Fully nonlinear phase-resolved wave modelling in the Norwegian fjords for floating bridges along the E39 coastal highway

Abstract

Coastal wave conditions are highly influenced by bathymetry variations and coastlines. The Norwegian fjords present large gradients of bathymetry changes and irregular coastline geometries that make the understanding of the near-coast wave conditions a challenging task. The proposed floating bridges for permanent fjord-crossings along the Norwegian E39 coastal highway require reliable and efficient numerical simulations of a large domain at the fjords. In this manuscript, a phase-resolving fully non-linear potential flow (FNPF) model is used to investigate wave propagations with the presence of complex bathymetry and coastlines at two fjords along the path of the highway. The FNPF model is equipped with a robust coastline algorithm, flexible wave breaking algorithms, a free-surface and bathymetry-following -grid and parallel high-performance computation capability. Both long-crested and short-crested offshore swell wave conditions are simulated at the two fjords, Sulafjord and Bjørnafjord. Sulafjord is more exposed to the offshore swell while Bjørnafjord is more sheltered. The phase-averaging spectral wave models are also applied for both fjords and compared with the phase-resolving FNPF model. The significance of applying phase-resolving model for strongly nonlinear wave transformations in the fjords is demonstrated. The wave transformations and the wave field inhomogeneity and incoherence are captured using the phase-resolving time domain simulation results, which reveal significant engineering considerations for floating bridge design. The presented numerical approach is seen to be able to simulate the complex transformations of irregular waves and identify key wave field characteristics with the presence of irregular bathymetry and coastlines such as the Norwegian fjords.