Correct generation of the bound set-down for surface gravity wave groups in laboratory experiments of intermediate to shallow depth

William Mortimer, Alison Raby, Alessandro Antonini, Deborah Greaves, Ton S. van den Bremer*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

Using linear (first-order) wave generation theory in laboratory experiments, leads to significant contamination of the wave field by free non-linear (second-order) error waves, increasingly so at shallower depths. Second-order wave generation theory has previously been established, and so has correct generation of the bound set-down, made up from second-order bound waves in the sub-harmonic part of the spectrum, for bichromatic and irregular wave fields in shallow to intermediate depth. In the present work, different from previous studies, we validate second-order wave theory explicitly for isolated wave groups, which provide a demanding test on the correct generation of sub-harmonic bound waves and the stroke length of the wavemaker. We do so for shallow to intermediate water depth, where some previous attempts at full elimination of sub-harmonic error waves have been hampered by limited paddle stroke. We overcome these limitations by applying second-order wavemaker theory to a piston-type paddle with an extended paddle stroke that can thence generate the bound set-down correctly. We show that sub-harmonic error waves are eliminated by considering wave groups in relative depths k0d = 0.6–1.1, with important applications in coastal engineering experiments, such as run-up and overtopping.

Original languageEnglish
Article number104121
Number of pages16
JournalCoastal Engineering
Volume174
DOIs
Publication statusPublished - 2022

Keywords

  • Error waves
  • Focused wave groups
  • Harmonic decomposition
  • Second-order wave generation
  • Set-down

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