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  • 简介:Theeffectoffullysubmergedbouldersontheflowstructureinchannelshasbeenstudiedbysomeresearchers.However,manynaturalstreamshavebedmaterialwithbouldersthatarenotfullysubmergedunderwater.Inmanynaturalstreams,boulderscoverbetween1%and10%oftheareaofthestreamreach.Theeffectofnon-submergedbouldersonthevelocityprofileandflowcharacteristicsisveryimportantforassessingriverbeddeformation.Theobjectivesofthispaperaretofindthepatternofvelocitydistributionaroundanon-submergedboulderandtocompareitwiththeclassicalstudiesonflowresistanceandReynoldsstressdistributioninopenchannels.Also,byconsideringthevariationintheReynoldsstressdistributionatdifferentlocationsaroundanon-submergedboulder,theeffectofanon-submergedboulderontheestimationofshearvelocityandresistancetoflowhasbeeninvestigated.Resultsindicatesthatinsidethescourholecausedbyanon-submergedboulderinarivervelocitydistributionsareirregular.However,velocitydistributionsareregularoutsidethescourhole.ThepresenceofthebouldercausesaconsiderabledeviationoftheReynoldsshearstressfromtheclassicdistribution,showinganon-specificdistributionwithnegativevalues.TheclassicalmethodsforcalculatingshearvelocityarenotsuitablebecausethesemethodsdonotgivedetailedvelocityandReynoldsstressdistributionsinnaturalriverswithalotofboulders.Thus,theeffectofanon-submergedboulderontheestimationoftheresistancetoflowbyconsideringthevariationsinvelocityandReynoldsstressdistributionsatdifferentlocationsaroundanon-submergedboulderisimportantandneedstobestudiedinanaturalriverinsteadofjustinlaboratoryflumes.ThenegativevaluesinReynoldsstressdistributionaroundaboulderindicatethattheclassicalmethodsareunabletopredictresistancetoflow,andalsoshowstrongturbulenceinsidethescourholewherethecomplexflowconditionspresentambi

  • 标签: Irregular velocity distribution Logarithmic law Non-submerged
  • 简介:Hydrodynamiccharactersonahorizontal,thin,rigidplatelocatedbeneaththefreesurfacearenumericallyinvestigated.Assumingalinear,time-harmonicpotentialflowandutilizingGreenidentity,thegoverningLaplaceequationcanbesimplifiedintoFredholmintegralequationofthesecondkind.Supposinglinear-orderdiscontinuouselementsalongintersectingverticalboundaries,andbyuseoftheboundaryelementmethod,numericalsolutionaboutsourcestrengthdistributionontheplatecanbechangedintoaseriesofalgebraicequations.The3DGreenfunctionisintroducedtosetuptheintegralequations,andtheGMRESsolverisperformedforsolvingthelargedenselinearsystemofequations.Theadded-mass,dampingforceandexcitingforceareevaluateddirectlyfromtheequations.Itisfoundthattheadded-masscoefficientbecomesnegativeforarangeoffrequencieswhentheplateissufficientlyclosetothefreesurface.

  • 标签: SUBMERGED plate Dreen function Added mass
  • 简介:Thebendingrigidityofsubmergedvegetationiscloselyrelatedwithvegetativedragforce.Thisworkaimsatdeterminingtheeffectsofflowconditionsandcharacteristicsofvegetationonthebendingrigidityofsubmergedvegetation.Basedonthedimensionalanalysismethod,thefactorsinfluencingthebendingrigidityofindividualsubmergedvegetationwereanalyzed.Therelationshipbetweentherelativebendingrigidityanditsinfluencingfactorswasinvestigatedbyexperimentalobservation,andarelativebendingrigidityexpressionforsubmergedvegetationwasobtainedbymeansofmultiplelinearregressionmethod.Theresultsshowthatthesubmergedvegetationhasthreestatesunderdifferentinflowconditions,andtheeachcriticalrelativebendingrigidityofindividualsubmergedvegetationwasdeterminedforthedifferentstatesofsubmergedvegetation.

  • 标签: 抗弯刚度 沉水植物 影响因素 多元线性回归方法 植被特征 三维分析
  • 简介:Submergedvegetationhasasignificantimpactonwaterflowvelocity.Currentinvestigationsincludetheimpactthroughaddingdragresistanceandincreasingbottomroughnesscoefficient,whichcannotelucidatethecharactersofrealsubmergedvegetation.Toevaluatetheeffectsofsubmergedvegetationonwatercurrentsatdifferentvelocities,alaboratoryexperimentwasconductedusingthreekindsofvegetations.Theeffectiveheightsofthesevegetationsonvaryingflowvelocitieswereevaluated.AnequationdescribingtherelationshipbetweenthenormalizedresistanceofthesubmergedplantsandtheReynoldsnumberbasedontheplanteffectiveheightwasthenestablishedandusedtocalculatethehydraulicresistanceparametersofsubmergedplantsindifferentstagesofgrowth.

  • 标签: 沉水植物 有效高度 液阻 作者 沉水植被 拖曳阻力
  • 简介:学习的paleoforest遗体在18000m~2的一个范围以内被散布在内部Qianhu海湾的潮汐的地区,福建省。89个古老的树树桩能清楚地在paleoforest遗体被认出。相对,低使碳化树桩取样的10的显微镜的研究毫无疑问显示出四种:Glyptostrobuspensili(Staunt)Kouch,Schima出色Gardn,CinnamomumSchaeffer,和Litsea打。一些样品标明日期的~(14)C产出42560±3的年龄50到>43000一B.P.,相应于晚迟了的更新世。

  • 标签: 福建 早第三纪 更新世 群落类型
  • 简介:INTRODUCTIONItisaninterestingresearchareausingureaseinhibitorstocurbureaseactivityinsoil,todecreasetherateofureahydrolysisandtoincreasetherecoveryofureanitrogen(Zhou,1984;Guan,1985).Fewstudieshavebeenconductedontherelationshipbetweentheeffectivenessoftheinhibitorsappliedtoriceandtheenvironmentalconditionsandits

  • 标签: 环境因子 脲酶抑制剂 氮素有效率 尿素 水解作用 淹水状态
  • 简介:题目:水下板桩叶片对移动河床的影响研究  目的:比较板桩叶片和简单的平板叶片在控制河床沉积物再分配时的效率。  方法:1.在不受当地侵蚀现象影响的接近障碍物和下游区域的直线水道中研究河床的形态;2.使用不同的实验装置测试简单几何形状的平板叶片和复杂形状的603K叶片的性能;3.在不同的叶片迎角和浸没参数下,测试与其面积接近的结构和在远场中的河床形态。  结论:1.叶片的形状和迎角影响其对河床形态所产生的作用,尤其是对于较大的淹没参数而言;2.平板叶片和板桩叶片对下游河床的重塑作用相似;3.随着迎角的增加,平板叶片将造成更深的冲刷孔。这可能归因于与平板叶片相关的马蹄形涡流增加的侵蚀能力,而板桩叶片的不均匀表面可减轻该涡旋的侵蚀强度。

  • 标签: 叶片 沉积物 冲刷 河流水力学 实验水力学
  • 简介:Aquaticvegetationhasasignificantimpactonwatercurrents.Toevaluatetheeffectsofchangesintheaquaticvegetationonwatercurrentsofdifferentvelocity,a3-Dhydrodynamicmodelwasthendevelopedbytakingintoconsiderationoftheadditionalhydraulicresistanceoftheaquaticplants.TheNavier-StokesequationswerethensolvedusingtheSIMPLEmethodandthek-εturbulencemodel.CalculationsusingtheestablishedmodelswereusedtoforecasttheverticaldistributionofthehorizontalvelocityandhorizontalflowunderthetransmissionconditionsoftheSouth-NorthWaterDiversionintheNansiLake.Andcomparativecalculationfortheflowvelocitywasalsoperformedusingthesimplifiedmethodofassigningahighroughnesscoefficienttothelakebedinthesamearea.Resultssuggestthataddingadditionalhydraulicresistanceoftheaquaticplantsisfeasible.Thecalculationerrorsbetweensimulationresultandthefieldobserveddataaresmallerthan15%,while,thoseerrorsareupto35%iftheinfluenceofaquaticvegetationisdealtwiththesimplifiedmethod.

  • 标签: 水生植被 数值模型 植物区 水动力学模型 斯托克斯方程 计算错误
  • 简介:Thepurposeofthispaperistodevelopafunctionalmethodfordesigningaseriesofsubmergedbreakwatersonpracticaltopography.ThemethodisusedtoverifythefeasibilityandeffectivenessofBraggbreakwatersforcoastalprotectionbyusingfieldtopography.ThefirstpartofthispaperprovidesdefinitionsandproceduresneededinthedesignprocessforapplyingthemechanismofBraggreflection.Next,Braggbreakwatersaredesignedonthebasisofthecross-sectionaltopographyandthenontheplanetopographyoftheMi-Tuocoastbyfollowingtheproposedprocessandprocedure.Numericalmodeling(Hsuetal.,2003;WenandTsai,2008)wasusedasadesignandassessmenttool.Finally,theeffectivenessandfeasibilityofaBraggbreakwaterwasassessedbypracticalcases.BasedonthemechanismofBraggreflection,anoptimumlayoutforaseriesofsubmergedbreakwatersisproposedtoprotecttheMi-Tuocoast.Theresultsindicatethattheproperlayoutofaseriesofsubmergedcreakwaterscanachievetheobjectiveofbeachprotection.

  • 标签: 设计过程 海岸保护 潜堤 布拉格反射 海岸地形 反射机制
  • 简介:Theproblemsofasolitarywavepassingoverrectangularcylindershavebeenanalysed.Thenumericalsimulationisbasedonthefullnonlineartwo-dimensionalNavier-Stokesequationswhicharesolvedbythefinitedifferencemethod.ThefreesurfaceisdealtwithbytheVolumeofFluidmethod(VOF).ResultsforasolitarywavepassingoverasinglecylinderarecomparedwiththeexperimentaldataofSeabra-Santos,PenouardandTempervilleandbetteragreementisobtainedthanthoseobtainedfromthelongwaveequationbasedonthepotentialflowtheory.Resultsarealsogivenfortwocylinderswithdifferentgaps.

  • 标签: multi-bodies SOLITARY wave VISCOUS flows VOF
  • 简介:暴露于波浪的跨岸的沉积运输率为沿海的形态学,象防波堤那样的海洋的结构的设计,突堤,防波提等等,和由于onoff岸沉积交通的沿海的侵蚀和生长的预防是很重要的。在现在的学习,跨岸的沉积运输的实验与1/8,1/10和1/15的起始的沙滩斜坡在一条实验室波浪隧道被执行。由使用常规波浪,不同深海的波浪险峻由一个踏脚板类型波浪生成器产生了,沙滩的几何特征在影响开关岸沉积运输的暴风雨条件和参数下面介绍与d50=0.25的中等直径为沙滩材料被调查,0.32,0.45,0.62和0.80公里。近海酒吧几何特征是从海岸线的水平距离到酒吧开始(Xb),冠(Xt),并且(Xs)结束指,从酒吧冠的深度到静止的水水平(ht),并且酒吧体积(V酒吧)。当时,试验性的结果显示了那深海的险峻(H0/L0)增加,到海滨的网运动增加了。与增加的波浪险峻,移动附此从静止的水拓宽垂直距离的酒吧铺平到酒吧开始(Xb),冠(Xt)并且结束(Xs)从海岸的点和水平距离排队到酒吧开始,冠和结束的点增加了。它也从试验性的结果被显示出来自开始并且结束点到海岸线的酒吧的水平距离与沙滩斜坡的减少增加了。从这研究获得的试验性的结果与以前的试验性的工作相比并且发现具有象试验性的大小的一样的大小并且跟随期望的基本趋势。

  • 标签: 沿海 沙质岸 淹没 水平距离 实验室 海洋结构物
  • 简介:—Theresultsofdesignandexperimentofasubmergedsemi-circularbreakwaterattheYangtzeestuaryshowthatthesubmergedstructurewillbeunsafewhenthegeneralempiricalwaveforceformulaforsemi-circularbreakwaterisusedindesign.Therefore,anewcalculationmethodforthewaveforcesact-ingonasubmergedsemi-circularstructureisgiveninthispaper,inwhichthewaveforceactingonthein-sidecircumferenceofsemi-circulararchisincluded,andthephasemodificationcoefficientinthegeneralempiricalformulaisadjustedaswell.Thenewwaveforcecalculationmethodhasbeenverifiedbythere-sultsofsevenrelatedphysicalmodeltestsandadoptedinthedesignofthesouthesturaryjettyofthefirststageprojectofDeepChannelImprovementProjectoftheYangtzeRiverEstuary,thetotaljettylengthbe-ing17.5km.

  • 标签: SEMI-CIRCULAR BREAKWATER SUBMERGED structure ESTUARY jetty
  • 简介:AbstractFor the detection of steatosis, quantitative ultrasound imaging techniques have achieved great progress in past years. Magnetic resonance imaging proton density fat fraction is currently the most accurate test to detect hepatic steatosis. Some blood biomarkers correlate with non-alcoholic steatohepatitis, but the accuracy is modest. Regarding liver fibrosis, liver stiffness measurement by transient elastography (TE) has high accuracy and is widely used across the world. Magnetic resonance elastography is marginally better than TE but is limited by its cost and availability. Several blood biomarkers of fibrosis have been used in clinical trials and hold promise for selecting patients for treatment and monitoring treatment response. This article reviews new developments in the non-invasive assessment of non-alcoholic fatty liver disease (NAFLD). Accumulating evidence suggests that various non-invasive tests can be used to diagnose NAFLD, assess its severity, and predict the prognosis. Further studies are needed to determine the role of the tests as monitoring tools. We cannot overemphasize the importance of context in selecting appropriate tests.

  • 标签: Fatty liver Non-alcoholic fatty liver disease Non-alcoholic steatohepatitis Liver fibrosis Cirrhosis Transient elastography FibroScan Magnetic resonance imaging
  • 简介:Thispaperinvestigatesthemathematicfeaturesofnon-linearmodelsanddiscussestheprocessingwayofnon-linearfactorswhichcontributestothenon-linearityofanonlinearmodel.Onthebasisoftheerrordefinition,thispaperputsforwardanewadjustmentcriterion,SGPE.Last,thispaperinvestigatesthesolutionofanon-linearregressionmodelinthenon-linearmodelspaceandmakesthecomparisonbetweentheestimatedvaluesinnon-linearmodelspaceandthoseinlinearmodelspace.

  • 标签: 非线性调节模型 测量误差 精确度 空间非线性模型