How can we calculate the driving and drag force?

Discussion in 'Hydrodynamics and Aerodynamics' started by metin_mehel, Aug 27, 2011.

  1. metin_mehel
    Joined: Jul 2009
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    metin_mehel mech.eng.

    Hello Guys.
    Unfortunately I still cant calculate the driving and drag force.
    I know there is a known formula F=1/2*Cl.... but,
    What will be the Cl (lift coef.) and Cd (Drag Coef.)?
    What will we consider the velocity in the formula? Is it true wind speed or apparent wind speed?
    Thanks
     
  2. metin_mehel
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    metin_mehel mech.eng.

    sorry driving force and heeling force...
     
  3. Erwan
    Joined: Oct 2005
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    Erwan Senior Member

    You can calculate Implicit Driving force

    Hi Metin,

    You should start with what you know and what you can mesure (with more or less precision).

    The righting moment
    The sail area
    The true wind speed
    The apparent wind speed.
    The angle of Incidence.
    The sail aspect ratio

    From these data you should be able to have an idea of the "Implicit lift coefficient" which balances the known righting moment.

    Then the Induced drag, and so on.

    Of course it is much easier for a C-Cat than for an East-Coast Schooner or even for an 18 feet skiff.

    Don't be shy, put the figures on a paper and take a beer, you willl make it

    Regards

    Erwan
     
  4. metin_mehel
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    metin_mehel mech.eng.

    I am designing a new catamaran.

    The righting moment: I think we will determine it after calculating sail force
    The sail area:7.39m2Mainsail area , 9.24m2Fore triangle area
    The true wind speed= It should be maximum according to standards
    The apparent wind speed: it will be calculated
    The angle of Incidence.: It will be determined to have maximum load at mast.
    The sail aspect ratio:6.05 Mainsail aspect ratio, 3.10 Fore triangle aspect ratio

    I have to unknown.
    1- which speed I will use in formula.
    2- what are the coefficients
     
  5. tspeer
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    tspeer Senior Member

    Since the heeling moment of the rig is limited by the righting moment of the hull (when on the verge of capsize), it's common to estimate the aerodynamic loads by working backwards from the allowable heeling moment rather than by trying to work the problem from first principles. Unfortunately, while this will give you some maximums for the global loads, it does not provide details as to how those loads are distributed. You need to make other assumptions in that regard.

    Take a look at Shuittleworth's stability indices to help match the size of the rig to the dimensions of the hull.
     
  6. metin_mehel
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    metin_mehel mech.eng.

    Thanks for the link.
     
  7. daiquiri
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    daiquiri Engineering and Design

    Very nice and informative article.
     
  8. Mikko Brummer
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    Mikko Brummer Senior Member

  9. metin_mehel
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    metin_mehel mech.eng.

    Thanks but I want to make my own excel spreadsheet.
     
  10. Mikko Brummer
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    Mikko Brummer Senior Member

    You can look at the source code and copy it to excel...
     
  11. metin_mehel
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    metin_mehel mech.eng.

    Is it possible? How?
     
  12. daiquiri
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    daiquiri Engineering and Design

    That's very generous of you, Mikko. :)

    By viewing the HTML source of the page with your browser.
     

  13. metin_mehel
    Joined: Jul 2009
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    metin_mehel mech.eng.

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