power exponent 10m wind buoy
12444325
A New Platform for the Determination of Air Sea Fluxes (OCARINA) Overview and First Results
The present paper describes a new type of floating platform that was specifically designed for estimating air sea fluxes, investigating turbulence characteristics in the atmospheric surface boundary layer, and studying wind wave interactions. With its design, it can be deployed in the open ocean or in shallow water areas. The system is designed to be used from a research vessel. It can operate for ~10 hours as a drifting wave rider and three hours under power. Turbulence and meteorological instrument packages are placed at a low altitude (1 1.5 m) It was deployed for validation purposes during the FROMVAR 2011 experiment off the west coast of Brittany (France) Wind friction velocity and surface turbulent buoyancy flux were estimated using eddy covariance, spectral, bulk and profile methods. The comparisons of the four methods show a reasonable agreement except for the spectral buoyancy flux. This suggests that the platform design is correct. Also the wind measured at a fixed height above the sea shows spectral coherence with wave heights, such that wind and swell are in phase, with largest wind values on top of swell crests. This result in qualitative agreement with current model predictions supports the capability of OCARINA to investigate wind swell interactions.
Denis Bourras Hubert Branger Gilles Reverdin Louis Marie Remi Cambra Lucio Baggio Christophe Caudoux Gerard Caudal Simon Morisset Nicolas Geyskens Alain Weill Daniele Hauser
131407664
Coastal impacts in the lee of a wave energy site waves, beach morphology and water users (Wave Hub, Cornwall, UK)
COASTAL IMPACTS IN THE LEE OF A WAVE ENERGY SITE: WAVES, BEACH MORPHOLOGY AND WATER USERS (WAVE HUB, CORNWALL, UK) The Wave Hub facility in Cornwall (South West UK) is a marine renewables test site, predominantly designed for the purpose of trialling wave energy converters prior to commercialisation. Beach water users such as bathers and surfers are of economic importance to tourism in Cornwall, and during the Wave Hub consultation there were concerns among stakeholders that wave energy extraction would reduce the height and quality of coastal waves for sur ng, as well as a ecting sediment transport and beach morphology. This thesis investigates the interaction between wave conditions, beach morphology, and beach water users, and proposes how a wave climate altered by wave energy extraction is likely to alter these interactions. A multidisciplinary research approach is adopted, involving the collection of qualitative and quantitative social data, the collection of over 5 years of physical wave and beach morphology data, and predictive modelling of the e ects of an attenuated wave climate. Quantitative, structured interview data from 403 water users, collected at two beaches (Perranporth and Porthtowan) in the lee of Wave Hub, indicate that the population of water users in the area is predominantly made up of surfers (53% but bodyboarding and swimming/bathing are also popular activities (29% and 11% respectively) In depth semi structured interviews reveal that water user perceptions of wave energy extraction and its potential coastal impacts are constructed using intuitive risk perceptions, rather than technical understanding. These risk perceptions are constructed through a weighing of their perception of wave energy devices `technology' and their perception of the coastal environment `nature' To investigate how waves are perceived, nearshore wave buoy measurements collected in 14 m water depth and transformed to breaking height, are compared to concurrent visual observations of mean breaker height and period. On average water users underestimated signi cant wave height and period by 48% and 17% respectively. Accounting for variations in wave perception, the wave preferences of di erent water user groups are determined. Water users are found to share a common preference towards wave
Christopher Stokes
53600251
A simplified wave enhancement criterion for moving extreme events
An analytical model is derived to efficiently describe the wave energy distribution along the main transects of a moving extreme weather event. The model essentially builds on a generalization of the self similar wave growth model and the assumption of a strongly dominant single spectral mode in a given quadrant of the storm. The criterion to anticipate wave enhancement with the generation of trapped abnormal waves defined as inline image, with inline image, inline image, and inline image, radial distance, average sustained wind speed, and translation velocity, respectively. Constants inline image and inline image follow the fetch law definitions. If forced during a sufficient time scale interval, also defined from this generalized self similar wave growth model, waves can be trapped and large amplification of the wave energy will occur in the front right storm quadrant. Remarkably, the group velocity and corresponding wavelength of outrunning wave systems will become wind speed independent and solely related to the translating velocity. The resulting significant wave height also only weakly depends on wind speed, and more strongly on the translation velocity. Compared to altimeter satellite measurements, the proposed analytical solutions for the wave energy distribution demonstrate convincing agreement. As analytically developed, the wave enhancement criterion can provide a rapid evaluation to document the general characteristics of each storm, especially the expected wavefield asymmetry.
Vladimir N Kudryavtsev Pavel Golubkin Bertrand Chapron
41255128
Wireless backhaul for broadband communication over Sea
A comprehensive survey of different possible solutions to provide wireless backhaul PTP links for broadband communication over Sea is presented. The main purpose of wireless backhaul network is to provide LongDistance Point To Point (PTP) broadband communication. Wireless Backhaul gives a low cost solution for access to remote areas with difficult terrain to install any wired link. Long range backhaul network with high capacity and reliability is limited to line of sight (LOS) distances requiring high antenna towers for further increase in range. A mirror image of WiMax like system used on land can be envisaged on Sea to provide similar services at even non line of sight (NLOS) distances. Satellite communication can also provide large distance coverage for communication over Sea. Tropospheric propagation using evaporation ducts over Sea is also explored for long range wireless communication over Sea to achieve Trans horizon NLOS distances. Current work and future challenges regarding backhaul broadband communication over Sea with some proposed solutions are discussed at the end.
2013 IEEE 11th Malaysia International Conference on Communications (MICC)
Khurram Shabih Zaidi Varun Jeoti Azlan Awang
132212156
On the predominance of unstable atmospheric conditions in the marine boundary layer offshore of the U.S. northeastern coast
The marine boundary layer of the northeastern U.S. is studied with focus on wind speed, atmospheric stability, and turbulent kinetic energy (TKE) the three most relevant properties in the context of offshore wind power development. Two long term observational data sets are analyzed. The first one consists of multilevel meteorological variables measured up to 60 m during 2003 2011 at the offshore Cape Wind tower, located near the center of the Nantucket Sound. The second data set comes from the 2013 2014 IMPOWR campaign (Improving the Modeling and Prediction of Offshore Wind Resources) in which wind and wave data were collected with new instruments on the Cape Wind platform, in addition to meteorological data measured during 19 flight missions offshore of New York, Connecticut, Rhode Island, and Massachusetts. It is found that, in this region: (1) the offshore wind resource is remarkable, with monthly average wind speeds at 60 m exceeding 7 m s 1 all year round, highest winds in winter (10.1 m s 1) and lowest in summer (7.1 m s 1) and a distinct diurnal modulation, especially in summer; (2) the marine boundary layer is predominantly unstable (61% unstable vs. 21% neutral vs. 18% stable) meaning that mixing is strong, heat fluxes are positive, and the wind speed profile is often nonlogarithmic ~40% of the time) and (3) the shape of the wind speed profile (log versus nonlog) is an effective qualitative proxy for atmospheric stability, whereas TKE alone is not.
Cristina L Archer Brian A Colle Dana L Veron Fabrice Veron Matthew J Sienkiewicz
4922191
Estimation of air water gas exchange coefficient in a shallow lagoon based on 222Rn mass balance.
The radon 222 mass balance is now commonly used to quantify water fluxes due to Submarine Groundwater Discharge (SGD) in coastal areas. One of the main loss terms of this mass balance, the radon evasion to the atmosphere, is based on empirical equations. This term is generally estimated using one among the many empirical equations describing the gas transfer velocity as a function of wind speed that have been proposed in the literature. These equations were, however, mainly obtained from areas of deep water and may be less appropriate for shallow areas. Here, we calculate the radon mass balance for a windy shallow coastal lagoon (mean depth of 6m and surface area of 1.55*10(8) m(2) and use these data to estimate the radon loss to the atmosphere and the corresponding gas transfer velocity. We present new equations, adapted to our shallow water body, to express the gas transfer velocity as a function of wind speed at 10 m height (wind range from 2 to 12.5 m/s) When compared with those from the literature, these equations fit particularly well with the one of Kremer et al. (2003) Finally, we emphasize that some gas transfer exchange may always occur, even for conditions without wind.
Journal of environmental radioactivity
Sabine Cockenpot Christelle Claude Olivier Radakovitch
55137947
Influence of bottom trawling on sediment resuspension in the 'Grande Vasiere' area (Bay of Biscay, France)
Sea trials were performed on two zones with different fishing efforts on the continental shelf of the Bay of Biscay 'Grande Vasiere' area of muddy sand) in order to assess particulate matter resuspension and seabed disturbances (i.e. penetration, reworking, grain size changes) induced by different types of trawls. Optical and acoustic measurements made in the water column indicate a significant trawling induced resuspension mainly due to the scraping action of doors. It manifests as a highly dynamic turbid plume confined near the seabed, where suspended sediment concentrations can reach 200 mg l 1. Concentration levels measured behind an "alternative" configuration (trawls with jumper doors instead of classical doors penetrating the sediment) are significantly lower (around 10 20 mg l 1) which indicates a potential limiting impact regarding the seabed. Grain size analyses of the surficial sediment led to highlight a potential reworking influence of bottom trawling. On the intensively trawled zone, this reworking manifests as an upward coarsening trend in the first 5 cm of the cores. A significant decrease in mud content (30 has been also witnessed on this zone between 1967 and 2014, which suggests an influence on the seabed evolution. The geometric analysis of bottom tracks (4 5 cm depth, 20 cm width) observed with a benthic video sledge was used to compute an experimental trawling induced erosion rate of 0.13 kg m 2. This erosion rate was combined with fishing effort data, in order to estimate trawling induced erosion fluxes which were then compared to natural erosion fluxes over the Grande Vasiere at monthly, seasonal and annual scales. Winter storms control the annual resuspended load and trawling contribution to annual resuspension is in the order of 1 However, results show that trawling resuspension can become dominant during the fishing high season (i.e. until several times the natural one in summer) In addition, the contribution of trawling induced resuspension is shown to increase with water depth, because of the rapid decay of wave effects. Finally, the seasonal evolution of the respective contributions for erosion (mainly trawling and waves) could be mapped for the whole study area.
Ocean Dynamics
Baptiste Mengual Florence Cayocca Pierre Le Hir Robin Draye Pascal Laffargue Benoit Vincent Thierry Garlan
135056227
Systematic Differences in Bucket Sea Surface Temperature Measurements among Nations Identified Using a Linear Mixed Effect Method
The International Comprehensive Ocean Atmosphere Dataset (ICOADS) is a cornerstone for estimating changes in sea surface temperatures (SST) over the instrumental era. Interest in determining SST changes to within 0.1degC makes detecting systematic offsets within ICOADS important. Previous studies have corrected for offsets among engine room intake, buoy, and wooden and canvas bucket measurements, as well as noted discrepancies among various other groupings of data. In this study, a systematic examination of differences in collocated bucket SST measurements from ICOADS3.0 is undertaken using a linear mixed effect model according to nations and more resolved groupings. Six nations and a grouping for which nation metadata are missing, referred to as "deck 156," together contribute 91% of all bucket measurements and have systematic offsets among one another of as much as 0.22degC. Measurements from the Netherlands and deck 156 are colder than the global average by 0.10deg and 0.13degC, respectively, both at p 0.01, whereas Russian measurements are offset warm by 0.10degC at p 0.1. Furthermore, of the 31 nations whose measurements are present in more than one grouping of data (i.e. deck) 14 contain decks that show significant offsets at p 0.1, including all major collecting nations. Results are found to be robust to assumptions regarding the independence and distribution of errors as well as to influences from the diurnal cycle and spatially heterogeneous noise variance. Correction for systematic offsets among these groupings should improve the accuracy of estimated SSTs and their trends.
Journal of Climate
Duo Chan Peter J Huybers
125363339
Combined wave current scale model testing at FloWave
As part of a global drive to produce renewable electricity, devices are being designed to harness energy from the waves and tidal currents. Physical scale model testing is an important part of the development process for this and other technologies. The FloWave Ocean Energy Research Facility at The University of Edinburgh is designed to conduct these tests. Here it is possible to produce multi directional waves combined with currents in the circular tank, re creating the complexity of the ocean. The research was driven by commercial requirements of the facility, aiming to highlight what can be learnt from testing at scale with complex conditions in a controlled environment. To enable this, it was first necessary to extend the characterisation of this new facility. Wave generation and reflections were assessed in a previous project. In this work, flow measurements taken throughout the test volume of the tank, allowed spatial and temporal variations in the currents to be determined. Waves and currents interact in a complex manner, compounded by the method of reproducing them in a tank. The influence of currents on waves in the basin was assessed. This included cases with an oblique angle between them, on which little has been published. The other part of the project addressed issues to be considered when testing in a combined wave current basin such as FloWave. At many sites of interest for offshore renewable energy, waves are influenced by water depth. Implications of not scaling depth consistently were considered, and design diagrams produced to facilitate understanding and quantification of potential errors. At FloWave, waves are generated in still water around the outside of the tank. A process was therefore developed and verified to produce the desired combined conditions in the central test area following their interaction with the current. There is a wealth of published guidance on tank testing, for ships, offshore structures, and more recently renewable energy. This has been reviewed and suggestions offered to augment this by including testing in the more advanced conditions possible in a facility like FloWave. Tools and guidance have been developed to highlight many of the issues to be considered by clients prior to testing at FloWave. This aims to facilitate planning of a test programme by highlighting potential knowledge gaps and recording decisions made. Flowcharts have been produced to represent this graphically, with a corresponding checklist of questions for clients, which have been trialled in a pilot study. Outputs from this research are being used to help deliver both academic and commercial client tests at FloWave. The test area in currents was shown to be >50m2 with <10% variation in flow, and the combined wave current conditions possible have been explored. Results that are important when designing client test plans.
Donald R Noble
111050293
METOCEAN DESIGN CONDITION FOR "FUKUSHIMA FORWARD" PROJECT
Metocean condition for the Fukushima FORWARD project is presented. Wind speeds and tsunami are predicted by Monte Carlo simulation and Tsunami simulation, respectively. For wave condition, extreme sea state and normal sea state are evaluated by published data and newly proposed wind wave and swell combination formula, respectively. Surface current and water level are evaluated by extreme value analyses of hindcast simulation and historical data, respectively.
Takeshi Ishihara Kenji Shimada Akihiko Imakita