Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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Flow- and Wave-Field Optimization of Surface Combatants Using CFD-Based Optimization Methods
Flow- and Wave-Field Optimization of Surface Combatants Using CFD-Based Optimization Methods
Pages 243-261
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From page 243... ...
The module is general in formulation, and basically independent from basic flow solver, e.g., different RANS solver or inviscid-panel method can be used with arbitrary combination of constraints and objective function to be minimized. In the following, an overview is given of the present numerical method and results are presented for flow- and wave field optimization of surface combatant Model 5415 hull form.
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From page 244... ...
on Advanced CFD Applications to Ship Flow md Hull Form Desigm Indicates that optim ization methods are am ehy being developed in the ship hyd odynamics comm mity Hino et cl, 1998; Suzuki md Mets moto, 2 1998; Taharc et cl, 1998) in general, OC98 show d that optimization methods are cable of stern ihrFe optimization for minimization of viscous nisi tance However, k ge compuhtiorLtl co t is still c major issue, but one that cm be overcome ff parallel high-pe formance prod cmmmg technique is adopted This paper concerns flow- md so t~e-lield optimization of surface combatmts using CFDbased optimization method Th mom focus is placed on development of c high pe 1:3nnul e optimization module for application to Model 5415 hull form optimization, which is capable m comhirLtrion with CFDSH P-IOWA (Stem et cl, 1996; Peterson et al, 1998; Wilson et tl ,1 99S I, c genercl-purpose parallel multiblock RANS code based on hig)
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From page 245... ...
for ~ 3 more details of 6he present RANS code z = z(; .1.; ) md hpil sp fae is expressed zs Comp htiopal Grids 7he present body-fltted, sh petmed, mpitiblock g ids are geperated psing commercial gid gep mtion code z=z(~i ;z ;3' GR DGEN fiom Pomtwise, ~c For zpplicationto Model y =y(~ ~ ~ ;3, 5415, patched mpitiblock g ids md bopmdary conditions ~ ~ 3 arepsed Gidcipstermgcmbedop asforotherhpils, z=z(; ,~,,~.; )
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From page 246... ...
mequa lity conshamt f mctions Th desigm parsmeters are used to express body geomeby, i e, 6he solutions of the optimization problem The objectiv fi:mtion giv s s value to be minimi:D:d, e g, viscous resistmce Equality md inequality conshamts limit 6he chmge of values. e g, di placement or maxim m depth, etc ~ the p~ese t st dy, desigm p~meters me used to defme modiflcstion function, 6he objectiv fmction is specffic value of flow or wa~ field, mddhe equality or inequality comt~ai ts me imposed such thst th di placement of modifledhull is equal to or larger 6 m thst of th originsl Also, value of flow such ss lif or d sg cm be used m equality or mequality con t~aint Th present problem is nonlmear, since F, G, md H are nonlinear fmctions of d Hence, s nonlinear prog ammmg slgorithm must be inhoduced to solv the p~esent problem Nonlinear Prog ammmg Algori6 m In the p~esent st dy, equations (9)
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From page 247... ...
simfitmeorsly execrte CF f medhod, ie, evaluationof,jf3) inthefgure Th pfuallelfuchitf tun, offers zdvfmtage ow~r the serial fuchitecture for consideraly higher comp htiork~l efhciency, ie, comp rtatiom~l speed of the former is nefu Iy m times fzYer th m 6~t of th ktter, since most of CPU time is e d for CF f method, fmd comm mication o uh zd betwen 6he processors is q 6te small Fmthemmon>, comp rtmionai speed for SQP in pfm~llel fuchitectun does not depend on n mber of desig pfuameters In the present zpplication of SQP, 6he pfuallel comp rtmion zigorithm was implemented zs fm indepf dent mod rle, i e ~ 6he optimization method is basically independent fiom basic flow solw~r, eg, diffenmt RANS sol u or inviscid-pa fl method f m be ued with fubiL:uy combi rtion of conxramts fmd objecti f f mction to be minimiY>d, that h~s ben demonshatedasshow inth presentremitsdescobed hter H fl Fomm Modifcation Function Choice of h ril-fomm modifcation f mction is import mt in optimization, becfmY the f mction m rst hz f Yfhcient expressi meyss for derinfd h ril modifcation in the preYnt st dy, z 6-pYzmetf fi :mtion, which is de f loped m the pnfcurrory work by Taharz et zl (1998)
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From page 248... ...
RESULTS In the followi g, remits me presented for flowmd wave field optimization of surface combat mt Model 5415 hull form, wh re discussions are focused on stern optimization, sonar dome optimization, md bow optimization, all of which are related to practical desig problem Prior to application of th prese t method to Model 5415 hull form optim ization, She comp tnhonal efhciency of the present optimization module has i en evaluated in comparison with results from th precursory work (Tahara et al, 1998; Kitamura et al, 1997; Tahara et al, 1999) , i e, Chose concern layout optimization of 2-D t mdem hyd of oils mder flee surface for minimization of wa~-makmg resi tance, md stern optimization of t mker hull form for minimization of iscous resistmce, in both of which the conve tional serial SQP module was used The comparison of computational speed Indicated that She present parallel SQP module is nearly 13 times faster thm She serial module The reset has appealed consistent with She earlier discussion on adv midge of the prese t method Model 5415 Stern Optimization Th Ist case is stern optimization for minimization of disturbance on h msom wake field Most rece t high- peed fme ships as w 11 as Model 5415 have transom tem m order to obtain wide waterphne area to secure sufhcient stability The wide t msoms tend to increase disturbance on h msom wave field, md it remits m mcrease of hulMesistance Th present authors md others ([wasaki et al, 1996; Tahara et al, 1997)
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From page 249... ...
, wave elevation at fihe h msom wall (Fst, defined as fihe difference in z coordinate betw en the wave contact pomt at h msom wall centerline md the on gm al stern~nd corner denoted as "A" m Fig I I ) , frictional resi tance coefficient Cd67, md p~e..me resistmce coefficie t cd pa, all of which Sue for fihe optimi:D:d hull form md show in % as compared to thom values for fihe original hull fomm Objective fixation md wave elevation at h msom wall Sue reduced in aho t 30% md 60%, re pectively Decrease in resistance coefficients Sue also men except for fi ictionsl part, which is nearly equal to that for th original hull form Th pres me resistance coefficient is reduced in about 5%, md that is mainly rented to reduction of reversed flow region m tr msom flow field md less disturbance on wave field for th optimized hull form The conflation betw off resistance md t msom wave md flow fields coincides with that fo md in z thors' earlier work 7waqki et al ,1996; Tstsrs et 91, 1997)
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From page 250... ...
, which ippinded comparison of Imear md nonlipear theories to predict bow wave, 6he Imear theory gep p~lly pmder p~edicts 6he wave elevation p ar th bow A nonlip ar panel medhod developed in 6he work was showp capable for prediction of 6he wa~ f eld aropmd bipmt pose body as w 11 as comme pial ships opemted zt high Fn, 6~t had been acomplish d by mtroduption of 6he O-type f~ee-surfae panels md nonimear fre-sp fae bopmdary conditions A16hough CFDSE P-IOWA version 3 02 cm be psed for prediction of bow wa~, the panel method was psed in 6he present optimization, m which evalpation of capability of 6he present optimization module was somewhat more focp ed, md zt present lower computatiorul effort was preferred Th ~espits w ~e verffied by psmg CFDSE P-IOWA version 3 02, md presented m 6he followmg discpssiop Npmbers of panels psed in 6he comp tation are 1600 md 2000 for hpil md flee surfaes, re pectively, 6~t had be p fopmd optimum based on panelization dependep y te ts Figs20 md21 showcomputedwa~contop s md profile for 6he origirul hull, re p ptively, by psmg 6he present nonimear panel method In Fig21, th experimental datz are ziso mcinded for comparison Th p~esent ~espits mdicate considerably good zg ement with 6he measurements especially for elevation of bow wave crest, on which focps of th present study is mainly plaed It mpst be noticed that prediction of 6he tpmsom wave fleld is not satisfatory, which is mainly dp to 6he limitation of th in iscid-flow zpproah This leads to m impo tmt cop Ipsion that, for optimization of h msom flow md wave fields, RANS solver mp t be psed zs demonshated m the present work ad discpssed in 6he earlier sectiop O 6he odher hmd, the present panel method has ben judged capable for 6he mitial validation of p~esent optimization medhod zs far as 8
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From page 251... ...
hr. clearly decreased, i e, that is clout 6 5%, which is consi tent with th low r wave mcki g resist mce for low r bow mare crest The ctove-discussed results hose show that th present method is very prom ~ Beg, md flasher verif cation of the results 6 ough model tests is of g eat mte~est On the oth r h Ed, it is also of i terest to replace The panel method by CFDSH P-lowc version 3 02, since The tANS solver is more comprehensive, m which viscous Ed wave mslrmg effects me cow idered m The Theory, Ed capable for accurate prediction of resi tance es w 11 es flow e pecially for hull forms with tr msom stern ~ addition, flasher mvestigstion mu t be done on the medhod to modify The bow chap All of The clove me issues for f tore work, Ed m part, curre fly m prom ess SUMMARY AND CONCLUSIONS his paper concerns flow- Ed ss3se field optimization of surface combat mts using CFDbased optimization method 7be mom focus is placed on development of c high pe fommance optimization module for application to Model 5415 hull form optimization, which is capable m combination with CFDSH P-IOWA Version 3 02 She optimization sch me is based upon fihe work of part of fihe present authors wherein tsrD.er hull forms w me optimized for fommulstion, md basically mdependent fiom basic flow solver, e A, different RANS solver or iniscid-panel method cm be used wish srbibsry combination of con Faints md oh jective fi motion to be minimi:md In 6 is paper, m owxvi w is given for fihe prese t primary RANS equation solver, computational g ids, once tsmty awes me t for th RANS code, g neral nonlmesr optimization problem, 9 high pe fommance nonlinear pr on am m mg Vigor id m, md th 6 parameter hull form modfficstion fimction he remits Sue presented for flow- md wave field optimization of surface combatmt Model 5415 hull form, where discussions are made on tem optimization, sonar dome optimization, md boss optimization, 911 of which are related to practical desigm problem Prior to application of th prese t method to Model 5415 hull form, fihe computational efficiency of the present optimization module hr.
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From page 252... ...
clearly smeller mcgmitude of longitudinal vorticity, which relates to reduction of junction vortices Finally, results for Model 5415 bow optimization w re presented md discussed ~ She optimization, mimmization of elevation of the bow wave ore t was considered he differences m wave profile between for th original md th present optimized bows me clearly seen m the region near She bow, i e, th elevation of bow wave Rest is oh iously decreased in She optimized results he m od to anon Sends are notable, i e, c ditch line hr. cppemed m She mid-gi ah legion, that may not commonly be predicted by the conventional hull form desigm In conclusion, the prese t method hr.
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From page 253... ...
L mdon, M, md Johm on, R "Aerodynamic Shape Optimization of ~temel Fluid Flow Sy tems," A AA-98-2896,1998 Proceedmgs 3~3 Osake Colloqui m on Advanced CFD Applications to Ship Flow md Hull Fomm D sigm, Osake, Jepen, Mey25-27,1998 Rhee, S H
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From page 254... ...
"IJn tecdy RANS Simuhtion of Model 5415 m Waves," Proceedmgs of fhe 22nd Symposi m on Naval Hydodynamics, Wcshmgton DC, Aug t 1998, pp 532-549 Zhu, ZW, md Chm, YY, "A New Genetic Algorif m for Aerodynamic Desig Bcsed on Geometric Concept," A AA-98-2900,1998 12
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From page 255... ...
Sol. converged \ , ,, \, / 10 20 30 40 50 Optimization cycle Fig.3 Comparison of convergence history of objective function between for SLP and SQP optimization algorithms (Tahara and Himeno, 19984.
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From page 256... ...
contours near the stern between for the original and optimized hull forms: Model 5415 stern optimization.
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From page 257... ...
~ ~ ~ ~ ~ 1 1.025 1.05 x Fig.12 Comparison of wave contours near the stern between for the original and optimized hull forms: Model 5415 stern optimization. TO signal 0 20 40 60 80 100 I Fit Cd~ Cd¢)
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From page 258... ...
. Fig.16 Comparison of sonar dome shape between for the original and optimized hull forms: Model 5415 sonar dome optimization.
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From page 259... ...
O -0.01 -0.02 N ~0 03 ~ -0.04 -0.05 -0.06 10 N 0.01 _ O tar -0.01 _ -0.02 _ -0.03 _ -0.04 _ -0.05 _ -0.06 _ -0.07 A -0.06 / ~:: , ,\, ,~\, Original Optimize _ 1 1 .02 d Fig.22 Comparison of bow geometry between for the original and optimized hull forms: Model 5415 bow optimization (minimization of maximum bow-wave crest with displacement constraint)
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From page 260... ...
, \ ,! \\ \' I I - t I I -0.1 0 0.1 x 0.2 0.3 0.4 Fig.24 Comparison of bow wave elevation between for the original and optimized hull forms (RANS solutions for verification)
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From page 261... ...
Unlike conventional commercial ships, for which m ost previous optim i ction work ht. been done, Mod 15415 has c very characteristic flmed bow form with large sonar dome located near the keel in addition, nonlinear fiee-surface effects are signffic mt for She conditions considered herefcre, optimization trends may be different th m that shown in previous investigations O the ocher hand, the present bow modification appeared m restively limited region, i e, midgirth region, where c ditch line had been created As such, further investigation of the present modification f notion is currently in progress Firnlh, it should be emphcsi ed that CFDbased optimization presents challenges to the verification md validation process md that there is c need for optimization validation data
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