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

Mortimer, William; Raby, Alison; Antonini, A.; Greaves, Deborah; van den Bremer, T.S.

doi:10.1016/j.coastaleng.2022.104121

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

Title

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

Author

Mortimer, William (Plymouth University; JBA Consulting)
Raby, Alison (Plymouth University)
Antonini, A. (TU Delft Coastal Engineering)
Greaves, Deborah (Plymouth University)
van den Bremer, T.S. (TU Delft Environmental Fluid Mechanics; University of Oxford)

Date

2022

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.

Subject

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

To reference this document use:

http://resolver.tudelft.nl/uuid:66a29385-7284-443d-8f84-d71651211512

DOI

https://doi.org/10.1016/j.coastaleng.2022.104121

ISSN

0378-3839

Source

Coastal Engineering, 174

Part of collection

Institutional Repository