Coherent Eddies Induced by Breakers on a Sloping Bed

Matsunaga, Nobuhiro; Takehara, Kosei; Awaya, Yoichi

doi:10.1061/9780872626874.016

Cited by 3 publications

(11 citation statements)

References 6 publications

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“…streamlines behind the plunging point in figure 9). Thus a vortex array, induced through K-H instability on the plane shear surface, may develop into the so-called offshore vortex train found by Matsunaga et al (1988Matsunaga et al ( , 1994. As the vortices remaining from the previous breaking event affect the formation of a new vortex structure via interaction among the vortices in the instantaneous field, the resulting aperiodic strains yield different vortex substructures over successive breaking events, resulting in varying turbulent flows at every breaking event.…”

Section: Discussionmentioning

confidence: 99%

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Three-dimensional vortex structures under breaking waves

2005

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The large-scale vortex structures under spilling and plunging breakers are investigated, using a fully three-dimensional large-eddy simulation (LES). When an overturning jet projecting from the crest in a breaking wave rebounds from the water surface ahead, the vorticity becomes unstable in a saddle region of strain between the rebounding jet and a primary spanwise vortex, resulting in spanwise undulations of the vorticity. The undulations are amplified on a braid in this saddle region, leading to a vortex loop with counter-rotating vorticity. This vortex loop consequently envelops adjacent primary vortices, to form a typical rib structure. This rib component (the stretched vortex loop) in the large-scale vortex structure, which intensifies in the strains associated with the multiple primary vortices generated throughout the splash-up cycle, appears to be the previously found obliquely descending eddy.

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Section: Discussionmentioning

confidence: 99%

“…In the mean shear surface, this process is analogous to Kelvin-Helmholz (K-H) instability. They concluded that the instability induced the formation of the so-called offshore vortex train, previously observed outside the surf zone (Matsunaga, Takehara & Awaya et al 1988.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional vortex structures under breaking waves

2005

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“…Craik (1982) later reached a similar conclusion. Matsunaga, Takehara & Awaya (1988, 1994 discovered in a small wave tank (12 m long, 0.4 m deep, 0.15 m wide and equipped with a sloping planar bed) that the mean flow in the cross-shore direction just offshore of the breaker line was subject to a remarkable instability. The mean flow in the seaward direction became unstable and created a single layer of very large (order of the wave height) eddies slowly rotating about a horizontal axis parallel to the shoreline.…”

Section: Introductionmentioning

confidence: 99%

“…Also, there was a threshold wave steepness below which no eddies occur. Matsunaga et al (1988Matsunaga et al ( , 1994 indicate that a shear instability may be responsible for the offshore vortex train, but provide no theoretical analysis.…”

Section: Introductionmentioning

confidence: 99%

“…Experiment set-up Figure 2 shows a schematic of the experimental set-up. Our experimental wave tank (35 m long, 0.6 m deep and 0.6 m wide) is 3 times longer, 4 times wider and 1.5 times deeper than the wave tank used by Matsunaga et al (1988Matsunaga et al ( , 1994. It had a constant depth section at the wavemaker and a sloping planar bed with 1:35 slope at the other end.…”

Section: Introductionmentioning

confidence: 99%

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Instabilities of the undertow

Dalrymple

1998

J. Fluid Mech.

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The steady undertow created by waves breaking at a beach and slowly flowing offshore can become unstable and create a train of submerged offshore migrating vortices with shorter length scales and longer time scales than the incident waves, as shown by Matsunaga, Takehara & Awaya (1988, 1994). These vortices rotate about horizontal axes parallel to the shoreline. Our larger-scale laboratory experiments show that an additional layer of vortices can exist over the water depth, with vortices near the water surface rotating in the same direction as the wave-induced water particle trajectories, while those located at about mid-depth rotate in the opposite direction.A theoretical and numerical analysis shows that these vortices are due to instabilities of the undertow. Far offshore of the surf zone, the vortex trains decay because the velocity profile for the undertow becomes linear over depth, hence neutrally stable to any disturbances.

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Sea waves and mass transport on a sloping beach

Blondeaux

Brocchini

Vittori

2002

Proc. R. Soc. Lond. A

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The steady streaming induced by a sea wave shoaling on a sloping beach and partly reflected at the coastline is determined in the region seaward of the breaker line. Shallow waters and waves of small amplitude are considered. Moreover, the Reynolds number is assumed to be large but still within the laminar regime and the flow domain is split into a bottom boundary layer and a core region. For an incoming wave which is fully absorbed at the coast the solution shows that close to the bottom the steady streaming is onshore directed even though the depth-averaged value represents an offshore directed flow. Moreover, the vertical velocity distribution depends on the ratio between the wave amplitude a * and the thickness δ * of the bottom boundary layer. For a fully reflected wave, steady recirculation cells are induced, the form and strength of which depend on the ratio a * /δ * . A complex flow is generated for reflection coefficients falling between 0 and 1.

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Coherent Eddies Induced by Breakers on a Sloping Bed

Cited by 3 publications

References 6 publications

Three-dimensional vortex structures under breaking waves

Three-dimensional vortex structures under breaking waves

Instabilities of the undertow

Sea waves and mass transport on a sloping beach

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