Wave Creation

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

  1. rwar
    Joined: Jan 2016
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    rwar Junior Member

    Hi Folks,

    I am not sure if this is the right place for this question but thought I'd give it a try.

    I am developing a "wavefoil" that attaches to a powerboat that will generate a surfable wave. The difference here is the wave generated will not be surfed behind the boat but rather projected toward shore where it will break along the shore and be surfed there. The inspiration for this comes from recent developments in the surf park industry where waves have been developed by Wavegarden and Kelly Slater Wave Company that are very surfable and are created by pulling a wavefoil through the water via a cable pulley system.

    I am wondering if it is theoretically possible for a boat to be able to generate enough power to push a wavefoil through the water and create a 3-5 foot ridable wave. I know there a lot of variables involved. Disregarding the shoreline aspect, what kind of power would be necessary to overcome the drag created by the foil. Lets assume that the foil was optimally designed to efficiently transfer the boats forward momentum into wave energy. Would you need tug boat power or could it be done with a high end wake boat or none of the above?

    As you can see, my understanding of the physics involved is limited and I don't want to take 4 years of university to find out if it is theoretically possible. But having seen the waves generated in these companies makes me think that at some level it is possible. Maybe the engine running the cable pulley system is impossibly large??? not sure.
     
  2. gonzo
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    gonzo Senior Member

    Do you have information on the bottom where the waves are supposed to break? The slope and other surface characteristics will affect the power and type of wave required. A boat will not be efficient to create a break on a small area though. Do you envision a long gradual break almost parallel to the beach?
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    The environmentalists will skin you ! Erosion, etc. You will also wave goodbye to a lot of money to produce a rideable wave, artificially, anywhere. And I hope the rider(s) is very grateful for it !
     
  4. rwar
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    rwar Junior Member

    The way the new wave parks are designed is with 1000' x 200' lagoons that are 10' deep on the deep end and then shallow via an artificial reef up a 15 degree slope then to a steeper 25 degree slope.

    The way I envision the boat version to work is with a wavefoil built on to the profile of a boat that extends down 10' in depth and approx 20' long at an angle of about 45-60 degrees to the boat. The boat would push this foil through the water at approx 8 kts at a distance of about 100' - 200' from shore and parallel with it.

    Lets assume, for arguments sake, that the shoreline profile is perfect for the wave to plunge (like its ocean counterpart) and we are permitted to operate there. (disclaimers on the product of course). Lets also assume that the wavefoil is optimally designed to maximize energy transfer to create the wave and is structurally sound to withstand the forces acting upon it. Lets also ignore for a moment how cumbersome this contraption may be. What kind of power would be needed by the boat to push this?

    Again, this technology exists though a cable pulley system and the wavefoil and shoreline profile have been optimized. Here is a link to an existing setup:

    http://www.kswaveco.com/

    I just want to replace the cable pulley with a motorized boat to push the foil instead. These waveparks are hugely profitable but prohibitively expensive to build (10 million +). With the 1000s of kms of lake shoreline, there will be places that such a device could operate. Either it would be operated like a lake based waterpark on permitted shoreline or individuals will find a piece of shoreline to operate on that is not regulated. As the manufacturer, the disclaimers will put the onus on the operator to use the product responsibly.
     
  5. W9GFO
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    W9GFO Senior Member

    Whatever forces the foil creates will have to be balanced so as to keep the boat pointing in the right direction. So that effectively doubles the power requirement.

    You don't say what the chord of this foil is or its angle of attack, impossible to predict the forces without knowing the geometry of the foil.
     
  6. gonzo
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    gonzo Senior Member

    It will take a bit of time to calculate. Basically, it is the power necessary to move a volume of water at a certain speed. It will take probably twice the power of a cable system, because the boat will have to move an equal amount of water in the opposite direction.
     
  7. rwar
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    rwar Junior Member

    So I figured it would most likely have to be a vee shape to be structurally sound and allow the boat to progress forward properly. This would also allow for an operator to go back and forth in either direction creating rights and lefts.

    As you said, this would most likely double the power requirement, not to mention the inefficiency of the boat compared to a sled pulled along a track by cable/pulley.

    As for the foil angle of attack and geometry. Well that will be the secret sauce and where the $$$ would have to be spent in development. So this is a chicken and egg question then?

    So what does the scientific gut say?... does a top of the line powerboat stand a chance or are we looking at a tug? Or neither? Or perhaps a purpose built submersible specifically designed for the task.... Remember, people are paying over 10 mil to develop these parks and individuals are willing to pay $50/hr to use them. Think ski hill or golf course and land locked people desperate to surf. Just look at the wakesurfing boom for the level of desperation. Knee high waves behind a boat is fun, but hanging on a beach with friends surfing knee to head high waves is better.
     
  8. W9GFO
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    W9GFO Senior Member

    My gut says you'll need something more like a tug. A huge slow turning prop that has a big bite.

    But once you need that big boat to pull the foil I can't help but think you would be better off just optimizing the hull shape of the tug to make the wave you want.
     
  9. jehardiman
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    jehardiman Senior Member

    Quick answer. To produce 20 feet (the minimum you can produce) of 5 foot high (trough to crest) wave, 77 ft between crests, 3.9 sec period, requires a minimum of 63.6 hp. This is the power required to equal the energy put into the wave. Power required to generate this wave would more likely to be 2 to 3 times that. Note that this is only for 20 feet of wave face per second, each additional foot of face requires an additional 3.2 hp
     
  10. gonzo
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    gonzo Senior Member

    I was thinking of something that looked like a plow.
     
  11. W9GFO
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    W9GFO Senior Member

    How much more power per foot of vertical face?
     
  12. rwar
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    rwar Junior Member

    Great replies. I was thinking of a plow shape also, below the surface with the leading edge up, curved and tapered like an aerofoil. Angle of attack much akin to that of a aircraft in slow flight My background is more on the aerodynamics side so I imagine the lift would aid in the equation, while drag would translate to pushing water particles down, creating the gravity wave needed?

    And 20' of wave face is all that is needed. Vertical height is what is desired most. My understanding is that you need a swell height of twice what is desired on the vertical face of a breaking wave? (Depending on the bottom contour of course)

    I am going in the right direction?
     
  13. jehardiman
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    jehardiman Senior Member

    Remember that maximum supportable height is a function of wave length and celerity. So a 6 foot crest to trough will have a wave length of 84 feet, have a period of 4.1 seconds and a celerity of 21 feet sec (minimum face length). So a 6 foot wave would require 115.5 hp with 5.5 hp for each additional foot of face length.

    Note that this is for naturally braking progressive wave, not a formed break like a cutwater feather (edit to add) like gonzo's plow idea. A formed break, like a jetted crest only happens once and does not progress.
     
    Last edited: Jan 26, 2016
  14. jehardiman
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    jehardiman Senior Member

    Other way around, breaking waves stack so breaking face is approximately twice swell height.

    If you really want to get into the theory, you need to read Oceanographical Engineering by Robert Wiegel.
     

  15. gonzo
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    gonzo Senior Member

    I think that a bow that looks like a modified wave piercing type could work. There needs to be a lot of reserve flotation, because the vertical force component will be quite large.
     
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