The paper investigates the motion response and wave loads on a moored barge over, or close to, an underwater ridge. Increased added mass and damping in very shallow water are important aspects which are given particular focus. It is also demonstrated that variations in the bottom topography, and the associated wave diffraction and wave enhancement over a submerged ridge, has a considerable influence on the magnitude and the general form of the barge response. One important observation is therefore that local bathymetry needs to be accounted for when assessing the response of a nearby floater. The overall conclusions in the paper are sustained by numerical examples, based on linear diffraction calculations, where the barge and the sloping sea floor are modelled as a combined two-body problem.
In recent years there has been a renewed interest in shallow water problems in connection with offshore exploration and production, most of which is related to the growing demand for hydrocarbons, especially to LNG production and offloading in benign areas, or in relatively sheltered coastal regions.
The challenge of permanently mooring a large structure in shallow water is amplified by some of the particular problems arising from changes in mass- and damping coefficients, as well as sea bed refraction and the general increase in steepness and other features encountered when waves are progressing from deep to shallow waters.
For deep water problems the sea floor is usally treated as constant. The resulting error when performing design calculations in order to evaluate the system response in deep water, is in practice minimal In very shallow water this approach is more dicult to justify Fluid dynamic effects are more pronounced throughout the entire water