Mechanisms of sound scattering and radiation of submerged elastic structure - vibro-acoustic coupling of structure and water

The mechanisms of the sound scattering and radiation of elastic structure submerged in water are summarized in three aspects particularly to emphasize the vibro-acoustic coupling or fluid loading. First the vibro-acoustic coupling is discussed in terms of the impedances. For the canonical problems both the scattering and radiation sounds can be expressed by impedances. The total impedance of the system equals to a sum of the mechanic impedance and the acoustic impedance. The sound fields depend on a ratio of the acoustic impedance to the total impedance, while the vibration velocities of surface depend only on the total impedance. The total impedance equals zero gives the characteristic equation of the system. The roots of it are namely the poles of the sound fields. Secondly the vibro-acoustic coupling is discussed by using the Resonance Scattering Theory and the Resonance Radiation Theory. The theories express the sound fields by a superposition of various resonance reradiation modes and reveal the vibro-acoustic coupling mechanism in viewpoint of vibration. It has specially proved that the reradiation efficiencies of resonance modes are nearly proportional to the imaginary parts of the complex frequency poles. Thirdly the vibro-acoustic coupling is discussed by using the Surface Elastic Wave Theory based on the Sommerfeld-Watson transformation. The theory expresses the sound fields by a superposition of various surface elastic waves-circumferential waves and reveal the vibro-acoustic coupling mechanism in viewpoint of wave. It is also proved that the reradiation efficiencies of circumferential waves are nearly proportional to the imaginary parts of the complex wavenumber poles.