Uncertainties in the design of support structures and foundations for offshore wind turbines

A novel hybrid MCDM approach for offshore wind farm site selection: A case study of Iran

“…The technology High Voltage Ac Current (HVAC) or High Voltage Dc Current (HVDC) e Voltage Source Converter (VSC), the voltage level of the system, the number and the size of transformers (or converter stations), the number and the size of the cables, amongst other factors are selected to achieve this aim. Barberis Negra et al (Negra et al, 2006) investigated the total transmission losses of three transmission solutions including HVAC, HVDC Line Commutated Converter (LCC) and HVDC-VSC for large offshore wind farms. Vicente Negro et al (Negro et al, 2014) analyzed some current uncertainties consist of the design of the transition piece and the difficulties for the soil properties characterization in the offshore wind market, with the aim of going one step further in the development of this sector.…”

“…Barberis Negra et al (Negra et al, 2006) investigated the total transmission losses of three transmission solutions including HVAC, HVDC Line Commutated Converter (LCC) and HVDC-VSC for large offshore wind farms. Vicente Negro et al (Negro et al, 2014) analyzed some current uncertainties consist of the design of the transition piece and the difficulties for the soil properties characterization in the offshore wind market, with the aim of going one step further in the development of this sector. These identified uncertainties are related to the lifetime and return period, loads combination, scour phenomenon and its protection.…”

An investigation into the effect of scour on the natural frequency of an offshore wind turbine

“…The DNV design codes recommend that a local scour hole depth of 1.3 pile diameters (1.3D pile ) should be considered for both the ultimate and serviceability limit state design cases in the case of a monopile subjected to current only-induced scour (Det Norske Veritas, 2007). In the marine environment however, it must be recognised that these structures can be jointly subjected to currents, tides and waves which makes the problem more complex than that of scour around structures in rivers (which are generally under steady current conditions) (Negro et al, 2014). It is also noteworthy that natural variation in seabed level over a large area can give rise to a further global scour effect, which could have an effect over an entire wind farm site leading to more severe scour depths.…”

“…This analysis revealed that the maximum observed scour depth was less than the estimated value in all but two of the cases considered, which further highlights the uncertainties present in accurate scour depth estimation. Furthermore, Negro et al (2014) acknowledges the requirement that for effective scour protection design, it is necessary to include sediment properties, geotechnical characteristics of the site, environmental parameters for wave loads and turbine foundation specifications in order to accurately predict the maximum scour that could occur in the absence of such protection. They also call into question the DNV's (Det Norske Veritas, 2013) recommendation for scour characterization around offshore wind turbines under combined current and waves, deeming it to be inaccurate.…”

Sinking of concrete modules into a sandy seabed: A case study

“…Scouring is one of the threats to the foundational stability of both riverine and maritime structures. Although flow-induced scour around bridge piers has received significant attention for many years, wave-induced scour around marine structures has not become a topic of interest to researchers till the 1990's (Bricker et al, 2012;Matutano et al, 2013;Negro et al, 2014;Sumer and Fredsøe, 2002;Whitehouse, 1998). The presence of marine structures in a coastal flow regime changes the flow pattern in the immediate neighbourhood of the structures.…”