Abstract
Marine growth is a known problem for oceanic infrastructure and has been shown to negatively impact the reliability of bottom-fixed or floating offshore structures submitted to fatigue or extreme loading. Among other effects, it has been shown to change drag forces by increasing member diameters and modifying the roughness. Bio-colonization being highly random, the objective of this paper is to show how one-site inspection data increases reliability by decreasing uncertainties. This can be introduced in a reliability-based inspection framework for optimizing inspection and maintenance (here, cleaning). The modeling and computation are illustrated through the reliability analysis of a monopile in the European Atlantic area subjected to marine growth and according to the plastic collapse limit state. Based on surveys of structures in the North Sea, long-term stochastic modeling (space and time) of the marine growth thickness is first suggested. A Dynamic Bayesian Network is then developed for reliability updating from the inspection data. Finally, several realistic (10–20 measurements) inspection strategies are compared in terms of reliability improvement and the accuracy of reliability assessment.
Highlights
Several weeks after immersion, a non-protected offshore structure is covered first by a bio-film and second by macro fouling [1]
This section is devoted to performing a reliability assessment of a monopile foundation subjected to marine growth from inspection data, i.e., the measurement of marine growth th σ g
This section is devoted to performing a reliability assessment of a monopile foundation subjected to marine growth from inspection data, i.e., the measurement of marine thickness
Summary
A non-protected offshore structure is covered first by a bio-film and second by macro fouling [1]. This biological phenomenon is affected by the nature (material) and shape of the colonized surface, the age of the structure and the season of installation, the hydrodynamic conditions that affect the fixing and arrival of larvae, the local bio-diversity and the extent of opportunities for colonization and competition [4], and long-term or short-term physio-chemical changes (death or development of the fouling) [8,9] Understanding this complexity remains challenging because it is site-specific, and it requires on-site measurements of the marine growth with time and the monitoring of environmental parameters. The development of specific image processing algorithms is promising [18,19,20], especially if coupled with underwater drones to increase the safety of divers and reduce costs
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