Mechanism of the acoustic radiation of semi-infinite plate below critical frequency: Radiation from the boundary

Engineering experience shows that in noise and vibration control for ships and aircraft, measures like stiffening can reduce vibration but may fail to lower radiated noise, as they disrupt structural continuity and create new radiation sources. This paper investigates the sub-critical frequency sound radiation from the boundaries of semi-infinite plates using analytical and discrete Fourier transform methods. A force-excited finite plate is also considered, generating its supersonic sound intensity map. Results demonstrate that the near- and far-field sound pressure and supersonic sound intensity manifest the radiation patterns of different boundary conditions as monopole, dipole, and quadruple pole patterns. At resonance, boundary acoustic radiation dominates in finite structures. Furthermore, as the plate size and frequency increase, the radiation differences among various boundary conditions converge to the results observed in semi-infinite plates. This study provides a mechanistic understanding of the relationship between vibration and sound radiation, offering valuable insights for controlling sound radiation in engineering applications.