Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “surface wave”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Surface-wave tomography of the Emeishan large igneous province (China): Magma storage system, hidden hotspot track, and its impact on the Capitanian mass extinction

Large igneous provinces (LIPs) are commonly associated with mass extinctions. However, the precise relations between LIPs and their impacts on biodiversity is enigmatic, given that they can be asynchronous. It has been proposed that the environmental impacts are primarily related to sill emplacement. Therefore, the structure of LIPs' magma storage system is critical because it dictates the occurrence and timing of mass extinction. We use surface-wave tomography to image the lithosphere under the Permian Emeishan large igneous province (ELIP) in southwestern China. We find a northeast-trending zone of high shear-wave velocity (Vs) and negative radial anisotropy (Vsv > Vsh; v and h are vertically and horizontally polarized S waves, respectively) in the crust and lithosphere. We rule out the possibilities of rifting or orogenesis to explain these seismic characteristics and interpret the seismic anomaly as a mafic-ultramafic, dike-dominated magma storage system of the ELIP. We further propose that the anomaly represents a hidden hotspot track that was emplaced before the ELIP eruption. A zone of higher velocity but less-negative radial anisotropy, on the hotspot track but to the northeast of the eruption center in the Panxi region, reflects an elevated proportion of sills emplaced at the incipient stage of the ELIP. Liberation of poisonous gases by the early sill intrusions explains why the mid-Capitanian global biota crisis preceded the peak ELIP eruption by 2–3 m.y.

58 GEOSCIENCES↗
DOE OSTI2023

Predicting Seafloor Seismic Noise from Sea Surface Wave Heights and Vice Versa

Seismic hazard monitoring and global seismic tomography efforts are improved by recording seismic signals close to sources and at a variety of azimuths surrounding the source. While seismic networks have been deployed at many locations on land, seafloor stations are still sparse. Inclusion of ocean-based data would greatly improve the global coverage of seismic networks. However, the use of seafloor seismic data to complement land-based detection and characterization of events is complicated by the fact that ambient noise on the seafloor is in general much higher than noise levels on land. This noise is driven primarily by sea surface waves and tides. In this project, I define an empirical relationship between wave height and seafloor seismic displacement, and tie this relationship to the microseism noise theory of Longuet-Higgins and Ursell (1948). I find that while there appears to be a linear relationship between wave height and seismic displacement, wave height values can only be used with low confidence to predict seismic displacement and vice versa, and furthermore, factors other than wave height are significant in determining the level of seismic noise at a particular site.

58 GEOSCIENCES↗
NASA NTRS1988

A theory for the radiation of magnetohydrodynamic surface waves and body waves into the solar corona

The Green's function for the slab coronal hole is obtained explicitly. The Fourier integral representation for the radiated field inside and outside the coronal hole waveguide is obtained. The radiated field outside the coronal hole is calculated using the method of steepest descents. It is shown that the radiated field can be written as the sum of two contributions: (1) a contribution from the integral along the steepest descent path and (2) a contribution from all the poles of the integrand between the path of the original integral and the steepest descent path. The free oscillations of the waveguide can be associated with the pole contributions in the steepest descent representation for the Green's function. These pole contributions are essentially generalized surface waves with a maximum amplitude near the interface which separates the plasma inside the coronal hole from the surrounding background corona. The path contribution to the integral is essentially the power radiated in body waves.

Davila, Joseph M.↗
NASA NTRS1984

The interpretation of SIR-B imagery of surface waves and other oceanographic features using in-situ, meteorological satellite, and infrared satellite data

The overall aim is to interpret Shuttle Imaging Radar-B imagery of selected ocean areas near the United Kingdom using available data from ships and buoys, with particular emphasis on understanding the mechanisms involved in the backscattering of microwaves from the sea surface and their relationship to surface gravity waves. The secondary objective is to use a multispectral approach to study sea-surface expressions such as slicks, internal waves, and eddies. Data acquisition, handling, and analysis approaches and expected results are discussed.

Allan, T.↗
NASA NTRS1983

Turbulent drag characteristic of small amplitude rigid surface waves

The paper discusses an experimental and theoretical investigation of low speed turbulent flow over transverse rigid wavy surfaces having a wavelength on the order of the boundary layer thickness. In addition the results of theoretical investigations of laminar flow over short wavelength waves and turbulent flow over long wavelength (wavelength much greater than the boundary layer thickness) wavy walls are presented. Surface pressure and net drag measurements obtained for the short wavelength symmetric and asymmetric waves in a turbulent flow agreed with the results obtained with a Navier-Stokes spectral code and indicated no significant drag reduction. Several asymmetric wave configurations did significantly reduce the pressure drag compared to sine wave geometries, but these waves still did not produce a net drag reduction. The Navier-Stokes calculations for laminar flow indicated a drag reduction of up to 17 percent for certain short wavelength waves. Boundary layer calculations for turbulent flow over long wavelength surface waves indicated that net drag reductions on the order of 10 percent may be possible for large-radius waisted bodies.

Lin, J. C.↗
NASA NTRS1981

Interferometric surface-wave acousto-optic time-integrating correlators

A structure for a coherent-interferometric acousto-optic (AO) time-integrating correlator was implemented by using a single surface acoustic wave (SAW) device with tilted transducers to reduce intermodulation terms. The SAW device was fabricated on Y-Z LiNbO3 with a center frequency of 175 MHz, a bandwidth of 60 MHz, and a time aperture of about 10 micros. The density of the photodetector array, with a potential of 120 MHz. Typical integration times are 30 to 40 ms, providing processing gains in excess of 10 to the 6th power. Such a device is useful in providing fast synchronization of communication links and in demodulating to base band and simultaneously acting as a synchronization lock monitor for moderate data rates. Where processing may be limited by Doppler shifts, a two dimensional architecture was implemented to allow full processing gain. Two one-dimensional, SAW AO time-integrating correlators and a two dimensional correlator are evaluated.

Berg, N. J.↗
DOE OSTI2020

High Resolution Ocean Surface Wave Hindcast (US Wave) Data

The development of this dataset was funded by the U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy, Water Power Technologies Office to improve our understanding of the U.S. wave energy resource and to provide critical information for wave energy project development and wave energy converter design. This high resolution publicly available long-term wave hindcast dataset will - when complete - cover the entire U.S. Exclusive Economic Zone (EEZ). Available data includes the Hawaiian Islands, West and Atlantic Coasts, with future additions including the Alaskan coasts, Gulf of Mexico and the Freely associated States. The data can be used to investigate the historical record of wave statistics at any U.S. site. As such, the dataset could also be of value to any entity with marine operations inside the U.S. EEZ. These data are available for download without login credentials through the free and publicly accessible Open Energy Data Initiative (OEDI) data viewer which allows users to browse and download individual or groups of files.

16 TIDAL AND WAVE POWER↗
NASA NTRS1981

The damping of ocean surface waves by a monomolecular film measured by wave staffs and microwave radars

Open ocean and wave tank experiments were carried out with the aim of studying the damping of capillary and gravity waves by a monomolecular film. These films of biogenic origin influence air-sea interaction processes and thereby affect the use of remote sensing techniques in oceanography. Measurement was carried out by wave staffs, by a coherent X band microwave scatterometer mounted on a sea-based platform, and by an incoherent K band microwave scatterometer carried by an aircraft under moderate wind conditions. A wave attenuation of about 40-60% is observed in the frequency range between 3.2 and 16 Hz. Tank experiments show that a direct influence of oleyl alcohol surface films on wave damping is confined to frequencies equal to or greater than 2 Hz; a further indirect effect of films on the damping of ocean waves in the frequency range between 0.12 and 0.7 Hz (by modifying the wind input and wave-wave interaction mechanisms) is also indicated

Huehnerfuss, H.↗
NASA NTRS1984

Non-Gaussian statistical models of surface wave fields for remote sensing applications

Based on the complete Stokes wave model with the bias term and using a simple mapping approach and an iteration solution method, we established a formula for the joint probability density function of the surface slope elevation of a nonlinear random wave field. The formula requires three parameters to define the whole density function: the rms surface elevation and slope values and the significant slope. This model represents the dynamics of the wave in a more direct way than the Gram-Charlier approximation. Based on this new statistical model and laboratory experiments, formula and numerical values of EM bias and dynamics bias are derived. The results indicate that various biases should be considered seriously if accuracy of the altimeter measurement is required in centimeter range.

Huang, N. E.↗
NASA NTRS1977

Models of radar imaging of the ocean surface waves

A number of models which would explain ocean wave imagery taken with a synthetic aperture imaging radar are analyzed analytically and numerically. Actual radar imagery is used to support some conclusions. The models considered correspond to three sources of radar backscatter cross section modulation: tilt modulation, roughness variation, and the wave orbital velocity. The effect of the temporal changes of the surface structure, parametric interactions, and the resulting distortions are discussed.

Elachi, C.↗
NASA NTRS1990

Synthetic-aperture-radar imaging of the ocean surface using the slightly-rough facet model and a full surface-wave spectrum

A new model of synthetic-aperture-radar (SAR) imaging of ocean waves is described. The model is based on mapping individual, slightly-rough surface facets through the SAR processor into the image and responses of the facets in the image domain are added together coherently to give the composite image. A windowing technique allows both the orbital motion and the phase velocity of the long waves to be included. It is determined that the azimuthal cut-off is due to a smearing of the response of the facets in the image induced by the random orbital motion of the intermediate large-scale waves and that the focus adjustment that gives the greatest image contrast is half the phase velocity of the dominant long wave. The optimal processing technique, however, may consist of spatially offsetting the multiple looks on the image domain to compensate the propagation of long waves during the integration time of the SAR.

West, James C.↗
NASA NTRS1996

Reconstruction of the Mesoscale Velocity Shear Seaward of Coastal Upwelling Regions from the Refraction of the Surface Wave Field

The objective of this project is to study fronts that develop at the boundary between cold water recently upwelled to the surface through Ekman divergence, and warmer surrounding waters. This specific objective was suggested by studying the small scale structure of upwelling fronts (coastal, island, and equatorial) through shipboard surveys and infrared satellite images. Constraints on the shuttle equator crossing imposed by other land sites precluded a coverage of the area targeted in the initial SIR-C proposal, the California Current. The site was then relocated to the Equatorial Pacific upwelling tongue, that can be satisfactorily imaged for a wide range of longitudes of the equator crossing. Some limited data was nevertheless obtained over coastal upwelling off California in 1989, using the JPL AIRSAR in multifrequency mode, and over island upwelling off Hawaii in 1990, using the radar in along-track interferometric mode.

Flament, Pierre↗
NASA NTRS1976

Optical technique for measurement of random water wave surfaces

An optical system using the refraction of a vertical light ray has been developed for measuring the slope of random wind-generated water waves. The basic elements of the system are photovoltaic cells which are connected to individual amplifiers so that when the refracted light beam is incident on a cell, the output of the cell is amplified and then supplied as input to a comparator. The comparator then provides a specified voltage output, independent of the incident light intensity, as long as it is above a designated background value. The comparators are designed to give output voltages comparable with standard TTL. This arrangement provides a high signal from the cell when it experiences incident light, and a low signal when there is only background light, with the high and low signals at TTL voltage levels.

Sorrell, F. Y.↗
NASA NTRS1992

A theory for narrow-banded radio bursts at Uranus - MHD surface waves as an energy driver

A possible scenario for the generation of the narrow-banded radio bursts detected at Uranus by the Voyager 2 planetary radio astronomy experiment is described. In order to account for the emission burstiness which occurs on time scales of hundreds of milliseconds, it is proposed that ULF magnetic surface turbulence generated at the frontside magnetopause propagates down the open/closed field line boundary and mode-converts to kinetic Alfven waves (KAW) deep within the polar cusp. The oscillating KAW potentials then drive a transient electron stream that creates the bursty radio emission. To substantiate these ideas, Voyager 2 magnetometer measurements of enhanced ULF magnetic activity at the frontside magnetopause are shown. It is demonstrated analytically that such magnetic turbulence should mode-convert deep in the cusp at a radial distance of 3 RU.

Farrell, W. M.↗
NASA NTRS1993

Low Wind Speed Radar Backscatter Measurements at C- and Ku-Band Obtained During the Surface Wave Dynamics Experiment

Radar backscatter measurements collected at both C- and Ku-Band during the recent SurfaceWaves Dynamics Experiment (SWADE) on 1 March 1991 show dramatic variabilities of thenormalized radar cross section (sigma degree) of the ocean surface at low wind speed. Additionally,measurements of the sigma degree in the cross wind direction fluctuated much more than the sigmadegree in the upwind direction. The C- and Ku-band data are quite similar, both exhibiting a morepronounced roll off of sigma degree with decreasing neutral stability wind than indicated bypreviously published empirical model functions. The data show extremely large azimuthalmodulations, in some cases greater than 20 dB, and show good qualitative agreement with theazimuthal modulation predicted.

Carson, S. C.↗