简介:NonlinearMHDKelvin-Helmholtz(K-H)instabilityinapipeistreatedwiththederiva-tiveexpansionmethodinthepresentpaperThelinearstabilityproblemwasdiscussedinthepastbyChandrasekhar(1961)andXuetal.(1981).Nagano(1979)discussedthenonlinearMHDK-Hinstabilitywithinfinitedepth.Heusedthesingularperturbationmethodandextrapolatedtheob-tainedsecondordermodifierofamplitudevs.frequencytoseekthenonlineareffectontheinstabilitygrowthrateγ.However,inourview,suchanextrapolationisinappropriate.Becausewhentheinstabili-tysetsin,thegrowthratesofhigher,ordertermsontherighthandsideofequationswillexceedthecor-respondingsecularproducingterms,sotheexpansionwillstillbecomemeaninglessevenifthesecularproducingtermsareeliminated.Mathematicallyspeaking,it’simpossibletoderiveformula(39)whenγ02isnegativeinNagano’spaper.Moreover,evenasearlyasγ02→O+,theexpansionbe-comesinvalidbecausethe2ndordermodifierγ2(inhisformula(56))tendstoinfinity.Thisweak-nessisremovedinthispaper,andtheresultisextendedtothecaseofapipewithfinitedepth.
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简介:采用低耗散WENO(weightedessentialnon-oscillatory)格式及锐界面方法模拟可压缩Kelvin-Helmholtz不稳定性问题.由于物质界面被描述成一种接触间断,该方法可精确求解切向速度间断.基于优化模板对原始光滑指标进行正规化后,得到一种低耗散WENO格式.修正后的方法显著降低了普通流动区域的过衰减问题,保持了良好的激波捕捉性能,并可获得与混合格式相当的求解精度.不同于以往求解单一流体或易混界面时,通过初始设定有限宽度的剪切层或快速数值耗散以抑制高波数模态,该方法允许高波数扰动的发展.计算结果表明,高波数扰动展现出与以往理想Kelvin-Helmholtz不稳定性问题数值模拟或线化理论结果不同的特征,但与有限厚度的剪切层结果相符.
简介:TheHelmholtzequationissometimessupplementedbyconditionsthatincludethespecificationoftheboundaryvalueofthedivergenceoftheunknown.Inthispaper,westudythevectorHelmholtzproblemindomainsofbothC~(1,1)andLipschitz.Wees-tablisharigorousvariationalanalysissuchasequivalence,existenceanduniqueness.Andweproposefiniteelementapproximationsbasedontheuncoupledsolutions.Fi-nallywepresentaconvergenceanalysisanderrorestimates.
简介:WeconsiderthenumericalsolutionfortheHelmholtzequationinR~2withmixedboundaryconditions.Thesolvabilityofthismixedboundaryvalueproblemisestab-lishedbytheboundaryintegralequationmethod.BasedontheGreenformula,weexpressthesolutionintermsoftheboundarydata.Thekeytothenumericalreal-izationofthismethodisthecomputationofweaklysingularintegrals.Numericalperformancesshowthevalidityandfeasibilityofourmethod.Thenumericalschemesproposedinthispaperhavebeenappliedintherealizationofprobemethodforinversescatteringproblems.
简介:ThereisnoaccurateanalyticalapproachfortheacousticperformancepredictionofHelmholtzresonatorwithconicalneck,whichhasbroadbandacousticattenuationperformanceinthelowfrequencyrange.Topredicttheacousticperformanceoftheresonatoraccurately,ageneraltheorymodelbasedontheone-dimensionalanalysisapproachwithacousticlengthcorrectionsisdeveloped.Thesegmentationmethodisusedtocalculatetheacousticparametersforsoundpropagationinconicaltubes.Andthen,anapproximateformulaisdeducedtogiveaccuratecorrectionlengthsforconicaltubeswithdifierentgeometries.Thedeviationsoftheresonancefrequencybetweenthetransmissionlossresultsobtainedbythegeneraltheorywithacousticlengthscorrectionandtheresultsfromthefiniteelementmethodandexperimentsarelessthan2Hz,whichismuchbetterthantheresultsfromone-dimensionalapproachwithoutcorrections.Theresultsshowthatthemethodofacousticlengthcorrectionfortheconicalneckgreatlyimprovedtheaccuracyoftheone-dimensionalanalysisapproach,anditwillbequickandaccuratetopredictthesoundattenuationpropertyofHelmholtzresonatorwithconicalneck.
简介:ElNi的影响?在热带太平洋上的对流地联合的凯尔文波浪上的o南部的摆动(ENSO)被在东方太平洋(EP)ElNi比较绝对温标波浪活动调查?o,中央太平洋(CP)ElNi?o,并且LaNi?一年,分别地到30年(19822011)意味着统计。在这研究的对流地联合的凯尔文波浪被过滤的225天的通带的实验直角的功能(文件结束)的二个领先的模式代表每天出去的longwave放射(OLR)与3或4的估计的带的wavenumber,8天的时期,并且东方宣传17ms1的速度。在绝对温标波浪活动的ENSO的最重要的影响在EPElNi期间是绝对温标波浪的增强?os。LaNi的影响?一上绝对温标波浪紧张的减小相对更弱,反映热带深传送对流和联系凯尔文的非线性响应ENSO海表面温度(SST)飘动异例。CPElNi的影响?绝对温标波浪上的o由于相对更弱的SST异例和更小的空间范围是不太重要的。ENSO可以也改变绝对温标波浪的频率,波长,和阶段速度。这研究证明低频率的ENSOSST异例调制高周波的热带骚乱,天气气候连接的一个例子。
简介:Spectralelementmethodiswellknownashigh-ordermethod,andhaspotentialbetterparallelfeatureascomparedwithlowordermethods.Inthispaper,aparallelpreconditionedconjugategradientiterativemethodisproposedtosolvingthespectralelementapproximationoftheHelmholtzequation.Theparallelalgorithmisshowntohavegoodperformanceascomparedtononparallelcases,especiallywhenthestiffnessmatrixisnotmemorized.Aseriesofnumericalexperimentsinonedimensionalcaseiscarriedouttodemonstratetheefficiencyoftheproposedmethod.
简介:ALegendrespectralelement/LaguerrecoupledmethodisproposedtonumericallysolvetheellipticHelmholtzproblemonthehalfline.Rigorousanalysisiscarriedouttoestablishtheconvergenceofthemethod.Severalnumericalexamplesareprovidedtoconfirmthetheoreticalresults.TheadvantageofthismethodisdemonstratedbyanumericalcomparisonwiththepureLaguerremethod.
简介:ThereareNdomainsDj.(j=0,1,……,N-1)ofdifferentphysicalparametersinthewholespaceandtheirinterfaces.Sjj+1arenon-horizontallysmoothcurvedsurfaces.ThefollowingboundaryproblemiscalledHelmholtzboundaryproblem:Theanalyticalsolutionoftheaboveproblemisgiveninthispaper.
简介:Forapracticalsuperconductingquantuminterferencedevice(SQUID)basedmeasurementsystem,theTesla/voltcoefficientmustbeaccuratelycalibrated.Inthispaper,weproposeahighlyefficientmethodofcalibratingaSQUIDmagnetometersystemusingthreeorthogonalHelmholtzcoils.TheTesla/voltcoefficientisregardedasthemagnitudeofavectorpointingtothenormaldirectionofthepickupcoil.Byapplyingmagneticfieldsthroughathree-dimensionalHelmholtzcoil,theTesla/voltcoefficientcanbedirectlycalculatedfrommagnetometerresponsestothethreeorthogonallyappliedmagneticfields.Calibrationwithalternatingcurrent(AC)fieldisnormallyusedforbettersignal-to-noiseratioinnoisyurbanenvironmentsandtheresultsarecomparedwiththedirectcurrent(DC)calibrationtoavoidpossibleeffectsduetoeddycurrent.Inourexperiment,acalibrationrelativeerrorofabout6.89×10-4isobtained,andtheerrorismainlycausedbythenon-orthogonalityofthreeaxesoftheHelmholtzcoils.ThemethoddoesnotneedprecisealignmentofthemagnetometerinsidetheHelmholtzcoil.Itcanbeusedforthemultichannelmagnetometersystemcalibrationeffectivelyandaccurately.
简介:介绍在光滑的开的弧上为Helmholtz方程建议了第一个客气的不可分的方程的一个数字答案的研究。照方法使用了;数字例子。