Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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Prediction of Vertical-Plane Wave Loading and Ship Responses in High Seas
Prediction of Vertical-Plane Wave Loading and Ship Responses in High Seas
Pages 112-125
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From page 112... ...
A'dSTF ACT Tne non-linear ti s m wa~ md shmmi g-md ced ngidbody moticns md tmct ral ~e pom s of ships such as heave, pit h md vedical bend g mome ts are consi te t y mve tigated based m c rational t me d mcm ship medhod (~, Wmg md Lm n, 199S1 A hyd odynamic mod I fcr p~edi ti g sectional r e water force i also outlined fcr fne mve tigati m of th effect of r e wabr loads m th global h 11 gi d r bend g m ome t Tne c mputstional ~ e nits based m fne non linmr time domcm ship fneo y a~e compared wih fhosebased mbuef llynon linmr3-D panelmedhod SWANDNV mdofnerpubbsh d~esults Fr m fne rath:r e tffnive c mputatbns md c mparisons, t is fommd thst non linear eff ts are sig d mt m heed mdb w wave mbue motion~e ~eso~mt regim forboh heave md pi h moLcns, b w accelemticns md ve tisal bend g m ome ts f cr two conluirvr ships consid ~ cd wh ~ eas not sig f~mtfcrcVLC TnenonkneartiesnmoLcns md tmct ;1 loads of conve tional monoh 11 ships em w r p~edictedbydnep~ese t m-linmrshipfheoy INTRODUCTION Linmr ship fnecries md 3D linmr pote tial fnecries hcve ben wid y accepted md used by naval archit ts as dne mcm toob fcr e timalmg fne p f~rna~ of c hip m wave d e to th ~ektively :nall computational effo t md fne gff~eralysatifactoyagreme twihexperime ts Thediff'culties come m higkr md e~eme ~as md wh n try~ng to estsbli h maxim m kf time loads fcr tmctural d sir Nonlineartiesmwave- mdskmmi g-md ced tmct cl ~e pcnses of i ips hcve ben ob~d fi m 911-~ale measmemeris md m mod I expemme ts Sham meEnreme ts m ships wih fm f ms such as wmships (Smif 1966 md con~irvr ships :;dek et ~, 19 2) m modemte md hec y seas hcve shovm f tt fne wave-md ced saggi g bend g mmme ts m be consid r~oly k ger f m fne wave-md ced hog gi g bend g m m nts Tne non-linmrity m he v rtisal-pkne bend g mome ts has to be taken i to accom t m tmctural d ig To ml mise wave m~mg ~e isl~e md erhame seakepmgp f mar~ect~ektiwlyhigh ped fastvessels a~e UtDaDy dEriff~ed wifh krge l ngth to beam mtio, krge b w ftare md I w block cceffcie t Tnese pmp dies put fnem outsid fne mplicati mrmge fordne mles of fne ckssidcati m sochi s fcrh llgad r loads calcubtion h~d6 idual c~nsid ticns based m dsect cal-ubti m pmcedures a~e herefore qwed to d rive fne d sign loads Zhe g, 1999)
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From page 113... ...
of heave, pitch, bow acceleration (FP) and midship bending moment of the original S175 container ship for different regular wave amplitudes, Fn=0.25 (Xia, Wang and Jensen, 19981.
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From page 114... ...
rep~esent ctime-domcmcowtemart of fl~e linmr ship fl~eori s, fcr example, Salvesen, Tuck md Falti en (19701 Gem erally, J=3 suffces fcr mo t sectionsl shapes for mmehic ship motionprobl ms By i teg ati m of fl~e high r crd r d ffererbal equati m m B uAi m (1) md by mcomomti m of fl~e hyd oststic buoyancy force f mmd r fl~e imtardamous wave miace md fl~e g e wAer fome fO,, fl~e total non linear exbmal fluid force Z(z,t)
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From page 115... ...
For instance, an increasing bow flare will increase Cs and thus decrease Ze When the wavelength is long or the wave frequency is small, the effective relative motion is close to the nominal relative motion, which indicates a physically rational asymptotic behaviour of the dynamic wave deformation, see Figure 3. The relative motion amplitude Za in Figure 3 is shown as a function of the wave frequency ce for the S175 ship sailing in a head sea with a Froude number of 0.25.
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From page 116... ...
of the original S175 container ship with respect to wave steepness, Fn=0.2. Solid lines for the present method, solid circle points for SWAN-DNV, dash lines for the partly non-linear simulation (Xia and Wang, 1997)
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From page 117... ...
Figure 7 illustrates the predicted force and response time histories of the S175 container ship in regular waves with two different wavelengths VL and W1.2L. The time histories include the input wave elevation (, the effective relative ze7 the buoyancy force Jib, the momentum slamming force f l, the green water force fgW and the hydrostatic part of the green water force fS, all at the FP and the midship wave bending moment M/.
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From page 118... ...
103 Excl it = A 3 sees Time , 3 sees, Time Figure 7: Time histories of the wave elevation A, the effective relative motion ze7 the buoyancy force fb, the momentum slamming force fat, the green water force fgW and the hydrostatic part of the green water force fS, all at the FP, together with the midship bending moment Me for the S175 container ship in regular head waves.
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From page 119... ...
The comparison of the frequency response functions of amplitude of heave zala, pitch Ga/(ka) , vertical acceleration Lwa /( ga ~ at the FP, midship bending moment Ma/(pgaBL2)
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From page 120... ...
The ship motion, the vertical and lateral bending moments amidships, the relative water level and the wave pressure were measured. The comparison of the frequency response functions of heave za/a, pitch (3al(ka)
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From page 121... ...
_ _ ' ,'.~ /f ~o . ~, 0.5 1 1.5 A/L A/L A/L Figure 13: Frequency response functions of the pitch °a/(ka)
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From page 122... ...
1979, "Waw-kdhced E nd mgM merismShps cQuadrdicThoy",Ttms RNA, Vol. 121, pp 151-165 Kmseriberg, G K md Brouwer, R 1998, "Hyd odynamic d velopme t r c fiigtte f r fue 2 cent y, F oc of Lm, W-M, M i hold M, Stivesen.
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From page 123... ...
Jem n, JJ mdXia, J 1998, "On fne ffect of G~Wct:r mD k mheWaveBendingMome t",Foc 7f ktemational Symposimm m F actical D sit of Ships md Mobile U its, PR4DS'96, rne Nednerkmd, pp 239-245 Watarribe, I, Ueno, M md Saw~, H
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From page 124... ...
Once again, I would like to express my appreciation to the mthors for c most i fommative paper AUTHOR'S REPLY As expressed in Equation 2, the non-lmearities are included m the theo y with re pect to She buoy m. truce, Been water loads, summing action Ed the other hyd odynamic effects such es inertia Ed damping temms calculated to the in d mt meous w t surface of the body On She other h Ed, the Imearized fiee-surface condition has been used for the hyd odynamic calculations et the in t mtaneous submersion Based on our calculations, the trend of non-linearity show m Figme I is generally co finned for container ships Ed frigates No opposite bend has yet been found for other ship types The poorer correction of heave m the 45-degree hecdmg in Figure 5 might be due to the difficulties in the hecdmg control of the self-propelled model tests in this heeding A other reason might be the non-linear coupling betw en the heave Ed roll motions, which is not Included m the calculation but could be signffic mt in the m odel testing for the 45-degree heeding DISCUSSION H Kcgemoto University of Tokyo, Jcp m The mfhors ckim that the nonlinear characteri tics of motion responses observed et reso mt region, where the motion responses per unit wave height are reduced es She wave height becomes larger, c m be accounted for by the potenticlbased nonlinear theo y However, I thi k Ed I under t Ed that it is generally ~ reed that such nonlmearities m She reso mt r mge are c msed due to the nonlinear characteristics of viscous damping forces AUTHOR'S REPLY We agree with Professor Kcgemoto that viscosity con have m effect on vertical ship motions For example, Beukelm m (I 953)
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From page 125... ...
md Svensen, T 1990, h~corporction of seckeepmg fheories m C D, Intl S mnosmm on CFD md C D m Ship Design, Wcgeningen, The Netherl mds ISSC, 2000, "Committee V 1: on Ext~eme Hull Girder Loading", Froc of the 14th Interm~tiorurl Shiu & Offshme Stmctures Con~ress, Vol.
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