声学基础教学课件电子教案全套课件.pptx

4.1球面波的声阻抗率：解：其中声压和质点速度间的相角：声阻抗率的幅值：

4.2解：脉动球的辐射阻抗：其中辐射阻辐射声功率：球体表面的速度幅值为：

4.5解：(1)线性点源阵列的声压：最大振幅：(2)零振幅时：

4.6解：脉动球辐射声压：当当＜＜＞＞■

4.7解：50米处：声压级：

4.8当点源辐射到绝对软边界，由声波性质，相当于在边界对称处再放置了一个相位相反的点声源（构成偶极子）1与1’偶极子：2与2’偶极子：由三角公式：证：带入上式即可证得由

4.9hh2h

4.9解：

4.11解：偶极声源的方向性：

4.12解：为近场为远场声轴上：

4.13解：辐射阻：辐射抗：附加同振动质量：球表面振速：

4.14解：活塞的指向性：

TheequationofstateTorelatethemotionofthefluidtoitscompressionordilatation,weneedafunctionalrelationshipbetweentheparticlevelocityuandtheinstantaneousdensityp.

Considerasmallrectangular-parallelepipedvolumeelementdV=dxdydzwhichisfixedinspaceandthroughwhichelementsofthefluidtravel.Thenetratewithwhichmassflowsintothevolumethroughitssurfacemustequaltheratewiththemasswithinthevolumeincreases.

Thatthenetinfluxofmassintothisspatiallyfixedvolume,resultingfromflowinthexdirection,isSimilarexpressionsgivethenetinfluxfortheyandzdirections,

SothatthetotalinfluxmustbeWeobtaintheequationofcontinuity

Notethattheequationisnonlinear;therightterminvolvestheproductofparticlevelocityandinstantaneousdensity,bothofwhichareacousticvariables.Considerasmallamplitudesoundwave,ifwewritep=p0(1+s).Usethefactthatp0isaconstantinbothspaceandtime,andassumethatsisverysmall,

Weobtain

Whereisthedivergenceoperator

FUNDAMENTALSOFACOUSTICS(1)XuXiaomeiEmail:xmxu@jingxian.xmu

Prerequisites:Anunderstandingofbasicmathematics,thefundamentalprinciplesofmechanics,electricity,andaccesstoascientificcalculator

Objective:Throughoutthecourseemphasisisplacedonfundamentals,withdiscussionsandproblemsextendingintosomephasesandapplicationsofacoustics

Thegeneration,transmissionandreceptionofacousticwavesOncompletionofthiscoursestudentswillbeabletounderstandthetermsusedtodescribesoundwa