SPECTRASAT: A concept for the collection of global directional wave spectra

The synthetic aperture radar (SAR) imagery from SEASAT revealed a rich tapestry of backscatter patterns from the surface of the ocean. Although still far from being fully understood, these patterns occurred on nearly all spatial scales accessible to the SAR, that is from its spatial resolution of 25 m to its full swath width of 100 km. Futhermore, the backscatter signature appear to reveal a large variety of atmospheric and oceanic processes that occur above, at, and below the ocean surface. Proper interpretation of these signatures of varying scales with respect to their underlying geophysical causes is a major objective of SAR ocean research. Even now, however, it is clear that SAR offers a unique means to monitor wind and waves over global scales. A properly designed, configured, and complimented orbiting SAR system should yield substantial improvements in operational forecasts vital to marine activities. Since wind and wave information is optimally extracted in the spectral domain, the name SPECTRASAT is proposed for this global collection scheme

Wave Energy: a Pacific Perspective

This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by The Royal Society and can be found at: http://rsta.royalsocietypublishing.org/.This paper illustrates the status of wave energy development in Pacific Rim countries by characterizing the available resource and introducing the region‟s current and potential future leaders in wave energy converter development. It also describes the existing licensing and permitting process as well as potential environmental concerns. Capabilities of Pacific Ocean testing facilities are described in addition to the region‟s vision of the future of wave energy

Semi-empirical dissipation source functions for ocean waves: Part I, definition, calibration and validation

New parameterizations for the spectra dissipation of wind-generated waves are proposed. The rates of dissipation have no predetermined spectral shapes and are functions of the wave spectrum and wind speed and direction, in a way consistent with observation of wave breaking and swell dissipation properties. Namely, the swell dissipation is nonlinear and proportional to the swell steepness, and dissipation due to wave breaking is non-zero only when a non-dimensional spectrum exceeds the threshold at which waves are observed to start breaking. An additional source of short wave dissipation due to long wave breaking is introduced to represent the dissipation of short waves due to longer breaking waves. Several degrees of freedom are introduced in the wave breaking and the wind-wave generation term of Janssen (J. Phys. Oceanogr. 1991). These parameterizations are combined and calibrated with the Discrete Interaction Approximation of Hasselmann et al. (J. Phys. Oceangr. 1985) for the nonlinear interactions. Parameters are adjusted to reproduce observed shapes of directional wave spectra, and the variability of spectral moments with wind speed and wave height. The wave energy balance is verified in a wide range of conditions and scales, from gentle swells to major hurricanes, from the global ocean to coastal settings. Wave height, peak and mean periods, and spectral data are validated using in situ and remote sensing data. Some systematic defects are still present, but the parameterizations yield the best overall results to date. Perspectives for further improvement are also given.Comment: revised version for Journal of Physical Oceanograph

Ocean Energy: Using the Ocean's Tides, Waves, and Heat to Generate Electricity

Key facts: - The oceans' tides, waves, current, and heat can be used to generate electricity. These resources are renewable, because the moon's gravity drives tides, and winds create waves. Covering 70 percent of the Earth's surface, the oceans collect significant amounts of heat from the sun. - A tidal dam with a capacity of 240 megawatts (MW) has operated in France since 1966; a 100 MW tidal dam has generated power in China since 1987; and a 20 MW tidal dam has operated in Canada since 1984. Several other, smaller ocean energy systems are also in use around the world. Theoretically, ocean waves could produce more than 2 million MW of electricity, according to the US Department of Energy. - The best locations for harnessing wave power are regions with the strongest winds. Areas off the Northwest and Northeast coasts of the United States have good potential for ocean energy

The sinking of the El Faro: predicting real world rogue waves during Hurricane Joaquin

We present a study on the prediction of rogue waves during the 1-hour sea state of Hurricane Joaquin when the Merchant Vessel El Faro sank east of the Bahamas on October 1, 2015. High-resolution hindcast of hurricane-generated sea states and wave simulations are combined with novel probabilistic models to quantify the likelihood of rogue wave conditions. The data suggests that the El Faro vessel was drifting at an average speed of approximately~$2.5$~m/s prior to its sinking. As a result, we estimated that the probability that El Faro encounters a rogue wave whose crest height exceeds 14 meters while drifting over a time interval of 10~(50) minutes is $\sim1/400$~$(1/130)$. The largest simulated rogue wave has similar generating mechanism and characteristics of the Andrea, Draupner and Killard rogue waves as the constructive interference of elementary waves enhanced by bound nonlinearities

Analysis of Dynamic Behaviour and Power Generation of a Wind-tidal System for Marine Environment

This work presents the analysis of dynamic behaviour and power generation of a wind-tidal hybrid system. Mathematical models and system design approach were used to investigate the feasibility, reliability and economic impact of the system. From the system design analysis carried out, by harnessing the tidal energy with wind energy in marine environment, the total power generated (approximately 180KW) by the hybrid power system showed a significant improvement over a wind turbine system which only generates a maximum power of 25KW at the rotor diameter as reported in literature. The effects of aerodynamics and hydrodynamics forces on the structure were investigated through the analysis of dynamic behaviour of the system under different loads and at various sites in the marine environment. The stability and the optimum turbine design were found to depend on the wind and tidal speed distribution of the specific site in the environment. The long term benefit of this work is aimed at meeting the energy needs of coastal dwellers by implementing the hybrid power system. Also, the gridless system could be used to generate power for both large and small scale industries in the marine environmen

Wind stress and its dependence on wind speed and sea state

The aim of the project is to detect and quantify the effect of sea state on the wind stress. An overview of the basic theory of wind stress in the surface layer is provided, along with a more detailed description of the inertial dissipation method which is used to obtain stress estimates for this study. Wind stress measurements by other researchers illustrate the large scatter which seems to be inherent in the drag coefficient/wind speed relationship, and parameterisations of the wave field have been suggested to explain at least some of this scatter. Past appraisals of the dissipation technique show it to be capable of measuring wind stress over the oceans. Details are given of the data collection and processing to date. The analysis of the data has so far resulted in an IOS report on the performance of a prototype sonic anemometer. and a paper presenting preliminary results at the 1991 !UGG. Drag coefficients from an early data set are higher than expected and possible reasons for this are discussed. The next stages of data analysis are discussed, and ways of achieving our overall aim of detecting the effect of sea state on wind stress are described

Surface Shear and Persistent Wave Groups

We investigate the interaction of waves with surface flows by considering the full set of conserved quantities, subtle but important surface elevation changes induced by wave packets and by directly considering the necessary forces to prevent packet spreading in the deep water limit. Narrow surface shear flows are shown to exert strong localizing and stabilizing forces on wavepackets to maintain their strength and amplify their intensity even in the linear regime. Subtle packet scale nonlinear elevation changes from wave motion are crucial here and it suggest that popular notions of wave stress and action are naive. Quantitative bounds on the surface shear flow necessary to stabilize packets of any wave amplitude are given. One implication of this mechanism is that rogue wave stabilization must be due to a purely nonperturbative process

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs