简介：Lyapunov'ssecondmethodwasusedtostudythenonlinearstabilityofparallelshearflowsforstress-freeboundaries.Byintroducinganenergyfunctional,itwasshownthattheplaneCouetteandplanePoiseuilleflowsareconditionallyandasymptoticallystableforallReynoldsnumbers.Inparticular,totwo-dimensionalperturbations,bydefiningnewenergyfunctionalstheunconditionalstabilityofthebasicflowswasproved.

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简介：Inthispaper,perturbationmethodandFourier-cosine-expansionmethodareusedtosolvea3-DnonlinearproblemofasupercavitatingflowinaninclinedfieldofgravityatlargeFroudenumbers.Byexpandingthevelocitypotentialintoapowerseriesofasmallparameter,theoriginal3-Dnonlinearproblemisreducedtoanumberof2-Dones.Thesolutionsofthefirstthreeordersarederivedindetailandexpressedintermsofthecompleteellipticintegralsofthefirstandsecondkinds.Thentheboundaryintegralequationmethodisappliedtogetthenumericalsolutionsforeachorder.Computationalresultsareprovidedforsupercavitatingflowspastconesundervariousflowconditions.

简介：AnumericalsimulationmodelbasedonanopensourceComputationalFluidDynamics(CFD)package-OpenFieldOperationandManipulation(OpenFOAM)hasbeendevelopedtostudyhighlynonlinearsteadyandunsteadyfreesurfaceflows.Atwo-fluidformulationisusedinthismodelandthefreesurfaceiscapturedusingtheclassicalVolumeOfFluid(VOF)method.TheincompressibleEuler/Navier-Stokesequationsaresolvedusingafinitevolumemethodonunstructuredpolyhedralcells.Bothsteadyandunsteadyfreesurfaceflowsaresimulated,whichinclude:(1)asubmergedNACA00122-Dhydrofoilmovingataconstantspeed,(2)theWigleyhullmovingataconstantspeed,(3)numericalwavetank,(4)greenwaterovertoppingafixed2-Ddeck,(5)greenwaterimpactonafixed3-Dbodywithoutorwithaverticalwallonthedeck.ThenumericalresultsobtainedhavebeencomparedwiththeexperimentalmeasurementsandotherCFDresults,andtheagreementsaresatisfactory.Thepresentnumericalmodelcanthusbeusedtosimulatehighlynonlinearsteadyandunsteadyfreesurfaceflows.

简介：Thispaperdealswiththeproblemofdeterminingtwounknownparametersofsomenonlinearreaction-diffusionmodels.Thesereaction-diffusionmodelsarederivedfromapplicationsinthegroundwaterflowtransport,environmentalsciences,gasdynamics,heatandmasstransfer,industrialautomatizationandsomeotherengineeringtechnologicalfields.Theadjointmethodbasedonthevariationalprincipleisarelativelynewoptimalcontrolmethod.Itisusedintheidentificationoftheunknowndiffusioncoefficient,andsomecoefficientsofthenonlinearsinkorsourcetermsinthesesystems.Atfirst,theproblemistransferredintoanoptimizationproblemofminimizingafunctional,andtheadjointequationsofthegoverningequationsarederivedfromtheadjointmethod.Then,theformulasaregiventocalculatethegradientoftheobjectivefunctionwithrespecttothecoupleofunknownparameters.Atlast,aniterativegradient-basedoptimizationalgorithmispresentedforsolvingtheoptimizationproblem.Anumericalexampleisofferedintheend.Itshowstheeffectivenessoftheproposedapproach.

简介：Theproblemofwavepartial/fullreflectionandtransmissionbywave-permeablestructureisapproachedbysolvingtheshape-relatedfunctionwithfocusontheunderstandingofwaveattenuation.2Ddepth-averagedBoussinesqtypewaveequationsaregivenwithnewdampingiteminsimulatingthenonlinearwavetransmissionthroughwave-permeablestructure.1Dwaveequationisexaminedtogivetheanalyticalexpressionoftheabsorbingcoefficient,andiscomparedwithlaboratorydatainflumetocalibratethecoefficients,andtheexpressionisapplieddirectlyinmodifiedBoussinesqtypeequations.Comparedwithwavebasindataforvariousincidentwaveconditions,theaccuratepredictionsofcombineddiffraction-refractioneffectsinsimulatingnonlinearwavegoingthroughwave-permeablebreakwaterintheengineeringapplicationcanbeobtained.Itshowsthatwave-permeablebreakwaterswithproperabsorbingeffectscanbeusedasaneffectivealternativetomassivegravitybreakwatersinreductionofwavetransmissioninshallowwater.

简介：ANonlinearFluidDamping(NFD)intheformofthesquare-velocityisappliedintheresponseanalysisofVortex-InducedVibrations(VIV).Itsnonlinearhydrodynamiceffectsonthecoupledwakeandstructureoscillatorsareinvestigated.AcomparisonbetweenthecoupledsystemswiththelinearandnonlinearfluiddampingsandexperimentsshowsthattheNFDmodelcanwelldescriberesponsecharacteristics,suchastheamplificationofbodydisplacementatlock-inandfrequencylock-in,bothathighandlowmassratios.Particularly,thepredictedpeakamplitudeofthebodyintheGriffinplotisingoodagreementwithexperimentaldataandempiricalequation,indicatingthesignificanteffectoftheNFDonthestructuremotion.

简介：Uptonow,therearenosatisfactorynumericalmethodsforsimulatingwaveresistanceoftrimarans,mainlyduetothedifficultyrelatedwiththestrongnonlinearfeaturesofthepiecehullwavemakingandtheirinterference.Thisarticleproposesanumericalmethodforquickandeffectivecalculationofwaveresistanceoftrimaranstobeusedinengineeringapplications.BasedonWyatt'swork,thenonlinearfreesurfaceboundarycondition,thetimedomainconcept,andthefullnonlinearwavemakingtheory,usingtheRankinesourceGreenfunction,the3-Dsurfacepanelmethodisexpandedtosolvethetrimaranwavemakingproblems,withhighordernonlinearfactorsbeingtakenintoaccount,suchastheinfluenceofthesinkingandtrim,transom,andshipwaveimmersedhullsurface.Andthesoftwareissuccessfullydevelopedtoimplementthemethod,whichisvalidated.Severaltrimaranmodels,includingapracticaltrimaranwithasonardomeandthetransom,areusedasnumericalcalculationsamples,theirwavemakingresistanceiscalculatedbothbythepresentmethodandsomeothermethodssuchaslinear(Dawson)methods.Moreover,samplemodelresistancetestswerecarriedouttoprovidedataforcomparison,validationandanalysis.Throughthevalidationbymodelexperiments,itisconcludedthatpresentmethodcanwellpredictthewavemakingresistance,sinkingandtrim,andtheaccuracyofwavemakingresistancecalculationissignificantlyimprovedbytakingthetrimandsinkingintoaccount,especiallyathighspeeds.

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