Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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Prediction of Nonlinear Motions of High-Speed Vessels in Oblique Waves
Prediction of Nonlinear Motions of High-Speed Vessels in Oblique Waves
Pages 157-170
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From page 157... ...
fLesis sch me, to calculate the nonlinear motions of a high speed vessel in oblique waves is p esented in fLis p per In this method, fLe equations of motions are described by fLe body fixed comdi ate, rather th m fLe conventionally used ship carried vertical coordinate More -: ., the timewarying submerged hull surface and the coupli g effect between hmsverse and ve ~i al motions are considered By using the moment m theory, the flare impact md dy mic lift are also talcen i to account in the time dom in simulation, to p went the ~ al divergence due to the d id of way my or y w motions, artificial springs in sway md y w modes are introduced In order to clarify the validity of fLe pmposed prediction method, a series of sealceepi g tests i oblique waves have been carried out in SSPA with a model of 90 meter patrol vessel, which is designed by USDDC United Ship Design & D=: elope : Center, Taiwan) The expedmental results are compared with the calculation by the present method and some of the selected results of comparison study are how i this p per As a practical tool Em predicting fLe nonlinear motions of high speed vessels in oblique waves, fLe validity of fLe present method is verified IN I RODI C I ION In fLis two dec des, fLe expanding d mmd of large sized high speed ocean goi g vessels urged fLe necessity of d : d pi g analytic tools to evaluate fLeir nonlinear behavim i mugh sea Up to the present, 5=: =:al more sophisticated methods have been pmposed to predict nonlinear motions and wave lo ds of a ship at forward speed in head sea Em ex mple, a th ee dimensional Rim me Pmel Method hi g et al 1996)
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From page 158... ...
is defined so fhat fLe X Y plme coincides with fLe undstu~bed watel sulface md the Z xis is vxtically dow wa~d The incident waves plopagate towa~d positive X dilection Ship ca~ied v xtical coold nate syst m o xyz (hxcafielFv f me) is moving at hip speed U in x di ection and k eping z xis veltically dow wa~d x xis is I id on fLe mdst bed watel sulface The mgle between x di ection md X xis is denoted with j A othel coxdnate system o yz is hip fixed hxcafiel Fo f me)
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From page 159... ...
denotes fLe velocity component related to fLe steady forward speed, while fLe second term denotes the velocity component related to fLe oscillatory motion speed md c m be defi ed a IVI=L8VI11I w ~ (10) Furthermore, we cm substitute ¢=;~=0, ~ = T~ into equation (9)
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From page 160... ...
fi me Cooldi ate system b yz hele ftx Fbfi me) isfixedinthe y Figuze 2 Cooldi ate system fol d fining sectional hyd ody mic coefficients hull section We denote the sectional added mass matfix f x oscillat xy motion with Lm ~ i fLe F*
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From page 161... ...
(Z8) Since u,v,w md p,q,r are denoted as fLe hanslational velocity md mgular velocity of the ship deschbed in Fo f~ me, then the avxage relative velocity md relative angular velocity to the water at section x described in Fo f~ me, denoti g with i7,,v,,w and p,,cmbegivena i',=u V~ _ 1 v,=v+xr v (Z9)
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From page 162... ...
, the state of steady mning in calm watev is consideved as fLe initisl veference state fmm which fLe hip motions sze veckoned Therefove, both the velative velocity md the hyd ody mic coefficients sze d composed i to fLe oscillatovy motion velated component md the steady forward motion velated c mponent By usi g equation (3)
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From page 163... ...
M' = i~P (4o) celative to o x xis Equnidons of Moldons T ing the mation of all fLe sectional fmce md moment stated above, fLen integ ati g fLe total sectional fxce and mom nt fmm fLe afimost watec hull i tecsection A to the f x most wat x hull intxsection F yields fLe equations of motions in Fo f me a follows ln which fLe state of ste dy mnni g in cam watx is considxed a fLe i itial cefxence state fmm which fLe ship motions are ceckmned sway | (F,m + F
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From page 164... ...
Artificial Spring In general, to solve the 5 degrees coupled motions in time domain, the stability of solution will be affected by sway and/or yaw motions due to no restoring force and moment in these two modes. Therefore, to prevent the numerical divergence due to the numerical drift of sway and/or yaw motions, artificial springs in sway and yaw modes are introduced.
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From page 165... ...
ate show i Table 2, varied 60m 0 476 to 4 gg5 md 1/29 9 to 1/136 5 respectively The corresponding data used i prediction for c mpamison are also how i Table 2 The Heave, roll md pitch motions a well a : -i al accelerations at mai deck of FF, LCG stations and at helicopter platform were measured and compared The steady mni g him md CG rise meauled at fLe ab we mentioned fo ward speed i ca m water are approximately 0 39 degree md 0 33 m respectively The roll d mping factor Eli and natural period T4Obtai ed 60m fLe mll decay test at fLe forward speed correspondi g to 24 mot of fLe 6 11 scale hip ate O I 5 md 5 I second respectively 71L 0 476 0 623 0 6g7 O 848 I 073 1 401 1 909 2 271 2 747 3 393 4 292 4 EE5 Table 2 Wave length md steepness Rend meats r Halt 1/29 9 1/39 0 1/30 0 1/29 9 1/37 9 1/39 1 1/53 3 1/63 4 1/76 7 1/94 g 1/1199 1/136 5 A/L r 06 1 _ OS I lo 1 _ 125 _ 15 1 175 1 _ 20 _ 25 So r 35 r 40 _ 450 H 1 1/30 1/30 1/40 1/40 1 1/40 1 1/60 1/60 1/90 1/90 1/120 1/120 1/120 Figures 4 fnrough 9 illustrate the wavelength d pend ace of responses of :' 200 havelli g i b w seas at fLe fo wand speed corresponding to the Fmude n mber of 0416 In these ~~ .5 the nondimensionalixed mplit d s of I order md the phase male, which is related to when the wave Cough is at the ship's CG, of heave 5/5, roll y/~ and pitch 0/~ as well as :~~i al accelerations at mai deck of FF station OF. /~5~, of LCG station ;~CG/~5~ md at helicopter platfomm I,, /a(5~ are plotted together with predicted responses obt ined by the present computation The abscissa of the fig es denotes fLe wavelength to ship length ratios ~ / 414~ ~U'~ l ~Present O Exp 180 ~ 1 of of 0~0 10 20 30 40 50 i/1 Figure 4 Heave response in b w sea atFn 0416 ¢1~ 24q 20~ .2 _ os on moo ~ for o ~ Con ang e (deg )
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From page 166... ...
e Lo lo 0 ange (deg ) _ _ ~ O 270 J 350 OK 450 O /L Figure 9 Response of vertical acceleration at helicopter peal -= in bow sea at Fn 0 416 he recorded time histories of m tions together with calculated results of two test runs of //L 1 073 and 1 909 ate show in Figure I O and Figure I I respectively in these figures wave as well a sway
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From page 167... ...
50 1 r 1 Figure 11 Comparison of time hi t Dies of motionsinbowseawith //L 1909 at En 0416 CONCLt SION A prediction method, basi g on a nonlinear ship .. thesis sch me, to calculate the nonlinear motions of a high speed vessel in oblique waves is presented md pplied to a high speed patml vessel :' 200 havening i b w sea The present results of ship motions and v xtical accel nations at th ee different positions, have been validated by a pmp X comparison with experimental data A d fLe following conclusion may be d awn Through fLe comparison between fLe dy mic responses predicted by the p esent nonli ear calculation and UP ximental results, it is confimmed that fLe present method can be applied to estimate fLe ship motions and v xtical accel nations along ship length of a high speed vessel i oblique waves with accuracy enough for practical use F th Am Be, it can be xpected that oth X dy mic responses for instance, wave load and p essure on hull pa :=l c m be p en cted by extend ng the present method
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From page 168... ...
Vndn, A Branthen,'Nonlinear ship motions and wave i duced lo ds by a Ranki e method'21 ONR Symposi m on Naval Hyd ody mics, Tmndheim, 1 996 W.-M.
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From page 169... ...
167, June 1990, pp 69-79 (in Japanese) AUTHOR'S REPLY Th predicted lateral moti ms me relatively sensitive to the values of artificial sprmg constmts, md the predicted sway md yaw amplitude is not satisfactory The mthors agree withthe discussor's opinion that it's better to use c mmmericcl filter to avoid the mmmericcl instability it requites et lea t N times of the computer time, where N denotes the order of the mmmericcl li lter, which values m ight be, say, 50 or 60 Basing on results show in this paper, She futme study on the employing of c mmmericcl filter into She present model is undergoing The physical d ffting in sway md yaw motions are not considered in the present method As show in the experimental records of Figures I O md I I, the overall yaw d if are no more f m 3 degrees The effect of the d fits on She encounter mgle seems to be little
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From page 170... ...
~ ~ ~ I vU_ Vow ~ 00 05 lO ~ ~ 20 091f Figme A E fects of artificial Spring Constmts on ship motions ( ~ I L =1 0 et Fn=0 416) DISCUSSION J xia The University of We tem Aushalic, Aushalic Could the mthors please comment on She i duence of neglecting memo y effects on Heir mod hng of hyd odynamic forces md vessel motions AUTHOR'S REPLY Since we just take into account the effects of noncimulatory part of dynamic Ifft on the ship motions, so Here is no need to consider She memory effects However, the reduced fiequency of c plarming vessel rumming in heed se seems not to be smell enough to neglect the memory effects if the circulatory part of dynamic lift is taken mto account The mfhors thirJc Nat it needs further study to clarify She influence of neglecting the circulatory part of dynamic lif on ship motions
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