Drag divergence in star ccm hull resistance

bgakhil · February 5, 2023, 13:21

Hi all,
I am simulating ships hull resistance. Mesh and all are looks fine. 4 m cells with correct y plus and al..But the simulation is not converging at all...I have tried so many ways, reducing time step. different meshing etc....Still problem is same...
Even first order implicit also tried...but no use.
Figures are attached...Can someone tell me what may be the possible reason for this.
Thank you in advance

Aeronautics El. K. · February 6, 2023, 15:17

What happened at 10s?
Is this free sink and trim?
What makes you think 105s are enough for a converged solution?
Also, what makes you think the mesh is fine? Have you done a mesh sensitivity study?

bgakhil · February 7, 2023, 04:40

Dear Aeronautics El. K.
Thanks for your reply.
The vessel is free to heave and pitch. I have tried so many meshes and from my point view i said mesh may be fine. Sensitivity study has not been performed and is planning to do after the convergence. And normally for model scale simulation simulations converge well before 100 s itself. I have tried with KCS.
Do you think it may be due to the meshing reasons..? I am still working on this...Remeshing and all...

Aeronautics El. K. · February 7, 2023, 04:55

Quote:

Originally Posted by bgakhil

Dear Aeronautics El. K.
Thanks for your reply.
The vessel is free to heave and pitch. I have tried so many meshes and from my point view i said mesh may be fine. Sensitivity study has not been performed and is planning to do after the convergence. And normally for model scale simulation simulations converge well before 100 s itself. I have tried with KCS.
Do you think it may be due to the meshing reasons..? I am still working on this...Remeshing and all...

It's not easy to know that. It depends on a lot.
How is the motion setup? Are you using free motion or equilibrium?

February 6, 2023, 15:17		#2
Aeronautics El. K. Senior Member Lefteris Join Date: Oct 2011 Location: UK Posts: 337 Rep Power: 15	What happened at 10s? Is this free sink and trim? What makes you think 105s are enough for a converged solution? Also, what makes you think the mesh is fine? Have you done a mesh sensitivity study? __________________ Lefteris

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February 7, 2023, 04:40		#3
bgakhil New Member Akhil Balagopalan Join Date: Apr 2018 Posts: 7 Rep Power: 8	Dear Aeronautics El. K. Thanks for your reply. The vessel is free to heave and pitch. I have tried so many meshes and from my point view i said mesh may be fine. Sensitivity study has not been performed and is planning to do after the convergence. And normally for model scale simulation simulations converge well before 100 s itself. I have tried with KCS. Do you think it may be due to the meshing reasons..? I am still working on this...Remeshing and all...