简介:随着MEMS技术工艺的发展,微型结构在工程领域的应用越来越广泛.对于微型结构,经典连续介质力学理论的本构关系中不包含任何特征长度尺度,不能反映结构在微米尺度下的尺寸效应.本文基于VonKarman大变形理论和一阶剪切变形理论,把考虑尺寸效应的应变梯度理论推广至微型Mindlin板的非线性问题.分别计算微结构的应变能,包括宏观变形应变能和微观变形应变能两部分,结合微型Mindlin板结构的动能及外力功,代入Hamilton原理,得到了微型Mindlin板在大变形情况下的非线性动力学方程及边界条件.
简介:AnewstabilizedfiniteelementmethodwhichisdifferentfromHughesandFranco’s(1988)ispresentedfortheReissner-Mindlinplatemodel.Theleastsquaremesh-dependentresidualformoftheshearconstituteequationisaddedtothePartialProjectionschemetoenhancethestability.Usingpiecewisepolynomialsoforderk≥1fortherotations,oforderk+1forthedisplacementandoforderk-1fortheshear,thekthordererror-estimatesareobtained.Besides,ourcomputingschemecanbealsoappliedtosomelowerorderelements.Allerror-estimatesareobtainedindependentoftheplatethickness,andthestabilityparameterisanarbitrarypositiveconstant.
简介:InthisshortnoteweusetheideaofR.Duran[5]andintroduceanewlow-ordertriangularelementbyreplacingthenonconforminglinearelementfortherotationin[2]withtheconforminglinearelement.Theoptimalordererrorestimatesareobtaineduniformlyintheplatethickness.
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简介:Parametricresonanceisoneofthemostimportantissuesinthestudyofdynamicalbehaviorofstructures.Inthispaper,dynamicinstabilityofamoderatelythickrectangularplateonanelasticfoundationisinvestigatedinthecaseofparametricandexternalresonancesduetoperiodicpassageofmovingmasses.Thegoverningcoupledpartialdifferentialequations(PDEs)ofthesystem,withconsiderationofthefirst-ordersheardeformationtheory(FSDT)orMindlinplatetheory,arepresentedandtheyarereducedtoasetofordinarydifferentialequations(ODEs)withtime-dependentcoefficientsusingtheGalerkinprocedure.Allinertialcomponentsofthemovingmassesareadoptedinthedynamicalformulation.Instabilitysurveyiscarriedoutforthreedifferentloadingtrajectoriesconsiderablyinterestedinmanypracticalapplicationsoftheissue,i.e.rectilinear,diagonalandorbitingtrajectories.Inordertoanalyzetheresonanceconditions,theincrementalharmonicbalance(IHB)methodisintroducedtocalculateinstabilityboundaries,aswellasexternalresonancecurvesinparametersplane.Acomprehensivestudyisdonetoassesseffectsofthicknessratioandfoundationstiffnessontheresonanceconditions.Itisfoundthatanincreaseintheplate'sthicknessratioleadstoareductioninvaluesofcriticalparameters.Moreover,itisobservedthatincreasingthefoundationstiffnessmovestheinstabilityregionsandresonaneecurvestohigherfrequenciesofthemovingmassesandalsoleadstofurtherstabilityoftheparametricallyexcitedsystematlowerfrequencies.TimeresponsesimulationsdoneviaRunge-KuttamethodconfirmedtheresultspredictedbyIHBmethod.
简介:2006年12期创想乐园答案想像测试1:2我们现在是站在魔术师的背后观察画面。因为摄像机是在魔术师前方拍摄的,因此和我们从背面观察到的图像肯定是相反的。只要找出与
简介:ASTUDYOFAL1NEARCOMPRESSORWITHAGASSPRING;LINEARRESONANCECOMPRESSORDRIVENBYAVARIABLEGAPRELUCTANCELINEARMOTOR;Methodforestimatingcargodamageduringtrucktranspoortation;Microweartestsbyusingatomicforcemicroscope:relationshipbetweencontactareaandpull-offforce;RelationbetweenfrictionandplasticdeformationexaminedbyusingperiodicasperityarraysfabricatedonanAFMmultipurposecantilever……