Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
Currently Skimming:
Ship Motions and Loads in Large Waves
Ship Motions and Loads in Large Waves
Pages 98-111
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 98... ...
technique is used for the computation, in which the equations of motion of water particles and those of a ship are solved simultaneously under the exact boundary conditions within the context of an inviscid flow. It is found that the theoretical computation can account for the nonlinear natures of the measured motions and loads fairly well, while distinct discrepancies exist from the measured results in some cases even in a moderate sea state.
|
From page 99... ...
et She Univ rsity of Tokyo The co hmer-ship model used for She experime t is show in Fig2 I Ed its principal particulars are specified in Table 2 I Six deg ees of motions, v tic i es w it es hori ontal bending mome t Ed hyd odynamic pressures acting on the ship hull et 15 locations w re measured es the ship was freely advancing without coy e ternal flesh ictions m c red lar wave ham Fig2 1 also shows the locations of the IS pressme gauges Pl~PIS) attached to She ship hull for She mecsmement of hyd odynamic pie..
|
From page 100... ...
represent th nondimensiom3lized motion amplih de of the Fourier component that has the same fiequency as the enco mtering fiequency with th incident waves Ibe legends -5 m-, '10cm', '15 m' indicate that th correspondi g remits w re obtained m waves of 5 m, 10cm, 15 m height respectively Since at the qua titles show m the figm es me normalized by th amplitude of the incident wave(5A) or the maxim m slope of th incident waved the results for 'Scm', '10cm', 'IScm' should coincide with each other if the phenomena w re of linear ones How ver, She so-called wave-height effect is observed in some cases, particularly in heave motions in z=120deg, 90deg Ed in roll motion in z=90deg, 30deg in such ~ way that
|
From page 101... ...
m 911 locations of fihe pressure Badges 3.3 Bendflng moment Fig 3 9, Fig 3 10 show fihe results on the vertical bending moment md fihe horizontal bending moment re pectively acting at th midship section The vertical axes of the flgures represent th nondimensionsli:osd amplitude of fihe con espondmg moment 7 he amplitude show in the flgmes is that of fihe Fourier component which ht. the same frequency as the enco mtering
|
From page 102... ...
r: 1 1 = 1 ~= 1 ~ j 2 : ~} 5 ml ~10 ml L ~ ~ | ~15 ml ,L +/ : ~ ~+ i i 12 14 16 0 02 04 06 08 1 i/L (4) 1,=30deg Fig 3 3 Ihe experimental re mits on pressme cmplitude(P~)
|
From page 103... ...
~15 ml 0 02 04 06 08 1 //L (4) 1,~30deg 12 14 16 Fig 3 5 Ihe experimental re mits on pressme amplitude(P~)
|
From page 104... ...
(1) 7he time history of th pressure mecsured et P I (x=180deg .
|
From page 105... ...
~ O 02 04 06 08 1 12 14 16 //L (4) X=30deg Fig 3 9 he e perime hi results on the verticei bending moment empiit des(MY)
|
From page 106... ...
Of her f m These, Although they are not show here, bodh She ve ticcl Ed the hori ontcl moments show fairly linear characteristics it is k ow that the ve ticcl moment on c container ship possesses c crest-trough c mmetricity Ed f is is redo firmed m Fig3 11, m which the sagging Ed She hogging bending moment et She midship measured fiom She moment level acting on She ship cdvancmg in c calm water are separately show lithe vertical axis is not nondimensiomdi:osd be represents She moment itself ) it is evident that the sagging m oment is larger th m the hogging moment Ed f is tendency is erJurxed sin Tic mtly es She waveheight becomes larger 4 COMPUTATION 4.1 Basic idea of the computation As for th Theoretical estimation of ship motions Ed loads m large waves, quite c few works are now bemg conducted, although the Ember of work that have been applied successfully to the computation of motions Ed loads of c practical ship advancing in large waves is till limited LAMP code developed by Lm, Yu et cl (1990)
|
From page 107... ...
evaluated by c fi st-order Enleri m scheme As for fhe spaticl derivativ s, c third-order upwind-diffe~ence scheme is used for fhe convection terms while c second-order central-dffference scheme is used for the of her temms After obtcini g fhe XYZ v locities of the body md fhe mgular v locities of the body aro md fhe XYZ cxes, the locations md fhe cttitudes of the body wifh re pect to the spae-fixed coordincte ystem me updated et eah time step 02 Og 0 02 04 06 08 1 12 y[m] Fig 41 he hy rid g id ystem used for the CF compubtion (one-hcff of the v ticcl cross section of the compubtioncl domcm)
|
From page 108... ...
~ ~ ~ l s os ~ ~15 0s 2s 2 I s I 0s 2s 2 0s !
|
From page 110... ...
(3) P12, waveheight=lOcm, 2/l=0 75 Fig4 5 She comparison of time histories of measured mdcalculatedp~essuesmhecdwaves 4.4 Resudts and their comparison with es loci males 4.4.1 Frequency response eharaeteristies Fig42, Fig43 compare She results of the CF computation on She motions md on She p~essmes respectively in heed waves of lOcm height with the conespondmg experimental ones Since She experimental results me th Fou ier component that has She same beers ncy es She encoumtermg frequ ncy of She incident waves, th cciculation results w re also Fou ier-decomposed so that the component that has She encou termg f~equ ncy m be compared 7be pitch motion is predicted w 11 by She prese t computshop whereas the calculation results on She heave motion me c little smaller th m the corresponding experimental ones As for th pressu es, She lard p~essmes acting at She bow section PI is predicted quite accurately by th present ccl Elation On th other h md, pressures on P7, P8, P9, P10, Pll, P12, P13, which me located clo g She cross section close to the midship(see Fig2 1)
|
From page 111... ...
Overcll, fhe nonlmear characteristics that me observed in the mecsu cd pressu es in large waves m be acco mted for fairly w 11 by the p~esented CFD comp htion On fhe other hmd, the~e exi t some distin t dismepancies m th cclcokted motions md pressu es fiom fhe mecsmed on s even in modercte waveheight, which may indicate fnat fhe presented CFD comp htion procedme still n eds futher improvements Acknowledgement: The cubhors w uld like to cck owledge D s Iwco Wctcrube, Shigesuke Ishidc, Kctsoji Tmizawc of Ship R search in titute, Ministry of Tr mspo t, hp m md Atsushi Kum mo of Nippon Kciji Kyokai for fheir support md valu~ble comments m condu tmg fhe experiments REFERENCES B.W.King, R.FBeek and A.R. Magee: Seakeeping ccl uhtions wifh forward peed usmg time-domcm crudy is, Proc 17fh Symposium on Naval Hyd odynsmics, The Hcgue, The Netherl mds, l 988 W-M.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.