Large Hydrofoil/heaveplate

Discussion in 'Hydrodynamics and Aerodynamics' started by Sherkin, Feb 13, 2014.

  1. Sherkin
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    Sherkin Junior Member

    I am investigating a HYSWAS design that will use two or three large heave plates for low speed stability.

    To reduce drag and plow in, I was considering making the heaveplates a hydrofoil.

    The heave plates would have a cord length of around 4 - 6m and be at a draft of 10m. the vessels max speed would not need to be greater than 20knots

    Has anyone here seen/know of a study with such long cord lengths?
    Or anyone any advise on how best to model the design?
     
  2. BMcF
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    BMcF Senior Member

    Why would you want the additional surface area associated with passive "appendages"? Why not simply rely on the active foil appendages that control flight height (heave) and pitch/roll stability?

    I guess its not clear to me what the "heave plates" are expected to be stabilizing....at any speed. Perhaps you could elaborate a bit further?
     
  3. Sherkin
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    Sherkin Junior Member

    Good question BMcF, I want the additional surface area to resist motion at zero speed.

    The project is for a crew transfer vessel to an offshore wind turbine and one of the criteria is for a very low RAO at zero speed. Similar to that a SWATH provides but a lower RAO.

    This design would be more fuel inefficient than a SWATH and that is acceptable, provided I can show by how much.
     
  4. BMcF
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    BMcF Senior Member

    Ah..I see. You mentioned chord lengths of 4-6m...what were you considering for the span?
     
  5. Sherkin
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    Sherkin Junior Member

    A span of 13m
     
  6. BMcF
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    BMcF Senior Member

    Wow...that is a big appendage. Must be quite a large vessel.

    I can't imagine you could build something with that large a planform area without it having significant thickness simply for structural reasons....in which, case, of course it would need to be a foil shape or the drag penalty would be even larger than it already will be due all that surface area.
     
  7. Sherkin
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    Sherkin Junior Member

    In the region of 130tonnes displacement and 24m in length.
    The heaveplates/hydrofoils would provide most of the buoyancy, the rest coming from the uprights attaching to the main vessel superstructure.
     
  8. BMcF
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    BMcF Senior Member

    Almost sounds like a hybrid between what I understood a HYSWAS to be (NSWCCDs "QUEST" being an example) and a vessel supported by lifting body(s) (essentially, bouyant underwater structures that produce dynamic lift). Except you don't seem to be expecting dynamic vertical lift from the foils?

    Where/what are your active pitch/roll control appendages?..flaps on the trailing edge of the large foils?

    Sorry..I can see that I'm asking more questions than I am answering.
     
  9. Sherkin
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    Sherkin Junior Member

    No worries BMcF, a question can't be answered unless it is understood!

    You are right I don't expect any dynamic lift from the foils, but I do want to reduce drag and know how they are going to behave and affect the vessels motions, when traveling to the wind farm and when transferring personnel to the wind turbine.

    I haven't looked at Active control appendages yet, but I was guessing they will more than likely be required. Are they not something that would be added towards the end of the design process though?
     
  10. BMcF
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    BMcF Senior Member

    I think part of my confusion may lie in a difference between what you and I consider a HYSWAS to be. My definition:

    A typical distribution (if there is such a thing as "typical" for a relatively rare vessel type) of the total lift would be 60% bouyant and 40% dynamic lift from the foils.

    A HYSWAS is, statically, inherently unstable in roll, of course, and is not very stable in pitch/trim either...divergently unstable at some speeds. So the active control is required not "just" for motion damping; it is a fundamental part of the basic design of a HYSWAS, necessary for underway control of list and trim.
     
  11. Sherkin
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    Sherkin Junior Member

    In that case the vessel would be more like a SWATH with the two underwater hulls connected to form a heaveplate/hydrofoil. A beam view of the vessel would look like a rectangle with the centre removed.

    Clear as mud?

    I'll work on a sketch...
     
  12. BMcF
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    BMcF Senior Member

    So no dynamic lift component... Yep..no "HY" in that vessel acronym.:)


    This pic is of a twin lifting body design connected by a crossfoil. The combination of bouyant and dynamic lift supported 100% of the vessel displacement when underway, lifting the upper hulls (ama-stabilized monohul) clear of the water.

    The low and zero-speed heave motions...all motions in fact...were very, very good. Underway, they were spectacularly low....but that was with a pretty elaborate computer system managing the control of flight via active trailing edge flaps, etc....
     

    Attached Files:

  13. Sherkin
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    Sherkin Junior Member

    Sorry about that BMcF.

    That picture is very similar to what I am after. except I was looking for a small water plane area at zero speed as well.
    There isn't by any chance anything published about that design?

    Also, was the computer control required at zero speed or was it just for when underway?

    I've attached a pdf of the design, The waterline is about one fifth of the way down the vertical struts. (Rotate 90deg clockwise to view)
     

    Attached Files:

  14. BMcF
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    BMcF Senior Member

    Computer control of such craft is for managing take-off and underway "flight". Such craft are marginably stable in different axes, at best, and are often completely unstable in at least one axis without active stabilization features.

    The craft in the picture I provided required automatic control of heave, pitch and roll and benefited greatly from active stabilization of yaw (heading) as well.
     

  15. Sherkin
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    Sherkin Junior Member

    If I was able to make my design statically stable, would the geometry provide any difficulties when underway, and how would I design them out with only basic active control?
     
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