Long-term extreme response of an offshore turbine: How accurate are contour-based estimates?

Reducing conservatism in highest density environmental contours

“…where 𝐹 𝑅 is the long-term response function, which can be estimated using a full long-term analysis (see, for example, [12,28,32,38]).…”

“…• for contours in the wind speed -wave height variable space if offshore wind turbines are analyzed [12,24,25,34]; and…”

“…Another way how IFORM's approximation of the failure region can become non-conservative is if a single structure has multiple response variables that have their highest response at different regions of the contour. This is for example the case in offshore wind turbine design [12]. Consider the bending moment of a turbine's support structure, a monopile, at various water depths.…”

“…Left: A response with two distinct eigenfrequencies [27]. Middle: The 10 m bending moment of an offshore wind turbine [12]. Right: A response of a structure that is designed to be stronger in the direction of the highest waves [27].…”

“…Right: A response of a structure that is designed to be stronger in the direction of the highest waves [27]. The relative contribution of wave forces is greater for the moment at 30 m than for the moment at 5 m water depth [12]. Consequently, their failure regions have different shapes and touch the contour at different positions.…”