Ive been working in wet renewables in the UK, mostly wave power, since 2006. Since 2002 the company (Wavegen, originally) has owned a state of the art wave tank test basin and are now looking to exploit it fully, since a change of ownership has freed us up to experiment more. Its 20 x 6 x 1.5m. We have load & pressure sensing equipment, data acquiring and analysis equipment. At the moment its set up to recreate any sea from anywhere in the world and the bathymetry can also be adjusted. We are looking at creating a tidal flow capability within the tank also, possibly using a bank of jet ski motors. The tank could then be setup to create a standing wave.
Do you think the surfboard industry would be interested in hydrodynamical testing in a wavetank to complement CFD calculations? In theory, a board could be setup in the tank, with strategically placed load cells and pressure transducers.
I did a bit of tank testing with surfboards back in 1992 but unless its capable of creating a 3-D circular flow you can only get basic feedback that’s related to 2 dimensional drag.
Standing waves also have a greatly different flow speed and direction as compared to a natural wave.
Ive been trying to work out what you mean by ‘3D circular flow’, is this like complex tidal current flow?
The pump system we were thinking about would in principle be highly configurable and stand a good chance of coming close to reality. I think most commercial surfing wave pools have only unidirectional flow?
Im not sure about surfboards but it would be realy interesting to get some numbers on distance paddleboards that i build but i expect cost would be very hight? . were in the uk are you based?
We’re based in Inverness but we’re involved in worldwide projects. We have some amazing brains and equipment, just got Qualisys motion capture feel free to send an inquiry and we’ll look at it.
Most of the guys who build surfboards professionally barely graduated from high school cause they were always cutting class to go surfing - setting up a scientific study is beyond their skill set. Also, everybody who makes surboards is just scraping by - profit margins are thin. Industries that utelize all sorf of fluid dynamic testing equipement that collects data that can then be used to create computer models have $$,$$$.$$$ or more budgets and are subsidized one way or another by their governments. Finding a customer who can afford your services is unlikely, finding one who can also devise a robust scientific test is even more unlikely.
Airplanes and boats go straight. Even when turning, the span and chord of an airplane wing is very small compared to the radius of the turn. A boat turns, and then goes straight for miles. A surfboard, and especially a performance shortboard, is constantly being turned. Turns can be so tight and fast that the fins will effectively be more cambered as they pass a single water molecule. This leads to higher achievable maximum lift coefficients than are possible in static testing conditions. When a surfboard turns, the rocker effectively becomes straighter. Then there is the whole weight shift to turn thing. How to duplicate all these components for a test, and then have a variation of parameters test set that yields worthwhile improvements in something is the challenge. And that ‘something’ is key - what is the product?
I’ve been involved in lots of tests - in fact that what my career was. We typicaly had $$,$$$,$$$ to $,$$$,$$$,$$$ budgets.
Every now and then, these sort of research ideas come up, and eventually people realize that the smartest thing to do is to go surfing.
However, there is useful testing that can be done on an elementary school allowance budget:
Early in my engineering career, I was the Design Engineer/Aerodynamicist on a hypersonic wind tunnel test. In addition to collecting force data and employing a schlieren imaging system to photograph the shock waves, we also tufted the test item with fluorescent dyed monofilament line that we photographed. The short pieces of monofilament line would weathervane in the flow, and the fluorescent dye would fluoresce under the broad spectrum of the photo flash. That’s all very expensive, but a surfboard could be tufted with black yarn and photographed with a GoPro or a housed DSLR as it passes by. More explanation is needed to define a good test series, and the addition of time-synced shore based and drone based cameras to document the maneuvers would significantly add to the integrity of the test. That’s all a lot more writing that I feel like doing.
Yarn is cheap. There is an abundance of GoPro or similar cameras laying about; lots of point and shoot cameras are waterproof enough to be submerged enough for such a test; and a couple years ago I bought an older but still decent Nikon Coolpix L20 point-and-shoot 10Mp camera with a water housing on eBay for $25 - and then I bought another L20 camera as a spare for another $25. All are within an elementary school allowance budget.
Anyway, a lot of folks wave their arms around and even draw diagrams while talking all about the flow on a surfboard, but they are all speaking out-of-turn cause they really don’t know anything cause nobody has ever done a proper flow visualization test. Here is a simple/cheap way to remedy our ignorance. A couple middle school groms could do this and take turns surfing/taking pictures for a day or few.
Rather than join Vimeo I’ll make my observations here.
1. Note that in a turn, the tufts closest to the water/air interface are parallel with that interface. This is obvious; water can’t cross the interface boundary so it must flow parallel to it.
2. Note that when water is directed off the side of the board, only that water fairly close to the interface is parallel to the interface. Well if (1) above is true, most of (2) would be expected. It follows that most of the water passing under the board still flows straight back.
3. The comment below the video about not seeing the 3-D flow pattern shows at best, a poor understanding of the flow. Much of the “lift” experienced by a flat plate (surfboard) passing over a liquid (water) occurs near the interface, that is to say, a disproportionate amount of lift comes in the first several inches back from the interface. Google it, it’s moderately basic fluid mechanics (I are engineer, took fluids at Univ. of Hawaii when not surfing).
4. Water pressure on a surfboard acts perpendicular to the surface (remember pressure = force times area). There’s also drag force, which acts parallel to the surface.
5. Other things being equal, a short, low-rocker board experiences little drag. Low drag from low area; low drag b/c there’s not much rocker which would receive forces other than normal to the “average rocker” that is, approximating the board as a plane surface. Such are the reasons why boogie boards and paipo boards generally are IMHO faster than most (almost all?) surfboards. The do have trouble with chop.
Nicely put. My eng school was a long time back, plus prolly a few head injuries. With apparently cumulative results. Anyhow-
A couple of things: I find it interesting that the water redirecting to the side seems to be doing so along an abrupt transition line. Lift/pressure versus/overcoming what? As I say, it’s been a while since school, so Im not clear on what’s going on at that transition. Your thoughts?
Rocker vs drag: flex kneeboards and original boogie boards flexing to better conform to the waterflow, come to think of it mats the same way, getting more speed than one might expect- I always though that stiffening up boogie boards was a step in the wrong direction.
Boogie and paipo riders are prone, have small frontal areas, have aerodynamic high fineness ratios, so have little aerodynamic drag compared to a stand up surfer that is about as aerodynamic as a tree stump. Recall those 15+ knot offshore days where you get blown out the back the moment you try to get to your feet. I saw a video a couple years ago of Maalaea Freights where the boogie boarders were significantly faster on the open face, but in the tube the stand up guys had a slight speed and significant control advantage.
Correction: lift is perpendicular to the velocity vector, and drag is parallel to the velocity vector. If a surface is tilted backwards slightly with angle theta, then psicos(theta) is lift and psisin(theta) is drag. Drag on a surfboard is from aerodynaic drag on the surfer, aerodynamic drag on the surfboard, a little drag on the surfboard from skin friction, quite a bit from psi*sin(theta), and some from dragging the leash behind.
feel free to send an inquiry and we’ll look at it.