An ugly wigley wave contour...

Hello,
I have tried to program a potential code base on the free surface panel method just from Dawson's method presented in the one of the most famous paper, A PRACTICAL COMPUTER METHOD FOR SOLVING SHIP-WAVE PROBLEMS. The result is...



Is there anyone who can tell me something or anything just from the picture?
And is it really possible to get the wonderful wave contour just from the original Dawson's method?

 

The best person to ask is possibly Leo Lazauskas. He lurks here sometimes or you can email him. He has a website that might provide some insight as well as contact details.
http://www.cyberiad.net/index.htm

Rick W

 

Thanks Rick, I would try connecting him.

 

You could check your analysis on an optimal Wigley hull. It has complete wave cancellation at design speed. If you go through this thread you can get details on the hull:
http://www.boatdesign.net/forums/design-software/michell-v-cfd-efd-round-2007-a-20497.html

If you have not tried Michlet you should have at look at it as well. There are many people who use it for hull drag analysis and it yields good results for slender hulls.

Rick W

 

Thanks again for the good informations.

I have not used Michlet yet, but somtime not so far I will start learining to use it.
Thinking of Michlet, always comes a limitation together, that Michlet is just for the "Slender ships", isn't it?
I need to enlarge the hull form to the "fat" and the answer from michlet is not clear.

 

I am not sure what constitutes fat. Michlet looks reasonable down to L/B of 4 from what I have looked at but my actual testing has been around L/B of 15 to 20.

Surprisingly Michlet corresponds reasonably to Savitsky with beamier hulls at initial planing speed. Again I have not done a complete comparison but I was surprised that they were not too far apart on the few times I have compared.

Rick W

 

L/B of 4 ! That's more than surprising.
It means Michlet covers all types of commercial ships.

Ok, now I have an idea. My potential code works reasonable in double model solution(DMS). Before the free surface condition is applied, the resistance value could be approximated with DBS and consequently the value could be considered as a measure of merit of the hull form optimization process.

With the bundle of results, the correlation with DMS and FMS(Free surface Model Solution ; by Michlet) could be examined.

I can not guess anything, but if the good result from DMS confirms also that from FMS, it could be very very useful, even hopeful, at least in our academic space practically.

Are you the messanger of hope in this christmas time ?

Thanks Rick.

 

You can probably save a lot of time if you use the in-built hull optimiser incorporated in the Michlet code. It is called GODZILLA and functions using a switch when Michlet is executed.

GODZILLA produces lowest drag hull within your pre-set constraints. I usually start with only displacement set and a design speed. I look at the hull form and the resulting drag. Then I apply different constraints such as length or stability to determine what these will cost in terms of added drag. It would take years to do the iterations that GODZILLA does in seconds if each was done manually.

Rick W

 

Nah, Rick's just helpful, knowledgeable and generous with his time and advice. Nothing special about Christmas, he's like that year round.

As for Michlet's limits of validity: The more mathematically inclined among us may wish to debate the details of why this is so, but as a general rule of thumb, Michlet will work well for shapes where the flow stays attached to the hull. It will fail (well, it'll still run, but the results will be meaningless) if the shape is such that the flow streamlines separate from the hull, ie. a pocket of turbulence is dragged along behind some section of the hull that curves so sharply the water can't flow around it smoothly. So a rowing scull is OK, most sailing yacht and displacement motoryacht forms are OK, most catamarans are OK. It can handle transoms, provided you input them as such in the offsets. But a 90' LOA, 24' beam, fat-bodied "quota cheater" fishboat won't work. Generally speaking, it's very hard to come up with a hull with L/B less than about 4 where there are no strong adverse pressure gradients that can cause separation.

 

Thanks mat!
Now I can understand why michlet usually works with "Slender Ship."
Yes the hull with L/B less than about 4 generates separation...
Hm...I see...

Daehwan Park.

 

Thanks Rick!
When I work with Michlet, I will go with GODZILLA, too.