Design and Verification of Large Floating Coastal Structures - Environmental description, structural loads, responses and mooring system

Floating structures have been suggested for various coastal and nearshore industrial and residential applications, often as alternatives to land reclamation. Floating bridges and submerged floating tunnels are of particularly high interest in Norway, due to the development of the coastal highway. This project was motivated by the research needs for the development of large floating coastal structures in general, but with focus on floating bridges. Research needs related to environmental description, loads from waves and current, structural response and the interaction between loads and response (hydro-/aeroelasticity) have been addressed. Established design and analysis methods for floating structures are based on wave field models that are uniform over the structure. In current design of offshore structures these methods are applied to large rigid bodies as well as systems of interconnected bodies. Considering large floating coastal structures for fjord crossing and near-shore development - terminals, storage facilities etc., every component of environmental loading (wind, waves and current) can vary over the structure. Waves can be quite different at the two sides of a fjord. Wind will be influenced by the local topography and current will vary with local bathymetry. These spatial variations need to be accounted for. The large dimensions (typically 2-5 km for fjord crossing floating bridges) will cause the structure to be quite flexible, and hydro- and aeroelasticity will not be negligible as in the case of many traditional offshore structures, and this interaction may become important for the design process. The first part of the project was devoted to a state-of-the-art review of available literature and documentation on the state of the art for the different project topics of environmental conditions, environmental loads, structural responses, mooring and model testing. The review is documented in public project reports for each topic and forms the basis for the description of further project activities. The reports have been published with open access. Further, the project has focused on numerical analysis of the global response of a straight floating bridge under the action of loads from an inhomogeneous wave field and from waves disturbed by current. The results from these studies have been published in well-known scientific journals and conference proceedings. Scaled model testing in hydrodynamic laboratories is a common method for verification of design of marine structures. However, the large dimensions of floating bridges combined with relatively small waves (compared to offshore) and strong current, challenge standard testing procedures. A comprehensive hydrodynamic model test of a truncated floating bridge has therefore been performed in the project. These model tests have been instrumental for development of experimental methods for large floating structures and have also provided a valuable data set for further validation of numerical simulation tools. Although floating bridges have been used for the case studies in this project, most of the results are applicable or relevant for other large floating coastal structures.

Prosjektet har gjort SINTEF Ocean i stand til å gjennomføre to svært komplekse modellforsøk av flytebro for Bjørnafjorden for Statens Vegvesen i etterkant av modellforsøkene i selvet prosjektet. Prosjektet ga SINTEF Ocean mulighet til å utvikle metodikk for å bygge skalamodeller, instrumentere og gjennomføre modellforsøk på høyt vitenskapelig nivå. For industripartnerne har prosjektet gitt økt kompetanse for å kunne ta oppdrag innen flytebroer og andre store og flytende kystkonstruksjoner, som for eksempel flytende sol, flytende havner og oppdrettsanlegg. Forskningspartnerne har fått økt kompetanse og utviklet bedre eksperimentelle og numeriske metoder for fremtidens flytende konstruksjoner. Kunnskapen fra prosjektet bidrar til risikoavlastning i store offentlige utbyggingsprosjekt (fjordkryssinger for E39). Videre vil kunnskapen fra prosjektet kunne bidra til muliggjøring av nye typer flytende konstruksjoner for energiproduksjon, matproduksjon, samferdsel og flytende byområder.

Established design and analysis methods for floating structures are based on wave field models that are uniform over the structure. In current design of offshore structures these methods are applied to large rigid bodies as well as systems of interconnected bodies. Considering large floating coastal structures for fjord crossing and near-shore development, every component of environmental loading can vary over the structure: waves can be very different at the two sides of a fjord, wind will be influenced by the local topography and current will vary with local bathymetry. The simplest way of dealing with this inhomogene is to apply the worst environmental condition to the whole structure. Instinctively this may be taken as conservative. However, in some cases the uniform load assumption may not be conservative, for instance in the case of horizontal forces towards the convex side of a curved bridge. The large dimensions (typically 2~4 km for fjord crossing floating bridges) will cause the structure to be quite flexible, and the coupling between the structural deflection and water movement due to waves and current (hydroelasticity) will not be negligible as in the case of traditional rigid bodies, and this interaction may become crucial. The primary objective of this project is to develop improved design guidelines for screening design stages of large floating coastal structures, and establish the corresponding methods/tools for hydroelasticity analysis of coastal structures in spatially inhomogeneous environmental conditions and bathymetry. The knowledge generated in this project will be directly relevant for floating bridges, submerged bridges, floating harbors and floating storage facilities. The knowledge developed in this project will also be applied to hydroelasticity of large fish farming structures in coastal area, hydroelastic responses of wave energy converters, dynamic responses of offshore floating wind turbines.