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naimishharpal September 27, 2010 17:32

Weighted Deformation Mesh technique in Fine/Marine
Hi all,
I am working on a DFBI project using NUMECA Fine/Marine software. Does anybody have any guidelines on how to use mesh deformation technique?

I will really help your suggestions and guidelines.

Thanking you,
Naimish Harpal

Rombzh September 28, 2010 11:23

I have only used grid deformation for a two solved DOF (sink and trim) problem.
Usually a time step of Tref/200 and 4 iterations per time step is enough for resistance cases (I use quasi-static method + sub cycling). If the amplitude of motions is going to be more significant (like in waves), I would advise 8 to 10 iterations per time step.

naimishharpal September 28, 2010 17:51

mutli-body DFBI
Hi Rombzh,
Thanks for the suggestions. I have already done this work, and the CFD results seem reasonable too. Now, the issue is to perform grid deformation when there are two boats placed close to each other. What could you suggest here?

Rombzh September 28, 2010 17:59

Oh sorry I did not get that.

Well all I know is that you need to activate the grid deformation for all DOF, even if some are fixed (that's some guideline I've read once, or maybe it's just in the manual).
I've never done any of this before though and I do not remember reading anything about such a case done with Fine/Marine.

About time step matter, I don't think you would need to change anything.

naimishharpal September 28, 2010 18:26

I know what you are talking about. The manual/user-guide suggests to turn-on mesh deformation for all 6DOF for multi-body DFBI. Even though following the suggested guidelines, the solution diverges in couple of iterations. :confused: Anyways, now, I have simplified my problem by considering Laminar flow. Let's see whether its problem with turbulence model compatibility or mesh problem.

Rombzh September 28, 2010 18:30

Do you end up with negative volumes ?

naimishharpal October 12, 2010 23:46

Hi Rombzh,
As you pointed out in previous conversation, I am ending with Negative volume problem with large deformation. I am planning to add Adaptive Mesh Refinement (AMR) on free surface to avoid negative volume. As my machine is out of order, I am off for this project for some time. Just waiting for to be fixed ASAP.

Anyways, do you have any suggestion and/or new recommendation to avoid negative volume problem?


Rombzh October 13, 2010 10:14

I guess there is no magical answer for that kind of problems unfortunately.
I would say :
- try to increase the non-linear iteration number, till 10 for instance
- lower the time step (but this cannot really help at some point, if you have to use Tref/400...
- refine the mesh close to the geometries.

naimishharpal December 11, 2010 18:03

Hi Rombzh,
I am glad to tell you that the problem of negative volume cells is resolved now. We tried the case with improved mesh quality near the walls, and that worked.

Thank you very much for your valuable suggestions.

C u.

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