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I use OpenFOAM for CFD simulations. A very popular preconditioner is GAMG which needs a low number of iterations per a time step in SIMPLE or PISO solvers that are used to simulate the fluid flow.

I would like to understand how GAMG prepares the internal structures.

Does it create the internal data structures used in GAMG only once in a single iteration on the basis of the geometry and then the entries in these data structures are only updated?

OR

Does it create the interal data structures multiple times in a single iteration? I read the documentation here but it does not have the answer.

Thanks for your answer.

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  • $\begingroup$ I believe it generates the structure only once if your geometry is static if the cached option is true. This is why the GAMG solver is less efficient if you have AMI (sliding mesh) or if you refine the mesh since it must reconstruct its internal structure with each change of the mesh topology. Concretly, the GAMG power lies in scaling very well in terms of the number of unknown (O(n)) when solving the Poisson equation for the pressure. $\endgroup$ – BlaB Oct 24 '17 at 19:10

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