简介:导航雷达在采集、传输和显示过程中,由于多种因素的影响导致最终形成的图像中舍有大量的噪声,影响了使用者对导航信息的分析和应用。传统的雷达图像去噪算法大多采用小波变换,但这种方法存在边缘模糊等问题。为了去除导航图像的噪声并解决小波变换中存在的边缘模糊问题,本文提出用基于多尺度几何变换的图像去噪方法对导航雷达图像进行处理,并利用基于多尺度几何变换的方法(包括基于Curvelet系数维纳滤波去噪方法和基于Contourlet域去噪方法)和基于小波变换的BayesShrink方法分别对含有模拟杂波和噪声的导航雷达图像进行仿真实验。实验结果表明:与基于小波变换的图像去噪方法相比,基于多尺度几何变换去噪方法能够更加有效去除雷达杂波和噪声。
简介:Thetransitionbetweenregularreflection(RR)andMachreflection(MR)oftypeVshock–shockinteractiononadouble-wedgegeometrywithhightemperaturenon-equilibriumeffectsisinvestigatedbyextendedshock-polarmethodandnumericalsimulation.First,thecriticalanglesoftransitionfromdetachmentcriterionandvonNeumanncriterionaredeterminedbytheextendedshock-polarmethodconsideringthenon-equilibriumeffects.Thenwavepatternsandthetransitionprocessarenumericallyobtained.Resultsofthecriticaltransitionanglesfromshock-polarcalculationandnumericalsimulationshowevidentdisagreement,indicatingtransitionmechanismbetweenRRandMRoftypeVinteractionischanged.Bycomparingwiththefrozencounterpart,itisalsofoundthatnon-equilibriumeffectsleadtoalargercriticalwedgeangleandalargerhysteresisinterval.
简介:TheRichtmyer–Meshkovinstabilityofa‘V'shapedair/heliumgaseousinterfacesubjectedtoaweakshockwaveisexperimentallystudied.Asoapfilmtechniqueisadoptedtocreatea‘V'shapedinterfacewithaccurateinitialconditions.Fivekindsof‘V'shapedinterfaceswithdifferentvertexanglesareformedtohighlighttheeffectsofinitialconditionsontheflowcharacteristics.Theresultsshowthataspikeisgeneratedaftertheshockimpact,andgrowsconstantlywithtime.Asthevertexangleincreases,vorticesgeneratedontheinterfacebecomelessnoticeable,andthespikedevelopslesspronouncedly.Thelineargrowthrateofinterfacewidthaftercompressionphaseisestimatedbyalinearmodelandarevisedlinearmodel,andthelatterisproventobemoreeffectivefortheinterfacewithhighinitialamplitudes.Thelineargrowthrateofinterfacewidthis,forthefirsttimeinaheavy/lightinterfaceconfiguration,foundtobeanon-monotonousfunctionoftheinitialperturbationamplitude–wavelengthratio.
简介:Theapplicabilityandlimitationofseveralquadraticstrengththeorieswereinvestigatedwithrespectto2D-C/SiCand2.5D-C/SiCcomposites.Akindofdamage-basedfailurecriterion,referredtoasD-criterion,isproposedfornonlinearceramiccomposites.Meanwhile,thenewlydevelopedcriterionispreliminarilyvalidatedundertension-shearcombinedloadings.ThepredictionshowsthatthefailureenvelopegivenbyD-criterionislowerthanthatfromTsai–HillandHoffmancriteria.Thisrevealsthatthedamage-basedcriterionisreasonableforevaluationofdamage-dominatedfailurestrength.
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简介:ThisisoneoftheapplicationsofPart(Ⅰ),inwhichtheangularstiffness,thelateralstiffnessandthecorrespondingstressdistributionsofC-shapedbellowswerecalculated.Thebellowswasdividedintoprotrudingsectionsandconcavesectionsfortheuseofthegeneralsolution(Ⅰ),butthecontinuityofthestressresultantsandthedeformationsateachjointofthesectionswereentirelysatisfied.Thepresentresultswerecomparedwiththoseoftheothertheoriesandexperiments,andarealsotestedbythenumericallyintegralmethod.Itisshownthatthegoverningequationandthegeneralsolution(I)areveryeffective.
简介:AlaminarpremixedPropane/Airflamewithafuelequivalenceratioof2.1wasemployedforanalysisofsootparticles.Zeroth-orderIognormaldistributions(ZOLD)wereusedintheanalysisofexperimentaldistributionphenomenaatdifferentresidencetimesduringsootformationintheflame.Rayleigh'stheoryandMie'sscatteringtheorywerecombinedwithagglomerateanalysisusingscatteringandextinctiondatatodeterminethefollowingsootcharacteristics:agglomerateparameters,volumetricfractions,massflowratesandsurfacegrowthrate.Sootdensitymeasurementswerecarriedouttodeterminedensityvariationsatdifferentstagesofgrowth.Themeasuredresultsshowthatmetricfractionandmassflowrateindicatethatthesurfacegrowthrateofsootparticlesexceedstheoxidationratesintheflamestudied.Thedataobtainedinthisworkwouldbeusedtostudysootoxidationrateunderflamingcondition.