Surface Wave Energy Research Articles

Surface-Wave Extraction Based on Morphological Diversity of Seismic Events

It is essential to extract high-fidelity surface waves in surface-wave surveys. Because reflections usually interfere with surface waves on X components in multicomponent seismic exploration, it is difficult to extract dispersion curves of surface waves. To make matters worse, the frequencies and velocities of higher-mode surface waves are close to those of PS-waves. A method for surface-wave extraction is proposed based on the morphological differences between surface waves and reflections. Frequency-domain high-resolution linear Radon transform (LRT) and time-domain high-resolution hyperbolic Radon transform (HRT) are used to represent surface waves and reflections, respectively. Then, a sparse representation problem based on morphological component analysis (MCA) is built and optimally solved to obtain high-fidelity surface waves. An advantage of our method is its ability to extract surface waves when their frequencies and velocities are close to those of reflections. Furthermore, the results of synthetic and field examples confirm that the proposed method can attenuate the distortion of surface-wave dispersive energy caused by reflections, which contributes to extraction of accurate dispersion curves.

On the Relationship between the Energy Dissipation Rate of Surface-Breaking Waves and Oceanic Whitecap Coverage

AbstractWave breaking is the most important mechanism that leads to the dissipation of oceanic surface wave energy. A relationship between the energy dissipation rate associated with breaking wave whitecaps and the area of whitecap foam per unit area ocean surface is expected, but there is a lack of consensus on what form this relationship should take. Here, mathematical representations of whitecap coverage and growth-phase whitecap coverage are derived, and an energy-balance approach is used to formulate and in terms of . Both and are found to be linearly proportional to but also inversely proportional to the bubble plume penetration depth during active breaking. Since this depth can vary for breaking waves of different scales and slopes, there is likely no unique relationship between and either or as bubble plume penetration depth must also be specified. Whitecap observations from the North Atlantic are used to estimate bubble plume penetration depth as a function of wind speed and then used with measurements to compute . An estimate of the relative magnitude of to the rate of energy input from the wind to the waves is made. Above wind speeds of about 12 m s−1, is largely balanced by . At lower wind speeds the ratio quickly drops below unity with decreasing wind speed. It is proposed that sea-state-driven variability in both and bubble plume penetration depth are significant causes of variation in whitecap coverage datasets and parameterizations.

Environmental conditions and herbivore biomass determine coral reef benthic community composition: implications for quantitative baselines

Our ability to understand natural constraints on coral reef benthic communities requires quantitative assessment of the relative strengths of abiotic and biotic processes across large spatial scales. Here, we combine underwater images, visual censuses and remote sensing data for 1566 sites across 34 islands spanning the central-western Pacific Ocean, to empirically assess the relative roles of abiotic and grazing processes in determining the prevalence of calcifying organisms and fleshy algae on coral reefs. We used regression trees to identify the major predictors of benthic composition and to test whether anthropogenic stress at inhabited islands decouples natural relationships. We show that sea surface temperature, wave energy, oceanic productivity and aragonite saturation strongly influence benthic community composition; overlooking these factors may bias expectations of calcified reef states. Maintenance of grazing biomass above a relatively low threshold (~ 10–20 kg ha−1) may also prevent transitions to algal-dominated states, providing a tangible management target for rebuilding overexploited herbivore populations. Biophysical relationships did not decouple at inhabited islands, indicating that abiotic influences remain important macroscale processes, even at chronically disturbed reefs. However, spatial autocorrelation among inhabited reefs was substantial and exceeded abiotic and grazing influences, suggesting that natural constraints on reef benthos were superseded by unmeasured anthropogenic impacts. Evidence of strong abiotic influences on reef benthic communities underscores their importance in specifying quantitative targets for coral reef management and restoration that are realistic within the context of local conditions.

Nonexponentially Decaying Electromagnetic Waves Localized at the Boundary of Anisotropic Metal–Dielectric Structures

The possibility of the existence of a special class of surface electromagnetic waves with amplitude decreasing nonexponentially as they pass into an anisotropic metal–dielectric structure that borders the isotropic dielectric has been shown. The dispersion equation describing the propagation of such special surface waves has been obtained, and their attenuation coefficients and formula for electric and magnetic fields in contacting media have also been found. The expressions for the longitudinal and transverse components of the Poynting vector and volume density of electric and magnetic energy of special surface waves have been obtained. Numerical calculations for the layered metal–dielectric nanostructure that is described by a uniaxial tensor of effective dielectric permeability have been carried out Decaying.

Half-cycle terahertz surface waves with MV/cm field strengths generated on metal wires

Irradiating a metal wire with an intense femtosecond laser pulse induces a terahertz (THz) surface wave that travels along the wire. Here, the characteristics of the THz surface wave generated by the laser–wire interaction are investigated in detail by using an electro-optical method to determine the dependence of surface wave properties on laser energy and wire diameter. The surface wave is distributed by the Hankel function in the wire radial direction. On the wire surface, the electric field is estimated to be MV/cm. The peak electric field of the surface wave and the conversion efficiency from laser energy to surface wave energy are found to be proportional to the laser energy raised to the power of 0.67 and 0.3, respectively.

The Issues of Development of Renewable Energy Sources for Marine Autonomous Underwater Robotic Complexes

The paper considers the options of renewable power sources development for marine objects operated in absence of solar energy. Operation of many undersea vehicles is evidently limited by their battery charge. When operating at shallow depths, such vehicles experience pitch and roll in the wave-perturbed environment. Buoys floating on the water surface are also disturbed by sea waves. Moreover, when they are operated during polar night, solar energy cannot be used for charging their batteries. To solve this problem, it is proposed to use the energy of surface waves or the vehicle pitch and roll. It is quite possible to transform the energy of wave current and the orbital velocity of water particles motion into propeller rotation. Basic theory of using such devices for energy accumulation and their capabilities are studied. It is stated that several such devices installed in orthogonal directions relative to each other will transform the energy that is also generated by the undersea vehicle's propulsion when its depth is changing. Furthermore, the vehicle pitch/roll energy transformation into electric power is discussed. This idea is extremely attractive, so it is not new. However, generators of this type have never been used on undersea robotic vehicles. The paper presents an induction generator designed and patented by the author. It is shown that its operation is described by a differential equation of the 2 nd order. It is proposed to adjust the electromechanical system of such transformers to be resonant with the dominant pitch/roll oscillations. This can be done by varying the degree of the oscillating system damping. Potential engineering solutions and physical principles of their operation are discussed. The proposed small-size transformers are estimated in terms of power capacity and compared to the existing similar devices. It is demonstrated that the proposed generators are able to generate power of a few dozens Watt.

Using surface wave amplitude spectra to estimate the source depth of Sichuan Jiuzhaigou <italic>M</italic>7.0 earthquake

The accurate source depth of earthquake is important for understanding plate-tectonic processes and structure of seismic faults, identifying natural earthquake and non-natural earthquake. The amplitude formula of seismic surface wave shows that the amplitude of surface wave is closely related to the focal mechanism, the azimuth from epicenter to station and the source depth. When the focal mechanism and the observation position are determined, the excitation energy of surface wave is sensitive to source depth. The surface wave amplitude spectrum can be applied to determine the focal depth. The amplitude energy of shallow earthquake shows the “notch” phenomenon in band of frequency between 0.01 and 0.08 Hz in amplitude spectra, i.e. the attenuation of amplitude energy. The position of the frequency-dependent “notch” is related to the source depth. In this study, the relationship between the position of the “notch” and the source depth is analyzed by theoretical seismogram. We obtain the amplitude spectrums of the far-field at different source depths and then locate the source depth by means of comparing with observed seismic waveforms. By the amplitude spectrum of theoretical surface wave, small changes in the source depth can cause the variation of the amplitude spectrum so that the source depth of shallow earthquake can be accurately determined. The focal mechanism is coupled with the source depth. In order to analyze the influence of the disturbance of source mechanism to source depth determination, the focal mechanism of Jiuzhaigou earthquake was inversed, with disturbance of 10 degrees to strike, dip and rake. The results show only rather small changes in locating depth. In order to eliminate the influence of low frequency noise, shear wave and surface wave of short-period on amplitude spectra, this study adopts the AK135 velocity model to remove the dispersion. In this study, the seismic source depth of the Jiuzhaigou M 7.0 earthquake of 8 August 2017 in Sichuan province, China, was determined at 8.2 km by the energy attenuation characteristics of Rayleigh amplitude spectrum.

Cylindrical Plasma Antenna with Large Longitudinal Density Irregularity

The efficiency of operation of a cylindrical plasma antenna as a function of the degree of longitudinal nonuniformity of the plasma density is examined. The study is based on the method of spectral field expansion into a complete set of functions comprising surface and pseudosurface waves of the plasma column. The system of integrodifferential equations for expansion coefficients determining radiation patterns and the amplitudes of transmitted, reflected, and scattered waves is solved in the case of rapid variation in the plasma density. Dependences of the coefficients of conversion of the surface-wave energy on the plasma-density gradient, the electric length of the section of plasma nonuniformity, and the electric radius of the plasma cylinder are calculated. It is demonstrated by examples that the portion of energy of the surface wave converted into radiation may exceed 50%. It has been found that the radiation patterns are narrow with a single lobe whose maximum is at an angle of several degrees to the direction of propagation of the surface wave. As the plasma-density gradient increases, the lobe width decreases and the lobe itself shifts toward 0°.

Frequency–Wavenumber (FK)-Based Data Selection in High-Frequency Passive Surface Wave Survey

Passive surface wave methods have gained much attention from geophysical and civil engineering communities because of the limited application of traditional seismic surveys in highly populated urban areas. Considering that they can provide high-frequency phase velocity information up to several tens of Hz, the active surface wave survey would be omitted and the amount of field work could be dramatically reduced. However, the measured dispersion energy image in the passive surface wave survey would usually be polluted by a type of “crossed” artifacts at high frequencies. It is common in the bidirectional noise distribution case with a linear receiver array deployed along roads or railways. We review several frequently used passive surface wave methods and derive the underlying physics for the existence of the “crossed” artifacts. We prove that the “crossed” artifacts would cross the true surface wave energy at fixed points in the f–v domain and propose a FK-based data selection technique to attenuate the artifacts in order to retrieve the high-frequency information. Numerical tests further demonstrate the existence of the “crossed” artifacts and indicate that the well-known wave field separation method, FK filter, does not work for the selection of directional noise data. Real-world applications manifest the feasibility of the proposed FK-based technique to improve passive surface wave methods by a priori data selection. Finally, we discuss the applicability of our approach.

Surface wave energy absorption by a partially submerged bio-inspired canopy

Aquatic plants are known to protect coastlines and riverbeds from erosion by damping waves and fluid flow. These flexible structures absorb the fluid-borne energy of an incoming fluid by deforming mechanically. In this paper we focus on the mechanisms involved in these fluid-elasticity interactions, as an efficient energy harvesting system, using an experimental canopy model in a wave tank. We study an array of partially-submerged flexible structures that are subjected to the action of a surface wave field, investigating in particular the role of spacing between the elements of the array on the ability of our system to absorb energy from the flow. The energy absorption potential of the canopy model is examined using global wave height measurements for the wave field and local measurements of the elastic energy based on the kinematics of each element of the canopy. We study different canopy arrays and show in particular that flexibility improves wave damping by around 40%, for which half is potentially harvestable.

Gap-dependent magnetic anisotropy and high-frequency property of micro-patterned NiFe film

To adjust the high-frequency properties of the soft magnetic film, micro-patterned NiFe films were fabricated on a (100) silicon substrate by using photolithography and magnetron sputtering. Their gap-width were changed from 15 to 60 µm with the strip-length of 5 mm and strip-width of 30 µm. The morphology and magnetic properties of the films were examined by scanning electron microscopy, vibrating sample magnetometer and vector network analysis, respectively. Compared with the continuous NiFe film, the in-plane magnetic anisotropy field (H k ) of micro-patterned NiFe film improved from 0 to 43 Oe. And as the designed gap-width (d) increased from 15 to 60 µm, H k increased from 43 to 80 Oe. The resonance frequency f r is increased up to 8.6 GHz, which is mainly from the demagnetization field and the magnetostatics surface wave energy in our study system. Therefore, the patterned films controlled by various stripe gap-width will also be essential in future high-frequency device design procedures.

Hybridized nanogenerator based on honeycomb-like three electrodes for efficient ocean wave energy harvesting

Ocean energy is one of the most promising clean and renewable natural energy sources, however, owing to traditional energy harvesting technology, the collection and utilization of ocean energy is extremely limited. In this work, a hybridized ocean wave nanogenerator (How-NG) based on honeycomb-like three electrodes has been proposed, which consists of a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG), where the TENG works in both in-plane sliding mode and vertical contact-separation mode. With innovative design in electrode structure and hybrid of TENG and EMG, the How-NG can harvest two types of wave energy, kinetic energy and potential energy of ocean surface wave. The honeycomb-like three electrode structure is designed to harvest wave energy in multi-angle range for random waves. In addition, by adjusting the weight of the magnet to achieve different resonance parameters, the How-NG could reach a resonant state and more efficient collection of ocean energy. Furthermore, the influence of the working frequency and sliding displacement on the electrical outputs of the TENG unit and EMG unit are investigated systematically. The maximum output energy of TENG and maximum power of EMG can reach 21.7 µJ and 8.23 µW respectively at fixed working frequency of 4.0 Hz and sliding displacement of 3.5 cm. In addition, those two basic units are assembled vertically into a sealed cylinder acrylic shell which is used to drive LEDs by harvesting the water wave energy. This work presents a novel and efficient approach toward large-scale blue energy harvesting from the ocean.

Partition Detection and Location of a Kelvin Wake on a 2-D Rough Sea Surface by Feature Selective Validation

The method for detecting and locating a Kelvin wake in the background of a two-dimensional (2-D), large-scale, random rough sea surface is studied. In this method, the large-scale, 2-D dynamic sea surface is partitioned, the correlation function between each partitioned sea surface is analyzed and extracted by the feature selective validation method, and the energy characteristic difference measures between each partitioned sea surfaces are obtained. By averaging the difference measures between the target partitioned sea surface and the adjacent sea surface, we can obtain the average value of the characteristic difference measure of each partitioned sea surface. Through the simulation and calculation, it was determined that, after the Kelvin wakes are superimposed on the partitioned sea surface, the characteristic difference measures are clearly larger than that of the partitioned sea surface without superimposed wakes. This finding shows that the method can effectively detect the changes in the sea surface wave energy caused by the wakes. The result shows that the method can accurately and efficiently identify the location of the partitioned sea surface where the Kelvin wakes are superimposed, after selecting a reasonable threshold, to realize the accurate location of the Kelvin wakes.

Dispersion Energy Analysis of Rayleigh and Love Waves in the Presence of Low-Velocity Layers in Near-Surface Seismic Surveys

High-frequency surface-wave analysis methods have been effectively and widely used to determine near-surface shear (S) wave velocity. To image the dispersion energy and identify different dispersive modes of surface waves accurately is one of key steps of using surface-wave methods. We analyzed the dispersion energy characteristics of Rayleigh and Love waves in near-surface layered models based on numerical simulations. It has been found that if there is a low-velocity layer (LVL) in the half-space, the dispersion energy of Rayleigh or Love waves is discontinuous and ‘‘jumping’’ appears from the fundamental mode to higher modes on dispersive images. We introduce the guided waves generated in an LVL (LVL-guided waves, a trapped wave mode) to clarify the complexity of the dispersion energy. We confirm the LVL-guided waves by analyzing the snapshots of SH and P–SV wavefield and comparing the dispersive energy with theoretical values of phase velocities. Results demonstrate that LVL-guided waves possess energy on dispersive images, which can interfere with the normal dispersion energy of Rayleigh or Love waves. Each mode of LVL-guided waves having lack of energy at the free surface in some high frequency range causes the discontinuity of dispersive energy on dispersive images, which is because shorter wavelengths (generally with lower phase velocities and higher frequencies) of LVL-guided waves cannot penetrate to the free surface. If the S wave velocity of the LVL is higher than that of the surface layer, the energy of LVL-guided waves only contaminates higher mode energy of surface waves and there is no interlacement with the fundamental mode of surface waves, while if the S wave velocity of the LVL is lower than that of the surface layer, the energy of LVL-guided waves may interlace with the fundamental mode of surface waves. Both of the interlacements with the fundamental mode or higher mode energy may cause misidentification for the dispersion curves of surface waves.

Intensity dependences of the nonlinear optical excitation of plasmons in graphene.

Recently, we demonstrated an all-optical coupling scheme for plasmons, which takes advantage of the intrinsic nonlinear optical response of graphene. Frequency mixing using free-space, visible light pulses generates surface plasmons in a planar graphene sample, where the phase matching condition can define both the wavevector and energy of surface waves and intraband transitions. Here, we also show that the plasmon generation process is strongly intensity-dependent, with resonance features washed out for absorbed pulse fluences greater than 0.1 J m-2 This implies a subtle interplay between the nonlinear generation process and sample heating. We discuss these effects in terms of a non-equilibrium charge distribution using a two-temperature model.This article is part of the themed issue 'New horizons for nanophotonics'.

Study of a longitudinally nonuniform plasma layer

Transformation of the energy of surface waves in a plane plasma layer with a longitudinal irregularity of density is studied by the method of spectral decomposition. The total field is represented by an expansion in surface and pseudo-surface waves. A system of integro-differential equation for the coefficients of expansion determining the amplitudes of the transmitted, reflected, and scattered waves is obtained. It is shown that, in some special cases, this system of equations is reduced to a system of ordinary differential equations even if the plasma density rapidly changes. The fraction of the energy of surface waves that transforms into radiation at an acute angle with the layer can reach 50–60%.

Phase-shift- and phase-filtering-based surface-wave suppression method

Aliased surface waves are caused by large-space sampling intervals in threedimensional seismic exploration and most current surface-wave suppression methods fail to account for. Thus, we propose a surface-wave suppression method using phase-shift and phase-filtering, named the PSPF method, in which linear phase-shift is performed to solve the coupled problem of surface and reflected waves in the FKXKY domain and then used phase and FKXKY filtering to attenuate the surface-wave energy. Processing of model and field data suggest that the PSPF method can reduce the surface-wave energy while maintaining the low-frequency information of the reflected waves.

Harnessing the energy of ocean surface waves by Pelamis System

Harnessing the energy of ocean surface waves by Pelamis System

Analysis of the Global Swell and Wind Sea Energy Distribution Using WAVEWATCH III

Over the past several decades, an increasing number of studies have focused on the global view of swell and wind sea climate. However, our understanding of wind sea and swell is still incomplete as is the lack of an integrated description for all the wave components. In this paper, the European Centre for Medium-Range Weather Forecasts (ECMWF) Era-medium wind data is used to run the WAVEWATCH III model and the global wave fields in 2010 are reproduced. Using the spectra energy partition (SEP) method, two-dimensional wave spectra were separated and detailed information for the components of wind sea and swell was obtained. We found that the highest seasonal mean energy of swell and wind sea are distributed in the respective winter hemispheres. In most seas, swell carries a large part of the wave energy withWsbeing higher than 50%. Compared to swell, the global distribution of wind sea energy is highly affected by the seasons. We also established a link between inverse wave age and the ratio of swell energy to total wave energy. This study aims to improve our understanding of surface wave energy composition and thus the parameterization of global-scale wind-wave interaction and air-sea momentum flux.

Seismic interferometry as a tool for improved imaging of the heterogeneities in the body of a landfill

It is challenging to image and characterize the body of a landfill. High-density areas that act as obstructions to fluid flow are of specific interest to the landfill operators (e.g., for improvement of treatment technologies), and thus their imaging is important. In seismic reflection sections, such areas manifest themselves as sources of scattered energy. The heterogeneities inside the landfill, in addition to the surface-wave energy which is difficult to remove, add to the complexity in the seismic data. We propose to make use of seismic interferometry (SI) not only as a tool to improve the imaging of the scatterers, but also as a tool to remove the undesired surface-wave energy. We investigate the results obtained from application of SI to field seismic reflection data recorded at a landfill. We show that the data, retrieved by SI, image the scattered energy better than the seismic reflection data when the latter is processed in a conventional way. The increased stacking power of SI and its implicit consideration of multiple scattering result in a better illumination of the scatterers. We also use SI to predict the surface-wave energy and remove it from the original seismic reflection data using an adaptive subtraction method. The result from the adaptive subtraction when compared to the reflection data, processed in a conventional way, shows improved imaging, especially of layers in the landfill. Combined interpretation of the stacked reflection sections together with the velocity fields obtained from the three different datasets (conventional seismic reflection, SI and adaptive subtraction) leads to an improved interpretation.