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Received6February2009 Accepted14July2009 Keywords: Holisticshipdesign Multi-objectiveoptimization Geneticalgorithms Minimizationofresistanceandwash Enhancedsurvivability technicalandnon-technicalnature,andofindividualexpertstoarriveatvaluabledesignsolutions. Inherentlycoupledwiththedesignprocessisdesignoptimization,namelytheselectionofthebest solutionoutofmanyfeasibleonesonthebasisofacriterion,orratherasetofcriteria.Asystemicapproach toshipdesignmayconsidertheshipasacomplexsystemintegratingavarietyofsubsystemsandtheir components,forexample,subsystemsforcargostorageandhandling,energy/powergenerationandship propulsion,accommodationofcrew/passengersandshipnavigation.Independently,consideringthat shipdesignshouldactuallyaddressthewholeshipslife-cycle,itmaybesplitintovariousstagesthat aretraditionallycomposedoftheconcept/preliminarydesign,thecontractualanddetaileddesign,the shipconstruction/fabricationprocess,shipoperationforaneconomiclifeandscrapping/recycling.Itis evidentthatanoptimalshipistheoutcomeofaholisticoptimizationoftheentire,above-definedship systemoverherwholelife-cycle.Buteventhesimplestcomponentoftheabove-definedoptimization problem,namelythefirstphase(conceptual/preliminarydesign),iscomplexenoughtorequiretobe simplified(reduced)inpractice.Inherenttoshipdesignoptimizationarealsotheconflictingrequirements resultingfromthedesignconstraintsandoptimizationcriteria(meritorobjectivefunctions),reflecting theinterestsofthevariousshipdesignstakeholders. Thepresentpaperprovidesabriefintroductiontotheholisticapproachtoshipdesignoptimization, definesthegenericshipdesignoptimizationproblemanddemonstratesitssolutionbyuseofadvanced optimizationtechniquesforthecomputer-aidedgeneration,explorationandselectionofoptimaldesigns. Itdiscussesproposedmethodsonthebasisofsometypicalshipdesignoptimizationproblemswith multipleobjectives,leadingtoimprovedandpartlyinnovativedesignswithincreasedcargocarrying capacity,increasedsafetyandsurvivability,reducedrequiredpoweringandimprovedenvironmental protection. The application of the proposed methods to the integrated ship system for life-cycle optimizationproblemremainsachallengingbutstraightforwardtaskfortheyearstocome. 2009ElsevierLtd.Allrightsreserved. 1. Introduction to holistic ship design optimization Shipdesignwasinthepastmoreanartthanascience,highly dependentonexperiencednavalarchitects,withgoodbackground invariousfundamentalandspecializedscientificandengineering subjects.Thedesignspacewaspracticallyexploredusingheuris- tic methods, namely methods derivedfrom knowledge gained through a process of trial and error, often over the course of decades. Inherentlycoupledwiththedesignprocessisdesignoptimiza- tion,namelytheselectionofthebestsolutionoutofmanyfeasi- bleonesonthebasisofacriterion,orratherasetofcriteria.A systemic approach to ship design may consider the ship as a complex system integrating a variety of subsystems and their Corresponding address: Heroon Polytechniou 9, 15 773 Athens-Zografou, Greece.Tel.:+302107721416/1409;fax:+302107721408. E-mailaddress:papadeslab.ntua.gr. URL:http:/www.naval.ntua.gr/sdl. components,forexample,subsystemsforcargostorageandhan- dling,energy/powergenerationandshippropulsion,accommoda- tionofcrew/passengersandshipnavigation.Theyareallserving well-definedshipfunctions.Shipfunctionsmaybedividedinto twomaincategories,namelypayloadfunctionsandinherentship functions(Fig.1).Forcargoships,thepayloadfunctionsarerelated totheprovisionofcargospaces,cargohandlingandcargotreat- mentequipment.Inherentshipfunctionsarethoserelatedtothe carriageofpayloadsafelyfromporttoportwithcertainspeed. Independently,consideringthatshipdesignshouldactually addressthewholeshipslife-cycle,itmaybesplitintovarious stagesthataretraditionallycomposedoftheconcept/preliminary design,thecontractualanddetaileddesign,theshipconstruc- tion/fabricationprocess,shipoperationforaneconomiclifeand scrapping/recycling.Itisevidentthattheoptimalshipwithrespect toherwholelife-cycleistheoutcomeofaholistic1optimizationof 1 PrincipleofholismaccordingtoAristotle(Metaphysics):Thewholeismorethan thesumoftheparts. Computer-AidedDesign Contents lists available Computer-Aided journal homepage: /locate/cad Holisticshipdesignoptimization ApostolosPapanikolaou ShipDesignLaboratory,NationalTechnicalUniversityofAthens,Greece a r t i c l e i n f o Articlehistory: a b s t r a c t Shipdesignisacomplexendeavor 0010-4485/$ seefrontmatter2009ElsevierLtd.Allrightsreserved. doi:10.1016/j.cad.2009.07.002 42(2010)1028 1044 at ScienceDirect Design requiringthesuccessfulcoordinationofmanydisciplines,ofboth (usuallytheshipownersrequirementsformerchantshipsormission statementfornavalships),ashipneedstobeoptimizedforcostef- fectiveness,forhighestoperationalefficiencyorlowestRequired Freight Rate (RFR), for highest safety and comfort of passen- gers/crew,forsatisfactoryprotectionofcargoandtheshipherself ashardwareand,lastbutnotleast,forminimumenvironmental impact,particularlyforoilcarrierswithrespecttomarinepollu- tionincaseofaccidentsandforhigh-speedvesselswithrespectto generatedwavewash.Recently,evenaspectsofshipengineemis- sionsandairpollutionneedtobeconsideredintheoptimization ofshipdesignandoperation(seeIMO2008,2).Manyofthese requirementsareclearlyconflictingandadecisionregardingthe optimalshipdesignneedstoberationallymade. Tomakethingsmorecomplexbutcomingclosertoreality,even thespecificationofasetofdesignrequirementswithrespectto shiptype,cargocapacity,speed,range,etc.iscomplexenough to require another optimization procedure that satisfactorily considers the interests of all stakeholders of the ship as an industrialproductandservicevehicleofinternationalmarkets orothers.Actually,theinitialsetofshipdesignrequirementsis 2 Theprincipleofreductionismmaybeseenastheoppositeofholism,implying that a complex system can be approached by reduction to its fundamental parts.However,holismandreductionismshouldberegardedascomplementary forspecificeconomiccriteriabygradient-basedsearchtechniques (Murphyetal.4,Nowackietal.5).Also,computer-aidedstud- iesontheoptimizationofashipshullformforleastresistanceand bestseakeepingbehavior(hydrodynamicdesignoptimization),or ofashipsmidshipsection/structuraldesignforleaststeelweight (structuraldesignoptimization)startedbeingintroducedtothe navalarchitecturalscientificcommunityuntiltheyledtomatured resultsinmorerecentyears(see,e.g.,Papanikolaouetal.6,Valde- nazzietal.7,Zaleketal.8). Withthefurtherandfasteradvanceofcomputerhardwareand softwaretools,alongwiththeirintegrationintopowerfulhard- wareandsoftwaredesignsystems,thetimehascometolookat thewayaheadinshipdesignoptimizationinaholisticway,namely byaddressingandoptimizingseveralandgraduallyallaspectsof shipslife(orallelementsoftheentireshipslife-cyclesystem), atleastthestagesofdesign,constructionandoperation;within aholisticshipdesignoptimizationweshouldhereinalsounder- standexhaustivemulti-objectiveandmulti-constrainedshipde- signoptimizationproceduresevenforindividualstagesofships life(e.g.conceptualdesign)withleastreductionoftheentirereal problem.Recentlyintroducedscientificdisciplinesinthegeneral frameworkofdesignforX,namelydesignforsafetyandrisk- baseddesign(SAFEDOR9,Vassalos10,Papanikolaou(ed)11), designforefficiency,designforproduction,designforopera- tion,etc.indicatetheneedforapproachesandtheavailabilityof A.Papanikolaou/Computer-Aided Machinery Crew Facilities Structure Tanks Comfort Systems Outdoor Decks Engine and pump rooms Crew spaces Service spaces Stairs and corridors Hull, poop, forecastle Superstructures Engine casing, funnel Steering and thrusters Fuel see,e.g.,optimizationstudiesforaspecificXshipfunction,like shipperformanceincalmwaterandinseaways,shipsafety, shipsstrengthincludingfatigue,etc.Theshipdesignoptimiza- tioncriteriaareingeneralcomplexnonlinearfunctionsofthe designparameters(vectorofdesignvariables)andareingen- eraldefinedbyalgorithmicroutinesinacomputer-aideddesign procedure. Constraints: This mainly refers to a list of mathematically definedcriteria(intheformofmathematicalinequalitiesor equalities)resultingfromregulatoryframeworkspertainingto safety(forshipsmainlytheinternationalSOLASandMARPOL regulations).Thislistmaybeextendedbyasecondsetofcriteria characterizedbyuncertaintywithrespecttotheiractualvalues andbeingdeterminedbythemarketconditions(demandand supplydataformerchantships),bythecostofmajormaterials (forships:costofsteel,fuel,workmanship),bytheanticipated financialconditions(costofmoney,interestrates)andother case-specificconstraints.Itshouldbenotedthatthelattersetof criteriaisoftenregardedasasetofinputdatawithuncertainty totheoptimizationproblemandmaybeassessedonthebasis ofprobabilisticassessmentmodels. Designparameters:Thisreferstoalistofparameters(vectorof designvariables)characterizingthedesignunderoptimization; forshipdesignthisincludestheshipsmaindimensions,unless specifiedbytheshipownersrequirements(length,beam,side depth,draught)andmaybeextendedtoincludetheships hullform,thearrangementofspacesandof(main)outfitting, of (main) structural elements and of (main) networking elements(piping,electrical,etc.),dependingontheavailability of topological-geometry models relating the ships design parameterstoagenericshipmodeltobeoptimized. Inputdata:Thisincludesfirstthetraditionalownersspecifica- tions/requirements,whichforamerchantshiparetherequired cargocapacity(deadweightandpayload),servicespeed,range, etc.,andmaybecomplementedbyavarietyoffurtherdata affectingshipdesignanditseconomiclife,likefinancialdata (profitexpectations,interestrates),marketconditions(demand andsupplydata),costsformajormaterials(steelandfuel),etc. Theinputdatasetmayincludebesidesnumeralsofquantities alsomoregeneraltypesofknowledgedata,likedrawings(of theshipsgeneralarrangements)andqualitativeinformation thatneedstobeproperlytranslatedforinclusioninacomputer- aidedoptimizationprocedure. Output: This includes the entire set of design parameters (vectorofdesignvariables)forwhichthespecifiedoptimization criteria/meritfunctionsobtainmathematicallyextremevalues (minimaormaxima);formulti-criteriaoptimizationproblems optimaldesignsolutionsareontheso-calledParetofrontand may be selected on the basis of tradeoffs by the decision maker/designer. For the exploration and final selection of Paretodesignsolutionsavarietyofstrategiesandtechniques maybeemployed. Inmathematicalterms,themulti-objectiveoptimizationprob- lemmaybeformulatedas minT 1.x/; 2.x/;:; n.x/UT; subjecttog.x/ 0and h.x/D0andxl x xu where i is the i-th objective function, g and h are a set ofinequalityandequalityconstraints,respectively,and x is thevectorofoptimizationorvectorofdesignvariables.The solution to the above problem is a set of Pareto solutions, namely solutions for which improvement in one objective cannotbeachievedwithoutworseningofatleastoneother objective.Thus,insteadofauniquesolution,amulti-objective optimization problem has (theoretically) infinite solutions, namelytheParetosetofsolutions. 3. Typical ship design optimization problems 3.1.Hull form optimization of high-speed vessels with respect to poweringandwash 3.1.1.Overviewoftheproblem Ashipshydrodynamicperformanceintermsofspeed,power- ing,seakeepingcharacteristics,maneuverabilityisofparamount importance,especiallyforHigh-SpeedCraft(HSC).Washwave generationhasworriedneitherthedesignersnortheshipoper- atorsuntilveryrecently.Itistheintroductionofnumerouslarge high-speedvesselsthatiscurrentlydrivingmaritimeauthorities toconsiderapplyingtoanextentpossiblerationalwashcriteriato theoperationofHSC,becauseoftheimpactonthemarineenvi- ronmentandthesafetyofactivitiesincoastalareas.Therefore,at leastforHSCdesigns,washreductionhasbecomeamajorrequire- mentofthevesselshydrodynamicperformance,alongwithother traditionalhydrodynamicobjectives. 3 NationalTechnicalUniversityofAthens ShipDesignLaboratory,NTUA SDL, http:/www.naval.ntua.gr/sdl. degreeofconfidence.Incorporationofsuchnumericaltoolswithin anintegrateddesignenvironmentisthemaingoalofthework presentedherein.Formulationoftheshipdesignprocedureinthe frameworkofamulti-objectiveoptimizationproblem,wherewash reductionisoneoftheobjectivefunctions,allowstheapplication offormaloptimizationmethodstoderivetheoptimumhullform subjecttotheownersrequirementsandtechnicalandregulatory constraints.Otherobjectivefunctionsmightbethevesselstotal resistance,seaworthiness,dynamicstabilityandsoon,provided thatadequatenumericaltoolsareavailablefortheirreliableandef- ficientcalculation.Inaddition,optimizationcriteriareflectingthe vesselseconomicpotential,likethebuildingandoperationalcosts, transportcapacity,netpresentvalueorrequiredfreightrate,may alsobeused. ThepresentstudyatNTUA SDLisfocusingprimarilyonthe minimizationofpoweringandtheenvironmentalimpactscaused byexcessivewashwaves.Thustheselectedobjectivefunctionsare limitedtototalresistanceandwashwaveminimization.Tofurther simplify the calculations, the effect of the vessels propulsion system,eitherwater-jetsorpropellers,onthegeneratedwash waveshasbeenomitted.Omissionofobjectivefunctionsreflecting theeconomicperformanceofthevesselsispartlyjustifiedbythe imposedconditionofconstanttransportcapacity.Inpracticethis A.Papanikolaou/Computer-Aided Fig. 2. Genericshipdesign TheuseofMultipleObjectivesGeneticAlgorithms(MOGAs), combinedwithgradient-basedsearchtechniquesinmicro-scale explorationandwithautilityfunctionstechniqueforthedesign evaluation,isadvancedinthepresentpaperasagenerictype optimizationtechniqueforgeneratingandidentifyingoptimized designsthrougheffectiveexplorationofthelarge-scale,nonlinear designspaceandamultitudeofevaluationcriteriaoccurringin shipdesign.Severalapplicationsofthisgeneric,multi-objective shipdesignoptimizationapproachbyuseofNTUA SDL3sdesign software system, integrating the naval architectural software package NAPA r , 4 the optimization software modeFRONTIER r 5 andvariousapplicationsoftwaretools,asnecessaryforthe evaluationofstability,resistance,seakeeping,etc.maybefound inthelistedreferences(seeFig.3,asketchofthegeneralapproach tothegenericshipdesignoptimizationproblem). Sometypicalexamplesofapplicationoftheintroducedgeneric shipdesignoptimizationprocedureofNTUA SDLarepresented andbrieflycommentedoninthefollowing. 4 NAPAOy(2005),NAPAsoftware,http:/www.NAPA.fi/. 5 E.STE.CO(2003),modeFrontiersoftwarev.2.5.x,http:/www.esteco.it/. Design42(2010)1028 1044 1031 optimizationproblem. Fromtheconceptualpointofview,longandslenderhullforms are recognized for their favorable resistance and wash chara- cteristics.Increasedseparationdistanceoftwin-hullvesselswill generally result in wave resistance and wash wave reduction. Unfortunately,theselectionofavesselsmainparticularsisacom- promiseofnumerousconsiderationsandconstraints,andthuscan- notbedictatedonlybylowwashrequirements.Therefore,the integrationofawashminimizationmethodologyinthedesignpro- cess,preferablyintheveryfirststages,whenthevesselsmainpar- ticularsaredefinedandthehullformisdeveloped,isbecominga prerequisitetoreducetheimpactofregulatoryspeedlimitations thatwilldrasticallyimpairthevesselsultimateeconomicpoten- tial.Ifsuchamethodologyistobeefficient,areliablewashpredic- tionnumericalmethodhastobeavailable.Althoughwashwave predictionisnotatallasimpleproblem,particularlyforvesselsin thesemi-planningandplanningcondition,recentprogressinCFD resultedinthedevelopmentofsoftwaretools,eitherbasedonthe KelvinorRankinesourcedistributionsthatcanbeusedwithagood isascertainedbytherequirementsforaspecifiedminimumRo Ro cargodeckareaandconstantdisplacement. ship application,dependingonthekindofwasheffectstobeassessed. In the present study, basically aimed at demonstrating the potentialoftheoptimizationconcept,asimplewashmeasurehas beenadopted,intheformofanaveragewaveheightWalonga longitudinalwavecutatacertaindistancefromthevesselscenter line: WD s 1 x2 x1 Z x2 x1 .x;y/2dx (1) where .x;y/ is the wave elevation, while x1 and x2 are the startingandendpointsoftheintegrationintervalalongawave cut. Alternative wash criteria can be easily introduced in the optimizationprocedure, such as the maximumoccurring local waveheight.Waveperiodorwavelengthmaybealsointroduced, combinedwithwaveheighttoobtainawashcriterionexpressing thelocalwaveenergydensity.Forthesolutionofthisoptimization problem,thegenericprocedureoutlinedinFig.2hasbeenapplied. 3.1.2.Referencevessels Tworeferencehigh-speedvesselshavebeenselectedforthe demonstrationoftheoutlinedoptimizationprocedure,namelya high-speedmonohullandatwin-hullvessel.Relevantworkhas beenconductedwithintheEU-fundedprojectFLOWMART16,17. TheselectedmonohullvesselistheCorsaire11000,byLeroux- Navale.Thevesselsmaintechnicalcharacteristicsarelistedin Table1. toadepthFroudenumberFnh D 0:641.Duetothenarrow beamofthetowingtank,significantreflectionswereexpected toaffectthemeasuredwashwaves.Therefore,calculationshave beenperformedforthevesselinunrestrictedwaterwidthand 90mdepth(fullscale)andalsoinachannelofwidthanddepth correspondingtothedimensionsofthetowingtank.Comparison ofthepredictedvs.measuredresultsat0:25Land0:5Ltransverse distanceoffcenterline(CL)arepresentedinFigs.4and5. Inthefirstpartofthewavecutsandforapproximatelythree ship lengths from the bow, the effect from the limited chan- nelwidthonthenumericalpredictionsiscomparativelyweak. Furtheraft,thiseffectincreasessignificantlywiththepredictions forthevesselinthechannelcomparingmuchbetterwiththeex- perimentalmeasurements.Averysteepwavecrest,approximately twoshiplengthsfromthebow,canbeobservedintheexperimen- talresultsforthewavecutat0:25L.Thiswavecrestisapprox- imately50%highercomparedtothenumericalpredictions.The samephenomenonisvisibleinthewavecutat0:5L,whereasteep waveobservedintheexperimentalmeasurementsbetween300m and400mfromthebowissignificantlyunderpredictedbythenu- mericalresults. Thesecondselectedvesselisthehigh-speedcatamaranRedJet III,designedbyFBM.Thevesselsmaintechnicalcharacteristicsare listedinTable2. With a length Froude number equal to 0.97 this ve