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Tiesda You November 13, 2000 06:38

Developing Windsurf boards on-scren
 
I am presently a Design Engineer for a major international windsurf board company and have been designing boards by custom-making each prototype and testing them empirically. This, of course, is time consuming and expensive in the longterm, and even it though gives us unquestionable feedback on the water, it is also a terribly inefficient way of designing boards.

So the question is, what program(s) (pre-processors, CFD and postprocessors) will allow me to input the board shape data, the loads acting on the board, and obtain a series of outputs which will allow the interpretation of the the board's virtual performance, all in a relatively user-friendly environment?

Any help is vey much appreciated.

Sincerely,

Tiesda.

Jas November 14, 2000 03:39

Re: Developing Windsurf boards on-scren
 
Hi,

You could approach it a number of ways. First, if your interested in how the board deflects and you know your forces acting - use FEA. If you want to find out how streamlined it is, you could use a sliding or moving grid simulation where you model the ocean as a control volume with inlet and outlets, so that you can apply a suitable boundary condition in order to model wave motion. The board can be modeled as a solid block that moves through/above the surface in some prescribed manner. The CFD calculation will provide you with the forces from the ocean upon your board, drag coefficients, and point data. I imagine the hardest part wil be telling the CFD code how the ocean and board move. You could however set up the software to perform a number of known tests that you know is validated and then use the CFD results relatively to find a good design.

There are also advances in fluid/structure interaction coming onto the market which may help. Probably best to contact software suppliers directly.

Regards

John C. Chien November 19, 2000 22:02

Re: Developing Windsurf boards on-scren
 
(1). I don't think it is practical today to use CFD approaches to "design windsurf board". (2). The chances of doing so is "almost zero". This is because (a). Accurate prediction of the transient flow field is hard to achieve, (b). The actual requirement from the expert surfer is still missing. (3). In other words, the tools are still yet to be invented for something which is largely unknown.

Jas November 20, 2000 05:02

Re: Developing Windsurf boards on-scren
 
There is no harm in giving it a go though!

We should promote all CFD on this forum and attempt the impossible otherwise how will we evolve?

We have tools, they may work or they may not work, if they don't work maybe this will tell us how to make it work. Isn't this the point of research?

Give it a go I say.

Jas


Jas November 20, 2000 05:18

Re: Developing Windsurf boards on-scren
 
In order to be creative........

"Do not follow where the path may lead, go instead where there is no path and leave a trail"

Sound good to me

Jas


John C. Chien November 20, 2000 10:20

Re: Developing Windsurf boards on-scren
 
(1). I think, the designer would be very happy to see your CFD results of surfboard design. (2). It is not practical today, does not mean that, it is not feasible today.

Jon Lewin November 24, 2000 07:03

Re: Developing Windsurf boards on-scren
 
Wow! Is this a comment from John Chien, that's not negative?.......

John C. Chien November 24, 2000 13:46

Re: Developing Windsurf boards on-scren
 
(1). The first step is to wire the expert surfer and take the data, so that the body motion, the surfboard motion, and the wave motion can be analyzied to sort out the effect from each component. (2). Once you know how to isolate the body motion, the wave motion from the surfboard, then it is possible to study the effect due to the surfboard design. In other words, if you know the particular wave motion, and the body motion, then you can determine whether the particular surfboard design is goo or bad. (3). Naturally, it takes an expert surfer to tell whether the subsequent surfboard motion is good or bad. I guess, it depends on what he is trying to achieve at that point. (4). By studying all of the combination, taken from the data, I think, it is possible to predict the surfboard motion of a particular design under that particular condition. Since the surfboard geometry is largely fixed, optimization is required so that it can perform under various conditions. (5). Since the expert surfer can exercise the active control over the surfboard, it is possible to narrow down the number of essential parameters of the surfboard geometry. (6). So, from this point of view, I think, it is feasible to use CFD to design the surfboard, assuming that the essential test data is available. Remember that the expert surfer's brain is more powerful than a PC or a super-computer. So, one needs to get help from the brain of the expert surfer first, in order to solve the fluid dynamic aspect of the surfboard design. (7). I think, the CFD application in sports is going to be an interesting area. And the surfboard design is going to take a lot of AI into CFD. I would be interested in the development of this new field of surfboard design. It shouldn't be that complicated, I hope.

Mike Stewart December 1, 2000 23:42

Re: Developing Windsurf boards on-scren
 
This seemed like the most logical place to insert this if not please post it independenly.

I am part of a design forum of some of the world's best wave riders and we are currently discussing the possibility of scaling high performance surfboards. This note is in response to a recent letter concerning the impossibility of scaling the surfboard. The idea is to take out the variable of the surfer and simply calculate forces based on the attitude of the board in relation to the water flow. If anyone has any further input on this I would be delighted to hear about it.

Kind Regards Mike Stewart

"Inspiring message Malcolm. I am eager to hear about your fins. I agree with a lot of your points. I can identify with many incalculable factors that contribute to the "stew" of design variables. How do you calculate aggressive or passive attitudes for instance? Or that thing intuitively all surfers know but everyone is reluctant to talk about in public; that there is something much more to this activity of wave riding/life (and the activity of creating anything for that matter) than what you see or can even come close to describing as soul. And the ethereal signature that results from creating things that didn't exists before. One thing is for sure any of these elusive variables will contaminate attempts at achieving definitive math. It could also be argued that these variables are so great they would not produce anything of any value. Conversely there are certain tangible things that can be defined; not perfectly but then that becomes an issue of relative semantics'. Generally length can be calculated, as can widths curves and volume. Where you take it from there, as I think everyone is realizing and what stimulates this dialogue becomes less definitive. So yes, it will be awhile, if ever, before an automaton/computer can come remotely close to shaping as good craftsman can. Yet the reality is that none of us knows the formula to make magic boards for everyone for all surf conditions. Rather we solicit our ideology and mainly our perspectives to what we think will work best. I have no idea how to calculate an accurate scaling factor on paper. However it's easy to scale a 3d object in a computer. But scaling performance is another matter all together. Instead of surrendering to the challenge perhaps we can gain insight with a concept to at least attempt the feat of scaling shape for one persons quiver. I have no idea if this would work but I am certain something could be learned from it.

1. Talented human creates many boards for a surfer, some work shity, some work ok, one is magic in six (or whatever) feet waves. 2. Take magic board and accurately digitize so there is a very accurate virtual 3d replica. 3. Design challenge two: There would have to be an accurate measurement of water flow rates in the magic boards optimum conditions to create a standard. 4. Insert 3d board into sophisticated computer aided fluid engineering soft wear. Need some connections at General Dynamics for this one. 5. Change the attitude of the board (in a sequence of movements if not stationary; (bottom turn, cut back etc.)) relative to water flow speed and compute forces exerted onto the entire board. 6. Virtually increase or decrease the water flow/speed and let the computer work the problem backwards creating an optimal 3d shape that creates similar forces for varying water flow rates (possibly based on a particular movement sequence). Ultimately if a surfer had two or three magic boards for different conditions they could be introduced for more accurate results. 7. Build prototypes based off of data, because there is no substitute for reality. Input any findings from tests back into system to enhance accuracy.

How deep in detail you go may or may not substantially impact the final outcome. It's conceivable that you could in-put foam, glass/resin skins and stringer density and their specifications, creating numbers for flex modulus. Fleshy feet location and movement. Viscosity and density of water in addition to random anomalies or chop on water surface. Perhaps this could be a project for a young engineer student to write his thesis on? Anyway just a stab at it ms"



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