On long-term fatigue damage and reliability analysis of gears under wind loads in offshore wind turbine drivetrains

• Published in: International journal of fatigue Vol. 61; pp. 116 - 128
• Main Authors: Nejad, Amir Rasekhi, Gao, Zhen, Moan, Torgeir
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2014; Elsevier
• Subjects: Applied sciences; Drivetrains; Exact sciences and technology; Fatigue; Fatigue failure; Gearboxes; Gears; Long-term fatigue; Mathematical models; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Offshore; Offshore engineering; Powertrains; Reliability; Reliability analysis; Wind turbine gears; Wind turbines; Long-term fatigue; Reliability; Wind turbine gears; Drivetrains; Mechanical properties; Turbine; Fatigue; Offshore structure; Application; Gear
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2013.11.023

•A long-term fatigue damage calculation method for gear tooth root bending in wind turbine drivetrains is presented.•A simplified method for calculating gear transmitted load is presented.•The load, load effect and resistance uncertainties are evaluated and included in failure function.•Gear tooth root fatigue damage for a case study 5MW gearbox is calculated.•The service life reliability and probability of failure of gears is presented. In this paper, a long-term fatigue damage analysis method for gear tooth root bending in wind turbine’s drivetrains is presented. The proposed method is established based on the ISO gear design codes which are basically developed for gears in general applications, not specifically for wind turbine gears. The ISO procedure is adapted and further improved to include the long-term fatigue damage of wind turbine’s gears. The load duration distribution (LDD) method is used to obtain the short-term stress cycles from the input load time series of global response analysis. Dynamic loads and load effects in the gearbox are obtained by two dynamic models; a simplified approach and Multi Body Simulation (MBS) method. A good agreement between these two methods is observed. The long-term fatigue damage is then calculated based on the SN-curve approach by considering all short-term damages and the long-term wind speed distribution. Finally, the reliability and service life probability of failure considering load and load effect uncertainties is calculated. The procedure is exemplified by a 5MW gearbox designed for a pitch controlled, bottom-fixed offshore wind turbine.