Design of Nacelle and Yaw Bearing for NOWITECH 10 MW Reference Turbine

Abstract

NOWITECH (Norwegian Research Centre for Offshore Technology) are developing a 10 MW offshore reference wind turbine to encourage increased production of renewable energy. This thesis present a mechanical design and dimensioning of a transition piece between the yaw bearing (part of the nacelle) and the tower in this reference turbine. A fatigue analysis to verify the lifetime of 20 years for the main shaft, bed plate and transition piece has also been performed.The final design has shape like a cone, which distributes the loads from the yaw bearing to the whole section of each tower leg. An extreme load case with 50 year occurrence period has been used for the Ultimate Limit State analysis. The material EN-GJS-400-18 is suggested for the transition piece, bed plate and main shaft. It has a yield strength of 240 MPa and a tensile strength of 370 MPa.The mass of the transition piece is 49.6 tonnes and a peak stress of 262 MPa in a single node was found. This is further discussed in chapter 12.3 and 18.The fatigue analysis was calculated with a detailed assessment described in the European standard, EN 13445-6 together with IEC 61400. The load case was calculated from a memo with fatigue loads for power production. A static analysis in the software NX/Nastran was performed with conservative estimations. A damage factor for each load each was calculated and used to compute a total damage factor for 20 years.The results confirmed the lifetime of 20 years for all parts despite all the conservative estimations (discussed in chapter 17 and 18.