Riprap Scour Protection for Monopiles in Offshore Wind Farms

Abstract

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.

Wind Turbines Offshore Foundations and Connections to Grid

“…In addition to their apparently conceptual simplicity, monopile foundations, seen in Figure 1A, are far from the usual standards of onshore engineering. This is mainly due to their size and usage of a transition piece between the pile and wind turbine tower [22,23].…”

Quantification of Measurement and Model Effects in Monopile Foundation Scour Protection Experiments

“…Exposed to the harsh sea environment of current and waves, the monopile foundations are protected with a layer of armour materials against the scouring around the monopile structure. Such a scour protection layer is mostly built with riprap, and can also be installed using concrete mattress and geotextile sand container [2,3]. Alternatively, flow-altering countermeasures, such as integrated tidal current turbine and anti-scour collar, are also promising engineering solutions for scour protection [4][5][6].…”

“…Other relevant works are seen in [17][18][19][20][21][22]. Failure modes (2) and (3) are addressed in [23][24][25][26]. In addition to the laboratory experiments, field surveys provide more details about how monopile scour protection behaves in real life sea conditions, such field data is available in [27].…”

“…In addition to the laboratory experiments, field surveys provide more details about how monopile scour protection behaves in real life sea conditions, such field data is available in [27]. Furthermore, the design of the scour protection layer has been recently discussed by [2,28].…”

Offshore Wind Farms

“…The papers are of very good quality, and deal with numerous topics related to offshore wind energy. They cover issues such as marine renewable energies on the Spanish coast [1], relevant factors for optimal locations for wind facilities [2], wind energy potential analysis on the Lebanese coast [3], the trailing-edge flap in large scale offshore wind farms [4], monopile foundations dimensional analysis [5], scour protection in monopile foundations [6], frequency response model tests in monopiles [7], gravity-based foundations [8], effect of the ice force in the support structures [9], dynamic response for submerged floating structures with different mooring configurations [10], tension leg platform wind turbines with non-rotating blades [11], the integration of offshore wind farms in future power systems [12], and transient overvoltage considering different electrical characteristics of vacuum circuit breaker [13].…”