Nowadays an increasing number of offshore wind farms (OWF) is getting built. Several disciplines are considered into this subject. The manual and sequential design approach used so far is not sufficient to guarantee optimized systems because interactions between the different components are disregarded. Therefore, engineering companies are looking for a multidisciplinary, modular, user-friendly and easy tool to be applied during the preliminary design assessment. This should take into consideration almost every crucial aspect of OWF design. Moreover, it should be able to perform some overall layout optimization, i.e. providing the best turbine positioning w.r.t. the energy yield, the costs, the cables, the installation and the O&M, ensuring some good constraint-handling techniques and guaranteeing a sufficient degree of robustness, precision, flexibility and speed. Therefore, the concept of MDAO (Multisciplinary Design Analysis and Optimization) workflow has been introduced. With respect to the common sequential design procedure, which optimizes the wind farm components separately, the MDAO analysis helps the user deal with the interactions between different design areas whilst automating the design process. The result is a design where all the parts are jointly optimized.Within the MDAO domain, two components are identified. The former is called analysis block and it comprehends all the modular tools which refer to a specific physical/economic discipline; the latter is the driver, i.e. an optimizing procedure which calls the analysis block in each iteration.This thesis focuses mostly on the analysis of the driver. In particular, the first goal is to identify the best optimizing strategy to be adopted, thanks to several quantitative assessment criteria. The second research goal is studying to what extent the different design areas - aerodynamics, support structure, cable topology etc. - affect the result of the optimization. The third research objective is to see whether the chosen optimizing procedures are able to deal with more complex design situations, such as more constraints or longer design vectors. In the end, an additional analysis on the effect of neighbouring wind farms on the layout optimization has been done, in order to see whether the optimization should consider the effect of those wind farms (disturbed wind conditions) or whether the results from the undisturbed case can be still valuable if re-computed in disturbed conditions.

In the design of offshore wind turbine generator (WTG) support structures, a large number of environmental parameters are used. The most important ones include the wind climate (wind speed and wind direction probability distributions), the wave climate (wave height and wave direction as well as peak frequencies of the waves, and water levels) and the soil conditions. These data in combination with the operational data of the wind turbine, such as the rotor speeds, pitch angle and yaw angle are used in dynamic simulations to determine the loads on the structure. Combining all these data correctly ensures that the support structure design, which is subject to large dynamic loads, is fitting for each specific location of the WTG. In particular, the environmental conditions should not coincide too much/often with the support structure natural frequencies, as that may result in resonance, thereby increasing fatigue life consumption. The dynamic behavior of these offshore support structures is of eminent importance. During the operation of WTGs, the actual dynamical properties of the WTG can be compared to the design. There are several reasons behind the goal of this comparison, for example verifying if the loading assumptions in the design were correct, assessing whether the life time can be extended or even whether the structure can be optimized (e.g. better foundations). Typically, this is done by comparing acceleration measurements of the WTG during idling (e.g. non-operational) conditions and applying Operational Modal Analysis algorithms. Given the high availability of modern wind turbines (e.g. >95% of time in operation) such measurements cannot be done as often as desired for this purpose. Therefore, the question arises to what extent the dynamical properties of WTGs can be estimated using measurement data obtained during operational (operational) conditions. This research explores the applicability of OMA algorithms in estimating the dynamical properties: the natural frequencies, the mode shapes and modal damping for operational conditions of offshore wind turbines on monopile foundations, using the Luchterduinen offshore wind park as a case study. The OMA technique explored in this thesis is Eigensystem Realization Algorithm. Test cases were used to confirm the performance of ERA for the estimation of the dynamic parameters. Stability diagrams were used to identify poles for stable modes (frequencies) in the frequency spectrum of data samples and to estimate a correct size of the Hankel matrices. It is concluded that this preprocessing and pre-analysis of the results is important to confirm the performance of ERA to correctly identify stable modes of support structures of operational offshore WTGs.Overall, it is concluded that ERA can yield useful results in estimating the natural frequencies for both ON and OFF, provided that an automated analysis is combined with a visual analysis. Even then, the accuracy and the consistency of the identified frequencies is moderate. ERA does not perform well for estimating the mode shapes, yielding inaccurate and inconsistent results. Based on the results of this work, ERA is found not to be capable of estimating modal damping ratios. The consistency for the mode shapes is not in all cases good and further study is recommended for both the mode shapes and the modal damping ratio. Another recommendation is to further study the size of Hankel matrices for this application. Furthermore, it is advised to also investigate the use of more advanced Operational Modal Analysis algorithms. The results of this study may be used to explore differences between wind turbines with and without scour protection and also to compare identified dynamic parameters to values used in the design.