Chapter 2 Meteorology and · PDF fileChapter 2 Meteorology and Oceanography ... Wind is one of...
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PART II ACTIONS AND MATERIAL STRENGTH REQUIREMENTS, CHAPTER 2 METROLOGY AND OCEANOGRAPHY – 57 – Chapter 2 Meteorology and Oceanography 1 Meteorology and Oceanography Items to be Considered for Performance Verification 1.1 General The following meteorology and oceanography items, shall be considered with regard to the performance verification of port facilities. ① Atmospheric pressure and its distribution are factors that generate winds. ② Winds generate waves and storm surge, and affect the wind pressure that acts upon port facilities and moored vessels, and become a factor to interfere with cargo handling and other port operations. See 2 Winds for details. ③ The tidal level affects soil pressure and water pressure, which act on port facilities, and becomes a factor to interfere with cargo handling and other port operations. Also, it has an effect on waves in areas of shallow water. See 3 Tidal level for details. ④ Waves exert wave force on port facilities, and become a factor to interfere with the functioning of port facilities. They also act on moored vessels, causing them to move and interfere with cargo handling and other port operations. They also can raise the mean water level, which has effects similar to the tidal level as mentioned above. See 4 Waves for details. ⑤ Tsunami exerts wave force and fluid force on port facilities, and becomes a factor to interfere with the functioning of port facilities. It also acts on moored ships, causing them to move. See 5 Tsunamis for details. ⑥ Water currents affect sediments on the sea bottom and become a factor to interfere with the functioning of port facilities. See 6 Water Currents etc. for details.
Transcript of Chapter 2 Meteorology and · PDF fileChapter 2 Meteorology and Oceanography ... Wind is one of...
PART II ACTIONS AND MATERIAL STRENGTH REQUIREMENTS, CHAPTER 2 METROLOGY AND OCEANOGRAPHY
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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.
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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
