Surf Zone Resonances associated with Anomalous Dispersion

Abstract

Analysing field measurements of high energetic surf waves, the author has come across an anomalous dispersion effect (ADE) that was previously unknown regarding gravity waves. For most kinds of waves, dispersion means the dependence of phase velocity c[m/s] on frequency f[Hz] or on wave length [L] respectively. With gravity waves, dispersion is normal, which means that dc/df ≤ 0 or dc/dL ≥ 0; - like what is known about electromagnetic waves (EM-waves) in the limited frequency range of the visible light (as demonstrated by the known sequence of spectral colours). With EM-waves, however, resonances appear together with the phenomenon of an ADE, marked by dc/df > 0 or dc/dL < 0 respectively. Seeking analogue conditions for water waves, the author had found two different model conceptions to be appropriate for (partial) standing waves regarding basin oscillations. In natural field conditions: incident waves from the sea (stimulator) resonating with partial standing half-waves in a definable water basin (resonator), and In a scale model: the wave maker (stimulator) resonating with partial standing quarter-waves in the wave tank (resonator).