Frisbee-circular plate aerodynamics

It's also good for me to see the differences in computer time between our methods.

I've been warned about the difficulty of tandem wakes, so I'll avoid it like I
avoid any work involving the formation and evolution of waves by wind.
Apparently that can drive you mad

 

I think of it as a "gift".

No, I only have mathematical references, nothing experimental.

It's the depth based Froude number that is important,
i.e. Fh = U/sqrt(g*h) where h is water depth, g = gravity and U = speed.
Near the (critical ) Fh=1, the hull can have a large trim.

Do you get solitons forming and shooting forwards ahead of the boat? That
does happen in towing tanks. Another problem in tanks is that the model
can take a long time to reach steady speed, and sometimes not at all
because the tank is too short.

I would search for papers by Tim Gourlay at Curtin University. His
specialty is the squat of displacement ships in shallow water.
He is also a very keen windsurfer and has some interest in planing.
http://cmst.curtin.edu.au/people/gourlay.cfm

Another expert in the field is Ian Dand, but I'm not sure if his work includes planing.

Good luck!

 

The depth of my channel is the same or less than the boat LWL, so maybe that is the problem - thanks! What are solitons?

I have a good planing validation case, and don't really care for shallow waters except that smaller domain is computationally less demanding. Sailboat model in waves would be nice.

 

Great link, thanks. This guy appears to know his stuff,

 

There are some other "critical" parameters that are important. For values
less than a certain critical parameter, dispersive effects are important, for
values greater than the critical, non-linear effects are important.

Finite width can play an important part in wave resistance prediction.
There is a well-known phenomenon where there is a very sudden drop in
wave resistance in finite-depth channels and towing tanks.
It is quite easy to predict the size of the drop in classical theory. I'm not
sure if it would come out in the total resistance prediction using your
CFD codes, but it should.

Solitons are non-dispersive waves. They can form in finite width, finite
depth channels. The attached graphic shows solitons shooting out ahead
of a model in a towing tank. That's right, they can travel faster than the
ship! I wonder if they would appear in your CFD codes.

 

Width, depth or both? One sentence has "width", the next has "depth". Are you talking about two different phenomena or one?

 

In the photo you included, is the depth of the water much less than the length of the vessel and width of the tank?

 

Both. The channel has to be narrow and shallow for the drop in wave resistance to occur.

 

Yes, it is.

 

Mikko, do you have a code which includes free surface effects? If you do does it explicity track the free surface, or does it use a multi-phase model and track the air/water ratio?

 

Any references available? I haven't heard of this before and it sounds quite interesting.

 

In linear theory, the drop in wave resistance (dRw) is
dRw = (3 W^2) /(2 * rho * g * H * h^2)
where
W = vessel weight
rho = water density
g = gravitational acceleration
H = channel width
h = channel depth

One reference is:
Kirsch, M.,
"Shallow Water and Channel Effects on Wave Resistance",
J. Ship Research,
vol 10, No. 4, 1964, pp. 164-181.

Also search work by Lunde in the 1950's and by Russians such as Sretensky and Haskind for earlier work.

Wehausen's monograph "Wave Resistance of Ships" is a classic reference for all things to do with wave resistance.

 

It does single phase & multi-phase air/water, although if I haven't managed to get anything sensible of the multi-phase yet. It is still a work in progress beta testing. The single phase (water against void) would appear to give reasonable results as is... have you any idea how badly physics is violated ignoring the other phase?