建筑工程及给排水专业中英文对照翻译（毕业设计用）

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”OROTHERMECHANICALMEANSTHETOTALAMOUNTOFEXTENSIONBETWEENTWOFIXEDPOINTSHASTOBECALCULATEDONBASISOFAMBIENTTEMPERATUREPREVAILINGANDOPERATIONALDESIGNTEMPERATURESSOTHATDISTRIBUTIONOFSTRESSESANDREACTIONSATLOWERANDHIGHERTEMPERATURESARECONTROLLEDWITHINPERMISSIBLELIMITSPRESTRESSINGDOESNOTAFFECTTHEFATIGUELIFEOFPIPINGTHEREFOREITDOESNOTFEATUREINCALCULATIONOFPIPEWORKSTRESSESTHEREARENUMEROUSSPECIALISTPUBLICATIONDEALINGWITHDESIGNANDSTRESSINGCALCULATIONSFORPIPINGANDESPECIALLYFORPROPRIETARYPIPINGANDEXPANSIONUNITSCOMPREHENSIVEEXPERIENCEBACKDESIGNDATAASWELLASCHARTSANDGRAPHSMAYBEOBTAINEDINMANUFACTURERSPUBLICATIONS,OFFERINGSOLUTIONSFOREVERYKINDOFPIPESTRESSINGPROBLEMASANALTERNATIVETOABOVEMENTIONEDMETHODSOFCOMPENSATIONFORTHERMALEXPANSIONANDUSEABLEINPLACESWHERESPACEISRESTRICTED,ISTHEMOREEXPENSIVEBELLOWSORTELESCOPICTYPEMECHANICALCOMPENSATORTHEREAREMANYPROPRIETARYTYPESANDMODELSONTHEMARKETANDTHEFOLLOWINGTYPESOFCOMPENSATORSAREGENERALLYUSEDTHEBELLOWSTYPEEXPANSIONUNITINFORMOFANAXIALCOMPENSATORPROVIDESFOREXPANSIONMOVEMENTINAPIPEALONGITSAXISMOTIONINTHISBELLOWSISDUETOTENSIONORCOMPRESSIONONLYTHEREAREALSOARTICULATEDBELLOWSUNITSRESTRAINEDWHICHCOMBINEANGULARANDLATERALMOVEMENTTHEYCONSISTOFDOUBLECOMPENSATORUNITSRESTRAINEDBYSTRAPSPINNEDOVERTHECENTEROFEACHBELLOWSORDOUBLETIEDTHUSBEINGRESTRAINEDOVERITSLENGTHSUCHCOMPENSATORSARESUITABLEFORACCOMMODATINGVERYPIPELINEEXPANSIONANDALSOFORCOMBINATIONSOFANGULARANDLATERALMOVEMENTS层流与紊流有两种完全不同的流体流动形式存在，这一点在1883年就由OSBORNEREYNOLDS用试验演示证明。在试验里，水通过玻璃管从水箱里放出。流量由出口处的阀门来控制，一股很细的染色流束由入口注入玻璃管内。在较低的流速时，可以看到染色流束在玻璃管中保持着一条完整的迁流。这表明流体粒子以平行的层状流动。这种粘性流体的流动就是我们所知的层流，流体各层的质点以有序的方式移动，并在连续的截面上保持着相同的相对位置。打开出口阀门，管子里的速度就提高。随着速度提高，最后会达到这样的程度，即染色流束起初开始摆动然后破碎，这样颜色就扩散在整个截面上，这表明流体粒子已不再有次序流动却在连续的截面上占有相对不同的位置。这种流体的流动形式就是紊流，它的特点就是不断产生无数大小不等的涡团，质点掺混使得空间各点的速度随时间无规则地变化。与之相关联，压强也随之无规则地变化。当一条流束中的某个流体粒子的运动被扰乱，则它的惯性会使它移向新的方向，但周围流体的粘滞力会使它与其余流束的运动保持一致。在粘性流体中，粘性切应力足以抵消任何偏差的影响，但在紊流中是不够的。因此，确定流动是粘滞性的还是紊流性的标准就是作用在粒子上的惯性力和粘性力之比VLCONSTFREVISCOUINTAL这样，用来判断流动是粘滞性的还是紊流性的标准就是VL/，也就是雷诺数。这是力之间的比，因此理论上也可以写成UL/V（V/，流体的运动粘滞系数）。在不同管径的直管里用许多不同流体所进行的试验已经证实，如雷诺数是通过使L等于管径并且使用平均速度V来计算，那么在低于临界值VD/2000的条件下流动一般是层流（粘滞流动），任何紊流的倾向都会由于粘滞摩擦而受到抑制。这个雷诺数的值仅适用于管道中的流体，但雷诺数的临界值可以用来确定其他形式的流动，例如选择合适的弦杆翼剖面来代替管道直径。对于已知直径的管道中的流体而言，会有一个临界流速VC，以及对应的雷诺数，如果低于这个数，则表明流体是粘滞流动。在管道中，雷诺数值大于2000的情况下，流体不一定就变为紊流。层流可以维持到RE50,000,但是条件并不稳定，任何干扰都会使其它又变为一般的紊流。在直径一定的直管中，如果雷诺数超过4000那么流体就有可能变为紊流。管网平行复合管道的延伸是市政分配系统中常见的一种情况，在这种情况下管道相互连接，使得通向某一出口的流体可以来自不同的路径。的确，通过观察往往很难说清楚流体将流经哪一个管路。但是，不管管网有多复杂，其中的流体都必须确保连续性与能量的基础关系。如下所述1流入接合处的流体必须与流出的等量；2在每根管中的流体都必须满足流体在单管中的管道摩擦定律；3在任何闭合回路中，水头损失的代数和必须为0。管网一般来讲由于太过复杂而难以分析解决，但在简单一些的情况下是可以的，例如平行管。CROSS介绍了一种实用的程序，采用的是连续性近似法。它由以下的原理组成，包括1通过仔细的观察采取最合理的流体分配方案以满足条件1；2对每根管道以方程HLKQN来判断是否满足条件2，式中K是每根管的特性常数。例如，标准管道摩擦方程中的K1/C2以及N2。任何环路中较小的沿程水头损失可能是包括的，但局部水头损失可以忽略不计。3为了研究条件3，计算每个基本环路中水头损失的代数和。HLKQN。假设顺时针方向流动的损失为正，逆时针的则为负，那么在第一次试验中，它们的和只有在非常幸运的情况下才会为零。4通过一个修正值Q来调整每条环路中的流体，使该管路中的水头平衡，并给出KQN0。这个方法的核心取决于Q的确定。对于任何管道我们有QQ0Q式中Q是准确的流量而Q0是假定的流量。那么，对于一个环路而言76010/QHNKL必须再次强调的是方程76的分子和分母都是采用了适当的计算符号确定的。方程76中的负号表明，当顺时针方向的环路上有过量的水头损失时，Q必须从顺时针方向的Q0中减去，并增加到逆时针方向上去。如果顺时针方向的环路上水头损失不足时，情况正好相反。5在每条环路都给予了一个最初的修正值后，由于环路之间的相互影响，损失仍不平衡（一些两条环路共有的管道就有两个单独的修正值，每个值对应一条环路）。重复这样的程序，获得第二个修正值，乃至第三、第四个等等，直到修正值可以忽略不计。方程76的两种形式都可以用来找出Q。由于K值同时出现在第一种形式的分子和分母上，相应实际的K值就可以用来确定分配量。结合水管的管道摩擦力图表，第二种方程形式使用起来最简便。近似法最吸引人的一个特点就是计算上的误差与判断误差有相同的效果，而最终它们会在过程中被加以改正。管网问题非常适合于采用计算机来解决。编制程序需花费大量的时间和精力，但是一旦完成，就有很大的机动灵活性，许多耗人费时的劳动就可省去。更高压力下塑料管道的前景美国煤气协会AGA的一个针对塑料管道的专案小组的成员讨论了在较高压力下使用聚乙烯输气管的的可能性。讨论的主题包括有设计方程（其中包括国际科学组织ISO在更新版本上完成的工作），以及对PE管树脂上裂缝快速扩展的评估。这一点非常重要，因为当管道在较高压力下使用、而管径更大的情况下，钢筋混凝土管的可能性增加了。若干年以前，AGA的塑料管道设计任务小组检查了设计方程，以确定是否能在塑料管道系统中使用更高的工作压力。小组成员认为管道树脂的性能并没有通过设计方程反映出来。一般认为新的树脂塑管在耐用性上远远胜过过去的树脂塑管，因此主要考虑的问题是新方程的发展以及合适的设计要素的选择。改良的管道性能许多设备用来监测塑料管道树脂的性能。在这里讲述一下一些针对典型的输气管道树脂进行过的耐久性测试，以及几种性能上的变化。温升爆裂测试他们使用像温升爆裂测试之类的测试。在这一测试中管系的耐久性能通过高温和高压下管壁形成脆裂所需的时间来校核（通常是80摄氏度和45MPA的环压下）。在供应燃气时我们希望老的树脂塑管在80摄氏度、3MPA的环压下至少可以坚持使用170个小时。推断表明通过了这些极限的树脂预期其寿命应该能超过50年。装运时对这些树脂塑管质量检测，有时会由于没有达到这一标准而对该产品拒绝使用。在相同温度条件下，今天的树脂塑管在46MPA环压下可持续使用数千小时。测试表明用新树脂制造的管道可使用超过5700小时而没有任何损坏。这些结果是在临测试前检出的（树脂）抽样得出的。这种压力从未在早期的测试中使用过。根据工作条件推断，测试性能上的区别与数百年的寿命增长是相等的（某些情况下甚至是数千年）。环压下的防裂测试也有些公司进行了环压下的防裂测试，用来测量管道中脆裂的形成，并加大了压力来减短测试的时间。这个试验表明了在防止脆裂上的惊人的改进。例如，在我的公司里对于我们的早期树脂塑管进行试验需要20小时以上的时间和50摄氏度的温度。而现在的树脂塑管能够良好地持续1000小时以上而没有损坏。槽口测试可以快速进行的槽口测试，用来测量带有槽口的管道或专门浇铸的试验管中脆裂的形成。这对新的树脂塑管非常重要，因为其他的试验需要很长的时间才能使管道发生损