专业英语重点段落翻译.doc

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1、专业英语重点段落翻译Unit4回转壳体的薄膜应力Ashellofrevolutionis回转壳体是由一条直线或曲线绕一根旋转形成的（一个回转实体是由一个面绕一根轴旋转而成的）。Mostprocessvesselsaremadeup大多数过程容器是由回转壳体组成的：圆柱形和圆锥形部件；半球形，椭圆形和准球形的封头；图.1.13。Thewallsofthinvesselscanbe薄的容器壁被称为“薄膜”；承受载荷不引起严重的弯曲和过大的剪切应力；就象气球的外壁一样。Theanalysisofthemembrane对受内压回转壳

2、的薄膜应力分析为确定容器壳体最小壁厚奠定了基础。实际的厚度要求同样取决于容器所承受的载荷所产生的应力。Considertheshellofrevolution假设大致形状如图1.14的回转壳体在载荷作用下做对称的旋转；在壳体单位面积上所受的载荷（压力）在周向方向是一致的，但是从顶部到底部并不是一模一样的。Unit5机械振动Vibrationsaresometimesusedtoproducedesirableeffects.Forexample,vibratorsareusedtocompactconcreteinthefo

3、rmsandtoseparatethegrainfromthechaffinthreshingmachines.Instrumentswhichfunctionproperlyonanairplanewithaconventionalenginemaytendtostickwhenusedinglidersorjet-poweredplanesbecauseofthelackofvibration.Insuchinstances,avibratorissometimesinstalledontheinstrumentpane

4、l.有时候振动也能产生有益的效果。比如，振动可以压实物体，用脱粒机将谷粒与谷壳分离。那些在具有常规发动机的飞机上可正常运行的仪器，当用于滑翔机或喷气机时，因为缺乏振动，可能会趋于粘滞。在这种情况下，就需在仪器的仪表板上安装振动器。Mechanicalvibrationswhicharemaintainedbyelastic,andsometimesgravity，forcesarecalledfreevibrations.Oncestarted,afreevibration,frequentlycalledanaturalv

5、ibration,continuestooscillateatitsnaturalfrequency.Aforcedvibrationisproducedandmaintainedbyaperiodicexcitingforceexternaltothesystem,andittakesplaceatthefrequencyoftheexcitingforce.Ifthesystemisnearlyfrictionlessandcontainsnodissipativeelements,theamplitudeofthefo

6、rcedoscillationwillbecomeverylargewhenthefrequencyoftheexcitingforceisclosetothenaturalfrequencyofthesystem.Thus,althoughthefrequencyofaforcedvibrationisindependentofthenaturalfrequencyoftheelasticsystem,theresultingamplitudeisaffectedbybothfrequencies.Vibrationsar

7、ealsoclassifiedasdampedorundamped.Whenfriction,airresistance，viscousdamping,andallotherresistingforcesarenegligiblethevibrationisundamped.Whenanyoftheseeffectsisappreciablethebodyhasdampedvibrations.Inpracticethereisalwaysafrictionaldampingforcewhichwilleventuallys

8、topafreevibration,eventhoughitmaybeneglectedformanypurposes.机械振动是通过弹力保持的，有时是重力，这些力被称为自由振动。自由振动通常称为固有振动，一旦开始，就将以固有频率持续振动。强迫振动由系统外的周期性激荡力产生并保持，它以激荡