[pavel915]

Dear all,

in gambit documentation( tutorial) there is a tutorial for sail boat. THis tutorial can also be found in internet in the following link:

http://progdata.umflint.edu/MAZUMDER...orial/tg15.pdf

Now my question is:

Boundary conditions are not defined in this tutorial. I really want to know what should be the boundary conditions here what will be the operations in fluent. If any one can give the answer in details with some pictures if possible it will be a great help for me.

I actually want to capcture the wake dsitribution in propeller plane and to see the free surface wave pattern.

Please help me.

[-mAx-]

Oops, I didn't want to reply to this thread.
Anyway...
This is a gambit tutorial for modelling the sailboat and surrounding domain.
So it's normal that there isn't any BC defined.
Check here , it may help you: http://www.boatdesign.net/forums/des...sis-17049.html
Sorry for the non prolific reply

[Dimo]

Hello Pavel,

Can you be more specific in what you're looking for? Are you looking at propeller wake behind a sailing yacht or other type of vessel? Are you planning to look at the propeller in open waters or attached to the boat?

Tutorial 15 from Gambit is a good way to start, but it's not very helpful if you're dealing with free-surface, which is underlined in the given tutorial.

Dimo

[pavel915]

Originally Posted by Dimo

Hello Pavel,

Can you be more specific in what you're looking for? Are you looking at propeller wake behind a sailing yacht or other type of vessel? Are you planning to look at the propeller in open waters or attached to the boat?

Tutorial 15 from Gambit is a good way to start, but it's not very helpful if you're dealing with free-surface, which is underlined in the given tutorial.

Dimo

thanks demo for your reply,
I want to capture the wake distribution on the propeller plane for a displacement ship( merchant ship).

I know how to simulate without free surface , but i want to know how i can use a free surface where wave will generate. I know i have to use VOF method, but dont know how to do that and what should be the boundary conditions. Please tell me in details what should i do.

[Dimo]

Ok, I'll get back to you tonight with some information. I think there was a student who did a PhD once on something similar so I need to find his thesis so watch this space.

[pavel915]

Thanks Dimo,,,, Waiting for your help,,,

[Dimo]

Hi Pavel,

I had a look through the theses and managed to find the one I mentioned yesterday.

The study was about a hull-propeller interaction. Initially, the student looked at meshing and simulating the hull alone (which was one of Cb=0.60 model), then the various propellers in open-water and finally combining hull and propeller together for the integrated finite volume domain.

The integrated domain was created by merging the the mesh of the propeller domain to that of the hull domain through a common interface (initial domains were slightly modified to fit the model).

Now the problem is that the person did not consider free-surface; the top boundary is considered to be a symmetry in this case as are the outter domain faces, the hull is set to wall, the propeller-shaft is set to moving wall with interface around it. In the interface, non-conformal mesh was used between the stationary (hull) and rotating (inside interface) fluid domains.

I don't know if that helps you or not. In my opinion, if you are to look at free-surface, you should do the following in Fluent:
1) Define>Models>VOF> 2 phases> Explicit (I think)> Courant Number:0.25
2) Define>Materials: air and water
3) Define>Phases: air as primary, water as secondary
4) Define>User-Defined>Functions. There you should either interpret/compile any UDF for prescribing e.g. pressure difference behind the ship, propeller rotation, or anything else you are looking for
5) Define>Boundary Conditions: There you set vel inlet, outlet, wall conditions (stationary, moving), etc...
6) Solve>Controls>solution (depending on what solver & viscous model you chose)
7) Solve>Monitors : residuals, forces, surfaces etc...
8) Solve> Initialize
9) Adapt>Region: Here you must, I think, adapt the region of the free surface/water with dimensions
10) Solve>Initialize>Patch: patch initial distribution of water phase

In general lines, that should be it. You might also have to add above the step Define>Dynamic Mesh althought I'm not 100% sure since I've never dealt with free-surface myself but I've seen in some cases they use it for wave modelling so be aware of that.

Hopefully that should give you a start. If in doubt, post again in the thread and I'll try to help you as much as I can. Good luck!

Dimo