Taylor, Paul Howard
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ceetphd@nus.edu.sg
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Publication Linear diffraction analysis of the three-float multi-mode wave energy converter M4 for power capture and structural analysis in irregular waves with experimental validation(Springer, 2017) Sun, L; Zang, J; Stansby, P; Moreno, E.C; Taylor, P.H; Taylor, R.E; CIVIL AND ENVIRONMENTAL ENGINEERINGA frequency domain dynamic model based on the DIFFRACT code has previously been applied to the moored, three-float, multi-mode wave energy converter M4 in regular waves, modelled as a two-body problem, showing good agreement of relative rotation and power capture with experiments for small wave height (Sun et al., 2016 J Ocean Eng Mar Energy 2(4):429–438). The machine has both a broad-banded and relatively high capture width for the range of wave periods typical of offshore sites. The float sizes increase from bow to stern facilitating alignment with the local wave direction; the bow and mid float are rigidly connected by a beam and the stern float is connected by a beam to a hinge above the mid float where the relative rotation is damped to absorb power. The floats are approximately half a representative wavelength apart so the float forces and motion in anti-phase generate relative rotation. The mid and stern floats have hemispherical and rounded bases giving negligible drag losses. Here the multi-body model is generalised to enable bending moment prediction in the beams and by including excitation by irregular wave fields with and without directional spreading. Responses are compared with experiments with input wave spectra of JONSWAP type. In uni-directional waves, the measured spectra were a close approximation to the target JONSWAP spectra and were input into the model giving excellent predictions of relative rotation and bending moment in all cases and slight overprediction of power. Predictions of bending moment in regular waves were surprisingly somewhat less accurate. With multi-directional waves the measured wave spectra did not match the target JONSWAP spectra as well, particularly for smaller periods, and the directional spreading was not measured. However with the target spreading function and the measured spectra input to the model the predictions were again excellent. Since the model is validated for uni-directional waves it seems likely that it will also be valid in multi-directional waves and the accurate predictions thus suggest that the actual spreading was indeed close to the target. The model indicates that realistic directional spreading can reduce power capture by up to about 30%. However, optimising the damping coefficient in the linear damper can increase power capture by a similar amount, and optimising the vertical hinge position can increase this further although this cannot be varied in situ. Power optimisation is inevitably less marked than with regular waves. Good agreement with experiment is thus achieved for small to moderate wave heights (about twice average) at typical full scales, indicating that this efficient frequency domain method is valuable for fatigue analysis and energy yield assessment. Accurate prediction based on linear diffraction theory in steep or extreme waves is however not expected. © 2016, The Author(s).Publication Decadal variability of extreme wave height representing storm severity in the northeast Atlantic and North Sea since the foundation of the Royal Society(Royal Society of London, 2016) Santo, H; Taylor, P.H; Gibson, R; CIVIL AND ENVIRONMENTAL ENGINEERING; OFFICE OF THE DEPUTY PRESIDENT(RES&TECH)Long-term estimation of extreme wave height remains a key challenge because of the short duration of available wave data, and also because of the possible impact of climate variability on ocean waves. Here, we analyse storm-based statistics to obtain estimates of extreme wave height at locations in the northeast Atlantic and North Sea using the NORA10 wave hindcast (1958-2011), and use a 5 year sliding window to examine temporal variability. The decadal variability is correlated to the North Atlantic oscillation and other atmospheric modes, using a six-term predictor model incorporating the climate indices and their Hilbert transforms. This allows reconstruction of the historic extreme climate back to 1661, using a combination of known and proxy climate indices. Significant decadal variability primarily driven by the North Atlantic oscillation is observed, and this should be considered for the long-term survivability of offshore structures and marine renewable energy devices. The analysis on wave climate reconstruction reveals that the variation of the mean, 99th percentile and extreme wave climates over decadal time scales for locations close to the dominant storm tracks in the open North Atlantic are comparable, whereas the wave climates for the rest of the locations including the North Sea are rather different. © 2016 The Author(s) Published by the Royal Society.Publication The waves at the Mulberry Harbours(Springer, 2017) Jackson, Z; Grey, S; Adcock, T.A.A; Taylor, P.H; Bidlot, J.-R; CIVIL AND ENVIRONMENTAL ENGINEERINGThe Mulberry Harbours were used during the Second World War as part of Operation Overlord, the invasion of northern Europe by the Allies in June 1944. This commenced with the D-Day landings on the Normandy beaches on 6th June. The harbours played an important role in the history of ocean engineering leading to the development of novel technology and new theory. A severe storm occurred soon after the harbours were deployed leading to the destruction of the American harbour and severe damage to the British one. In this paper, we analyse this storm using hindcast data from ECMWF and SWAN modelling. We find that the waves were significantly more severe at the American harbour than at the British one, which may partially explain why the latter experienced less damage. We also find that the usually quoted figure for the storm severity of 1 in 40 years is a reasonable estimate for a summer storm at these locations. © 2017, The Author(s).Publication Current blockage in a numerical wave tank: 3D simulations of regular waves and current through a porous tower(Elsevier, 2015) Santo H.; Taylor, Paul Howard; Bai, Wei; Choo, Yoo Sang; CIVIL & ENVIRONMENTAL ENGINEERINGPublication Linear diffraction analysis for optimisation of the three-float multi-mode wave energy converter M4 in regular waves including small arrays(2016) Sun, L; Stansby, P; Zang, J; Carpintero Moreno, E; Taylor, P.H; CIVIL AND ENVIRONMENTAL ENGINEERINGA general frequency domain dynamic model based on the DIFFRACT code has been developed to predict the motion and power generation of the three-float multi-mode wave energy converter M4, modelled as a two-body problem. The machine has previously been shown experimentally and numerically to have broad-band high capture widths for the range of wave periods typical of offshore sites. The float sizes increase from bow to stern; the bow and mid float are rigidly connected by a beam and the stern float is connected by a beam to a hinge above the mid float where the rotational relative motion is damped to absorb power. The floats are approximately half a wavelength apart so the float forces and motion in antiphase generate relative rotation. Here regular waves representative of swell are investigated and the model is shown to give accurate predictions of experimental results for motion and power for small wave heights and motion which are representative of operational conditions. A linear damper is used to model the power take-off. Without changing the float geometry or the hinge position, adjusting the linear damping factor for each frequency is shown to increase the power by up to three times the experimental value, with a maximum close to the theoretical value for a single float. Increasing the height of the hinge point above the mid float increases the power for the higher periods but can reduce power at lower periods. Since float motion can be quite large, this result can only be indicative of qualitative trends. The effect of small rows has been investigated, up to five machines, and it is shown in particular how the performance of wave energy devices in a row was affected by the multi-body interactions and wave directions. These results are important since the optimum damping factor is shown to be frequency dependent, and increase power generation by up to three times. Furthermore, hydrodynamic interference between M4 machines in a row may significantly increase the power generation when appropriate spacings are chosen. @ 2016, The Author(s).