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ID:59414856
大小:67.50 KB
页数:32页
时间:2020-09-19
《Sediment Transport by Water A world top 100 University 输沙的水世界100强大学ppt课件.ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、SedimentTransportbyWaterTheoryProcessesRainsplashoverlandflowtransportRillingandgullyingMassmovementsWeatheringlimitedversussupplylimitedTheextremeeventTheoryMechanicsofflowStreamenergyEntrainmentMechanicsofflowWaterissubjecttotwoforces:gravity(Wa=gsin)frictionDefinesabil
2、ityofwatertoerodeandtransportsedimentTypesofflowinopenchannelsLaminarFlowEachfluidelementmovesalongaspecificpathwithnosignificantmixingbetweenlayersBoundarylayerincontactwiththebedhasnoforwardvelocityEachlayercanslippasteachotherTurbulentflowAtacriticalvelocityordepthlamin
3、arflowbecomesunstableandtheparallelstreamlinesaredestroyedAdjacentlayersmix,transferringmomentumbylargescaleeddiesVelocitymoreevenlydistributedwithdepthSteepernearbedvelocitygradientReynoldsNumber(Re)Re=hu/where=fluiddensityh=flowdepthu=fluidviscosity=viscositylargerva
4、lues,largerturbulenceEntrainmentMovementofmaterialdependsonitsphysicalproperties;grainsizeshapedensitystructualarrangementBasicdistinction;cohesive(silt-claysize)non-cohesiveShearstressCausesinitialmovementShearstress=estimateofforceexertedonthebedbythefluidcrDbutdoesn’t
5、includeliftforcesLiftdueto:eddiesdifferenceinvelocityattopandbottomofgrainCriticalshearstressShields(1936)DimensionlesscriticalshearstressPlotagainstparticleReynoldsno.(ratioofgrainsizetothicknessoflaminarsublayer)Factorsproducingscatteruseofaverageorspatialvariabilityov
6、erbedchannelsizeirregularityofeddiesdegreeofexposurepivotanglesimbricationdegreeofpackinggrainshapemicrotopographyErosionEntrainment/detatchmentTransportDetatchmentvsTransportRainsplashWeatheringTillageTramplingRunoffRainsplashOverlandflowRillflowGullyflowRainsplashvariesw
7、ithrainfallintensityvarieswithlandcovervarieswithslopevarieswith%ofareawhichisrilledvarieswithlithologycrusting?SurfaceWashparticlesdetatchedandtransportedbysurfaceflowingwaterforce=velocityxmass(i.e.Q)controlsrelatetocharacterofmaterials,especiallyabilitytoproducerainfall
8、excessResistancetodetatchmentnon-uniformvarieswithparticlesizecyclicvariationwithseasonsa
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