Design of the Gearbox of a 22 MW Offshore Wind Turbine

In a world where the climate crisis is the dominating topic discussed all over the news and the internet, the necessity of developing new renewable technologies to keep up the progress while fighting global warming seems fundamental. Being carbon-free and simultaneously satisfying the energy demands of billions of people worldwide is one of science's biggest challenges. Sometimes, it is not just a matter of finding something new but of improving what already exists, and that is the direction taken by this master's thesis. Wind turbines are energy systems that have existed since ancient times, with different purposes from today, but still, they were highly used. After several centuries of being substituted by fossil fuels, they become one of the most critical renewable technologies able to satisfy several demands at the same time. It is known that the latest wind turbine studied and designed is the 15 MW offshore wind turbine, but in early 2023, the necessity to have something more drives towards a 22 MW wind turbine. The design of this specific system is still at the beginning, and further development will be added in the following years before being commercialized. For now, the work is based on the design and, mostly, on the sizing of the turbine gearbox. Starting with the choice of the location where this hypothetical wind turbine could be placed, which specifically for this thesis is 5 km from the shore of the city of Bergen, Norway, the global analysis is carried out by using peculiar software such as OpenFAST. Wind data (torque and the Weibull wind speed distribution) are gathered, followed by the LDD and ultimate strength analysis. The initial configuration of the gearbox is then selected: a medium-speed gearbox with three planetary stages to have a more compact design while keeping the efficiency high. The first and the secondary stages are designed in KISSsoft with five planets due to the enormous torque they have to face, even though at the end of the work it is observed that probably seven planets for the first stage would have been a better solution to decrease the weight of the device while keeping still the other results. The third stage has three planets and a helix angle lower than the first two stages to decrease the axial loads. After finding the optimal solution for the gears of each stage, bearings and shafts are then designed in KISSsotf, a design software used to size, analyze, and optimize machine elements and gearboxes. While the gears are designed according to both LDD and Ultimate strength analysis, the bearings' design is based on the fatigue analysis. The final and optimal configuration is selected according to the rating life and the safety factor of the bearings, keeping in mind that having a machine working for such a high power would lead to an overdesigned condition, mainly when it comes to the bearings of the last stage. Further studies and optimization analysis will be carried out to make the device ready to be commercialized sooner.