Influence of Marine Growth on the Static Response of Jacket Wind Turbine

Offshore wind energy is one of the renewable energy sources. Wind energy can be extracted using vertical or horizontal axis wind turbines. These turbines need supporting system in the offshore region. In the present study, a horizontal axis offshore wind turbine (HAWT) supported on an offshore jacket structure is considered. The main structural components of an offshore wind turbine are four-legged jacket structure of height 61.0 m (51 m submerged) and tower of 70 m height. This tower is supported by transition piece of height 4 m length. The HAWT is subjected to different environmental loads such as aerodynamic, wind, wave and current. A common challenge in this supporting structure is marine growth (MG). The growth of algae on the structural elements starts with the process of transportation of the structure from main land to offshore site. The growth of algae continues after the installation and continues to an optimum thickness depending upon the exposed area and site conditions. A detailed study of the effect of marine growth on the structure is performed by developing a finite element model. Beam elements are used to model the structural elements of jacket, transition piece and tower of the wind turbine. The wind and aerodynamic loads are estimated by the provisions of API (2005) and Betz theory considering cut-in, rated, cut-out and extreme conditions. Wave forces are estimated using Airy’s wave theory and Morison equation, by varying wave period from 4 to 20 s with an increment of 2 s. A parametric study on wave approach angles such as 0° and 45° is simulated to study the effect of wave direction. Linear current profile is considered in the estimation of current forces. A static analysis is performed using SACS 13.2 software. It is observed that the structural response is higher when marine growth (MG) is taken into consideration.