Corrosion in the marine environment is a complex and expensive form of damage. It is commonly studied by the deployment of coupons that reflect the marine corrosion a structure will experience, thus allowing design and maintenance prevention strategies to be developed accordingly. This study stems from the lack of information in the literature regarding the profiling of corrosion with respect to marine depth in the North Sea where important wind farm developments have been undertaken. To address such issue a field experiment has been designed and carried out in the vicinity of the Westermost Rough Windfarm in the North Sea. The field experiment consists of deploying steel S355 coupons below the tidal area and capturing the effects of corrosion, the mass loss from which the corrosion rate is derived and the chemical products that makes up the rust with water depth. The study involves proper planning and logistics to ensure that the field experiment survives the rough conditions of the North Sea for a duration of 111 days. A high corrosion rate of 0.83 mm/year has been observed in this experiment. This paper goes into the details of the deployment blueprint employed and the analyses of the coupons to provide a conclusive observation and modelling of corrosion with respect to water depth under free or open sea water corrosion condition.
With single components weighing up to hundreds of tonnes and lifted to heights of approximately 100 m, offshore wind turbines can pose risks to personnel, assets, and the environment during installation and maintenance interventions. Guidelines and standards for health and safety in lifting operations exist; however, having people directly beneath the load is still common practice in offshore wind turbine installations. Concepts for human-free offshore lifting operations in the categories of guidance and control, connections, and assembly are studied in this work. This paper documents the process of applying Multi-Criteria Decision Analysis (MCDA), using experts' opinions for the importance of defined criteria obtained by conducting an industry survey, to benchmark the suitability of the concepts at two stages. Stage one streamlined possible options and stage two ranked the remaining suite of options after further development. The survey results showed that criteria such as 'reduction of risk', 'handling improvement' and 'reliability of operation' were most important. The most viable options, weighted by industry opinion, to remove personnel from areas of high risk are: Boom Lock and tag lines, a camera system with mechanical guidance, and automated bolt installation/fastening for seafastening. The decision analysis framework developed can be applied to similar problems to inform choices subject to multiple criteria.
Offshore wind turbine (OWT) support structures are invariably subject to colonisation by marine organisms. Marine growth is by no means spatially or temporally linear. It may vary based on location and season, and with structural characteristics such as materials, surface roughness and spatial orientation. Marine growth is a major consideration for engineers. As organisms settle on the structure they may increase surface roughness and cross-sectional area, altering drag and inertia coefficients and increasing hydrodynamic loading. It can be assumed that variability in marine growth would lead to fluctuations in corresponding loading and inertia. Furthermore, the added mass from marine growth also influences structural integrity (i.e. buckling and natural frequency). As such there is considerable uncertainty surrounding the long-term dynamic response of OWTs to marine growth, as this phenomenon is often overlooked in FEA modelling. Parametric FEA modelling is a powerful design tool often used in offshore wind. It is so effective because key design parameters (KDPs) can be modified directly in the code, to assess their effect in the structure's integrity, saving time and computational resources. This paper uses a parametric FEA model of an OWT support structure to analyse how marine growth affects the structural integrity of the system. ULS, FLS, buckling and natural frequencies are investigated against different growth rates and patterns of zonation.
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