建筑工程及給排水專業(yè)中英文對(duì)照翻譯（畢業(yè)設(shè)計(jì)用）

LAMINARANDTURBULENTFLOWOBSERVATIONSHOWSTHATTWOENTIRELYDIFFERENTTYPESOFFLUIDFLOWEXISTTHISWASDEMONSTRATEDBYOSBORNEREYNOLDSIN1883THROUGHANEXPERIMENTINWHICHWATERWASDISCHARGEDFROMATANKTHROUGHAGLASSTUBETHERATEOFFLOWCOULDBECONTROLLEDBYAVALVEATTHEOUTLET,ANDAFINEFILAMENTOFDYEINJECTEDATTHEENTRANCETOTHETUBEATLOWVELOCITIES,ITWASFOUNDTHATTHEDYEFILAMENTREMAINEDINTACTTHROUGHOUTTHELENGTHOFTHETUBE,SHOWINGTHATTHEPARTICLESOFWATERMOVEDINPARALLELLINESTHISTYPEOFFLOWISKNOWNASLAMINAR,VISCOUSORSTREAMLINE,THEPARTICLESOFFLUIDMOVINGINANORDERLYMANNERANDRETAININGTHESAMERELATIVEPOSITIONSINSUCCESSIVECROSSSECTIONSASTHEVELOCITYINTHETUBEWASINCREASEDBYOPENINGTHEOUTLETVALVE,APOINTWASEVENTUALLYREACHEDATWHICHTHEDYEFILAMENTATFIRSTBEGANTOOSCILLATEANDTHENBROKEUPSOTHATTHECOLOURWASDIFFUSEDOVERTHEWHOLECROSSSECTION,SHOWINGTHATTHEPARTICLESOFFLUIDNOLONGERMOVEDINANORDERLYMANNERBUTOCCUPIEDDIFFERENTRELATIVEPOSITIONINSUCCESSIVECROSSSECTIONSTHISTYPEOFFLOWISKNOWNASTURBULENTANDISCHARACTERIZEDBYCONTINUOUSSMALLFLUCTUATIONSINTHEMAGNITUDEANDDIRECTIONOFTHEVELOCITYOFTHEFLUIDPARTICLES,WHICHAREACCOMPANIEDBYCORRESPONDINGSMALLFLUCTUATIONSOFPRESSUREWHENTHEMOTIONOFAFLUIDPARTICLEINASTREAMISDISTURBED,ITSINERTIAWILLTENDTOCARRYITONINTHENEWDIRECTION,BUTTHEVISCOUSFORCESDUETOTHESURROUNDINGFLUIDWILLTENDTOMAKEITCONFORMTOTHEMOTIONOFTHERESTOFTHESTREAMINVISCOUSFLOW,THEVISCOUSSHEARSTRESSESARESUFFICIENTTOELIMINATETHEEFFECTSOFANYDEVIATION,BUTINTURBULENTFLOWTHEYAREINADEQUATETHECRITERIONWHICHDETERMINESWHETHERFLOWWILLBEVISCOUSOFTURBULENTISTHEREFORETHERATIOOFTHEINERTIALFORCETOTHEVISCOUSFORCEACTINGONTHEPARTICLETHERATIOVLCONSTFREVISCOUINTALTHUS,THECRITERIONWHICHDETERMINESWHETHERFLOWISVISCOUSORTURBULENTISTHEQUANTITYVL/,KNOWNASTHEREYNOLDSNUMBERITISARATIOOFFORCESAND,THEREFORE,APURENUMBERANDMAYALSOBEWRITTENASUL/VWHEREISTHEKINEMATICVISCOSITYV/EXPERIMENTSCARRIEDOUTWITHANUMBEROFDIFFERENTFLUIDSINSTRAIGHTPIPESOFDIFFERENTDIAMETERSHAVEESTABLISHEDTHATIFTHEREYNOLDSNUMBERISCALCULATEDBYMAKING1EQUALTOTHEPIPEDIAMETERANDUSINGTHEMEANVELOCITYV,THEN,BELOWACRITICALVALUEOFVD/2000,FLOWWILLNORMALLYBELAMINARVISCOUS,ANYTENDENCYTOTURBULENCEBEINGDAMPEDOUTBYVISCOUSFRICTIONTHISVALUEOFTHEREYNOLDSNUMBERAPPLIESONLYTOFLOWINPIPES,BUTCRITICALVALUESOFTHEREYNOLDSNUMBERCANBEESTABLISHEDFOROTHERTYPESOFFLOW,CHOOSINGASUITABLECHARACTERISTICLENGTHSUCHASTHECHORDOFANAEROFOILINPLACEOFTHEPIPEDIAMETERFORAGIVENFLUIDFLOWINGINAPIPEOFAGIVENDIAMETER,THEREWILLBEACRITICALVELOCITYOFFLOWCORRESPONDINGTOTHECRITICALVALUEOFTHEREYNOLDSNUMBER,BELOWWHICHFLOWWILLBEVISCOUSINPIPES,ATVALUESOFTHEREYNOLDSNUMBER2000,FLOWWILLNOTNECESSARILYBETURBULENTLAMINARFLOWHASBEENMAINTAINEDUPTORE50,000,BUTCONDITIONSAREUNSTABLEANDANYDISTURBANCEWILLCAUSEREVERSIONTONORMALTURBULENTFLOWINSTRAIGHTPIPESOFCONSTANTDIAMETER,FLOWCANBEASSUMEDTOBETURBULENTIFTHEREYNOLDSNUMBEREXCEEDS4000PIPENETWORKSANEXTENSIONOFCOMPOUNDPIPESINPARALLELISACASEFREQUENTLYENCOUNTEREDINMUNICIPALDISTRIBUTIONSYSTEM,INWHICHTHEPIPESAREINTERCONNECTEDSOTHATTHEFLOWTOAGIVENOUTLETMAYCOMEBYSEVERALDIFFERENTPATHSINDEED,ITISFREQUENTLYIMPOSSIBLETOTELLBYINSPECTIONWHICHWAYTHEFLOWTRAVELSNEVERTHELESS,THEFLOWINANYNETWORKS,HOWEVERCOMPLICATED,MUSTSATISFYTHEBASICRELATIONSOFCONTINUITYANDENERGYASFOLLOWS1THEFLOWINTOANYJUNCTIONMUSTEQUALTHEFLOWOUTOFIT2THEFLOWINEACHPIPEMUSTSATISFYTHEPIPEFRICTIONLAWSFORFLOWINASINGLEPIPE3THEALGEBRAICSUMOFTHEHEADLOSSESAROUNDANYCLOSEDCIRCUITMUSTBEZEROPIPENETWORKSAREGENERALLYTOOCOMPLICATEDTOSOLVEANALYTICALLY,ASWASPOSSIBLEINTHESIMPLERCASESOFPARALLELPIPESAPRACTICALPROCEDUREISTHEMETHODOFSUCCESSIVEAPPROXIMATIONS,INTRODUCEDBYCROSSITCONSISTSOFTHEFOLLOWINGELEMENTS,INORDER1BYCAREFULINSPECTIONASSUMETHEMOSTREASONABLEDISTRIBUTIONOFFLOWSTHATSATISFIESCONDITION12WRITECONDITION2FOREACHPIPEINTHEFORMHLKQN75WHEREKISACONSTANTFOREACHPIPEFOREXAMPLE,THESTANDARDPIPEFRICTIONEQUATIONWOULDYIELDK1/C2ANDN2FORCONSTANTFMINORLOSSESWITHINANYCIRCUITMAYBEINCLUDED,BUTMINORLOSSESATTHEJUNCTIONPOINTSARENEGLECTED3TOINVESTIGATECONDITION3,COMPUTETHEALGEBRAICSUMOFTHEHEADLOSSESAROUNDEACHELEMENTARYCIRCUITHLKQNCONSIDERLOSSESFROMCLOCKWISEFLOWSASPOSITIVE,COUNTERCLOCKWISENEGATIVEONLYBYGOODLUCKWILLTHESEADDTOZEROONTHEFIRSTTRIAL4ADJUSTTHEFLOWINEACHCIRCUITBYACORRECTION,Q,TOBALANCETHEHEADINTHATCIRCUITANDGIVEKQN0THEHEARTOFTHISMETHODLIESINTHEDETERMINATIONOFQFORANYPIPEWEMAYWRITEQQ0QWHEREQISTHECORRECTDISCHARGEANDQ0ISTHEASSUMEDDISCHARGETHEN,FORACIRCUIT76010/HNKLITMUSTBEEMPHASIZEDAGAINTHATTHENUMERATOROFEQ76ISTOBESUMMEDALGEBRAICALLY,WITHDUEACCOUNTOFSIGN,WHILETHEDENOMINATORISSUMMEDARITHMETICALLYTHENEGATIVESIGNINEQ76INDICATESTHATWHENTHEREISANEXCESSOFHEADLOSSAROUNDALOOPINTHECLOCKWISEDIRECTION,THEQMUSTBESUBTRACTEDFROMCLOCKWISEQ0SANDADDEDTOCOUNTERCLOCKWISEONESTHEREVERSEISTRUEIFTHEREISADEFICIENCYOFHEADLOSSAROUNDALOOPINTHECLOCKWISEDIRECTION5AFTEREACHCIRCUITISGIVENAFIRSTCORRECTION,THELOSSESWILLSTILLNOTBALANCEBECAUSEOFTHEINTERACTIONOFONECIRCUITUPONANOTHERPIPESWHICHARECOMMONTOTWOCIRCUITSRECEIVETWOINDEPENDENTCORRECTIONS,ONEFOREACHCIRCUITTHEPROCEDUREISREPEATED,ARRIVINGATASECONDCORRECTION,ANDSOON,UNTILTHECORRECTIONSBECOMENEGLIGIBLEEITHERFORMOFEQ76MAYBEUSEDTOFINDQASVALUESOFKAPPEARINBOTHNUMERATORANDDENOMINATOROFTHEFIRSTFORM,VALUESPROPORTIONALTOTHEACTUALKMAYBEUSEDTOFINDTHEDISTRIBUTIONTHESECONDFORMWILLBEFOUNDMOSTCONVENIENTFORUSEWITHPIPEFRICTIONDIAGRAMSFORWATERPIPESANATTRACTIVEFEATUREOFTHEAPPROXIMATIONMETHODISTHATERRORSINCOMPUTATIONHAVETHESAMEEFFECTASERRORSINJUDGMENTANDWILLEVENTUALLYBECORRECTEDBYTHEPROCESSTHEPIPENETWORKSPROBLEMLENDSITSELFWELLTOSOLUTIONBYUSEOFADIGITALCOMPUTERPROGRAMMINGTAKESTIMEANDCARE,BUTONCESETUP,THEREISGREATFLEXIBILITYANDMANYMANHOURSOFLABORCANBESAVEDTHEFUTUREOFPLASTICPIPEATHIGHERPRESSURESPARTICIPANTSINANAGAMEETINGPANELONPLASTICPIPEDISCUSSEDTHEPOSSIBILITYOFUSINGPOLYETHYLENEGASPIPEATHIGHERPRESSURESTOPICSINCLUDEDTHEDESIGNEQUATION,INCLUDINGWORKBEINGDONEBYISOONANUPDATEDVERSION,ANDTHEEVALUATIONOFRAPIDCRACKPROPAGATIONINAPEPIPERESINTHISISOFCRITICALIMPORTANCEBECAUSEASPIPEISUSEDATHIGHERPRESSUREANDINLARGERDIAMETERS,THEPOSSIBILITYOFRCPINCREASESSEVERALYEARSAGO,AGASPLASTICPIPEDESIGNEQUATIONTASKGROUPREVIEWEDTHEDESIGNEQUATIONTODETERMINEIFHIGHEROPERATINGPRESSURESCOULDBEUSEDINPLASTICPIPINGSYSTEMSMEMBERSFELTTHEPERFORMANCEOFOURPIPERESINSWASNOTTRULYREFLECTEDBYTHEDESIGNEQUATIONITWASGENERALLYACCEPTEDTHATTHELONGTERMPROPERTIESOFMODERNRESINSFARSURPASSEDTHOSEOFOLDERRESINSMAJORCONSIDERATIONSWERENEWEQUATIONSBEINGDEVELOPEDANDSELECTIONOFANAPPROPRIATEDESIGNFACTORIMPROVEDPIPEPERFORMANCEMANYUTILITIESMONITOREDTHEPERFORMANCEOFPLASTICPIPERESINSHEREARESOMEOFTHELONGTERMTESTSUSEDANDTHEKINDSOFPERFORMANCECHANGETHEYHAVESHOWNFORTYPICALGASPIPERESINSELEVATEDTEMPERATUREBURSTTESTTHEYUSEDTESTSLIKETHEELEVATEDTEMPERATUREBURSTTEST,INWHICHTHELONGTERMPERFORMANCEOFTHEPIPEISCHECKEDBYMEASURINGTHETIMEREQUIREDFORFORMATIONOFBRITTLECRACKSINTHEPIPEWALLUNDERHIGHTEMPERATURESANDPRESSURESOFTEN80DEGREESCANDAROUND4TO5MPAHOOPSTRESSATCONSUMERSGASWEEXPECTEDEARLYRESINSTOLASTATLEAST170HRSAT80DEGREESCANDAHOOPSTRESSOF3MPAEXTRAPOLATIONSHOWEDTHATRESINSPASSINGTHESELIMITSSHOULDHAVEALIFEEXPECTANCYOFMORETHAN50YRSQUALITYCONTROLTESTINGONSHIPMENTSOFPIPEMADEFROMTHESERESINSSOMETIMESRESULTEDINPRODUCTREJECTIONFORFAILURETOMEETTHISCRITERIONATTHESAMETEMPERATURE,TODAYSRESINSLASTTHOUSANDSOFHOURSATHOOPSTRESSESOF46MPATESTSPERFORMEDONPIPEMADEFROMNEWRESINSHAVEBEENTERMINATEDWITHNOFAILUREATTIMESEXCEEDING5,700HRSTHESERESULTSWEREPERFORMEDONSAMPLESTHATWERESQUEEZEDOFFBEFORETESTINGSUCHSTRESSESWERENEVERAPPLIEDINEARLYTESTINGWHENEXTRAPOLATEDTOOPERATINGCONDITIONS,THISDIFFERENCEINTESTPERFORMANCEISEQUIVALENTTOANINCREASEINLIFETIMEOFHUNDREDSANDINSOMECASESEVENTHOUSANDSOFYEARSENVIRONMENTALSTRESSCRACKRESISTANCETESTSOMECOMPANIESALSOUSEDTHEENVIRONMENTALSTRESSCRACKRESISTANCETESTWHICHMEASUREDBRITTLECRACKFORMATIONINPIPESBUTWHICHUSEDSTRESSCRACKINGAGENTSTOSHORTENTESTTIMESTHISTESTHASALSOSHOWNDRAMATICIMPROVEMENTINRESISTANCEBRITTLEFAILUREFOREXAMPLE,ATMYCOMPANYATESTTIMEOFMORETHAN20HRSAT50DEGREESCWASREQUIREDONOUREARLYRESINSTODAYSRESINSLASTWELLABOVE1,000HRSWITHNOFAILURENOTCHTESTSNOTCHTESTS,WHICHAREQUICKLYRUN,MEASUREBRITTLECRACKFORMATIONINNOTCHEDPIPEORMOLDEDCOUPONSAMPLESTHISISIMPORTANTFORTHENEWERRESINSSINCESOMEOTHERTESTSTOFAILURECANTAKEVERYLONGTIMESNOTCHTESTRESULTSSHOWTHATWHILEEARLYRESINSLASTEDFORTESTTIMESRANGINGBETWEEN1,000TO10,000MIN,CURRENTRESINSUSUALLYLASTFORLONGERTHAN200,000MINALLOFOURTESTSDEMONSTRATEDTHESAMETHINGNEWERRESINSAREMUCHMORERESISTANTTOTHEGROWTHOFBRITTLECRACKTHANTHEIRPREDECESSORSSINCEBRITTLEFAILUREISCONSIDEREDTOBETHEULTIMATEFAILUREMECHANISMINPOLYETHYLENEPIPES,WEKNOWTHATNEWMATERIALSWILLLASTMUCHLONGERTHANTHEOLDTHISISESPECIALLYREASSURINGTOTHEGASINDUSTRYSINCEMANYOFTHESEOLDERRESINSHAVEPERFORMEDVERYWELLINTHEFIELDFORTHEPAST25YRSWITHMINIMALDETECTABLECHANGEINPROPERTIESWHILETHETESTSSHOWEDGREATLYIMPROVEDPERFORMANCE,THEEQUATIONUSEDTOESTABLISHTHEPRESSURERATINGOFTHEPIPEISSTILLIDENTICALTOTHEORIGINALEXCEPTFORACHANGEIN1978TOASINGLEDESIGNFACTORFORALLCLASSLOCATIONSTOMANYITSEEMEDTHATTHEMETHODSUSEDTOPRESSURERATEOURPIPEWERENOWUNDULYCONSERVATIVEANDTHATANEWDESIGNEQUATIONWASNEEDEDATTHISTIMEWEBECAMEAWAREOFANEWEQUATIONBEINGBALLOTEDATISOTHEMETHODOLOGYBEINGUSEDSEEMEDTOBEAMORETECHNICALLYCORRECTMETHODOFANALYZINGTHEDATAANDOFFEREDANUMBEROFADVANTAGESTHERMALEXPANSIONOFPIPINGANDITSCOMPENSATIONAVERYRELEVANTCONSIDERATIONREQUIRINGCAREFULATTENTIONISTHEFACTTHATWITHTEMPERATUREOFALENGTHOFPIPERAISEDORLOWERED,THEREISACORRESPONDINGINCREASEORDECREASEINITSLENGTHANDCROSSSECTIONALAREABECAUSEOFTHEINHERENTCOEFFICIENTOFTHERMALEXPANSIONFORTHEPARTICULARPIPEMATERIALTHECOEFFICIENTOFEXPANSIONFORCARBONSTEELIS0012MM/MCANDFORCOPPER00168MM/MCRESPECTIVEMODULEOFELASTICITYAREFORSTEELE207106KN/M2ANDFORCOPPERE103106KN/M2ASANEXAMPLE,ASSUMINGABASETEMPERATUREFORWATERCONDUCTINGPIPINGAT0C,ASTEELPIPEOFANYDIAMETERIFHEATEDTO120CWOULDEXPERIENCEALINEAREXTENSIONOF14MMANDASIMILARLYIFHEATEDTOCOPPERPIPEWOULDEXTENDBY2016MMFOREACHMETEROFTHEIRRESPECTIVELENGTHSTHEUNITAXIALFORCEINTHESTEELPIPEHOWEVERWOULDBE39GREATERTHANFORCOPPERTHECHANGEINPIPEDIAMETERISOFNOPRACTICALCONSEQUENCETOLINEAREXTENSIONBUTTHEAXIALFORCESCREATEDBYEXPANSIONORCONTRACTIONARECONSIDERABLEANDCAPABLEOFFRACTURINGANYFITMENTSWHICHMAYTENDTOIMPOSEARESTRAINTTHEMAGNITUDEOFSUCHFORCESISRELATEDTOPIPESIZEASANEXAMPLE,INSTRAIGHTPIPESOFSAMELENGTHBUTDIFFERENTDIAMETERS,RIGIDLYHELDATBOTHENDSANDWITHTEMPERATURERAISEDBYSAY100C,TOTALMAGNITUDEOFLINEARFORCESAGAINSTFIXEDPOINTSWOULDBENEARENOUGHPROPORTIONATETOTHERESPECTIVEDIAMETERSITISTHEREFOREESSENTIALTHATDESIGNOFANYPIPINGLAYOUTMAKESADEQUATECOMPENSATORYPROVISIONFORSUCHTHERMALINFLUENCEBYRELIEVINGTHESYSTEMOFLINEARSTRESSESWHICHWOULDBEDIRECTLYRELATEDTOLENGTHOFPIPEWORKBETWEENFIXEDPOINTSANDTHERANGEOFOPERATIONALTEMPERATURESCOMPENSATIONFORFORCESDUETOTHERMALEXPANSIONTHEIDEALPIPEWORKASFARASEXPANSIONISCONCERNED,ISONEWHEREMAXIMUMFREEMOVEMENTWITHTHEMINIMUMOFRESTRAINTISPOSSIBLEHENCETHESIMPLESTANDMOSTECONOMICALWAYTOENSURECOMPENSATIONANDRELIEFOFFORCESISTOTAKEADVANTAGEOFCHANGESINDIRECTION,ORWHERETHISISNOTPARTOFTHELAYOUTANDLONGSTRAIGHTRUNSAREINVOLVEDITMAYBEFEASIBLETOINTRODUCEDELIBERATEDOGLEGOFFSETCHANGESINDIRECTIONATSUITABLEINTERVALSASANALTERNATIVE,ATCALCULATEDINTERVALSINASTRAIGHTPIPERUNSPECIALLYDESIGNEDEXPANSIONLOOPSOR“U”BENDSSHOULDBEINSERTEDDEPENDINGUPONDESIGNANDSPACEAVAILABILITY,EXPANSIONBENDSWITHINASTRAIGHTPIPERUNCANFEATURETHESOCALLEDDOUBLEOFFSET“U”BANDORTHEHORSESHOETYPEOR“LYRE”LOOPTHELASTNAMEDARESELDOMUSEDFORLARGEHEATINGNETWORKSTHEYCANBESUPPLIEDINMANUFACTURERSSTANDARDUNITSBUTREQUIREELABORATECONSTRUCTIONALWORKSFORUNDERGROUNDINSTALLATIONANCHOREDTHERMALMOVEMENTINUNDERGROUNDPIPINGWOULDNORMALLYBEABSORBEDBYTHREEBASICTYPESOFEXPANSIONBENDSANDTHESEINCLUDETHE“U”BEND,THE“L”BENDANDTHE“Z”BENDINCASESOF90CHANGESINDIRECTIONTHE“L”AND“Z”BENDSAREUSEDPRINCIPLESINVOLVEDINTHEDESIGNOFPROVISIONFOREXPANSIONBETWEENANCHORPOINTSAREVIRTUALLYTHESAMEFORALLTHREETYPESOFCOMPENSATORTHEOFFSET“U”BENDISUSUALLYMADEUPFROMFOUR90ELBOWSANDSTRAIGHTPIPESITPERMITSGOODTHERMALDISPLACEMENTANDIMPOSESSMALLERANCHORLOADSTHANTHEOTHERTYPEOFLOOPTHISSHAPEOFEXPANSIONBENDISTHESTANDARDISEDPATTERNFORPREFABRICATEDPIPEINPIPESYSTEMSALLTHERMALCOMPENSATORSAREINSTALLEDTOACCOMMODATEANEQUALAMOUNTOFEXPANSIONORCONTRACTIONTHEREFORETOOBTAINFULLADVANTAGEOFTHELENGTHOFTHERMALMOVEMENTITISNECESSARYTOEXTENDTHEUNITDURINGINSTALLATIONTHUSOPENINGUPTHELOOPBYANEXTENTROUGHLYEQUALTHEHALFTHEOVERALLCALCULATEDTHERMALMOVEMENTTHISISDONEBY“COLDPULL”O(jiān)ROTHERMECHANICALMEANSTHETOTALAMOUNTOFEXTENSIONBETWEENTWOFIXEDPOINTSHASTOBECALCULATEDONBASISOFAMBIENTTEMPERATUREPREVAILINGANDOPERATIONALDESIGNTEMPERATURESSOTHATDISTRIBUTIONOFSTRESSESANDREACTIONSATLOWERANDHIGHERTEMPERATURESARECONTROLLEDWITHINPERMISSIBLELIMITSPRESTRESSINGDOESNOTAFFECTTHEFATIGUELIFEOFPIPINGTHEREFOREITDOESNOTFEATUREINCALCULATIONOFPIPEWORKSTRESSESTHEREARENUMEROUSSPECIALISTPUBLICATIONDEALINGWITHDESIGNANDSTRESSINGCALCULATIONSFORPIPINGANDESPECIALLYFORPROPRIETARYPIPINGANDEXPANSIONUNITSCOMPREHENSIVEEXPERIENCEBACKDESIGNDATAASWELLASCHARTSANDGRAPHSMAYBEOBTAINEDINMANUFACTURERSPUBLICATIONS,OFFERINGSOLUTIONSFOREVERYKINDOFPIPESTRESSINGPROBLEMASANALTERNATIVETOABOVEMENTIONEDMETHODSOFCOMPENSATIONFORTHERMALEXPANSIONANDUSEABLEINPLACESWHERESPACEISRESTRICTED,ISTHEMOREEXPENSIVEBELLOWSORTELESCOPICTYPEMECHANICALCOMPENSATORTHEREAREMANYPROPRIETARYTYPESANDMODELSONTHEMARKETANDTHEFOLLOWINGTYPESOFCOMPENSATORSAREGENERALLYUSEDTHEBELLOWSTYPEEXPANSIONUNITINFORMOFANAXIALCOMPENSATORPROVIDESFOREXPANSIONMOVEMENTINAPIPEALONGITSAXISMOTIONINTHISBELLOWSISDUETOTENSIONORCOMPRESSIONONLYTHEREAREALSOARTICULATEDBELLOWSUNITSRESTRAINEDWHICHCOMBINEANGULARANDLATERALMOVEMENTTHEYCONSISTOFDOUBLECOMPENSATORUNITSRESTRAINEDBYSTRAPSPINNEDOVERTHECENTEROFEACHBELLOWSORDOUBLETIEDTHUSBEINGRESTRAINEDOVERITSLENGTHSUCHCOMPENSATORSARESUITABLEFORACCOMMODATINGVERYPIPELINEEXPANSIONANDALSOFORCOMBINATIONSOFANGULARANDLATERALMOVEMENTS層流與紊流有兩種完全不同的流體流動(dòng)形式存在，這一點(diǎn)在1883年就由OSBORNEREYNOLDS用試驗(yàn)演示證明。在試驗(yàn)里，水通過玻璃管從水箱里放出。流量由出口處的閥門來控制，一股很細(xì)的染色流束由入口注入玻璃管內(nèi)。在較低的流速時(shí)，可以看到染色流束在玻璃管中保持著一條完整的遷流。這表明流體粒子以平行的層狀流動(dòng)。這種粘性流體的流動(dòng)就是我們所知的層流，流體各層的質(zhì)點(diǎn)以有序的方式移動(dòng)，并在連續(xù)的截面上保持著相同的相對(duì)位置。打開出口閥門，管子里的速度就提高。隨著速度提高，最后會(huì)達(dá)到這樣的程度，即染色流束起初開始擺動(dòng)然后破碎，這樣顏色就擴(kuò)散在整個(gè)截面上，這表明流體粒子已不再有次序流動(dòng)卻在連續(xù)的截面上占有相對(duì)不同的位置。這種流體的流動(dòng)形式就是紊流，它的特點(diǎn)就是不斷產(chǎn)生無數(shù)大小不等的渦團(tuán)，質(zhì)點(diǎn)摻混使得空間各點(diǎn)的速度隨時(shí)間無規(guī)則地變化。與之相關(guān)聯(lián)，壓強(qiáng)也隨之無規(guī)則地變化。當(dāng)一條流束中的某個(gè)流體粒子的運(yùn)動(dòng)被擾亂，則它的慣性會(huì)使它移向新的方向，但周圍流體的粘滯力會(huì)使它與其余流束的運(yùn)動(dòng)保持一致。在粘性流體中，粘性切應(yīng)力足以抵消任何偏差的影響，但在紊流中是不夠的。因此，確定流動(dòng)是粘滯性的還是紊流性的標(biāo)準(zhǔn)就是作用在粒子上的慣性力和粘性力之比VLCONSTFREVISCOUINTAL這樣，用來判斷流動(dòng)是粘滯性的還是紊流性的標(biāo)準(zhǔn)就是VL/，也就是雷諾數(shù)。這是力之間的比，因此理論上也可以寫成UL/V（V/，流體的運(yùn)動(dòng)粘滯系數(shù)）。在不同管徑的直管里用許多不同流體所進(jìn)行的試驗(yàn)已經(jīng)證實(shí)，如雷諾數(shù)是通過使L等于管徑并且使用平均速度V來計(jì)算，那么在低于臨界值VD/2000的條件下流動(dòng)一般是層流（粘滯流動(dòng)），任何紊流的傾向都會(huì)由于粘滯摩擦而受到抑制。這個(gè)雷諾數(shù)的值僅適用于管道中的流體，但雷諾數(shù)的臨界值可以用來確定其他形式的流動(dòng)，例如選擇合適的弦桿翼剖面來代替管道直徑。對(duì)于已知直徑的管道中的流體而言，會(huì)有一個(gè)臨界流速VC，以及對(duì)應(yīng)的雷諾數(shù)，如果低于這個(gè)數(shù)，則表明流體是粘滯流動(dòng)。在管道中，雷諾數(shù)值大于2000的情況下，流體不一定就變?yōu)槲闪?。層流可以維持到RE50,000,但是條件并不穩(wěn)定，任何干擾都會(huì)使其它又變?yōu)橐话愕奈闪?。在直徑一定的直管中，如果雷諾數(shù)超過4000那么流體就有可能變?yōu)槲闪?。管網(wǎng)平行復(fù)合管道的延伸是市政分配系統(tǒng)中常見的一種情況，在這種情況下管道相互連接，使得通向某一出口的流體可以來自不同的路徑。的確，通過觀察往往很難說清楚流體將流經(jīng)哪一個(gè)管路。但是，不管管網(wǎng)有多復(fù)雜，其中的流體都必須確保連續(xù)性與能量的基礎(chǔ)關(guān)系。如下所述1流入接合處的流體必須與流出的等量；2在每根管中的流體都必須滿足流體在單管中的管道摩擦定律；3在任何閉合回路中，水頭損失的代數(shù)和必須為0。管網(wǎng)一般來講由于太過復(fù)雜而難以分析解決，但在簡(jiǎn)單一些的情況下是可以的，例如平行管。CROSS介紹了一種實(shí)用的程序，采用的是連續(xù)性近似法。它由以下的原理組成，包括1通過仔細(xì)的觀察采取最合理的流體分配方案以滿足條件1；2對(duì)每根管道以方程HLKQN來判斷是否滿足條件2，式中K是每根管的特性常數(shù)。例如，標(biāo)準(zhǔn)管道摩擦方程中的K1/C2以及N2。任何環(huán)路中較小的沿程水頭損失可能是包括的，但局部水頭損失可以忽略不計(jì)。3為了研究條件3，計(jì)算每個(gè)基本環(huán)路中水頭損失的代數(shù)和。HLKQN。假設(shè)順時(shí)針方向流動(dòng)的損失為正，逆時(shí)針的則為負(fù)，那么在第一次試驗(yàn)中，它們的和只有在非常幸運(yùn)的情況下才會(huì)為零。4通過一個(gè)修正值Q來調(diào)整每條環(huán)路中的流體，使該管路中的水頭平衡，并給出KQN0。這個(gè)方法的核心取決于Q的確定。對(duì)于任何管道我們有QQ0Q式中Q是準(zhǔn)確的流量而Q0是假定的流量。那么，對(duì)于一個(gè)環(huán)路而言76010/QHNKL必須再次強(qiáng)調(diào)的是方程76的分子和分母都是采用了適當(dāng)?shù)挠?jì)算符號(hào)確定的。方程76中的負(fù)號(hào)表明，當(dāng)順時(shí)針方向的環(huán)路上有過量的水頭損失時(shí)，Q必須從順時(shí)針方向的Q0中減去，并增加到逆時(shí)針方向上去。如果順時(shí)針方向的環(huán)路上水頭損失不足時(shí)，情況正好相反。5在每條環(huán)路都給予了一個(gè)最初的修正值后，由于環(huán)路之間的相互影響，損失仍不平衡（一些兩條環(huán)路共有的管道就有兩個(gè)單獨(dú)的修正值，每個(gè)值對(duì)應(yīng)一條環(huán)路）。重復(fù)這樣的程序，獲得第二個(gè)修正值，乃至第三、第四個(gè)等等，直到修正值可以忽略不計(jì)。方程76的兩種形式都可以用來找出Q。由于K值同時(shí)出現(xiàn)在第一種形式的分子和分母上，相應(yīng)實(shí)際的K值就可以用來確定分配量。結(jié)合水管的管道摩擦力圖表，第二種方程形式使用起來最簡(jiǎn)便。近似法最吸引人的一個(gè)特點(diǎn)就是計(jì)算上的誤差與判斷誤差有相同的效果，而最終它們會(huì)在過程中被加以改正。管網(wǎng)問題非常適合于采用計(jì)算機(jī)來解決。編制程序需花費(fèi)大量的時(shí)間和精力，但是一旦完成，就有很大的機(jī)動(dòng)靈活性，許多耗人費(fèi)時(shí)的勞動(dòng)就可省去。更高壓力下塑料管道的前景美國(guó)煤氣協(xié)會(huì)AGA的一個(gè)針對(duì)塑料管道的專案小組的成員討論了在較高壓力下使用聚乙烯輸氣管的的可能性。討論的主題包括有設(shè)計(jì)方程（其中包括國(guó)際科學(xué)組織ISO在更新版本上完成的工作），以及對(duì)PE管樹脂上裂縫快速擴(kuò)展的評(píng)估。這一點(diǎn)非常重要，因?yàn)楫?dāng)管道在較高壓力下使用、而管徑更大的情況下，鋼筋混凝土管的可能性增加了。若干年以前，AGA的塑料管道設(shè)計(jì)任務(wù)小組檢查了設(shè)計(jì)方程，以確定是否能在塑料管道系統(tǒng)中使用更高的工作壓力。小組成員認(rèn)為管道樹脂的性能并沒有通過設(shè)計(jì)方程反映出來。一般認(rèn)為新的樹脂塑管在耐用性上遠(yuǎn)遠(yuǎn)勝過過去的樹脂塑管，因此主要考慮的問題是新方程的發(fā)展以及合適的設(shè)計(jì)要素的選擇。改良的管道性能許多設(shè)備用來監(jiān)測(cè)塑料管道樹脂的性能。在這里講述一下一些針對(duì)典型的輸氣管道樹脂進(jìn)行過的耐久性測(cè)試，以及幾種性能上的變化。溫升爆裂測(cè)試他們使用像溫升爆裂測(cè)試之類的測(cè)試。在這一測(cè)試中管系的耐久性能通過高溫和高壓下管壁形成脆裂所需的時(shí)間來校核（通常是80攝氏度和45MPA的環(huán)壓下）。在供應(yīng)燃?xì)鈺r(shí)我們希望老的樹脂塑管在80攝氏度、3MPA的環(huán)壓下至少可以堅(jiān)持使用170個(gè)小時(shí)。推斷表明通過了這些極限的樹脂預(yù)期其壽命應(yīng)該能超過50年。裝運(yùn)時(shí)對(duì)這些樹脂塑管質(zhì)量檢測(cè)，有時(shí)會(huì)由于沒有達(dá)到這一標(biāo)準(zhǔn)而對(duì)該產(chǎn)品拒絕使用。在相同溫度條件下，今天的樹脂塑管在46MPA環(huán)壓下可持續(xù)使用數(shù)千小時(shí)。測(cè)試表明用新樹脂制造的管道可使用超過5700小時(shí)而沒有任何損壞。這些結(jié)果是在臨測(cè)試前檢出的（樹脂）抽樣得出的。這種壓力從未在早期的測(cè)試中使用過。根據(jù)工作條件推斷，測(cè)試性能上的區(qū)別與數(shù)百年的壽命增長(zhǎng)是相等的（某些情況下甚至是數(shù)千年）。環(huán)壓下的防裂測(cè)試也有些公司進(jìn)行了環(huán)壓下的防裂測(cè)試，用來測(cè)量管道中脆裂的形成，并加大了壓力來減短測(cè)試的時(shí)間。這個(gè)試驗(yàn)表明了在防止脆裂上的驚人的改進(jìn)。例如，在我的公司里對(duì)于我們的早期樹脂塑管進(jìn)行試驗(yàn)需要20小時(shí)以上的時(shí)間和50攝氏度的溫度。而現(xiàn)在的樹脂塑管能夠良好地持續(xù)1000小時(shí)以上而沒有損壞。槽口測(cè)試可以快速進(jìn)行的槽口測(cè)試，用來測(cè)量帶有槽口的管道或?qū)ｉT澆鑄的試驗(yàn)管中脆裂的形成。這對(duì)新的樹脂塑管非常重要，因?yàn)槠渌脑囼?yàn)需要很長(zhǎng)的時(shí)間才能使管道發(fā)生損