Added Resistance in Wave

Discussion in 'Hydrodynamics and Aerodynamics' started by PHQ, Jun 30, 2013.

  1. PHQ
    Joined: Jun 2013
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    PHQ Junior Member

    Hi guys,

    I know the forum is mainly for small craft designers but I am currently working on big merchant ships and kinda stucking at some calculation methods, hope someone may help me out on this problem...

    It is the calculation of Added resistance in Wave, Raw.

    I have looked at the ITTC 7.5-02 07-02.1 & 7.5-02 07-02.2, but could not actually work out...

    I have attached the formula that we should follow.

    Thank you very much and hope to see your ideas soon.

    :)
     

    Attached Files:

  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Not so. Anything that floats :)

    Below are draft and i do stress draft guidelines relating to the new IMO rules on the forthcoming EEDI. So, whilst these may still be draft, the calculations for added resistance to establish the EEDI may be of help. Excerpt taken for your ref:
     

    Attached Files:

  3. PHQ
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    PHQ Junior Member

    Thanks Ad Hoc, so glad to see your reply because this is also what I am doing, but I am dealing with the MEPC 65, ANNEX 5, the new rule adopted last month, about Determining the Propulsion Power for Adverse Condition.

    I have been away from university for quite a while, so it is a little hard for me to deal with these formulas.

    I have been looking through many papers on internet for ref, but still cannot understand how to put all the formulas into use properly...

    Thats why I am looking for some more detailed explanation, if anyone can help.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    This sample calculation shall help then :)
     

    Attached Files:

  5. PHQ
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    PHQ Junior Member

    Thanks Ad Hoc, I will try to get through it...

    If you have any other related papers, please show me if you dont mind.

    And if you have time to look at the MEPC 65 - ANNEX 5, please let me know your ideas.

    Thanks alot.
     
  6. Crowsnest
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    Crowsnest Junior Member

    Hi PHQ:
    As far as I remember, the key around that formula is arriving to a good value of the term Raw for each wave into the studied spectrum.
    Once got, things become easier and just an addition of each spectral term effect.

    Im digging in my archieves looking for some more information.

    Regards
     
  7. PHQ
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    PHQ Junior Member

    Hi Crownest,

    Thanks for your advice, I am still working on it, spending hours for reading papers in relation... But still no clue...

    As I found in the ITTC 7.5-02 07-02.1 & 7.5-02 07-02.2, there is the formula for the wave spectrum S(omega), which I think we can calculate it. But I still dont understand the whole thing in the Resistance (Raw) formula.

    If anyone can explain me in more details for each elements of the formula, and how to calculate them, It would be very much appreciated...

    I have attached the formula again and the ITTC documents, just let me know how you feel.

    Thank you and have a nice day.
     

    Attached Files:

  8. daiquiri
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    daiquiri Engineering and Design

  9. tspeer
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    tspeer Senior Member

    The formula assumes you have the added resistance for a particular speed and wave frequency. That's the function Rw(Vs, omega) in the integrand. The rest of the formula is the integration of the added resistance function over the wave spectrum to get the total added resistance.

    The hard part is getting Rw(Vs, omega). This can be calculated by a sea-keeping code like SMP.
     
  10. PHQ
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    PHQ Junior Member

    Hi daiquiri,

    Yes you are right, the guideline Ad Hoc posted is very useful and I am following it now.

    To be honest, I have never seen the Bessel's function before, I didnt learn it in university for some reasons... thats pretty odd... But I am trying to go through it now, thanks for the webs daiquiri.

    If someone can explain it in a more in-person-way with examples and how we can apply it into calculations, that would be rather brilliant...

    Thank you & nice day.
     
  11. PHQ
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    PHQ Junior Member

    Hi tspeer,

    Thats also what I am concerning...

    The wave spectrum function S(omega) I can calculate according to the ITTC, but the Raw(Vs,omega) I have no idea what to do with it.

    The formula Raw I posted is given out for the calculation method to base on, so I am quite struggling with the method Ad Hoc posted (because it is for different calculation guideline, not mine..) , not sure if I can apply it or not, even though I know its also the correct one.
     

  12. Erwan
    Joined: Oct 2005
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    Erwan Senior Member

    Hi Everybody,

    Thanks for this smart topic, I apologize in advance if the following question is a bit candid, if not stupid:

    Is it relevant to apply these formulas for 16 feet to 25 feet beach cat's hulls,
    adjusting H,T and other parameters for bay chop ?

    Best Regards

    EK
     
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