Acoustic radiation generated by local excitation of submerged beams and strings

Free and forced motions of submerged one-dimensional waveguides have been investigated. Both the submerged beam and the submerged string can support a wave system which includes a pure surface wave in the fluid adjoining the waveguide, provided that certain conditions on the frequency (for the beam) or the physical parameters of the system (for the string) are satisfied. Dispersion curves are presented for steel beams and steel strings in water. Steady-state solutions have been derived for excitation by a concentrated time-harmonic load. The displacement responses at the point of application of the load and in the far field have been examined. Polar plots display and radiated far field in the fluid. At low frequencies the polar plots are circular in planes containing the waveguide, but the radiation pattern develops lobes as the frequency increases. Reflection, transmission and scattering into the fluid of an incident wave system by an elastic support of stiffness κ and mass m have also been examined, and the possibility of resonance phenomena has been investigated.