Incident Wave Research Articles

Метаповерхности Патчаратнама-Берри с генерацией углового орбитального момента и комбинированным фазовым кодированием для широкополосного широкоугольного снижения ЭПР

The phase mechanism of a broadband wide-angle radar cross-section (RCS) reduction is examined, based on the use of non-absorbing Patcharatnam-Berry (PB) metasurfaces (MSs) with the generation of orbital angular momentum (OAM) and a combination of different phase profiles. MS unit cells contain a thin shielded single-layer substrate and meta-particles in the form of perforated rectangular patches with a coded rotation angle. The purpose of the work is to compare the scattering characteristics and scattered field cancelation efficiency for structural elements (modules) of a MS, consisting of the same number of meta-particles, but having different PB-phase profiles. A profile with an azimuthal gradient, which forms broadband scattering of vortex waves with OAM, profiles with radial and linear gradients and anomalous scattering, parabolic profiles with wide-angle scattering, and various combined phase profiles are analyzed. The purpose of the work is comparing the scattering characteristics. The MS modules scattering characteristics are studied using the HFSS (finite element method) for co-polarization and cross-polarization in the case of irradiation with a normally incident plane circular polarized wave. The simulation showed that the scattering diagrams of the co-polarized MS field in these cases have a funnel-shaped vortex character with an intense OAM minus the first order (the order of the OAM remains the same as for an MS with an azimuthal phase gradient). OAM generation significantly suppresses backscattering by co-polarization. The far-field phase in the vortex region depends not only on the azimuthal, but also on the meridional observation angles. The combination of OAM and parabolic profile increases the diffusion of broadband scattering, realizes a wider-angle scattering of the resulting field with a vortex opening angle of about 100° (at an average frequency of 14 GHz), which is important for RCS reduction.

Dynamic spin polarization in time domain for electron in single ferromagnetic-metal stripe device

One nanosized, horizontally-magnetized ferromagnetic-metal stripe, patterned on top of semiconductor heterostructure, is known as single ferromagnetic-metal stripe device. It is well established that, there is no spin polarization in this device, due to spin-independent transmission coefficient by an intrinsic symmetry. However, we demonstrate that the dwell time is closely related to electron spins owing to the interference between incidence and reflection waves. Therefore, electron spins can be separated in time domain, underlying dynamic spin polarization, that is, such a device can act as a temporal spin splitter.

Equilibrium configurations of line arrays with respect to the deviatoric mean drift forces

Monochromatic waves incident on an array of structures give rise to nonlinear, time-constant mean drift forces (MDFs). These forces depend on the array's spatial configuration; their magnitude and the direction is, in general, different for every structure in the array. If the spatial configuration of an array is not fixed, as is the case in arrays of individually anchor-moored structures, the time-constant differences in MDF on individual bodies can lead to a change in spatial configuration, which could, in turn, significantly affect both the first-order, time-harmonic response of the array, as well as the downwave component of the MDF. Here, we explore the dependency of these deviatoric forces on array configurations and on the frequency of the incident monochromatic waves. We consider configurations of line arrays (consisting of 2–5 vertical circular cylinders) that are described by 1 or 2 parameters, and we focus on the along-array component of deviatoric forces. Using multiple scattering computational simulations, we identify the array configurations in which the deviatoric drift forces are zero, and we discuss the stability of these equilibrium configurations with respect to class-preserving configuration perturbations. Both stable and unstable equilibria exist, but the relative number of unstable equilibria grows as the number of degrees of freedom of the configuration perturbations increases. Interestingly, the stable configurations experience a generally lower downwave mean drift force on the entire array than the unstable ones. Overall, the variations in the deviatoric and the downwave MDFs between equilibria are significant (on the order of the isolated body MDF).

Analytical solutions for hydrodynamic responses of arrays of floating truncated cylinders using multi-term Galerkin method and its application to a new wave energy converter device

In the context of linear water wave theory, the analytical solutions for the diffraction and radiation of a truncated cylinder array are developed in the presence of ambient incident waves. Each cylinder in the array can oscillate with five degrees of freedom (DOFs), i.e., surge, sway, heave, roll, and pitch. This paper adopts the multi-term Galerkin method to expand the fluid velocity at the interface of different regions into a set of basis functions containing Gegenbauer polynomials, which accurately and efficiently characterizes the cube root singularity of the fluid velocity near the edges of the truncated cylinders. Using the dynamic equilibrium equations, the amplitudes of each DOF of the cylinders in the array are solved. The analytical solution presented in this paper converges rapidly, and high-precision hydrodynamic response results can be obtained using just a few truncated terms (e.g., the upper bounds of m0 = 5 and p0 = 22 can yield results of five-figure accuracy). For the 4-cylinder array, under the same accuracy conditions (the error less than 1%), the computation time of the conventional method developed by Zeng et al. [“Hydrodynamic interactions between waves and cylinder arrays of relative motions composed of truncated floating cylinders with five degrees of freedom,” J. Fluids Struct. 115, 103785 (2022d)] based on the exact algebraic method [Kagemoto and Yue, “Interactions among multiple three-dimensional bodies in water waves: An exact algebraic method,” J. Fluid Mech. 166, 189–209 (1986)] is 3.9 times longer than that of the present method. As the number of cylinders increases, the advantage of the present method in terms of convergence speed becomes more apparent, e.g., for the 16-cylinder array, the conventional solution takes 6.3 times longer than the present solution. To extract wave energy more efficiently, a new 5DOF wave energy converter (WEC) device that can extract energy in 5DOFs is proposed. The present method is adopted to investigate the hydrodynamic performance of the 5DOF WEC arrays. Compared with the traditional 1DOF (heave) WEC, the 5DOF WEC can significantly improve the energy capture performance of arrays, especially in the high-frequency wave region.

Wave and Roller Transformation Over Barred Bathymetry

AbstractThe cross‐shore transformation of breaking‐wave roller momentum and energy on observed barred surfzone bathymetry is investigated with a two‐phase Reynolds Averaged Navier Stokes model driven with measured incident waves. Modeled wave spectra, wave heights, and wave‐driven increases in the mean water level (setup) agree well with field observations along transects extending from 5‐m water depth to the shoreline. Consistent with prior results the roller forcing contributes 50%–60% to the setup, whereas the advective terms contribute ∼20%, with the contribution of bottom stress largest (up to 20%) for shallow sandbar crest depths. The model simulations suggest that an energy‐flux balance between wave dissipation, roller energy, and roller dissipation is accurate. However, as little as 70% of the modeled wave energy ultimately dissipated by breaking was first transferred from the wave to the roller. Furthermore, of the energy transferred to the roller, 15%–25% is dissipated by turbulence in the water column below the roller, with the majority of energy dissipated in the aerated region or near the roller‐surface interface. The contributions of turbulence to the momentum balance are sensitive to the parameterized turbulent anisotropy, which observations suggest increases with increasing turbulence intensity. Here, modeled turbulent kinetic energy dissipation decreases with increasing depth of the sandbar crest, possibly reflecting a change from plunging (on the steeper offshore slope of the bar) to spilling breakers (over the flatter bar crest and trough). Thus, using a variable roller front slope in the roller‐wave energy flux balance may account for these variations in breaker type.

Numerical study on ultrasonic detection of cracks in metallic structures with variable cross-sectional thickness

The metal structures are widely used in aerospace engineering, especially in joints and spars. The safety of these parts is important to ensure the safe service of the whole structures. The ultrasonic wave is a traditional technique to detect cracks in metals. However, it is usually difficult to find all the cracks because of its difficulty in variable directions of the crack and the irregular shapes of the metals. This paper aims to address the challenge of detecting cracks in metallic structures with varying cross-sectional thicknesses using ultrasonic methods. The research investigates the behavior of ultrasonic longitudinal and transverse waves as they propagate through aluminum plates with variable cross sections. Additionally, it examines how cracks in different orientations influence these wave types. The theoretical analyses are performed which explore the reflection of oblique incidence waves and the diffraction of ultrasonic waves when they encounter semi-infinite cracks. Subsequently, numerical simulations are performed to validate the theoretical findings and to detect both horizontal and vertical cracks within metal plates of varying cross-sectional thicknesses. The findings indicate that both longitudinal and transverse waves are effective in identifying the location of damage caused by horizontal cracks. However, when it comes to vertical cracks, only transverse waves are successful in detecting their precise location. From the research of this paper, transverse ultrasonic wave is suggested to detect cracks in metal structures with irregular cross sections.

Extreme wave impacts on a suspended box above free surface

A systematic approach incorporating precision-controlled experiments and high-fidelity numerical simulations has been employed to delve deeper into the physics of extreme wave impact pressures. Using a suite of high-speed imaging and high-resolution pressure sensing techniques that are accurately synchronized with the wave generation, a consistent and well-correlated set of data providing details of the focusing incident wave front, flow velocities, and impact pressure time histories has been successfully obtained. The numerical simulations using a validated incompressible smoothed particle hydrodynamics (ISPH) provided further details that were not tractable in the experiments. Based on the results obtained, there were five broad impact scenarios identified, ranging from focusing crest impacts to plunging jet impacts with varying entrapped air. Among these impact types, the highest impact pressures were those associated with a focusing wave crest. It has been found that high impact pressures were correlated with a convergence of the horizontally impinging overturning crest and the vertical surge of the wall boundary water mass, but with the overturning crest impingement just ahead of the arrival of the wall boundary water mass, which in essence amounted to the impingement of a focusing wave front. Depending on the relative arrival times of the impinging crest and the wall boundary upsurge, the impact scenarios could vary from an up-slosh to a jet impingement with a clear entrapped air pocket, followed by a flip-through of the incident crest. For the scenario with the highest impact pressures, broadly classified as type II impact in this paper, the peak pressures could reach as high as 85ρC2, an order of magnitude higher than impact scenarios without the focusing effect, such as the scenario with a plunging jet impact with entrapped air (classified as types III and IV impact in this study). As the volume of entrapped air for this scenario was relatively small, the one-phase ISPH model used in this study was able to capture the peak pressure characteristics, including the peak pressure amplitudes. However, in scenarios with significantly highly entrapped air during impact, a two-phase model would be necessary.

Experimental investigation on gap resonance between two floating vessels

This paper explains the influence of gap resonance phenomena in floating vessels having unequal draughts. Two separate model configurations are considered here: one is a vessel having a shallow draught at the weather side (SW), and the other is a deep draught vessel that comes at the weather side. An experimental investigation was carried out in beam sea conditions, where the vessel could only move freely in the heave and roll directions. By beam sea, we mean the incident waves come at a right angle to the broadside of the vessels. Regular wave tests reveal that even though only a slight difference in the gap resonance frequency is observed for the two configurations, the wave amplification at resonance is 57% higher for SW. The reason for this behavior is explained using the instantaneous velocity and vorticity obtained from the particle image velocimetry analysis for a selected test case. Furthermore, the turbulent characteristics of the flow inside the gap for the configurations are compared at different time instances. The horizontal force acting on the vessels and motions (heave and roll) of the vessels in the beam sea condition are also reported in the study.

Active frequency-selective rasorber with wide range passband continuous tunability

In this paper, an active frequency-selective rasorber (AFSR) with a wide tunable range of passband windows is proposed. The proposed AFSR includes an absorption layer, a frequency selective layer, and an air spacer between them. The absorption layer is embedded with resistors to aid in the absorption of out-of-band unprofitable signals, and the frequency selective layer is designed to provide tunable transmission passbands through in-band beneficial signals. A design method for the AFSR embedded with varactors based on equivalent circuit model is proposed. Driven by an applied voltage, the transmission passband of the proposed AFSR can be shifted from 3.4 to 6.9 GHz. The absorption bandwidth covers from 6.4 to 14.1 GHz. In addition, the proposed AFSR exhibits stable performances up to 45° angle of incidence wave. The measurement results of the fabricated prototype are in good agreement with the simulation results. This work provides a feasible solution for flexible simultaneous regulation of radiation and scattering.

NEWTS1.0: Numerical model of coastal Erosion by Waves and Transgressive Scarps

Abstract. Models of rocky-coast erosion help us understand the physical phenomena that control coastal morphology and evolution, infer the processes shaping coasts in remote environments, and evaluate risk from natural hazards and future climate change. Existing models, however, are highly complex, are computationally expensive, and depend on many input parameters; this limits our ability to explore planform erosion of rocky coasts over long timescales (thousands to millions of years) and over a range of conditions. In this paper, we present a simplified cellular model of coastline evolution in closed basins through uniform erosion and wave-driven erosion. Uniform erosion is modeled as a constant rate of retreat. Wave erosion is modeled as a function of fetch, the distance over which the wind blows to generate waves, and the angle between the incident wave and the shoreline. This reduced-complexity model can be used to evaluate how a detachment-limited coastal landscape reflects climate, sea-level history, material properties, and the relative influence of different erosional processes.

Study of hydrodynamic characteristics in oscillating wave surge converter

In the realm of renewable energy, researchers worldwide have been paying close attention to developing the Oscillating Wave Surge Converter (OWSC) device. This device has the potential to harness the power of ocean waves and convert it into a reliable source of clean energy. Hydrodynamic characteristics are essential parameters in developing OWSC devices. Therefore, this research conducted a hydrodynamic study on the OWSC device with variations in ocean wave periods, including T= 1.5, 1.7, 1.9, 2.1, and 2.3. The Boundary Element Method (BEM) describes the interaction between sea waves and floating body structures. This method assumes incompressible, inviscid, and irrotational flow. A numerical approach is used as a calculation method followed by verification and validation to support the level of actualization. The research results showed that the incident wave caused the OWSC device to experience a deviation from its equilibrium position in the form of an oscillating flap inclination angle as a form of hydrodynamic characteristics. The sea wave period correlatedwith the rate of change in flap position over time, including the maximum deviation in the flap angle. As a power plant, the performance of the OWSC device can work at reasonably short-wave period intervals based on the device's ability to produce mechanical power. The highest average mechanical power was achieved in the T= 1.5 period of 34.49 Watts with an efficiency of up to 52.43%. The OWSC device requires a high intensity of wave energy in a short duration to generate optimal mechanical power. It is important to note that optimal mechanical power generation is crucial for the OWSC device to function effectively. Therefore, the device should be placed in a location where the wave energy intensity is consistently high.

Armor Damage On Groins Under Ship Wave Attack Using Field Data

The severity of damages to riverine structures, such as groynes or revetments, across German estuaries has increased in the past years due to the increase in the ship-induced loads. However, few studies can be found in the literature focused on the damage of rock slopes under ship wave attack. In this study, the field data of a rock-armored groyne (lateral slope 1/4 and rocks with nominal diameter Dn50»12.6cm and high density ρs=3.7t/m3) tracked for a year by Melling et al. (2020) is analyzed; the field campaign began after the structure was rebuilt and finished when the structure already presented severe damage. During this field campaign, the incident ship-induced primary waves and water levels were recorded, and laser scans of the groyne armor were taken. Using those field laser scans, damage curves along the life of the structure were derived. Also, ship data from the AIS was retrieved. Then, each increment of the damage (increment of the dimensionless eroded area, ΔSe) was related to a ship-wave event and a passing ship. The most significant variable to describe ΔSe was found to be the primary wave height Hp, while the best explanatory variables for Hp were the partial blockage factor, the ship length and width and the relative velocity of the ship. The shape of the dependence between these variables is also analyzed by pairs using copula space. A clear tail dependence is observed between several pairs. For instance, the pair ΔSe and Hp presents upper tail dependence, meaning that the high values of ΔSe and Hp are more correlated than the smaller ones. This implies that models more complex than Gaussian copula, which is commonly used in Coastal Engineering applications, might be needed to model the probabilistic dependence between the variables.

Low-Crested Structures In Front Of Rubble Mound Breakwaters

Climate adaptation of coastal structures has become more important due to climate change, resulting in sea level rise and increased wave loading for coastal structures with depth-limited wave conditions. If sea level rise causes wave loading that becomes too severe, one of the options is to reduce the wave loading before the waves reach the existing coastal structure (see for instance Van Gent, 2019, and Van Gent and Teng, 2023). This can be achieved by increasing the foreshore (e.g. sand nourishment) or by constructing a low-crested structure in front of the coastal structure. In this study the climate adaptation measure to add a submerged low-crested structure in front of an existing (emerged) coastal structure has been studied. Between the two structures, structure-induced wave set-up occurs. This structure-induced wave set-up has been studied based on wave flume tests. The effects of structure-induced wave set-up on wave transmission at the low-crested structures and the effects on wave overtopping at the emerged coastal structure were also measured and analyzed. To evaluate the performance of submerged low-crested structures Van Gent et al (2023) performed wave flume tests to examine wave transmission at various types of submerged low-crested structures, without an emerged structure behind the low-crested structures. For a submerged low-crested structure in front of an emerged coastal structure, the transmitted waves can be used as incident waves for estimates of wave overtopping at a rubble mound breakwater, using wave overtopping expressions described in Van Gent et al (2022). However, to verify whether the expressions for wave transmission and wave overtopping can be applied for submerged low-crested structures in front of rubble mound breakwaters, new physical model tests have been performed at Deltares. The new wave flume tests were performed with impermeable and permeable low-crested structures in front of impermeable and permeable emerged structures (see Figure 1 for permeable structure).

A Simplified Method for the Evaluation of Floating-Body Motion Responses over a Sloping Bottom

Recently, many floating renewable energy platforms have been deployed in coastal regions, where sloping bottoms are an important factor when evaluating their safety. In this article, a simplified method coupling an eigenfunction matching method (EMM) and a finite-depth Green’s function (FDGF) is developed to evaluate floating-body motion responses over a sloping bottom for which bathymetry is homogeneous in the longshore direction. We propose an extended EMM to create an incident wave model over the sloping bottom, thereby obtaining the Froude–Krylov (F–K) force and Neumann data on the wet surfaces of the floating body for the diffraction problem. An equivalent depth is introduced to account for the interaction between the sloping bottom and floating bodies when dealing with the diffraction and radiation problems. The accuracy of the present method is validated through a comprehensive comparison with numerical and/or experiment results for a liquefied natural gas (LNG) ship and a floating hemisphere from the literature. Generally, the present, simplified method can give predictions with sufficient accuracy.

An In-Band Low-Radar Cross Section Microstrip Patch Antenna Based on a Phase Control Metasurface

An in-band low radar cross section (RCS) microstrip patch antenna based on a phase control metasurface is proposed. As the size of the phase control metasurface changes, it will have different phase adjustments to the incident electromagnetic wave. Two kinds of phase control metasurfaces with a 90° reflection phase difference are arranged in a checkerboard configuration and loaded above a microstrip array antenna. The metal of the microstrip array antenna can fully reflect the electromagnetic wave, so the incident wave passes through the metasurface again and forms a reflected wave with a phase difference of 180° ± 37° when passing through the phase control metasurfaces of different sizes. Thus, the microstrip array antenna can achieve in-band RCS reduction. The metamaterial forms a transmission window in the microstrip patch array antenna band to maintain the radiation performance. Finally, a reasonable agreement is obtained between the measured and simulated results.

Hybrid Forecast System Of Overtopping With Infragravity Wave Included

The overtopping over a structure is related to the run up, which in turn depends mainly on the wave and the physical characteristics of the structure. However, it is known that there are other oscillations of longer periods (infragravity waves) which, when the incident wave is of the swell type and the product of storms, become relevant because they have a direct influence on the calculation of the overtopping. The aim of this study was to evaluate the non-hydrostatic version of the XBeach model using a one-dimensional scheme to simulate overtopping events. The model was forced in three different ways: free surface data collected in field, wave parameters representing by Hs and Tp, and directional energy spectra generated by an operational wave and infragravitational wave system (SO3). The main results show that XBeach is able to transfer wave energy at low frequencies along the beach profile. In addition, the XBeach model can be coupled with the directional spectra of energy from the operational system to propagate them into the swash zone and generate overtopping in advance. This could potentially serve as an operational overtopping tool to assist the relevant authorities in managing this issue.

Spinning spoof surface plasmons and their topological responses

Spoof surface plasmons (SSPs) mimic characteristics of optical surface plasmons in microwave and terahertz frequencies. Manipulating SSPs has attracted widespread attention for extending plasmon applications into the low-frequency range. In this Letter, we show that spinning SSPs can be excited on a twisted groove (TG) metallic cylinder by oblique incident waves. The incident angle of waves and the twist angle of the grooves play essential roles in manipulating the propagation orientation and the rotation direction of spinning SSPs (SSSPs). Finally, we discuss an application of the SSSPs in topological photonic systems. By periodically arranging the TG cylinders, we show that this spinning feature will lead to topologically non-trivial bands in such a photonic crystal, where the topologically protected edge modes arise near the boundary.

Directional Spectrum Estimation For Sea States Generated By The Single Summation Method

The influence of directional spreading of waves is significant for wave-induced loads, wave breaking and nonlinearity of the waves. For physical model testing performed at test facilities such as the Ocean and Coastal Engineering Laboratory at Aalborg University, it is crucial to validate if the test conditions match the target sea states by measurement and analysis of the generated directional wave field. Most of the existing methods assumes a double summation sea state to be present which is valid in the prototype. However, waves in the laboratory are usually generated by single summation. The current paper presents a method to analyse short-crested waves generated by the single summation method. Compared to similar methods oblique reflections are considered instead of only in-line reflections. The results show that the method successfully decomposes the incident and reflected wave fields in the time domain. Thus, for example the incident wave height distribution may be obtained. The sensitivity of the new method to additional reflective directions, noise, calibration errors and positional errors of the wave gauges was found small.

Mueller Matrix Polarizing Power

The transformation of the states of polarization of electromagnetic waves through their interaction with polarimetrically linear media can be represented by the associated Mueller matrices. A global measure of the ability of a linear medium to modify the states of polarization of incident waves, due to any combination of enpolarizing, depolarizing and retarding properties, is introduced as the distance from the Mueller matrix to the identity matrix. This new descriptor, called the polarizing power, is applicable to any Mueller matrix and can be expressed as a function of the degree of polarimetric purity and the trace of the Mueller matrix. The graphical representation of the feasible values of the polarizing power provides a general view of its main peculiarities and features. The values of the polarizing power for several typical devices are analyzed.

Four-channel near-field focusing metasurface lens based on frequency-polarization multiplexing

In response to the issue of traditional near-field focusing metasurfaces having a single working frequency band and limited focusing functionality, this paper proposes a four-channel focusing metasurface based on frequency-polarization multiplexing. Utilizing the principles of anisotropy and metasurface resonant phase, a metasurface unit composed of two sets of orthogonal resonators was designed. The designed units have independent transmission amplitude and phase at 15 GHz and 23 GHz, with the transmission phase of the two sets of resonators encoded in 2-bit and 1-bit based on phase differences of 90° and 180°, respectively. Based on the units, combined with the focusing principle of metasurface lenses and the principle of phase superposition, a four-channel near-field focusing metasurface lens was designed. The lens is composed of 20 × 20 units, measuring 200 × 200 mm2. Numerical simulations and experimental results demonstrate that the designed metasurface lens achieves single-point and dual-points focusing at 15 GHz under x- and y-polarized wave incidence, with the focus at the z = 70 mm plane and a maximum focusing efficiency of 48.5%. At 23 GHz under x- and y-polarized wave incidence, metasurface lens focuses electromagnetic waves at different positions, with the focus at the z = 80 mm plane and a maximum focusing efficiency of 27.8%. The metasurface lens designed by this method is expected to find applications in fields such as Medical Sensing, Microwave Imaging, and Integrated Optics.