Near‐bottom flow and flow resistance for currents obliquely incident to two‐dimensional roughness elements

Barrantes, A.; Madsen, Ole Secher

doi:10.1029/2000jc900132

Cited by 18 publications

(11 citation statements)

References 11 publications

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“…Log-profile analysis at ~40 such profiles produces an experimental value for the roughness experienced by the current in the mainstream direction c It is encouraging to notice that this value falls between the roughness values of 18.7 cm and 0.025 cm, obtained for perpendicular and parallel current directions relative to the direction of the ripples. Thus, our experiments conclusively demonstrate the reality of a direction-dependent roughness for current flows over strictly 2D ripples, in agreement with the physical argument presented by Barrantes and Madsen (2000) and their experimental results.…”

Section: Case 4: Current Alone At 30° To Ripplessupporting

confidence: 79%

“…Following Barrantes and Madsen (2000), we resolve the measured current velocity vector, (u = U x , υ), into its components perpendicular and parallel to the ripple axis, and , respectively. Typical semi-log plots of the profiles of and are shown in Figures 5a and 5b, respectively, and carrying out log-profile analyses for some 40 profiles we obtain the corresponding bottom roughness value, c c (6) (7) (8) It should be pointed out that there is no theoretical justification for the assumption of the validity of the log-profile describing the variation of and (or U x for that matter).…”

Section: Case 4: Current Alone At 30° To Ripplesmentioning

confidence: 99%

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Near-Bottom Flow Characteristics of Currents at Arbitrary Angle to 2d Ripples

Madsen

Negara²,

Lim³

et al. 2011

Int. Conf. Coastal. Eng.

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Experimental results for near-bottom current velocity profiles for flows over artificial, definitely 2D ripples made of 1.5 cm high aluminum angle-profile spaced at 10 cm intervals are obtained for the following cases: (i) current alone perpendicular to ripples; (ii) current alone parallel to ripples; (iii) combined orthogonal wave-current flows for current parallel to ripples; and (iv) current alone at an angle of 30° to the ripple axis. The velocity profiles are analyzed by the log-profile method, and show the roughness experienced by the current to increase as the angle between ripple and current direction increases, i.e. demonstrating convincingly the reality of the concept of a direction-dependent roughness for flows over a 2D rippled bottom. Roughness experienced by the velocity component perpendicular to the ripples is, however, found to be independent of the direction of the mainstream flow relative to that of the ripples, and the different roughness experienced by the perpendicular and parallel velocity components gives rise to a turning of the current velocity vector to become increasingly aligned with the ripple crests as the bottom is approached from above. Implications of this feature, in terms of net sediment transport direction in combined wave-current flows in inner-shelf coastal waters, is discussed.

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Section: Case 4: Current Alone At 30° To Ripplessupporting

confidence: 79%

Section: Case 4: Current Alone At 30° To Ripplesmentioning

confidence: 99%

Near-Bottom Flow Characteristics of Currents at Arbitrary Angle to 2d Ripples

Madsen

Negara²,

Lim³

et al. 2011

Int. Conf. Coastal. Eng.

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“…It is shown that, in many cases, the profiles of current velocity in the WBBL obey a logarithmic law (in the first approximation) [14,35,[38][39][40].…”

mentioning

confidence: 99%

Structure of the Wave Bottom Boundary Layer over Smooth and Rough Bottoms

Kushnir

2005

Phys Oceanogr

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The comparison of six well-known models of the wave bottom boundary layer shows that they are identical in the case of a smooth bottom but exhibit serious differences for the other types of conditions. The thickness of the wave bottom boundary layer and the coefficient of vertical diffusion of momentum are studied by using the relations of the k -ε -model. The validity of these estimates is checked by comparing the measured and computed values of the friction velocity. This comparison demonstrates fairly good agreement between the results characterized by a coefficient of correlation equal to 0.851.

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“…Second, the mean flow changes direction across the entire water depth upon superposition of waves, due to the presence of wave-induced streaming or mass transport. This complicates the process of validating theoretical wave-current models, since k n is dependent on the angle of intersection between the flows and 2D roughness elements (Barrantes & Madsen, 2000). Hence, more experimental studies involving orthogonal or near-orthogonal wave-current interaction over 3D fixed bottom roughness configurations are necessary.…”

Section: Introductionmentioning

confidence: 99%

Current Characteristics in the Presence of Near-Orthogonal Waves

Lim

Madsen

Cheong

2012

Int. Conf. Coastal. Eng.

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An experimental study involving near-orthogonal wave-current interaction in a wave basin is reported in this paper. Due to previous shortcomings associated with 2D bottom configurations, i.e. occurrence of ripple-induced turning of flows close to the bed, the present experiments were conducted with the bottom covered by closely packed ceramic marbles (mean diameter of 1.25cm). Three types of flows were generated over this bottom: current-alone, wave-alone and combined wave-current flow. For current-alone and wave-current cases, the log-profile analysis was used to resolve the equivalent Nikuradse sand grain roughness, kn, while the energy dissipation method was used to estimate kn for wave-alone case. The results show that kn obtained for current-and wave-alone tests is roughly 2.2 times the diameter of the marbles. For orthogonal wave-current flows, the kn value, when used in combination with the GrantMadsen (GM) model to reproduce the experimental apparent roughness, is found to be smaller than the measured current-alone and wave-alone kn. Similar under-prediction of bottom roughness is also observed when the GM model is compared with a numerical study, thus supporting the conjecture that when the current is weak compared to the waves, simple theoretical models like GM are not sufficiently sensitive to the angle of wave-current interaction. Experiments with currents at angles of 60° and 120° to the wave direction yield apparent roughness smaller than the 90° case, which is counter-intuitive since one would expect the mean flow to experience a stronger wave-induced turbulence when it is more aligned with the wave direction. This result indicates a possible contamination from waveinduced mass transport to the mean flow profile for non-orthogonal combined flow cases, and therefore highlights the need for other alternatives to the log-profile analysis when attempting to resolve kn from current velocity profiles from combined wave-current flows.

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Near‐bottom flow and flow resistance for currents obliquely incident to two‐dimensional roughness elements

Cited by 18 publications

References 11 publications

Near-Bottom Flow Characteristics of Currents at Arbitrary Angle to 2d Ripples

Near-Bottom Flow Characteristics of Currents at Arbitrary Angle to 2d Ripples

Structure of the Wave Bottom Boundary Layer over Smooth and Rough Bottoms

Current Characteristics in the Presence of Near-Orthogonal Waves

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