Direct Numerical Simulation of Transverse Ripples: 2. Self‐Similarity, Bedform Coarsening, and Effect of Neighboring Structures

Zgheib, Nadim; Fedele, J. J.; Hoyal, D. C. J. D.; Perillo, M. M.; Balachandar, S.

doi:10.1002/2017jf004399

Cited by 26 publications

(24 citation statements)

References 62 publications

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“…Similar responses are also observed in the foresets of Gilbert deltas and nearshore foresets of hyperpycnal deltas. Here, we demonstrate the underlying self‐similarities in sediment flux and bed growth rate that come into play for attaining the self‐similar morphology of an evolving delta, an argument that was raised yet untested in a previous numerical study of sand‐ripple morphodynamics (Zgheib et al, ).…”

Section: Resultssupporting

confidence: 60%

Self‐Similar Morphodynamics of Gilbert and Hyperpycnal Deltas Over Segmented Two‐Slope Bedrock Channels

Lai

Chiu

2019

Water Resources Research

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Delta progradation over segmented two‐slope bedrocks is prevalent in nature, where the bedrock slope upstream or downstream of the slope‐break knickpoint is steepened by continued tectonic uplift or subsidence. Understanding the morphodynamics of the most common types of delta in different slope settings is important for interpreting the observed delta progradation into reservoir and predicting delta evolutions under future tectonic/climate scenarios or anthropogenic interventions. Here, we present an experimental and analytical study demonstrating the morphological responses of Gilbert‐type and hyperpycnal deltas to variations of bedrock slopes. Steepening the upstream slope accelerates shoreline migration; steepening the downstream slope decelerates shoreline migration. In either case, the subaqueous volume is enhanced yet the subaerial volume is reduced. Both types of delta exhibit self‐similar morphologies when evolving over segmented bedrocks. Hyperpycnal deltas, through enhanced sediment fluxes driven by dense underflows, develop larger subaqueous volumes. We further demonstrate the underlying self‐similarities in sediment flux and bed growth rate that come into play for attaining the self‐similar morphologies. The combined effect of flowrate (Q) and sediment supply rate (I) may be characterized by a dimensionless Q/I ratio. Increasing Q/I advances the entire delta. For Gilbert deltas, shoreline migration accelerates with Q/I. For hyperpycnal deltas, shoreline migration exhibits a “first‐accelerate‐then‐decelerate” trend with Q/I in a limited range of slope combinations close to the single‐slope setting, indicating that the effect of Q/I emerges only when the two‐slope effect is weak or absent. Away from this near‐single‐slope range, the two‐slope effect becomes dominant, thus suppressing the effect of Q/I.

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Section: Resultssupporting

confidence: 60%

Self‐Similar Morphodynamics of Gilbert and Hyperpycnal Deltas Over Segmented Two‐Slope Bedrock Channels

Lai

Chiu

2019

Water Resources Research

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“…In the companion paper (Zgheib et al, ), referred to hereafter as Paper 2, we compare our results to published experimental data and provide an extensive quantitative analysis of the bed, where we demonstrate the importance of neighboring structures, especially upstream neighbors, on bedform dynamics (growth/decay and speed), and wave coarsening. We also provide a quantitative analysis on ripple self‐similarity and examine ripple properties such as bedform spectra, Fourier expansions, and two‐point correlations.…”

Section: Introductionmentioning

confidence: 69%

Direct Numerical Simulation of Transverse Ripples: 1. Pattern Initiation and Bedform Interactions

et al. 2018

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We present results of coupled direct numerical simulations between flow and a deformable bed in a horizontally periodic, turbulent open channel at a shear Reynolds number of Reτ = 180. The feedback between the temporally and spatially evolving bed and the flow is enforced via the immersed boundary method. Using the near‐bed flow field, we provide evidence on the role of locally intense near‐bed vortical structures during the early stages of bed formation, from the emergence of quasi‐streamwise streaks to the formation of incipient bedform crestlines. Additionally, we take a new look at a number of defect‐related bedform interactions, including lateral linking, defect and bedform repulsion, merging, and defect creation, and show that the underlying mechanisms, in these flow‐aligned interactions, are very similar to each other. Consequently, the interactions are labeled differently depending on the geometry of interacting structures and the outcome of the interaction. In the companion paper, we compare our results to published experimental data and provide an extensive quantitative analysis of the bed, where we demonstrate the importance of neighboring structures, especially upstream neighbors, on bedform dynamics (growth/decay and speed) and wave coarsening. Video files of bed evolution are available in the supporting information.

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“…Currently, fully resolved DNS or DNS with some degree of modeling for the bed have been unable to produce sinuous‐crested bedforms. Fully developed bedforms from such simulations (e.g., Kidanemariam & Uhlmann, , ; Zgheib et al, , ) have remained largely two‐dimensional; that is, bedform crestlines remain straight.…”

Section: Introductionmentioning

confidence: 99%

“…Alternatively, the slope on the stoss side is relatively mild. Once fully developed, ripples usually attain a self‐similar profile where slopes on the stoss and lee sides remain nearly unchanged as the ripple height varies (e.g., Yalin, ; Zgheib et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…modifiedMeyer-Peter and Müller (1948) relationship. The values of φ = 0.6 and ε = 4 are identical to those used inZgheib et al (2018aZgheib et al ( , 2018b. Additional details on the time integration of the governing equations and the numerical implementation of the immersed boundary method are available inAkiki and Balachandar (2016) andZgheib et al (2018a).…”

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confidence: 99%

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On the Role of Sidewalls in the Transition From Straight to Sinuous Bedforms

Zgheib

Balachandar

2019

Geophysical Research Letters

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We present results from direct numerical simulation on the transition from straight‐crested to sinuous‐crested bedforms. The numerical setup is representative of turbulent open channel flow over an erodible sediment bed at a shear Reynolds number of Reτ = 180. The immersed boundary method accounts for the presence of the bed. The simulations are two‐way coupled such that the turbulent flow can erode and modify the bed, and in turn, the bed modifies the overlying flow. Coupling from the flow to the bed occurs through the Exner equation, while back coupling from the bed to the flow is achieved by imposing the no‐slip and no‐penetration condition at the immersed boundary. The simulation setup is similar to that by Zgheib et al. (2018a, https://doi.org/10.1002/2017JF004398) except for the presence of sidewalls to better mimic laboratory flume conditions. Sidewalls are observed to significantly increase bedform sinuosity.

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Direct Numerical Simulation of Transverse Ripples: 2. Self‐Similarity, Bedform Coarsening, and Effect of Neighboring Structures

Cited by 26 publications

References 62 publications

Self‐Similar Morphodynamics of Gilbert and Hyperpycnal Deltas Over Segmented Two‐Slope Bedrock Channels

Self‐Similar Morphodynamics of Gilbert and Hyperpycnal Deltas Over Segmented Two‐Slope Bedrock Channels

Direct Numerical Simulation of Transverse Ripples: 1. Pattern Initiation and Bedform Interactions

On the Role of Sidewalls in the Transition From Straight to Sinuous Bedforms

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