DOUBLE-ROOT RESONANCES AND COMPLEX MODAL SLOWNESSES IN A FLUID-SOLID MEDIUM

摘要

The mono-frequency field in a range-independent fluid-solid medium can be represented as a wavenumber integral or as a sum of modes. The modal wavenumbers are in general simple roots of the dispersion function. However, multiple roots may appear as well causing certain complications and anomalies. Using accurate and efficient algorithms for wavenumber integration and modal synthesis, we discuss double-root phenomena for four cases. In particular, complex modal wavenumbers can enter the real axis at a double root for a certain frequency if some solid region is present. Implications for safe computation of the wave-field are discussed.