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mach000 February 18, 2010 12:58

planning hull
 
Hi to everybody,
i'm an aerospace engineer and I'm working as CFD and Structural Engineer.
For my simulation I use Ansys CFX v11.
Most of my simulations are about multiphase flowfields. I've simulated semi submerged rudder, flaps and also a semi submerged propeller (there are two videos about it on youtube. Look for "cfd semi submerged propeller").
Now, I'm trying to simulate planing hulls but i've a great problem.
A very thin air layer appears between the hull and the free surface. Infact, at the and of the simulation the hull is completely dry.
i would like to know if someone studied this kind of simulation and have some idea or solution of this problem.
Thank you very much to everyone!

ghorrocks February 18, 2010 18:02

I think you will need to go to the literature for this. I doubt you will find people with experience in a specialised area like this on the forum (but you never know your luck).

openfoam_user February 24, 2010 03:42

Hi Ciro,

could you give me our personal email address at Victory Design.

I will write you soon.

Stephane.

mach000 February 24, 2010 04:38

Quote:

Originally Posted by openfoam_user (Post 247158)
Hi Ciro,

could you give me our personal email address at Victory Design.

I will write you soon.

Stephane.


Hi stephane,
you can write me at victory@victory.it

Thank you

Ciro

mach000 February 24, 2010 05:34

Dear Stepane,
if you want you can write me at my personal mail address cannavacciuolociro@gmail.com.

Bye

Ciro

mach000 February 24, 2010 12:22

Hi Stephane,
i received your email at victory address.
First of all, thank you very much for the instructions that yuo gave me.
I'll start some simulation in order to set all the parameters.
You told me about a newsletter that you sent me today, but i never received it.
I don't know openfoam but now I'll try to have some news about it.
If you can, and you you want, i would like to continue to have contact with you in order to share ideas and "problems". In order to have the possibility to read your message in every moment, I prefer to receive your msg in this forum or at my private address (cannavacciuolociro@gmail.com). I hope it will not be a problem for you. Thank you very much.
Ciro

ziyasaydam May 11, 2011 02:37

Dear all,

I am experiencing a very similar problem with Star-CCM and Fluent during analysis of a planing yacht. As speeds are increased (and hence the trim) a layer of air travels aft below the hull and the bottom of the hull dries...

Could you please share how you managed to overcome the situation?

Kind regards,

Ziya

ghorrocks May 11, 2011 06:49

I would imagine in this case the air under the hull would form a very thin layer. You will need a fine mesh to resolve this thin air layer. Have you done a mesh refinement check to ensure it is not fixed by simply a finer mesh?

ziyasaydam May 11, 2011 06:55

Actually, the problem gets worse as the mesh gets finer.
If the mesh is coarsened and the boundary layer mesh is not applied, the air film under the hull no longer forms. But then, the wall treatment is no longer valid and the drag values are no longer reliable...

ghorrocks May 11, 2011 07:29

Quote:

Actually, the problem gets worse as the mesh gets finer.
Then is sounds like you are a long way away from an adequate mesh. You need to go much finer until it starts to converge.

Of course a coarser mesh makes it disappear - the thin layer is smeared across a big element and quickly dissipates. The wall treatment and drag is the least of your worries. You need a mesh fine enough to resolve the feature.

Deepak Bansal August 9, 2013 16:17

air phase being formed on the bottom of the hull
 
hey buddy i am also facing same problem in planing craft that air phase being formed on the bottom of the hull.................how did u solve this problem.................reply as soon as possible...............


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