Soliton modeling

svanmunster · January 17, 2012, 22:16

Hi all,

I currently have no experience with CFD at all however my client has asked me to model a solitary bow wave (Soliton) created by a boat at near critical speed (Froudes number = 1) with the intent on determining potential wave heights and total drag for different configurations.

I have access to CFX only. I am just wondering if this is possible in CFX and whether it will be hard to model. Also does CFX have the capabilities to model breaking waves?

I am going to begin to do the inbuilt CFX tutorials to extend my knowledge on CFD. Some steps as to where to start would be greatly appreciated.

Thanks in advance!

ghorrocks · January 17, 2012, 23:14

Quote:

I am just wondering if this is possible in CFX

Yes

Quote:

and whether it will be hard to model.

Yes, especially if you have no experience in CFD.

Quote:

Also does CFX have the capabilities to model breaking waves?

Yes, but only by setting it up correctly such that it can do it.

This is really quite a tricky problem. How are you going to deal with the trim of the boat? How are you going to model the free surface? What boundary conditions are required to keep wave reflections under control? Each of these questions is complex enough you could do a PhD on it, so make sure you are aware of the complexity of this simulation.

If you are new to CFD then you have a lot of learning to do. I hope you have set aside several months for this. Start with tutorials sure, but the real challenge starts when you try to get accurate answers. The tutorials do not discuss accuracy at all (in my opinion they should so people know what is really involved).

svanmunster · January 18, 2012, 04:25

Thanks for your reply. I know I know its a big ask. The positive thing is I do have plenty of time.

Also the model is actually semi-fixed as in it is not allowed to trim or pitch, hopefully that will be make it easier.

I will be sure to keep you posted with my progress.

Thanks

ghorrocks · January 18, 2012, 05:30

Yes, a fixed body will take one of the big unknowns out of the simulation. In that case I recommend the following:

1) Start off with the tutorials. But they simply explain what buttons to press and give little insight into the theory and practise of getting accurate solutions.
2) Choose a simple benchmark case. Make start off with single phase and something with published accurate answers. Maybe flow over a back step or the lid driven cavity. Only when you are getting accurate solutions to these really simple simulations do you proceed.
3) Choose more complex benchmarks which start focussing on your simulation topic. Is there published benchmark flows of surface waves on a reference body? This would be ideal. Alternately tank sloshing or something similar would be good. Again, only after you get this accurate do you proceed.
4) By now you should have a pretty good idea of what is involved in getting and accurate CFD simulation in your two-phase flows. Now you can attempt your first simulation on your body.

For most people new to CFD this will take several months to work though.

January 17, 2012, 22:16	Soliton modeling	#1
svanmunster New Member Join Date: Jan 2012 Posts: 11 Rep Power: 14	Hi all, I currently have no experience with CFD at all however my client has asked me to model a solitary bow wave (Soliton) created by a boat at near critical speed (Froudes number = 1) with the intent on determining potential wave heights and total drag for different configurations. I have access to CFX only. I am just wondering if this is possible in CFX and whether it will be hard to model. Also does CFX have the capabilities to model breaking waves? I am going to begin to do the inbuilt CFX tutorials to extend my knowledge on CFD. Some steps as to where to start would be greatly appreciated. Thanks in advance!

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January 18, 2012, 04:25		#3
svanmunster New Member Join Date: Jan 2012 Posts: 11 Rep Power: 14	Thanks for your reply. I know I know its a big ask. The positive thing is I do have plenty of time. Also the model is actually semi-fixed as in it is not allowed to trim or pitch, hopefully that will be make it easier. I will be sure to keep you posted with my progress. Thanks

January 18, 2012, 05:30		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Yes, a fixed body will take one of the big unknowns out of the simulation. In that case I recommend the following: 1) Start off with the tutorials. But they simply explain what buttons to press and give little insight into the theory and practise of getting accurate solutions. 2) Choose a simple benchmark case. Make start off with single phase and something with published accurate answers. Maybe flow over a back step or the lid driven cavity. Only when you are getting accurate solutions to these really simple simulations do you proceed. 3) Choose more complex benchmarks which start focussing on your simulation topic. Is there published benchmark flows of surface waves on a reference body? This would be ideal. Alternately tank sloshing or something similar would be good. Again, only after you get this accurate do you proceed. 4) By now you should have a pretty good idea of what is involved in getting and accurate CFD simulation in your two-phase flows. Now you can attempt your first simulation on your body. For most people new to CFD this will take several months to work though.