Geometry, migration and evolution of small-scale bedforms generated by regular and irregular waves

Faraci, Carla; Foti, Enrico

doi:10.1016/s0378-3839(02)00097-2

Cited by 68 publications

(45 citation statements)

References 19 publications

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“…Orbital ripples, for which both wavelength and height depend directly on d o , and steepness is constant, occur for [Nielsen, 1981;Grant and Madsen, 1982;Mogridge et al, 1994;Styles and Glenn, 2002;Faraci and Foti, 2002;Grasmeijer and Kleinhans, 2004;Williams et al, 2005]. The predictions tend to differ most for suborbital ripples.…”

Section: Ripple Dimensionsmentioning

confidence: 98%

“…Rollinggrain ripples have been observed in laboratory experiments but their existence in the field is disputed [Miller and Komar, 1980]. Faraci and Foti [2002] found in experiments in a wave tank with regular waves that rolling-grain ripples (characterized by steepness $0.1) developed initially and evolved into vortex ripples after 100-200 s (1.5 s < T < 4.2 s). Our runs that had delayed ripple growth, suggesting a transient stage of rolling-grain ripples, were characterized by small waves and slow currents.…”

Section: Ripple Wavelength Evolutionmentioning

confidence: 99%

“…The general form for this pattern of growth is h(t)/h f = C exp (Àbt/T), where the subscript f denotes the final or equilibrium value [e.g., Voropayev et al, 1999;Davis et al, 2004;Smith and Sleath, 2005;Doucette and O'Donoghue, 2006]. For vortex ripples it is reasonable to assume that the evolution of l follows the same pattern as that of h. Faraci and Foti [2002], Doucette and O'Donoghue [2006], and others have found that the evolution time for ripple height and wavelength are similar. To determine the number of wave periods for l to evolve to 90% of its equilibrium value for each run, we used the expression from Smith and Sleath [2005] for evolution of ripple wave number k = 1/(2pl):…”

Section: Ripple Wavelength Evolutionmentioning

confidence: 99%

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Bed forms created by simulated waves and currents in a large flume

et al. 2007

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[1] The morphology and evolution of bed forms created by combinations of waves and currents were investigated using an oscillating plate in a 4-m-wide flume. Current speed ranged from 0 to 30 cm/s, maximum oscillatory velocity ranged from 20 to 48 cm/s, oscillation period was 8 s (except for one run with 12 s period), and the median grain size was 0.27 mm. The angle between oscillations and current was 90°, 60°, or 45°. At the end of each run the sand bed was photographed and ripple dimensions were measured. Ripple wavelength was also determined from sonar images collected throughout the runs. Increasing the ratio of current to wave (i.e., oscillatory) velocity decreased ripple height and wavelength, in part because of the increased fluid excursion during the wave period. Increasing the ratio of current to waves, or decreasing the angle between current and waves, increased the three-dimensionality of bed forms. During the runs, ripple wavelength increased by a factor of about 2. The average number of wave periods for evolution of ripple wavelength to 90% of its final value was 184 for two-dimensional ripples starting from a flat bed. Bed form orientations at the end of each run were compared to four potential controlling factors: the directions of waves, current, maximum instantaneous bed shear stress, and maximum gross bed form normal transport (MGBNT). The directions of waves and of MGBNT were equally good predictors of bed form orientations, and were significantly better than the other two factors.

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Section: Ripple Dimensionsmentioning

confidence: 98%

Section: Ripple Wavelength Evolutionmentioning

confidence: 99%

Section: Ripple Wavelength Evolutionmentioning

confidence: 99%

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Bed forms created by simulated waves and currents in a large flume

et al. 2007

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“…Ripple steepness h*/l* where the relative depth has been defined with reference to the wavelength instead of the wave orbital amplitude. It is worth pointing out that, of the two ripple characteristics, only one has been considered here since it is assumed that at the equilibrium ripple steepness h*/l* is constant, at least in the present experimental apparatus [Faraci and Foti, 2002].…”

Section: C07018 Faraci Et Al: Waves Plus Currents At Right Anglementioning

confidence: 99%

Waves plus currents at a right angle: The rippled bed case

2008

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[1] The present paper deals with wave plus current flow over a fixed rippled bed. More precisely, modifications of the current profiles due to the superimposition of orthogonal cylindrical waves have been investigated experimentally. Since the experimental setup permitted only the wave dominated regime to be investigated (i.e., the regime where orbital velocity is larger than current velocity), also a numerical k-e turbulence closure model has been developed in order to study a wider range of parameters, thus including the current dominated regime (i.e., where current velocity is larger than wave orbital one). In both cases a different response with respect to the flat bed case has been found. Indeed, in the flat bed case laminar wave boundary layers in a wave dominated regime induce a decrease in bottom shear stresses, while the presence of a rippled bed behaves as a macroroughness, which causes the wave boundary layer to become turbulent and therefore the current velocity near the bottom to be smaller than the one in the case of current only, with a consequent increase in the current bottom roughness.

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“…We obtain a good agreement between results issued from the theoretical model and the experimental results. (NIELSEN, 1981 ;FARACI & FOTI, 2002) afin de comprendre les processus pilotant la formation et la morphologie des rides, mais la plupart considèrent que le fond granulaire ne contient que des sédiments homogènes en taille et en densité. Cependant, les études in-situ montrent que la taille et la densité des sédiments naturels sont très variées.…”

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Trajectoires de particules et tri sédimentaire sous l'action d'un écoulement oscillant au dessus d'un fond ridé

Chu

Jarno

Ezersky

et al. 2010

XIèmes Journées, Les Sables d'Olonne

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Résumé :Les travaux présentés concernent une étude sur les trajectoires de particules en suspension sous l'action d'une houle stationnaire au dessus d'un fond ridé fixe. Expérimentalement, un tri sédimentaire est observé. Il se caractérise par des zones de dépôt différentes pour les petites et les grosses particules. Lorsque l'écoulement s'amortit, les petites particules se concentrent dans des zones étroites localisées à la crête des rides. Par contre, les grosses particules se déposent partout. Un modèle théorique simple est développé dans le but d'expliquer le mouvement des petites particules dans la phase d'amortissement de l'écoulement oscillant. Nous obtenons un bon accord entre les résultats issus du modèle théorique et les résultats expérimentaux. Mots-clés :Trajectoire de particule -Tri sédimentaire -Ride -Houle -Canal à houle Abstract:This work deals with a study of the suspended particles trajectories under standing waves above a fixed rippled bed. Sediment segregation is experimentally observed. It is characterized by different deposits zones for small and coarse particles. When the flow is damping, the small particles concentrate in localized narrow zones on the ripple crests. On the other hand, the coarse particles settle everywhere. A simple theoretical model is developed in order to explain the motion of small particles when the oscillatory flow is damping. We obtain a good agreement between results issued from the theoretical model and the experimental results. (NIELSEN, 1981 ;FARACI & FOTI, 2002) afin de comprendre les processus pilotant la formation et la morphologie des rides, mais la plupart considèrent que le fond granulaire ne contient que des sédiments homogènes en taille et en densité. Cependant, les études in-situ montrent que la taille et la densité des sédiments naturels sont très variées. Un tri sédimentaire se produit mais les mécanismes de celui-ci sont mal connus. Récemment, le développement de la technique de mesure PIV (Particle Image Velocimetry) (BALASUBRAMANIAN et al., 2008) a permis d'étudier complètement l'écoulement au dessus d'un fond ridé. Mais à notre connaissance, il n'y a pas d'étude expérimentale concernant la trajectoire des particules sous l'action d'un écoulement oscillant. Des tests sont effectués en canal à houle afin d'analyser les processus de tri sédimentaire à partir de mesures des trajectoires de sédiments en suspension au-dessus d'un fond ridé. L'influence de la taille des sédiments sur leurs trajectoires et sur leurs zones de dépôt est considérée. Les résultats expérimentaux sont comparés avec les résultats issus d'un modèle théorique que nous avons développé.

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Geometry, migration and evolution of small-scale bedforms generated by regular and irregular waves

Cited by 68 publications

References 19 publications

Bed forms created by simulated waves and currents in a large flume

Bed forms created by simulated waves and currents in a large flume

Waves plus currents at a right angle: The rippled bed case

Trajectoires de particules et tri sédimentaire sous l'action d'un écoulement oscillant au dessus d'un fond ridé

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