Climate inputs [1–7] in the developed methodology are
explained in Table 1. Offshore access by vessels/helicopter is
influenced by the inputs [1–5]; whilst the turbine power production
is only influenced by the input [1]. The inputs [4 and 5] are
utilised to calculate the length of period with sun light in each
working shift, which is a constraint for CTV, helicopter, and OAV
access. The input [6] is related to the helicopter operations, since
helicopters can only fly if the visibility is sufficient enough (Joint
Aviation Authorities, 2004). If the wind speed observations are
measured from a single altitude, these values have to be extrapolated/interpolated
to the hub level and sea level. In this context,
sea level observations are used for the operational activities; on
the other hand, hub level observations are used for the power
production calculations, for the maintenance activities that require
equipment lifting, and also for the helicopter access. Although
there are many models to extrapolate wind speed to different
altitudes, the wind power law developed by Justus and Mikhail
(1976) is the most widely used method (Fırtın et al., 2011);
therefore, the wind power law in Eq. (1) is adopted to calculate
the wind speed values at hub level and sea level.
v2=v1 ¼ h2=h1
α