路桥专业外文翻译中英对照Word格式.docx
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路桥专业外文翻译中英对照Word格式.docx
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专业班级09路桥1班
Aconvection-conductionmodelforanalysisofthefreeze-thawconditionsinthesurroundingrockwallofatunnelinpermafrostregions
Abstract
Basedontheanalysesoffundamentalmeteorologicalandhydrologicalconditionsatthesiteofatunnelinthecoldregions,acombinedconvection-conductionmodelforairflowinthetunnelandtemperaturefieldinthesurroundinghasbeenconstructed.Usingthemodel,theairtemperaturedistributionintheXiluoqiNo.2Tunnelhasbeensimulatednumerically.Thesimulatedresultsareinagreementwiththedataobserved.Then,basedontheinsituconditionsofsirtemperature,atmosphericpressure,windforce,hydrogeologyandengineeringgeology,theair-temperaturerelationshipbetweenthetemperatureonthesurfaceofthetunnelwallandtheairtemperatureattheentryandexitofthetunnelhasbeenobtained,andthefreeze-thawconditionsattheDabanshanTunnelwhichisnowunderconstructionispredicted.
Keywords:
tunnelincoldregions,convectiveheatexchangeandconduction,freeze-thaw.
AnumberofhighwayandrailwaytunnelshavebeenconstructedinthepermafrostregionsandtheirneighboringareasinChina.Sincethehydrologicalandthermalconditionschangedafteratunnelwasexcavated,thesurroundingwallrockmaterialsoftenfroze,thefrostheavingcauseddamagetothelinerlayersandseepingwaterfrozeintoicediamonds,whichseriouslyinterferedwiththecommunicationandtransportation.SimilarproblemsofthefreezingdamageinthetunnelsalsoappearedinothercountrieslikeRussia,NorwayandJapan.Henceitisurgenttopredictthefreeze-thawconditionsinthesurroundingrockmaterialsandprovideabasisforthedesign,constructionandmaintenanceofnewtunnelsincoldregions.
Manytunnels,constructedincoldregionsortheirneighboringareas,passthroughthepartbeneaththepermafrostbase.Afteratunnelisexcavated,theoriginalthermodynamicallyconditionsinthesurroundingsareandthawdestroyedandreplacedmainlybytheairconnectionswithouttheheatradiation,theconditionsdeterminedprincipallybythetemperatureandvelocityofairflowinthetunnel,thecoefficientsofconvectiveheattransferonthetunnelwall,andthegeothermalheat.Inordertoanalyzeandpredictthefreezeandthawconditionsofthesurroundingwallrockofatunnel,presumingtheaxialvariationsofairflowtemperatureandthecoefficientsofconvectiveheattransfer,LunardinidiscussedthefreezeandthawconditionsbytheapproximateformulaeobtainedbySham-sundarinstudyoffreezingoutsideacirculartubewithaxialvariationsofcoolanttemperature.Wesimulatedthetemperatureconditionsonthesurfaceofatunnelwallvaryingsimilarlytotheperiodicchangesoftheoutsideairtemperature.Infact,thetemperaturesoftheairandthesurroundingwallrockmaterialaffecteachothersowecannotfindthetemperaturevariationsoftheairflowinadvance;
furthermore,itisdifficulttoquantifythecoefficientofconvectiveheatexchangeatthesurfaceofthetunnelwall.Thereforeitisnotpracticabletodefinethetemperatureonthesurfaceofthetunnelwallaccordingtotheoutsideairtemperature.Inthispaper,wecombinetheairflowconvectiveheatex-changeandheatconductioninthesurroundingrockmaterialintoonemodel,andsimulatethefreeze-thawconditionsofthesurroundingrockmaterialbasedontheinsituconditionsofairtemperature,atmosphericpressure,windforceattheentryandexitofthetunnel,andtheconditionsofhydrogeologyandengineeringgeology.
1.Mathematicalmodel
Inordertoconstructanappropriatemodel,weneedtheinsitufundamentalconditionsasaba-sis.HereweusetheconditionsatthesceneoftheDabanshanTunnel.TheDabanshanTunnelislo-totedonthehighwayfromXiningtoZhangye,southoftheDatongRiver,atanelevationof801.23m,withalengthof1530mandanalignmentfromsouthwesttonortheast.Thetunnelrunsfromthesouthwesttothenortheast.
Sincethemonthly-averageairtemperatureisbeneath0`}Cforeightmonthsatthetunnelsiteeachyearandtheconstructionwouldlastforseveralyears,thesurroundingrockmaterialswouldbecomecoolerduringtheconstruction.Weconcludethat,afterexcavation,thepatternofairflowwoulddependmainlyonthedominantwindspeedattheentryandexit,andtheeffectsofthetemperaturedifferencebetweentheinsideandoutsideofthetunnelwouldbeverysmall.Sincethedominantwinddirectionisnortheastatthetunnelsiteinwinter,theairflowinthetunnelwouldgofromtheexittotheentry.Eventhoughthedominantwindtrendissoutheasterlyinsummer,consideringthepressuredifference,thetemperaturedifferenceandthetopographyoftheentryandexit,theairflowinthetunnelwouldalsobefromtheexittoentry.Additionally,sincethewindspeedatthetunnelsiteislow,wecouldconsiderthattheairflowwouldbeprincipallylaminar.
Basedonthereasonsmentioned,wesimplifythetunneltoaroundtubeandconsiderthattheairflowandtemperaturearesymmetricalabouttheaxisofthetunnel,Ignoringtheinfluenceoftheairtemperatureonthespeedofairflow,weobtainthefollowingequation:
wheret,x,rarethetime,axialandradialcoordinates;
U,Vareaxialandradialwindspeeds;
Tistemperature;
pistheeffectivepressure(thatis,airpressuredividedbyairdensity);
visthekinematicviscosityofair;
aisthethermalconductivityofair;
Listhelengthofthetunnel;
Ristheequivalentradiusofthetunnelsection;
Disthelengthoftimeafterthetunnelconstruction;
(t),
(t)arefrozenandthawedpartsinthesurroundingrockmaterialsrespectively;
and
arethermalconductivitiesandvolumetricthermalcapacitiesinfrozenandthawedpartsrespectively;
X=(x,r),
(t)isphasechangefront;
Lhisheatlatentoffreezingwater;
andToiscriticalfreezingtemperatureofrock(hereweassumeTo=-0.1℃).
forsolvingthemodel
Equation
(1)showsflow.Wefirstsolvethoseconcerningtemperatureatthatthetemperatureofthesurroundingrockdoesnotaffectthespeedofairequationsconcerningthespeedofairflow,andthensolvethoseequationseverytimeelapse.
2.1Procedureusedforsolvingthecontinuityandmomentumequations
Sincethefirstthreeequationsin
(1)arenotindependentwederivethesecondequationbyxandthethirdequationbyr.Afterpreliminarycalculationweobtainthefollowingellipticequationconcerningtheeffectivepressurep:
Thenwesolveequationsin
(1)usingthefollowingprocedures:
(i)AssumethevaluesforU0,V0;
(ii)substitutingU0,V0intoeq.
(2),andsolving
(2),weobtainp0;
(iii)solvingthefirstandsecondequationsof
(1),weobtainU0,V1;
(iv)solvingthefirstandthirdequationsof
(1),weobtainU2,V2;
(v)calculatingthemomentum-averageofU1,v1andU2,v2,weobtainthenewU0,V0,thenreturnto(ii);
(vi)iteratingasaboveuntilthedisparityofthosesolutionsintwoconsecutiveiterationsissufficientlysmallorissatisfied,wethentakethosevaluesofp0,U0andV0astheinitialvaluesforthenextelapseandsolvethoseequationsconcerningthetemperature..
2.2Entiremethodusedforsolvingtheenergyequations
Asmentionedpreviously,thetemperaturefieldofthesurroundingrockandtheairflowaffecteachother.Thusthesurfaceofthetunnelwallisboththeboundaryofthetemperaturefieldinthesurroundingrockandtheboundaryofthetemperaturefieldinairflow.Therefore,itisdifficulttoseparatelyidentifythetemperatureonthetunnelwallsurface,andwecannotindependentlysolvethoseequationsconcerningthetemperatureofairflowandthoseequationsconcerningthetemperatureofthesurroundingrock.Inordertocopewiththisproblem,wesimultaneouslysolvethetwogroupsofequationsbasedonthefactthatatthetunnelwallsurfacebothtemperaturesareequal.Weshouldbearinmindthephasechangewhilesolvingthoseequationsconcerningthetemperatureofthesurroundingrock,andtheconvectionwhilesolvingthoseequationsconcerningthetemperatureoftheairflow,andweonlyneedtosmooththoserelativeparametersatthetunnelwallsurface.Thesolvingmethodsfortheequationswiththephasechangearethesameasinreference[3].
Determinationofthermalparametersandinitialandboundaryconditions
Determinationofthethermalparameters.Usingp=H,wecalculateairpressurepatelevationHandcalculatetheairdensity
usingformula
whereTistheyearly-averageabsoluteairtemperature,andGisthehumidityconstantofair.Letting
bethethermalcapacitywithfixedpressure,
thethermalconductivity,
thedynamicviscosityofairflow,wecalculatethethermalconductivityandkinematicviscosityusingtheformulas
and
.Thethermalparametersofthesurroundingrockaredeterminedfromthetunnelsite.
Determinationoftheinitialandboundaryconditions.Choosetheobservedmonthlyaveragewindspeedattheentryandexitasboundaryconditionsofwindspeed,andchoosetherelativeeffectivepressurep=0attheexit(thatis,theentryofthedominantwindtrend)and
onthesectionofentry(thatis,theexitofthedominantwindtrend),wherekisthecoefficientofresistancealongthetunnelwall,d=2R,andvistheaxialaveragespeed.WeapproximateTvaryingbythesinelawaccordingtothedataobservedatthesceneandprovideasuitableboundaryvaluebasedonthepositionofthepermafrostbaseandthegeothermalgradientofthethawrockmaterialsbeneaththepermafrostbase.
3Asimulatedexample
Usingthemodelandthesolvingmethodmentionedabove,wesimulatethevaryin
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