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简介：Noncoherentunderwateracousticcommunicationchannelinadverseconditionsismodeledasaphase-randomRayleighfadingchannel,anditscapacitycurveisderived.Toapproachthechannelcapacitycurve,theconcatenatedcodeofthenonbinaryLDPCcodeandtheconstantweightcodeisproposedfornoncoherentcommunicationwhichcanlatebeiterativelydecodedintheprobabilitydomain.Withoutinformationofchannelamplitudeorphaseinthereceiver,statisticparametersoftherespectivesignalandnoisebinswereestimatedbasedonthemomentestimationmethod,theposteriorprobabilitiesoftheconstantweightcodewordswerefurthercalculated,andthenonbinaryLDPCcodewasdecodedwiththenonbinaryfactorgraphalgorithm.Itisverifiedbysimulationsthatbyutilizingtheproposedconcatenatedcodeanditsprocessingalgorithm,gaptochannelcapacitycurveisreducedby3dBwhencomparedtotheexistingmethod.Underwatercommunicationexperimentswerecarriedoutinbothdeepocean(verticalcommunication,5km)andshallowlake(horizontalcommunication,near3km,delayspreadlargerthan50ms),inwhichthesignalfrequencybandwas6kHzto10kHz,andthedatatransmissionrateWas357bps.Theproposedschemecanworkproperlyinbothexperimentswithasignal-to-noiseratiothresholdof2dB.TheperformanceoftheproposedalgorithmWaswellverifiedbytheexperiments.

简介：Theoreticalandexperimentalresearchoflowfrequencypulsecompressionandchannelmatchinshallowwatersoundchannelwerecarriedoutbasedon2000-WinterYellowSeaexperiment.Usingpulsecompressionmethod,signalswithhighsignaltonoiseratio(SNR)werereceivedoverrangeof110kilometersintheexperiment.TheSNRgainintheprocessisconsistentwiththetheoreticalprediction.Theexperimentalmeasurementindicatedthatthechannelishighlycoherentoveralengthof500s.ChannelmatchmethodwasusedtocompensatethedegradationofpulsecompressionSNRcausedbythemulti-pathpropagation.AndtheSNRgaininthechannelmatchprocesscanbetheoreticallypredicted.ExperimentalresultsshowthatlowfrequencypulsecompressionandchannelmatchmethodcanbeusedinshallowwatersoundchanneltoimprovetheSNR.

简介：Inthispaperlargeeddysimulationofthefullydevelopedturbulentflowinacurvedchanneliscarriedout.ThecomputationalresultsarepresentedandcomparedwiththeexperimentalresultsofEskinaziandYeh.ItisshownthatthenumericalresultsofthepresentLESarereliableandtheinfluenceofthecurvatureontheturbulencefeatureiscorrectlyrevealed.

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简介：A16-channeldualtuningwavelengthdivisionmultiplexer/demultiplexerbasedonsilicononinsulatorplatformisdemonstrated,whichisbothpeakwavelengthtunableandoutputopticalpowertunable.Thewavelengthdivisionmultiplexer/demultiplexerconsistsofanarrayedwaveguidegratingforwavelengthdivisionmultiplexing/demultiplexing,aheaterforpeakwavelengthtuningandavariableopticalattenuatorbasedonp–i–ncarrier-injectionstructureforopticalpowertuning.Theexperimentalresultsshowthattheinsertionlossonchipofthedeviceis3.7dB–5.7dBandthecrosstalkis7.5dB–9dB.Forthetunabilityofthepeakwavelength,1.058-nmwavelengthtunabilityisachievedwith271.2-mWpowerconsumption,andtheaveragemodulationefficiencyis3.9244nm/W;forthetunabilityoftheopticalpower,theopticalpowerequalizationisachievedinall16channels,20-dBattenuationisachievedwith144.07-mWpowerconsumption,andtheraise/falltimeofVOAis35ns/42ns.

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简介：NumericalsimulationsandexperimentalresearcharebothcarriedouttoinvestigatethecontrolledeffectofspanwiseoscillatingLorentzforceonaturbulentchannelflow.ThevariationsofthestreaksandtheskinfrictiondragareobtainedthroughthePIVsystemandthedragmeasurementsystem,respectively.Theflowfieldinthenear-wallregionisshownthroughdirectnumericalsimulationsutilizingspectralmethod.Theexperimentalresultsareconsistentwiththenumericalsimulationresultsqualitatively,andboththeresultsindicatethatthestreaksaretiltedintothespanwisedirectionandthedragreductionutilizingspanwiseoscillatingLorentzforcescanberealized.Thenumericalsimulationresultsrevealmoredetailofthedragreductionmechanismwhichcanbeexplained,sincethespanwisevorticitygeneratedfromtheinteractionbetweentheinducedStokeslayerandintrinsicturbulentflowinthenear-wallregioncanmakethelongitudinalvorticestiltandoscillate,andleadstoturbulencesuppressionanddragreduction.

简介：Inrealmultiple-inputmultiple-output(MIMO)systems,theperfectchannelstateinformation(CSI)maybecostlyorimpossibletoacquire.Butthechannelstatisticalinformationcanbeconsideredrelativelystationaryduringlong-termtransmission.Thestatisticalinformationcanbeobtainedatthereceiverandfedbacktothetransmitteranddonotrequirefrequentupdate.Byexploitingchannelmeanandcovarianceinformationatthetransmittersimultaneously,thispaperinvestigatestheoptimaltrans-missionstrategyforspatiallycorrelatedMIMOchannels.Anupperboundofergodiccapacityisderivedandtakenastheper-formancecriterion.Simulationresultsarealsogiventoshowtheperformanceimprovementoftheoptimaltransmissionstrategy.

简介：AnumericalschemeisdevelopedtoextendthescopeofthespectralmethodwithoutsolvingthecovariantandcontravariantformsoftheNavier-Stokesequationsinthecurvilinearcoordinates.TheprimitivevariablesarerepresentedbytheFourierseriesandtheChebyshevpolynomialsinthecomputationalspace.Thetimeadvancementisaccomplishedbyahigh-ordertime-splittingmethod,andacorrespondinghigh-orderpressureconditionatthewallisintroducedtoreducethesplittingerror.Comparedwiththepreviouspseudo-spectralscheme,inwhichtheNavier-Stokesequationsaresolvedinthecovariantandcontravariantforms,thepresentschemereducesthecomputationalcostand,atthesametime,keepsthespectralaccuracy.Theschemeistestedinthesimulationsoftheturbulentflowinachannelwithastaticstreamwisewavywallandtheturbulentflowoveraflexiblewallundergoingthestreamwisetravelingwavemotion.Theturbulentflowoveranoscillatingdimpleisstudiedwiththepresentnumericalscheme,andtheperiodicgenerationofthevorticalstructuresisanalyzed.

简介：基于雷纳兹压力方程的简化格式，为各向异性的骚乱模型的一个崭新的旋转修正的方法被介绍了。有模型(=0.1和=1)和标准k-骚乱建模的这新旋转的修改的k-骚乱的三维的海军司烧代码在旋转被用于流动和热转移特征的预言光滑的方形的隧道。雷纳兹数字Re基于冷却空气和水力的直径的入口速度是6000。旋转速度是300，600，900，1200rpm分别地。使用三个骚乱模型的计算结果与试验性的数据相比。研究结果证明(1)旋转修正系数Rf13在新各向异性的k-模型使用了将与标准k-模型相比在后面的表面/铅表面上增加/减少热转移的预言。并且这个趋势将被增加与增加。(2)标准k-模型的模拟表演在领先的表面上好。然而，在走以后出现它下面预言在高旋转的热转移速度。(3)有=0.1的新各向异性的k-模型的计算结果由礼品建议纸与试验性的数据同意了很好，两个在领先、后面的表面上。而且与1相比，0.1是更适当的大小以在现在的论文的条件。

简介：到spanwise墙摆动(SWO)的突然的实现的狂暴的enstrophy的反应经由直接数字的模拟在狂暴的隧道流动被学习。在SWO的申请的开始，重要关联在y和z。狂暴的enstrophy的短暂生长发生，它直接提高狂暴的驱散并且漂流向一个新降低拖条件的狂暴的流动。以后，与拉长涡度有关的学期(x,y，和z),由\的y(\frac{\partialw}{\partialy}\)，由\的z的拐弯(\frac{\partialv\prime}{\partialz}\)，并且水平由\z砍(\frac{\partialw\prime}{\partialx}\)由于SWO的存在被压制，导致狂暴的enstrophy的变细。

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简介：ThispaperdescribesaLeastSquares(LS)channelestimationschemeforMIMOOFDMsystemsbasedontime-domaintrainingsequence.Wefirstcomputetheminimummeansquareerror(MSE)oftheLSchannelestimation,andthenderivetheoptimalcriteriaofthetrainingsequencewithrespecttotheminimumMSE.Itisshownthatoptimaltime-domaintrainingsequenceshouldsatisfytwocriteria.First,theautocorrelationofthesequencetransmittedfromthesameantennaisanimpulsefunctioninaregionlongerthanthechannelmaximumdelay.Second,thecross-correlationbetweensequencestransmittedfromdifferentantennasiszerointhisregion.Simulationresultsshowthattheestimatorusingoptimaltime-domaintrainingsequenceshasbetterperformancethanthatusingoptimalfrequencytrainingsequenceatlowsignal-to-noiseratio(SNR).Toreducethetrainingoverhead,asuboptimaltrainingsequenceisalsoproposed.Comparingwithoptimaltrainingsequence,ithaslowcomputationcomplexityandhightransmissionefficiencyattheexpenseoflittleperformancedegradation.

简介：Thispaperreportsthatanexperimentalstudyisconductedtoexaminethedynamicsoftheoutflowintwo-layerexchangeflowsinachannelconnectingbetweentwowaterbodieswithasmalldensitydifference.TheexperimentsrevealthegenerationofKelvin-Helmholtz(KH)instabilitieswithinthehydraulicallysub-criticalflowregionofthechannel.Duringmaximalexchange,thoseKHinstabilitiesdevelopsintolarge-amplitudeKHwavesastheyescapethechannelexitintothereservoir.Thepropagationspeed...

简介：作为冷却剂的与燃料的再生冷却在超音速冲压式喷气发动机引擎被使用。为了掌握引擎燃料的动态特征，供应过程，这篇文章在隧道以内学习烃燃料的动态特征。一个维的动态模型被证明的A，热精力存储效果，燃料体积效果和化学动态效果在模型，被考虑了平常的微分方程用第4顺序Runge-Kutta方法被解决。模型的精确被三组试验性的数据验证。输入的效果发信号，工作状况，压力的动态特征上的试管尺寸，流动率，温度被模仿了。裂开的反应增加了燃料热分解混合的压缩的可能性，这被发现并且导致插头流动的更长反应的时间。将极大地影响引擎戳系统的控制性能的试管长是5m的插头流动罐头活动范围3s的反应时间。同时，当入口流动率出现时步变化，入口压力导致射，overshoot能到达差不多100%，如此的高度短暂的推动将在燃料泵上导致有害效果。

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简介：Inthispaperinvestigationsontheflowpatternsandthethermaldragphenomenoninone-dimensionalinviscidchannelflowwithheatingorcoolingaredescribedanddiscussed:expressionsofflowrateratioandthermaldragcoefficientfordifferentflowpatternsanditsphysicalmechanismarepresented.

简介：Anexperimentalstudyofheattransfercharacteristicsinsuperheatedsteamcooledrectangularchannelswithparallelribswasconducted.Thedistributionoftheheattransfercoefficientontherib-roughedchannelwasmeasuredbyIRcamera.Theblockageratio(e/Dh)ofthetestedchannelis0.078andtheaspectratio(W/H)isfixedat3.0.Influencesoftheribpitch-to-heightratio(P/e)andtheribangleonheattransferforsteamcoolingwereinvestigated.Inthispaper,theReynoldsnumber(Re)forsteamrangesfrom3070to14800,theribpitch-to-heightratioswere8,10and12,andribangleswere90°,75°,60°,and45°.Basedonresultsabove,wehaveconcludedthat:Incaseofchannelswith90°tranverseribs,forlargerribpitchmodels(theribpitch-to-heightratio=10and12),areaswithlowheattransfercoefficientinfrontofribislargeranditsminimumislower,whilethepositionoftheregionwithhighheattransfercoefficientnearlyremainsthesame,butitsmaximunofheattransfercoefficientbecomeshigher.Incaseofchannelswithinclinedribs,heattransfercoefficientsonthesurfacedecreasealongthedirectionofeachribandshowanapparentnonuniformity,consequentlytheregionswithlowNusseltnumbervaluescloselyfollowingeachribexpandalongtheaforementioneddirectionandthatofrelativehighNusseltnumbervaluesvaryinversely.Forasquarechannelwith90°ribsatRe=14800,widerspacingribconfigurations(theribpitch-to-heightratio=10and12)giveanarea-averagedheattransferontherib-roughenedsurfaceabout8.4%and11.4%morethanP/e=8model,respectively;forinclinedparallelribswithdifferentribanglesatRe=14800,thearea-averagedheattransfercoefficientsof75°,60°and45°ribbedsurfacesincreaseby20.1%,42.0%and44.4%incomparisonwith90°ribanglemodel.45°anglerib-roughenedchannelleadstoamaximalaugmentationofthearea-averagedheattransfercoefficientinallresearchobjectsinthispaper.