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Symmetryplane, cyclic and wedge boundary conditions

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Old   November 3, 2011, 08:11
Question Symmetryplane, cyclic and wedge boundary conditions
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I am a bit confused as to what the difference between these boundary conditions are. Any help would be appreciated. My take on these BC's:

1) SymmetryPlane
Mirrors along a plane so to reduce the amount of cells needed for a full model. For instance you have a model of a car, then you would only need to compute half of the car as the other half is symmetric.
2) Cyclic
Looping back information from one bc to another. For instance a pipe, where the outlet loops back to the inlet.
3) Wedge
This is the one I am the least confident about. Apparently this is only for 2D simulations for axisymmetric problems, for instance a pipe. But I though (hoped) that it was a way to reduce amount of cells in an axisymmetric 3D problem where you would only need to model a fraction of the pipe.
In the case I am working on I have a pipe which is axisymmetric with about 4 million cells and I wish to reduce this amount. Intuitively the wedge approach seemed good as I would only need the mesh for a small section of the pipe. However if this is only for 2D then my simulation would probably fall apart as I intend to model LES.

So hopefully the symmetryPlane approach would work in my case perhaps? Where I would revolve my pipe only 180 degrees and use symmetryPlane bc on the resulting flat surface.
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Old   February 7, 2018, 07:24
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Hi Taltan

Be careful of these boundary conditions. They should be used with great care. The symmetry example you gave will only work if the flow is laminar. If it is not, there would be vortices behind the car, which is not symmetrical any more. But the mirror explanation is correct.

The wedge BC is to reduce a 3D case to a 2D case... If the flow is axisymmetric, thus f(r,z), then you should be able to use this boundary condition (not sure about the LES thing).

The symmetry approach might also work and you only need to revolve the pipe by 90 degrees if you think about it
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Old   April 16, 2018, 09:38
Gautami Erukulla
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Dear All,

1. To simulate a floating cylinder (using 6DOF rigid body motion solver) with symmetryPlane option, dividing the computational domain into half, does the mass and moment of inertia of cylinder defined in the dynamicMeshDict be divided to half. Taking full mass sinks the cylinder.
2. To simulate a floating cylinder (using 6DOF rigid body motion solver) with 3 DOF motion in heave, surge and pitch, and be restrained with linear spring, should the spring stiffness be taken half value for half the domain using symmetry plane option.
Kindly please advise. Thank You.

Gautami Erukulla.
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