Gap resonance and higher harmonics driven by focused transient wave groups

Zhao, Wenhua; Wolgamot, Hugh; Taylor, R. Eatock; Taylor, Paul H.

doi:10.1017/jfm.2016.824

Cited by 122 publications

(103 citation statements)

References 23 publications

(33 reference statements)

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“…In order to extract the bound waves contained within our measurements, we repeat each experiment with a phase shift of 180 • . By subtracting the out-of-phase tests, it is then possible to separate the second-order sum and difference bound waves after filtering (Baldock, Swan & Taylor 1996;Fitzgerald et al 2014;Mai et al 2016;Zhao et al 2017). Evidently, this technique cannot be applied to field measurements of the Draupner wave.…”

Section: Second-order Bound Harmonicsmentioning

confidence: 99%

“…Although the widely used (Mai et al 2016;Zhao et al 2017;McAllister et al 2018) method of harmonic extraction (Baldock et al 1996;Fitzgerald et al 2014) we use relies on a generalised Stokes expansion and is thus not affected by cubic interactions, it cannot be fully relied on in the event of wave breaking. In our experiments, wave breaking occurs at the crest and not at the corresponding 180 • phase-inverted trough.…”

Section: Second-order Bound Harmonicsmentioning

confidence: 99%

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Laboratory recreation of the Draupner wave and the role of breaking in crossing seas

et al. 2018

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Freak or rogue waves are so called because of their unexpectedly large size relative to the population of smaller waves in which they occur. The 25.6 m high Draupner wave, observed in a sea state with a significant wave height of 12 m, was one of the first confirmed field measurements of a freak wave. The physical mechanisms that give rise to freak waves such as the Draupner wave are still contentious. Through physical experiments carried out in a circular wave tank, we attempt to recreate the freak wave measured at the Draupner platform and gain an understanding of the directional conditions capable of supporting such a large and steep wave. Herein, we recreate the full scaled crest amplitude and profile of the Draupner wave, including bound set-up. We find that the onset and type of wave breaking play a significant role and differ significantly for crossing and non-crossing waves. Crucially, breaking becomes less crest-amplitude limiting for sufficiently large crossing angles and involves the formation of near-vertical jets. In our experiments, we were only able to reproduce the scaled crest and total wave height of the wave measured at the Draupner platform for conditions where two wave systems cross at a large angle.

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Section: Second-order Bound Harmonicsmentioning

confidence: 99%

Section: Second-order Bound Harmonicsmentioning

confidence: 99%

Laboratory recreation of the Draupner wave and the role of breaking in crossing seas

et al. 2018

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“…In Feng and Bai (2015), it was reported that the free surface nonlinearity does not account for the over-estimation of resonant responses. An experimental study was conducted by Zhao et al (2017) who excited first and higher harmonic components of the resonant response in NewWaves. The unrealistic prediction is related to the small damping near the resonant frequency in potential flow models.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of viscous effects on the gap resonance between side-by-side barges

et al. 2017

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This paper presents a numerical study of the gap resonance between two side-by-side barges by using a multiphase Navier-Stokes equations model. In order to verify the multiphase flow model, it is firstly applied to simulate a two-dimensional gap resonance problem for two fixed boxes under various wave conditions. A comparison of the free surface elevations obtained on successively refined grids confirms the mesh convergence of numerical solutions. The calculated wave elevation response amplitude operators (RAOs) in the gap compare well with the experimental measurements. The multiphase flow model is further extended to calculate a three-dimensional gap resonance problem for two adjacent rectangular barges. The computed free surface RAOs in the gap also agree well with the experimental results. A close examination of the flow velocity and vorticity in the gap region at the piston resonant mode reveals that large amount of vortices are generated by the sharp corners of the two barges and shed downwards, which provide an effective mechanism to dissipate the flow kinematic energy and to reduce the wave elevation in the gap. On the contrary, rounded corners are not able to induce the same level amount of vortices to dampen the gap resonance. The effects of incident wave steepness on the viscous damping associated with the twin-barge system are highlighted.

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“…• allows for separation of higher-order harmonics, including for higher-bandwidth signals, in physical experiments (Fitzgerald et al 2014;Mai et al 2016;Zhao et al 2017). We examine these four-phase combinations for spreading tests A.3-4 and A.13 and find that two-and four-phase combinations produce very similar results (see appendix B).…”

Section: Category B -Crossing Testsmentioning

confidence: 93%

The set-down and set-up of directionally spread and crossing surface gravity wave groups

et al. 2017

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For sufficiently directionally spread surface gravity wave groups, the set-down of the wave-averaged free surface, first described by Longuet-Higgins and Stewart (J. Fluid Mech. vol. 13, 1962, pp. 481-504), can turn into a set-up. Using a multiple-scale expansion for two crossing wave groups, we examine the structure and magnitude of this wave-averaged set-up, which is part of a crossing wave pattern that behaves as a modulated partial standing wave: in space, it consists of a rapidly varying standing-wave pattern slowly modulated by the product of the envelopes of the two groups; in time, it grows and decays on the slow time scale associated with the translation of the groups. Whether this crossing wave pattern actually enhances the surface elevation at the point of focus depends on the phases of the linear wave groups, unlike the set-down, which is always negative and inherits the spatial structure of the underlying envelope(s). We present detailed laboratory measurements of the wave-averaged free surface, examining both single wave groups, varying the degree of spreading from small to very large, and the interaction between two wave groups, varying both the degree of spreading and the crossing angle between the groups. In both cases, we find good agreement between the experiments, our simple expressions for the set-down and set-up, and existing second-order theory based on the component-by-component interaction of individual waves with different frequencies and directions. We predict and observe a set-up for wave groups with a Gaussian angular amplitude distribution with standard deviations of above 30-40• (21-28 • for energy spectra), which is relatively large for realistic sea states, and for crossing sea states with angles of separation of 50-70• and above, which are known to occur in the ocean.

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Gap resonance and higher harmonics driven by focused transient wave groups

Cited by 122 publications

References 23 publications

Laboratory recreation of the Draupner wave and the role of breaking in crossing seas

Laboratory recreation of the Draupner wave and the role of breaking in crossing seas

Numerical investigation of viscous effects on the gap resonance between side-by-side barges

The set-down and set-up of directionally spread and crossing surface gravity wave groups

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