Experimental and numerical study of wave-induced backfilling beneath submarine pipelines

Ersan, D. Bayraktar; Ahmad, Joseph; Larsen, B.; Carstensen, Stefan; Fuhrman, David R.

doi:10.1016/j.coastaleng.2016.08.010

Cited by 20 publications

(17 citation statements)

References 15 publications

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“…The model is a fully coupled RANS model, with k − ω turbulence closure, bed load transport, suspended load transport and morphology. The model is very well validated and has been used to simulate breaker bar development by Jacobsen et al (2014), current, wave and wave-plus-current induced scour and backfilling beneath submarine pipelines by Fuhrman et al (2014), Larsen et al (2016) and Bayraktar et al (2016) as well as current, wave and tsunami induced scour around a monopile by Baykal et al (2015), Baykal et al (2017) and Larsen et al (2017). For more details on the model implementation the reader is referred to Jacobsen et al (2014).…”

Section: Model-experiments Comparisonmentioning

confidence: 99%

Experimental study of tsunami-induced scour around a monopile foundation

Larsen

Arbøll

Kristoffersen

et al. 2018

Coastal Engineering

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Section: Model-experiments Comparisonmentioning

confidence: 99%

Experimental study of tsunami-induced scour around a monopile foundation

Larsen

Arbøll

Kristoffersen

et al. 2018

Coastal Engineering

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“…,Bayraktar et al (2016),Larsen et al (2016),Larsen et al (2017) andLarsen et al (2018a), and allow for near-bed cells to lie in either the logarithmic or viscous sub-layer. On the flat region the domain is discretized into cells with ∆x = ∆z = 0.01 m, and on the slope the mesh is gradually refined towards the shore while keeping a constant aspect…”

mentioning

confidence: 99%

On the over-production of turbulence beneath surface waves in Reynolds-averaged Navier–Stokes models

2018

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In previous computational fluid dynamics studies of breaking waves, there has been a marked tendency to severely over-estimate turbulence levels, both pre- and post-breaking. This problem is most likely related to the previously described (though not sufficiently well recognized) conditional instability of widely used turbulence models when used to close Reynolds-averaged Navier–Stokes (RANS) equations in regions of nearly potential flow with finite strain, resulting in exponential growth of the turbulent kinetic energy and eddy viscosity. While this problem has been known for nearly 20 years, a suitable and fundamentally sound solution has yet to be developed. In this work it is demonstrated that virtually all commonly used two-equation turbulence closure models are unconditionally, rather than conditionally, unstable in such regions. A new formulation of the $k$–$\unicode[STIX]{x1D714}$ closure is developed which elegantly stabilizes the model in nearly potential flow regions, with modifications remaining passive in sheared flow regions, thus solving this long-standing problem. Computed results involving non-breaking waves demonstrate that the new stabilized closure enables nearly constant form wave propagation over long durations, avoiding the exponential growth of the eddy viscosity and inevitable wave decay exhibited by standard closures. Additional applications on breaking waves demonstrate that the new stabilized model avoids the unphysical generation of pre-breaking turbulence which widely plagues existing closures. The new model is demonstrated to be capable of predicting accurate pre- and post-breaking surface elevations, as well as turbulence and undertow velocity profiles, especially during transition from pre-breaking to the outer surf zone. Results in the inner surf zone are similar to standard closures. Similar methods for formally stabilizing other widely used closure models ($k$–$\unicode[STIX]{x1D714}$ and $k$–$\unicode[STIX]{x1D700}$ variants) are likewise developed, and it is recommended that these be utilized in future RANS simulations of surface waves. (In the above $k$ is the turbulent kinetic energy density, $\unicode[STIX]{x1D714}$ is the specific dissipation rate, and $\unicode[STIX]{x1D700}$ is the dissipation.)

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“…Larsen et al (2016). Considering wave-induced backfilling, likewise found that equilibrium scour depth corresponded simply to that predicted by the new wave condition alone, and this finding is backed by later numerical (Fuhrman et al, 2014, who also extended this to other profile features) and experimental (Bayraktar et al, 2016) studies. An experimentally-based expression for predicting the wave-induced backfilling time scale following pure-current scour beneath pipelines (so-called currentto-wave backfilling scenarios) has been provided recently by Bayraktar et al (2016).…”

Section: Introductionmentioning

confidence: 66%

“…The present work aims to fill this gap by first presenting several new experiments involving wave-to-wave backfilling scenarios, adding significantly to the data set of . The collective data sets involving wave-induced backfilling (the present work, Bayraktar et al, 2016) will then be analyzed, resulting in a new expression suitable for the general engineering prediction of the wave-induced backfilling time scale. To ease smoothing of the bed at the beginning of each experiment, the sand pit was equipped with two 0.012 m wide plywood guide leveling boards having the same standing height as the sand pit (0.11 m).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

“…Local pipeline scour and/or backfilling processes due to current and/or waves have been commonly studied both experimentally (e.g. Sumer and Fredsøe, 1990;Zhang et al, 2016;Bayraktar et al, 2016) as well as numerically (e.g. Brørs, 1999;Liang and Cheng, 2005;Kazeminezhad et al, 2012;Zanganeh et al, 2012;Fuhrman et al, 2014;Larsen et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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