简介:Basedondynamicrupturesimulationsonaplanarfaultinahomogeneoushalf-space,weinvestigatedthenucleationprocessesusingthetime-weakeningfrictionlaw.Boththecharacteristictimeandtherupturespeedinthenucleationasperityplayanimportantroleindeterminingrupturebehaviorsonafaultplanefollowingthetime-weakeningfrictionlaw,withwhichrupturestartsfromasinglepointinthenucleationasperityandpropagatesatagivenspeedtowardtheboundaryofthenucleationarea.Rupturewithasmallcharacteristictimeoralargerupturespeedinthenucleationasperitypropagatesearlierfromthehypocenter.Rupturefollowingtheslipweakeningfrictionlawrequiresasmallerradiusofnucleationpatchtohavesimilarrupturefrontcontoursofthetime-weakeningfrictionlaw.Eveniftherupturevelocityinthenucleationpatchofthetime-weakeningfrictionlawincreasestoinfinity,thepeaksliprateinthenucleationasperityissmallerthanthatoftheslip-weakeninglaw.Thepeakgroundvelocitydistributionsofrupturesfollowingthetwofrictionlawsarealsocompared.
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简介:Backconversionisanintrinsicphenomenoninnonlinearfrequencydown-conversionprocesses.However,thephysicalreasonforitsoccurrenceisnotwellunderstood.Here,wetheoreticallyrevealthatbackconversionistheresultofaπ-phasejumpassociatedwiththedepletionofoneinteractingwave.Bysuppressingtheidlerphasejumpthroughadeliberatecrystalabsorption,thebackconversioncanbeinhabited,thusenhancingtheconversionefficiencyfromthepumptothesignal.TheresultspresentedinthisLetterwillfurthertheunderstandingofnonlinearparametricprocessesandpavethewaytowardthedesignofhighlyefficientdown-conversionsystems.
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简介:Asanimportantelementinsustainablebuildingdesign,thebuildingenvelopehasbeenwitnessingaconstantshiftinthedesignapproach.Integratingmulti-objectiveoptimization(MOO)intothebuildingenvelopedesignprocessisverypromising,butnoteasytorealizeinanactualprojectduetoseveralfactors,includingthecomplexityofoptimizationmodelconstruction,lackofadynamic-visualizationcapacityinthesimulationtoolsandconsiderationofhowtomatchtheoptimizationwiththeactualdesignprocess.Toovercomethesedifficulties,thisstudyconstructedanintegratedbuildingenvelopedesignprocess(IBEDP)basedonparametricmodelling,whichwasimplementedusingGrasshopperplatformandinterfacestocontrolthesimulationsoftwareandoptimizationalgorithm.ArailwaystationwasselectedasacasestudyforapplyingtheproposedIBEDP,whichalsoutilizedagrid-basedvariabledesignapproachtoachieveflexibleoptimumfenestrations.Tofacilitatethestepwisedesignprocess,anovelstrategywasproposedwithatwo-stepoptimization,whichoptimizedvariouscategoriesofvariablesseparately.Comparedwithaone-stepoptimization,thoughtheproposedstrategyperformedpoorlyinthediversityofsolutions,thequantitativeassessmentofthequalitiesofPareto-optimumsolutionsetsillustratesthatitissuperior.
简介:Tandemgasmetalarcwelding(T-GMAW)processshowsahighdepositionratethatuptothreetimesofthesingleelectrodeGMAW,sotheweldingspeedcouldbesignificantlyincreasedinthisprocess.However,themajorityofthisprocessapplicationsarebasedonthepre-programmedroboticwelding,whichdoesnotallowthemtotracktheseamreal-timeduringwelding.Rotatingarcsensor,sensingtheseampositionbydetectingthechangingofweldingcurrents,hasbeenwidelyadoptedintheautomaticrobotweldingprocess.Itisproposedinthispapertointegratetherotatingarcsensorwithatrailingtorchtodevelopanewapproachofrotatingarcleadtandemgasmetalarcwelding(RLT-GMAW)process.Thecharacteristicsoftheweldingcurrentsintheproposednewweldingprocesswerefirstlystudied,andthenaself-turningfuzzycontrolseamtrackingstrategywasdevelopedforthemobilerobotautomaticwelding.TheexperimentalresultsshowedthattheproposedRLT-GMAWprocesshadanexcellentseamtrackingperformanceandhighweldingdepositionrate.Evenifthereweresomeelectromagneticinteractionsbetweenthetwoarcs,thedeviationoftheweldingseamcouldalsobereflectedbythefluctuationoftheweldingcurrentsontheleadingarconcethecorrectweldingparameterswereselected.Basedonthedetecteddeviation,theweldingtrackingexperimentsshowedthattheproposedself-turningfuzzycontrollerhadagoodperformancefortheRLT-GMAWprocessseamtracking.
简介:Inthisstudy,atwo-stepheatingprocessisintroducedfortransientliquidphase(TLP)diffusionbondingforsoundjointswithT91heatresistantsteels.Atfirst,ashort-timehighertemperatureheatingstepisaddressedtomelttheinterlayer,followedbythesecondsteptocompleteisothermalsolidificationatalowtemperature.Themostcriticalfeatureofournewmethodisproducinganon-planarinterfaceattheT91heatresistantsteelsjoint.WeproposeatransitionalliquidphasebondingofT91heatresistantsteelsbythisapproach.Sincejointmicrostructureshavebeenstudied,wetestedthetensilestrengthtoassessjointmechanicalproperty.Theresultindicatesthatthesolidifiedbondmaycontainaprimarysolid-solution,similarcompositiontotheparentmetalandfreefromprecipitates.Jointtensilestrengthofthejointisnotlowerthanparentmaterials.Jointbend'sstrengthsareenhancedduetothehighermetal-to-metaljunctionproducinganon-planarbondlines.Nevertheless,thetraditionaltransientliquidphasediffusionbondingproducesplanarones.Bondingparametersofnewprocessare1260℃for0.5minand1230℃for4min.
简介:Nb-Ti-Si-based合金粉末被元素的粒子的机械alloying(麻省)准备。形态学,尺寸,阶段成分,雏晶尺寸,格子紧张,作文和内部微观结构的进化,等等,合金,粉末被X光检查衍射(XRD)分析,扫描电子显微镜学(SEM),精力散的光谱学(版本),激光粒子尺寸分析器和传播电子显微镜(TEM)分析。合金粒子逐渐地被精制,他们的形状随milling时间的增加变得球状。Nb稳固的答案(Nbss)的衍射山峰分阶段执行移动向从2~5在球milling期间降低2个角度?h,并且在那Nbss衍射以后,山峰变向更高,有milling的增加的2个角度从5~70预定?h,它主要由于alloying元素原子的溶液被归因于Nbss粉末的格子参数的改变进Nb格子形成Nbss。在球milling过程期间,在雏晶尺寸的减少和粉末导致他们的衍射的连续拓宽的Nbss的格子紧张的增加达到顶点。典型薄片状的微观结构为5在球milling以后在粉末粒子内被形成?h并且变得更多随milling时间的增加精制了并且一致。在40-h-ballmilling以后,典型薄片状的微观结构消失并且很同类的微观结构相反被形成。这同类的微观结构被证明由仅仅使过饱和的Nbss阶段构成。
简介:Inordertotheoreticallystudythebucklepropagationofsubseapipelineswithslip-onbucklearrestors,atwo-dimensionalringmodelwassetuptorepresentthepipelineandanonlinearspringmodelwasadoptedtosimulatethecontactbetweenpipeline’sinnerwallsandbetweenpipeline’souterwallandslip-onbucklearrestor’sinnerwallduringbucklepropagation.Inaddition,somereversespringsareaddedtopreventthewallofleftandrightsidesseparatingfromtheinnerwallofslip-onbucklearrestors.Consideringlargedeformationkinematicsrelationsandtheelastic-plasticconstitutiverelationofmaterial,balanceequationswereestablishedwiththeprincipleofvirtualwork.Thevariationofexternalpressurewithrespecttothecross-sectionalareaofpipelineswasanalyzed,andthelowerboundofthecrossoverpressureofslip-onbucklearrestorswascalculatedbasedonMaxwell’senergybalancemethod.Bycomparingthetheoreticalresultswithexperimentandfiniteelementnumericalsimulation,thetheoreticalmethodisprovedtobecorrectandreliable.