ORC 2013 VPP - radical Resistance Changes - Help!

Discussion in 'Hydrodynamics and Aerodynamics' started by quequen, Jul 9, 2013.

  1. quequen
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    quequen Senior Member

    ORC 2013 VPP - radical Resistance Changes

    ORC VPP 2013 (attached) incorporated many radical changes in Resistance calculations, both Residuary and Frictional. Classical Delft Series has been dismissed for Rr calc. and now a Base Boat having LVR = BTR = 6 (LVR = Lenght/Volume Ratio, BTR = Beam/Draft Ratio) is used. A huge coefficient list is published (file attached), based on Fn, LVR and BTR
    I wish someone could obtain a Resistance curve from this data *, to compare with old Resistance methods (like Delft93, 98, 2008, ORC2011 etc.). I'm not shure on how to do that. BTR calculation seems particularly complex (page 21).

    Also attached is the Nico spreadsheet, I added the ORC2011 Rr for comparisson. (There must be some mistakes on my addings, given the weird outcomes!?)

    Comments are welcome...

    * Edit: spreadsheet done, attached at post #10
     

    Attached Files:

    Last edited: Jul 13, 2013
  2. DCockey
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    DCockey Senior Member

    Thanks for the post about the new ORC VPP.

    Questions and Answers about the changes can be found at http://www.orc.org/rules/2013 ORC VPP FAQ.pdf

    From the Residual Resistance section of the ORC VPP Documentation 2013, page 58
    Recognizing that previous attempts to accurately calculate the effect of several hull parameters such as Prismatic Coefficient, Longitudinal Center of Buoyancy (LCB) and water plane area coefficient have led to undesirable type‐formed hull shapes and that this trend could not be addressed within the existing model, it was decided to simplify the input parameters accounting for 2 main parameters only: dynamic Length‐Volume ratio (LVR), and Beam to Canoe‐body‐draft ratio (BTR) to avoid as much as possible any type‐forming. The effects of hull volume distribution are still captured by the use of the traditional integrated lengths.​
    I assume by "type-forming" the author(s) meant attempts to design boats so that they perform better than predicted by the previous ORC VPP.

    Does anyone believe that that designers will not seek designs which which will perform better than predicted by the revised ORC VPP?
     
  3. quequen
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    quequen Senior Member

    Well, that's my thought also... It would be useful to see what "type-forming" is intended to be. Does someone knows an ORC-targeted design that can serve as an example? We all remember de IMS boats that seemed shoeboxes, but I don't think that kind of boats are still benefited by the 2011 formula.

    Anyway soon or later, Rr issues were going to rely on Towing Tank tests and CFD. Actual computers give support to this, they can make hundreds of analysis related to a cup of TT experiments, making things much more realistic. I think it's the unavoidable way to follow.
     
  4. quequen
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    quequen Senior Member

    Attached the Nico spreadsheet with some corrections and Rr from PYD 3rd ed. added. Note that Delft formula is totally different (both coefficients and polynomials) to the '98 RINA formula laid by Nico. (I don't have the RINA98 paper).
    Some more questions:
    1- What are the output units of the attached ORC2011 formula?
    2- B/Tc is a typo? Shouldn't it be BWL/Tc ? (It seems to characterize underwater volume)
    3- How is LCB meassured in ORC? %forward amidship?, meters from fpp?
     

    Attached Files:

  5. DCockey
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    DCockey Senior Member

    What do you mean by "Nico" in the name of the spreadsheet?
     
  6. quequen
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    quequen Senior Member

    Nico is the author of the original file, he posted it in bd somewhere, I downloaded the spreadsheet and modified it ;)

    Any clue on the weird numbers over Fn=0.75 for the ORC2011 Rr?
     
  7. DCockey
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    DCockey Senior Member

    "B" for the 2011 ORC VPP formulas is defined in section 4.2.3 of the ORC VPP 2011 Documentation, p 20 http://www.orc.org/rules/ORC VPP Documentation 2011.pdf The same definition is given in the 2013 Documentation.
     
  8. quequen
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    quequen Senior Member

    Ok, I see. This is a complex geometric formula that is calculated internally by the LPP. Can't see the way to formulate it in a simple spreadsheet :?:
     
  9. quequen
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    quequen Senior Member

    From ORC:
    In answering your questions, LCB and LCF are always calculated from the stem (foremost point oof the hull) and you are right, there are two typos in 2011 Rr coefficients:
    the coefficients A7 for Fn=0.85 and 0.90 are 8.02 and 8.27 respectively, and not 1.784 and 4.37 as written in the documentation.
    Hope this helps

    Best regards
    Zoran Grubisa
    ORC


    Now the curves are much more credible (Note that PYD3rd ed don't include Rr of the appendages). For ORC2011, I'm using LCB = LCBfpp + Overhang. Attached the spreadsheet with fixes.
    As you'll note, all formulae but Delft93, have negative values at low speed, wich is confuse.
     

    Attached Files:

  10. quequen
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    quequen Senior Member

    Rr according to ORC2013

    'ORC 2013 Residuary Resistance' spreadsheet attached. Just input LVR, BTR and Displacement to obtain the Rr curve.
     

    Attached Files:

    1 person likes this.

  11. quequen
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    quequen Senior Member

    I'm attaching a new spreadsheet to compare four boats and deveil the trend of the new Rr formula. Some thoughts:
    1- Clearly the ORC programmers try to avoid the artificial variation of Cp, TCB and LCB that was seen on the "boxy" IMS boats many years ago, wich produced boats that performed "not as bad" as Delft polynomial predicted.
    2- They use an artful system of abstract math surfaces that allows fast and easy modifications for future releases and guarantee soft transitions between the coefficients.
    3- The new formula, strongly based in CFD analysis, claims to reflect what happens in reality at the regata fields, anyway it compares really bad to the previous ORC 2011 Rr, also to Delft '93 and '98. Differences reach 25% for the same boat (!).
    4- All that said, I'm not sure on the accuracy of this formula as a Performance Prediction tool.

    Be aware that this spreadsheet doesn't interpolate, it just picks up the nearest value from the coeff. table. Interpolation would be very useful, but I'll leave that to you guys!.

    -
     

    Attached Files:

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