Spectral analysis of irregular waves in wave–mud and wave–current–mud interactions

The dissipation of irregular waves passing over muddy beds is investigated through two series of wave flume laboratory experiments with and without currents, where commercial kaolinite is used as the muddy sediment bed material. The changes in spectral characteristics of waves along the muddy bed and the effects of following and opposing currents are investigated. A numerical multi-layered model was also employed to simulate the attenuation of regular/irregular waves assuming viscoelastic rheological behavior for fluid mud, and the outputs were compared with the laboratory data. The first series of the experiments show that propagation of a wave spectrum over a short fluid mud section does not result in a shift in peak frequencies of wave spectra. The comparisons of spectral width parameters of various wave spectra also reveal that higher values of spectral peakedness parameters generally result in higher rates of wave energy dissipation. This can be related to the frequency dependency of wave energy dissipation on the mud layer. The results of the second series of experiments show higher dissipation rates in the opposing current and lower rates in the following current, which can be attributed to the changes in incident wave heights due to existence of currents. The study confirms that the dynamic pressure of wave propagation on the mud surface is the governing factor in regular/irregular wave–current–mud interaction and the current itself has little direct effect on the mud layer.