Experimental Studies of Wave Filters and Absorbers

Laboratory wave studies are of importance in explaining the natural phenomena, determining the remedial measures for harbor protection and beach erosion, and providing design information for various laboratory wave installations. The objective of the research reported here was to investigate the basic equipment and methods associated with laboratory wave studies. Of particular interest was the investigation of wave absorbers. A limited study was conducted on wave filters, primarily to obtain information which would contribute to the study of absorbers. Studies of absorbers included impermeable-beach types, as well as permeable types such as gravel, crushed rock, wire-mesh, perforated plate, round-rod, triangular wedge and rectangular bar, or a combination of these. Observations and analysis indicated that the wave absorption depends on wave characteristics, such as steepness (H_I/L) and depth-to-length ratio (d/L), as we11 as the absorber characteristics, such as surface slope and shape in the case of impermeable absorbers; and surface slope, shape, volume, and porosity in case of permeable absorbers. For selected wave conditions absorbers with reflection coefficients (H_R/H/I) as low as 0.02 were developed during the studies. Filters were developed which produced severe attenuation of the incident wave causing excessive reflections. However, additional studies will be necessary to provide adequate design information for wave filters. The absorber studies in a small channel led to a preliminary design of an efficient, inexpensive absorber of minimum length for the proposed Maneuvering Basin at the David Taylor Model Basin. The preliminary design will be checked in a large test channel.