As part of the HIGHWAVE project we are delighted to announce that some recent work has been accepted for publication in the Journal of Marine Science and Engineering (Special issue on Extreme Waves). The work focuses on comparing the effects of the wave spectrum, computed using the Discrete Interaction Approximation (DIA) and the Webb–Resio–Tracy (WRT) methods, on statistical wave properties such as skewness and kurtosis. In addition, we investigate the minimum spatial domain size required to obtain meaningful statistical wave properties.

Last week we have seen a lot of reports in media about the phenomenal sea state off the west coast of Ireland. An example is The Skipper (a journal of the Irish & UK Fishing Industries) releasing an article claiming a recorded monster wave of 30 meters. RTE had a few articles, where excited surfers mention 18 meter waves. Met Eireann and the Marine Institute M6 buoy recorded a maximum individual wave height of 21.7 meters between 27 and 28 October, with significant wave height being 15.7 meters. These were the remnants of hurricane Epsilon, that brought the extreme waves to the Irish coasts. These values are phenomenal indeed.

These reports bring us to the long standing discussion on quality control of the data. Can we trust a single instrument measuring the wave height?

My Chinese colleagues from Shanghai Jiao Tong University performed nice experiments to study the interaction between a solitary wave and a finite horizontal plate submerged at a depth equal to 1/4 of the water depth. The spatial and temporal variation of the three-dimensional (3D) surface deformation were measured using a multi-lens stereo reconstruction system. The hydrodynamic loads were measured by underwater load cells. The plate-induced shoaling causes 3D wave focusing, leading to an increased maximum elevation along the streamwise centerline of the plate. The detailed wave focusing process and the influence of wave amplitude on focusing are presented in a paper that just came out in Physics of Fluids (https://doi.org/10.1063/5.0015903). A 6-stage loading process based on the maxima of vertical wave force and pitching moment is proposed. It is coupled with the synchronous surface deformation to reveal the loading mechanism. It proves that the vertical wave force on the plate reduces compared with the results from 2D experiments. The surface elevation and wave-induced load data provide an excellent benchmark for further studies on the 3D nonlinear interaction between a solitary wave and a submerged plate.

HIGHWAVE involves a lot of numerical simulations, dealing in particular with extreme sea states and using nonlinear wave propagation models. ICHEC, the Irish Centre for High-End Computing, provides core-hours to three kinds of projects. Class A projects are intended for consortia concerned with high impact problems. Prof. Dias was successful with his Class A application. The project has been given 5M core-hours. It will start on 1 June 2020 and will last for a couple of years. 

In these dark times, when good news is scarce, science always pushes the boundaries and offers hope…

The world record set by Engineer Arnaud Disant and his team in 2018 has now been officially verified: offshore WiFi transmission of 19.4 nautical miles off Cork harbour, “The longest ever attempted transmission between a vessel offshore and a lighthouse on a distant shore, without using satellite communication of cellular data like 3G or 4G…”

Ireland's Atlantic nearshore coastal waters experience storms several times every year. Over the last few Winters/Springs, the UCD Wave Group has deployed a Teledyne Sentinel V acoustic Doppler current profiler (ADCP) device into these waters to measure the sea state over a period of months, in the hope of observing these stormy conditions.
In our new paper in Scientific Reports, we present results from two such storms. One was from our 2015 measuring campaign off Killard Point, and the other from the 2017 campaign off the Aran Islands. We analyze the non-stationary surface-elevation series and compare the distributions of crest and wave heights observed with theoretical predictions based on the Forristall, Tayfun, and Boccotti models. Adapting and applying these models in the nearshore, and compensating for the significant variability of both sea states in time, was a novel approach.
The largest nearshore waves observed during the two storms do not exceed the rogue thresholds as the Draupner, Andrea, Killard or El Faro rogue waves do in intermediate or deep-water depths. However, the story does not end here. Our analysis reveals that modulational instabilities are ineffective, third-order resonances negligible and the largest waves observed here have characteristics quite similar to those displayed by rogue waves for which second order bound nonlinearities are the principal factor that enhances the linear dispersive focusing of extreme waves.
Wave measurements and statistics in the nearshore is a challenging topic, with many new and exciting results yet to be discovered!

Giant rogue waves on the ocean are a mysterious phenomenon as much the stuff of legend as of science. Despite much anecdotal evidence of their destructive power, their scientific study has proven elusive, mainly because of the danger and difficulty of making measurements in the natural environment of the open sea. This changed dramatically in 2007, however, when researchers showed that injecting powerful ultrafast laser pulses into an optical fibre could generate similar large amplitude waves – but waves of light and not of water.

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Figure above: Timeline illustrating the parallel developments in fibre optics (top) and hydrodynamics (bottom).

A storm in 1953 halted the construction of the slipway at Gort Na gCapall on the Aran Islands and also sank the Princess Victoria in the Irish Sea when “the stern gates to the car deck were forced open in heavy seas”, with the loss of 132 people (The Irish Times, 5 June 2003, and BBC News, 1 January 1953).

Williams and Hall (2004) document eyewitness accounts from Gort Na gCapall. The storm caused the total destruction of the construction machinery and a large number of megaclasts (up to 2 m in length and 15 m above sea level) were transported so that there was no longer access to the slipway for boat launching. Waves reached breaking heights of approximately 12 to 15 m.