A Physical and Numerical Study of an Interconnected Wave Energy Array

Key to the progression of the wave energy extraction sector is reducing capital costs whilst maintaining or improving energy extraction efficiency. To achieve this, multiple devices in farm configurations, known as arrays, are likely to be developed. Mooring and anchorage systems of large scale arrays have been highlighted as notable contributors to high structural costs. To minimize the number of anchors required, and thus the cost, one option is to interconnect devices within the arrays. The implication on array performance and line tension of this mooring design needs to be understood to realize the true possibility for cost reduction. Large scale physical tests were performed in the COAST Laboratory at the University of Plymouth. An array of five individually moored oscillating water column type wave energy converters (WEC) were initially tested in operational and extreme conditions, followed by four interconnected designs of reducing levels of interconnectivity. Results showed considerable performance implications due to the interconnecting of devices, with a 75% increase in annual yield for all levels of connectivity, relative to the individually moored control case. The performance enhancement was attributed to the interconnecting moorings altering the system resonant frequency, resulting in a beneficial phase difference between the water column and the device. Whilst the overall array performance was not significantly effected by the level of connectivity the spatial variation in power distribution within the array was. The fatigue line loading experienced by the interconnecting lines in operational states showed iv beneficial results compared to that experienced by the individually moored array. However, in extreme sea states, some interconnecting and seabed lines displayed higher extreme loads compared to the individually moored array and so would require a higher strength material, incurring possible higher costs. Due to the improved fatigue characteristics of the interconnected arrays during operational conditions, these higher performance lines required would likely have an increased service life that requires complex cost modelling. This thesis demonstrates a beneficial potential for interconnected WEC arrays worthy of further investigation

Use of constrained focused waves to measure extreme loading of a taut moored floating wave energy converter

© 2017 The Authors This paper concerns experimental measurements of the interaction of a taut moored floating body, representing a point absorbing wave energy converter in survivability mode, with extreme waves. The extreme waves are modelled in four ways. NewWave theory is first used to generate focused wave groups of varying steepness. Steepness is shown to have negligible effect on peak mooring loads, but causes significant differences in the resulting motion. The NewWave group is then constrained into both regular and irregular background wave trains so that the floating body has a load history caused by previous waves when interacting with the focused wave group. It is shown that an independent focused wave group is insufficient to properly model the extreme response of the floating body. However differences between the target and measured constrained time series due to non-linear wave-wave interaction limited the potential benefits of this approach. Finally the results from these tests are compared with measurements taken using irregular waves without any deterministic focused wave groups present. This comparison found cases where the floats response was greater than during any of the constrained NewWave tests, indicating that the assumption made that NewWave will generate the largest response was incorrect in this case

The supernatural characters and powers of sacred trees in the Holy Land

This article surveys the beliefs concerning the supernatural characteristics and powers of sacred trees in Israel; it is based on a field study as well as a survey of the literature and includes 118 interviews with Muslims and Druze. Both the Muslims and Druze in this study attribute supernatural dimensions to sacred trees which are directly related to ancient, deep-rooted pagan traditions. The Muslims attribute similar divine powers to sacred trees as they do to the graves of their saints; the graves and the trees are both considered to be the abode of the soul of a saint which is the source of their miraculous powers. Any violation of a sacred tree would be strictly punished while leaving the opportunity for atonement and forgiveness. The Druze, who believe in the transmigration of souls, have similar traditions concerning sacred trees but with a different religious background. In polytheistic religions the sacred grove/forest is a centre of the community's official worship; any violation of the trees is regarded as a threat to the well being of the community. Punishments may thus be collective. In the monotheistic world (including Christianity, Islam and Druze) the pagan worship of trees was converted into the worship/adoration of saints/prophets; it is not a part of the official religion but rather a personal act and the punishments are exerted only on the violating individual

Copernicus Ocean State Report, issue 6

The 6th issue of the Copernicus OSR incorporates a large range of topics for the blue, white and green ocean for all European regional seas, and the global ocean over 1993–2020 with a special focus on 2020