Wave Characteristics Research Articles

Evolving Phase Propagation in an Intermediate‐m ULF Wave Driven by Substorm‐Injected Particles

AbstractAn ultralow frequency (ULF) wave was simultaneously observed in the ionosphere by the Super Dual Auroral Radar Network (SuperDARN) radar at Hankasalmi, Finland and on the ground by the International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers with close proximity to the radar. The onset time of the wave event was around 03:00 magnetic local time. Fourier wave analysis of the event suggests a wave period of about 1,340 s with an equatorward latitudinal and eastward longitudinal wave phase propagation, and an effective azimuthal wave number of 17 ± 1, in the intermediate range of those observed in ULF waves. This wave has been interpreted as resulting from drifting electrons of energies of 13 ± 5 keV in a drift resonance condition linked to energetic particle populations during a magnetospheric substorm. The latitudinal phase characteristics of this wave experienced temporal evolution, believed to be caused by additional injected particle populations associated with the same substorm driving the wave, which resulted in an observed loss of HF backscatter. This observation of a unique type of temporal evolution in the phase propagation characteristics of ULF waves enhances current understanding about the structure, dynamics and source of these types of ULF waves.

Study of defect mode characteristics in acoustic metamaterials

The development of novel material architectures incorporating unconventional geometric designs (e.g., microstructural instabilities, multi-length scale geometries), or adaptive constituent elements (e.g., piezo electrics) has created a powerful tool to design metamaterials for efficient dispersion manipulation and precise control of acoustic waves. Various aspects of the acoustic dispersion (e.g., wave speed, damping ratio, band gap position and widths) have been investigated with a primary focus on wave characteristics in the acoustic pass bands, promoting their utility in applications, e.g., wave guiding, energy harvesting. However, recent studies on topological waves, truncation and bandgap resonances have highlighted potential benefits of leveraging acoustic waves in the bandgap, e.g., signal propagation, passive flow control. Motivated by this, we explore the dispersion behavior of finite mass-spring-damper acoustic metamaterial models with material defects. The eigen analysis reveals a (defect) resonance in the acoustic band gap, producing a highly localized defect mode. The dependence of this resonance frequency, the degree of localization and phase response of the eigenmode, on the defect parameters are explored. Subsequently, the potential utility of these defect modes in flow control applications is also explored and presented.

On the dynamics of large-amplitude ion-acoustic waves in a non-Maxwellian plasma with nonthermal electrons and an electron beam

This work investigates the characteristics of nonlinear large-amplitude ion-acoustic waves that occur and propagate in a non-Maxwellian plasma consisting of inertial ions and electrons beam as well as inertialess Cairns-distributed electrons. For this purpose, this inquiry utilizes a two-fluid model with the Sagdeev pseudopotential technique. By utilizing the Sagdeev pseudopotential, a mathematical equation similar to an energy balance equation is derived. The effects of the related physical parameters, including the inertialess electron concentration, the electron beam concentration, and the electron beam velocity, on the existence region of the solitary waves (SWs), and accordingly, the properties of ion-acoustic SWs (IASWs) are examined. Also, the Cairns distribution of electrons can significantly affect the features of large-amplitude IASWs, depending on the parameter that controls the distribution (the inertialess electron nonthermality). Additionally, the distinctive features of the solitary waves and their existence domain in connection with the relevant plasma parameters are also addressed.

Experimental investigation on the characteristics of the shock wave emitted by the cavitation bubble near the air bubble

This study explores the mitigation of cavitation damage in hydraulic engineering through air entrainment. The primary aim is to experimentally analyze the shock wave characteristics emitted by cavitation bubbles adjacent to air bubbles affixed to a tube nozzle. The schlieren optical system is utilized to visualize the shock wave, while a hydrophone measures its pressure. Experiments are conducted on cavitation bubbles induced by the spark-generated method in the vicinity of air bubbles, varying the dimensionless distances and sizes of the air bubbles. The results indicate that (1) The introduction of an air bubble noticeably changes the morphology, kinematic behavior, and shock wave features of the cavitation bubble. (2) Four distinct shock wave patterns are identified based on the quantity and shape of the shock wave, with variations in the cavitation bubble's collapsing behavior and shock wave characteristics across different patterns. (3) The dimensionless distance γ and size δ exert significant influence on the shock wave's quantity, pressure peak, shape, and energy. With γ decreases or δ increases, the shock wave quantity increases while the shock wave intensity decreases. This investigation of the interaction between cavitation bubbles and air bubbles is essential for elucidating the mechanism through which air entrainment mitigates cavitation damage.

Propagation Characteristics of Acoustic Emission Waves in Three Different Asphalt Pavement Materials

Propagation Characteristics of Acoustic Emission Waves in Three Different Asphalt Pavement Materials

Experimental investigation of propagation evolution characteristics of internal solitary waves passing through downslope topography

In contrast to the extensive research on the propagation evolution of internal solitary waves (ISWs) over continental shelf topography, few investigations have been conducted on the propagation evolution of ISWs over downslope topography. In this experiment, the characteristics of the ISWs passing over a downslope topography were investigated in an immiscible two-layer fluid system to clearly capture the waveform information. The main objective of this study was to analyze the propagation evolution of ISWs with different incident amplitudes passing through a downslope topography. Using the particle image velocimetry technique, the evolutionary characteristics of ISWs (such as waveform, wave height, energy budget, and flow field) are investigated. According to the flow field analysis results, the phase velocity near the downslope topography changes with the propagation of ISWs. Moreover, the gradient distribution of velocity progressively becomes perpendicular to the right surface of the topography. Furthermore, a counterclockwise vortex gradually forms at the right upper vertex of the topography. The propagation of ISWs is influenced by varying water depth and topography. The front waveform of ISWs is significantly flat, and the back is steeper than the original back waveform. Around the tail wave, an upward convex wave packet is generated. The trends of wave energy and wave height losses are broadly consistent. Furthermore, the energy loss is related to the incident wave height with a 20% higher loss rate for large-amplitude ISWs than small-amplitude ISWs at the inflection point of the topography.

Deformation characteristics of a ring-stiffened cylindrical shell induced by shock waves and coalesced bubbles in double-charge underwater explosions

This study investigates the deformation characteristics of a ring-stiffened cylindrical shell induced by shock waves and coalesced bubbles in double-charge underwater explosions. A numerical model for coupling underwater multi-point explosion loads with the cylindrical shell is established by the Arbitrary Lagrange Euler method, and underwater explosion experiments with double charges are also conducted. The numerical model's effectiveness is validated by comparing shock wave superposition characteristics, bubble coalescence processes, and bubble pulsation periods with the experimental results. Based on the numerical model, the influences of detonation intervals and layout angles of charge on shock wave superposition effects, temporal and spatial distribution characteristics of shock waves, and the evolution process of coalesced bubbles in underwater explosions with double charges are explored. Additionally, the deformation characteristics of cylindrical shells induced by shock waves and coalesced bubbles for double charges with different detonation intervals and layout angles of charge are analyzed. The results indicate that double charges can induce more substantial deformation on the cylindrical shell at a specific detonation interval than a single charge with equal total mass. During the shock wave phase, the cylindrical shell's deformation decreases nonlinearly with an increased layout angle. Conversely, during the bubble load phase, the deformation of the cylindrical shell shows an approximately linear decrease with an increase in layout angle. A critical angle exists, below which the impact of double charges on the cylindrical shell is more substantial when detonated with an interval than simultaneous detonation.

Propagation characteristics of elastic longitudinal wave in a piezoelectric semiconductor metamaterial rod and its tuning

Elastic metamaterial structures have many distinct wave properties such as band gap structure and topological phase inversion. The coexistence and interaction of piezoelectricity and semiconductor behavior in piezoelectric semiconductor (PS) materials endow metamaterials with some new physical effects. We investigate the propagation characteristics of elastic longitudinal waves in a metamaterial rod made of n-type PS material and piezoelectric (PE) dielectric material. Based on one-dimensional rod model, we present the transfer matrixes for the PS and PE phases as well as the interfacial transfer matrix of unit cell. The analytical dispersion relations of the considered PS-PE metamaterial rod are obtained by utilizing Bloch's theorem. Numerical results show that band gap structures of the metamaterial rod are dependent on the initial electron concentration, length ratio of PE phase, interfacial condition, and capacitor connected with the PE phase. The selection of certain initial electron concentration, length ratio of PE phase, and capacitor can lead to the appearance of topological phase inversion, highlighting the potential for controlling and manipulating the wave propagation properties of PS metamaterial structures. This paper provides a theoretical guidance on the development of smart devices based on PS metamaterial structures. The novel combination of piezoelectricity and semiconductor behavior in these materials opens up new avenues for designing and engineering advanced devices with tailored wave properties and functionalities.

Formation and propagation characteristics of a weak shock wave in maglev tube

The propagation of the weak shock wave (WSW) to the tunnel exits and their radiation as micro-pressure waves (MPWs) may cause sonic booms or structural resonance of buildings, posing potential hazards to humans, animals, and buildings in the exit's environment. The characteristics of the WSW and sonic booms of a maglev train/tube coupling model were studied based on the two-dimensional axisymmetric unsteady Reynolds average Navier–Stokes turbulence model. In the later stage of a MPW, the formation mechanism, geometry, and kinematic characteristics of compressible vortex rings (CVRs) were systematically analyzed. The inertial effect causes the initial wavefront to gradually transition from a Gaussian-shape waveform to a triangular waveform during its propagation, eventually coalescing into a WSW. The overpressure, density jump, and shock Mach number at the WSW location all increase with the increasing train speed, while the WSW thickness decreases accordingly. The formation distance of the WSW is inversely proportional to the amplitude of the initial wavefront gradient, and the WSW directly causes the occurrence of the exit sonic boom. The MPW amplitude has significant directionality with a largest value in the axial direction. Within the speed range of 450–700 km/h, the sound pressure level of the MPW exceeds the hearing threshold and even reaches the feeling threshold. The evolution of CVRs includes primary CVR, secondary CVR, and Kelvin–Helmholtz vortices. Primary CVR has the greatest impact on the axial MPW among them. The occurrence of CVRs will cause a second small noise level other than the sonic boom.

Loss Characteristics of TeraHertz Surface Waves on Laser Micromachined Textured Metals

Loss Characteristics of TeraHertz Surface Waves on Laser Micromachined Textured Metals

SO-FDTD simulation on the transmission characteristics of terahertz waves in inhomogeneous magnetized dusty plasma

SO-FDTD simulation on the transmission characteristics of terahertz waves in inhomogeneous magnetized dusty plasma

Second Harmonic Electromagnetic Wave Emissions from a Turbulent Plasma with Random Density Fluctuations

In the solar wind, electromagnetic waves at the harmonic plasma frequency 2ω p can be generated as a result of coalescence between forward- and backward-propagating Langmuir waves. A new approach to calculate their radiation efficiency in plasmas with external background density fluctuations is developed. The evolution of Langmuir wave turbulence is studied by solving numerically the Zakharov equations in a two-dimensional randomly inhomogeneous plasma. Then, the dynamics of the nonlinear electric currents modulated at frequencies close to 2ω p are calculated, as well as their radiation into harmonic electromagnetic waves. In the frame of this non-self-consistent approach where all transformations of Langmuir waves on density inhomogeneities are taken into account, the electromagnetic wave radiation rate (emissivity) is determined numerically as well as analytically, providing in both cases similar results. Moreover, scaling laws of the harmonic wave emissivity as a function of the ratio of the light velocity to the electron plasma thermal velocity are found. It is also shown how the emissivity depends on the average level of density fluctuations and on the isotropic/anisotropic character of the Langmuir waves’ and density fluctuations’ spectra.

Effect of dust size distribution and nonadiabatic charge variation on dispersion relation for linear waves in inhomogeneous complex plasmas

This paper explores linear waves’ instability in nonuniform complex plasmas with dust size distribution and non-adiabatic dust charge fluctuation. For this purpose, the dispersion relation is obtained with the aid of linearizing the hydrodynamic equations governing the properties of linear waves. The contribution of physical parameters such as inhomogeneity, nonadiabatic dust charge fluctuation, and dust size distribution to the features of dust acoustic waves is examined at great length. The numerical results show that the present research results are very important in the phenomenon of space astrophysical and experimental plasmas.

Features of a Low-Temperature Charge Density Wave in the Monoclinic Phase of NbS3 Manifested in the NMR and in Transport Properties

The relaxation of the transverse nuclear magnetization in the monoclinic phase of NbS3 has been studied by the 93Nb nuclear magnetic resonance method near the temperature TP2 = 150 K, at which a low-temperature charge density wave is formed. It has been shown that the critical slowing down of one of the vibrational modes of the lattice, which is quite slow even above TP2, occurs slightly below TP2. The transition at TP2 occurs not only in low-resistance samples, as thought previously, but also in high-resistance ones, and involves Nb atoms in the bulk of a sample. The transport properties of high-resistance samples, namely, the smearing of the depinning threshold for the charge density wave below TP2, confirm that the phase transition in them occurs at TP2. It has been concluded that the distortion of the lattice at TP2 is not due to the Peierls mechanism and can be attributed to the Keldysh–Kopaev transition. Another possible mechanism is the fluctuation distortion of the lattice above TP2 that prevents the sliding of the charge density wave.

Heterogeneous ultrasonic wave properties in leg cortical bones of Thoroughbreds

Safe and inexpensive diagnosis of leg bone disease in the field is very important for Thoroughbreds and large animals, because large animals are difficult to transport, and prompt diagnosis is required. The quantitative ultrasound (QUS) is attracting attention for the evaluation of leg bones because it can give us information of elasticity, which is related to the bone quality. For the development of a QUS system of animal leg bones, understanding of characteristic ultrasonic wave properties (velocity and attenuation) is a key issue. Therefore, wave properties in Thoroughbreds’ leg bones were obtained experimentally using an ultrasonic pulse technique. Precise measurements showed clear heterogeneity of ultrasonic wave properties due to the location. Opposed to the other large animals like bovines, high wave velocities were found in the medial and lateral parts, which possibly tells the effects of hard training in the fields. From a clinical perspective, the medial and lateral parts are less prone to diseases such as periostitis. The attenuation was greater in the posterior part, especially in the porous area near the trabecular bone. We also found that attenuation depended on bone matrix. Further investigation is necessary to discuss on the heterogeneity of wave properties in detail.

Quantitative ultrasonic characterization of Ti-6Al-4V components with surface roughness

Ultrasonic immersion testing enables nondestructive characterization of material microstructure through quantitative linkages between wave propagation parameters and features of interest. However, accurate measurements of metrics such as wave speed and attenuation generally require smooth test samples to ensure the reflected wave packets are not distorted. Thus, rough surfaces are mechanically polished before ultrasonic testing, which compromises the nondestructive nature of the measurement, distorting the sample geometry and imparting local damage. This challenge is particularly salient with the advent of manufacturing processes, such as metal additive manufacturing, that result in rough samples that must be characterized for heterogeneities in their as-manufactured state. This work examines the influence of surface roughness on longitudinal wave speed and attenuation in wrought and additively manufactured Ti-6Al-4V specimens. Samples are measured in an ultrasonic immersion setup before and after mechanical polishing using varying transducer frequencies and focal profiles. The resulting data informs the error generated in ultrasonic measurements as a function of roughness parameters, thereby informing the sample preparation needed for desired precision levels. Lastly, new measurement protocols are explored to correct for the presence of surface irregularities in a point-by-point fashion. This work was supported by the Robert W. Young Award for Undergraduate Student Research.

Theoretical modeling and dynamic analysis of designable grillages for repairing material surface defect

Designing structural grillages is an innovative solution to repair material surface defects. The grillages have advantages as lightweight and directionally enhanced, but their stability and stress concentration under dynamic loads may pose significant risks. Three analytical models of grillages above a semicircular defect are constructed. The analytical solution of the frequency-domain wave field around the semicircular defect under SH wave incidence is solved. The complex variable function method is introduced to simplify the wave field expression. The accuracy is verified by comparing it with classic examples. Applying the Modified Time-Frequency Transform to obtain the time-domain wave field. Based on the Multipoint Transient Input Method (MTIM), the transient surface displacement response of the grillage above the defect is derived, mainly discussing the superposition behavior of input waves in the grillage. MTIM is based on the analytical solution of local time-domain wave field and takes the time histories of the surface characteristic points as the wave input. It has been validated as an effective method for studying the dynamic response of structures. The numerical results show that grillage form, incident angle, and wave velocity ratio are important factors affecting the structural responses of grillage above the defect. This research aims to reveal the propagation characteristics of waves in grillages in filling material defects, providing theoretical guidance for the design and application of grillages in this field.

A hydrodynamic modelling of wave-activated bodies for wavelet marine regions

Abstract Recently, most wave energy research has targeted sea areas with high power density under extreme wave conditions for deployment. This trend often leads to higher energy costs for wave power plants. However, many marine areas with low power density, characterized by wavelet conditions and less destructive forces than extreme wave conditions, remain underexplored. Therefore, this study aimed to propose a wave-activated body model for sea regions with wavelet conditions. The wave-activated body design process encompassed site selection, parameter determination, geometry design, comparison and performance evaluation using the ANSYS® AQWA model. The results indicated that the proposed device achieved the desired heave motion, with an amplitude range of 1.2 to –2.5 m, validating its potential for deployment in marine regions with wavelet conditions. Notably, while the proposed design is optimized for wavelet conditions, it was found to have potential limitations in extreme wave environments. This observation emphasizes the challenge of formulating a generalized design suitable for both conditions. Consequently, it is pivotal for wave-activated body designs to be customized based on the specific ocean conditions they target, underscoring the need for specialized designs of wave energy converters that consider the unique wave characteristics of their deployment sites.

Wave climate change analysis based on long time-series buoy data

Using the buoy dataset from 2011 to 2022, the trend of wave climate change was analyzed at DaChen station located in the Taizhou City, Zhejiang Province. The results show a decreasing trend of the maximum significant wave height (Hs). Whereas the wave height is higher than 4 m, the corresponding wave period is in the range of 8-14s. Disastrous waves mainly occur between July and October. The relevant analysis presents the wave characteristics at the DaChen station, which is helpful for protecting the life safety along the coast and providing references for offshore engineering design.

Exploring implications of wave characteristics on the functionality of mimetic tubular sponges

Marine sponges influence the flow hydrodynamics by suction/pumping mechanism. They provide a recirculation flow and remove pollutants from their residence. Previous studies have validated the efficacy of mimetic sponges in improving momentum transfer in marine environments. This study endeavors to explore the impact of wave characteristics (i.e., wave height and period) on the momentum transfer near the mimetic sponges. Both physical and numerical simulations were undertaken to explore this phenomenon. Experimental results unveiled that the efficiency of the mimetic sponge is contingent upon some circumstances. When waves have a short period and height, the suction effects prevail. In such cases, orbital velocity tends to be in a negative direction, leading to suppressed fluctuating velocities and a reduction in turbulent kinetic energy throughout the water column. Thus, the penetration of the shear layer to the water column and occurrence of wake-street diminish. Conversely, an increase in wave height enhances the momentum exchange through the water column. Surface Line Integral Convolution and Three-Dimensional stream trace visualizations using OpenFOAM provide insights into the generation of spirals and vortices through the water column induced by mimetic sponges.