Measuring a rogue? An investigation into an apparent giant wave

An apparent giant wave event having a maximum trough-to-crest height of 21 metres and a maximum zero-upcrossing period of 27 seconds was recorded by a wave buoy at a nearshore location off the southwestern coast of Australia. It appears as a group of waves which are significantly larger both in height and period than the waves preceding and following them. This paper reports a multifaceted analysis into the plausibility of the event. We first examine the statistics of the event in relation to the rest of the record, where we look at quantities such as maximum-to-significant wave height ratios, ordered crest-trough statistics, and average wave profiles. We then investigate the kinematics of the buoy, where we look at the relationship between the horizontal and vertical displacements of the buoy, and also attempt to numerically reconstruct the giant event using Boussinesq and nonlinear shallow water equations. Additional analyses are performed on other sea states where at least one of the buoy's accelerometers reached its maximum limit. Our analysis reveals incompatibilities of the event with known behaviour of real waves, leading us to conclude that it was not a real wave event. Wave events similar to the one reported in our study have been reported elsewhere and have sometimes been accepted as real occurrences. Our methods of forensically analysing the giant wave event should be potentially useful for identifying false rogue wave events in these cases

Experimental observation of a near-motion trapped mode: free motion in heave with negligible radiation

A simple geometry which exhibits near-motion-trapping is tested experimentally, along with perturbed versions of the structure. The motion of the freely floating structure and the surrounding wave field is tracked and the near-motion-trapped mode is found, characterised by a slowly decaying heave motion with very small linear radiation of energy. It is found that the latter property is a better discriminator of the perturbed geometries as viscous damping masks fine differences in radiation damping as far the motion of the structure is concerned. The magnitude of this viscous damping is reasonably well predicted by a simple Stokes oscillatory boundary layer analysis

A concept for seabed rare earth mining in the eastern South Pacific

This report presents a concept for mining of rare earth elements from seabed sediment in a promising area of the eastern South Pacific. The document begins with an introduction to the seabed, its regulation and resources. The rare earth elements and their uses, productionand trade are then considered – although demand for rare earths is forecast to grow, price forecasts are very difficult.The available data on rare earth elements in seabed sediment is analysed, and a promising region selected for investigation; acoustic and geophysical/geochemical methods to explore and gather new data using underwater vehicles are discussed.The environmental, legal and social context of the chosen mining site is considered and the impacts of mining on the environment analysed; suspended sediment and tailings release are identified as major issues. It is clear that much is still not understood about the potential environmental effects of deep sea mining.A system for mining seabed mud rich in rare earth elements is then proposed – the method involves processing on the seafloor to minimise the volume that must be lifted to the surface and eliminate the uneconomic riser system. Aspects of this seabed processing apparatus are considered in some detail, though many problems remain unresolved.Finally, some financial and risk analyses of the project are completed, making an assumption that successful exploration has taken plac