Scour Around an Offshore Windturbine

Louwersheimer, Willem Frederik; Verhagen, H.J.; Olthof, J.

doi:10.1142/9789814282024_0168

Cited by 3 publications

(5 citation statements)

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“…Two studies of the Egmond aan Zee offshore windfarm have been reported by Raaijmakers et al (2007) and Louwersheimer et al (2009) for a medium grade sand with d 50 of 0.25mm. The windfarm was completed in 2006 and comprises 36 turbines of 4.6m outside diameter foundations with scour protection in water depths of 16 to 21m below mean sea level.…”

Section: Egmond Aan Zee Owfmentioning

confidence: 96%

“…3.5. Egmond aan zee OWF Louwersheimer et al (2009) reported on scour at the met mast for the Egmond aan Zee offshore windfarm with foundation diameter 2.9m. This had been installed without scour protection in a medium grade sand seabed with d 50 of 0.25mm.…”

Section: Met Mast On Scarweather Sands Sandbankmentioning

confidence: 99%

“…The towers, turbines and cables were installed and the rock protection completed by rock dumping to a minimum diameter of 18m on top of the filter layer. Armour 400 Louwersheimer et al (2009) investigated the filter performance around the turbines after periods of elapsed time of 13 to 114 days. They found that average filter bed lowering over the whole protection was in the range 0.07 to 0.11m and that a longer period of exposure did not necessarily result in more lowering.…”

Section: Egmond Aan Zee Owfmentioning

confidence: 99%

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The nature of scour development and scour protection at offshore windfarm foundations

Whitehouse

Harris

Sutherland

et al. 2011

Marine Pollution Bulletin

181

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Analysis and interpretation of monitoring data for the seabed bathymetry local to offshore windfarm foundations has shown how the scour develops in time and highlighted variations between sites with different seabed sediment characteristics, i.e. sands and clays. Results from European offshore windfarms have generated a unique dataset for comparison with previously published data. Where surficial sediment is underlain by a marine clay the scour (to date) has been limited, whilst those with unconstrained depths of sandy sediments show scour as deep as 1.38 times the monopile diameter. Scour protection has been installed at some sites for structural stability of the foundation or for cable protection. The flow interaction with the protection causes edge scour or secondary scour in the seabed around the protection. In some cases this scour is deeper than the unprotected case. The analysis has resulted in an improved evidence base for scour in the marine environment.

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Section: Egmond Aan Zee Owfmentioning

confidence: 96%

Section: Met Mast On Scarweather Sands Sandbankmentioning

confidence: 99%

Section: Egmond Aan Zee Owfmentioning

confidence: 99%

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The nature of scour development and scour protection at offshore windfarm foundations

Whitehouse

Harris

Sutherland

et al. 2011

Marine Pollution Bulletin

181

View full text Add to dashboard Cite

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“…Table 3 includes the general characteristics, Table 4 the characteristics of foundations and scour protections and Table 5 the metocean conditions. The information included in these three tables are taken, mainly, from the [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. Table 3.…”

Section: Case Studiesmentioning

confidence: 99%

Riprap Scour Protection for Monopiles in Offshore Wind Farms

Esteban

Gutiérrez

Negro

et al. 2019

JMSE

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The scour phenomenon is critical for monopile structures in offshore wind farms. There are two possible strategies: allowing the development of scour holes around the monopile or avoiding it by placing scour protection. The last one is the most used up to now. This paper is focused on the determination of the weight of the stones forming the scour protection. There are some formulas for the design of these parameters, having a lot of uncertainties around them. Some of them were created for fluvial environment, with a different flow to the marine one. Other formulas were elaborated specifically for coastal structures, closer to the coast than offshore wind farms, and with dimensions completely different. This paper presents the analysis of three formulas: Isbash, corresponding to fluvial environment, and Soulsby, and De Vos, corresponding to marine environment. The results of the application of those formulas are compared with real data of scour protection systems showing good results in five offshore wind facilities in operation (Arklow Bank phase 1, Egmond aan Zee, Horns Rev phase 1, Princess Amalia, and Scroby Sands), giving conclusion about the uncertainties of the use of these formulas and recommendations for using them in offshore wind.

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“…Depending on the flow conditions in the field, scour holes with maximum depths of several metres can develop over a short period around offshore foundation structures. Use of a rock-armour apron around the base of the pile is by far the most common scour protection measure for this type of structure (Louwersheimer, Verhagen & Olthof 2009;Petersen et al 2014). Designing the apron in terms of its size and the mean diameter of the rock to be used requires accurate information on the maximum bed shear stress and the positions of the regions of high bed shear induced by the unsteady flow before scour begins (e.g.…”

Section: Introductionmentioning

confidence: 99%

Oscillatory flow around a vertical circular cylinder placed in an open channel: coherent structures, sediment entrainment potential and drag forces

Chang

2023

J. Fluid Mech.

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Flow and turbulent structures generated by the interaction of forced incoming oscillatory flow with a circular, vertical cylinder placed in an open channel with a horizontal bed are investigated using eddy-resolving simulations. Validation simulations performed with a Keulegan–Carpenter (KC) number of 20 and multiple-mode forcing corresponding to the laboratory experiment of Sumer et al. (J. Fluid Mech., vol. 332, 1997, pp. 41–70) show that detached eddy simulation (DES) predicts more accurately the amplification of the bed shear stress beneath the horseshoe vortex system (upstream side of the cylinder) and the maximum magnitude of the bed shear stress at the downstream (wake) side of the cylinder compared with unsteady Reynolds-averaged Navier–Stokes simulations. High-Reynolds-number DES simulations are then conducted with 1.5 ≤ KC ≤ 30.8 and one-mode sinusoidal forcing of the streamwise velocity in the approaching flow to investigate the changes in the wake vortex-flow regimes, the coherence of the horseshoe vortices and the generation of other near-bed coherent structures in the wake during the oscillatory cycle. The flow is periodic, no horseshoe vortices form and no vortices are shed in the wake for KC = 1.5. By contrast, for KC ≥ 8 horseshoe vortices are present over part of the oscillatory cycle and up to three wake vortices are shed over each half-cycle as KC is increased to 30.8. For an intermediate range of KC numbers, one (KC = 15.4) or two (KC = 8) of the vortices forming at the back of the cylinder during each half-cycle are washed around it when the flow reverses. The main horseshoe vortex and other horizontal near-bed vortices have a large capacity to amplify the bed shear stresses when the incoming velocity magnitude is significantly less than its peak value. Assuming the depth-averaged velocity in the incoming (undisturbed) oscillatory flow is the same in simulations conducted with different KC numbers, the peak values of the sediment entrainment potential measured by the mean (cycle-averaged) volumetric flux of sediment entrained from the bed over one oscillatory cycle occur for 8 ≤ KC ≤ 15.4. For all KC numbers, the in-line force variation over the oscillatory cycle is fairly well approximated by the Morison equation. For KC = 1.5, the in-line force is only due to inertia effects. For KC = 30.8, the maximum and minimum values of the phase-averaged in-line force are approximatively in phase with those of the incoming flow velocity. For KC ≥ 15, the phase-averaged in-line force coefficients vary between 0.8 and 1.1 during most of the oscillatory cycle (e.g. when the incoming flow velocity is not close to zero). This is different from cases with KC ≤ 8 where the in-line force coefficient is equal to zero twice during the oscillatory cycle as the in-line force becomes equal to zero for non-zero values of the incoming velocity. The largest cycle-to-cycle variations of the in-line force coefficient and in-line force are observed around KC = 8. For KC = 8 and 15.4, the cylinder is subject to relatively large phase-averaged spanwise drag forces that are comparable to the peak phase-averaged streamwise drag forces. As KC is increased to 30.8, the phase-averaged spanwise drag force becomes zero over the whole oscillatory cycle but the cylinder is still subject to large instantaneous spanwise forces over part of the oscillatory cycle.

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Scour Around an Offshore Windturbine

Cited by 3 publications

References 0 publications

The nature of scour development and scour protection at offshore windfarm foundations

The nature of scour development and scour protection at offshore windfarm foundations

Riprap Scour Protection for Monopiles in Offshore Wind Farms

Oscillatory flow around a vertical circular cylinder placed in an open channel: coherent structures, sediment entrainment potential and drag forces

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