Swimming obstructed by dead-water

Ganzevles, Sander; Nuland, Fons S. W. van; Maas, Leo R. M.; Toussaint, H.M.

doi:10.1007/s00114-008-0493-6

Cited by 5 publications

(4 citation statements)

References 15 publications

(13 reference statements)

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“…Already in a cool sea such variations need only be 0.5–1°C to be sensed by humans. This T-difference provides stratification that is too weak to be a mechanical hazard to swimmers, who will lose only <5% of their energy to generate IW by their action [22]. They are likely more hampered by the shock of 1°C+ T-difference when naturally generated IW pass; that is, near a Texel-beach in early summer, as in the Adriatic cooler blobs may be felt more refreshing.…”

Section: Discussionmentioning

confidence: 99%

Internal Wave Turbulence Near a Texel Beach

et al. 2012

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A summer bather entering a calm sea from the beach may sense alternating warm and cold water. This can be felt when moving forward into the sea (‘vertically homogeneous’ and ‘horizontally different’), but also when standing still between one’s feet and body (‘vertically different’). On a calm summer-day, an array of high-precision sensors has measured fast temperature-changes up to 1°C near a Texel-island (NL) beach. The measurements show that sensed variations are in fact internal waves, fronts and turbulence, supported in part by vertical stable stratification in density (temperature). Such motions are common in the deep ocean, but generally not in shallow seas where turbulent mixing is expected strong enough to homogenize. The internal beach-waves have amplitudes ten-times larger than those of the small surface wind waves. Quantifying their turbulent mixing gives diffusivity estimates of 10−4–10−3 m2 s−1, which are larger than found in open-ocean but smaller than wave breaking above deep sloping topography.

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Section: Discussionmentioning

confidence: 99%

Internal Wave Turbulence Near a Texel Beach

et al. 2012

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“…One can argue that the stratification considered might have been inadequate for swimmers to generate waves and led to mixing of the thermocline mainly. An energetic budget is given in a more detailed and idealized study (Ganzevles et al, 2009) where the authors also observed some retarding effects on the swimmers.…”

Section: Ekman's Phd Thesismentioning

confidence: 99%

Resurrecting dead-water phenomenon

Mercier

Vasseur

Dauxois

2011

Nonlin. Processes Geophys.

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Abstract.We revisit experimental studies performed by Ekman on dead-water (Ekman, 1904) using modern techniques in order to present new insights on this peculiar phenomenon. We extend its description to more general situations such as a three-layer fluid or a linearly stratified fluid in presence of a pycnocline, showing the robustness of dead-water phenomenon. We observe large amplitude nonlinear internal waves which are coupled to the boat dynamics, and we emphasize that the modeling of the wave-induced drag requires more analysis, taking into account nonlinear effects.Dedicated to Fridtjöf Nansen born 150 yr ago (10 October 1861).

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“…One can argue that the stratification considered might have been inadequate for swimmers to generate waves and mainly led to the thermocline mixing. An energetic budget is given in a more detailed and idealised study Ganzevles et al, 68 where the authors also observed some retarding effects on the swimmers. In a slightly different perspective, Nicolaou et al 69 demonstrated that an object accelerating in a stratified fluid generates oblique and transverse internal waves; the latter can be decomposed as a sum of baroclinic modes with the lowest mode always present.…”

Section: Effect Of Bottom Permeability On Dead Water Analoguementioning

confidence: 99%

A mathematical study of water wave interaction with a thin perforated barrier in a two-layer fluid over a permeable bottom

Barman

Bora

2023

Proceedings of the Institution of Mechanical Engineers, Part M:

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This article studies the impact of a submerged interface-piercing perforated barrier in a two-layer fluid flowing over a permeable bottom. We investigate oblique wave scattering, trapping and radiation due to the structure focusing on the bottom permeability. The dead water phenomenon is analysed with the consideration of the bottom permeability, which results in a higher variation of the interfacial wave due to the bottom permeability. The matched eigenfunction expansion method and the least square technique are used to calculate various hydrodynamic coefficients. Wave energy identity relation is derived for the scattering scenario, and the associated energy loss due to the barrier is calculated. In order to attain the maximum wave dissipation, an ideal porous-effect parameter of the barrier is proposed for consideration, and it is observed that larger values of porous-effect parameter result in the lowest feasible pressure distribution. A good comparison with a prior result justifies the current semi-analytical procedure. Furthermore, the verification of the energy-identity terms aid in the validation of the computed results. Additionally, wave trapping in a confined region is examined by investigating reflection coefficients by considering a rigid wall. The thin perforated barrier model is further considered for examining the radiation aspect while considering its slow motion. For various porous-effect parameters of the barrier, the amplitude ratio of the radiated potential is investigated, and it is clearly observed that higher frequency significantly lowers the amplitude for both free surface and interfacial propagating modes. The impact of the perforated barrier is analysed by investigating the essential hydrodynamic coefficients, namely, added mass and damping coefficient.

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Swimming obstructed by dead-water

Cited by 5 publications

References 15 publications

Internal Wave Turbulence Near a Texel Beach

Internal Wave Turbulence Near a Texel Beach

Resurrecting dead-water phenomenon

A mathematical study of water wave interaction with a thin perforated barrier in a two-layer fluid over a permeable bottom

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