Unit5HydraulicStructures水工建筑物OpenChannelFlow明渠流Wemaydivideopenchannelflowintosteadyandunsteadyflow.Steadyreferstotime.Ifthedischargeinachannelatanyonepointdoesnotchangewithtime,wearedealingwithsteadyflow.Ifitdoeschangewithtime,wehaveunsteadyflow,forinstance,whenawaveistravelinginachannelorwhenthedischargeisgradual.我们可以把明渠流分为恒定流和非恒定流。恒定是指时间。如果渠道中任意一点的流量不随时间变化,我们认为是恒定流。如果它随着时间的改变而改变,我们认为是非恒定流,例如,当波浪在渠道中传播或当流量渐进变化时。Wemaydivideopenchannelflowalsointouniformandnon-uniformflow.Uniformreferstodistance.Ifthewettedcross-sectionalareaofanopenchannelisthesamefromonelocationtoanother,wearedealingwithuniformflow.Ifitdoeschangefromplacetoplace,wehavenon-uniformflow;forinstance,whentheslopeofthechannelsteeps,whenthechannelcontainsanobstruction,orwhentheflowisbackedupbyadam.我们也可以把明渠流分为均匀流和非均匀流。均匀是指距离。如果一个明渠从一个地方到另一个地方的湿横截面积是相同的,我们认为是均匀流。如果它从一个地方到另一个地方是变化的,我们认为是非均匀流;例如,当渠道的坡度陡峭,渠道中有一个障碍物,或当水流被大坝阻挡时。Inthefollowingparagraphsweshallfirstdealwithsteady,uniformflow.Themainproblemhereistodeterminethedischargeofachannelwhenitscharacteristicsaregiven,orviceversa.InordertosolvesuchproblemswewillderivetheManningformula.Thenexttopicwillbesteady,non-uniformflow.Thissubjectwillbedividedintotwoparts.Thefirstgroupofproblemswillbeconcernedwithsituationswherefrictionlossesarerelativelyunimportant.Inotherwords,thenon-uniformityofflowtakesplaceovershortdistances:forinstance,channeltransitionsandchannelobstructions.Themainproblemhereistodeterminethewatersurfaceprofile.ThiswillbedonebyusingtheBernoulliequationandbyintroducingsuchconceptsasthespecifichead.Thesecondgroupofproblemsinsteady,non-uniformflowwillbeconcernedwithsituationswherebyfrictionlossesdoplayanimportantrole.Thisgroupincludesbackwaterproblems.接下来的段落我们讨论恒定均匀流。当渠道的特征给定时这里的主要问题是确定渠道的流量,反之亦然。为了解决这些问题,我们将导出曼宁公式。下一个主题将是恒定非均匀流。这个主题将被分为两个部分。第一组问题会讨论摩擦损失相对不重要的情况。换句话说,水流的不均匀性发生在很短的距离:例如,渠道转换和渠道障碍物。这里的主要问题是确定水面轮廓。这可以通过使用伯努利方程,通过引入这些概念例如特定的水头来实现。第二组有关恒定非均匀流的问题将会涉及摩擦损失确实发挥重要作用的情况。这类情况包括壅水问题。MultiplePurposeReservoirs多用途水库Therecentinthisco