OBLIQUE WAVE DIFFRACTION BY PARALLEL THIN VERTICAL BARRIERS WITH GAPS

The problem of oblique water wave diffraction by two equal thin, paral lel, fixed vertical barriers with gaps present in uniform finite-depth water is investigated here. Three types of barrier configurations are considered. A one-term Galerkin approximation is used to evaluate upp er and lower bounds for reflection and transmission coefficients for e ach configuration. These bounds are seen to be very close numerically for all wave numbers and as such their averages produce good numerical estimates for these coefficients. Only the bounds for the reflection coefficient are numerically computed. These are also numerically compa red with the results obtained by using multiterm Galerkin approximatio ns involving Chebyshev polynomials for a wide range of parameters. Num erical results for the reflection coefficients for the three barrier c onfigurations are presented graphically. It is seen that total reflect ion occurs only for the surface-piercing barriers while total transmis sion occurs for all the three configurations considered here. It is al so observed that the introduction of an equal second barrier to a subm erged barrier increases the reflection coefficient considerably in som e frequency bands and as such submerged double barrier configurations are preferable to a submerged single barrier for the purpose of reflec ting more wave energy into the open sea.