Direction Of Energy Propagation Research Articles

Finite element modeling of ultrasonic attenuation and dispersion in graded multilayer polymer composites

In this paper, finite element models of ultrasonic wave propagation in Cu–PMMA composites are established. The effects of second-phase particles, ultrasonic properties, and graded interfaces on the ultrasonic propagation behavior are investigated, and the contributions of particle-independent scattering, particle interactions, and matrix viscoelasticity to the ultrasonic attenuation are quantitatively evaluated. The results show that there is no obvious coupling between particle scattering and matrix viscoelasticity in Cu–PMMA composites, and the longitudinal wave speed has little effect with the variation of particle size, ultrasonic frequency, and graded interface, while the variation of the acoustic attenuation coefficient is related to the disorder of ultrasonic energy propagation direction. In the intra-layer uniform model, with the increase in Cu particle size and ultrasonic frequency, the scattering effect of Cu particles on the ultrasonic waves is enhanced, resulting in a significant increase in the acoustic attenuation coefficient. In the inter-layer graded multilayer model, there is a strong reverse energy propagation between the layers, causing the acoustic attenuation coefficient to increase significantly.

Evaluating the Applicability of Mainstream Wave Energy Converters in the South China Sea

Based on the past ten years of ERA5 wave field data, this study analyzed the distribution of wave energy resources in the coastal waters of each province around the South China Sea. In view of the single resource evaluation method, a regional classification method was established that comprehensively considered the three factors that impact wave energy resource reserves, the suitable water depth of the wave energy conversion device, and the device layout mode that affects energy absorption efficiency. From this information, the locations of key deployment stations around the coastal provinces were determined. Additionally, the CRITIC method was used to build indicators that can comprehensively evaluate the performance of different devices, and the most suitable devices for deployment in the five provinces were identified. The wave energy propagation direction of each key station was analyzed. The results show that the wave energy propagation direction of each station is relatively concentrated, which is convenient since this helps the device absorb and utilize energy more efficiently. Finally, the power generation performance and economic benefits of each key station’s most suitable device were analyzed. This article provides an assessment of the applicability of mainstream wave energy conversion devices in the nearshore area of the South China Sea, which is of great significance for the development and utilization of wave energy resources in the South China Sea’s nearshore waters. It provides a scientific basis for the selection, deployment, operation, and other practical operations of the follow-up devices in the South China Sea, as well as the power generation performance and economic benefits of the devices.

Interdecadal Variation in Rossby Wave Source over the Tibetan Plateau and Its Impact on the East Asia Circulation Pattern during Boreal Summer

The wave activity flux representing the energy propagation direction of planetary Rossby wave generally originates from a large wave source area. This study investigates the interdecadal variability and formation mechanism of Rossby wave source over the Tibetan Plateau (TP-RWS) and its impact on the atmospheric circulation and precipitation pattern in East Asia based on the ERA-20C reanalysis dataset in summer (June–July–August) during 1900 to 2010. Results show that the region with the maximum variabilities of Rossby wave source (RWS) in the past 110 years appears over the Tibetan Plateau (TP) during boreal summer, and the TP-RWS shows prominent characteristics of interdecadal oscillation. Secondly, the TP-RWS is mainly composed of the vortex stretching term (RWS-S1) and the absolute vorticity advection term (RWS-S2). The interdecadal TP-RWS is a synergistic result of the snow cover over northwestern TP associated with the RWS-S1, and the deep convection over southeastern TP associated with the RWS-S2. Furthermore, the interdecadal TP-RWS can lead to an alternatively positive and negative pattern of geopotential height anomalies from the northwestern TP to the North Pacific, which has a great climate effect on the precipitation in Huang-huai River Basin, South Korea and Japan Island. Under the guidance of the anomalous cyclonic circulation in East Asia, the prevailing southerly and easterly winds occur over the West Pacific and the Huang-huai River Basin, which lead to the water vapor convergence and upward movement at middle and lower troposphere.

Automatic Tsunami Hazard Assessment System: “Tsunami Observer”

The current prototype of a fully automatic earthquake tsunami hazard assessment system, “Tsunami Observer”, is described. The transition of the system to the active phase of operation occurs when information about a strong earthquake (Mw ≥ 6.0) is received. In the first stage, the vector field of coseismic displacements of the Earth’s crust is calculated by using the Okada formulas. In the calculations, use is made of data on the coordinates, the seismic moment, the focal mechanism, and the depth of the earthquake, as well as empirical patterns. In the second stage, the initial elevation of the water surface at the tsunami’s focus is determined with the vector field of coseismic displacements of the bottom and the distribution of ocean depths, and the earthquake’s potential energy is calculated. In the third stage, the intensity of the tsunami is estimated on the Soloviev–Imamura scale in accordance with the magnitude of the potential energy by using the empirical relationship that is obtained as a result of a statistical analysis of historical tsunami events. In the final stage, if the energy exceeds the critical value of 109 J, a numerical simulation of the tsunami is performed, which allows the determination of the predominant directions of wave energy propagation and estimation of the runup height on the nearest coast. In this work, data on the operation of the system over the last 3 years are presented.

An Improved Approach to Wave Energy Resource Characterization for Sea States with Multiple Wave Systems

Generally, wave energy resource assessment and characterization are performed based on an entire wave spectrum, ignoring the detailed energy features that belong to wave systems, i.e., wind waves and swells. In reality, the energy is separately possessed by multiple wave systems, propagating at different directions and velocities. Therefore, it is the wave system that is the most fundamental unit of the wave energy resource. Although detailed analyses of wind waves and swells can be conducted via wave system partitioning, operational assessment methods that can reveal the detailed wave energy characteristics of wave systems still deserve further development. Following a two-step partitioning procedure, this paper presents an improved approach to the characterization of wave energy resources based on grouped wave systems. Wave systems classified as the same group are consistent in terms of propagation direction, velocity, and other characteristics of wave energy, but these characteristics between the groups are obviously different. Therefore, in comparison with the traditional method, the new approach can reveal more comprehensive and more detailed characteristics of the wave energy resource in terms of (i) wind-sea and swell components, (ii) directionality, and (iii) wave conditions; details that represent valuable information for the improvement of the performance of wave energy converter devices and the optimization of the layout of device arrays in wave farms.

Leveraging nonlinear wave mixing in rough contacts-based phononic diodes for tunable nonreciprocal waves

In recent years, phononic material-based diodes or “phononic diodes” have been explored to enable nonreciprocal wave propagation for novel applications such as unidirectional filters and waveguides. Despite extensive studies, the functionality and tunability of these diodes have been restricted to specific frequencies. Here, we exploit mixing of double-frequency (pump and probe) waves in nonlinear phononic materials to design a diode that can control the frequency, mode, and direction of energy propagation of the nonreciprocal waves. Our one-dimensional phononic diode is based on local and periodic nonlinearity, and global asymmetry. The weak nonlinearity is incorporated in the form of precompressed rough contacts, where contacts exhibit a quadratic force–displacement relationship. Using finite element models, we demonstrate tuning of the dispersion branch associated with the nonreciprocal wave by controlling the frequency of the pump waves. This allows propagation of nonreciprocal waves at frequencies lower or higher than the probe wave frequencies. Further, we show the ability to switch between reciprocal and nonreciprocal wave propagation, where the nonreciprocal response can cause either unidirectional or bidirectional energy propagation. This switching is possible through suitable selections of a pair of frequencies, and external precompression that controls the band gaps. The proposed phononic diode exhibits nonreciprocal wave propagation over a broad frequency range yet is simple in design and purely mechanical in construction. Moreover, due to its ability to filter and tune the frequencies of nonreciprocal waves, this diode will have potential applications as mechanical sensors and devices.

Deterministic tsunami hazard assessment and zoning approach using far-field and near-field sources: Study of Cixi County of Zhejiang Province, China

Investigating the potential tsunami hazard for coastal regions is helpful for urban development and emergency evacuation. In this paper, we present a deterministic method for tsunami hazard assessment (DTHA) in terms of tsunami amplitude and tsunami-induced currents. 21 extreme far-field transoceanic tsunami sources located in the Pacific Rim and, 14 near-field sources in Ryukyu Trough and Manila Trench are suggested. The Digital Elevation Model (DEM) data of 50 m combined with coastal breakwater data is adopted. The tsunami hazard is analyzed based on tsunami amplitude and tsunami-induced velocity. The coastal risk of Cixi County is presented and discussed. The results highlight the necessity of combining the tsunami amplitude and tsunami-induced currents in hazard assessment with the protective role of breakwaters. Further study manifests the effects of astronomical tide on tsunami hazard. The submarine topography consisted of ridges and trenches could trap tsunami energy and change propagation direction. The heterogeneous effect of slip distribution on tsunami hazard assessment is investigated, indicating the feasibility of using uniform slip source in DTHA. This study provides a comprehensive and quantitative assessment method incorporating tide, DEM, breakwater, and multiple sources to evaluate the tsunami risk for hazard reduction and urban planning.

Integrated monitoring and assessments of marine energy for a small uninhabited island

Marine renewable energy (wind energy, wave energy, and tidal current energy) has important application potential for the construction and development of uninhabited islands, however, it is necessary to assess the richness and stability of resources before energy development. In this study, a marine renewable energy integrated monitoring system was deployed on a small island, Dongluo Island, in the northwestern South China Sea. Based on the observation data over one year, the energy density and availability are systematically assessed. The results show that the renewable energy resources in the sea area around the island have a certain utilization potential, in which the average wind energy density is 81 W/m2 and the available frequency is 44.6%, the average wave energy density is 1.74 kW/m and the available frequency is 29.2%, and the average tidal current energy density is 32.4 W/m2 and the available frequency is 18.4%. All three types of energy propagation directions are relatively uniform. In addition, because the seasonal variations of the intensity and stability of the three types of energy are different, the three energy resources show obvious complementary advantages. Although the available frequency of single energy is relatively low, the available frequency will be significantly improved by comprehensively superimposing the three resources. Therefore, for the energy development of the island, it is necessary to integrate and optimize the allocation of different types of marine energy resources.

A comprehensive study of the Kappa value by borehole and surface strong-motion acceleration records

The spectral decay parameter of the amplitudes of high-frequency ground motion, Kappa (k), is widely used in many seismological and earthquake engineering studies. This parameter is dependent on the local characteristics of the site, the propagation path, and the earthquake source. In this paper, the values of k and its variation with subsurface anisotropy and the direction of energy propagation of seismic waves at the source are studied. For this purpose, k values for 508 accelerograms of 141 earthquakes with a moment magnitudes between Mw 3.3 to 7 and epicentral distances less than 100 km are calculated. Various portions of records (P- and S-wave) are used. Records were collected at 20 surface and borehole accelerometery stations of KiK-net strong-motion seismograph networks of Japan’s National Research Institute for Earth Science and Disaster (NIED). Our results show that for all the wave segments considered in this study, k values for the horizontal component are larger than the vertical component at surface stations. In addition, the estimated value of this parameter for surface stations is greater than that of the borehole stations. Differences in k values for the surface and the borehole records also show that k values for S-wave are greater than of the P-wave. The effect of the radiation pattern of seismic waves and source directivity on the k values is another parameter that assessed for our database. The results of this study clearly show that the k changes with the angle at which the wave reaches the station.

Scattering of flexural-gravity waves by a crack in a floating ice sheet due to mode conversion during blocking

Abstract

Root‐finding absorbing boundary condition for anisotropic scalar waves in infinite media

AbstractA root‐finding absorbing boundary condition (RFABC) for scalar‐wave propagation problems in infinite anisotropic media was developed. Although the phase velocity and the group velocity in isotropic media have the same sign, the sign of the latter can differ from that of the former in anisotropic media. Therefore, a RFABC for anisotropic scalar waves consistent with the group velocity of the considered media is developed, as the velocity is closely related to the direction of energy propagation. The developed boundary condition is shown to satisfy a criterion for an “enough accurate” boundary condition. The well‐posedness of the boundary condition is proven at the continuous level. Its finite‐element formulation, which ensures well‐posedness at a discrete level, is derived, after which it is demonstrated that accurate and stable solutions to the problem of antiplane shear‐wave propagation in an anisotropic elastic waveguide, an example of anisotropic scalar‐wave propagation, can be obtained using the proposed numerical approach.

Topographic Rossby Waves at Two Different Periods in the Northwest Pacific Basin

AbstractTo clarify characteristics and mechanisms of mesoscale variability in the deep ocean, we conducted a two-dimensional observation with a 3 × 3 grid mooring array around site R (30°N, 147°E) during 2014–16. We analyze the obtained velocity data together with past mooring observation data in the northwest Pacific basin and outputs of an ocean general circulation model (OGCM). In our two-dimensional mooring observations, the variability of zonal and meridional velocities at a depth of 4000 m was prominent at periods of 174 and 58 days, respectively. The variability at periods of 174 and 58 days propagated to the northwest and west-southwest, respectively, as a single plane wave. The variability at the period of 58 days was considered to be topographic Rossby waves (TRWs) under stratification originated in the Kuroshio Extension region north of site R, as demonstrated by our previous study. At the period of 174 days, zonal and meridional wavenumbers estimated from the phase lag for zonal velocities also satisfied the dispersion relation of TRWs under stratification. Backward ray tracing from site R indicated that energy of TRWs propagated from the eastern slope of the Shatsky Rise to site R almost along f/H contours, where f is the Coriolis parameter and H is water depth. The orientation of major axis of variance ellipses at periods of 174 days and longer, obtained from the past mooring observations and the OGCM outputs, tended to be parallel to f/H contours, being consistent with the direction of energy propagation of TRWs.

Symmetrical and anti-symmetrical topological edge states based on two-dimensional magneto-optical photonic crystals

We report our design of a topological waveguide at the boundary of two adjacent magneto-optical photonic crystals with opposite magnetic biases which can simultaneously support symmetrical and anti-symmetrical topological edge states. In this non-reciprocal topological photonic model, the symmetrical and anti-symmetrical topological edge states possess the same direction of backscattering-immune chiral energy propagation. However, their directions of phase propagation are opposite, i.e., forward phase propagation for the symmetrical state while backward for the anti-symmetrical one. Using a finite-size structure, we can selectively couple one topological edge state to free space via oblique incidence to realize one-way transmission and reflection in a compact configuration. Furthermore, we design an all-photonic tunable splitter by hybridizing these two topological states. Based on manipulating the phase propagation of topological edge states, our work may offer promising applications in tunable topological photonics and extend the scope of topological photonics.

Anisotropic azimuthal surface‐wave inversion for a vertically fractured and transverse isotropy medium: Theory and examples from a controlled field experiment

ABSTRACTFractures in elastic media add compliance to a rock in the direction normal to the fracture strike. Therefore, elastic wave velocities in a fractured rock will vary as a function of the energy propagation direction relative to the orientation of the aligned fracture set. Anisotropic Thomson–Haskell matrix Rayleigh‐wave equations for a vertically transverse isotropic media can be used to model surface‐wave dispersion along the principal axes of a vertically fractured and transversely isotropic medium. Furthermore, a workflow combining first‐break analysis and azimuthal anisotropic Rayleigh‐wave inversion can be used to estimate P‐wave and S‐wave velocities, Thomsen's ε, and Thomsen's δ along the principal axes of the orthorhombic symmetry. In this work, linear slip theory is used to map our inversion results to the equivalent vertically fractured and transversely isotropic medium coefficients. We carried out this inversion on a synthetic example and a field example. The synthetic data example results show that joint estimation of S‐wave velocities with Thomsen's parameters ε and δ along normal and parallel to the vertical fracture set is reliable and, when mapped to the corresponding vertically fractured and transversely isotropic medium, provides insight into the fracture compliances. When the inversion was carried out on the field data, results indicated that the fractured rock is more compliant in the azimuth normal to the visible fracture set orientation and that the in situ normal fracture compliance to tangential fracture compliance ratio is less than half, which implies some cementation may have occurred along the fractures. Such an observation has significant implications when modelling the transport properties of the rock and its strength. Both synthetic and field examples show the potential of azimuthal anisotropic Rayleigh‐wave inversion as the method can be further expanded to a more general case where the vertical fracture set orientation is not known a priori.

Vertical structure of Convectively Coupled Equatorial Waves (CCEWs) during Boreal Summer and Winter

Atmospheric variability in the tropics on the daily to intraseasonal timescale is often related to convectively coupled equatorial waves (CCEWs), including Kelvin, MRG, ER, and TD-type waves. This study aims toanalyze the observed vertical structures of the CCEWsduring boreal summer and winter fromthe NCEP-DOE reanalysis dataset. Consistent with a linear wave theory, the vertical structure of CCEWs is characterized by a distinctive phase tilt, indicatinga distinct direction of wave energy propagation. The vertical structure of Kelvin, MRG and ER waves is signified by westward phase tilts with height, especially in the upper troposphere when the waves become dry (i.e. there is noeffect of moisture), while in the lower troposphere, the phase tiltsdeviatesignificantly from the linear wave theory, whenthe waves become moist. On the other hand, the TD-type waves exhibit a perpendicular, baroclinic structure with height. The vertical structures of the Kelvin, MRG and TD-Type waves are more clearly observed during boreal summer, while ER waves are more observed during boreal winter. This is consistent with the increasing wave amplitudesdue to a stronger wave sourceduring those periods. Future studies are still required in order to understand how the vertical modulation of CCEWs on RH and wind fields can be used to better improve weather predictions in the tropics.

Expansion of Wave Rays and Fronts in Media with Inhomogeneous Structure

In the article on the principles of Fermet, Huygens obtaine the differential equations in the form of Hamilton, which describe the ray trajectories and wave fronts in inhomogeneous media. Established that the vector of Poynting-Umov's determining the direction of energy propagation in inhomogeneous medium is coincident with the vector tangent to the ray. In the second part of the article established that the equations of the theory of rays' propagation in inhomogeneous media have the form of equations of nonlinear dynamics and describe the emergence of deterministic chaos in the geometry of rays for a wide variety of types of heterogeneous structures. In this case, the rays behave randomly and their description you must go to the description based on the theory of random functions and fields. In the third part of the paper is considered a model which is equivalent to the random medium and the calculation of the coordinates of the ray (the mathematical expectation and correlation functions). Understanding of these characteristics gives information about the behavior of the trajectories of the rays for these models of media. The description of the behavior of rays on the basis of the equations of statistical mechanics is discussed in the article for functions of Markov's type.

Optical wave parameters for spatially dispersive and anisotropic nanomaterials

Spatial dispersion is an intriguing property of essentially all nanostructured optical media. In particular, it makes optical waves with equal frequencies and polarizations have different wavelengths, if they propagate in different directions. This can offer new approaches to control light radiation and propagation. Spatially dispersive nanomaterials, such as metamaterials, are often treated in terms of wave parameters, such as refractive index and impedance retrieved from reflection and transmission coefficients of the material at each incidence angle. Usually, however, the waves are approximated as transverse, which simplifies the description, but yields wrong results, if spatial dispersion or optical anisotropy is significant. In this work, we present a method to calculate the wave parameters of a general spatially dispersive and optically anisotropic medium without applying such an approximation. The method allows one to evaluate the true impedances and field vectors of the effective waves, obtaining thus the true light intensity and energy propagation direction in the medium. The equations are applied to several examples of spatially dispersive and anisotropic materials. The method introduces new insights into optics of nanostructured media and extends the design of such media towards optical phenomena involving significant spatial dispersion.

Mathematical Analysis of Inertial Waves in Rectangular Basins with One Sloping Boundary

AbstractWe consider the problem of small oscillations of a rotating inviscid incompressible fluid. From a mathematical point of view, new exact solutions to the two‐dimensional Poincaré–Sobolev equation in a class of domains including trapezoid are found in an explicit form and their main properties are described. These solutions correspond to the absolutely continuous spectrum of a linear operator that is associated with this system of equations. For specialists in Astrophysics and Geophysics, the existence of these solutions signifies the existence of some previously unknown type of inertial waves corresponding to the continuous spectrum of inertial oscillations. A fundamental distinction between monochromatic inertial waves and waves of the new type is shown: usual characteristics (frequency, amplitude, wave vector, dispersion relation, direction of energy propagation, and so on) are not applicable to the last. Main properties of these waves are described. In particular, it is proved that they are progressive. Main features of their energy transfer are described.

Sound Intensity Distribution Around Organ Pipe

Abstract The aim of the paper was to compare acoustic field around the open and stopped organ pipes. The wooden organ pipe was located in the anechoic chamber and activated with a constant air flow, produced by an external air-compressor. Thus, a long-term steady state response was possible to obtain. Multi-channel acoustic vector sensor was used to measure the sound intensity distribution of radiated acoustic energy. Measurements have been carried out on a defined fixed grid of points. A specialized Cartesian robot allowed for a precise positioning of the acoustic probe. The resulted data were processed in order to obtain and visualize the sound intensity distribution around the pipe, taking into account the type of the organ pipe, frequency of the generated sound, the sound pressure level and the direction of acoustic energy propagation. For the open pipe, an additional sound source was identified at the top of the pipe. In this case, the streamlines in front of the pipe are propagated horizontally and in a greater distance than in a case of the stopped pipe, moreover they are directed downwards. For the stopped pipe, the streamlines of the acoustic flow were directed upwards. The results for both pipe types were compared and discussed in the paper.

A Study on the Scattering Energy Properties of an Elastic Spherical Shell in Sandy Sediment Using an Improved Energy Method

An elastic wave is composed of compressional (longitudinal) waves and shear (transverse) waves which have different wave velocities in solids. The acoustic field presents complex interference patterns which means its phenomena and properties are difficult to reveal. Fortunately, the energy method is more accurate than the potential function approach in describing the physical properties of the acoustic field. However, the polarization state of particle vibration excited by an elastic wave is spatially periodic in the wave propagation direction. Therefore, the energy propagation direction is not consistent with the wave propagation direction using commonly used energy method. According to the polarization state of particle vibration, a time-space averaging method based on the spatial periodicity of energy flux in the solid is proposed. The method could eliminate the influence of the interference due to local energy exchange and retain the trend of energy propagation. Several conclusions are illustrated through the analysis of the scattering energy properties of a steel shell in sandy sediment. Sandy sediment can not be regarded as a fluid nor a general solid. Scattering energy excited by an incident shear wave mainly concentrates in the vicinity of the directions of backscattering and forward scattering. Especially, at low frequency, it plays an important role in the total scattering energy excited by an incident compressional and shear wave.