EnviSim4Mare - The development of a test bed and the investigation of the influence of marine vegetation on supporting structures of offshore wind turbines; Project: Experimental investigations of marine growth on test bodies.
The goals of the "EnviSim4Mare" project include the development of growth monitoring of marine invertebrates on test bodies, including the taxonomic determination of species communities and the documentation of their succession and dominance to determine their surface roughness.
As part of this project, test bodies were deployed at various study locations. These test bodies comprise larger stainless-steel tubes and plates (>100 cm), which reflect the surfaces of wind farm elements (jacket structure of wind turbines) and are to be used for later investigations (measurement trials) in a saltwater-current-and-wave-flume (SWCWF). Additionally, small stainless-steel plates (< 20 cm) are used for the biological investigations, including the documentation of the succession patterns.
The carrier units used for the test bodies include two spar buoys moored in the Nordergründe area (southern North Sea, northeast of the Nordergründe wind farm), a test station for material managed by the University of Stuttgart (Westmole Helgoland), and a steel construction developed by AWI (Northeast-Harbour, Helgoland). In addition, small moorings with fender and test bodies (steel plates) were deployed in the southern port of Helgoland and carrying structures with stainless steel tubes were attached to pontoons of jetties (cooperation with HES-International, Wilhelmshaven) in the Außenjade. In 2023, small stainless-steel plates for biological monitoring will also be installed at these pontoons.
The large number of study locations shall ensure the provision of sufficient test bodies for the measurement trials in the SWCWF. Additionally, it enables the investigation of different biofouling communities since the different local environmental conditions (e. g. flow conditions) in the selected study locations will probably lead to differently composed biofouling communities.
While the Nordergründe area is shallow and exhibits a clear mixing of the water mass (no zoning by tidal currents), in the study site Helgoland a depth profile is taken into account. This site provides the opportunity to compare biofouling communities of the intertidal zone (Eulittoral) and the zone below (Sublittoral). Since previous studies indicated that depth-dependent light conditions and other abiotic parameters (e. g. waves, dehydration during low tide, rain) can influence the growth. Biofouling communities are analysed by means of regular sampling at the different locations. For these biological studies of the succession patterns, stainless-steel plates are taken monthly and evaluated in the laboratory according to the above criteria (taxonomic, determination of coverage, abundance, wet weight).
In general, an important part of the project is the development of the carrying structures and test bodies for their use in different locations. These comprise sheltered sites, e. g. on the harbour wall, as well as exposed areas such as open water. This also includes the necessary moorings, marking buoys and attached steel frames. These developments should serve as a possible template for investigations in other areas or in studies with other research foci.
In addition to the flume development, a closed-circuit system (Recirculating Aquaculture System (RAS)) is also being designed and installed at the Leichtweiss Institute for Hydraulic Engineering (LWI) (Braunschweig), benefitting from the expertise at the AWI (Centre of Aquaculture Research). This should enable husbandry of the growth communities on the test bodies under natural flow conditions in the laboratory. The planning envisages that in the course of the project, the steel tubes an large plates will be removed once or twice a year for measurement trials in the newly built SWCWF to determine the loads and load flows. This approach is intended to provide information on the wave and current loads on artificial structures overgrown by biofouling. Among other things, this data is intended to provide the renewable energy sector with data for improvements in the resistance and life expectancy of artificial structures in the marine environment.
This project is funded by the Federal Ministry for Economic Affairs and Climate Action (BMWi) (Funding code: 03SX495B). The administration of the grant is carried out by the project management agency (Research Center Jülich GmbH, Department of Maritime Technologies).