Wave Creation

Discussion in 'Hydrodynamics and Aerodynamics' started by rwar, Jan 25, 2016.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    Key would be the forward speed needed for the boat producing the wave. If is more than, say, 7 or 8 knots, you have big problems. If you need a boat doing 12 knots or more, the game is over, imo. Producing waves is power-hungry, and if it coincides with a speed when the hull itself becomes very power-hungry, you have a double whammy. Unless gonzo can come up with a hull shape that does the generating without a separate appliance. And no sooner you do that, the environmental police will arrive to shut you down.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Six feet wave crests height sounds like total overkill to me, and not friendly to anyone except experienced surfers. Three feet sounds more like it. And why does the boat need to travel parallel to the beach ? Why not motor in perpindicular, lower the wave generator into the water, like a bulldozer lowers its blade, and use the momentum of the boat to supply the energy. Reverse and repeat.
     
  3. rwar
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    rwar Junior Member

    The boat would only need to progress at 7 or 8 knots, similar to a wakeboarding setup.

    As far as driving parallel, the reason for this is that giving one blast towards shore will have little effect... Think traditional wave park. They have very large water tanks that plunge water toward the pool. This creates a wave that is initially powerful and dissipates quickly. There is little length to ride. Going parallel to shore and close to the reef allows the boat to continuously supply power to the wave. This works similar to a wakesurfing wave but uses the shoreline and the foil to enlarge the wave.
     
  4. rwar
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    rwar Junior Member

    Here is a quick drawing I made on sketchup. Keep in mind the foils are not optimized in any way, it is for visual reference only. If a powerboat could generate enough power, I envision 4 components and the supports. The middle spline and to sides could fold in half horizontally to make them easy to transport. The forth piece, not pictured here, would be a mould of the underside of the boat which the three other pieces would attach to. All made out of carbon fiber. They would be assembled then attached to the underside of the boat via tie down points.

    Now I know there are a lot of logistical problems here, it's just a starting point. I plan on making a 1:10 scale of a similar design to attach to an RC boat. I plan on using balsa wood and Apoxie Sculpt to make it. Hopefully it will generate a 4" - 7" breaking wave, if I can find a friendly shoreline. I might just make an artificial rock reef if not.

    Any wagers?
     

    Attached Files:

  5. Mr Efficiency
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    Mr Efficiency Senior Member

    The snow-plough arrangement makes the waves ? You will need considerably more forward speed than your desired wave speed, looking at that.
     
  6. W9GFO
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    W9GFO Senior Member

    Based upon my extensive 30 minutes of research into wave making, that is extreme overkill for making a 5 foot wave. There's a video of some guy that has built wave making machines, he explains and shows how he uses a boat shaped hull pulled through the water to create the waves.

    Here's the video;

     
  7. gonzo
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    gonzo Senior Member

    It always makes sense to study existing systems.
     
  8. rwar
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    rwar Junior Member

    I had visited that website before but not watched the video. The wave he creates is good but about half the desired size. Though it doesn't look like he is using a very powerful boat, which is encouraging. I have been studying the patents for these various systems but they are short on details about the foil and it's size. They cite the deep end of the wave pool at 10' so I figured the foil must extend down most of that depth.

    Think I should call them up and see if they'll tell me?

    Now for some testing. Thanks guys.
     
  9. daiquiri
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    daiquiri Engineering and Design

    rwar,

    the problem with your solution, and with other similar solutions which use symmetrical hulls, is that you obtain a symmetrical wave train. But only one half of the generated waves will reach the shore and be used. So you have wasted 50% of the wave energy right at the start. That's costly, inefficient and the unused waves on the opposite side of the vessel can create troubles on the other shore (if there is one), or to other vessels or swimmers around.

    IMO, you should explore the possibility to use a catamaran boat with hulls arranged in a so-called Weinblum configuration, which is visible here: http://www.cyberiad.net/wakeweinblum.htm
    The picture shows the effect of this configuration, which creates an augmented wave-train on one side of the boat, and almost zero waves on the opposite side. This allows you to use the available power in a more focused and efficient way.

    While it is true that such neat wave distribution is attainable only for slender hulls, I am pretty sure that other hull types can be arranged in such way to exploit, at least partially, the said effect. The closer you get to the Weinblum wave distribution, the better for your purpose. It will require a good deal of engineering and a lots of testing, of course.

    By the way, the calculations of the wake field visible in that picture in the Cyberiad site were done by a member of this forum, Leo Lazauskas (http://www.boatdesign.net/forums/profile/leo-lazauskas.html), who can certainly tell you more about the feasibility of this idea.

    I agree with those who say that you need a heavy displacement boat for the generation of waves of desired height. A water-ballast system might be a good idea if there is a need to create waves of varying height. Filling and emptying the ballast tanks would allow you to vary the displacement of the boat, and to generate wave trains of different height for a given speed.

    Cheers
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    How does that Weinblum set-up run in a straight-line ?
     
  11. daiquiri
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    daiquiri Engineering and Design

    With a good rudder. :)
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    A good, big, drag-inducing rudder ?
     
  13. daiquiri
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    daiquiri Engineering and Design

    Yeah, something like that. :p
    But if you don't like rudders, an assymetric propulsion layout would do the job too. ;)
    Intuitively I would say that the yawing effect of the assymmetrical wave train in the wake should not be very high. The viscous drag is IMO more important in that regard. But I might be wrong and, unfortunately, I am not aware of any research which has dealt with this issue. So only tests would tell.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    One problem with using such a vessel, it would only work in one direction of travel, you wouldn't get two passes from every cycle.
     

  15. rwar
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    rwar Junior Member

    Does the Weinblum configuration cancel out the the undesired wake or is it deflecting it in the desired direction? It looks like it uses interference to cancel the wave but I am not an expert. If that is the case, is it gaining efficiency?

    I like the idea of deflecting the energy back in the desired direction but not sure if this is practical or possible.
     
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