Rogue waves in opposing currents: an experimental study on deterministic and stochastic wave trains

The evolution of surface gravity waves is driven by nonlinear interactions that trigger an energy cascade similarly to the one observed in hydrodynamic turbulence. This process, known as wave turbulence, has been found to display anomalous scaling with deviation from classical turbulent predictions due to the emergence of coherent and intermittent structures on the water surface. In realistic oceanic sea states, waves are spread over a wide range of directions, with a consequent attenuation of the nonlinear properties. A laboratory experiment in a large wave facility is presented to discuss the effect of wave directionality on wave turbulence. Results show that the occurrence of coherent and intermitted structures become less likely with the broadening of the wave directional spreading. There is no evidence, however, that intermittency completely vanishes.

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“…1). Data were recorded at a sampling frequency is 100 Hz (the set up for this experiment is described in details in [25,26]).…”

Section: Experimental Conditionsmentioning

confidence: 99%

Wave turbulence and intermittency in directional wave fields

et al. 2018

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“…From this perspective of anomalous behavior, rogue waves can be considered under the more general framework of turbulent dynamical systems [17,23,25,24,7,16]. Several physical mechanisms have been shown to produce rogue waves, most notably the Benjamin-Feir (BF) instability that occurs in deep water 1 [2,20,6,32,1,8,5,10], as well as wind excitation [3,28], opposing currents [21,29], and geometric ray focusing from 2D bathymetry [13,33].…”

Section: Introductionmentioning

confidence: 99%

Anomalous wave statistics induced by abrupt depth change

2019

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Laboratory experiments reveal that variations in bottom topography can qualitatively alter the distribution of randomized surface waves. A normally-distributed, unidirectional wave field becomes highly skewed and non-Gaussian upon encountering an abrupt depth transition. A short distance downstream of the transition, wave statistics conform closely to a gamma distribution, affording simple estimates for skewness, kurtosis, and other statistical properties. Importantly, the exponential decay of the gamma distribution is much slower than Gaussian, signifying that extreme events occur more frequently. Under the conditions considered here, the probability of a rogue wave can increase by a factor of 50 or more. We also report on the surface-slope statistics and the spectral content of the waves produced in the experiments.1 A mechanism analogous to the BF instability can also arise in optical systems, giving rise to 'optical rogue waves' [27].

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“…The effect of a background current on the resonance has been studied for the degenerate case of modulational instability of a Stokes wave, which plays a pivotal role in freak wave generation, by Toffoli et al (2013Toffoli et al ( , 2015. They have experimentally confirmed the foresight of Onorato, Proment & Toffoli (2011), who have shown that the generation of rogue waves is triggered when waves enter a field of opposing current.…”

Section: Introductionmentioning

confidence: 94%

“…Therefore, the flow makes an abrupt 90 • turn behind the guide walls under the wavemaker and beneath the beach. Because of this configuration, the mean current field is not uniform across the tank and has a vertical shear as well (figure 1 and also Toffoli et al 2013Toffoli et al , 2015. The coflowing current is better regulated than the opposite condition because of the different inlet and outlet configurations.…”

Section: Facility and Experimental Conditionsmentioning

confidence: 99%

Third-order resonant wave interactions under the influence of background current fields

et al. 2015

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A series of experiments were conducted in a wave basin (50 m long, 10 m wide and 5 m deep) generating two waves propagating at an angle by a directional wavemaker. When the two waves were selected from a resonant triplet, an initially non-existing wave grew as the waves propagated down the tank. The linear growth rate of the resonating wave agreed well with third-order resonance theory based on Zakharov's reduced gravity equation. Additional experiments with opposing and coflowing mean current with large temporal and spatial variations were conducted. As the flow rate increased, the linear growth was suppressed. As reproduced numerically with Zakharov's equation, the resonant interaction saturated at time scales inversely proportional to the magnitude of the forced random resonance detuning. It is conjectured that the resonance is detuned by the variation and not by the mean of the current field due to wavelength-dependent Doppler shift and to the refraction of wave rays. Further analysis of the spectral evolution revealed that while discrete peaks appear at high frequencies as a result of dynamical cascading, a continuously saturated spectrum develops in the background as the current speed increases. Additional experiments were conducted studying the evolution of the random directional wave on a dynamical time scale under the influence of current. Due to random resonance detuning by the current, the spectral tail tended to be suppressed.

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Rogue waves in opposing currents: an experimental study on deterministic and stochastic wave trains

Abstract: Rogue waves in opposing currents: An experimental study on deterministic and stochastic wave trains / Toffoli, A; Waseda, T.; Houtani, H.; Cavaleri, L.; Greaves, D.; Onorato, M

Cited by 64 publications

References 47 publications

Wave turbulence and intermittency in directional wave fields

Wave turbulence and intermittency in directional wave fields

Anomalous wave statistics induced by abrupt depth change

Third-order resonant wave interactions under the influence of background current fields

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