An Investigation of Offshore Wind Installation Strategies - A Discrete-Event Simulation Model Used to Investigate Installation Vessel Operability
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- Institutt for marin teknikk 
The offshore wind industry has experienced an immense growth during the past years, but one of the main limitations for development is the high installation costs which may account for almost 20 % of total life cycle costs. The objective of the thesis is to assess installation methods for jacket foundations, and investigate how vessel operability impacts total installation time. The results can be used as a decision tool for offshore wind farm developers, when evaluating the best installation strategy during the planning phase. The development of the industry is trending towards distances farther from shore, larger turbines and increased offshore wind farm sizes. This means that new technology for foundations is being introduced, that is able to support larger loads in deeper waters. Due to the increased distance from shore, the logistics connected to installation must be assessed, to ensure efficient installation at low cost levels. Several installation scenarios are investigated, including installation with a jack-up vessel, installation with a jack-up installation vessel and feeder vessels to support component transportation, and installation with a DP-vessel. The installation scenarios are tested with case studies in discrete-event simulation models, to evaluate the best strategy for installation. The case studies includes changes in offshore wind farm size, from 50 to 500 turbines, and distances from shore, from 10 to 100 kilometers. The discrete-event simulation models were created using MATLAB SimEvents. The stochastic impact of the weather is implemented into the models by using Markov Chain simulated weather states for wind and wave data, gathered from the FINO1 weather station outside Germany. The operability of the models is verified by comparing the results with an operability study made from the observed weather data, showing a correlation between expected and simulated operability. The results from the operability study show that the use of feeder vessels is valuable to increase the installation rate. However, this is assumed to increase both the cost levels and the risk of collisions, because more assets are being introduced in the system. The scenario with only one jack-up vessel for installation and transportation provides the lowest installation rate, but this solution will probably provide the least cost intensive solution. The scenario where a DP-vessel performs all operations has high operability during positioning, thus increasing installation efficiency offshore. Introducing feeder vessels to this solution is likely to increase installation efficiency, but will include high day rates due to the increased number of vessel assets, and the high day rates for the DP-vessel. Operability during lifting operations is observed to be the governing limitation for installation. Both operations with loading in- and offshore, and installation of the jacket foundation, are depending on wind-limitations, and measures to improve installation efficiency should be taken within the area of lifting operations. The most effective installation strategy should be chosen based on information about the required installation rate, when distance from shore and number of turbines have been decided. The decision tool presented in this Master Thesis may present a valuable contribution for the project developers, and provides insight for evaluating the best installation strategy, considering how weather impacts vessel operability and installation efficiency.