Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
Currently Skimming:
Practical CFD Applications to Design of a Wave Cancellation Multihull Ship
Practical CFD Applications to Design of a Wave Cancellation Multihull Ship
Pages 206-222
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From page 206... ...
, where experimentcl measurements md theoretical cclcohtions based on Michell's 6hin-ship approximation are given The wave carmelhtion multihull ship At is considered consists of c mom center hull md two identical outer hulls centered et ( Y.} ~)
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From page 207... ...
foll w from fhe dispersion rektion F ~3 = f with i = :}~ 7he velocity representtition of free-surflice fl ws imd the rekted Fourier-Kochin representation of ws s given in [4] deflme fhe spect 3m function 5 in temms of the velocity dish ibution s t fhe ship hull smfa (or m ore generally s t s bo mdii y surfti cc fm~t suno mds the ship)
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From page 208... ...
Here, u 11 rmd u ~ re pectively represent c wrr component rmd c loccl component 6~t rr~e cssocicted with the decomposition G = Glt—G~' of 6he Gren funriti on G cs s oc icted wi6h the free -suricce bomdrrycondition o—F2ur=U 7hewrr component u 11 is givenby c smgle Fourier mteg cl Speciflcclly, the ship hull ~ (which here st mds for the h nter hull ~< or the outer hull ~O) is divided into c set of patches ~p rrrisocicted with reference points (; p l/p ~r ~ 0)
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From page 209... ...
shows that The velocity dishibution to associated with the trivial velocity dishibution t = 0 is given by t1 = 11 it his velocity distribution is non ill to the ship surfae ~ 16X tangential velocity component ah x it is mall) , imd evidently satisfies The hull bo mdary condition us it = 11' The velocity di trlbution Ih = Tl: it co responds to The sift der-ship approximation (12)
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From page 210... ...
, withm Che "negligible nearfield interation" cpproximction hus, Chis cpproximation effectively uncouples the outer-hull location pcMmeters (a ~ hl md nearfield fiow cclculati ons For the p mp o se of est mm ating the im port mce of nearfield fi w interations upon the wave dLcg <.1t, the nearfield velocity dish~bution is evalucted here using the slender-ship cpproximation clrecdy used in method 3 his cpproah is identff cd es meChod 2 hereafter hus, comparison of meChods 2 md 3 provides msight mto the import mce of nearfield fiow intffation effects Method 2 conesponds to Che fikst-order siff der-ship cpproximation defimed in [5] Insight into Che importmce of usmg c sophisticated nearfield fi w calcoktion method c m be gained by comparmg method 2 md meChod I, which conesponds to Che :D:roCh-order slender-ship cpproximation in [5]
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From page 211... ...
have be s mmk iced The WE csmcelhtion mult hull ship considered in [1] kmd here consists of k mam center hull kmd two identical outer hulls centered at hi-.
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From page 212... ...
with U ~ 9 <, /2 Thus, the outer hulls zre deflmed by the fl e pzMmeters L°, G°, D°, i-f; md V~4 The centers of the waterpkmes of 6he two outer shuts are located zt A- =—L Y md } - = =LI wi6h respect to the center of 6he waterplane of the mam center hull D flme 6he ystem of coordim~tes (A-~}.Z) with origm zt 6he center of 6he waterpkme of 6he center hull Thus, 6he coordinates ~ V.} - Z)
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From page 213... ...
~) for —L: < ,~' < .;'; hus, The local beam md the top waterline of the mom center hull are defmed by the si parameters 1'', D'', L', Lo, ,X'/: md An;: Every tramebne consists of c straight horizontal bottom md c straight But not vertical)
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From page 214... ...
The six parameters LC, DC, BC, BoC, -YB and _Ys that define the main center hull and the five parameters L', By, D-, -YB and _Ys. that define the outer hulls are given by Lc=0 5 DC ~ o 0,-49 Bc~ 0.0245 B,2 ~ 0.0128 ~ ~ 0.105 _Y,sC ~ 0.0401 L~~ 0.2436 D°~ 0.0356 B°~ 0.00847 YE ~ 0.175 As ~ -0.134 for the wave cancellation multihull ship considered in [1]
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From page 215... ...
~ r ~ ~ ~ ~ r ~ '& ' 025 03 03s 04 045 Fmde sumbelfa-0365) Fig I Cmicohted wxwe d mg and experi ental residuary d mg
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From page 216... ...
2a. Wave drag coefficient predicted by methods 1,2,3 for F=0.5 Cw method 1 Cw method 3 7' Fig.
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From page 217... ...
2c. Wave drag coefficient predicted by methods 1,2,3 for F=0.3 Cw method 1 Cw method 2 Cw method 3 Fig.
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From page 218... ...
3. Wave drag coefficient at three best arrangements of outer hulls Cw method 1 Cw method 2 -- -- -~ -- -Cw method 3 -- -- -~ -- -- Cw method 4 -- -- -- -- -- ~ -- -- -- -- - ...
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From page 219... ...
5a. Wave drag coefficient for 10 Froude numbers F=0.5124 1 F=0.4521 F=0.4220 F=0.331 6 F=0.31 65
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From page 220... ...
5b. Wave drag coefficient for 10 Froude numbers F=0.2713 F=0.2524 F=0.2449 1 F=0.2374 F=0.2223 1 F=0.2147
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From page 221... ...
~ B ' ! ~ tY tt ~ —~ ''' ~ tK 02 025 03 035 04 045 05 055 Froude number Fig 7 Wave d cg md parameters c md b for best md nearbest arr mgements of ooter holls
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From page 222... ...
AUTHOR'S REPLY Thmk you for your interest in our paper Ed for providing Information cutout your own work on She effect of hull arr in emenr upon wave dmg We agree Nat the outer hulls should m principle be treated es lifting surfaces, Ed that lifting effects c m be expected to be larger if She outer hulls are closer to the center hull The 3 simple potenticlflow methods w have used (methods 1, 2, 3) do not include lifting effects Medhod 4, based on She Euler equations, accounts for lid ing effects The restively good agreement between experimental residuary d cg Ed wave d cg predicted by all 4 methods show in Fig I sugge ts that Ifftmg effects may not be very impo t mt in the present case
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