简介：Informationofdropletsizeandsizedistributionlaysthebasisforinvestigationsofatomizationmechanismsandperformanceoptimization.However,thelaserdiffractionandphaseDopplerparticleanalyzershavedifficultyinaccuratelycharacterizingsprayswithawiderangeofdropletsizesandverylargedroplets,especiallyifalargenumberofdropletsareaspherical.Amethodtomeasuresizeinsuchlargedropletspraysbasedondigitalimagingwithbackwardilluminationwasdeveloped,includinganimageacquisitionsystemandimageprocessprograms.Calibrationofthemeasurementsystemwasperformedusingadotcalibrationtargetwithdifferentdotsizes.Anexperimentalsetupwasdesignedandestablishedtocharacterizespraynozzlesunderdifferentoperationloads,aswellasdifferentnozzlearrangements.Resultsshowthatthedropletsizeofspraysrangesfromdozensofmicronstoseveralmillimeters.Thesuperiorityofwideloadrangeforsuchnozzleswasindicatedbythesize-measurementresultsunderhalf-loadtofull-loadoperations.Thepresentstudyrevealedthattheimageprocessingtechniquecanbeeffectivelyimplementedforin-linesizemeasurementsofsprayswithawidedistributionofdropletsizeandasphericaldroplets,whichwouldbedifficulttocharacterizebyothermethods.

简介：AchargedspacecraftissubjecttotheLorentzforcewhenitorbitsacentralbodywithamagneticfield.TheinducedLorentzforceprovidesanewmeanofpropellantlesselectromagneticpropulsionfororbitalcontrol.ModelingtheEarthmagneticfieldasatilteddipolethatco-rotateswiththeEarth,thispaperdevelopsanonlineardynamicalmodelthatdescribestherelativemotionoftheLorentzspacecraftaboutanarbitraryreferenceorbit.Basedontheproposeddynamicalmodel,feasibilityofLorentz-propelledrendezvouswithnorestrictionsontheinitialstatesisinvestigated.Therendezvousproblemisthenformulatedasanoptimalcontrolproblem,andsolvedwiththeGausspseudospectralmethod(GPM).Numericalsimulationssubstantiatethevalidityofproposedmodelandmethod,andresultsshowthatthepropellantlessrendezvousisachievedatbothfixedandfreefinaltime.

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简介：Freevibrationanalysisofcompositelaminateswithdelaminationsisperformedbasedonathree-dimensionalsemi-analyticalmodelestablishedbyintroducingthelocalradialpointinterpolationmethod(LRPIM)intoaHamiltonsystem.Thegoverningequationisderivedwithatransfermatrixtechniqueandaspringlayermodelbasedonalocalweak-formequivalenttothemodifiedHellinger-Reissnervariationalprinciple.Mainsuperiorityofthepresentmodelisthatthescaleofthegoverningequationinvolvesonlytheso-calledstatevariablesatthetopandbottomsurfaces,andisinsensitivetothethicknessandthelayernumberofthecompositelaminates.Severalnumericalexamplesforanalyzingthevibrationfrequenciesandmodeshapesofdelaminatedcompositebeamsandplatesaregiventovalidatethemodel.Theresultsareingoodagreementwiththepre-existingresults.

简介：Acoupledimmersedboundary-latticeBoltzmannmethod(IB-LBM)isintroducedtosolvebiomimeticproblems.ComparedtotheconventionalIB-LBM,thestrictsatisfactionofno-slipboundaryconditionisimplementedinthecurrentmethod.Consequently,thephenomenonofflowpenetrationthatisfrequentlyobservedintheconventionalIB-LBMisfullyprevented,andsubsequentlytheforceontheboundarycanbecalculatedmoreaccurately.Thisfeatureisofimportanceforthesimulationofbiomimeticproblems.Moreover,byapplyingtherelationshipbetweenthevelocitycorrectionandforcingterm,theboundaryforcecanbecalculatedeasily.Severalbiomimeticproblemsarethensimulated.Basedonthegoodagreementbetweenthecurrentresultsandthoseintheliterature,itmaybeconcludedthatthepresentIB-LBMhasthecapabilitytohandlevariousbiomimeticproblems.

简介：Dynamicfluid-solidinteractionsarewidelyfoundinchemicalengineering,suchasinparticle-ladenflows,whichusuallycontaincomplexmovingboundaries.Theimmersedboundarymethod(IBM)isaconvenientapproachtohandlefluid-solidinteractionswithcomplexgeometries.Inthiswork,Uhlmann’sdirect-forcingIBMisimprovedandimplementedonasupercomputerwithCPU-GPUhybridarchitecture.Thedirect-forcingIBMismodifiedasfollows:thePoisson’sequationforpressureissolvedbeforeevaluationofthebodyforce,andtheforceisonlydistributedtotheCartesiangridsinsidetheimmersedboundary.Amultidirectforcingschemeisusedtoevaluatethebodyforce.Thesemodificationsresultinadivergence-freeflowfieldinthefluiddomainandtheno-slipboundaryconditionattheimmersedboundarysimultaneously.Thismethodisimplementedinanexplicitfinite-differencefractional-stepscheme,andvalidatedby2Dsimulationsoflid-drivencavityflow,Couetteflowbetweentwoconcentriccylindersandflowoveracircularcylinder.Finally,themethodisusedtosimulatethesedimentationoftwocircularparticlesinachannel.Theresultsagreeverywellwithpreviousexperimentalandnumericaldata,andaremoreaccuratethantheconventionaldirect-forcingmethod,especiallyinthevicinityofamovingboundary.

简介：Ultra-puremesoporoussilicamicrosphereswithgoodmonodispersityweresynthesizedintwosteps:nanometer-sizedsilicasolwasproducedbythesol-gelprocess,thenmicrometer-sizedsilicamicrospheresweresynthesizedbypolymerization-inducedcolloidaggregationofthesilicasol.Thetotalmetalcontentofthemicrosphereswasextremelylow,whicheliminatedthetailingofchromatographicpeaksbychelatingreagents.Theporestructureofthesilicamicrospherescouldbecontrolledbyalteringthesol-gelconditions.Thesilicamicrosphereparticlesizecouldbeadjustedbyusingdifferentpolymerizationinducedcolloidaggregationconditions.

简介：针对惯导平台连续翻滚自标定中安装误差标定精度不高这一现状,提出了一种解决方案。通过对惯性器件的输出误差模型和安装误差的分析,建立了系统的姿态动力学方程和观测方程,利用输出灵敏度理论分析了系统的可观性,指出加速度计安装误差可观性较差是影响标定精度的主要原因。利用Kalman滤波中的估值方差矩阵计算了安装误差之间的相关系数,计算结果表明可观性差是由安装误差之间的线性相关性造成的,并确定了具体的不可观参数。以加速度计输入轴为基准建立平台坐标系可以减少安装误差项,使所有的安装误差的变得可观。最后的仿真结果表明在新的方案下,安装误差的估值偏差小于5＂,标定精度得到了显著提高。

简介：对于具有一定机动能力的弹道式再入目标跟踪问题,稳定性好、鲁棒性强、收敛精度高的估计方法是保证跟踪精度的关键。针对再入运动模型和测量体制的强非线性以及目标机动引起的滤波精度下降问题,提出一种将强跟踪滤波（STF）和基于三阶球面-向径容积规则的容积卡尔曼滤波（CKF）相结合的强跟踪-容积卡尔曼滤波（STCKF）。通过将强跟踪算法中的自适应渐消因子引入到滤波时间更新和测量更新方程中,在线实时调整滤波增益矩阵,能有效避免模型失准造成的滤波性能下降,使该算法兼具CKF滤波精度高和STF鲁棒性强的优点。通过数学仿真表明,改进后的STCKF可以实现对具有机动的弹道式再入目标的高精度跟踪,相对于CKF精度提高50%,并且具有更强的鲁棒性和自适应能力。