畢業(yè)論文外文翻譯-密封的建筑排水系統(tǒng)和通氣系統(tǒng)-活性氣壓的瞬變控制和抑制

外文文獻(xiàn)：Sealedbuildingdrainageandventsystems—anapplicationofactiveairpressuretransientcontrolandsuppressionAbstractTheintroductionofsealedbuildingdrainageandventsystemsisconsideredaviablepropositionforcomplexbuildingsduetotheuseofactivepressuretransientcontrolandsuppressionintheformofairadmittancevalvesandpositiveairpressureattenuatorscoupledwiththeinterconnectionofthenetwork'sverticalstacks.Thispaperpresentsasimulationbasedonafour-stacknetworkthatillustratesflowmechanismswithinthepipeworkfollowingbothappliancedischargegenerated,andsewerimposed,transients.Thissimulationidentifiestheroleoftheactiveairpressurecontroldevicesinmaintainingsystempressuresatlevelsthatdonotdepletetrapseals.Furthersimulationexerciseswouldbenecessarytoprovideproofofconcept,anditwouldbeadvantageoustoparallelthesewithlaboratory,andpossiblysite,trialsforvalidationpurposes.Despitethiscautiontheinitialresultsarehighlyencouragingandaresufficienttoconfirmthepotentialtoprovidedefinitebenefitsintermsofenhancedsystemsecurityaswellasincreasedreliabilityandreducedinstallationandmaterialcosts.Keywords:Activecontrol;Trapretention;TransientpropagationNomenclatureC+-——characteristicequationsc——wavespeed,m/sD——branchorstackdiameter,mf——frictionfactor,UKdefinitionviaDarcyΔh=4fLu2/2Dgg——accelerationduetogravity,m/s2K——losscoefficientL——pipelength,mp——airpressure,N/m2t——time,su——meanairvelocity,m/sx——distance,mγ——ratiospecificheatsΔh——headloss,mΔp——pressuredifference,N/m2Δt——timestep,sΔx——internodallength,mρ——density,kg/m3ArticleOutlineNomenclature1.Introduction—airpressuretransientcontrolandsuppression2.Mathematicalbasisforthesimulationoftransientpropagationinmulti-stackbuildingdrainagenetworks3.Roleofdiversityinsystemoperation4.Simulationoftheoperationofamulti-stacksealedbuildingdrainageandventsystem5.Simulationsignconventions6.Waterdischargetothenetwork7.Surchargeatbaseofstack18.Sewerimposedtransients9.Trapsealoscillationandretention10.Conclusion—viabilityofasealedbuildingdrainageandventsystem1.Airpressuretransientsgeneratedwithinbuildingdrainageandventsystemsasanaturalconsequenceofsystemoperationmayberesponsiblefortrapsealdepletionandcrosscontaminationofhabitablespace[1].Traditionalmodesoftrapsealprotection,basedontheVictorianengineer'sobsessionwithodourexclusion[2],[3]and[4],dependpredominantlyonpassivesolutionswhererelianceisplacedoncrossconnectionsandverticalstacksventedtoatmosphere[5]and[6].Thisapproach,whilebothprovenandtraditional,hasinherentweaknesses,includingtheremotenessoftheventterminations[7],leadingtodelaysinthearrivalofrelievingreflections,andthemultiplicityofopenrooflevelstackterminationsinherentwithincomplexbuildings.Thecomplexityoftheventsystemrequiredalsohassignificantcostandspaceimplications[8].Thedevelopmentofairadmittancevalves(AAVs)overthepasttwodecadesprovidesthedesignerwithameansofalleviatingnegativetransientsgeneratedasrandomappliancedischargescontributetothetimedependentwater-flowconditionswithinthesystem.AAVsrepresentanactivecontrolsolutionastheyresponddirectlytothelocalpressureconditions,openingaspressurefallstoallowareliefairinflowandhencelimitthepressureexcursionsexperiencedbytheappliancetrapseal[9].However,AAVsdonotaddresstheproblemsofpositiveairpressuretransientpropagationwithinbuildingdrainageandventsystemsasaresultofintermittentclosureofthefreeairpaththroughthenetworkorthearrivalofpositivetransientsgeneratedremotelywithinthesewersystem,possiblybysomesurchargeeventdownstream—includingheavyrainfallincombinedsewerapplications.Thedevelopmentofvariablevolumecontainmentattenuators[10]thataredesignedtoabsorbairflowdrivenbypositiveairpressuretransientscompletesthenecessarydeviceprovisiontoallowactiveairpressuretransientcontrolandsuppressiontobeintroducedintothedesignofbuildingdrainageandventsystems,forboth‘standard’buildingsandthoserequiringparticularattentiontobepaidtothesecurityimplicationsofmultiplerooflevelopenstackterminations.Thepositiveairpressureattenuator(PAPA)consistsofavariablevolumebagthatexpandsundertheinfluenceofapositivetransientandthereforeallowssystemairflowstoattenuategradually,thereforereducingthelevelofpositivetransientsgenerated.TogetherwiththeuseofAAVstheintroductionofthePAPAdeviceallowsconsiderationofafullysealedbuildingdrainageandventsystem.Fig.1illustratesbothAAVandPAPAdevices,notethatthewaterlesssheathtrapactsasanAAVundernegativelinepressure.Fig.1.Activeairpressuretransientsuppressiondevicestocontrolbothpositiveandnegativesurges.Activeairpressuretransientsuppressionandcontrolthereforeallowsforlocalizedinterventiontoprotecttrapsealsfrombothpositiveandnegativepressureexcursions.Thishasdistinctadvantagesoverthetraditionalpassiveapproach.Thetimedelayinherentinawaitingthereturnofarelievingreflectionfromaventopentoatmosphereisremovedandtheeffectofthetransientonalltheothersystemtrapspassedduringitspropagationisavoided.2.Mathematicalbasisforthesimulationoftransientpropagationinmulti-stackbuildingdrainagenetworks.ThepropagationofairpressuretransientswithinbuildingdrainageandventsystemsbelongstoawellunderstoodfamilyofunsteadyflowconditionsdefinedbytheStVenantequationsofcontinuityandmomentum,andsolvableviaafinitedifferenceschemeutilizingthemethodofcharacteristicstechnique.Airpressuretransientgenerationandpropagationwithinthesystemasaresultofairentrainmentbythefallingannularwaterinthesystemverticalstacksandthereflectionandtransmissionofthesetransientsatthesystemboundaries,includingopenterminations,connectionstothesewer,appliancetrapsealsandbothAAVandPAPAactivecontroldevices,maybesimulatedwithprovenaccuracy.Thesimulation[11]provideslocalairpressure,velocityandwavespeedinformationthroughoutanetworkattimeanddistanceintervalsasshortas0.001

sand300

mm.Inaddition,thesimulationreplicateslocalappliancetrapsealoscillationsandtheoperationofactivecontroldevices,therebyyieldingdataonnetworkairflowsandidentifyingsystemfailuresandconsequences.Whilethesimulationhasbeenextensivelyvalidated[10],itsusetoindependentlyconfirmthemechanismofSARSvirusspreadwithintheAmoyGardensoutbreakin2003hasprovidedfurtherconfidenceinitspredictions[12].Airpressuretransientpropagationdependsupontherateofchangeofthesystemconditions.Increasingannulardownflowgeneratesanenhancedentrainedairflowandlowersthesystempressure.Retardingtheentrainedairflowgeneratespositivetransients.Externaleventsmayalsopropagatebothpositiveandnegativetransientsintothenetwork.Theannularwaterflowinthe‘wet’stackentrainsanairflowduetotheconditionof‘noslip’establishedbetweentheannularwaterandaircoresurfacesandgeneratestheexpectedpressurevariationdownaverticalstack.Pressurefallsfromatmosphericabovethestackentryduetofrictionandtheeffectsofdrawingairthroughthewatercurtainsformedatdischargingbranchjunctions.Inthelowerwetstackthepressurerecoverstoaboveatmosphericduetothetractionforcesexertedontheairflowpriortofallingacrossthewatercurtainatthestackbase.Theapplicationofthemethodofcharacteristicstothemodellingofunsteadyflowswasfirstrecognizedinthe1960s[13].TherelationshipsdefinedbyJack[14]allowsthesimulationtomodelthetractionforceexertedontheentrainedair.Extensiveexperimentaldataallowedthedefinitionofa‘pseudo-frictionfactor’applicableinthewetstackandoperableacrossthewaterannularflow/entrainedaircoreinterfacetoallowcombineddischargeflowsandtheireffectonairentrainmenttobemodelled.ThepropagationofairpressuretransientsinbuildingdrainageandventsystemsisdefinedbytheStVenantequationsofcontinuityandmomentum[9],(1)(2)Thesequasi-linearhyperbolicpartialdifferentialequationsareamenabletofinitedifferencesolutiononcetransformedviatheMethodofCharacteristicsintofinitedifferencerelationships,Eqs.(3)–(6),thatlinkconditionsatanodeonetimestepinthefuturetocurrentconditionsatadjacentupstreamanddownstreamnodes,Fig.2.Fig.2.StVenantequationsofcontinuityandmomentumallowairflowvelocityandwavespeedtobepredictedonanx-tgridasshown.Note,.FortheC+characteristic:(3)when(4)andtheC-characteristic:(5)when(6)wherethewavespeedcisgivenbyc=(γp/ρ)0.5.(7)Theseequationsinvolvetheairmeanflowvelocity,u,andthelocalwavespeed,c,duetotheinterdependenceofairpressureanddensity.Localpressureiscalculatedas(8)Suitableequationslinklocalpressuretoairflowortotheinterfaceoscillationoftrapseals.Thecaseoftheappliancetrapsealisofparticularimportance.Thetrapsealwatercolumnoscillatesundertheactionoftheappliedpressuredifferentialbetweenthetransientsinthenetworkandtheroomairpressure.TheequationofmotionfortheU-bendtrapsealwatercolumnmaybewrittenatanytimeas(9)Itshouldberecognizedthatwhilethewatercolumnmayriseontheapplianceside,converselyonthesystemsideitcanneverexceedadatumleveldrawnatthebranchconnection.Inpracticaltermstrapsealsaresetat75or50

mmintheUKandotherinternationalstandardsdependentuponappliancetype.Trapsealretentionisthereforedefinedasadepthlessthantheinitialvalue.Manystandards,recognizingthetransientnatureoftrapsealdepletionandtheopportunitythatexistsforre-chargeonappliancedischargeallow25%depletion.Theboundaryequationmayalsobedeterminedbylocalconditions:theAAVopeningandsubsequentlosscoefficientdependsonthelocallinepressureprediction.EmpiricaldataidentifiestheAAVopeningpressure,itslosscoefficientduringopeningandatthefullyopencondition.Appliancetrapsealoscillationistreatedasaboundaryconditiondependentonlocalpressure.Deflectionofthetrapsealtoallowanairpathto,orfrom,theapplianceordisplacementleadingtooscillationalonemaybothbemodelled.Reductionsintrapsealwatermassduringthetransientinteractionmustalsobeincluded.3.RoleofdiversityinsystemoperationIncomplexbuildingdrainagenetworkstheoperationofthesystemappliancestodischargewatertothenetwork,andhenceprovidetheconditionsnecessaryforairentrainmentandpressuretransientpropagation,isentirelyrandom.Notwosystemswillbeidenticalintermsoftheirusageatanytime.Thisdiversityofoperationimpliesthatinter-stackventingpathswillbeestablishediftheindividualstackswithinacomplexbuildingnetworkarethemselvesinterconnected.Itisproposedthatthisdiversityisutilizedtoprovideventingandtoallowseriousconsiderationtobegiventosealeddrainagesystems.Inordertofullyimplementasealedbuildingdrainageandventsystemitwouldbenecessaryforthenegativetransientstobealleviatedbydrawingairintothenetworkfromasecurespaceandnotfromtheexternalatmosphere.Thismaybeachievedbytheuseofairadmittancevalvesoratapredeterminedlocationwithinthebuilding,forexampleanaccessibleloftspace.Similarly,itwouldbenecessarytoattenuatepositiveairpressuretransientsbymeansofPAPAdevices.InitiallyitmightbeconsideredthatthiswouldbeproblematicaspositivepressurecouldbuildwithinthePAPAinstallationsandthereforenegatetheirabilitytoabsorbtransientairflows.ThismayagainbeavoidedbylinkingtheverticalstacksinacomplexbuildingandutilizingthediversityofuseinherentinbuildingdrainagesystemsasthiswillensurethatPAPApressuresarethemselvesalleviatedbyallowingtrappedairtoventthroughtheinterconnectedstackstothesewernetwork.Diversityalsoprotectstheproposedsealedsystemfromsewerdrivenoverpressureandpositivetransients.Acomplexbuildingwillbeinterconnectedtothemainsewernetworkviaanumberofconnectingsmallerboredrains.Adversepressureconditionswillbedistributedandthenetworkinterconnectionwillcontinuetoprovideventingroutes.Theseconceptswillbedemonstratedbyamulti-stacknetwork.4.Simulationoftheoperationofamulti-stacksealedbuildingdrainageandventsystemFig.3illustratesafour-stacknetwork.ThefourstacksarelinkedathighlevelbyamanifoldleadingtoaPAPAandAAVinstallation.WaterdownflowsinanystackgeneratenegativetransientsthatdeflatethePAPAandopentheAAVtoprovideanairflowintothenetworkandouttothesewersystem.PositivepressuregeneratedbyeitherstacksurchargeorsewertransientsareattenuatedbythePAPAandbythediversityofusethatallowsonestack-to-sewerroutetoactasareliefroutefortheotherstacks.Thenetworkillustratedhasanoverallheightof12m.Pressuretransientsgeneratedwithinthenetworkwillpropagateattheacousticvelocityinair.Thisimpliespipeperiods,fromstackbasetoPAPAofapproximately0.08sandfromstackbasetostackbaseofapproximately0.15s.Inordertosimplifytheoutputfromthesimulationnolocaltrapsealprotectionisincluded—forexamplethetrapscouldbefittedwitheitherorbothanAAVandPAPAasexamplesofactivecontrol.Traditionalnetworkswouldofcourseincludepassiveventingwhereseparateventstackswouldbeprovidedtoatmosphere,howeverasealedbuildingwoulddispensewiththisventingarrangement.Fig.3.Fourstackbuildingdrainageandventsystemtodemonstratetheviabilityofasealedbuildingsystem.Ideallythefoursewerconnectionsshownshouldbetoseparatecollectiondrainssothatdiversityinthesewernetworkalsoactstoaidsystemselfventing.Inacomplexbuildingthisrequirementwouldnotbearduousandwouldinallprobabilitybethenorm.Itisenvisagedthatthestackconnectionstothesewernetworkwouldbedistributedandwouldbetoabelowgrounddrainagenetworkthatincreasedindiameterdownstream.Otherconnectionstothenetworkwouldinallprobabilitybefrombuildingsthatincludedthemoretraditionalopenventsystemdesignsothatafurtherlevelofdiversityisaddedtooffsetanydownstreamsewersurchargeeventsoflongduration.Similarconsiderationsledtothecurrentdesignguidancefordwellings.Itisstressedthatthenetworkillustratedisrepresentativeofcomplexbuildingdrainagenetworks.Thesimulationwillallowarangeofappliancedischargeandsewerimposedtransientconditionstobeinvestigated.Thefollowingappliancedischargesandimposedsewertransientsareconsidered:1.w.c.dischargetostacks1–3overaperiod1–6sandaseparatew.c.dischargetostack4between2and7s.2.Aminimumwaterflowineachstackcontinuesthroughoutthesimulation,setat0.1L/s,torepresenttrailingwaterfollowingearliermultipleappliancedischarges.3.A1sdurationstackbasesurchargeeventisassumedtooccurinstack1at2.5s.4.Sequentialsewertransientsimposedatthebaseofeachstackinturnfor1.5sfrom12to18s.Thesimulationwilldemonstratetheefficacyofboththeconceptofactivesurgecontrolandinter-stackventinginenablingthesystemtobesealed,i.e.tohavenohighlevelroofpenetrationsandnoventstacksopentoatmosphereoutsidethebuildingenvelope.Theimposedwaterflowswithinthenetworkarebasedon‘real’systemvalues,beingrepresentativeofcurrentw.c.dischargecharacteristicsintermsofpeakflow,2l/s,overallvolume,6l,andduration,6s.Thesewertransientsat30mmwatergaugearerepresentativebutnotexcessive.HYPERLINK"://sciencedirect/science?_o