Search Results (244)

Pipelines are extensively used in offshore equipment. Accurate and non-destructive measurement of hoop stress conditions within pipes is critical for ensuring the integrity of offshore structures. However, the existing technology to measure the hoop stress of the pipeline needs to planarize the surface of the pipeline, which greatly limits the detection efficiency. This study proposes a method for pipeline hoop stress measurement using a planar longitudinal critically refracted (LCR) probe, based on correcting LCR wave-propagation paths, which solves the problem of pipeline planarization in pipeline hoop stress measurement. First, a linear relationship between stress variations and ultrasonic time-of-flight changes in the material was established based on the acoustoelastic effect. Finite element analysis was then used to construct an acoustic simulation model for the hoop direction of the pipeline. Simulation results showed that LCR waves propagated within a wedge as quasi-plane waves and, upon oblique incidence into the pipeline, traveled along the chordal direction. Furthermore, using ray tracing methods, a mapping relationship between the pipeline geometry and the ultrasonic propagation path was established. Based on this, the LCR pipeline hoop stress measurement (LCR-HS) method was proposed. Finally, a C-shaped ring was employed to verify the measurement accuracy of the LCR-HS method. Experimental results indicated that the measurement error decreased with increasing pipe diameter and fell below 8% when the diameter exceeded 400 mm. This method enables precise measurement of hoop stress on curved surfaces by revealing the hoop propagation behavior of LCR waves in pipelines. The findings provide a technical reference for evaluating pipeline stress states, which is of significant importance for assessment of pipeline integrity. Full article

In optical one-dimensional grating-on-layer planar structures, an optical resonance occurs when the incident light wave becomes phase-matched to a leaky waveguide mode excited in the layer underneath the grating by an appropriate tuning of the grating periodicity. Changing the refractive indices of the grating’s constituents, and/or thickness, changes the resonance frequency. In the case of a two-dimensional grating atop such a smooth layer, a similar and also cavity-mode resonance can occur. This idea has straightforward usage in diverse optical sensor applications. In this study, a novel guided-mode resonance sensor design for detecting glucose and hemoglobin in minute concentrations at a wide range of incidence angles is presented. In this design, materials of the grating, such as a polymer and cesium-lead halide with a perovskite crystal structure, are examined, which will allow flexible, low-cost fabrication by soft-lithography/imprint-lithography methods. The sensitivity, figure of merit, and quality factor are reported for one- and two-dimensional grating structures. The simulations performed are based on rigorous coupled-wave analysis. Optical resonance quality factor of ∼$5·{10}^5$ is achieved at oblique incidence for a structure comprising a one-dimensional grating etched in a poly-vinylidene chloride layer atop a silicon nitride waveguide layer on a substrate. Record values of the above-noted characteristics are achieved with a synergetic interplay of the materials, structural dimensions, incidence angle, polarization, and grating geometry. Full article

Interference caused by multiple reflections is a critical issue in transmission measurements using continuous wave (CW) terahertz and sub-terahertz radiation. This study proposes a practical method to reduce interference effects and improve the stability of transmittance measurements. By deriving analytical expressions for interference patterns under both normal and oblique incidence conditions, we demonstrate that oblique incidence simplifies the interference behavior and allows the reliable extraction of transmittance values from maximum and minimum signal intensities. Using a 95 GHz CW oscillator (Model SFD-753114-103-10SF-P1, Eravant, Torrance, CA, USA) and a 1 mm-thick PET sample, we conducted transmission measurements while varying the detector position. The derived method enabled the calculation of interference-free transmittance values that were consistent across different sample positions. This approach offers a practical technique for material characterization, especially in applications such as nondestructive testing and plastic recycling. Full article

The typical structure of an oblique detonation wave (ODW) consists of a leading shock wave followed by a coupled shock-flame complex. The distance from the leading shock’s originating point to the ignition onset is referred to as the induction length. This work numerically studies the induction length effect using a two-step induction-reaction kinetic model. Results reveal that the induction length governs the transition pattern of ODWs. By testing four distinct induction lengths, four ODW regimes are identified, including a prompt ODW, a delayed smooth ODW, a delayed abrupt ODW, and a delayed abrupt ODW with an upstream triple point in oscillatory motion. The mechanisms behind these regimes are analyzed in detail. Additionally, hysteresis is observed when the induction length decreases from a larger value, demonstrating that this phenomenon can be influenced by the kinetic process. Full article

Taking the segmented utility tunnel crossing f5 ground fissures in Xi’an Xingfu forest belt as the research object, this paper investigates the acceleration response and the variation of displacement and stress of the segmented utility tunnel under the El-Centro seismic wave through 3D finite element simulation. The results show that under the orthogonal condition, the peak acceleration of foot wall soil is greater than that of hanging wall soil; conversely, under oblique loading, the hanging wall exhibits higher peak acceleration. In both loading conditions, the peak soil acceleration initially increases and then decreases with depth, while the amplification effect weakens as depth increases. Furthermore, the seismic response and deformation of the tunnel are more pronounced under oblique loading than under orthogonal loading. This study offers quantitative guidance for the seismic design of segmented utility tunnels crossing ground fissures. Full article

Wave deformation and sediment transport nearest the shoreside are among the main reasons for sand erosion and beach profile changes. In particular, identifying the areas of incident-wave breaking and longshore current generation parallel to the shoreline is important for understanding the morphological changes of coastal beaches. In this study, a two-phase incompressible flow model along with a sandy sloping topography was employed to investigate the wave deformation and longshore current generation areas in a circular wave basin model. The finite volume method (FVM) was implemented to discretize the governing equations in cylindrical coordinates, the volume-of-fluid method (VOF) was adopted to differentiate the air–water interfaces in the control cells, and the zonal embedded grid technique was employed for grid generation in the cylindrical computational domain. The water surface elevations and velocity profiles were measured in different wave conditions, and the measurements showed that the maximum water levels per wave were high and varied between cases, as well as between cross-sections in a single case. Additionally, the mean water levels were lower in the adjacent positions of the approximated wave-breaking zones. The wave-breaking positions varied between cross-sections in a single case, with the incident-wave height, mean water level, and wave-breaking position measurements indicating the influence of downstream flow variation in each cross-section on the sloping topography. The cross-shore velocity profiles became relatively stable over time, while the longshore velocity profiles predominantly moved in the alongshore direction, with smaller fluctuations, particularly during the same time period and in measurement positions near the wave-breaking zone. The computed velocity profiles also varied between cross-sections, and for the velocity profiles along the cross-shore and longshore directions nearest the wave-breaking areas where the downstream flow had minimal influence, it was presumed that there was longshore-current generation in the sloping topography nearest the shoreside. The computed results were compared with the experimental results and we observed similar characteristics for wave profiles in the same wave period case in both models. In the future, further investigations can be conducted using the presented circular wave basin model to investigate the oblique wave deformation and longshore current generation in different sloping and wave conditions. Full article

We propose a single-phase chiral elastic metamaterial capable of simultaneously exhibiting negative effective mass density and negative bulk modulus in the ultrasonic frequency range. The unit cell consists of a regular hexagonal frame connected to a central circular mass through six obliquely oriented, slender aluminum beams. The design avoids the manufacturing complexity of multi-phase systems by relying solely on geometric topology and chirality to induce dipolar and rotational resonances. Dispersion analysis and effective parameter retrieval confirm a double-negative frequency region from 30.9 kHz to 34 kHz. Finite element simulations further demonstrate negative refraction behavior when the metamaterial is immersed in water and subjected to 32 kHz and 32.7 kHz incident plane wave. Equifrequency curves (EFCs) analysis shows excellent agreement with simulated refraction angles, validating the material’s double-negative performance. This study provides a robust, manufacturable platform for elastic wave manipulation using a single-phase metallic metamaterial design. Full article

Using numerical simulations, this study investigated the seismic response of concrete dams when subjected to near-fault obliquely incident P waves. For comparison, several near-fault pulse-like movements with different motion parameters were selected and decomposed into non-pulse residual components. A seismic input procedure for P wave oblique incidence was developed and verified based on the viscous-spring artificial boundary theory. A finite element model of a concrete dam system was used for nonlinear time history analyses. The damage and displacement responses were analyzed under pulse-like and non-pulse motions with incident angles varying from −90° to 90°. The response differences induced by the pulse characteristics incident direction were examined. The relationship between the seismic parameters and response indices was also determined to obtain the optimal seismic parameter describing the variation under different incident conditions. Moreover, the coupled effect of the pulse feature and oblique incidence on the dynamic response and seismic behavior was examined. Finally, a nonlinear three-dimensional predictive model was proposed based on the optimal seismic parameter S_a(T₁) and incident angle, exhibiting high correlation and accuracy. The results demonstrated that incident angles between 60° and 75° (with higher spectral acceleration values) intensified the dam damage and vibration when subjected to the oblique near-fault P waves, a crucial discovery for improving the seismic design and safety measure of concrete dams located in regions prone to near-fault seismic hazards. Full article

The theory of orbital forcing as formulated by Milankovitch involves the mediation by the advance (retreat) of ice sheets and the resulting variations in terrestrial albedo. This approach poses a major problem: that of the period of glacial cycles, which varies over time, as happened during the Mid-Pleistocene Transition (MPT). Here, we show that various hypotheses are called into question because of the finding of a second transition, the Early Quaternary Transition (EQT), resulting from the million-year period eccentricity parameter. We propose to complement the orbital forcing theory to explain both the MPT and the EQT by invoking the mediation of western boundary currents (WBCs) and the resulting variations in heat transfer from the low to the high latitudes. From observational and theoretical considerations, it appears that very long-period Rossby waves winding around subtropical gyres, the so-called “gyral” Rossby waves (GRWs), are resonantly forced in subharmonic modes from variations in solar irradiance resulting from the solar and orbital cycles. Two mutually reinforcing positive feedbacks of the climate response to orbital forcing have been evidenced: namely the change in the albedo resulting from the cyclic growth and retreat of ice sheets in accordance with the standard Milankovitch theory, and the modulation of the velocity of the WBCs of subtropical gyres. Due to the inherited resonance properties of GRWs, the response of the climate system to orbital forcing is sensitive to small changes in the forcing periods. For both the MPT and the EQT, the transition occurred when the forcing period merged with one of the natural periods of the climate system. The MPT occurred 1.25 Ma ago, when the dominant period shifted from 41 ka to 98 ka, with both periods corresponding to changes in the Earth’s obliquity and eccentricity. The EQT occurred 2.38 Ma ago, when the dominant period shifted from 408 ka to 786 ka, with both periods corresponding to changes in the Earth’s eccentricity. Through this paradigm shift, the objective of this self-consistent approach is essentially to spark new debates around a problem that has been pending since the discovery of glacial–interglacial cycles, where many hypotheses have been put forward without, however, fully answering all our questions. Full article

Rip currents at featureless beaches (i.e., beaches lacking sandbars or channels) are often hydrodynamically controlled, exhibiting intermittent and unpredictable behaviors that pose significant risks to recreational beach users. This study assessed occurrences of rip currents under a range of idealized morphology configurations and hydrodynamic wave forcing parameters using a wave-resolving Boussinesq-type model. Numerical experiments revealed that rip currents with durations on the time scale of 10 min are generated in the forms of vortex pairs, intensified eddies, mega-rips, and eddies shedding from longshore currents. In general, the key conditions that promote rip current formation at featureless beaches include shoreline curvature, headlands, moderately mild beach slopes (e.g., 0.02–0.03), normal or near-normal wave incidence, and large wave heights. Most importantly, this study highlights inherent uncertainties in rip current occurrences, particularly under conditions usually perceived as low risk: low wave heights, short wave periods, oblique wave incidence, and straight shorelines. These conditions can lead to transient rip currents and pose an unexpected hazard that coastal communities should be aware of. Full article

In this paper, we design an ultra-thin broadband transparent absorber based on indium tin oxide (ITO) film, and we choose polymethyl methacrylate (PMMA) high-transmittance dielectric sheet instead of the traditional dielectric sheet and polyethylene glycol terephthalate (PET) as the ITO film substrate. Simulation results indicate that the absorber achieves more than 90% absorption for positively incident electromagnetic waves in the broadband range of 5–21.15 GHz with a fractional bandwidth (FBW) of 123.5% and a thickness of 6.3 mm (0.105 λ_L, where λ_L is the wavelength at the lowest frequency). Meanwhile, this paper introduces the interference theory to explain the broadband absorption mechanism of the absorber, which makes up for the defect that the equivalent circuit model (ECM) method cannot analyze the oblique incidence electromagnetic wave. This paper also compares the HFSS simulation results, ECM theoretical values, and interference theoretical values under positively incident electromagnetic waves to clarify the advantages of interference theory in the design of wave absorbers. Full article

An analytical hydroelastic model formulation in three-dimensional and oblique wave cases is developed to analyze the dynamic response of a horizontal, floating elastic plate subject to wave-current interaction under linearized small-amplitude wave theory. The floating elastic plate is moored to the bottom bed and free to the channel walls. Green’s function’s technique is utilised to determine the dispersion relation in 3D, and the series form of Green’s function in different water depths is derived in the oblique wave case. Further, the comparative analysis of phase and group velocities for different wave angles, between the present the existing models, is discussed. The derived dispersion relation is used in the solution by applying the geometrical symmetry velocity decomposition method. The present theoretical results of wave quantities are validated with the recently published and existing numerical hydroelastic model. A comparative analysis revealed a 1.7% difference between the present model and the existing hydroelastic models, and a 7.7% difference when compared to the model’s limiting cases. Several numerical results of the wave quantities, wave force, and vertical displacements are conducted to investigate the influence of current velocity on the hydroelastic response in three dimensions. It has been noted that the value of reflection coefficient diminishes for larger values of current velocity and the vertical displacement correspondingly becomes greater. This analysis will inform the design of elastic plate-based wave energy converters and breakwaters by clarifying how current loads affect the hydroelastic of a floating elastic plate with an oblique angle and three dimensions. Full article

A causal electromagnetic (EM) metasurface is backed by a lossless substrate and partially absorbs obliquely incoming rays. The integral of the absorbed power along the entire frequency axis is analytically evaluated, and the obtained sum rules indicate the global absorption by such a generic configuration. The beneficial influence of the plasma frequency and damping factor on the total absorbance score as well as the opposite effect of the angle of excitation, is noted. An overall lossless behavior at the incidence direction where the propagating waves into the substrate turn into evanescent is identified, once the magnetic field is parallel to the interface. The reported results can be useful in the tailoring of spectrally dependent absorption by a whole class of planar structures and, accordingly, in the forward and inverse design of lossy photonic metasurface setups. Full article

Metasurfaces, as subwavelength planar structures, offer unprecedented electromagnetic wavefront manipulation capabilities. However, most existing focusing metasurfaces operate in a single polarization mode, support only one focusing function, or rely on complex multi-unit configurations, limiting their versatility in practical applications. This study proposes a dual-polarization multiplexed transmissive focusing metasurface operating at 5.8 GHz. Through theoretical analysis and full-wave simulations, the electromagnetic response of the metasurface unit is systematically investigated. To overcome the limitations of conventional transmissive units, an anisotropic low-profile unit is designed using a hybrid stacking strategy that combines dielectric substrates and an air layer, achieving a compact profile of only 0.16λ. This unit achieves 360° phase modulation with a transmission magnitude exceeding 0.85 while being lightweight and cost-effective. Based on the unit, three metasurface arrays are developed to achieve various focusing functions, including single-point offset focusing, dual-point focusing, and multi-focal energy-controlled focusing, offering over 15% operational bandwidth and maintaining satisfactory performance under a 25° oblique incidence, with respective efficiencies of 35.59%, 25.11%, and 33.42%. This work provides a novel solution for multifunctional focusing applications, expanding the potential of metasurfaces in wireless communication, wireless power transfer, and beyond. Full article

With the rapid development of 5G communication technology, there is an increasing demand for high-performance antennas and beam control technologies, making the development of novel metamaterial structures capable of precise electromagnetic wave manipulation a current research hotspot. This paper presents a coding metasurface specifically designed for 5G communication applications, operating at a frequency of 3.5 GHz. The design employs a unique annular metasurface unit structure capable of achieving both single-beam and dual-beam functionalities. Through convolution operations, precise control over the reflection angle is achieved, with an adjustable range from 51.5° to 17.5° and a resolution of 10°. This design overcomes the inherent limitations of traditional gradient coding methods, providing a comprehensive framework for wide-angle reflection control in metasurface design. The research results demonstrate that the coding metasurface can effectively control the reflection direction of electromagnetic waves at 3.5 GHz, exhibiting dual-polarization modulation capabilities and maintaining stable performance under oblique incidence conditions within 20°. Experimental validation confirms the beam control functionality of the design in real-world environments, highlighting its potential to enhance signal reception sensitivity and transmission efficiency in 5G wireless communications. This work opens new avenues for research in reconfigurable and intelligent metasurfaces, with potential applications extending beyond 5G to future 6G networks and Internet of Things (IoT) systems. Full article