Characteristics Of Surface Waves Research Articles

On research of dispersion characteristics of multi-component surface waves from traffic-induced seismic ambient noise

As one of the commonly used sources in passive surface wave exploration, traffic-induced seismic ambient noise is widely used in urban underground velocity structure detection at present. However, characteristics of the dispersion curve extracted from such kind of ambient noise lack systematical research, especially for the multi-component surface wave. Due to the complex character of the real-world underneath structures, dispersion characteristics concluded from real-world traffic-induced seismic ambient noise that is hard to verify. The numerical simulation technique is a good choice for systematical research of characteristics of dispersion curves extracted from multi-component traffic-induced seismic ambient noise. Most of the numerical examples that appeared in the present literature, however, are based on the dispersion-curve-based numerical simulation technique. Hence, most of these can only simulate the vertical component. In this paper, the two-dimensional finite difference method is used to simulate multi-component traffic seismic ambient noise. The characteristics of original traffic noise are analyzed, and the effect of trace intervals on surface wave imaging of different types of traffic-induced noise is studied. Rayleigh wave dispersion energy image is extracted by the passive surface-wave frequency wavenumber transformed method. The differences in Rayleigh-wave dispersion images in traffic noise with different components are analyzed and compared. The results show that Rayleigh wave dispersion energy images appearing different characteristics in different components. The surface wave dispersion information presented by different types of traffic noise is frequency-dependent. The trace spacing also strongly affect the surface-wave dispersion energy images extracted from different types of traffic-induced noise. The numerical results are significant for guiding the traffic-induced seismic noise data acquisition and processing.

Dispersion characteristics of surface wave in SCCS: theoretical analysis, numerical simulation and MASW-based NDT

To fully validate the feasibility of multichannel analysis of surface waves (MASW)-based interfacial debonding detection for steel–concrete composite structures (SCCS), dispersion characteristics of surface waves in SCCS are systematically investigated using theoretical analysis and elaborate 3D numerical simulations. First, the influences of material strength and thickness of concrete core, steel plate thickness on the dispersion figures are analyzed based on the theoretical dispersion characteristic of Rayleigh wave. Scientific layering strategy, including single steel plate, double-layer, and three-layer medium assumptions, is investigated using the theoretical dispersion analysis of Lamb wave. Besides, the dispersion characteristics of surface wave in circular steel pipes are calculated to determine the appropriate theoretical dispersion curves for MASW measurement. Finally, the stress wave propagation processes in SCCSs with various internal structures, including stiffeners, studs, and diaphragms, as well as the debonding width, are simulated using 3D numerical simulation to validate the research finding of theoretical analysis and detectability of MASW-based non-destructive testing on interfacial debonding defects in rectangular and circular concrete-filled steel tubulars. Finally, the dispersion characteristics corresponding to displacement, velocity, and acceleration of surface waves are comparatively discussed. The research findings of this study are the cornerstone of experimental study and essential theoretical support for identifying interfacial debonding and bond-slip damage of SCCS components utilizing MASW method.

Abnormal Waves Observation and Analysis of the Mechanism in the Pearl River Estuary, South China

The Pearl River Estuary is a typical estuary region in southern China, and the study of surface wave occurrence and characteristics is of great importance for shipping management, nearshore engineering, and monitoring shoreline changes and other human activities. Long-term and continuous observational data are critical for achieving a better understanding of waves. In this study, the wave measurements based on a high-precision wave gauge were analyzed and observation data over approximately two years at a sampling frequency of 2 Hz were obtained. The wave system in the Pearl River Estuary was found to deviate from the assumption of a stationary stochastic process similar to that in the open ocean, due to the effects of abnormal waves caused by human activities. Therefore, traditional distribution functions such as Rayleigh and Weibull were not suitable for accurately fitting the main wave parameters (Hs, Tp, etc.), particularly in the tail. Consequently, abnormal wave signals were extracted from all wave sets, and through the comparison and analysis of the wave spectral features, it was determined that these abnormal waves are caused by the ship wakes. The spectral characterization of these waves was performed to determine the characteristics of different ship wake processes. Ship wakes in the Pearl River Estuary are an important part of the wave system, and their wave height is significantly larger than the normal wave. Based on the spectral characteristics of ship wakes, this study proposed some news characteristics of ship wakes in the main channel of the Pearl River Estuary.

Characteristics of Surface Wave on the Unstable Interface in Gas Jet Forming

The surface accuracy and quality of the mirror blank determine the performance of the optical mirror after coating; therefore, it is crucial to seek a simple and effective method for mirror blank processing. The gas jet forming provides a new idea, which employs a gas jet to impinge on a liquid pool, forms a specific curved surface and solidifies it. However, due to the interface instability that occurred with a specific range of jet velocity, periodical fluctuations appear on the interface and affect the forming of the mirror blank. In this study, the amplitude and transfer period of surface waves in the air gas/dimethyl silicone oil system are taken as the research objects. After conducting orthogonal experiments, this study uses a high-speed camera to record the generation of the surface wave and the fluctuation of the gas–liquid interface during its transfer. Subsequently, this study analyses the influences of jet velocity and viscosity of dimethyl silicone oil on the amplitude and transfer period of the surface wave. In the following experiments, multiple groups of parameters were selected in the range of jet velocity of 11~13 m/s and dimethyl silicone oil viscosity of 500~2000 Pa·s. This study measures the interface morphology with different parameters using the method of image recognition. Finally, using the measured data, this study establishes the calculation model of surface wave amplitude and transfer period, realizing the study of the characteristics of surface waves on the unstable interface. This research can be used to enhance the forming accuracy of the gas jet-forming method.

Audio-frequency surface wave characteristics above porous and comb-like surfaces

Part of the solution for the sound field due to a point source in air over a porous boundary has the form of an airborne surface wave. Analytical expressions for the surface wave characteristics are reviewed and corresponding analytical expressions for group speed are obtained from a thin air layer approximation for the impedance of a comb-like surface, from two approximate models for the acoustical properties of porous media and from a model for identical slanted slit pores. Predictions of absorption coefficient spectra for a hard-backed porous layer with flow resistivity sufficiently low that there is extended reaction are made using two of the approximate models and compared with those of a relatively exact slanted slit pore model. The model derived specifically to predict the acoustical properties of porous asphalt is found to be the least satisfactory. The various models are used to obtain analytic expressions for the surface wave group speed. Predictions of surface wave characteristics including group velocity are compared with data obtained over arrays of parallel aluminium strips.

Multiscale homogenization numerical study on the mechanism of interface debonding detection for steel–concrete composite structures with multichannel surface wave measurements

In order to understand the interface debonding detection mechanism for steel–concrete composite structures (SCCSs) efficiently using multichannel analysis of surface waves (MASW) when the heterogeneity and randomness of the mesoscale structure of concrete are considered, mesoscale homogenization numerical analysis on surface wave propagation in SCCSs is carried out. Firstly, for exploring the theoretical dispersion characteristics of surface waves in SCCSs, dispersion curves of both Lamb wave and Rayleigh wave of three different layering scenarios, including single-layer, two-layer, and three-layer composite models where concrete is treated as homogeneous material, are investigated. Meanwhile, the effect of the steel plate thickness on the dispersion curves is studied. Secondly, to evaluate the effect of mesoscale structure variation of concrete in SCCSs on surface waves, a random aggregate method (RAM) is employed to establish the mesoscale model of concrete composed of randomly distributed aggregates with different shapes. Thirdly, for enhancing numerical simulation efficiency on surface wave propagation, an equivalent homogenization approach and Voigt parallel model are developed to establish the mesoscale homogenization models of SCCSs. Dispersion curves from forwarding analysis on surface wave measurement of the mesoscale models are compared with the corresponding theoretical dispersion curves to reveal surface wave attribution and optimum layering scenarios of SCCSs for MASW method. The influence of mesoscale concrete variation on surface wave fields in SCCSs using equivalent homogenization models is investigated comprehensively and compared with that of the corresponding mesoscale models. Finally, the feasibility of the proposed MASW method for interface debonding length estimation is validated, and wavelength selection criteria of excitation signals considering interface dimension, as well as steel plate thickness, are discussed. The results from the mesoscale homogenization numerical study can provide helpful guidance on the practical application of MASW-based debonding detection for SCCSs where concrete is heterogeneous.

Possibilities of Using of Surface and Subsurface Waves’ Amplitude-Angle Characteristics for Control of Materials with Surface-Hardened Inhomogeneous Layer

Improving the efficiency of ultrasonic control of hardened surface layers of metal products with a heterogeneous structure obtained using different technologies is a pressing problem of industrial production. The purpose of this work was to investigate the possibilities of measuring the depth of the surface inhomogeneous layer of steel objects on the basis of the use of amplitude and amplitude-angle characteristics of surface and subsurface transverse waves.The analysis of ultrasonic methods of control of physical and mechanical properties of metals by using surface and subsurface waves and experimentally investigated amplitude-angular characteristics of surface waves, the maximum angle of which increases by 3° at change of dimensionless layer depth hλ from zero to0.82. For the first time, the ratio of normalized amplitudes of surface waves taken at certain angles on theamplitude-angle characteristic curve obtained in the echo mode was proposed to be used as correlating parameters with the depth of the hardened layer. As a result of this research, the possibility of using a phased array transducers to solve the above problems.The effect of the hardened layer depth varying from zero to five in the working frequency range of 1.8– 10 MHz on the peculiarities of the refraction effect (including interference) and dependence of the subsurface wave amplitude on the acoustic base has been studied, making it possible to establish conditions that provide for the determination of the hardened layer depth.Circuit solutions have been offered in order to increase the efficiency of control of properties of the surface layers of metal articles on the basis of utilization of small-aperture transducers and ultrasonic reflectors making it possible to form fields of surface waves of different directional pattern.

An accurate method for dispersion characteristics of surface waves in layered anisotropic semi-infinite spaces

In this paper, we develop a novel method for the dispersion characteristics of surface waves in layered anisotropic semi-infinite spaces. Compared to solving the algebraic transcendental eigenequations directly, this method can find all surface waves accurately. For solving accurately, the first-order state equation is formed by introducing the dual variable. Some properties of the complex Hamiltonian matrix are presented and proved, then based on these properties, the radiation condition for the homogeneous anisotropic half-space is given. And, based on the scaling and squaring algorithm and mixed energy matrix, the precise integration method (PIM) is presented for solving accurately the eigenvalue problem of ordinary differential equations (ODEs) corresponding to surface waves. All eigenfrequencies can be found with certainty by using the concept of the eigenvalue count in the Wittrick-Williams (W-W) algorithm. Numerical examples show that the proposed method is highly accurate and efficient for solving dispersion relations of surface waves in layered anisotropic semi-infinite spaces, which involves the comparison of other previously published methods.

Analysis on the dispersion characteristics of surface waves in a layered slope

For landslide detection and monitoring, surface wave methods (such as multichannel analysis of surface waves and array microtremor measurements), can be exploited to infer the subsurface shear-wave velocity (VS), which is a key physical parameter for calculating the soil vulnerability index and slope stability. To facilitate implementation, the seismic sources and geophones of survey lines traversing the slope of a landslide are commonly deployed along the direction of gravity. Considering that single (vertical)-geophones are extensively utilized in a variety of practical applications, it is meaningful to analyze the dispersion characteristics of the gravity-oriented component in a layered slope. Based on the stiffness matrix method and a coordinate rotation, we derive an explicit relationship for the gravity-oriented component in a layered slope. We further analyze the dispersion characteristics of the gravity-oriented component in three typical layered slopes by using a new developed tool comprising a seismic wavefield simulation and a modified frequency–Bessel transform. The results show that the dispersion spectra of the gravity-oriented component may be contaminated by Love waves, which can cause the Rayleigh wave dispersion curves to be misidentified. As the slope angle and the included angle between the survey line and dip direction increase, Love waves interfere more with the dispersion spectra of the gravity-oriented component. Numerical experiments indicate that if the slope angle is <17° or the angle between the survey line and dip direction is kept below a certain reasonable threshold, the dispersion spectra of the gravity-oriented component are determined mainly by Rayleigh waves. Moreover, we propose an azimuth filter method to suppress the interference of Love waves for passive surface wave dispersion measurements. The presented method offers useful guidance and emphasizes the great potential of surface wave methods in landslide detection and monitoring applications.

NON-DESTRUCTIVE CONTROL OF PVD COATING SURFACE DEFECTS

Nanostructured ZrN coatings were deposited by the vacuum arc method with partial separation of the plasma flow from macroparticles using a curvilinear magnetic filter. With the proposed deposition parameters, a ZrN coating with an fcc lattice and (111) texture is formed. Theoretical studies are carried out to assess the defects of the surface layer in the presence of an adsorbed impurity of an fcc lattice with the surface orientation plane (111), and the characteristics of surface waves in the ZrN coating are considered. Equations are obtained for the dispersion laws and parameters of the splitting off of the surface wave from the zone of bulk vibrations in the nearest-neighbor approximation.

Phase-velocity and intercept-time scanning (PIS) technique for extracting experimental dispersion characteristics of surface waves

In active surface wave methods, the ability to extract the true dispersion trends from surface wave field data is critical for inferring accurate shear-wave velocity profiles. However, dispersion images such as those generated by the conventional wavefield transformation method are usually accompanied by numerical artifacts including side-lobes and aliasing, both of which decrease the dispersion image resolution and may lead to misinterpretation of dispersion modes. For example, the side lobes can be misinterpreted as higher or lower modes, which would introduce additional errors into the inverted stiffness profiles. A new experimental dispersion analysis method is presented to improve the resolution and sharpness of dispersion images and minimize the side lobes. The proposed method employs scanning of the phase-velocities and intercept-times of a series of harmonic signals obtained by Fourier transformation of raw multichannel data in the space-time (x-t) domain. Results obtained from synthetic and real field data demonstrate that the improved method can yield high-quality dispersion images compared to those of the conventional dispersion-imaging method. In addition, the improved method do not rely on the assumption that the impact point is the generation point of the Rayleigh waves, which is needed for the conventional method.

Shear Horizontal Surface Waves in a Layered Piezoelectric Nanostructure with Surface Effects.

This work aims to provide a fundamental understanding on the dispersive behaviors of shear horizontal (SH) surface waves propagating in a layered piezoelectric nanostructure consisting of an elastic substrate and a piezoelectric nanofilm by considering the surface effects. Theoretical derivation based on the surface piezoelectricity model was conducted for this purpose, and analytic expressions of the dispersion equation under the nonclassical mechanical and electrical boundary conditions were obtained. Numerical solutions were given to investigate the influencing mechanism of surface elasticity, surface piezoelectricity, surface dielectricity, as well as the surface density upon the propagation characteristics of SH surface waves, respectively. The results also reveal the size-dependence of dispersive behaviors, which indicates that the surface effects make a difference only when the thickness of the piezoelectric nanofilm stays in a certain range.

General characteristics of surface waves in Iraq marine water, Northwest of Arabian Gulf

General characteristics of surface waves in Iraq marine water, Northwest of Arabian Gulf

Multimode dispersion measurement of surface waves extracted by multicomponent ambient noise cross-correlation functions

SUMMARY Cross-correlation functions of ambient seismic noise sometimes show multimode characteristics of surface waves, especially in observations in sedimentary areas and ocean areas. Multimode dispersion curves are useful for improving the depth resolution of subsurface imaging; nevertheless, measuring the multimode dispersion curves is not easy. Multimode interference of surface waves makes the cross-correlation functions complicated even without lateral heterogeneity of the subsurface structure, and the complex waveforms may result in unphysical dispersion measurement. We developed a method to determine multimode phase velocity dispersion curves based on the fitting of the synthetic cross-spectra to observed ones. The phase velocity in the synthetic cross-spectra is modelled as the function of a 1-D velocity structure, which achieves the measurement of physically realizable dispersion curves. The 1-D structures do not necessarily represent the Earth structure directly but act as model parameters of the dispersion curves within station pairs. The cross-spectral fitting has two steps, that is, array-based and single-pair fittings. The first step estimates the amplitude of each surface wave mode and the reference 1-D structure from the cross-spectral data within an array. The second step estimates the pair-dependent dispersion curves from the cross-spectra of a single station pair using the modal amplitudes and the reference structure estimated by the first step. The dispersion measurement based on the cross-spectral fitting can work even at short distances where the multimode inference is significant in the time-domain cross-correlation functions. We applied this method to synthetic and field data in seafloor observations. The synthetic and field applications show that the simultaneous use of multicomponent cross-correlation functions is effective to determine multimode dispersion curves. The multimode phase velocity dispersion curves in the ocean area are estimated stably even though the signal-to-noise ratio of cross-correlation functions is not high. The pair-dependent multimode dispersion curves estimated by the present method can serve as robust input data for high-resolution surface wave tomography.

Surface waves in a linearly graded-index and an intensity-dependent index layered structure.

A new type surface wave is found that propagates in a linearly graded-index and an intensity-dependent index layered structure characterized by an abrupt change in the dielectric constant. The main surface wave characteristics are calculated analytically. The optical domain, the thickness of which increases with an increasing effective refractive index and decreases with an increasing characteristic distance, is formed. It is discovered that the characteristic distance of the graded-index medium and effective refractive index can control wave energy redistribution between the semiconductor layers.

Understanding the surface wave characteristics using 2D particle-in-cell simulation and deep neural network

The characteristics of the surface waves along the interface between a plasma and a dielectric material have been investigated using kinetic particle-in-cell simulations. A microwave source of GHz frequency has been used to trigger the surface wave in the system. The outcome indicates that the surface wave gets excited along the interface of plasma and the dielectric tube and appears as light and dark patterns in the electric field profiles. The dependency of radiation pressure on the dielectric permittivity and supplied input frequency has been investigated. Further, we assessed the capabilities of neural networks to predict the radiation pressure for a given system. The proposed deep neural network model is aimed at developing accurate and efficient data-driven plasma surface wave devices.

Использование понятия геофизической модельной функции при интерпретации данных скаттерометра

Within the framework of a two-scale Bragg (resonant) scattering model, the relationship between the spatial characteristics of sea surface waves and the geophysical model function (GMF) is analyzed. The dependence of the GMF on the angle between the direction of sounding and the wind velocity vector is determined by the function of the angular distribution of Bragg waves and the angular distribution of longer waves. In strong winds, the wave breaking makes a noticeable contribution to the radar signal. With calm and moderate winds, the main characteristics of the GMF can be interpreted within the framework of a two-scale Bragg scattering model. The exception is the appearance of negative values of the longitudinal-transverse asymmetry of GMF, which is observed in the L band of radio waves. Negative longitudinal-transverse asymmetry corresponds to lower values of the normalized cross-section of backscattering when probing along the wind direction than in the transverse direction.

Rayleigh-type surface waves in a thermally conducting mixture of an elastic solid and a Newtonian fluid

PurposeThe purpose of this paper is to analyze the propagation characteristics of the Rayleigh-type surface wave in a thermally conducting mixture of an elastic solid and a Newtonian fluid by applying the mixture theory.Design/methodology/approachThe governing equations are formulated in context of both Green–Lindsay (G-L) and Lord–Shulman (L-S) theories of generalized thermoelasticity. The specialized governing equations in a plane are solved by using the traditional approach, and a dispersion equation of the Rayleigh surface wave is obtained.FindingsA program in MATLAB software is developed to solve the dispersion equation. The numerical results demonstrate a significant dependence of the wave speed and the attenuation coefficient of the Rayleigh wave on the frequency and porosity.Originality/valueThe problem considered on Rayleigh wave on the surface of a half-space containing a thermally conducting mixture is not studied in the literature yet. The theoretical and numerical findings of the study will guide the experimental scientists while finding applications in various engineering fields.

Scale effects on the torsional surface waves propagation in an initially stressed dissipative nanoplate

The effects of small length scale on the torsional surface waves propagating in a pre-stressed dissipative nanoplate were examined in this paper. Biot’s incremental deformation principle as well as nonlocal elasticity theory were implemented to form the governing and frequency equations of torsional surface waves in nanoplate under considered conditions. In this work, we proposed a new approach to determine the phase velocity of torsional disturbances. Different categories are used to investigate the dispersion relations such as: wave number, scale coefficient, initial stress parameter, and dissipation coefficient. The results show that small length scale influences causes torsional dispersion of the wave propagation, which disappear in local elasticity theory. In addition, it is recognized that the torsional surface waves propagating in the pre-stressed dissipative nanoplates can be differentiated in a clear manner from those propagated in the absence of small length scale effects. The initial stress parameter can also be utilized to change the characteristics of the torsional surface wave's phase velocity in nanoplates. It is also observed that, the dissipation has a great effect on the phase velocity of torsional surface waves in propagating in the nanoplate. Therefore, this research is theoretically useful to convey information on nonlocal and dissipation properties of the nanomaterials: for example, through a precise measurement of the phase velocity of torsional surface wave propagates in a nanocomposite material by presence of the medium’s dissipation. This work could be useful in understanding the way of designing the Nano devices and Nano resonators.

Characteristics of individual surface waves measured by moored buoys in the coastal waters of the eastern Arabian Sea

In this study, the characteristics of the individual surface waves in the eastern Arabian Sea over one year are examined based on the measured time-series data using Waverider buoys at four locations covering ∼500 km of the western Indian coastline. At all locations, the number of waves is high during the non-monsoon compared to the monsoon period (June–September). Number of waves in a year is higher in the northern location (∼6,417,657) than in the southern locations (∼5,497,168) since comparatively more short-period waves are observed in the north. Maximum wave height varied from 7.0 to 7.6 m, and the steepness of the largest waves varies from 0.056 to 0.082 at different locations and is much smaller than the wave breaking limit. Number of short-period waves observed is higher than the long-period waves at all locations except in the monsoon, when a significant number of intermediate-period waves are present. The mean wave steepness of the 30-min record is ∼22% higher than the conventionally reported significant wave steepness based on mean wave period. Hilbert–Huang transform method is used to detect the freak wave and analyze the abnormal wave group structure. It is observed that freak wave occurrence is high during the monsoon.