Surface Waves Research Articles

Insight into intracontinental deformation and crustal reworking of ancient continents implied by crustal structure imaging of the Yangtze Craton

The crustal imprints from multistage tectonic activities in cratons offer valuable insights into continental evolution. Utilizing seismic data from two densely deployed, nearly perpendicular linear arrays, and a newly developed stepwise joint inversion of depth-domain receiver function and surface wave dispersion, we constructed a detailed crustal layering model for the Yangtze Craton. Our analysis revealed elongated double velocity reversal zones as salient features of the crust, which likely record ancient crustal reworking and juvenile crustal growth associated with Neoproterozoic rift-related magmatic processes. The interlayering of low- and high-velocity structures may contribute to the enduring stability of the Yangtze Craton. Additionally, superimposed layers separated by east-dipping interfaces and abrupt changes in crustal thickness in the boundary belts surrounding the Yangtze Craton document the crust's structural responses to intracontinental deformation during continent assembly.

Investigation of droplet splashing behavior during oblique jet impact onto a wall

For the issue of jet impingement on the wall in industrial cooling processes, an experimental setup based on high-speed photography for oblique jet impingement onto the wall was constructed. The experimental focus was on the study of liquid droplet splashing behavior after oblique jet impingement on the wall, discussing the liquid droplet splashing behavior under three jet impingement modes: Rayleigh regime, first wind-induced regime, and secondary wind-induced regime. By employing methods such as trajectory imaging and particle image velocity for liquid droplet parameter image measurement, obtaining the particle size, velocity, and distribution of splashed droplets after oblique jet impact on walls under different working conditions. The impact of jet impingement velocity and angle on droplet splashing parameters was analyzed. The results showed that when the impingement point is before the breakup length, with increasing flow velocity, the surface wave of the liquid column, and the spreading liquid film became more pronounced, but the loss of liquid-phase components due to splashing was relatively small. When the impingement point is after the breakup length, the secondary breakup resulting in a “crown”-shaped liquid film after droplet impingement leads to a significant loss of liquid-phase components through splashing. As the inlet velocity of the jet increases, there is a decreasing trend in droplet size and an increasing trend in droplet velocity. With an increase in jet angle, there is a decreasing trend in droplet size and velocity. Based on the concentration, size, and velocity distribution characteristics of splashing droplets, the area after oblique jet impingement on the wall can be divided into the impingement zone, low-concentration low-velocity zone, high-concentration high-velocity zone, and lateral splashing zone. This has significant implications for understanding the splashing mechanism after oblique jet impingement on the wall and optimizing operating conditions.

Spin Photonics‐Based on a Twinning Hyperbolic Metamaterial

AbstractRouting and multiplexing of the optical surface waves are critical for the ultra‐compact nano‐photonic systems. Given this background, traditional metal‐based systems, despite of the ability of supporting the surface plasmon polariton propagation, are constrained on manipulations due to the optical isotropy, and artificially designed structures are always required at the input or output to help attain the additional selectivity. Here, a spin‐dependent multi‐channel scheme is proposed based on the modulation ability of the hyperbolic metamaterial's anisotropy on Dyakonov Surface Waves. The input coupling, propagation direction, as well as the output coupling of the optical single are well determined by the certain spin feature carried by the light and the orientation of the interface's anisotropy because of the spin‐momentum locking. Specially, by constructing a twinning hyperbolic metamaterial, which contains the structural symmetry and materials symmetry, a photonic chip with 4 routing channels are demonstrated experimentally, where the spin of an incident beam can be maintained during the propagation on‐chip and then delivered back into the free space, offering a new planar scheme for metamaterial‐based spin‐controlled nano‐photonic applications.

Genesis and Propagation of Low‐Frequency Abyssal T‐Waves

AbstractAbyssal T‐waves are seismo‐acoustic waves originating from abyssal oceans. Unlike subduction‐zone‐generated slope T‐waves which are generated through multiple reflections between the sea surface and the gently dipping seafloor, the genesis of abyssal T‐waves cannot be explained by the same theory. Several hypotheses, including seafloor scattering, sea surface scattering, and internal‐wave‐induced volumetric scattering, have been proposed to elucidate their genesis and propagation. The elusive mechanism of abyssal T‐waves, particularly at low‐frequencies, hinders their use to quantify ocean temperatures through seismic ocean thermometry (SOT) and estimate oceanic earthquake parameters. Here, using realistic geophysical and oceanographic data, we first conduct numerical simulations to compare synthetic low‐frequency abyssal T‐waves under different hypotheses. Our simulations for the Romanche and Blanco transform faults suggest seafloor scattering as the dominant mechanism, with sea surface and internal waves contributing marginally. Short‐scale bathymetry can significantly enhance abyssal T‐waves across a broad frequency range. Also, observed T‐waves from repeating earthquakes in the Romanche, Chain, and Blanco transform faults exhibit remarkably high repeatability. Given the dynamic nature of sea surface roughness and internal waves, the highly repeatable T‐wave arrivals further support the seafloor scattering as the primary mechanism. The dominance of seafloor scattering makes abyssal T‐waves useable for constraining ocean temperature changes, thereby greatly expanding the data spectrum of SOT. Our observations of repeating abyssal T‐waves in the Romanche and Chain transform faults could provide a valuable data set for understanding Equatorial Atlantic warming. Still, further investigations incorporating high‐resolution bathymetry are warranted to better model abyssal T‐waves for earthquake parameter estimation.

Multipath Characteristics of Orbital Angular Momentum Vortex Electromagnetic Radio Waves Over an Infinite Ground Plane

In this paper, the effect of an infinitely sized ground plane on the orbital angular momentum (OAM) vortex electromagnetic (EM) radio waves is investigated. Although the effect of an infinite ground on OAM wave propagation and communication has already been numerically examined in the literature using the method of moments (MoM), this situation needs to be examined analytically and theoretically derived final form expressions need to be obtained. The multipath characteristics of OAM waves in a superconducting ground plane are theoretically presented considering both horizontal and vertical polarization conditions. In addition to direct radiation to an observation point in the far-field from the array antenna, many reflected radiations from the ground plane are also transmitted. The most fundamental reflected radiation is analyzed over a uniform circular array (UCA), adopting electromagnetic image theory. Furthermore, the transmitted field expressions obtained by considering both the circular array parallel to the ground plane and the circular array upright to the ground plane are formulated in a general analytical form for an OAM wave on a superconducting ground plane. In addition, numerical simulations are applied to exemplify the properties of OAM waves in the superconducting ground plane, unlike the isolated medium.

Bluestein–Gulyaev(B-G) waves in a piezo-thermoelastic half-space in the context of modified multi-phase-lag theory

In the years 1968–69, Bluestein and Gulyaev discovered a new kind of surface wave in a piezoelectric material known as B-G wave after their name. Although it was discovered in few decades ago, but till now, no work has been done related to B-G wave propagation based on modified multi-phase-lag theory. In the present work, the authors have investigated the propagation behavior of Bluestein-Gulyaev-type waves in a piezo-thermoelastic half-space in the context of modified multi-phase-lag theory. The normal mode technique is employed to obtain the principal variables, for example, displacements, temperature, electric potential, electric displacements, and thermo-mechanical stresses. The boundary conditions are adopted in such a way that the upper surface of the piezo-thermoelastic half-space is stress free and the half-space is implicated by a perfectly conducting electrode that is grounded (i.e., electrically short conditions at the free surface). Based on these boundary conditions, secular equations are derived for the proposed model. Some special cases have also been discussed, and it is found that the secular equation is in well-agreement with the pre-established thermoelasticity theory. Moreover, some analyses are made to highlight the important peculiarities of the problem. The mathematical framework of the present study is momentous for both theoretical and practical expositions for temperature sensors and piezoelectric surface acoustic wave (SAW) devices. Also present study helps the researchers who are engaged on this domain.

2D Sedimentary structures at the southeast margin of the Tarim Basin, China, constrained by love wave ambient noise tomography

Summary Imaging the detailed structure of sedimentary basins is crucial for natural resource exploration and essential for better analysis and correction of sediment responses when studying deeper interior earth structures using seismic data. In the Tarim Basin, previous studies on the sedimentary structures are mostly obtained by active-source seismic surveys, which can provide high-resolution underground interface information but are highly costly or environmentally unfriendly. In this paper, ambient noise tomography, an efficient and economical method based on background vibration, is employed to construct the sedimentary velocity structure at the southeast margin of the Tarim Basin. Based on ambient noise data collected from a linear dense short-period seismic array, we extract Love wave signals from T-T component cross-correlation functions (CCFs) and measure Love wave dispersion curves at a period band of ∼0.3–11.5 s. Then, we utilize a one-step direct surface wave tomography method to image a fine 2D sedimentary shear wave velocity structure with a depth reaching 10 km. Our results reveal a clear layered sedimentary structure, the paleo Tadong uplift, and the thrust Cherchen fault. Our study provides reference sedimentary velocity models for the southeastern Tarim Basin, focusing on depths shallower than 10 km. This model is intended to serve as crucial input for studies requiring detailed shallow sedimentary velocity data. Moreover, our research demonstrates that the application of the ambient noise tomography method with dense arrays has great potential for enhancing resource exploration efforts in sedimentary basins.

Simulation and Experimental Research of V-Crack Testing of Rail Surfaces Based on Laser Ultrasound

Rail surface cracks are widespread damage that can lead to uneven surfaces of railheads and affect traveling safety. Non-destructive testing is needed to inspect rails regularly to ensure the normal operation of railroads. This paper proposes a laser ultrasonic testing method combining variational mode decomposition and diffractive Rayleigh wave time-of-flight to detect tiny cracks on the rail surface quantitatively. The finite element method was combined with experiments to simulate and experimentally investigate cracks of different sizes numerically. In the numerical simulation, the location of the crack was determined by B-scan. Afterward, the interaction between various types of ultrasound and cracks was comparatively analyzed, and the crack size was quantitatively characterized using useful information from the ultrasound signals. The results show that the time-of-flight method can detect arbitrary cracks with low error. Therefore, the experimentally acquired ultrasound signals used the time difference between the diffracted Rayleigh wave and other ultrasound waves to detect the crack information quantitatively. The variational mode decomposition method was used to separate the ultrasonic signals and extract the best surface wave modes to improve the signal-to-noise ratio. The results show that the combination of variational mode decomposition and time-of-flight method can effectively detect the size of cracks.

A new method for enhancing signatures of ocean surface waves in nautical X-band radar images

Nautical X-band radars are used to continuously monitor large ocean surface areas with high temporal and spatial resolution. The signatures of ocean surface waves in nautical X-band radar images are typically present as straight or curved stripes with distinct directional and frequency characteristics. Curvelet transform (CT) is a multi-resolution technique with the capability of locational and directional resolving. This study presents a new method for enhancing the signatures of ocean surface waves in nautical X-band radar images. A radar image is decomposed at different scales, directions, and locations using forward CT. The surface wave signals are distributed in the curvelet coefficient (CC) of certain directions and scales. The signals of surface waves are extracted by retaining the CCs in specific directions and scales, whereas the CCs in other directions and scales are all set to zero. Wave signatures are enhanced by adding the extracted signals back to the original image. The proposed method is also feasible for enhancing signatures of surface waves in synthetic aperture radar or optical remote sensing images.

Continuous evolution of Fermi arcs in a minimal ideal photonic Weyl medium

Propagation properties of electromagnetic waves in an optical medium are mainly determined by the contour of equal-frequency states in k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\boldsymbol{k}}$$\\end{document}-space. In photonic Weyl media, the topological surface waves lead to a unique open arc of the equal-frequency contour, called the Fermi arc. However, for most realistic Weyl systems, the shape of Fermi arcs is fixed due to the constant impedance of the surrounding medium, making it difficult to manipulate the surface wave. Here we demonstrate that by adjusting the thickness of the air layer sandwiched between two photonic Weyl media, the shape of the Fermi arc can be continuously changed from convex to concave. Moreover, we show that the concave Fermi-arc waves can be used to achieve topologically protected electromagnetic pulling forces over a broad range of angles in the air layer. Our finding offers a generally applicable strategy to shape the Fermi arc in photonic Weyl media.

Numerical Analysis of Debris Cloud Formation in UHMWPE Wavy Plates during Hypervelocity Impact

This paper presents and analyses the numerical results of hypervelocity impact against ultra-high molecular weight polyethylene (UHMWPE) plates with four different surface wave profiles. UHMWPE wavy plates (WP) are intended to be used in Whipple Shield bumper plate, which is of paramount importance for space vehicles against micro-meteorite and orbital debris (MMOD) impact protection. Numerical work was carried out as a hybrid combination of smoothed particle hydrodynamics (SPH) and finite element modelling (FEM). Circular plates were subjected to hypervelocity impact of a spherical aluminium projectile travelling at 3000 m/s. The outcomes of the simulations were analysed in terms of debris cloud generation, projectile fragmentation, and impact energy dissipation performance of wavy plates, and compared with a conventional flat counterpart. Results of this study indicate that surface wave profile has a clear positive influence in terms of hypervelocity impact protection performance.

Long-term tracking for high-frequency surface wave radar based on heading constraint filtering combined ELM

Abstract Aiming at the problem of low measurement resolution and poor tracking accuracy in High-frequency surface wave radar (HFSWR) tracking field, a tracking method that combines the heading constraint filter and Extreme Learning Machine (ELM) is proposed. Compared with the existing research, the innovation of this study lies in proposing a two-stage tracking method based on the short-term stable state of the target, and similarity of long-term trajectory. Firstly, the heading constraint information is introduced into the estimator and improve the estimation accuracy. In multi-target tracking scenarios, many tracklets can be obtained. Then, the ELM learns robust features of tracklets to achieve the trajectory segment classification from the same target. This method can be widely applied to long-term tracking of cargo or passenger ships with fixed destinations, significantly improving tracking performance by utilizing implicit domain knowledge without additional information. The actual data of this paper comes from HFSWR on Bohai Bay. Both the simulation and actual measurement experiments show that the proposed cascaded tracking method achieves long-term continuous tracking, and generates more complete trajectories. Moreover, the proposed Extended Kalman filter based on pseudo-measurement and intercept parameters (IPM-EKF) exhibits better tracking stability and accuracy in limited scan steps. This study provides new ideas and methods for improving the tracking performance of special targets in the HFSWR field by utilizing motion features.

Real-time phase-resolved ocean wave prediction in directional wave fields: Second-order Lagrangian wave models

The Improved Choppy Wave Model (ICWM) was established to achieve a second-order Lagrangian expansion of surface waves. The second-order Lagrangian nonlinear interaction terms were found to be negligible and were therefore discarded. However, these interactions in directional wave fields remained unexplored. ICWM was successfully used, especially for floating offshore wind turbines, but it was noted that its accuracy in predicting directional sea states needed improvement. Hence, we formulated the Complementary ICWM (CICWM) with the nonlinear terms for free surface elevation in directional waves. Detailed formulations for data assimilation and wave propagation were provided, enabling real-time wave forecasting for directional seas using a simplified assimilation method. Comparing the model performances against tank-scale experiments showed that CICWM enhances the surface elevation description in directional seas. Ultimately, it was confirmed that the second-order Lagrangian model can reduce the prediction error of the linear wave model by 90% in directional seas for the experimental setups and sea states investigated in this study.

Shallow crustal structure of the northern Longmen Shan fault zone revealed by a dense seismic array with ambient noise analysis

The Longmen Shan (LMS) fault zone located in the southwest of China is not only the boundary tectonic zone of the Tibetan Plateau and South China block, but also an important part of the north–south seismic belt of China. To investigate the detailed crustal structure of the LMS fault zone, we deployed a dense seismic array of 151 short-period temporary stations in its northern section from March 16 to April 6, 2023. Continuous vertical component ambient noise waveforms recorded by these stations were cross-correlated for all station pairs, enabling the extraction of Rayleigh wave phase velocity dispersion curves across periods ranging from 0.5 s to 6 s. We then inverted these data to derive the crustal shear wave velocity using direct surface wave tomography. Meanwhile, a linear sub-array consisting of 54 stations and crossing the surface rupture of the 2008 Wenchuan earthquake was used to image the fault structure by applying the Transmitted Surface Wave Reverse Time Migration method (TSW-RTM). The ambient noise tomography results show that strong lateral heterogeneity exists in the shallow crust in the study area, with a high shear velocity in the northwest and a low shear velocity in the southeast. The low shear velocity is generally distributed between the Yingxiu-Beichuan fault (YBF) and the Guanxian-Jiangyou fault (GJF). The results of TSW-RTM indicate that the Wenchuan-Maoxian fault (WMF) and the YBF are both characterized with a steep dip to the northwest. Our results could serve as the important basis for the study of segmentation characteristics of the LMS fault and seismic hazard preparation and mitigation.

Optimal reconstruction of water-waves from noisy pressure measurements at the seabed

We consider the problem of recovering the surface wave profile from noisy bottom pressure measurements with (a priori unknown) arbitrary pressure at the surface. Without noise, the direct approach developed in Clamond and Labarbe (2023) provides an effective way to recover the sea surface. However, the assumption of analyticity for the measured pressure renders this method inefficient in the presence of noise. In order to address this issue, we introduce here an optimisation procedure based on the minimisation of a distance between a recovered bottom pressure and its measurement. Such method proves to be well-designed to handle perturbed signals. We illustrate the effectiveness of this approach in the recovery of gravity-capillary waves from unfiltered noisy data.

Focusing Monochromatic Water Surface Waves by Manipulating the Phases Using Submerged Blocks

Focusing Monochromatic Water Surface Waves by Manipulating the Phases Using Submerged Blocks

Investigating surface and internal waves and viscosity effects in two-layer fluids with a streamlined moving body using fully nonlinear simulation and experiment

Waves generated by a moving submerged moving body were analyzed in a two-layer density fluid. The experiments were performed in a two-dimensional towing tank and compared to the numerical results from a two-dimensional, fully nonlinear numerical towing tank (NTT) based on potential flow. The experimental conditions were determined by the relationship between the depth-dependent Froude number and the critical Froude number in baroclinic mode. The study was performed with various body velocities, changing the upper and lower fluid depth while maintaining the total water depth. An artificial damping coefficient was applied to the entire free surface and interface boundary condition to simulate the viscosity effect of the fluid interface. When the baroclinic mode was dominant, internal precursor soliton waves and depression waves were similar to the experimental results with strong nonlinearity. In contrast, the trailing waves were significantly different from the experimental results without applying an artificial damping scheme. A comparison with the experimental data showed that the effects of the fluid viscosity can be simulated with an appropriate damping coefficient. As the body velocity increases, the depressed or rising waves associated with the baroclinic mode are mixed with the trailing waves of the barotropic mode. As the depth of the upper fluid decreases, the characteristics of the baroclinic mode decrease, and the barotropic mode becomes dominant under the same velocity conditions.

Mechanism of enhanced impulse and entrainment of a pulsed jet through a flexible nozzle

The present experimental study shows that a nozzle with optimal flexibility can enhance the impulse and entrainment of a pulsed jet. Near the nozzle exit, vortex rings emanating from the flexible nozzle move faster because of the timely release of the elastic energy (stored during the expansion) to the jet, which is maximized at the structural stiffness that needs to be optimally tuned to the jet acceleration. The total circulation, hydrodynamic impulse and entrained fluid volume are enhanced substantially. Interestingly, we find that the same condition for optimal flexibility to maximize the hydrodynamic impulse and circulation of the primary vortex ring of the continuous jet (Choi & Park, J. Fluid Mech., vol. 949, 2022, A39) holds universally for the pulsed jet, indicating that abrupt jet termination is irrelevant to the impulse augmentation mechanism. Compared to the rigid counterpart, increments of the impulse ( ${\sim }400\,\%$ ) and entrainment ( ${\sim }220\,\%$ ) of a pulsed jet in the present study are considerably larger than those ( $200\,\%$ and $50\,\%$ , respectively) in a continuous jet from previous studies, which is attributed to the significant suppression of negative pressure at the nozzle exit by the collapsing motion of the flexible nozzle in the phase with the jet-driven upstream propagation of the surface wave on the nozzle. This universal mechanism provides a guideline for a novel jet propulsor using a flexible nozzle, for example, for small-scale underwater robots.

Assessment of seismic station performance in north Chhattisgarh, India: a comprehensive ambient noise analysis

A new network of 16 broadband seismic stations is operational in the northern Chhattisgarh region to monitor the seismicity arising in the otherwise seismically quiescent zone. Ambient noise is comprehensively analyzed to evaluate station performance and validate the data quality. Power spectral densities are computed for all stations, comparing ambient noise levels against global limits for data from November 2022 to December 2023. Results indicate that noise levels consistently fall within global noise limits. The study emphasizes the pronounced effect of instrumental tilt on the horizontal components of broadband seismometers. Spatial variation of ambient noise levels across various period bands of the noise spectrum highlights the contribution of diverse noise sources such as anthropogenic activities, surface waves, body waves, and barometric effects. Seasonal variations in short-period, microseism, and long-period bands reveal temporal variation of noise levels. Diurnal variation in the short-period band indicates a prominent effect of cultural noise. Furthermore, the proximity of seismic stations to major mining areas induces high noise levels in the very short-period band during blasting activities compared to non-blasting periods. Our study thus explores the variability of the ambient noise environment while validating the robustness and stability of the seismic installation across the study region.

Effects of nonthermality on dust-acoustic surface waves with dust rotation

Abstract Dust Acoustic Surface Waves (DASWs) real frequency and group velocity are investigated for semi-bounded dusty plasma whose electrons and ions are modeled by Cairn s Distribution Function (CDF) while massive particles i.e. dust are treated Maxwellian. Kinetic approach based on Vlasov-Poisson s set of equations is used for the derivation of plasma dispersion relation. It is observed that in the presence of rotational parameter r and the variation of nonthermal index α affect both real frequency and group velocity of the wave significantly. This study has wide astrophysical applications.