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Is overset mesh required?

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Old   February 20, 2017, 04:49
Question Is overset mesh required?
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Andreas M. Hildershavn
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Hello, I am new to the world of CFD, and especially OpenFoam.

We are not yet sure how to tackle OpenFoam for the cases we are interested in, and I was hoping to get some meaningful replies in this forum.

I have a case with a planning hull which I would like to simulate and I during my search for information I have come to the understanding that I most likely need to use overset mesh. For the three cases below, do I need overset mesh? And why do I need it? Is it possible to do any of them without?

1.) Towing simulation with 2DOF.
2.) Thrust from rotating propeller(propeller mated to hull of course to see how the hull reacts to a given rpm/propeller design). 3DOF.
3.) Imposed thrust on hull (push force) without modelling the propeller.

If 3.) does not need overset mesh, would it be possible to break simulation into two separate?: one simulation with propeller submerged to find the thrust at different rpm-> use results to add a thrust to hull (without modelling propeller.). Could this give accurate results?

In case I need to use overset mesh the only methods I've found involve sugar++, DiRTlib and foamedOver, but if I understand correctly they all cost money and are also subject to export limitations.
a.) Are there any free/opensource alternatives to sugar++, DiRTlib, FoamedOver or are any of the mentioned free to use now?
b.) Any idea how much these cost if I need to buy them? Will it be cheaper to buy software from Numeca or Starccm?

I understand OpenFoam is a very powerful tool, but it requires a lot of skills and training to master, but it is an open source which should make it cheaper to use. This will not, however, be the case if I need to purchase all sorts of commercial tools/ad-ons for it. Programs such as starccm+ do have meshing tools, mesh repair tools, over set mesh enabled etc. etc. I do not know if the same can be said for Numeca's fine/marine.

Please help me out here, I do not want to embark on a journey without havin achievable goals(economically and intellectually).

Best regards,
Andreas
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Old   August 3, 2017, 14:09
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Giovanni
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Hi Andreas,
I will try to be concise in the answer even if you touch the entire world of Marine RANSE simulation with your curiosity

It is very difficult to get a planning hull simulations work properly in terms of physical behaviour and accuracy compared to towing tank results.
Overset mesh can give you tremendous advantages but is the least of your problem in this case.

For the simulation as you would like to do, you need some budget unfortunately, both for the open source or commercial solver.

On one side the modification on the OF mesher/solver would need a highly experienced programmer/user. Plus the simulation will be longer than the a commercial software.

On the other side the commercial software still needs some tweaking but it will be faster. And it will cost more.

The geometry of the hull and the propeller would also affect the entire CFD process.

I am sorry to put an edge on your capability, but will be stupid to tell you "Yes you are going to play for sure in the NBA!!" when you just got as gift your first basket ball.

Cheers,
Giovanni
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Old   August 4, 2017, 04:23
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What makes a commercial solver faster? Do you have relevant benchmarks?

Quote:
Originally Posted by Gio Baila View Post
Hi Andreas,
I will try to be concise in the answer even if you touch the entire world of Marine RANSE simulation with your curiosity

It is very difficult to get a planning hull simulations work properly in terms of physical behaviour and accuracy compared to towing tank results.
Overset mesh can give you tremendous advantages but is the least of your problem in this case.

For the simulation as you would like to do, you need some budget unfortunately, both for the open source or commercial solver.

On one side the modification on the OF mesher/solver would need a highly experienced programmer/user. Plus the simulation will be longer than the a commercial software.

On the other side the commercial software still needs some tweaking but it will be faster. And it will cost more.

The geometry of the hull and the propeller would also affect the entire CFD process.

I am sorry to put an edge on your capability, but will be stupid to tell you "Yes you are going to play for sure in the NBA!!" when you just got as gift your first basket ball.

Cheers,
Giovanni
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