Extrapolation of towing tank results

Discussion in 'Hydrodynamics and Aerodynamics' started by Remmlinger, Oct 15, 2012.

  1. Remmlinger
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    Remmlinger engineer

    We discussed in this forum several times the usage of towing tank results for the full scale performance prediction. I questioned the applicability of the ITTC 57 friction line and Leo shared a paper by the ITTC, showing the large scatter of resistance results between different towing tank facilities (perhaps caused by scale effects). I found a comprehensive paper on this subject that might be of interest to some of you.


    Have fun
  2. Mikko Brummer
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    Mikko Brummer Senior Member

    Great paper, thank you.
  3. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Thanks Uli.
    They add weight to one of Grigson's observations about several large ships
    built in the 1980-1990s being under-powered by about 5%. (Raven et al
    show that resistance could be under-estimated by about 7%.)

    Grigson put the blame for the under-prediction on the ITTC line and the form
    factors back in about 1996, and he fought for a long time to have the issue
    of a new standard friction line opened up for debate. He died a few years
    ago and the issue is still not resolved.
    Hydrodynamics sometimes moves through a very viscous medium! :)
  4. BMcF
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    BMcF Senior Member


    Thanks for the paper, Uli.
  5. Remmlinger
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    Remmlinger engineer

    The Reynolds number of this process is too low > no boundary layer exists > the entire global mass has to be moved, not just the neighborhood > that takes generations.
    If anything can make the learning process more turbulent, then it's the internet.
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Thanks Uli, I'll have a read.

    I think this is being "serialised" in the Maritime Reporter magazine. As MARIN have written a few short article on this very subject recently.
  7. J Feenstra
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    J Feenstra Junior Member

    That's why MARIN has constructed a new tank, that operates under a lower atmospheric pressure, therefore reducing viscosity.

  8. DCockey
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    DCockey Senior Member

    Changing atmospheric pressure has negligable effect on the viscosity of the water. It does have a major effect on cavitation though which is not related to viscosity.

    Page on the new MARIN tank: http://www.marin.nl/web/Facilities-Tools/Basins/Depressurised-Wave-Basin.htm
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