Wave Field Distribution Research Articles

Pitch-Angle Diffusion of Radiation Belt Electrons and Precipitating Particle Fluxes: Dependence on VLF Wavefield Parameters

The dependence of the pitch-angle diffusion efficiency of energetic electrons in the Earth’s magnetosphere on the distribution of the whistler wave field along the geomagnetic flux tube is quantitatively studied for parameters corresponding to the location of the Sura and HAARP HF heating facilities. The expansion of the precipitation energy range with the increase of the region of geomagnetic latitudes occupied by the waves is shown. Using the calculated pitch-angle diffusion coefficient for a given spectrum of waves and their distribution along the flux tube, the ratio of the fluxes of precipitating and trapped particles at low altitude is determined. It is shown that at typical wave intensities corresponding to chorus VLF waves and plasmaspheric hiss, the fluxes of precipitating and trapped electrons can be comparable to each other. At the same time, for the wave amplitudes observed as a result of the action of heating facilities, the flux of precipitating electrons is negligible.

Dynamic responses of steep bedding slope-tunnel system under coupled rainfall-seismicity: Shaking table test

The coupling effects of rainfall, earthquake, and complex topographic and geological conditions complicate the dynamic responses and disasters of slope-tunnel systems. For this, the large-scale shaking table tests were carried out to explore the dynamic responses of steep bedding slope-tunnel system under the coupling effect of rainfall and earthquake. Results show that the slope surface and elevation amplification effect exhibit pronounced nonlinear change caused by the tunnel and weak interlayers. When seismic wave propagates to tunnels, the weak interlayers and rock intersecting areas present complex wave field distribution characteristics. The dynamic responses of the slope are influenced by the frequency, amplitude, and direction of seismic waves. The acceleration amplification coefficient initially rises and then falls as increasing seismic frequency, peaking at 20 Hz. Additionally, the seismic damage process of slope is categorized into elastic (2-3 m/s2), elastoplastic (4-5 m/s2) and plastic damage stages (≥ 6.5m/s2). In elastic stage, ΔMPGA (ratio of acceleration amplification factor) increases with increasing seismic intensity, without obvious strain distribution change. In plastic stage, ΔMPGA begins to gradually plummet, and the strain is mainly distributed in the damaged area. The modes of seismic damage in the slope-tunnel system are mainly of tensile failure of the weak interlayer, cracking failure of tunnel lining, formation of persistent cracks on the slope crest and waist, development and outward shearing of the sliding mass, and buckling failure at the slope foot under extrusion of the upper rock body. This study can serve as a reference for predicting the failure modes of tunnel-slope system in strong seismic regions.

A numerical model approach of wave dynamic

The numerical model of wave field distribution using time dependent of wave combination from refraction-diffraction equation on a gentle slope was carried out in Modeling Laboratory of Marine and Fisheries Faculty of Syiah Kuala University. The research of numerical modeling was conducted to understand how the impact of the presence of coastal structures on the coast toward the wave dynamic approach. In the theory, the greater of wave angle, the greater of wave height distribution will be behind the breakwater, thus allowing large sediment transport to make changes to the coast. Therefore, this research is important because the knowledge of the relationship between waves and coastal structure is still limited while the dynamics of the coast have a distinctive significance in the regions. The study aims to determine the wave phenomena that interact with the structure of the coastal building so that the results of this study can be used and utilized as substantial study for future coastal planning. The method used in this study is the application of wave equations that may be solved by numerical model. The model results show that the greater the angle of incidence of waves on the southwest coast, the greater the wave height produced when it hits coastal structures. However, this characteristic does not occur in the west coast region. This is caused by the topographic nature of coastal areas and different coastal characteristics.

A simulation approach for site-city interaction in basin under oblique incident waves and its applications

The coexistence of basin effects and site-city interaction (SCI) effects will result in a more complex spatially differentiated distribution of seismic wavefields and building responses. However, current research still lacks investigation into the SCI effect under three-dimensional (3D) oblique incidence in basins. This paper employs the Spectral Element Method (SEM) to simulate the propagation of seismic wavefields in near-surface soil, utilizes a nonlinear Multi-Degree-of-Freedom (MDOF) model to simulate buildings, and combines the Frequency-Wavenumber (FK) domain method to input oblique incident seismic wavefields as equivalent seismic loads, thereby establishing the FK-SE-MDOF approach. This approach addresses the limitation of neglecting the influence of oblique incidence when studying the impact of SCI in basins, and has been developed into SPECFEM 3D. First, the theory of the FK-SE-MDOF approach was introduced, and the correctness of this approach was validated. Furthermore, taking a series of SCI model in an ideal basin as an example, calculations and analyses were conducted to investigate the effects of factors such as the relative layout of the basin and building cluster, incidence angles, and basin stratigraphy on site seismic wavefields and building responses. This approach can provide a quantitative reference for seismic design, risk assessment, and post-earthquake rescue efforts.

An alternative method to mimic mode conversion for ion cyclotron resonance heating

Ion cyclotron range of frequency waves in hot plasmas exhibit spatial dispersion effects and the wave equation takes the integro-differential form. Under the local plasma model assumption, the wave equation can be simplified to the differential form and adapts to the numerical scheme of the finite element method (FEM). Even though direct absorption of fast waves by ions and electrons can be described well by the local plasma model, linear mode conversion associated with non-local effects is absent. To deal with this issue, an alternative method is put forward in this paper where quasi-electrostatic fluid waves based on the multi-fluid warm plasma model are employed to take the place of ion Bernstein waves in mode conversion. On this basis, an interative fluid-kinetics (INTFLUK) code based on the FEM is developed for full-wave simulation in hot plasmas. Derivation of the wave equations as well as benchmarking of the INTFLUK code against other wave simulation codes are carried out. In both one- and two-dimensional cases, the validity of the INTFLUK code was verified by comparison of the wave field distributions and power deposition. As a useful illustration of the INTFLUK code including the scrape-off layer and a realistic antenna, the influence of the poloidal antenna phasing difference on ion cyclotron resonance heating is analyzed. Finally, it should be noted that the method in this paper has the potential to be extended to the three-dimensional case, which will be considered in the near future.

Numerical modelling of wave run-up heights and loads on multi-degree-of-freedom buoy wave energy converters

With the development of wave energy converters (WECs), multi-degree-of-freedom (multi-DOF) buoy has become popular. The effect of nonlinear phenomena, such as wave run-up and wave impact, on an oscillating buoy WEC, may decrease its efficiency and even lead to overturning, plastic deformation, and fatigue failure. This study used a Fortran code for the custom development of Flow-3D software to apply independent power take-off (PTO) damping to each DOF. A hydrodynamic simulation model of the interaction between a wave and cylindrical buoy under six types of motions was developed and verified through model tests of the motion response of the buoy and wave run-up on it. Wave run-up heights and maximum wave loads on buoys with different motions and PTO combinations were investigated and compared. The numerical results show that coupled motion can lead to a less intense wave field distribution than a single motion and reduce the risk of overtopping. In addition, the bottom pressure of the buoy for the pitch–surge motion increased by a maximum of 101.6 % compared to the initial pressure. For independent linear PTO damping, heave damping has the most significant influence on the maximum wave load on the coupled motion buoys, followed by surge damping, while pitch damping has no significant effect. The results of this study can guide the designing of safe and reliable multi-DOF buoy WECs.

Experiment and numerical simulation study on resistance performance of the shallow-water seismic survey vessel

In this paper, a new type of shallow-water seismic survey vessel is proposed to solve the problem that the traditional seismic survey vessels cannot satisfy the requirements of the shallow-water marine resources exploration. To reveal the influence of shallow water effect on resistance and flow field, this research is to obtain the resistance and shallow-water characteristics of this shallow-water seismic survey vessel through ship model experiments and numerical methods. Firstly, the ship model experiment predicted the resistance at different speeds in shallow water and obtained the benchmark data to validate numerical methods. Then, the CFD methods were used to calculate the resistance of the ship in deep and shallow water. The numerical results are in good agreement with the experimental results. Finally, this paper provided details of the distribution of wave, pressure and flow fields at different water depth conditions in order to explain the causes of increased resistance in shallow water, providing a reference for the shallow-water seismic survey vessel design.

Surface waves Fabry-Perot modes of the finite magnetophotonic crystal in Voigt configuration

We have solved the problem of plane wave scattering by a finite gyrotropic magnetophotonic crystal in the Voigt configuration. To find an analytical solution, the method of the Floquet-Bloch wave theory with Cauchy boundary conditions for a one-dimensional magnetophotonic crystal and the transfer matrix method were used. The reflection and transmission coefficients are obtained in analytical form for arbitrary material parameters of the gyrotropic layers of the crystal. The field distributions within the finite crystal are found in explicit form. The regime of excitation of modified Zenneck-Sommerfeld waves and a new regime of unusual gyrotropic surface waves with positive values of the effective permittivity of one of the crystal layers are revealed. The features of the distribution of surface wave fields for the considered regimes of all Fabry–Perot modes at full transmission are studied. The nonreciprocal properties of the considered crystals are established depending on the incidence angle sign.

DESIGN AND DEVELOPMENT OF SUPER WIDEBAND DIELECTRIC RESONATOR ANTENNA FOR NEXT-GENERATION TELECOMMUNICATIONS

The dielectric resonator antenna (DRA) has revolutionized the latest generation of communication systems with their obvious advantages of small size, bandwidth, and power-consuming capabilities. In this paper, an analysis of the impact of the dielectric material on the radiation characteristics of the DRA is presented with simulation reports. The proposed antenna takes the shape of a circular patch with the dielectric resonator having different shapes. This helps to analyze the impact of the tapering adjustments on the features of the antenna. The simulations are performed using the latest version of the complex electromagnetic modeling tool, and results are analyzed in terms of simulated reports like reflection coefficient (S11), voltage standing wave ratio, radiation patterns, and field distribution plots. The overall size of the proposed antenna is 18 × 12 mm<sup>2</sup>. The measured results are in good agreement with the simulation results. The proposed DRA is suitable for mobile wireless applications.

Analysis and research on the resonance of mobile phone shielding cabinet

In order to cut off the connection between the mobile terminal and mobile communication base stations or Wi-Fi, it is necessary to improve the electromagnetic shielding efficiency of the mobile phone shielding cabinet. This paper analyzes the resonant characteristics of mobile phone shielding cabinets. The test method of electromagnetic shielding has been introduced. Through Maxwell wave equation and boundary conditions, the cavity resonant frequency of every small drawer on the mobile phone shielding cabinet has been derived, and the rectangular cavity research model was established. Using the high-frequency finite element method (FEM) simulation to calculate the cut-off frequency of the first 10-order high-order mode in the cavity, the resonant standing wave field distribution of every small drawer on the mobile phone shielding cabinet has been analyzed. This paper can offer a theory instruction for the product design of mobile phone shielding.

Multi-frequency blocking effects by multiple vertical cylinders designed using combination grating theories

A novel waveguide type breakwater has been developed based on wave space modulation and grating control technologies. The waveguide to the distribution of wave field is analyzed with the boundary integral equation to study the blocking effects by multiple vertical cylinders designed based on the combination grating theories. For the bottom mounted multiple vertical cylinders scattering problems, the Helmholtz equations with Neumann boundary conditions are solved using boundary integer equation (BIE) method. The proposed model has been successfully validated through a comparison with Thompson et al.‘s results. Three cases consisted of 57 vertical cylinders with same radius: [a] linear topology with same spacing using multi-slit gratings conditions, [b] sinusoidal topology with same longitudinal projection spacing designed by multi-slit grating and sinusoidal grating conditions and [c] linear topology with unstructured spacing. Numerical results illustrate that case [b] has better blocking effect than the others not only for short period waves but also for medium or long period waves using combination grating theories. To the best of authors' knowledge, this is the first work devoted to presenting thorough combination grating theories using the topology control in multiple cylinders. This paper opens up a new field of mathematical analysis on wave barrier designs.

Numerical Investigation of Wave Run-Up and Load on Fixed Truncated Cylinder Subjected to Regular Waves Using OpenFOAM

In the interaction between waves and structures, the maximum wave run-up height on the surface of the structure and the wave field distribution around the cylinder are important factors to be considered in the design of marine structures. In this paper, the open source software OpenFOAM is used to simulate the wave run-up phenomenon of a truncated cylinder under regular waves by solving the Reynolds-averaged Navier–Stokes equation. The established numerical model is verified with the experimental data, and the good consistency demonstrates the accuracy in simulating the interaction between waves and fixed truncated cylinders. The numerical results show that the draft of the cylinder under regular waves has little effect on its maximum wave run-up height, but has a significant effect on the horizontal wave force. At the same wave steepness, the radial dimensionless run-up height increases with the increase of scattering parameters ka, where k is the wave number and a is the cylinder radius. The radial run-up height decreases gradually along the radial direction in the upstream, and increases gradually along the radial direction in the downstream.

Global field performance of monopile-supported offshore wind turbines with sinusoidal layouts using innovative combined grating conditions

For the global performance of monopile wind farms, the desired wave field distribution using traditional layout methods is hard to obtain. In this study, the investigation aims to efficiently explore the potential wave response reduction of the multiple layer design of wind farm layouts using novel grating conditions. It is very important and necessary to optimize the layouts of monopile-supported OWTs (offshore wind turbines) by analyzing the wave field performance, especially considering scour protection and avoiding the proximity of the wave frequency to natural frequency of OWTs. This paper presents a layout and a design method of monopile-supported OWTs using combined grating theorems, which can take space modulation into account to deal with various issues in existing layouts. The results show that the present method can modulate the wave field responses more evenly than the conventional cases. More specifically, total wave field distribution sensitivities were discussed under different wavelengths, amplitudes, layouts, pile-radius, and the angles of incident waves. It can be illustrated that the monopile-supported OTWs with sinusoidal configurations can have more modulation effects on wave fields in an appropriate wavelength band. As indicated, this method not only provides wave space modulation control but also sheds light on the wave field reduction mechanisms.

A Surface Plasmon–Polariton in a Symmetric Dielectric Waveguide with Active Graphene Plates

A theoretical study of the plasmon modes’ characteristics is carried out in a structure consisting of two active graphene layers separated by a dielectric barrier layer. A general dispersion relation is obtained, the numerical analysis of which reveals the possibility of controlling the parameters of amplified surface modes in the region of graphene negative conductivity. In particular, their dispersion is controlled by changing the chemical potential of the graphene layers. For antisymmetric plasmons, their dependence on the barrier layer parameters was revealed. An increase in the chemical potential makes it possible to expand the region of existence of the amplified plasmons, which is accompanied not only by an increase in the amplification coefficient but also by a shift to the region of higher frequencies of the amplified modes. For the first time, modal bistability was also demonstrated in a limited frequency range for antisymmetric plasmons, due to the appearance of additional modes, in which the phase velocity decreases sharply near the cutoff, and the group velocities of the modes entering the bistability turn out to be opposite in sign. The frequency dependences of the real and imaginary parts of the plasmon propagation constant are analyzed, the distributions of wave fields in the structure are plotted, and the frequency dependence of the depth of the plasmon–polariton is given.

Paraxial sharp-edge diffraction: a general approach.

A general reformulation of classical sharp-edge diffraction theory is proposed within paraxial approximation. The, not so much known, Poincaré vector potential construction is employed directly inside Fresnel's 2D integral in order for it to be converted into a single 1D contour integral over the aperture boundary. Differently from the recently developed paraxial revisitation of BDW's theory, such approach should be applicable, in principle, to arbitrary wavefield distributions impinging onto arbitrarily shaped sharp-edge planar apertures. However, in those cases where such a conversion were not analytically achievable, our approach allows Fresnel's integral to be easily converted, irrespective of the shape and the regularity features of the aperture geometry, into a double integral defined onto a square domain. A couple of interesting examples of application of the proposed method is presented.

Chocolate inspection by means of phase-contrast imaging using multiple-plane terahertz phase retrieval.

Terahertz (THz) radiation has shown enormous potential for non-destructive inspection in many contexts. Here, we present a method for imaging defects in chocolate bars that can be extended to many other materials. Our method requires only a continuous wave (CW) monochromatic source and detector at relatively low frequencies (280 GHz) corresponding to a relatively long wavelength of 1.1 mm. These components are used to construct a common-path configuration enabling the capturing of several images of THz radiation diffracted by the test object at different axial depths. The captured diffraction-rich images are used to constrain the associated phase retrieval problem enabling full access to the wave field, i.e., real amplitude and phase distributions. This allows full-field diffraction-limited phase-contrast imaging. Thus, we experimentally demonstrate the possibility of identifying contaminant particles with dimensions comparable to the wavelength.

Deep-Learning Estimation of Complex Reverberant Wave Fields with a Programmable Metasurface

Electromagnetic environments are becoming increasingly complex and congested, creating a growing challenge for systems that rely on electromagnetic waves for communication, sensing, or imaging, particularly in reverberating environments. The use of programmable metasurfaces provides a potential means of directing waves to optimize wireless channels on demand, ensuring reliable operation and protecting sensitive electronic components. Here we introduce a technique that combines a deep-learning network with a binary programmable metasurface to shape waves in complex reverberant electromagnetic environments, in particular ones where there is no direct line of sight. We apply this technique for wavefront reconstruction and control, and accurately determine metasurface configurations based on measured system scattering responses in a chaotic microwave cavity. The state of the metasurface that realizes desired electromagnetic wave field distribution properties was successfully determined even in cases previously unseen by the deep-learning algorithm. Our technique is enabled by the reverberant nature of the cavity, and is effective with a metasurface that covers only approximately 1.5% of the total cavity surface area.

Tapered Multicore Fiber for High-Power Laser Amplifiers

The problem of coherent amplification of the out-of-phase mode in tapered multicore fibers with cores arranged in a ring and in a square lattice is studied theoretically. The stability of out-of-phase field distributions with respect to both inhomogeneities of the refractive index and the initial wave field distribution is demonstrated in numerical modeling. Coherent combining of radiation into a single beam with good quality and efficiency of about 80% for ring cores arrangement and more than 90% for square cores arrangement is possible. Achievement of 55 MW of total power at the output of a fiber with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$11 \times 11$</tex-math></inline-formula> cores is numerically demonstrated.

An assessment of uncertainties in VS profiles obtained from microtremor observations in the phased 2018 COSMOS blind trials

Site response is a critical consideration when assessing earthquake hazards. Site characterization is key to understanding site effects as influenced by seismic site conditions of the local geology. Thus, a number of geophysical site characterization methods were developed to meet the demand for accurate and cost-effective results. As a consequence, a number of studies have been administered periodically as blind trials to evaluate the state-of-practice on-site characterization. We present results from the Consortium of Organizations for Strong Motion Observation Systems (COSMOS) blind trials, which used data recorded from surface-based microtremor array methods (MAM) at four sites where geomorphic conditions vary from deep alluvial basins to an alpine valley. Thirty-four invited analysts participated. Data were incrementally released to 17 available analysts who participated in all four phases: (1) two-station arrays, (2) sparse triangular arrays, (3) complex nested triangular or circular arrays, and (4) all available geological control site information including drill hole data. Another set of 17 analysts provided results from two sites and two phases only. Although data from one site consisted of recordings from three-component sensors, the other three sites consisted of data recorded only by vertical-component sensors. The sites cover a range of noise source distributions, ranging from one site with a highly directional microtremor wave field to others with omni-directional (azimuthally distributed) wave fields. We review results from different processing techniques (e.g., beam-forming, spatial autocorrelation, cross-correlation, or seismic interferometry) applied by the analysts and compare the effectiveness between the differing wave field distributions. We define the M index as a quality index based on estimates of the time-averaged shear-wave velocity of the upper 10 (VS10), 30 (VS30), 100 (VS100), and 300 (VS300) meters and show its usefulness in quantitative comparisons of VS profiles from multiple analysts. Our findings are expected to aid in building an evidence-based consensus on preferred cost-effective arrays and processing methodology for future studies of seismic site effects.

Optimal deployment of seafloor observation network for tsunami data assimilation in the South China Sea

We propose an optimal deployment scheme of the Seafloor Observation Network (SON) in the South China Sea (SCS), aiming at early warning of potential tsunami hazards based on the data assimilation approach. The SON is composed of offshore bottom pressure gauges (OBPGs). We design the initial location of OBPGs along the isobaths of 500, 1000, and 2000 m. The energy distribution of the tsunami wavefield based on Empirical Orthogonal Function (EOF) analysis is used as a reference. Then, synthetic tsunamis generated by stochastic slip sources along the Manila Trench are adopted to evaluate the performance of the SON. The OBPGs at a depth of 1000 m can make an accurate early warning based on tsunami data assimilation at a reasonable engineering cost. Finally, based on the quantitative evaluation, the optimal deployment scheme of the SON is suggested. Our results indicate that at least three stations are required to cover the coast along southern China to forecast the tsunami in the SCS successfully. We note that our method could also be applied to other regions to design the SON against potential tsunami hazards.