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Resistance

saji vf

Hello,

 we are doing a resistance case for a vessel with appendages like bilge_keel, rudder etc.,

1. while running the simulation it was running smoothly at start , the velocity is ramping to the final time, but after some time steps like (1200) the solution is diverging with negative volumes.

2. we have used AGR (adaptive grid refinement) but no use , how can we solve this issue.

Thank you.

Parents
  • +1

    Hi,


    Most of the time, this would come from a relatively low quality cell, as mentioned in the documentation in page: "FineTm Marine > FAQ > My calculation stopped abnormally. How can I manage?"
    Hence, a good idea would be to verify the quality at first, then if there is no particular bad cell that you could think of, you will have to save the simulation before the simulation diverges and inspect the solution in CFView, plotting the pressure and velocity field. A spot will certainly appear and indicate the location of the issue.
    Do not forget that the mesh quality can degrade during the simulation with the mesh deformation and the addition of extra cells coming from AGR.

    Best regards,

Reply
  • +1

    Hi,


    Most of the time, this would come from a relatively low quality cell, as mentioned in the documentation in page: "FineTm Marine > FAQ > My calculation stopped abnormally. How can I manage?"
    Hence, a good idea would be to verify the quality at first, then if there is no particular bad cell that you could think of, you will have to save the simulation before the simulation diverges and inspect the solution in CFView, plotting the pressure and velocity field. A spot will certainly appear and indicate the location of the issue.
    Do not forget that the mesh quality can degrade during the simulation with the mesh deformation and the addition of extra cells coming from AGR.

    Best regards,

Children
  • 0 in reply to Benoit Mallol

    Hello,

    We have rectified the negative cells and increased the refinements either wise simulation is diverging.

    but when we try with higher y_plus (150) the simulation is running smooth without crashing.

    if we try with y_plus=1 the solution is diverging .

    how to resolve this?

    Thank you.

  • 0 in reply to saji vf

    Hello,

    Thanks for the confirmation.

    Solvers are always more sensitive when we switch from "wall function" to "wall resolved". Hence, the solver now needs to fully resolve what is happening in the viscous layers instead of imposing a wall function. Hence, mesh quality is even more important.
    Hence, I would propose the same procedure: try to save the solution to check the pressure and velocity just before the divergence to see where the divergence is coming from. Check that the mesh quality is good enough at this location, remembering that for resistance, we usually solve trim and sink meaning mesh quality might evolve during the simulation as well.
    By the way, this could also be a good idea: maybe you could run the simulation fixing the trim and sink, it has no particular physical meaning but at least, it will tell you if the mesh quality is guilty or not.

    Best regards,

    Benoit

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