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Old   May 20, 2011, 22:33
Default Absorbing Boundary Conditions
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Nick Mai
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Hi Everyone,

I'm just wondering if anyone's ever done wave propagation with OpenFOAM. If so, how did you specify the boundary conditions on the domain? That is, how did you do totally absorbing boundaries for the wave propagation?

I know for flow simulations, the pressure's usually set to 0 and the velocity is set to zeroGradient to simulate the flow through an infinitely long tube, or over a large area.

Any suggestions? I thought about using groovyBC to do this. Thanks guys!

--Nick
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Old   May 23, 2011, 17:40
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Pablo Higuera
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Hi

actually there is no unique answer, neither a universal way to make a 100% absorbent bc for interFoam.

As a simple approach you can try to increase the cell length in the dissipation area, but your domain may grow quite a lot.
Another option is to set an artificial beach in which waves break, but once again the domain is increased.
It can also done by means of adding a so called "sponge layer", this is just a porous medium. I have never used porous media in OF, so I ignore if this approach is suitable.

The most versatile option is to program a custom BC which allows the waves to flow out. This is what I am currently doing, along with wave generation.

Absorbing in a 2D domain is nearly straightforward to develop and there are a lot of well-performing formulations (10% reflection coefficient).

3D absorption is more tricky, there are also a lot of formulations, mainly based on digital filters. The difficult part is to estimate the direction of the wave to absorb, the rest is the same as 2D one.

I am sorry I cannot currently comment anything on specific theories. As soon as my work is finished and published I will share the code if I am allowed to do so.

Pablo H
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