Mooring solution of a wave energy convertor

Discussion in 'Stability' started by Ptinou, Jan 13, 2014.

  1. Ptinou
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    Ptinou Junior Member

    I m working on the design of the mooring of an oscillating water column wave energy convertor. The particulars of the device that the float like a cork. So the mooring must reduce the pitch motion witch is undesirable for the device. I would like your advice on the design of the mooring, so I propose 3 solutions, a classic catenary line with chains and two other one with buoy and a second with additional weight on the line.
    Which one could reduce the pitch? Is there another mooring solution which can be tested?

    Thanks in advance

    Ptinou
     

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  2. Ad Hoc
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    Ad Hoc Naval Architect

    Ptinou

    It is heave you need to control/reduce, not pitch.
     
  3. gonzo
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    gonzo Senior Member

    A long bar with a horizontal plate at the end will reduce heave. It will also reduce roll.
     
  4. Ptinou
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    Ptinou Junior Member

    The heave motion is reasonable on the device.
    In the following graph you can see the RAO heave (m/m) with a max of 1.2 and the RAO pitch (rad/m) with a max of 300 !
    So I am really thinking that the heave motion is more problematic.
     

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  5. Ad Hoc
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    Ad Hoc Naval Architect

    Clearly an RAO 0f 300 is nonsense. Check your inputs and variables.

    But for a vertical cylinder, heave is the concern, not pitch.
     
  6. Ptinou
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    Ptinou Junior Member

    Sorry for the RAO of 300, it s in (deg/m) for a scale model of 0.5m high.
     
  7. tspeer
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    tspeer Senior Member

    I don't think any of those will do what you ask. All of them will induce pitching disturbances when the device is subjected to a horizontal force.

    I think a better solution would be to configure the device as a spar buoy and attach the moorings as close to the center of vertical plane area as possible. That way horizontal pressure will be reacted with minimum net moment. Vertical force on the device will also result in minimum moment when it is a long and narrow spar buoy.
     
  8. Ptinou
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    Ptinou Junior Member

    Hi tspeer

    Indeed I have allready done some simulation with the mooring attach on the center of the vertical plane, but results show that it s increess the pich motion on is resonance frenquency.
     
  9. johneck
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    johneck Senior Member

    I think that Mr Speer means at the center of the area in the vertical direction(below the waterline). That way the mooring forces and the horizontal force from the waves will be aligned. Your 2nd sketch looks somewhat like that, though the attachment is probably too close to the surface.
     

  10. Murat124
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    Murat124 Junior Member

    :) Yes this motion's name is heaving no doubt
    it would be necessary to know about details and vertical acceleration restriction for the device??

    as I understood that it will be necessary to damp this motion to bring acceptable limits.

    Some constructional measures could be taken on device to dump this vertical
    motion first of all.
     
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