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英文翻译--计算机与设计.doc

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英文翻译--计算机与设计.doc

ComputerandDesignThecomputerhashadamajorimpactonthewayeverydaytasksassociatedwithdesignareaccomplished.Itcanbeusedinmanywaystodomanythings.However,alldesigntasksaccomplishedusingacomputerfallintooneoffourbroadcategoriesdesignmodelingdesignanalysisdesigndocumentation1.DesignModelingInCAD/CAMdesignmodeling,ageometricmodelofaproductisdevelopedthatdescribesthepartmathematically.ThismathematicaldescriptionisconvertedtographicformanddisplayedonacathoderaytubeCRT.Thegeometricmodelalsoallowsthegraphicimagetobeeasilyeditedandmanipulatedoncedisplayed.TheprocessbeginswhenadesignercreatesagraphicimageusingaspecialICGsoftwarepackage.Theimageiscreatedbyenteringcommandsthatcausethecomputertoconstructtheimageoutofpoints,lines,circles,andcurves.Tocreateagraphicimage,thecomputermusttranslatethegeometriccharactersintoacorrespondingmathematicalmodel.Whatappearstothedesignerasagraphicimageisstoredinthecomputerasaseriesofmathematicalcoordinates.Asthedesignerissuescommandstoeditormanipulateagraphicimage,thecomputerrevisesthemathematicalmodel.Thecomputermustfirstchangethegeometricmodelbeforeitcanchangethegraphicimage,anditmustcalculatethemathematicalcoordinatesofageometriccharacterbeforeitcandisplaythatcharacter.Graphicimagesaredisplayedinoneofthreeformats.twodimensionalor2D.twoandahalfdimensionalor21/2D.threedimensionalor3DThesethreeformatsareillustratedinFig.2.3,2.4and2.5.A2Dgraphicimageshowsanorthographicflatrepresentationandusuallyshowstwoormoreviewse.g.,top,front,andrightside.A21/2Dgraphicimageisanobliquerepresentation.A3Dgraphicimagemaybeawireframemodeloratrue3DsolidmodelFig2.6.Communicationcanbeenhancedfurtherwhengraphicimagesaredisplayedincolor.ManycapabilitiesofCAD/CAM,includingfiniteelementanalysis,wireframe3D,andsolidsmodeling,aremoreeasilyunderstoodwhenthegraphicimagesareFig1displayedincolor.Specificapplicationssuchaspipingdrawingsarealsoeasiertoreadwhendisplayedinanappropriatevarietyofcolors.Whengraphicimagesaredisplayedinonlyonecolor,itissometimesdifficulttodeterminewhenlinescrossoverorunder,whatisnearandwhatisfaraway,whatistheoriginalimageandwhatisthedistortedimageasinthecaseoffiniteelementanalysis,andwhichlayeragivencomponentison.Theuseofcolorallowsforamoredefinitivedistinctionbetweenoverandunder,nearandfar,andoriginalanddistorted.Italsohelpsclarifyobjectsconsistingofnumeroussurfacesorseveralcomponentparts.2.DesignAnalysisThecomputerhassimplifiedthedesignanalysisstageofthedesignprocesssignificantly.Onceaproposeddesignhasbeendeveloped,itisnecessarytoanalyzehowitwillstanduptotheconditionstowhichitwillbesubjected.Suchanalysismethodsasheattransferandstressstraincalculationsaretimeconsumingandcomplex.WithCAD/CAM,specialcomputerprogramswrittenspecificallyforanalysispurposesareavailable.Fig2Onesuchprogramthathassimplifiedtheanalysisofmanufacturedproductsiscalledfiniteelementanalysis.FiniteelementanalysisinvolvesbreakinganobjectupintomanysmallrectangularortriangularelementsFig.2.7,thenanalyzingeachindividualelementbycomputer.Thisapproachgivesathoroughanalysisthatmightnotbefeasiblewithouttheaidofacomputer.Italsoofferstheadvantageofspecificallypinpointingthelocationsofproblemssothatdesigncorrectionscanbemoreeasilymade.Withfiniteelementanalysis,thecomputermusthaveapowerfulprocessingcapability.Thecomputeranalyzesthewholeobjectbyanalyzingeachindividualinterconnectedfiniteelement.Byanalyzingtheresponseofeachfiniteelementoftheobjecttothestress,strain,heat,orotherforceactingonit,thecomputercanpredictthereactionofthewholeobject.ModernCAD/CAMsystemswithfiniteelementanalysiscapabilitymaketheprocesssimpletoachieve.Usersdefinetheareathatistobedivided.Thecomputerthenautomaticallydividestheareaintotheinterconnectednetworkoffiniteelements.Fig3Aparticularlyvaluablecharacteristicoffiniteelementanalysisisitsabilitytovisuallydisplaytheresultsoftheanalysis.Forexample,ifapartistobeanalyzedtodeterminehowitwillbehavewhensubjectedtoaspecifiedamountofstress,thecomputerisablesuperimposetheimageofthestressedpartovertheunstressedpart.Inthisway,theresultantdistortioncanbeeasilyseen.Suchvisualevidenceoftheresultscanmakeiteasierforthedesignertopinpointthenecessarydesignchanges.3.DesignReviewAnotherstepinthedesignprocessthathasbeensimplifiedbythecomputerisdesignreview.Thisinvolvescheckingtheaccuracyofallaspectsofthedesign.ThereareseveralICGcapabilitiesthatmakedesignreviewinCAD/CAMeasierthanwithmanualdesign.ThefirstisthesemiautomaticdimensioningcapabilityofmanyCAD/CAMsoftwarepackages.Toproduceagraphicimage,anICGsystemmustfirstcreateamathematicalmodel.Thedatainthismodelcanbeusedbythecomputerforcalculatingdimensionsautomatically.MostgoodCAD/CAMsoftwarepackagescandisplaythesedimensionsaccordingtostandarddimensioningandtolerancingpractices.Thismeansfewerdimensioningerrors,acommonproblemwithmanualdimensioning.ThelayeringcapabilityofCAD/CAMsoftwarealsosimplifiesdesignreview.Ifamultisidedprintedcircuitboardhasbeendesigned,thetracesforeachsuccessivelayercanbedisplayedsimultaneously.Inthisway,tracescanbeeasilycheckedto

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