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The Norwegian Public Roads Administration is running a project "Ferry Free Coastal Route E39" to replace existing ferry crossings by bridges across eight fjords in western Norway. Since most of the fjords are wide and deep, construction of traditional bridges with fixed foundations is not possible. Therefore, floating bridge concepts are proposed for the fjord-crossing project. Since the floating foundations of the bridges are close to the water surface, the concern of accidental ship collisions is raised. Considering the displacement and speed of the passing ships and the significant compliance of the bridge, interaction between the bridge and the ship can be significant should a collision occur. Many studies have been conducted on ship collision with bridge structures with a special focus on bridge piers. However, the research on ship collision with bridge girders is quite limited. The purpose of this study is to investigate the collision response of a floating bridge for ship-girder collision events. Both the local structural damage and the global dynamic response of the bridge are assessed. Local structural deformation and damage are first investigated by numerical simulations with detailed finite element (FE) models in ls-dyna. Subsequently, the bridge global response to the collision loads is analyzed in usfos using the force-deformation curves from the local analysis. By combining the local and global analysis results, a comprehensive overview of the bridge response during ship-girder collisions can be obtained. [ABSTRACT FROM AUTHOR]

The Norwegian Public Roads Administration is running a “Ferry free coastal route E39” project to install bridges or tunnels across fjords in Western Norway. A floating bridge concept is proposed for the fjord-crossing project in Bjørnafjorden. One of the key aspects in design is to ensure bridge safety under accidental ship collision loads. The objective of this paper is to study the dynamic behaviour of the floating bridge subjected to ship collision loads on bridge girders. Numerical models of the ship-bridge collision system are developed using the dynamic analysis software USFOS. The curved floating bridge is modelled by beam elements and the striking ship is represented by a nodal mass-nonlinear spring system. Numerical analyses of ship collision with a bridge girder are carried out for three impact locations, i.e. middle spam, a span in quarter position and at the end span of the bridge. Bridge responses including the displacement, axial and shear forces and bending moment are calculated. Results show that the floating bridge can endure the proposed ship collision energy of 250 MJ. [ABSTRACT FROM AUTHOR]

Due to limited nearshore areas and great impact to local ecosystems, the aquaculture industry is moving the fish farms into more exposed sea regions where the environmental conditions are much more severe. Like other offshore installations operating at sea, fish cages are also exposed to the risk of collisions from attendant or visiting vessels. This paper evaluates the structural strength of the world's first offshore fish farm operating in Norway subjected to supply vessel collisions by the use of nonlinear finite element simulations. The fish cage is a semi-submersible floating structure consisting of ring-stiffened columns connected by braces. A standard 7500-ton supply vessel is used as the striking vessel. Both local shell deformation analysis using LS-DYNA and beam deformation analysis using USFOS are carried out. In the local shell analysis, collision scenarios with both decoupled and coupled methods are simulated for several representative impact locations. The decoupled model adopts prescribed paths for ship motions, while in the coupled model, the ship motions are calculated based on hydrodynamic forces from linear potential theory as well as inertia and collision forces. In the global beam-column analysis in USFOS, the force-deformation curves of the supply vessel from local shell analysis are used as the input. The resulting damage and energy absorption are compared with those from local shell simulations. The results are discussed with respect to the impact resistance, energy absorption and structural damage. • We carried out both local and global ship collision analysis with a novel offshore fish farm. • Local shell analysis using LS-DYNA was carried out on several representative locations of the fish farm. • Coupled ship collision simulations were conducted, and the results were compared with decoupled methods. • Global beam analysis with USFOS were conducted to account for global motions of the fish cage. • Results were discussed with respect to structural resistance, damage and motions. [ABSTRACT FROM AUTHOR]

Knowledge about extreme ocean currents and their vertical structure is important when designing offshore structures. We propose a method for statistical modelling of extreme vertical current velocity profiles, accounting for factors such as directionality, spatial and temporal dependence, and non-stationarity due to the tide. We first pre-process the data by resolving the observed (vector) currents at each of several water depths into orthogonal major and minor axis components by principal component analysis, and use harmonic analysis to decompose the total (observed) current into the sum of (deterministic) tidal and (stochastic) residual currents. A complete marginal model is then constructed for all residual current components, and the dependence structure between the components is characterized using the conditional extremes model by Heffernan and Tawn (2004). By simulating under this model, estimates of various extremal statistics can be acquired. A simple approach for deriving design current velocity profiles is also proposed. The method is tested using measured current profiles at two coastal locations in Norway, covering a period of 2.5 and 1.5 years. It is demonstrated that the method provides good extrapolations at both locations, and the estimated 10-year design current velocity profiles appear realistic compared to the most extreme velocity profiles observed in the measurements. • Description of extreme ocean current profiles is important for marine design. • Orthogonal current components are decomposed into tidal and residual currents. • Modelling based on the conditional extremes model by Heffernan and Tawn (2004). • Directionality, dependence, and non-stationarity due to the tide are accounted for. • The method is shown to perform well, and design current profiles are obtained. [ABSTRACT FROM AUTHOR]