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Empirical formulations for the engineering prediction of equilibrium scour depths, as well as time scales (for both scour and backfilling), are re-visited for monopiles. Following prior work, it is argued on physical grounds that dimensionless time scales ought to scale proportionally to the Shields parameter raised to the − 3 / 2 power, based on scaling common to numerous sediment transport rate formulae. This is in contrast to stronger power dependence found in many existing formulations based on laboratory experiments, which may become unreliable when extrapolated to (storm/strong) field scales. In light of this, existing data sets for scour and backfilling time scales are re-analyzed. Novel parameterizations are developed for their prediction which are in line with the argument above, while maintaining similar coherency with existing data as in previous parameterizations. Re-analysis of existing data sets for equilibrium scour depths is likewise performed. An existing framework valid for slender monopiles is extended to incorporate the so-called large monopile regime (non-negligible diffraction), especially important e.g. for modern wind turbine installations. • Existing parameterizations of scour and backfilling time scales are reparametrized. • Suggested time scales scale according to the Shields parameter to the −3/2 power. • Existing framework for predicting equilibrium scour depth is extended to include large monopiles. [ABSTRACT FROM AUTHOR]

This paper presents results from numerical simulations of the propagation and run-up of full scale tsunamis, using a Reynolds-Averaged Navier-Stokes model, with emphasis on the resulting boundary layers and bed shear stresses. Spatial distributions of the Shields and Rouse parameters during run-up and draw-down show that for the tsunamis considered, with a sediment grain size corresponding to medium sand, considerable sediment transport (Shields parameter O(10) O(100)) can be expected during run-up and that the sediment transport can be expected to be dominated by suspended load. The results likewise show that the expected sediment transport during draw-down will similarly be considerable and dominated by suspension. The tsunami-induced boundary layers are monitored in time, and the observed boundary layer thickness ranges from spanning only a small fraction of the water depth to spanning the entire depth. The velocity profiles beneath the tsunamis are shown to have good correspondence with a logarithmic profile within the boundary layer. Similarly, the bed shear stresses beneath the tsunamis are investigated and a new and simple engineering model is developed for predicting the temporal variation of the bed shear stress based only on a free-stream velocity signal. The new engineering model is shown give better predictions for the bed shear stress than a standard Manning approach, and is likewise shown (in the Appendix) to produce reasonable predictions for shorter (wind scale) waves. It is finally also shown how the temporal evolution of the boundary layer thickness can be predicted based on the free-stream velocity signal alone. The results presented here are Part 2 of a larger study, where Part 1 presents the model validation and detailed descriptions of the run-up process. • Presented full-scale highly resolved CFD simulations of propagating and inundating tsunamis. • Showed spatio-temporal distribution of Shields parameters and Rouse numbers for inundating tsunamis. • Demonstrated that tsunami-induced boundary layers may span a small fraction of the depth or may span the entire water depth. • Presented a new engineering model for predicting the time varying bed shear stress beneath tsunamis. • Demonstrated that the new engineering model works also for shorter waves. [ABSTRACT FROM AUTHOR]

The performance of a recently developed "stabilized" turbulence (k − ω) closure model, which avoids un-physical over-production of turbulence prior to wave breaking, is investigated in the computational fluid dynamics (CFD) simulation of cross-shore sediment transport and breaker bar morphology. Comparisons are made with experiments as well as results from simulations employing (otherwise identical) "standard" turbulence closure. The stabilized turbulence model is demonstrated to result in major (qualitative and quantitative) improvements of the predicted breaker bar position and height. Conversely, the established over-production of turbulence in the standard closure, coupled with associated inaccurate undertow structure in the outer surf zone, contribute to erroneous offshore migration of the breaker bar. By correcting these shortcomings, the stabilized turbulence closure model rightly predicts initial onshore morphological migration of the breaker bar without any calibration. This work thus establishes proper turbulence modeling as a prerequisite for accurate CFD prediction of cross-shore sediment transport and profile morphology. • A recently developed "stabilized" turbulence model is used to simulate morphology. • The stabilized turbulence model leads to accurate breaker bar position and height. • A standard turbulence model leads to erroneous offshore breaker bar migration. [ABSTRACT FROM AUTHOR]

Experimental results involving shoreface nourishment scenarios are presented. The experiments are performed at small scale and the effects of nourishment placement and timing in relation to long-term cross-shore profile development are investigated. Four different nourishment scenarios are tested experimentally, with nourishment positioned both in the trough of a pre-developed profile as well as along the bar of the profile. The results demonstrate that under all scenarios the erosion of the shoreline slows relative to the case without nourishment. The two cases where the nourishment was placed along the bar reduced erosion of the shoreline more compared to the two cases with nourishment in the trough onshore of the bar. Compared to past experiments on nourishment presented in the literature, the present experiments were run for a longer duration, and the concepts of equilibrium profile and the development towards such an equilibrium were investigated. Curiously, the experiments showed a reversal of the sediment transport rate from being primarily offshore directed across the entire profile to onshore directed in the inner surf zone region closest to the shoreline. This reversal of transport rate occurred without changing the incoming wave conditions and resulted in deposition at the shoreline. This either questions the existence of equilibrium beach profiles or at the very least shows that the development towards such an equilibrium will not always be monotonic in time. • Shoreface nourishments are performed at model scale investigating the influence of timing and placement on long term profile development. • Placement of nourishment can disturb the cross-shore profile shape over long time. • After long time running with the same wave climate the transport rate changed from offshore directed to onshore directed in the inner surf zone. • The change in sign was related to cessation of wave-breaking and resulted in sand returning to an otherwise eroding beach. [ABSTRACT FROM AUTHOR]

A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier-Stokes equations, coupled with k-ω turbulence closure, with additional bed and suspended load descriptions forming the basis for seabed morphology. The model was successfully validated against experimental measurements involving scour development and eventual equilibrium in pure-current flows over a range of Shields parameters characteristic of both clear-water and live-bed regimes. This validation complements previously demonstrated accuracy for the same model in simulating pipeline scour processes in pure-wave environments. The model was subsequently utilized to simulate combined wave-plus-current scour over a wide range of combined Keulegan--Carpenter numbers and relative current strengths. The resulting equilibrium scour depths and trends were shown to be in accordance with existing experimentally based expressions from the literature. The variety of scour profile types emerging under various flow conditions is detailed and reconciled with experimental observations. The resulting matrix of scour depth time series was systematically analyzed, resulting in a new generalized expression for the scour time scale in combined waveplus-current flow environments. This expression is fully consistent with existing experimentally based relations at both pure-current and purewave limits and is appropriate for engineering use. [ABSTRACT FROM AUTHOR]

This paper presents results of complementary experimental and numerical studies involving wave-induced backfilling of current-generated scour holes beneath submarine pipelines. The laboratory experiments are conducted in a wave-plus-current flume, utilizing Laser Doppler Anemometry to measure velocities, synchronized flow visualizations using digital image technology, along with live-bed scour and backfilling measurements. Each experiment is based on a two-stage process: (1) initial scour induced by a pure current, followed by: (2) backfilling induced by pure waves (either regular or irregular). The time series of scour depths are closely monitored through video recordings. Systematic analysis of these has resulted in a closed form expression for the backfilling time scale, which is demonstrated to be a full order of magnitude greater than the well-known time scale of scour (with both governed primarily by the Shields parameter). The developed expression is strictly valid for the current-to-wave backfilling scenarios considered, while likely serving as an upper limit for more general wave-induced backfilling circumstances. The experiments are complemented by similar backfilling simulations utilizing a fully-coupled hydrodynamic and morphodynamic CFD model. The numerical simulations demonstrate the ability of the model to predict backfilling towards expected equilibrium scour depths based on the new wave climate, with time scales reasonably in line with experimental expectations. [ABSTRACT FROM AUTHOR]