF model in order to treat shallow water equations with free surface which is not height (included in the original equation) but width.
(That is, shallowWaterFoam+interFoam)

First, I think it is so simple, but in fact it is difficult for the difference in treatment of PISO loop or so.

Have you ever treated such a case?

Or, if you know the below questions, please teach me references?

(1) detailed solving steps in shallowWaterFoam or interFoam (particularly, in momentum(+h)-height coupling in shallowWaterFoam)
(2) In such a treatment, the equations of alpha (da/dt+v.div(a)=0) should be modified?

Sincerely,
MIT
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Old   May 23, 2011, 02:04
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Bernhard
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I don't understand how this combined solver should look like? What physics do you want to describe that VOF cannot?
I suppose VOF + shallowWaterFoam = VOF?

Furthermore, I am missing the point why your free surface is width, and not height, what is the difference?

For reference on interFoam, you can look here: http://foamcfd.org/resources/theses.html
for the PhD theses of Ubbink and Rusche. Or the PhD thesis of Berberovic, Google "Investigation of Free-surface Flow Associated with Drop Impact: Numerical Simulations and Theoretical Modeling"
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Old   May 23, 2011, 03:30
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Mitsuru Nishikawa
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Thank you for your reply.

At first, I apologize for the lack of my explanations. And because I do not have much experience in CFD, there should be a lot of my mistakes. It will give me much pleasure if you point out them.

The physics I want to describe is the flow of thin liquid films, paticularly how it spreads spatially (I defined Height as thickness of films, and Width of film width. Height is included in the schemes of SWE, I want to treat the free surface of the edge of film by VOF).

As you say, the only VOF (interFoam) is enough to treat a free-surface flows even in the case of the thin liquid film, so physics does not change.
However, I want to couple shallow water equations and VOF due to the two reasons,
(1) the problems of high aspect ratio in height/width due to thin films
(2) the reduction of computational cost (3D to 2D)

Yesterday, I merged SWE and VOF, but I cannot be sure it works correctly. Therefore, I am looking of its theoretical backbones (or mistakes) or a previous researches.

Sincerely,
MIT
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Old   May 26, 2011, 09:37
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Robin Koldeweij
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Could you may be explain more carefully what you're trying to do physically? I.e. start with the navier stokes equations, which assumptions do you want to make and what do you want to solve. Just merging two solvers won't bring you the joy of a physically correct solution..

May be you can just use the shallow water equations for a thin liquid film along a wall, with an extra source term for gravity effects. You'll have to think about relative viscosities and densities however.

It might be I don't understand correctly, but it seems you have an idea of what to solve, but haven't looked into the physics/assumptions of both solvers.
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Old   May 26, 2011, 20:27
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Mitsuru Nishikawa
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Dear RBJ,

Thank you for your suggestion. And I apologize my insufficient explanations.

Of course, I haven't simply merged the two codes. In swallowWatterFoam(SWF), viscosity term etc are not included. I omited the details of interactions I included because it is cumbersom to start from Navier-Stokes and it is not essential for my questions. But I write down the interations I want to inculde.
(Momentum equations:time derivative of momentum,inertia,viscosity,gravity,surface tension, pressure(pressure is displaced with the derived equation of height)) and the morphology of free surface.

Please image 3D plate, in which vertical length is much shorter than lateral length. Of course, it has 6 surfaces.Two of them are perpendicular to vertical directions, and the four are to lateral. I mentioned the vertical ones are included in SWE scheme as height(h), and I want to treat the remainders by VOF.

SWF is able to treat the free-surface of faces perpendicular to height directions, isn't it?
So, ocean wave in Picked-up area of sea which is surrounded by sea can be treated.
But is it able to treat movement of surf in sand beach only by SWF?
(If it is correct, is the area of h!=0 regarded as the area where water is? I can't understand.
If so, free surface(what I say as a faces of width) is able to be treated as the boundary between(h=0 or h!=0)
and surface tensions is calculated from the curvature of this boundary, my purpose is accomplished).

Last edited by MIT; May 26, 2011 at 21:03.
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