Ship stability in bow/beam seas ?

Discussion in 'Stability' started by kaptcatb, Apr 25, 2013.

  1. kaptcatb
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    kaptcatb Junior Member

    Hello all ,
    I am looking for papers / software results for ship stability for different angles between ship and wave direction ( see attached picture , my calculations regards to 90,120,135,150 deg ) . I am trying to calculate metacentric height for different angles Beta and for different wave crest position .

    Is there any comersial software that can calculate hydrostatics for my needs or any paper ? Hope you can help
     

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

    It all depends upon the length of the boat and the length of the wave.

    For example, if your boat, under investigation is 10m long and the wave is 100m long, clearly the effects will be negligible.

    However if the boat is 100m long and the wave is 100m long then this can have an effect on its stability.

    You're also forgetting the other critical input, that of speed, which yields the encounter frequency. This is important in parametric rolling.

    But for your 'simplistic' review, so long as you have the lines plan of the hull and stability software (for ease of calculations), you can simply apply a wave of varying lengths and direction onto your "model hull" under investigation and obtain the GM using a standard wave profile laid onto the hull, from the hydrostatic output. Unless you wish to calculate each waterline by hand!!
     
  3. kaptcatb
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    kaptcatb Junior Member

    Thanks for reply . My "boat" is 113.75m long . Wave lenght is equal to lenght between PP . I dont take speed/wave period into account - I just need GM .
    I put wave profile in wave crest position I want , measure area , centroids , tr.moment of inertia for all frames and then calculate GM . I use AutoCAD / Excel .

    In other hand I have Hydromax and Freeship . I am more familiar with Hydromax but in my version there is no option to set angle between ship and wave direction . By my knowledge I can only set wave form and its crest position . I think my Hydromax version is 13 or older .
     
  4. jehardiman
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    jehardiman Senior Member

    You need to be very careful here as what you are proposing is not the correct way to approach the problem.

    As Ad Hoc says, you aren't covering all the relevant inputs and generally such investigations are covered by stoichastic methods because you cannot predict all necessary inputs (i.e. in order be complete you need to cover the zero, first, 2nd, and 3rd derivatives of the 6-DoFs).

    See:

    Dynamics of Marine Vehicles; (Rameswar Bhattacharyya,John Wiley & Sons, 1978, ISBN 0-471-07206-0)

    A Capsizing Probability Computation Method; Belenky, Vadim L. Journal of Ship Research, Vol. 37, No. 3 9/1/1993

    Risk Analysis Applied to Capsize of Fishing Vessels; Dahle, Emil Aall Myrhaug, Dag Marine Technology, Vol. 32, No. 4 10/1/1995

    The Transient Capsize Diagram- A New Method of Quantifying Stability in Waves; Rainey, R.C.T. Thompson, J.M.T. Journal of Ship Research, Volume 35, Number 1 3/1/1991

    Theoretical Modeling of Ship Motions and Capsizing in Large and Steep Waves; Grochowalski, Stefan Hsiung, C.C. Huang, Z.J. Cong, L.Z. SNAME Transactions, Vol. 106, 1998 1/1/1998

    and this old thread.

    http://www.boatdesign.net/forums/stability/effects-waves-ship-stability-calculation-19533.html
     
  5. kaptcatb
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    kaptcatb Junior Member

    I am sorry I cant give you link now to paper I study ( I cant open ABS site , I get error ) . File name is : ABS - Guide for the Assessment of Parametric Roll Resonance in the Design of Container Carriers , ABS , 2008 .

    In part for calculation of metacentric height there is only basic hydrostatic calculations . The unique is only wave profiles .
    If you open 22/70 page there is formulae for GM for any wave crest positions .
    I want to say again - I try to calculate GM for different wave crest positions . I have already calculated metacentric height for 0 and 180 deg , now I try for 30;45;60;90 .
    I just place ship @ wave ( or wave @ ship if you want ) and calculate Area;Centroids;Moments;BM;GM .
    In my knowledge I dont need to take into account chapter 2.3/2.4/3.0 - they describe GZ , not GM .

    Any way thaks for papers and link to other topic . I have already read N2 and N3 , will try to find others .
    Best regards
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    If you’re more concerned about parametric rolling you’ll need to define the limits of the operational speed which then results in defining the wave blocking as well as the lower speed limits which define the so called surf-riding threshold. You then apply a polynomial approximation to wave induced surge force including the nonlinear surge equation. From this you compare the results of each. This is usually performed by Melnikov’s method and a continuous piecewise linear approximation. The maths for these are beyond me.

    But I know a very good Prof whose research into parametric rolling is proving to be a very good “design guide”. But, unless you’re able to, at this stage since his research is still being validated by IMO et al, plough through pages of higher order polynomials you’ll have to wait until his papers are published.

    Although just search Prof Umeda he is one of the world’s leading experts on the subject. You may find this paper he wrote some time ago useful:
    http://link.springer.com/content/pdf/10.1007/s00773-007-0253-x.pdf#page-1
     
  7. kaptcatb
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    kaptcatb Junior Member

    can you give me your email ?
     

  8. Ad Hoc
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    Ad Hoc Naval Architect

    To whom are you asking?...why not them a PM.
     
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