机械噪声控制技术.ppt

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1、Chapter7MechanicalNoiseControlTechniques第7机械噪声控制技术7.1NoiseReductionbySoundAbsorption7.2NoiseInsulation7.3SilencersandMufflers7.4VibrationandNoiseReductionbyDampingTypesofsound-absorbingmaterialsSound-absorbingmaterialsareutilizedinalmostallareasofnoisecontrolengineering.Theporoussound-absorbingma

2、terialsareavailableintheformofmats,boards,mineralfibers,opencellfoams.Theyhaveopenporeswithtypicaldimensionsbelow1mmthatareverysmallerthanthewavelengthofsound.Here,eachcanbetreatedasalossyhomogeneousmedium.Chapter7MechanicalNoiseControlTechniques7.1NoiseReductionbySoundAbsorption7.1.1PorousSound-

3、AbsorbingMaterials（多孔吸声材料）Fullreticulatedplasticfoam,Partiallyreticulatedplasticfoam,Glassfiber,Mineralwool.Chapter7MechanicalNoiseControlTechniques7.1NoiseReductionbySoundAbsorption7.1.1PorousSound-AbsorbingMaterials（多孔吸声材料）HowporousmaterialsabsorbsoundOwingtotheactingsoundpressure,theairmolecul

4、esoscillateintheinterstices[in’tə:stis](空隙)ofaporousmaterialwiththefrequencyofexcitingsoundwave.Theoscillationsresultinfrictionallosses,andtheyconvertthesoundenergyintoheat.Changesinflowdirectionandexpansionsandcontractionsoftheflowthroughirregularporesresultinlossofmomentuminthedirectionofwavepr

5、opagation.Chapter7MechanicalNoiseControlTechniques7.1NoiseReductionbySoundAbsorption7.1.1PorousSound-AbsorbingMaterials（多孔吸声材料）Physicalpropertiesofporoussound-absorbingmaterialsItisimpossibletopredictthebehaviourofmostsound-absorbingmaterialsentirelyonthebasisoftheoreticalmodels,principallybecaus

6、eoftheirgeometricandstructuralcomplexities.Commercialsoftwareformodellingvibro-acousticfieldsinporoelasticmaterialsisnowavailable,butitrequiressubstantialinputsofempirical[em’pirikəl]（实验）data.Chapter7MechanicalNoiseControlTechniques7.1NoiseReductionbySoundAbsorption7.1.1PorousSound-AbsorbingMater

7、ials（多孔吸声材料）Manyexperimentalstudiesofthebehaviourofcommonsound-absorbingmaterialofwhichthestructuralskeletonsareeffectivelyrigidhasshownthattherearethreegrossparametersthatprincipallycontroltheirsoundabsorptioncharacte