Biofouling is resulting from a biological process
Biofouling is the result of a biological process called biocolonisation which takes place when a support is added to the aquatic environment, or when a surface already present in the environment is free. ORE structures are supports where fixed living organisms can grow and around which other more mobile organisms gravitate. Biofouling is diversified: it can be composed of more or less indurated organisms and can reach several centimetres in thickness. Its characteristics vary a lot in time and space. It is therefore difficult to predict its development, which nevertheless poses several important challenges in the field of ORE.
Biofouling and ORE engineering
Biocolonisation affects all structures of anthropogenic origin placed in the marine environment, including offshore renewable energy systems. Biofouling can make structures heavier, modify the hydrodynamic response, affect heat exchanges, block mechanical functions, increase the fatigue of certain materials and generate or accelerate corrosion and biodegradation. By modifying the external geometry of the components, let alone the hydrodynamic forces exerted on them, it can also cause fluid/structure instabilities that are not expected, leading to cyclic solicitations that can be significant. These issues vary depending on the technology considered, but also on the component concerned. It is therefore essential to take this phenomenon into account in the design of structures, while ensuring their resistance and proper functioning in the long term and to ensure that regulations evolve.
Environmental issues of biofouling
At the scale of a ORE farm, biofouling forming on offshore renewable energy systems can alter local ecosystem structure and function, for example by locally increasing the level of organic matter after an on-site clean-up. ORE systems are installed in highly dynamic environments that are far from the coast and/or deep and therefore not easily accessible. The biofouling that forms in these areas is often not well known. However, to predict its effects on offshore renewable energy systems, it is essential to know its composition in ORE areas and to better understand its spatial and temporal variability. The application of an antifouling coating on submerged components is also a potential issue because biocidal components can diffuse progressively into the natural environment.
Collaborative projects to study the influence of biofouling
To answer the questions of engineers, organisations involved in the environmental authorisation of ORE projects, and more generally the local stakeholders, France Energies Marines is leading, with its members and partners, many collaborative cross-disciplinary projects on this theme. The available knowledge on biocolonisation on the French coasts has been synthesised in a bibliographic atlas of biofouling. A first collaborative project on the biofouling of ORE systems has highlighted the vulnerability of bottom-surface links to the phenomenon of biocolonisation (ABIOP project). Several experiments completed and in progress will make it possible to assess the effects of the presence of biofouling on the mechanical, hydrodynamic and thermal behaviour of the dynamic export cable (ABIOP+ and OMDYN2 projects), and to understand the influence of the nature of the mooring on biocolonisation (MONAMOOR project).
The impact of biofouling on the long-term behaviour of subsea components, and in particular their fatigue life, is also being studied as part of a collaborative project (MHM-EMR project). This project focuses on the evolution of the mooring system through measurement as well as the meteo-oceanic conditions conducive to the updating of models and the triggering of observation or even clean-up operations.
Another major challenge in this area is the development of standardised protocols for measuring the engineering and environmental critical biofouling variables at ORE sites: fresh weight, thickness (translated into equivalent roughness), specific composition, volume and coverage. This must be achieved by considering a sufficiently long time scale, i.e. several years (ABIOP, ABIOP+, SPECIES, MONAMOOR and APPEAL projects). In-situ monitoring of colonisation is already being carried out at several ORE sites in the Atlantic and Mediterranean (ABIOP+, SPECIES and APPEAL projects).
Photo credit: Xavier Caisey / Ifremer
Consideration of biofouling using quantification protocols useful for engineering
Dynamic umbilicals for floating marine renewable energies technologies - Phase 2
Subsea power cables interactions with environment and associated surveys
Accounting for biofouling through established protocols of quantification
Socio-ecosystemic approach to the impact of floating wind farms
Effective lifetime extension in the marine environment for tidal energy
Mooring health monitoring for offshore renewable energy systems
Monitoring of polyamide mooring lines
Coordination and participation in expert panels on ORE
Training in the field of offshore renewable energies
Expert in fluid-structure interactions
Benthic Ecology Researcher
Published on 02/11/2020