Numerical modelling of solitary internal waves in the Browse Basin.

Abstract

Shell is developing a floating liquefied natural gas (FLNG) facility to extract and process natural gas in the Browse Basin on the North West Shelf of Australia. This shelf break area is known for its strong tidal currents and year-round stratification. Tidal currents transporting stratified water over steep bathymetry can generate large internal waves called solitary waves (sometimes called solitons). A field survey in the Browse Basin showed that internal solitary waves have passed the FLNG location on several occasions. Solitons are known to have severely disrupted offshore operations in other areas in the past. In the case of the Prelude FLNG project, the production risers, steel tubular water intake risers and mooring chains can all be subject to fatigue or clashing due to internal wave events. The safety and effectiveness of the FLNG project can be improved if it is possible to forecast when solitons will occur and what their magnitude will be. For that reason, Shell wants to use a numerical model that is capable of predicting the internal wave activity in the Browse Basin. Finlab is a non-hydrostatic, finite element model that solves the full Navier-Stokes equations on unstructured grids. It was designed for small-scale flow problems with complex topography. However it has never been extensively tested for internal solitary waves. Therefore, the objectives of this project are to investigate whether Finlab can be used for the numerical simulation of internal waves in the Browse Basin and to gain a better understanding of internal wave dynamics in the Browse Basin through data analysis and numerical simulations.