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一、选择
1、在明渠均匀流中取一六面体,其所受的外力作用在该六面体上有(正压力、切向力、重力)
2、在水箱上接出一条等直径长细圆管,末端设有阀门以控制流量,若水箱内水面不随时间变化,当阀门开度一定时,管中水流为(恒定均匀流)
3、对实际流体,总水头总是(沿程下降)
4、按短管进行水力计算的管路是(虹吸管)
5、跌水的形成条件是(从缓流过渡到急流)1.在明渠均匀流中取一六面体,其所受的外力作用在该六面体上有(正压力、切向力、重力)2.在水箱上接出一条等直径长细圆管,末端设有阀门以控制流量,若水箱内水面不随时间变化,当阀门开度一定时,管中水流为(恒定均匀流)3.对实际流体,总水头总是(沿程下降)
4.按短管进行水力计算的管路是(虹吸管)
5.跌水的形成条件是(从缓流过渡到急流)1.在静水中取一六面体,分析其所受的外力作用在该六面体上的力有正压力、重力2.在水箱上接出一条逐渐收缩锥形管道,末端设有阀门已控制流量,当水箱内水面不变、阀门开度一定时,管中水流为非恒定非均匀流3.按短管进行水力计算的管路是虹吸管4.外延管嘴的正常工作条件是管长l=3-4d,作用水头小于9米水柱5.两段长直的棱柱形渠道,通过的流量相同,粗糙系数不同n1n2,其他参数相同i,b,m,Q,则h01h021.在静水中取一六面体,分析其所受的外力作用在该六面体上的表面力有正压力2.在水箱上接出一条逐渐收缩锥形管道,末端设有阀门以控制流量,当水箱内水面不变、阀门开度一定时,管中水流为恒定非均匀流3.等直径圆管中层流的过流断面流速分布是呈抛物线分布4.流体内部某点压强为2个工程大气压,用液柱高度为20米水柱5.总水头线与测压管水头线的基本规律之一,是总水头线总是在测压管水头线的上方1.流体运动的连续性方程是根据(质量守恒)原理导出的2.判断层流和紊流的临界雷诺数是下临界雷诺数3.圆管的水力半径为
二、判断题
1.流体内部切应力的大小仅与流速梯度有关(×)
2.真空压强是指没有大气存在时的压强(×)
3.均匀流一定是恒定流(√)
4.动能修订系数与断面流速分布有关(√)
5.壁面光滑的管道一定是水力光滑管(×)
6.若两孔口形状、尺寸完全相同,作用水头相同,一个为自由出流,一个为淹没出流,二者的流量是相同的(√)
1.流体内部切应力的大小仅与流速梯度有关(×)
2.真空压强是指没有大气存在时的压强(×)
3.均匀流一定是恒定流(√)
4.动能修订系数与断面流速分布有关(√)
5.壁面光滑的管道一定是水力光滑管(×)
6.若两孔口形状、尺寸完全相同,作用水头相同,一个为自由出流,一个为淹没出流,二者的流量是相同的(√)1.非均匀流一定是非恒定流×2.流体内部切应力的大小仅与流速梯度有关×3.壁面光滑的管道一定是水力光滑管×)4.流体中某点的静压强大小与受压面方位无关√5.明渠水流,从急流过渡到缓流,发生跌水水跌×6.明渠水流的测压管水头线不可能沿程上升×1.理想流体与实际流体的区别仅在于,理想流体具有不可压缩性×2.无论流体作何种运动,流体内任何一个水平面都是等压面×3.在恒定流情况下,流线与迹线重合√4·对于渐变流,过流断面上动水压强分布符合静水压强分布规律√5.壁面粗糙的管道一定是水力粗糙管×6.在进行水力计算时,短管是指管道几何长度较短的管道×1.实际流体在等直径长管中流动时的总水头线是水平的直线(×)2.流体内切应力方向与流体运动方向相同(错误)3.等压面与质量力垂直(正确)4.阻力平方区内阻力系数与雷诺数无关(正确)
三、简答题(共5小题,每题10分,共50分)1流体静压强的两个特征?
(1)垂直指向受压面
(2)某点压强的大小与受压面的方位无关(某点压强的大小仅与该点的淹没深度有关)
2、根据尼古拉兹试验,说明紊流各区沿程阻力系数与Re和K/d的关系?
(1)水力光滑区××=f(Re)
(2)过渡粗糙区=f(ReK/d)3粗糙区=f(K/d0)
3、为什么对于孔口淹没出流无小孔口与大孔口的区别?在划分小孔口和答孔口时,若H/d10视为孔口各点的压强仅似相等,定义为小孔口,对于孔口淹没出流其作用水头H为上下游水面差,孔口各点的压强相等,故对于孔口淹没出流无小孔口与大孔口之分
4、何种流动为恒定流?若流体中任一点的运动要素与时间无关,或者说流体中任一点的运动要素不随时间变化
5、圆管中层流与紊流,其断面流速分布有什么不同?圆管中层流断面流速分布为抛物线状,而圆管中紊流断面流速分布为对数曲线,紊流的断面流速分布均匀化了1流体静压强的两个特征?
(1)垂直指向受压面
(2)某点压强的大小与受压面的方位无关(某点压强的大小仅与该点的淹没深度有关)
2.根据尼古拉兹试验,说明紊流各区沿程阻力系数与Re和K/d的关系?答
(1)水力光滑区××=f(Re)
(2)过渡粗糙区=f(ReK/d)3粗糙区=f(K/d
03.为什么对于孔口淹没出流无小孔口与大孔口的区别?答在划分小孔口和答孔口时,若H/d10视为孔口各点的压强仅似相等,定义为小孔口,对于孔口淹没出流其作用水头H为上下游水面差,孔口各点的压强相等,故对于孔口淹没出流无小孔口与大孔口之分
4.何种流动为恒定流?若流体中任一点的运动要素与时间无关,或者说流体中任一点的运动要素不随时间变化
5.圆管中层流与紊流,其断面流速分布有什么不同?圆管中层流断面流速分布为抛物线状,而圆管中紊流断面流速分布为对数曲线,紊流的断面流速分布均匀化了1.动力粘滞系数∥和运动粘滞系数v布什么区别两者都反映流体的粘滞性,为动力量,v为运动量,,量纲不同3.简述明渠恒定非均匀流的水力特征答
①过水断面面积A,水深h,沿程改变即
②底坡线,水面线,总线头线三线不再平行,即1.等压面是水平面的条件有哪些答1必须是同一种流体2必须是连续流体3必须是单一重力作用条件下4必须为静止流体5分2.管道内流态为紊流时,水力光滑与水力粗糙是如何定义的答固体边界表面存在当量粗糙度K,流体运动时在固体边界存在粘性底层艿;1当粘性底层艿远远大于当量粗糙度KK-0.4a,粘性底层完全掩盖当量粗糙度K,称为水力光滑3分2当粘性底层不能掩盖当量粗糙度K时K6δ,称为水力粗糙2分1.流体力学中连续介质假定的含义是什么?答案流体是一个紧挨着一个的连续的质点所组成的,没有任何空隙的连续体,即所谓的“连续介质”同时认为,流体的物理力学性质,例如密度、速度、压强和能量等,为空间坐标和时间的连续函数2.描述流体运动的两种方法是什么?简述其内容答案
(1)拉格朗日法以流体质点为研究对象,研究质点空间位置随时间的变化过程
(2)欧拉法以流体空间位置的质点为研究对象,研究在确定位置上,流体质点速度随时间的变化过程3.简述尼古拉兹实验中沿程阻力系数λ的变化规律答案通过尼古拉兹实验发现在层流中λ仅是雷诺数Re的函数并与Re成反比;在层流到紊流过渡区,λ仅是Re的函数;在紊流光滑区λ=f1(Re),过渡区λ=f2(Re,),粗糙区λ=f3(),紊流粗糙区又称阻力平方区
4.在渗流计算中达西定律与杜比公式有何区别?答案达西定律适用于任一点的渗流流速u=kJ,其适用于恒定均匀层流渗流;而杜比公式是适用于恒定非均匀渐变层流渗流,同一过水断面上各点的渗流流速都相等且等于v=kJVisa-freepolicybringsChengdubiztourismboost.MakingnationalheadlinesseveraltimesChengdus72-hourvisa-freepolicyhasattractedwideattentionfrombothChineseandforeignexpertsandbusinessmensinceittookeffectonSept1lastyear.Theprogrampermitscitizensfrom51countriesandregionsincludingtheUnitedStatesAustraliaCanadaandJapanwhohavevalidvisasandflightticketstoathirdcountrytospendthreedaysinthecity.ThecapitalofSichuanprovinceisthefirstcityinthewesternregionofChinatoofferforeigntouristsathree-dayvisaandthefourthnationwidetoadoptthepolicyfollowingShanghaiBeijingandGuangzhou.LiZhiyongdeputydeanofthetourisminstituteatSichuanUniversitysaidthemovecontributestoalargeincreaseinthenumberofoverseastouristsandraisesthecityslevelofinternationalization.ThepolicywillalsobringdirecteconomicrevenueLisaid.Chengduhasmanyculturallegaciesandisalsoaparadiseforpandaloverswiththeworldslargestbreedingandresearchcenter.Threedaysarelongenoughforforeignvisitorstovisitthoseiconictouristspotshenoted.ThecityishometotheremainsoftheJinshacivilizationthatdatesbackmorethan3000yearsaswellastheQingchengMountainsandtheDujiangyanirrigationsystem.QingchenghaslongbeenrecognizedasthebirthplaceofTaoismChinasancientindigenousreligionwhileDujiangyanisconsideredtobetheoldestfunctioningwater-controlprojectintheworld.Chengdurankedthirdintouristfacilitiesmanagementandservicesamong60Chinesecitiesinacustomersatisfactionsurveyreleasedlastyear.ButLiaddedthateffortsarestillneededtodevelopmoretourismproductsimproveEnglishservicesandprovideaccuratetranslationoftrafficsignsandscenicbillboards.ZhaoYunchairwomanofBritishChamberofCommerceSouthwestChinatoldChinaDailythathiscolleaguesfoundthepolicyveryconvenient.ABritishclientonceflewhereandstayedforjustonedaytocheckherorderedgoodsshesaid.ZhaowasborninShanxiprovincebutshehaslivedinChengduformorethan10years.Mylifewaslikearunningracemovingfromplacetoplace.IalsolivedinBeijingandShanghaibeforeshesaid.ButChengduisaplacethatyouneverwanttoleaveoncesettlingdown.Itisnowmysecondhometownshesaid.Iftheenvironmentisfurtherimprovedthecitywillattractmorepeopletovisitandlivewiththe72-hourvisa-freepolicyandcompellingconditionsintransportationcultureclimateandcuisinehesaid.Foreignersalsogavepositivefeedbackonthepolicy.AspokesmanfromDellIncsaidthecompanyhasaglobalhubofoperationinChengdusothethree-dayvisahasanimmediateandpositiveinfluenceonthecompanysbusinessdevelopment.RudyButtignolpresidentofthepublicbroadcastingcompanyinBritishColumbiaCanadasaidhisworkrequiresfrequenttraveltoChengduandthepolicymakesthetripseasier.Datafromthecityspublicsecuritybureaushowssome100foreignvisitorsenjoyedthe72-hourpolicybytheendofMarchmostofthemfromtheUnitedStatestheUnitedKingdomandGermany.Chengdualsoreportedrobustgrowthinitsoveralltouristindustrylastyear.Officialstatisticsshowthatitreceivedsome150milliontouristslastyearanincreaseof28percentfrom
2012.Around
1.7millioncamefromabroadanincreaseof12percent.Totalrevenuefromtourismsurpassed133billionyuan$
21.7billion.DuringhisvisittoKazakhstaninSeptemberChinesePresidentXiJinpingproposedthatChinaandCentralAsiajoinhandstobuildaSilkRoadeconomicbelttoboostcooperation.TheideahasbeenwidelyechoedinCentralAsiancountriesbecominganencouragingblueprintforChineseareasalongtheSilkRoadthathaslinkedAsiaandEuropeformorethan2000years.InthenextthreeweeksChinaDailyreporterswilltravelthroughthebeltinChinaandinKazakhstanUzbekistanandTurkey.Theywillshowtheprogressandexpectationsofthecountriesbusinessesandpeoplesontheroute.Shaanxi-thestartoftheancientSilkRoad-haspositioneditselfasthenewstartingpointforthedevelopmentoftheSilkRoadEconomicBeltwhichwillstrengthenChinascooperationwithCentralAsiancountriesaseniorofficialsaid.ShaanxiGovernorLouQinjiansaidtheprovinceisfreshrichanduniqueasitwaswhenitanchoredoneendoftheancientSilkRoad.ItisthebestoptionforaccommodatingindustrialtransfersfromEastChinaortheworldatlargehesaidonWednesdayinXian.Louheldajointinterviewwith27mediaincludingChinaDailythefirstinaseriesofinterviewsentitledChineseMediaAlongtheSilkRoad.TheinterviewswillbeinShaanxiandGansuprovincesandtheXinjiangUygurautonomousregionaswellasKazakhstanUzbekistanandTurkey.ThemediagroupheldthefirstinterviewonWednesdaymorninginXianthestartingpointoftheancientSilkRoadatradechannelestablishedmorethan2000yearsagolinkingChinaCentralAsiaandEurope.。