Sinking of armour layer around a vertical cylinder exposed to waves and current

Nielsen, Anders Paarup; Probst, Thomas; Petersen, Thor Ugelvig; Sumer, B. Mutlu

doi:10.1016/j.coastaleng.2015.03.010

Cited by 28 publications

(21 citation statements)

References 16 publications

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“…In an attempt to explain the sinking a major test program including physical and numerical modelling of the sinking in case of current, waves, and combined waves and current was initiated. The results of the test program are reported in Nielsen et al (2011Nielsen et al ( , 2013, Sumer and Nielsen (2013), Nielsen et al (2014), and Sumer (2014). The findings presented in these papers have made it possible both to improve the analysis of the survey data from Horns Rev 1 Offshore Wind Farm and to give better explanations for the damage; this work is presented in the present paper.…”

Section: Introductionmentioning

confidence: 86%

“…One of the major problems of the understanding of the Horns Rev 1 sinking has been that the layout of the scour protections is rather irregular, which has made it difficult to compare the different scour protections. However, the findings in Nielsen et al (2014) made a strong indication that sinking due to waves was to a large extent controlled by the total volume of the scour protections rather than the actual height adjacent to the pile. This has been used to quantify the damage to the scour protections based on the change in volume of the entire scour protections.…”

Section: Introductionmentioning

confidence: 97%

“…However, the frequency of currents strong enough to mobilize the sediment beneath the scour protections was too low to fully explain the observed sinking of the scour protections. Nielsen et al (2014) showed that waves can cause the same magnitude of sinking and that the sinking is controlled both by the removal of sediment adjacent to the pile and by the in-filling of sediment from the surrounding seabed; in fact, the sinking of the scour protection could increase for a thicker scour protection as it took longer time to fill the pores between the stones with sediment from the surrounding seabedleaving longer time for the removal process to work.…”

Section: Introductionmentioning

confidence: 99%

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Sinking of Scour Protections at Horns Rev 1 Offshore Wind Farm

Nielsen

Sumer

Petersen

2014

Int. Conf. Coastal. Eng.

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The present study is an attempt to explain the reason for the sinking of the scour protection observed at Horns Rev 1 Offshore Wind Farm. A new method for analyzing the survey data has been developed based on detailed descriptions in the literature of the processes causing sinking. The results of the analysis of the survey data have shown that the largest relative damage was observed at shallow water and for the largest scour protections. This is foundbased on descriptions found in the literatureto be characteristic for sinking in wave dominated climate and as the current at Horns Rev is found to be too weak to mobilize the sediment underneath the scour protections, it is found likely that the waves had a major influence on the sinking of the scour protections at Horns Rev 1 Offshore Wind Farm.

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Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Sinking of Scour Protections at Horns Rev 1 Offshore Wind Farm

Nielsen

Sumer

Petersen

2014

Int. Conf. Coastal. Eng.

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“…The stability of scour protections in the marine environment involves also the hydrodynamic loading by waves and combined waves and current. The failure mechanisms have been presented by Chiew [21], Chiew and Lim [23], Lauchlan and Melville [24], De Vos et al [25,26], Nielsen et al [27][28][29], Sumer and Nielsen [30] and Petersen et al [19,31]. As in the case of unprotected monopiles, numerical models to predict the dynamic response of a scour protection over long time spans have been presented and validated against field measurements; see Petersen and Nielsen [32].…”

Section: Introductionmentioning

confidence: 99%

Onset of Motion of Sediment underneath Scour Protection around a Monopile

Nielsen

Petersen

2018

JMSE

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The stability of scour protections is, potentially, an important issue during the design of fixed foundations for offshore wind turbines. One of the failure mechanisms observed at placed scour protection around offshore foundations is suction of sediment through the scour protection and subsequent sinking of the scour protection. Incipient motion of sediment and the initiation of suction underneath scour protections around piles in the marine environment were studied under waves, current and combined waves and current conditions. The motion of a thin layer of sediment underneath the scour protection was studied through the glass bottom of the test flume, which provided a clear view of the initiation of the motion of the sediment. The results show that the mobility depends on the Keulegan–Carpenter ( K C ) number for the pile, the ratio between waves and current flow and the ratio between the thickness of the scour protection and the base sediment. The critical mobility number is smaller for the wave-dominated situation compared to current-dominated conditions, which again are smaller than for combined waves and current conditions. Consequently, larger K C -numbers cause larger critical mobility numbers than smaller K C -numbers. Design diagrams are presented for the threshold of incipient motion of sediment underneath a scour protection in waves, current and combined waves and current.

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“…Yet, piping mode of failure received relatively less attention in the literature compared to other failure modes as far as coastal structures are concerned. Sumer and Nielsen [6] and Nielsen et al [20] studied the necessary filter layer thickness for preventing or limiting the sinking of scour protection layers of monopile foundations exposed to current and/or wave action. Their approach mostly involved the horizontal migration of base material from underneath the filter, however vertical pressure gradients were also seen to be effective in the case of waves.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Steady and Unsteady Piping in Coastal and Hydraulic Structures with a Sloped Face

Kirca

Kilci

2018

Water

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Coastal and hydraulic structures, such as revetments, embankments and levees—as well as their underlying soil—may experience piping when exposed to outward pressure gradients. The aim of the present study is twofold: (1) to derive the force-balance equation for soils with a sloping surface exposed to a steady hydraulic gradient (relevant to hydraulic structures) and to seek a criterion for piping, including the friction terms; (2) to study the case of unsteady hydraulic gradient forcing (relevant to coastal structures) by means of a series of experiments. The derived force-balance equation is compared with the available experimental and numerical model data from the literature and extended to soils protected by a filter/armour layer or rip rap. The experiments conducted to study the mechanism of piping under unsteady hydraulic gradients involved two types of loadings; sudden and oscillatory. The results show that although the mechanism of steady and unsteady piping has some similar aspects, the soil is generally more prone to piping in the unsteady hydraulic loading compared to the steady case, attributed to the inertia terms. The hydraulic conductivity of the soil becomes more distinctive for the unsteady piping case. Finally, remarks are made about practical applications.

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Sinking of armour layer around a vertical cylinder exposed to waves and current

Cited by 28 publications

References 16 publications

Sinking of Scour Protections at Horns Rev 1 Offshore Wind Farm

Sinking of Scour Protections at Horns Rev 1 Offshore Wind Farm

Onset of Motion of Sediment underneath Scour Protection around a Monopile

Mechanism of Steady and Unsteady Piping in Coastal and Hydraulic Structures with a Sloped Face

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