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EffectiveRoughnessHeightinHigh-ConcentratedFlows
Reporter:JiayuFangSupervisor:Prof.YongpingChenData:November5,2015Contents
BackgroundandIntroduction1
Methods2
ExperimentalSetup3ResultsandDiscussion4ConclusionsandLimitations5BackgroundandIntroductionEffectiveRoughnessBedResistanceNikuradse(1933)FlowmodelSedimenttransportmodelthevelocityofzeroreferenceconcentrationWhyBackgroundandIntroductionEffectiveRoughnessBedResistanceGrantandMadsen(1982)-Grainroughnessheight-Formroughnessheight-Bed-loadroughnessheight:skinfrictiondrag:horizontalpressuregradient:energydissipationFWaveonlyconditionsBackgroundandIntroductionEffectiveRoughnessBedResistanceGrantandMadsen(1982)-Grainroughnessheight-Formroughnessheight-Bed-loadroughnessheight:skinfrictiondrag:horizontalpressuregradient:energydissipationWaveonlyconditionsLietal.(1998)CombinedflowconditionsYou(1996)“Cleanwater”assumptionWave-currentvelocitydistributionsSand图2东中国海海岸类型分布图（引自shi,2012）Fig.1
SedimentclassificationanddistributionalongtheJiangsucoast(fromShi,2012)BackgroundandIntroduction-Caoetal.(2003):SiltycoastDefinitionCharacteristics-Easytomoveandsettle-High-concentratedflows
-ResearchStatus-Sedimentconcentration
-Sedimenttransportrate
EffectiveroughnessheightfewBackgroundandIntroductionSuspendedlayerHigh-concentratedlayerBed-loadlayerExtremeweather(storms)Howtogetit?BackgroundandIntroductionMethodsEffectiveRoughnessHeightVelocityProfilesEnergyDissipationSheet-flowlayerthicknessOscillatoryFlowMethodsYou’s(1994)modeldonotneediterationsVelocitygradientShearstressEddyviscosityconceptFig2.Distributionofeddyviscosity（fromYou,1991）MethodsYou’s(1994a)modelCorrelationcoefficient>0.900.1~0.3hVelocityProfilesExperimentsExperimentalSetupFig3.Schematicdesignofthewind-wave-currentflumeandthelayoutofmeasuredinstruments.WaveHeight:ThreewaveheightmetersVelocity:AcousticDopplerVelocimeter(ADV)SedimentConcentration:OpticalBackscatterSensors(OBS)andsuctionsystem0.6h0.5h0.4h0.3h0.2h0.1h0.6cmExperimentalSetupGeneratewaveGeneratecurrentMeasurerippleheightandripplelengthFormripplesMeasureExperimentalProcessMeasuringinstrument-AcousticDopplerVelocimeter（ADV）Frequency：25Hz
Totalsamplingtime:60s
currentvelocitysedimentconcentrationManualmeasurement-OpticalBackscatterSystem（OBS）Frequency：1Hz
ExperimentalSetupCasesNUMBERWaveHeightH(m)WaterDepthh(m)WavePeriodT(s)S1CWF10.120.31.50.34S1CWF20.120.31.50.36S1CWF30.120.31.50.38S1CWO10.120.31.50.32S1CWO20.120.31.50.34S1CWO30.120.31.50.38S2CWF10.120.31.50.28S2CWF20.120.31.50.33S2CWF30.120.31.50.37S2CWO10.120.31.50.30S2CWO20.120.31.50.35S2CWO30.120.31.50.38d50=47μmd50=88μmfollowingopposingResultsandDiscussionVelocityProfilesFig.4Wave-currentvelocityprofilesofthefirstkindofsediment0.1~0.3hResultsandDiscussionVelocityProfilesFig.5Wave-currentvelocityprofilesofthesecondkindofsedimentResultsandDiscussionVelocityProfilesDeviations:1)Nearthefreesurface:Calculatedvelocities>MeasuredonesLimitationofflumeSide-wallEffectYou’smodel(1994):OpenchannelResultsandDiscussionVelocityProfilesDeviations:2)Nearthebottom:Calculatedvelocities<MeasuredonesSedimentconcentrationisprettyhighthedecreaseofeddyviscosityhinderwaveboundarylayerWinterwerp,2006“cleanwater”assumptionResultsandDiscussionVelocityProfilesReferencecurrentvelocity:0.2hSedimentconcentration:“L”patternOutsidehigh-concentratedlayer“Cleanwater”assumptionReasonableResultsandDiscussionEffectiveRoughnessHeightFig.6Comparisonof‘measured’effectiveroughnessheightwiththeonespredictedbythemodelofGrantandMadsen(1982)ResultsandDiscussionEffectiveRoughnessHeightD50=47μmOverestimatesignificantlyUpto2000timesD50=88μmDeviatemildly0.62~2.30timesPredictedvalueActualoneResultsandDiscussionEffectiveRoughnessHeightFig.7Comparisonof‘measured’effectiveroughnessheightwiththeonespredictedbythemodelofLietal.(1998)ResultsandDiscussionEffectiveRoughnessHeightD50=47μmOverestimatesignificantlyUpto2000timesD50=88μmDeviatemodestly0.52~2.00timesPredictedvalueActualoneResultsandDiscussionEffectiveRoughnessHeightFig.8Comparisonof‘measured’effectiveroughnessheightwiththeonespredictedbythemodelofYou(1996)ResultsandDiscussionEffectiveRoughnessHeightD50=47μmDiscrepanciesarerelativelysmallThemaximumratiois3.70D50=88μmAlittledeviation1.04~2.73timesPredictedvalueActualoneResultsandDiscussionEffectiveRoughnessHeightFig.9Comparisonof‘measured’effectiveroughnessheightswiththeonespredictedbyaforementionedthreemodelswhen(a)themediansizeis47μmand(b)themediansizeis88μmResultsandDiscussionEffectiveRoughnessHeightGrantandMadsen(1982);Lietal.(1998)D50=88μmSedimentsactmorelikesandD50=47μmSuspendedsedimentconcentrationishighTheviscosityofflowIschangedMuchfiner;SiltDeviatemodestlyPredictedvalue>ActualoneEnergydissipationdecreasedYou(1996)DerivedfromsandybedsDeriveddirectlyfromthemodelofvelocitydistributionsSandybeds“Cleanwater”assumptionisreasonableSiltybedsHigh-concentratedflowsexistnearthebedShouldbechallengedConclusio
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