Dynamic simulation of sails

For the technically inclined, we've posted a new article about dynamic sail simulation at http://www.wb-sails.fi/news/DynaSim

Mikko Brummer/WB-Sails

 

Very useful link. I deal with dynamic simulation of sails too.

 

Very interesting,

I have also considered using a vortex-lattice method and FEA for sail optimisation.

I would be interested to know why you chose to use only 100 panels for the 470 sails. Typically, I'd have expected to see at least 5000, probably more. After all, CPU time is cheap these days.

I have heard that the use of 3D CFD with adaptive grids is now being considered to help solve this problem. That will require some serious cluster computing.

Tim B.

 

Back in 1990, when that 470 run was done, CPU time was a major concern. It took 2 hours 20 minutes for the Mac SE-30 to solve that set of sails at the time.

For vortex lattice, you don't need more panels than that, it is quite accurate with 100 or so - for wings with thickness & general panel methods, you need more panels. Not so awfully many though, as you can see from the included panel method simulation on a Star. N-S simulations are of course in a class of their own, requiring easily 100.000 elements or so.

 

Flatting of spinnakers

From the website under Gaussian curvature & sail shape: "In sail terms, if the sail gets more curved in the vertical direction, it will get less curved (flatter) in the horizontal direction. This is what happens when you lift the spinnaker pole, for instance".

That would explain why unstayed flexible spinnaker poles work so well on skiffs. When a gust hits, the pole bends (dramatically) decreasing the distance between head and tack causing it to get more curved up the luff but flatter in horizontal section and hence depowering. Another trick is to flatten a spinnaker by easing the halyard.

I have never heard a sensible explanation of this effect and was hence dubious of the claim.

 

Mikko
I'd like to have a look but the site is not talking to my computer.

Get a 404

Cheers

 

Hey Mike,

It's working now, I just tried it.

Bill