Issue 51

D. Vasconcelos et alii, Frattura ed Integrità Strutturale, 51 (2020) 24-44; DOI: 10.3221/IGF-ESIS.51.03

the structure was structurally reinforced, in order to improve its response to the applied loads. Finally, the improved design was tested in transient analyses at 11.4 m s -1 and 24 m s -1 . This project does not yet include a fatigue damage evaluation. However, in following work, this evaluation should be performed, as this structure are subjected to fatigue damage accumulation, due to variable cyclic loading, thus resulting in the appearance of fatigue cracks that lead to the reduction of

the structure service life [14]. Tower and Turbine Properties

A Wind Turbine consists of several parts, namely: the blades, the tower, the hub (where the blades are connected) and the nacelle (which stands on top of the tower and supports the hub). The nacelle contains the generator and the gearbox. As stated before, the turbine used within this research is the NREL 5 MW Reference Turbine. Tab. 1 displays its most relevant properties:

Hub Height above SWL 2

90 m

Hub Mass

56 780 kg 240 000 kg

Nacelle Mass Tower Height

75.6 m 87.6 m 126 m 61.5 m

Tower Height above SWL

Tower Mass

347 460 kg

Rotor Diameter Blade Length

Blade Mass

17 740 kg

Cut-In Wind Speed Rated Wind Speed Cut-Out Wind Speed

3 m/s

11.4 m/s

25 m/s Table 1 : NREL 5 MW Reference Turbine Properties [7].

DeepCWind Foundation The original model is made of circular section members only. The following pictures show the overall dimensions of the foundation. The members are identified as MC (main column), UC (upper columns) and BC (bottom columns). The tubular thin walled members that make the connections between each columns are identified as DU (delta upper pontoon), DL

UC

CB

BC

DL

DU

YU

YL

MC

Figure 1 : Dimensions of the DeepCWind Platform; adapted from [6]. YL member is hidden.

2 Sea Water Level

26