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Dias, Frédéric
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Dias, Frédéric
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Dias, Frédéric
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Now showing 1 - 5 of 5
- PublicationSpatial Bayesian hierarchical modelling of extreme sea states(Elsevier, 2016-11)
; ; ; ; A Bayesian hierarchical framework is used to model extreme sea states, incorporating a latent spatial process to more effectively capture the spatial variation of the extremes. The model is applied to a 34-year hindcast of significant wave height off the west coast of Ireland. The generalised Pareto distribution is fitted to declustered peaks over a threshold given by the 99.8th percentile of the data. Return levels of significant wave height are computed and compared against those from a model based on the commonly-used maximum likelihood inference method. The Bayesian spatial model produces smoother maps of return levels. Furthermore, this approach greatly reduces the uncertainty in the estimates, thus providing information on extremes which is more useful for practical applications.325Scopus© Citations 9 - PublicationIncorporating Wave Spectrum Information in Real-time Free-surface Elevation Forecasting: Real-sea Experiments(Elsevier, 2018-09-12)
; ; ; ; Real-time prediction of free-surface elevation is necessary for a variety of applications. Assuming a Gaussian wave field, the wave spectrum can be used to calculate the statistically optimal predictor, for a given prediction configuration (i.e. for a given combination of measurement instants and spatial locations, relative to the instants and locations where and when the wave is predicted). More specifically, the optimal predictor is linear, and its coefficients need only be updated as the wave condition evolves. This spectrum-based prediction (SBP) approach encompasses, in a unified theoretical framework, both “time-series” and “spatially-distributed” prediction configurations. In this paper, the validity of the SBP theoretical framework is tested against real-sea wave data, which originate from a measurement campaign using an Acoustic Doppler Current Profiler (ADCP), and consist of free-surface elevation time series, at the corners and centre of a 25m-by-25m square. The directional wave spectra, corresponding to the sea states where the time series are provided, have also been calculated. The empirical SBP accuracy, obtained by applying the SBP in the real-sea time series, is assessed in various sea conditions and prediction configurations, and compared with the theoretical SBP accuracy, evaluated based on the wave spectra. Although the ADCP measurement layout is clearly not ideal for the purpose of wave forecasting, empirical results are physically and statistically consistent, and show good agreement with theoretical results, thus supporting the relevance of the SBP framework.432Scopus© Citations 6 - PublicationThe Future Northeast Atlantic Wave Energy Potential under Climate Change(International Society of Offshore and Polar Engineers, 2017-06-30)
; ; The potential changes to the wave energy flux and wave directionality of the Northeast Atlantic region towards the end of the 21st century are examined using a two-grid WAVEWATCH III model ensemble, driven by the EC-Earth global climate model under Representative Concentration Pathways (RCPs) RCP4.5 and RCP8.5. A decrease in the wave energy flux across all seasons and a change in the directionality (mean and peak wave direction) was found, with both clockwise and anticlockwise rotations of up to 10° in some regions of the Northeast Atlantic by the end of the century.166 - PublicationWave Energy Extraction in the Northeast Atlantic: Future Wave Climate Availability(2017-09-01)
; ; To examine the long-term viability of wave energy extraction locations, we analyse how the wave energy resource of the Northeast Atlantic may change both annually and seasonally towards the end of the twenty first century, using a three-grid WAVEWATCH III (WW3) model ensemble. Two greenhouse gas emission scenarios or Representative Concentration Pathways (RCPs) RCP4.5 and RCP8.5 are analysed, with three members in each RCP wave model ensemble. We examine in detail the percentage of time for which energy extraction is possi- ble, discounting sea states where the Wave Energy Converters (WECs) will be non-operational. This provides a useful analysis of locations around the coast of Ireland, Scotland and France not only where the most energetic wave climate can be found, but also the locations where WEC deployment is the most productive in terms of hours of potential operation of the WEC, compared to the total length of the observed period. The model is forced by EC-Earth data (10 m winds and sea ice fields). A hindcast driven by ERA-Interim fields is also produced for validation. Although a significant reduction in the overall wave energy flux towards the end of the century was found, the subsequent change in potential hours of operation remained stable.200 - PublicationDynamic Cliff-Top Beam Response to Wave Impact(International Conference on Hydrodynamics, 2018-09-26)
; ; Boulders are fractured and excavated by large waves along steep coastlines, contributing to coastal erosion. Intense fluid pressures enter cracks in attached bedrock, inducing bending stresses that may result in hydraulic fracture of a block. We consider the dynamic response of an attached rock beam to loading during wave impact. We verify the computational method using a known steady-state solution. We show that fast loading leads to greatest stress in the beam and that the beam oscillates before settling to an equilibrium position. These oscillations can produce large stresses long after the impact time.263