港航外文翻译Word格式.docx

港航外文翻译Word格式.docx

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PGRemya,RajKumar,SujitBasuandAbhijitSarkar

OceanScienceDivision，AtmosphericandOceanicSciencesGroup,

SpaceApplicationsCentre,Ahmedabad380015,India.

Wavepredictionandhindcaststudiesareimportantinoceanengineering,coastalinfrastructuredevelopmentandmanagement.Inviewofsparseandinfrequentin-situobservations,modelderivedhindcastwavedatacanbeusedfortheassessmentofwaveclimateinoffshoreandcoastalareas.Inthepresentstudy,MIKE21SWModelhasbeenusedtocarryoutwavehindcastexperimentsintheIndianOcean.Modelrunshavebeenmadefortheyear2005usingQuickSCATscatterometerwindsblendedwithECMWFmodelwinds.Inordertostudytheimpactofsouthernoceanswells,themodelhasbeenrunintwodifferentdomains.Themodelsimulatedwaveparametershavebeenvalidatedbycomparingwithbuoyandaltimeterdataandvariousstatisticalyardstickshavebeenemployedtoquantifythevalidation.PossiblereasonforthepoorerperformanceofthemodelintheArabianSeahasalsobeenpointedout.

1.Introduction

Oceanwavehindcastandforecastareofparamountimportanceforthemanagementofoffshorestructureconstruction,shipnavigation,andnavaloperations.In-situobservationsarelocation-specificandgenerallysparse.IntheIndianOceanthesituationisworse,comparedtotheAtlanticandPacific,becauselongtimeseriesdataofin-situobservationsaremostlyunavailable.Ontheotherhand,itissimplyimpossibletoestimatethewaveclimateandextremeseastatewithoutsuchalongtimeseries.Hence,inrecentyears,theattentionisshiftedtotheuseofnumericalwavemodelgeneratedwavedatafortheassessmentofwaveclimate.SverdrupandMunk（1947）werethefirsttodevelopoperationalwavepredictiontechnique.Thetechniquewaspurelystatisticalandwasbasedonjustoneparameter,viz.,thesignificantwaveheight.Inotherwords,thespectralcharacteroftheseastatewascompletelyneglected.Later,thespectralcharacteristicsofwavesweretakenintoaccountforthedevelopmentofmethodsbasedonwavespectrum.Currently,therearemanyspectralwavemodelsforwavehindcastandforecaststudiesintheopenoceanaswellasinthecoastalocean.Inthepresentstudy,MIKE21SWmodelhasbeenutilizedprimarilyforhindcastexperiments.MIKE21SWisanewgenerationspectralwindwavemodel,basedonunstructuredmeshes,andisdevelopedbyDanishHydraulicInstitute（DHI2005）.Themodelsimulatesgrowth,decay,andtransformationofwindgeneratedwavesandswellsinoffshoreandcoastalareas.Asmentionedearlier,theprincipalobjectiveofthepresentstudyistocarryouthindcastexperimentswithMIKE-21modelintheIndianOceanandtovalidatethehindcastswithavailablein-situandremotelysenseddata.Asaspinoff,wehavealsostudiedtheimpactofsouthernoceanwaveconditionsonthewaveconditionsofnorthIndianOcean.

Keywords.Wavemodelling;

MIKE21SW;

swell;

altimeter.

2.Dataandmethodology

MIKE21SWmodelisbasedonflexiblemesh,whichallowsforcoarsespatialresolutionintheoffshoreareaandhighresolutionintheshallowcoastalwaters.MIKE21SWmodelincludestwodifferentformulations:

adirectionaldecoupledparametricformulationandafullyspectralformulationofthewaveactionbalanceequation.Thefirstformulationissuitableonlyfornearshoreconditions,whereasthesecondoneisapplicableinbothnearshoreandoffshoreregions.Hence,inthisstudythesecondformulationhasbeenusedasthestudyareacontainsbothshallowandoffshoreregions.InthefullyspectralformulationthesourcefunctionsarebasedontheWAMCycle4formulation（Komenetal1994）.ThesourcetermfordepthlimitedwavebreakingisbasedontheformulationbyBattjesandJanssen（1978）.AshortdescriptionofthesourcetermcanbefoundinSø

rensenetal（2004）.Inthepresentstudy,themodeldomaincoverstheIndianOceanregion,60°

S~25°

N;

40°

~100°

E.Forthemodelruns,thespatialresolutionhasbeenchosentobe0.25°

inthecoastalwatersand1°

fortherestoftheregion.This,however,doesnotmeanthattheresolutionisconstanteverywhereinthisdomain.MIKE21SWmodelusesaflexiblemeshformodelruns.Theflexiblemeshallowsfineresolutionnearthecoast.Infact,theresolutionreachesasfineas0.003◦nearthecoastintheflexiblebathymetrygridusedforthisstudy.ThebathymetryisfromGEBCO（GeneralBathymetricChartsoftheOcean）producedbyIntergovernmentalOceanographicCommission（2003）.TheresolutionofGEBCObathymetrygridis1×

1minute.ThemodelhasbeenforcedbyQuickSCATscatterometerwindsblendedwithECMWFmodelwinds.ThewinddataareobtainedfromIFREMER,France,andareavailableataspatialresolutionof0.25°

inlongitudeandlatitude.Thequalityoftheblendedwindshasbeencheckedbycomparingthemwithbuoywindsandthecomparisonhasproducedencouragingresults.Thewindspeedcorrelationcoefficientsrangefrom0.80to0.90.TheRMSdifferencebetweenbuoywindsandblendedwindsis<

2m/s.TheJASON1satellitesystemcarryingastate-of-the-artaltimetersensor,launchedonDecember7,2001,isprovidingwindandwave（besidessealevel）informationoverglobaloceansregularly.

3.Modelexperiments

Asmentionedearlier,thebasicobjectiveistocarryouthindcastswithMIKE-21andsubsequentlytovalidatethehindcasts.Forthispurpose,themodelhasbeenearliercalibratedusingnumberofin-situdataofIndianOceanregionandvariousmodelparameterssuchasbreakingparameter,bottomfrictionandwhitecappingweretunedtoprovidebetterwavepredictions.Intheexperiments,wavebreakingparameter（γ=0.5）,bottomfriction（Nikuradseroughness）（KN=0.04m）,andwhitecappingcoefficients（Cdis=3.5）werefoundtobeoptimum.Andthesecoefficientshavebeenusedintheexperimentsperformedforthepresentstudy.However,inordertofulfillthesecondaryobjectiveofstudyingtheimpactofsouthernoceanwavesonthenorthernoceanwavecharacteristics,apartfromtheearlierselectedmodeldomain,asmallerone（10°

S–25°

N,50°

–100°

E）wasalsoselected.Spatialresolutionforthesmallerdomain（Domain10S）modelisidenticalwiththatforthelargerdomain（Domain60S）.Themodelsimulationswereperformedfortheyear2005.Themodelderivedwaveparameterslikesignificantwaveheight（Hs）,swellwaveheight（Hss）,windseaheight（Hsw）,meanwaveperiod（Tm）andmeanwavedirection（MWD）werecomparedwithsimilarparametersobtainedfromNIOTbuoys,mooredintheArabianSea（AS）andBayofBengal（BOB）.

4.Resultsanddiscussions

Asmentionedearlier,performanceofthemodelwasevaluatedbothinthelargerandsmallerdomains.Weevaluatedtheperformanceintermsofsignificantwaveheight,swellheight,windseaheight,meanwaveperiod,meanwavedirectioninbothASandBOB.Inbuoymeasurements,forseaandswellseparation,thewavespectrummeasurementsbetween0.04and0.1Hzisconsideredlowfrequency（swell）componentsandbetween0.1and0.5Hzistakenashighfrequency（sea）components.Modelalsofollowsthesamecriteriafortheseaandswellseparation.Thedefinitionofmeanwaveperiodfromthebuoyis

.Althoughwecomparedthesimulatedandobservedwaveparametersatsixdifferentbuoylocationsforeachofthebasins,theresultsareshownatonlyonerepresentativelocationforeachofthebasins.TheArabianSeaexperiencesthreedifferentseasonsinayear:

pre-monsoon（February–May）,southwestmonsoon（June–September）andnortheastmonsoon（October–January）.Itcanbeseenthatthedeviationismorepronouncedinpremonsoonandnortheast（NE）monsoonseasons.ThisfindingwastrueforallthesixbuoysintheAS.Duringsouthwest（SW）monsoonseason,thewindseasaredominatingandthismightbethereasonforthechangeinperformanceduringSWmonsoon.Duringpre-monsoonseason,largescalewindsareweakandhenceseabreezehasanimpactonthediurnalcycleoftheseastatealongthewestcoastofIndia.ThestudyalsoclearlyshowsthatMIKE21SWmodeliscapableofprovidinggoodqualitysimulationofwindgeneratedwavesandswellsintheoffshoreandcoastalareas.

5.Summary

Inthisstudy,anattempthasbeenmadetocarryouthindcastsofwaveparametersintheIndianOceanusingMIKE21SWmodel.Suchhindcastsareimportantinoceanengineeringandcoastalinfrastructuredevelopmentandmanagement.Avariableresolutionhasbeenusedfortheproperrepresentationofdeepwaterwavesandcoastalwaves.Inordertoevaluatetheeffectofsouthernoceanswells,twodifferentmodeldomainshavebeenchosen.IthasbeenfoundthatthereisindeedasignificantimpactoftheseswellsonthemodelsimulationintheBayofBengalbasin.Allthevalidationresultspointtothefactthattheperformanceofthemodelisquitesatisfactory.HenceitcanbeconcludedwithreasonableconfidencethatthemodelwiththisparticularconfigurationcanservethepurposeofreliablewavehindcastsintheIndianOceanregion.

References

AboobackerVM,VethamonyPandRashmiR2011‘Shamal’swellsintheArabianSeaandtheirinfluencealongthewestcoastofIndia;

Geophys.Res.Lett.38（3）7p,doi:

10.1029/2010GL045736.

BattjesJAandJanssenJPFM1978Energylossandset-upduetowavebreakingofrandomwaves;

Proc.16thInternationalConferenceonCostalEngineering,ASCE,pp.569–587.

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