The expansion of offshore wind farms in the North Sea has raised serious concerns about maritime safety, in particular the increased risk of collisions—or 'allisions'—where a ship adrift hits a stationary structure, such as a wind turbine. For Rijkswaterstaat, the executive agency of the Ministry of Infrastructure and Water Management, managing this expansion requires developing a comprehensive understanding of the integral image of allision risks of drifting ships in the Dutch North Sea region. This understanding must be valid, reliable, and insightful, and include factors such as dynamic weather conditions and shipping activity. Unfortunately, current state-of-the-art methods for estimating the probability of allision rely heavily on assumptions, leading to significant variations in risk estimates, as highlighted by Ellis et al. (2008). These methods usually lack a North Sea-wide perspective and instead focus on risks specific to individual turbines. This study proposes an approach based on trajectory prediction using the OpenDrift model, which is simple and accessible for simulating ship drift trajectories based on wind, wave, and current data. A method is developed to estimate the probability of allision by combining the probability of a ship drifting into a wind farm, analysed through a ship's potential trajectories, with ship density data for specific locations. This method facilitates the calculation of allision risks under the influence of different environmental conditions and can be applied to multiple wind farms, providing a detailed assessment of the origins of potential threats and available response times. Overall, the assumptions in state-of-the-art methods might not sufficiently capture the risks associated with drifting ships. In addition, the established method broadens the ability to improve monitoring accuracy and optimise the positioning of ERTVs, even for specific environmental conditions. As a next step, this method should be extended to estimate actual risk levels by considering the potential consequences of an allision. With this approach, decision-making regarding allision threats can be contextualised alongside other maritime safety risks, facilitating the development of a robust risk mitigation strategy that enables Rijkswaterstaat to responsibly exploit the abundant potential the North Sea has to offer.

Nautical radar systems are subjected to random vibrations during their service life, which may lead to the degradation of the materials and a possible fatigue failure. Assessing the impact of these vibrations to the structural integrity of the radar is crucial for drafting appropriate maintenance plans and therefore, the development of a new tool is required, which will be capable of evaluating the fatigue lifetime of the radar system. This thesis examines a 5.7-meter-long radar antenna, supported by a lattice tower with a height of 20 meters, located in Rijkswaterstaat’s test environment in Stellendam. Although the lattice structure and the radar system are coupled, they are treated separately in this study. Firstly, a Finite Element Model of the tower is developed in ANSYS, where the radar is represented by an added mass at the top floor. The aim of the model is to identify the vibrations of the structure under the influence of the incoming wind. The stochastic description of the turbulent wind is taken into account in the evaluation of the wind loads and a random vibration analysis is performed, resulting into the response of the structure in the frequency domain. Furthermore, a second, simplified Finite Element Model of the radar system is built in ANSYS. Time series of the fluctuating wind velocity are generated and the wind load acting on the radar is approximated by the aerodynamic force in the along-wind direction, considering also the rotation of the radar antenna. In addition, the previously obtained response of the lattice structure serves as input for the radar model, representing the vibrations induced to the radar due to the motion of the structure below. The output of the model is the occurring stress response, which is subsequently used to assess the fatigue damage of the radar antenna. The results show that the development of stresses at the bottom surface of the antenna mainly occurs at its central area. Given the assumptions used throughout the thesis, the motion of the lattice tower is found to be the governing loading condition for the resulting stresses and the magnitude of the motion significantly influences the fatigue damage of the antenna. Finally, the fatigue lifetime appears to be very sensitive to the construction materials used for the radar system. These results should be verified by future measurements in order to improve the suggested models.