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Boris July 12, 2002 04:16

Meshing ship flow with Hex???
I have tried hard to use Gambit to mesh a ship flow with Hex. I always have a problem with the mesh quality. Has anyone done the similar job using Gambit? It is mostly appreciated if the domain decomposition strategy (particularly,the areas around the bulbous bow and stern part) for a typical shiphull geometry can be provided.

Thank you very much.

alireza ablaghdar July 15, 2002 16:27

Re: Meshing ship flow with Hex???
hi i have used this type of mesh what is exatly your problem?

boris July 15, 2002 23:18

Re: Meshing ship flow with Hex???
Thank you so much for your response. I have been looking for an expert who has the experiences in ship flow CFD simulation. I am so glad that you have such an experience.

My problems or my queries regarding the ship model pre-processing are as follows:

1)Can Tets be used for a ship VOF model? If yes, how to overcome the problem of the huge cell numbers?

2)Is that necessary to use Hex for a ship VOF model? If yes, how to decompose the domain so that the Hex can be used for the whole domain? To do so, is that necessary to use multi-block concepts (to generate several separate mesh files and later merge them together by using grid interfaces). Normally how many blocks need to be used for a typical ship flow model?

3) I used a hybrid mesh for the model (tet for the blocks close to bulbous bow and stern, hex for the rest of the domain). I encountered convergence problem. The drag monitored can't reach a constant value. What may be the reason?

In pre-processing, is that necessary to form a surface to capture the wave flow ( the surface is the interface of still water and air). It that necessary to use very dense cells to capture the wave?

4) As the Reynolds number is very big for a real ship model, any particular attentions need to be paid?

5) Can Gambit be really used to generate a fully structured mesh for a typical ship flow model?

In a word, I need your valuable advises on the meshing strategy and block topology for a ship flow model. I need your help desperately.

I am looking forward to your reply. Thank you again.

alireza ablaghdar July 16, 2002 15:29

Re: Meshing ship flow with Hex???
hi u have a lot quastions!!! i have modeled compressor of a jet engine not a big ship but it is not important if u have some experience about gambit ,u will found that type of your mesh depend on the complexibility of your model it is clear that structured meshes are better for boundary layer simulation but in your model it is not too important. so u can use only tringular meshes.this type of mesh is better for convergence.but if u want to have more exact results it is better that u use more grids .it causes that your cpu time become more. about multi block mesh ,it is a good way for meshing but u have to spend more time for meshing. gambit is too powerfull for modeling and meshing. usually 50% of modeling is neede for geometry and 50 % else for meshing if u have some problem about convergence i would be happy to help u if u like i would be happy to know u better and more bye

Boris July 17, 2002 02:31

Re: Meshing ship flow with Hex???
Thank you. I found that it is not easy to mesh a ship flow domain with Hex by using Gambit, as the geometry is quite complex and the computational domain is huge. Without a correct meshing strategy, it is almost impossible to obtain a mesh with good quality for a VOF model. I appreciate your reply.

Best regards!

alireza ablaghdar July 17, 2002 16:47

Re: Meshing ship flow with Hex???
u can seperate domain around of ship from other places and use a good mesh for it then for outside u can use less meshes.

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