An Experimental Study of Surface Instabilities During Wave Breaking

Narayanaswamy, Muthukumar; Dalrymple, Robert A.

doi:10.1142/9789812791306_0030

Cited by 6 publications

(7 citation statements)

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“…Some longitudinal depressions are also observed on the back of the plunging jet, which correspond to the scars investigated by Watanabe et al (2005) and Saruwatari et al (2009). These local surface patterns are expected to be linked to the striations or the fingers detailed respectively by Longuet-Higgins (1995) and Narayanaswamy & Dalrymple (2002). The longitudinal distribution of the vortex filaments has been observed to be correlated with the striations visualised on the back of the impinging jet, the cavities being the main source of aeration of the vortex filaments when they first appear.…”

Section: P Lubin and S Glocknermentioning

confidence: 77%

“…pre-impact plunging jets) to scars, droplets and spray (Longuet-Higgins 1995;Watanabe et al 2005;Lakehal & Liovic 2011). Narayanaswamy & Dalrymple (2002) experimentally presented evidence of 'fingers' appearing at the tip of the plunging jet, prior to impact. More recently, Saruwatari, Watanabe & Ingram (2009) numerically studied the formation of fingers and scars on the surface of secondary planar jets and suggested that, as the influence of surface tension increases, the jet surface is prevented from being scarified and fingered.…”

Section: Introductionmentioning

confidence: 97%

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Numerical simulations of three-dimensional plunging breaking waves: generation and evolution of aerated vortex filaments

2015

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The scope of this work is to present and discuss the results obtained from simulating three-dimensional plunging breaking waves by solving the Navier-Stokes equations, in air and water. Recent progress in computational capabilities has allowed us to run fine three-dimensional simulations, giving us the opportunity to study for the first time fine vortex filaments generated during the early stage of the wave breaking phenomenon. To date, no experimental observations have been made in laboratories, and these structures have only been visualised in rare documentary footage (e.g. BBC 2009 South Pacific. Available on YouTube, 7BOhDaJH0m4). These fine coherent structures are three-dimensional streamwise vortical tubes, like vortex filaments, connecting the splash-up and the main tube of air, elongated in the main flow direction. The first part of the paper is devoted to the presentation of the model and numerical methods. The air entrainment occurring when waves break is then carefully described. Thanks to the high resolution of the grid, these fine elongated structures are simulated and explained.

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Section: P Lubin and S Glocknermentioning

confidence: 77%

Section: Introductionmentioning

confidence: 97%

Numerical simulations of three-dimensional plunging breaking waves: generation and evolution of aerated vortex filaments

2015

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“…We observed on the back of the plunging jets some local surface patterns (Figure 2), which are expected to be linked to the striations or the fingers detailed respectively by Longuet-Higgins (1995) and Narayanaswamy & Dalrymple (2002). This could be a key phenomenon explaining the transverse distribution of the vortex filaments.…”

Section: Yesmentioning

confidence: 75%

“…Moreover, only a limited number of researchers have also focused attention on some smallerscale processes (Longuet-Higgins 1995). Narayanaswamy & Dalrymple (2002) experimentally presented evidence of "fingers" appearing at the tip of the plunging jet, prior to impact. More recently, Saruwatari et al (2009) studied numerically the formation of fingers and scars at the surface of secondary planar jets and suggested that, as the influence of surface tension increases, the jet surface is prevented from being scarified and fingered.…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Numerical Simulations of Aerated Vortex Filaments Under Plunging Breaking Waves

Lubin

Glockner

2014

Int. Conf. Coastal. Eng.

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The scope of this work is to present and discuss the results obtained from simulating three-dimensional plunging breaking waves. A numerical tool based on the Navier-Stokes equations is used to describe the plunging breaking processes including overturning, splash-up and the occurrence of air entrainment. Initial 3D conditions corresponding to unstable periodic sinusoidal waves of large amplitudes in periodic domains are used to study the air entrainment occurring when waves break. The numerical results highlight the major role of this phenomenon in the energy dissipation process, through a high level of turbulence generation. The numerical model represents a substantial improvement in the numerical modelling of breaking waves since it includes the air entrainment process neglected in most previous existing models.

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“…Through the orbits in the wave kinematic motion, these vortices end up in the impact zone (figure 4 b ). Narayanaswamy & Dalrymple (2002) observed that independently of the wave height and period, the typical width of the perturbation in their experiments was about 0.02–0.03 m, at full scale. Based on that, we used five parallel aluminum wires with diameter 0.0025 m and a constant distance 0.03 m to generate the perturbations.…”

Section: Experimental Set-upmentioning

confidence: 94%

Wave front perturbation effect on the variability of monopile wave impact loads

Moalemi,

Bredmose,

Kristiansen

et al. 2024

J. Fluid Mech.

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The slamming wave force and pressure variabilities for monopile wave impacts are studied as functions of wave breaking shape and transverse perturbations on the breaking wave front. The impacting wave topology is characterized as slosh, flip-through, $\varOmega$ , overturning and fully broken. Fifty test repetitions are conducted for each type of wave impact to assess the variability of force impulse, force and pressure. The results for the unperturbed cases show that the slamming force is highest among the nominal slosh, flip-through and $\varOmega$ tests, and that the slamming force variability is highest for the first two. We demonstrate that the slamming force and pressure variabilities decrease notably after selecting and regrouping the tests by similar crest heights and temporal slopes measured at an upstream wave gauge. The group representing $\varOmega$ wave impacts shows the largest mean slamming force and peak pressure, and their variability is the highest among all groups. Further, the effect of lateral perturbations on the pressure, force and impulse variabilities is investigated. Due to the perturbations, the slamming pressure variability for the wave impacts in which the wave front hits the monopile surface increases significantly. The variability of the slamming force is also increased for the perturbed impacts; however, it is smaller than the slamming pressure variability. The force impulse variability shows a low sensitivity to perturbations, and its magnitude is smaller than that of the force variability. Finally, the slamming pressure using fifteen pressure sensors for five selected events is studied. For these tests, oscillations at frequencies associated with structural or bubble oscillations are seen. Further, the air entertainment is documented through video recordings.

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An Experimental Study of Surface Instabilities During Wave Breaking

Cited by 6 publications

References 0 publications

Numerical simulations of three-dimensional plunging breaking waves: generation and evolution of aerated vortex filaments

Numerical simulations of three-dimensional plunging breaking waves: generation and evolution of aerated vortex filaments

Three-Dimensional Numerical Simulations of Aerated Vortex Filaments Under Plunging Breaking Waves

Wave front perturbation effect on the variability of monopile wave impact loads

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