Aeronautical Engineering - Wind Engineering

Completed notes of the course

Complete course

Wind engineering Wind climate AT M O S P H E R E•THEAT M O S P H E R EISACLOUDOFGASANDSUSPENDEDSOLIDS-THE99,99997'-OFITSMASSISBELOW100kmLAYERS1)TROPOSPHERE•0-1216km•ITCONTAINSTHE80e.OFTHEMASSOFTHEAT M O S P H E R E•NEARLYAllTHEWEATHERPHENOMENAOCCURHERE2)STRATOSPHERE•AIRISEXTREMELYDRYANDOZONERICH'THEABSORPTIONOFSOLARRADIATIONISTHEREASONWHYTEMPERATUREINCREASESWITHHEIGHT3)MESOSPHERE 4) THERMOSPHERESCALESOFAT M O S P H E R I CMOTION'METER-50LOGICALPHENOMENAINVOLVINGWINDGENERATIONOCCUROVERAWIDERANGEOFSPACEANDTIMESCALESLARGETIMESCALESAREASSOCIATEDTOLARGESPACESCALESANDVICE-VERSA:•THEMOVEMENTOFAT M O S P H E R EAROUNDTHEGLOBEISAMIXTUREOFDIFFERENTSCALEMOTIONS GLOBALCIRCULATION•SEASONALTIMESCALE+PLANETARYLENGHTSCALEMODERATEWINDS:SMALLIMPACTONSTRUCTURES,BIGIMPACTONCLIMATEINCOMINGSOLARRADIATION•THESUNRADIATESMOSTLYINTHEVISIBLEBAND,BUTALSOINTHEULTRAVIOLETBAND-ANNUALLYANDGLOBALLYTHEINCOMINGSOLARRADIATIONISABOUT3.42VVMZ101"aDIRECTLYABSORBEDBYTHEAT M O S P H E R E020m05HERESELECTIVELYABSORBWV49..ABSORBEDBYTHESURFACE&e-REFLECTEDB.ACKINTOSPACEBYTHESURFACE23'.REFLECTEDBACKINTOSPACEBYTHECLOUDSOUTGOINGTERRESTRIALRADIATION-THEEARTH'SSURFACE,AT M O S P H E R EANDCLOUDSEMITSRADIATIONINTHEINFRAREDGLOBALENERGYBALANCE-MEANOVERYEARS:POWERIN=POWEROUTLATITUDINALANDSEASONALVA R I AT I O N SMUSTBEINCLUDEDINTHEANALYSIS•THEVA R I AT I O NOFTHENETRADIATIONDEPENDINGONTHELATITUDEISTHEPRIMARYMECHANISMTHATDRIVESTHEAT M O S P H E R I CANDOCEANICCIRCULATIONS ENERGYBUDGETBYLATITUDE•TROPICTOTROPICiENERGYSURPLUS38°.•POLES:ENERGYDEFICIT/EQUILIBRIUM38°.•ASPREVIOUSLYSHOWN,colossalCIRCULATIONARISESBECAUSEOFTHEENERGYUNBALANCEOVERDIFFERENTALTITUDESSINGLECELLMODEL-HADLEY(1-735)•SIMPLIFYINGASSUMPTIONSI1)EARTHISNOTROTATINGNOCORIOLISEFFECT2)EARTHISCOMPOSEDOFSIMILARMATERIALS3)TITEGLOBALRECEPTIONOFSOLARINSOLATIONANDLOSSOFLONGWAVERADIATION(VV)CAUSEATEMPERATUREGRADIENTWITHHOTAIRATTHEEQUATORANDCOLDAIRATTHEPOLESHEIGHTISOBARS•NOPRESSUREGRADIENTNOWINDHEIGHT•EQUATOR:ITRECEIVESMORESOLARRADIATION,AIRWA R M SUPANDRISES•THEVERTICALDISTANCEBETWEENTHEISOBARSBECOMESGREATERASTHEAIRRISES•POLES:LESSSOLARRADIATIONISRECEIVEDANDAIRCOOLSDOWN •CONTINUITY:AIRCAN'TACCUMULATEINTHEPOLESTHREE-CELLSMODEL(19205)-EARTH'SROTATIONISINTRODUCEDCORIOLISEFFECT•INSTEADOFWINDBLOWINGDIRECTLYFROMHIGHTOLOWPRESSURE,THEROTATIONOFTHEEARTHCAUSESWINDTOBEDEFLECTEDTHESTRONGERISWINDTHEMOREIT'SDEFLECTED•THE3CELLSAREASSOCIATEDWITH3PRESSUREBELTSSECONDARYCIRCULATION•DAILY-WEEKLYTIMESCALES•100-1000kmLENGHTSCALES•WINDSINHIGHANDLOWPRESSUREZONESDUETOTHECOOLINGORHEATINGOFLOWERAT M O S P H E R I CLAYERS◦RELEVANTWINDSPEED•HIGHINFLUENCEONLOCALWEATHER •COLORS:INTENSITYOFTHEWIND-CYCLONES:howP,BADWEATHER•ANTICYCLONES:HIGHP,NICEWEATHER°ISOBARSAREUSUALLYPLOTTEDATUNIFORMINCREMENTS•THELOCALPRESSUREGRADIENTISORTHOGONALTOTHEISOBARSANDORIENTEDFROMLOWTOHIGHPRESSURETHESTRENOHTOFTHEPRESSUREGRADIENTISINVERSELYPROPORTIONALTOTHEHORIZONTALSPACINGBETWEENISOBARSHIGHGRADIENT=INTENSEWINDGEOSTROPHICWINDAPPROXIMATION•LET'SCONSIDERA2DCASEINWHICHISOBARSARESTRAIGHTLINES([email protected])•JLZiEARTH'SANGULARSPEEDPROJECTEDONZa)GRADIENTP=①PISNORMALTOTHEISOBARS-It b) DUETO-PTHEPARTICLESTARTSMOVINGFROMHIGHPTOLOWPWITHVELOCITYVt-•REMARK:U= V1 °CORIOLISACCELERATION: If =2≥^V1'CORIOLISFORCE:Fc= }f- UWITH f- =2525170C)CORIOLISFORCESTARTSDEFLECTINGTHEPARTICLEPATH d) THEPARTICLEKEEPSTURNINGRIGHTUNTILTHEVELOCITYVECTORV1ISPARALLELTOTHEISOBARSINTHISSITUATIONTHEREISC-Quit'BRLUMBETWEENTHEPRESSUREGRADIENTFORCEANDTHECORIOLISFORCE/STATIONARYSCENARIO ) INTHEGEOSTROPHICAPPROXIMATIONWINDBLOWSPARALLELTOTHEISOBARS•IFTHEEARTHDIDN'TROTATEWINDWOULDfollowPERPENDICULARTOTHEISOBARSFROMHTOL GRADIENTWINDAPPROXIMATION•LET'SCONSIDERA2DCASEINWHICHISOBARSHAVEACURVATUREWHICHISNOTNEGLIGIBLE:FORSIMPLICITYWECONSIDERCIRCULARCONCENTRICISOBARS-INTHISCASETOEVALUATETHEEQUILIBRIUMCONDITIONOFTHEPARTICLEWEALSONEEDTOTA K EINTOACCOUNTTHECENTRIPETALACCELERATION,HENCETHECENTRIFUGALINERTIAFORCE(0WP:CICCONE•ATTHECENTER:HIGHP:ANTICYCLONELOCALWINDSYSTEMS◦HOURLYTIMESCALES•1-10kmLENGHTSCALES◦MODERATETORELEVANTWINDSPEEDS•AFFECTSLOCALWEATHERSYSTEMS,WHICHDEPENDONTHERMALOROGRAPHICEFFECTSGRADIENTWINDAPPROXIMATION•CORIOLISFORCECANBENEGLECTED Atmospheric boundary layer AT M O S P H E R I CBOUNDARYLAYER'FRICTIONFORCESCAUSEDBYTHETERRAINMAKETHEFLOWATU2BOLENTFLOWTHATVA R I E SRANDOMLYB.0THINSPACEANDTIME•GRADIENTHEIGHT/2-f):HEIGHTWHERETHEEFFECTSOFSURFACEFRICTIONAREZEROEKMANSPIRAL•THESURFACESHEARSTRESSMODIFIESTHEGEOSTROPHICEQUILIBRIUM,HENCETHEWINDVECTOR,WHICHWA SPARALLELTOTHEISOBARS,TURNSINTRODUCINGACOMPONENTTOWARDSTHELOWPRESSURE°THETYPICALTURNISABOUT20°THROUGHTHEABLWINDCHARACTERISTICS•WINDMEASUREMENTSAREUSUALLYTA K E NATTHESTANDARDHEIGHTOF10MINLOCATIONSFARFROMOBSTACLESWHERETEMPERATUREANDHUMIDITYMEASU@MENTSAREPERFORMEDAVO I D I N GDIRECTSOLARRADIATION.1)THEWINDSPEEDPROFILEVA R I E SIRREGULARLY,REVEALINGITSTURBULENTNATURESTATISTICALMETHODSMUSTBEUSED 2) ITCANBEIDENTIFIEDAMEANWINDSPEEDOVERTHEDAYDURATION 3) FLUCTUATIONSCOVERAWIDERANGEOFFREQUENCIES G) THEMEANWINDSPEEDINCREASESWITHTHEHEIGHTFROMTHEGROUND-THERE'SASPACIALCORRELATIONBETWEENTHEGUSTSATDIFFERENTHEIGHT VA NDERHOVENWINDSPECTRUM&ONLYSHORTTERMFLUCTUATIONS(T0=1☐OFINSTABILITY°7☐OFINSTABILITYCANBEEXCITEDIFONEOFTHEDIAGONALTERMSOFISNEGATIVE,WHICHMEANSTHAT C2J SUB-SPANSARESHORTIFTHISSPACERSAREUSEDSPACER-DAMPERS°AFLEXIBLESPACERABLETODISSIPATEASIGNIFICANTAMOUNTOFENERGYISCALLEDSPACER-DAMPER SUB.SPANOSCILLATONS.SU @SPANOCCURSONCONDUCTORBUNDLESANDIT'SDUETOTHEWA K 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