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Chapter 2 Meteorology and Oceanography

1 Meteorology and Oceanography Items to be Considered for Performance Verification1.1 GeneralThefollowingmeteorologyandoceanographyitems,shallbeconsideredwithregardtotheperformanceverificationofportfacilities.

Atmosphericpressureanditsdistributionarefactorsthatgeneratewinds.

Windsgeneratewavesandstormsurge,andaffectthewindpressurethatactsuponportfacilitiesandmooredvessels,andbecomeafactortointerferewithcargohandlingandotherportoperations.See2 Windsfordetails.

The tidal level affects soil pressure andwater pressure,which act onport facilities, andbecomes a factor tointerferewithcargohandlingandotherportoperations.Also,ithasaneffectonwavesinareasofshallowwater.See3 Tidal levelfordetails.

Wavesexertwaveforceonportfacilities,andbecomeafactortointerferewiththefunctioningofportfacilities.Theyalsoactonmooredvessels,causingthemtomoveandinterferewithcargohandlingandotherportoperations.Theyalsocanraisethemeanwaterlevel,whichhaseffectssimilartothetidallevelasmentionedabove.See4 Wavesfordetails.

Tsunamiexertswaveforceandfluidforceonportfacilities,andbecomesafactortointerferewiththefunctioningofportfacilities.Italsoactsonmooredships,causingthemtomove.See5 Tsunamisfordetails.

Watercurrentsaffectsedimentsontheseabottomandbecomeafactortointerferewiththefunctioningofportfacilities.See6 Water Currents etc.fordetails.

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2 WindsPublic NoticeWinds

Article 6Characteristicsofwindsshallbesetbythemethodsprovidedinthesubsequentitemscorrespondingtothesingleactionorcombinationoftwoormoreactionstobeconsideredintheperformancecriteriaandtheperformanceverification:(1) Oceansurfacewinds tobeused in theestimationofwavesandstormsurge shallbeappropriately

definedintermsofwindvelocity,winddirectionandothersbasedonthelong-termwindobservationorweatherhindcasting.

(2) Windstobeusedinthecalculationofwindpressuresshallbeappropriatelydefinedintermsofthewindvelocityanddirectioncorrespondingtothereturnperiodthroughthestatisticalanalysisofthelong-termdataofobservedorhindcastedwindsorothermethods.

(3) Windstobeusedinthecalculationofwindenergyshallbeappropriatelydefinedintermsofthejointfrequencydistributionofwindvelocityanddirectionforacertaindurationoftime,basedonthelong-termdataofobservedorhindcastedwinds.

[Commentary]

1) WindstobeusedintheEstimationofWavesandStormSurge:Windstobeusedintheestimationofwavesandstormsurgeshallbeobservedorhindcastedvaluesfor30yearsormoreasastandard.

2) WindstobeusedintheCalculationofWindPressure:Windstobeusedinthecalculationofwindpressureshallbeobservedorhindcastedvaluesfor30yearsormoreasastandard.

[Technical Note]

2.1 General

(1)Windisoneofthemostdistinctivemeteorologicalphenomena,namely,thephenomenonthattheairmovesduetoatmosphericpressuredifferencesandheat.Theconditionsunderwhichwindsblowovertheoceanareusuallyverydifferentthanforthoseoverland.Windvelocitiesovertheoceanaremuchhigherthanthoseoverlandneartheshore.1)Forperformanceverificationofportfacilities,theeffectsofwindsmustbeappropriatelyevaluated.

(2)GradientWinds

Thevelocityofthegradientwindcanbeexpressedasafunctionofpressuregradient,radiusofcurvatureofbarometicisolines,latitude,andairdensityasinequation(2.1.1).

(2.1.1)

where Vg :velocityofgradientwind(m/s);inthecaseofananticyclone,equation(2.1.1)givesanegative

valueandsotheabsolutevalueshouldbetaken. p/r :pressuregradient(takentobepositiveforacyclone,negativeforananticyclone)(kg/m2/s2) r :radiusofcurvatureofbarometicisolines(m) :angularvelocityofEarth'srotation(1/s) =7.2710-5/s :latitude() a :densityofair(kg/m3)

Beforeperformingthecalculation,measurementunitsshouldfirstbeconvertedintotheMKSunitslistedabove.Notethat1oflatitudecorrespondstoadistanceofapproximately1.11105m,andanairpressureof1.0hPais100kg/m/s2.

PART II ACTIONS AND MATERIAL STRENGTH REQUIREMENTS, CHAPTER 2 METROLOGY AND OCEANOGRAPHY

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Agradientwindforwhichthebarometicisolinesarestraightlines(i.e.,theirradiusofcurvatureinequation(2.1.1)isinfinite)iscalledthegeostrophicwind.Inthiscase,thewindvelocityisasequation (2.1.2).

(2.1.2)

Theactualseasurfacewindvelocityisgenerallylowerthanthevalueobtainedfromthegradientwindequation.Moreover, although the direction of a gradientwind is parallel to the barometic isolines in theory, the seasurfacewindblowsatacertainangletothebarometicisolinesinrealityasillustratedinFig. 2.1.2.Inthenorthernhemisphere,thewindsaroundacycloneblowinacounterclockwisedirectionandinwards,whereasthewindsaroundananticycloneblowinaclockwisedirectionandoutwards.Itisknownthattherelationshipbetweenthevelocityofgradientwindsandthatoftheactualseasurfacewindvarieswiththelatitude.ThisrelationshipundertheaverageconditionsissummarizedasinTable 2.1.1.3)

Low

High

(a) Cyclone (b) Anticyclone

Fig. 2.1.2 Wind Direction for a Cyclone (Low) and an Anticyclone (High)

Table 2.1.1 Relationship between Sea Surface Wind Speed and Gradient Wind SpeedLatitude() 10 20 30 40 50

Angle() 24 20 18 17 15

VelocityratioVs /Vg 0.51 0.60 0.64 0.67 0.70

(3)TyphoonWindsIncalculationsconcerningthegenerationofstormsurgeorwavesduetoatyphoon,itiscommontoassumethattheairpressuredistributionfollowseitherFujitasequation (2.1.3)4)or Myers equation (2.1.4) 4);theconstantsinthechosenequationaredeterminedbasedonactualairpressuremeasurementsintheregionoftyphoons.

Fujitasformula

(2.1.3)

Myersformula

(2.1.4)

where p :airpressureatadistancer fromthecenteroftyphoon(hPa) r :distancefromthecenteroftyphoon(km) pc :airpressureatthecenteroftyphoon(hPa) r0 :estimateddistancefromthecenteroftyphoontothepointwherethewindvelocityismaximum

(km) p :airpressuredropatthecenteroftyphoon(hPa) p=p-pc p :airpressureatr =(hPa); p=pc+p

Thesizeofatyphoonvarieswithtime,andso r0andp mustbedeterminedasthefunctionsoftime

(4)MeteorologicalGPVOrganizations such as the Japan Meteorological Agency, the European Center for Medium-Range Weather

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Forecasts(ECMWF),andAmericasNationalCenterforEnvironmentalProtection(NCEP),calculatethevaluesofitemssuchasairpressure,windvelocity,winddirection,andwatervaporflux,basedoncalculationmodelsformeteorologicalvaluesthatuseathree-dimensionalcalculationgrid,andthevaluesatthegridpoints(GPV:gridpointvalues)aresaved.TheseGPVsmaybeusedinsteadofwindhindcastingsbasedonequation (2.1.1) throughequation (2.1.4). However,whenagridwithlargespacingisusedformeteorologicalcalculationstheatmosphericpressureandwindsmaynotbesatisfactorilyreproducedatplaceswheremeteorologicalconditionschangedrasticallywithposition,suchasnear thecentersof typhoons. Therefore,whenGPVsareused, it ispreferabletouseobservationalvaluestoverifytheprecision.

(5)WindEnergyIfwindsareconsideredasthemovementoftheairthenthewindenergythatcrossesaunitcross-sectionalareainunittimeisgivenbyequation(2.1.5).1) Winds forestimating thewindenergyshallbeappropriatelyspecifiedwith jointstatisticdistributions forvelocity and direction for a fixed time (usually, one year), based on long-term (usually, three years ormore)observedorhindcasteddata.

(2.1.5)

where P :windforceenergyperunitcross-sectionalarea(W/m2) a :airdensity(kg/m3) V :windvelocity(m/s)

Inotherwords,thewindforceenergyisproportionaltothecubeofthewindvelocity,soasmalldifferenceinwindvelocitycanmeanabigdifferenceinenergy(powergeneration).Therefore,duringperformanceverificationoffacilitiesthatusewindforceenergy,itisimportanttoaccuratelyunderstandhowtheconditionschangewithregardtotimeandspace. Inthecoastalzonethewindconditionsvariesdrasticallybetweenlandandsea.Also,windvelocityshowsgreatvariationonlandduetoaltitude,butovertheseathechangesinwindvelocitywithaltitudearegradual,soitispossibletoobtainhighlystabilizedwindsthatareappropriateforpowergenerationatrelativelylowaltitudes.Forexample,theresultsofmeasurementsinthevicinityoftheKansaiInternationalAirport,showthatthewindenergyoverthecourseofayearatameasurementtower(MTstation)placedataheightof15metersovertheoceanwereroughlythesameasatalandstation(Cstation)withanaltitudeof100meters,andaboutfivetimesgreaterthanatalandstationwithanaltitudeof10meters.5)

2.2 Characteristic Values of Wind Velocity

(1)DeterminationofWindCharacteristicsTheelementsofwindsaredirectionandvelocity,wherethewinddirectionisexpressedasoneofsixteendirectionsand thewindvelocity is themeanvelocityover10minutes. Thevelocityofwinds thatactsdirectlyonportfacilitiesandmooredshipsisspecifiedingeneralasavelocityforacertainperiodofoccurrence,asestimatedfromtheprobabilityofoccurrencedistributionofwindvelocitybasedonlong-termmeasuredvaluesover30yearsormore.Usingtheannualmaximum10-minutemeanwindvelocitiesoverabout35years,basedonMeasurementTechnicalDataSheet#34oftheJapanMeteorologicalAgency,7)andassumingadoubleexponentialdistribution,theexpectedwindvelocitiesover5,10,20,50,100,and200yearshavebeencalculatedat141meteorologicalstations. Forperformanceverificationoffacilities, thesedatacanbeusedasreferencevalues,however if thelocationofstudyhasdifferenttopographicalconditionsfromtheclosestofthesemeteorologicalstationsthenitisnecessarytotakemeasurementsforatleastoneyeartodeterminetheeffectofthetopography.8)

(2)Thewindvelocitiesobtainedatthemeteorologicalstationsarethevaluesatabout10metersabovetheground.Therefore,whenusingthemeasuredvaluestoestimatethewindsovertheocean,iftheheightofthetargetfacilityisverydifferentfromtheheightmentionedabove,thencorrectionoftheheightshallbeperformedforthewindvelocity.Theverticaldistributionofwindvelocityisusuallyshownonalogarithmicscale,howeverforsimpli