简介：AMarkovianriskprocessisconsideredinthispaper,whichisthegener-alizationoftheclassicalriskmodel.ItisproperthatariskprocesswithlargeclaimsismodelledastheMarkovianriskmodel.Insuchamodel,theoccurrenceofclaimsisdescribedbyapointprocess{N(t)}_(t≥0)withN(t)beingthenumberofjumpsduringtheinterval(0,t]foraMarkovjumpprocess.TheruinprobabilityΨ(u)ofacompanyfacingsuchariskmodelismainlystudied.AnintegralequationsatisfiedbytheruinprobabilityfunctionΨ(u)isobtainedandtheboundsfortheconvergencerateoftheruinprobabilityΨ(u)aregivenbyusingageneralizedrenewaltechniquedevelopedinthepaper.

简介：Thevehicleswithhighgravitycentrearemorepronetorollover.Thepaperdealswithamethodofdynamicsanalysisoffireengineswhichisanexampleofthesetypesofvehicle.AlgorithmsforgeneratingtheequationsofmotionhavebeenformulatedbyhomogenoustransformationsandLagrange’sequation.Themodelpresentedinthisarticleconsistsofasystemofrigidbodiesconnectedonewithanotherforminganopenkinematicchain.Roadmaneuverssuchasalanechangeandnegotiatingacirculartrackhavebeenpresentedasthemainsimulationswhenacarlosesitsstability.Themethodhasbeenverifiedbycomparingnumericalresultswithresultsobtainedbyexperimentalmeasurementsperformedduringroadtests.

简介：Intheapplicationsofaircrafts,automobiles,railways,biomedicineandoff-shorestructures,manycomponentsmayexperiencecyclicloadingconditionsoveralongperiodoftime,runninguptoseveralhundredmillioncycles.1Determinationoflonglifefatiguebehaviorbecomesextremelyimportantforbetterunderstandinganddesignofcomponentsandstructures.

简介：Inthispaper,auniformanalysisoftheasymptoticpropertiesofhighfrequenciesofnon-uniformbars,beamsandcircularmembranesisgivenbyusingperturbationmethod,andthecaseofdiscontinuousphysicalparametersisalsodiscussed.

简介：Forthepurposeofachievinghigh-resolutionoptimalsolutionsthispaperproposesanodaldesignvariablebasedadaptivemethodfortopologyoptimizationofcontinuumstructures.Theanalysismesh-independentdensityfield,interpolatedbythenodaldesignvariablesatagivensetofdensitypoints,isadaptivelyrefined/coarsenedaccordingtoacriterionregardingthegray-scalemeasureoflocalregions.Newdensitypointsareaddedintothegrayregionsandredundantonesareremovedfromtheregionsoccupiedbypurelysolid/voidphasesfordecreasingthenumberofdesignvariables.Apenalizationfactoradaptivitytechniqueisemployedtopreventprematureconvergenceoftheoptimizationiterations.Suchanadaptiveschemenotonlyimprovesthestructuralboundarydescriptionquality,butalsoallowsforsufficientfurthertopologicalevolutionofthestructurallayoutinhigheradaptivitylevelsandthusessentiallyenableshigh-resolutionsolutions.Moreover,comparedwiththecasewithuniformlyandfinelydistributeddensitypoints,theproposedadaptivemethodcanachieveahighernumericalefficiencyoftheoptimizationprocess.

简介：作为与不同焊接不规则通过一个磁道的车辆，磁道部件的动态性能被使用acoupled车辆鈥搕rack模型详细调查。在模型，车辆与自由的35个学位作为一个多身体系统被建模，并且一根Timoshenko横梁被用来为被睡眠者分离地支持的栏杆建模。在课程模型，睡眠者为他们的垂直、侧面、滚动的运动作为僵硬身体财务被建模并且假定以经常的速度向后移动模仿以一样的速度沿着课程跑的车辆。在联合车辆和课程动力学的学习，Hertizian接触理论和理论由沈鈥揌edrick鈥揈l建议分别地，家族被用来计算正常并且爬在车轮和栏杆之间的力量。在正常力量的计算，正常接触僵硬的系数被车轮和栏杆表面的短暂接触状况决定。在蠕动的计算，侧面，栏杆的连接运动和在在他们的普通正常方向的车轮和栏杆之间的相对速度等于零的事实同时被考虑。车辆和磁道的运动方程借助于一个明确的集成方法，栏杆焊接不规则作为垂直偏差由一些理想的余弦函数描述了的本地轨道在被建模被解决。不规则的火车速度，轴负担，波长和深度的效果，和在一个睡眠者的焊接中心位置在装载的车轮鈥搑ail影响上跨越被分析。获得的数字结果是极大地在引起由的焊接栏杆侧面不规则的忍耐设计有用在栏杆焊接和轨道维护以后磨手。关键词栏杆焊接-不规则-车辆鈥搕rack联合动力学这个工程被中国(2007CB714702)和中国(50821063，50675183和50875221)的国家自然科学基础的国家基本研究节目支持。

简介：Thefatiguelifeofnumerousaerospace,locomotive,automotiveandbiomedicalstructuresmaygobeyond10~8cycles.Determinationoflonglifefatiguebehaviorbecomesextremelyimportantforbetterunderstandinganddesignofthecomponentsandstructures.Initially,beforetheinventionofultrasonicfatiguetesting,mostoftheengineeringmaterialsweresupposedtoexhibitfatiguelifeupto10~7cyclesorless.Thispaperreviewscurrentunderstandingofsomefundamentalaspectsonthedevelopmentofacceleratedfatiguetestingmethodanditsapplicationinultra-highcyclefatigue,crackinitiationandgrowthmechanismsofinternalfracture,S-Ndiagram,fatiguelimitandlifeprediction,etc.

简介：Inthispaper,wederivetheanalyticalsolutionsinathree-dimensionalanisotropicmagnetoelectroelasticbimaterialspacesubjecttouniformextendeddislocationsandtractionswithinahorizontalcirculararea.ByvirtueoftheStrohformalismandFouriertransformation,thefinalexpressionofsolutionsinthephysicaldomaincontainsonlylineintegralsover[0,2π]ratherthaninfiniteintegrals.Asthereducedcases,thehalf-spaceandhomogeneousfull-spacesolutionscanbedirectlyderivedfromthepresentsolutions.Also,intermsofmaterialdomains,thepresentsolutionscanbereducedtothepiezoelectric,piezomagnetic,purelyelasticmaterialswithdifferentsymmetriesofmaterialproperty.Tocarryoutnumericalcalculations,Gaussquadratureisadopted.Inthenumericalexamples,theeffectofdifferentloadinglocationsontheresponseattheinterfaceisanalyzed.Itisshownthat,whenthemagnetictractionorelectricdislocationisapplied,thephysicalquantitiesontheinterfacemaynotdecreasemonotonicallyastheloadingareamovesawayfromtheinterface.Thedistributionsofdifferentin-planephysicalquantitiesontheupperandlowerinterfacesundervariousextendedhorizontalloadingsarecomparedandthedifferencesarediscussed.Theworkpresentedinthispapercanserveasbenchmarksforfuturenumericalstudiesinrelatedresearchfields.

简介：Intensiveturbulenceexistsinthewakesofhighspeedtrains,andtheaerodynamicperformanceofthetrailingcarcoulddeterioraterapidlyduetocomplicatedfeaturesofthevorticesinthewakezone.Asaresult,thesafetyandamenityofhighspeedtrainswouldfaceagreatchallenge.Thispaperconsidersmainlythemechanismofvortexformationandevolutioninthetrainflowfield.ArealCRH2modelisstudied,withaleadingcar,amiddlecarandatrailingcarincluded.Di?erentrunningspeedsandcrosswindconditionsareconsidered,andtheapproachesofunsteadyReynold-averagedNavier–Stokes(URANS)anddetachededdysimulation(DES)areutilized,respectively.ResultsrevealthatDEShasbettercapabilityofcapturingsmalleddiescomparedtoURANS.However,forlargeeddies,thee?ectsoftwoapproachesarealmostthesame.Inconditionswithoutcrosswinds,twolargevortexstreetsstretchfromthetrainnoseandinteractstronglywitheachotherinthewakezone.Withthereinforcementoftheground,acomplicatedwakevortexsystemgeneratesandbecomesstrengthenedastherunningspeedincreases.However,thelocationsofflowseparationsonthetrainsurfaceandtheseparationmechanismkeepunchanged.Inconditionswithcrosswinds,threelargevorticesdevelopalongtheleewardsideofthetrain,amongwhichtheweakestonehasnoobviousinfluenceonthewakeflowwhiletheothertwostretchtothetailofthetrainandcombinewiththehelicalvorticesinthetrainwake.Thus,optimizationoftheaerodynamicperformanceofthetrailingcarshouldbeaimingatreducingtheintensityofthewakevortexsystem.

简介：Thermalcontactresistanceplaysaveryimportantroleinheattransferefficiencyandthermomechanicalcouplingresponsebetweentwomaterials,andacommonmethodtoreducethethermalcontactresistanceistofillasoftinterfacematerialbetweenthesetwomaterials.AtestingsystemofhightemperaturethermalcontactresistancebasedonINSTRON8874isestablishedinthepresentpaper,whichcanachieve600Cattheinterface.Basedonthissystem,thethermalcontactresistancebetweensuperalloyGH600ma...

简介：Pantographsystemofhigh-speedtrainsbecomesignificantsourceofaerodynamicnoisewhentravellingspeedexceeds300km/h.Inthispaper,ahybridmethodofnon-linearacousticsolver(NLAS)andFfowcsWilliams-Hawkings(FW-H)acousticanalogyisusedtopredicttheaerodynamicnoiseofpantographsysteminthisspeedrange.Whenthesimulationmethodisvalidatedbyabenchmarkproblemofflowsaroundacylinderoffinitespan,wecalculatethenearflowfieldandfaracousticfieldsurroundingthepantographsystem.Andthen,thefrequencyspectraandacousticattenuationwithdistanceareanalyzed,showingthatthepantographsystemnoiseisatypicalbroadbandonewithmostacousticpowerrestrictedinthemedium-highfrequencyrangefrom200Hzto5kHz.Theaerodynamicnoiseofpantographsystemsradiatesoutwardsintheformofsphericalwavesinthefarfield.Analysisoftheoverallsoundpressurelevel(OASPL)atdifferentspeedsexhibitsthattheacousticpowergrowsapproximatelyasthe4thpoweroftrainspeed.Thecomparisonofnoisereductioneffectsforfourtypesofpantographcoversdemonstratesthatonlycase1canlessenthetotalnoisebyabout3dBasbafflesonbothsidescanshieldsoundwaveinthespanwisedirection.ThecoversproduceadditionalaerodynamicnoisethemselvesintheotherthreecasesandleadtotheriseofOASPLs.

简介：Veryhighcyclefatigue(VHCF)behaviorsofbridgesteel(Q345)weldedjointswereinvestigatedusinganultrasonicfatiguetestsystematroomtemperaturewithastressratioR=-1.Theresultsshowthatthefatiguestrengthofweldedjointsisdroppedbyanaverageof60%comparingtothebasemetalandthefatiguefailurestilloccurredbeyond10~7cycles.Thefatiguefractureofweldedjointsinthelowcycleregimegenerallyoccurredatthesolderwhileattheheat-affectedzone(HAZ)intheveryhighcycleregime.Thefatiguefracturesurfacewasanalyzedwithscanningelectronmicroscopy(SEM),showingweldingdefectssuchaspore,micro-crackandinclusionwerethemainfactorsondecreasingthefatiguepropertiesofweldedjoints.Theeffectofweldingdefectsonthefatiguebehaviorsofweldedjointswasdiscussedintermsofexperimentalresultsandfiniteelementsimulations.

简介：Thispapernumericallystudiestheinfluenceofthedownwardspoilerdeflectionontheboundarylayerflowofahigh-lifttwo-elementairfoilconsistingofadroopnose,amainwing,adownwarddeflectingspoilerandasingleslottedflap.Bothoftheboundarylayeroftheuppersurfaceofthespoilerandtheconfluentboundarylayeroftheuppersurfaceoftheflapbecomethicker,asthedownwardspoilerdeflectionincreases.Comparedtotheattachedflowattheangleofattackof10°,theflowoftheuppersurfaceofthespoilerbecomesseparatedattheangleofattackof16°whenthespoilerdeflectionislargeenough,whichcorrespondstotheboundarylayerflowreversalinvelocityprofiles.

简介：Thispaperpresentsacomputationalmodelforthefluiddynamicsinafracturedductilepipeunderhighpressure.Thepressureprofileinfrontofthecracktip,whichisthedrivingsourceofcrackpropagation,iscomputedusinganonlinearwaveequation.Thesolutioniscoupledwithaonedimensionalchokedflowanalysisbehindthecrack.Thesimulationutilizesahighorderoptimizedprefactoredcompact-finitevolumemethodinspace,andlowdispersionanddissipationRunge-Kuttaintime.Asthepipefracturestherapiddepressurizationtakeplaceinsidethepipeandthepropagationofthecrack-inducedwavesstronglyinfluencestheoutflowdynamics.Consistentwiththeexperimentalobservation,themodelpredictstheexpansionwaveinsidethepipe,andthereflectionandoutflowofthewave.Themodelalsohelpscharacterizethepropagationofthecrackdynamicsandfluidflowsaroundthetipofthecrack.

简介：Thefatiguebehaviorofahighstrengthsteel300Minthegigacycleregimewasinvestigated.Fullyreversedtension-compressionfatiguetestsatambienttemperaturewereperformedusinganultrasonicfatiguesystemoperatingat20kHz.Thestaircasetestmethodwasemployedtoobtainaccuratevaluesofthemeanfatiguestrengthcorrespondingtofixednumbersofcyclesupto10~9.Theseresultswerecomparedtothecurvewhichisestimatedbythedatatestedinthemid-longliferegimeonconventionalservohydraulictestmachineat20Hz.Resultsindicatethatthefatiguestrengthdeterminedfromultrasonicfatiguetestingislightlyhigherthanconventionaltestingintherangeof10~6-10~7cycles.Itisobviousthatnucleationsoffracturestendtooccurbelowthesurface,iffractureshappenaftermorethan10~7cycles.AllthefracturedspecimensfailsfrominternalSiO_2inclusionsorsmallercarbidesandcarbideclusters.

简介：Spreadoffiresmokeintheelevatorshaftofahigh-risebuildingisinfluencedbymanydrivingfacts.Wesimulatesmokespreadingintheelevatorshaft,stairroom,andpre-chamberwithandwithoutdifferentsuppliedpressurizedair.Thesimulationshowsthatsmokemovesveryfastintheelevatorshaft.Whena12floorhigh-risebuildingisinfire,smokecanfilluptheelevatorshaftinlessthan1.5minafterafirestarted,temperatureintheelevatorshaftcanbehigherthan187?Cin5min,andtheconcentrationofCOcanalsoreachahighlevel.Theelevatorshafthasaverylowvisibilityinlessthanabout100s.

简介：BytheaidofanideaoftheweightedENOschemes,someweight-typehigh-resolutiondifferenceschemeswithdifferentordersofaccuracyarepresentedinthispaperbyusingsuitableweightsinsteadoftheminmodfunctionsappearinginvariousTVDschemes.Numericalcomparisonsbetweentheweightedschemesandthenon-weightedschemeshavebeendoneforscalarequation,one-dimensionalEulerequations,two-dimensionalNavier-StokesequationsandparabolizedNavier-Stokesequations.

简介：

简介：Thispaperfirstanalyzesthefeaturesoftwoclassesofnumericalmethodsforglobalanalysisofnonlineardynamicalsystems,whichregardstatespacerespectivelyascontinuousanddiscreteones.Onbasisofthisunderstandingitthenpointsoutthatthepreviouslyproposedmethodofpointmappingundercellreference(PMUCR),haslaidaframeworkforthedevelopmentofatwoscalednumericalmethodsuitablefortheglobalanalysisofhighdimensionalnonlinearsystems,whichmaytaketheadvantagesofb...

简介：Theyaweffectofthesideflowaroundahigh-speedtrainisstudiedbymeansoflargeeddysimulationattwotypicalyawanglesofφ=30°and60°,respectively.Boththemeanandfluctuatingvaluesofliftforceandsideforcecoefficientsincreaseobviouslyastheyawangleincreases.Thespectralanalysisindicatesthatthetime-dependentaerodynamicforcesaredominatedbyseveralenergeticfrequenciesandthefrequencyrangeisbroadenedtoahigherextentforthelargeyawangle.Tohaveabetterunderstandingofthetrainaerodynamicbehaviors,thededicatethree-dimensionalvorticalstructuresareanalyzedfortheflowatthetwoyawangles.Moreover,thetime-averagedflowpatterns,turbulentstatisticsandthesurfaceforcesarealsostudiedonsectionalplanesalongthetrain.