简介：Thedirect-forcingfictitiousdomainmethodisextendedtosimulatethelocomotionofapassivelypitchingfoil.Ourstudyfocusesonthehysteresisphenomenonthatthecriticalfrequencyforthereverseofthelocomotiondirectionofthewingincaseofdecreasingfrequencyissmallerthanthatincaseofincreasingfrequency.Inoursimulations,thehysteresisphenomenonisproducedbyimposingdifferentinitialconditionsatasamefrequency.Ourresultsindicatethattheratiooftheheavingamplitudesoftwofoiledgesiscrucialtothedirectionofthefoil'shorizontalmotion,andtheamplitudeoftheleadingedgeisgenerallysmaller.Thecriticalfrequenciesforthereverseofthelocomotiondirectionareincreased,whenthefoil-fluiddensityratioisdecreasedorthespringconstantisincreased.Thecriticalfrequenciesinthebi-stabilityregimealsodependontheinitialvelocityimposed,andthehysteresisloopgenerallybecomeslargeriftheinitialvelocitiesareclosertotheterminallocomotionvelocitiesofthefoil.

简介：Aninvestigationoftheventilatedsupercavitationforasupercavitatingvehiclepitchingupanddowninthesupercavitywascarriedoutinahigh-speedwatertunnel.Theemphasisislaidontheunderstandingoftheinteractionofthevehicleaftbodywiththecavityboundary.Theflowcharacteristicsweremeasuredandthestabilityofsupercavitingflowwithdifferentpitchingfrequenciesandamplitudeswasanalyzed.Inparticular,theobjectivesofthisstudyaretounderstandtheeffectoftheimpactuponthecavitydistortion,andtoquantifytheimpactprocessbyinvestigatingtheevolutionofthepressureinsidethecavityandthentheloadsonthevehicleduringthepitchingmotion.Itisalsoshownthattheevolutionofthepressuredetectedindifferent,asinsidethesupercavity,iscoherentanduniformduringtheperiodsofthepitchingmotion.Thisstudyisofdirectrelevancetoreliableandaccuratepredictionofhydrodynamicloadsassociatedwiththeslammingandimpactonsupercavitatingvehicles.

简介：<正>Thereisaneedforthepreventionofupperextremityinjuriesthataffectalargenumberofcompetitivebaseballplayers.Currentlyavailableevidencealludestothreepossiblewaystopreventtheseinjuries:1)regulationofunsafeparticipationfactors,2)implementationofexerciseinterventiontomodifysuboptimalphysicalcharacteristics,and3)instructionalinterventiontocorrectimproperpitchingtechniques.Ofthesethreestrategies,instructionofproperpitchingtechniqueisunder-exploredasamethodofinjuryprevention.Therefore,thepurposeofthisreviewwastoexploretheutilityofpitchingtechniqueinstructioninpreventionofpitching-relatedupperextremityinjuriesbypresentingevidencelinkingpitchingtechniqueandpitching-relatedupperextremityinjuries,aswellasidentifyingconsiderationsandpotentialbarriersinpursuingthisapproachtopreventinjuries.Variouskinematicparametersmeasuredusinglaboratory-basedmotioncapturesystemhavebeenlinkedtoexcessivejointloading,andthuspitching-relatedupperextremityinjuries.Aswegainmoreknowledgeabouttheinfluenceofpitchingkinematicsonjointloadingandinjuryrisk,itisimportanttostartexploringwaystomodifypitchingtechniquethroughinstructionandfeedbackwhileconsideringthespecificskillcomponentstoaddress,modeofinstruction,targetpopulation,durationofprogram,andwaystoeffectivelycollaboratewithcoachesandparents.

简介：Theobjectiveofthisstudyistodealwithunsteadyforceactingonapitchingfoilinshearflowandtostudytherelationoftheforcecharacteristicswithvortexsheddingnearthefoil.Thetwo-dimensionalincompressibleNavier-Stokesequationsinthevorticityandstream-functionformulationweresolvedwiththefourth-orderessentiallycompactfinitedifferenceschemesforthespacederivativesandafourth-orderRunge-Kuttaschemeforthetimeadvancement.Theforcecharacteristicsandvortexsheddingofthepitchingfoilinshearflowswereinvestigated.Theeffectsofsometypicalfactors,includingtheincomingflowshear,theoscillatingfrequencyandamplitude,onthevortexsheddingandforcebehaviorwereanalyzedanddiscussed.

简介：Theuseofoscillatingflexiblefinsinpropulsionhasbeenthesubjectofseveralstudiesinrecentyears,butattentionisrarelypaidtothespecificroleofstiffnessprofileinthrustproduction.Stiffnessprofileisdefinedasthevariationinlocalchordwisebendingstiffness(EI)ofafin,fromleadingtotrailingedge.Inthisstudy,flexiblefinswithastandardNACA0012shapeweretestedalongsidefinswithastiffnessprofilemimickingthatofaPumpkinseedSunfish(Lepomisgibbosus).Thefinswereoscillatedwithapitchingsinusoidalmotionoverarangeoffrequenciesandamplitudes,whiletorque,lateralforceandstaticthrustweremeasured.Overtherangeofoscillationparameterstested,itwasshownthatthefinwithabiomimeticstiffnessprofileofferedasignificantimprovementinstaticthrust,comparedtoafinofsimilardimensionswithastandardNACA0012aerofoilprofile.Thebiomimeticfinalsoproducedthrustmoreconsistentlyovereachoscillationcycle.Acomparisonoffinmaterialsofdifferentstiffnessshowedthattheimprovementwasduetothestiffnessprofileitself,andwasnotsimplyaneffectofalteringtheoverallstiffnessofthefin.Finsofthesamestiffnessprofilewereobservedtofollowthesamethrust-powercurve,independentofthestiffnessofthemouldingmaterial.Biomimeticfinswereshowntoproduceupto26%greaterthrustperwattofinputpower,withintheexperimentalrange.

简介：Inthispaperweinvestigatedhowtherunningspeedwouldaffectthedynamicsofbodypitching,andwhetherbodyinertiaisimportantforanimals.Passivetrottingofspring-massmodelandpassiveboundingofspring-beammodelwerestudiedatdifferentspeedsfordifferentsetsofbodyparametersrespectively.Furthermore,differentbodyinertiaswereusedinbounding.Wefoundthatrunningspeedexertseffectonlegperformancebymeansofcentrifugalforce.Thecentrifugalforcecanbeunderstoodasanenhancementtothenaturalfrequencyofthespring-masssystem.Thedisadvantageofbodypitchingmaybeoffsetbythegreatincreaseincentrifugalforceathighspeed.Theresultsalsorevealthatbodymassdistributionmightnotbethemainreasonforthedifferenceinmaximalrunningspeedsofdifferentanimals.

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简介：Thepitching-downflappingisanewtypeofbionicflapping,whichwasinventedbytheauthorbasedonpreviousstudiesontheaerodynamicmechanismsoffruitfly(pitching-up)flapping.ThemotivationofthisinventionistoimprovetheaerodynamiccharacteristicsofflappingMicroAirVehicles(MAVs).Inthispaperthepitching-downflappingisbrieflyintroduced.Themajorworksinclude:(1)Computingthepowerrequirementsofpitching-downflappinginthreemodes(advanced,symmetrical,delayed),whichwerecomparedwiththoseofpitching-upflapping;(2)Investigatingtheeffectsoftranslationalaccelerationtime,Δτ_t,androtationaltime,Δτ_r,attheendofastroke,andtheangleofattack,α,inthemiddleofastrokeontheaerodynamiccharacteristicsinsymmetricalmode;(3)Investigatingtheeffectofcamberonpitching-downflapping.Fromtheaboveworks,conclusionscanbedrawnthat:(1)Comparedwiththepitching-upflapping,thepitching-downflappingcangreatlyreducethetime-averagedpowerrequirements;(2)TheincreaseinΔτtandthedecreaseinΔτ_rcanincreaseboththeliftanddragcoefficients,butthetime-averagedratiooflifttodragchangesalittle.Andαhassignificanteffectontheaerodynamiccharacteristicsofthepitching-downflapping;(3)Thepositivecambercaneffectivelyincreasetheliftcoefficientandtheratiooflifttodrag.