Oblique Incident Waves Research Articles

Fast Water Waves in Stationary Surface Disk Arrays.

Traditionally, the phase and group velocities of water waves can be increased by increasing water depth but possess upper bounds, which are related to the gravitational acceleration and difficult to exceed. Here, we theoretically propose and experimentally demonstrate that when water is covered with a periodic array of stationary rigid disks, both the gravitational acceleration and reduced water depth can be effectively increased in the lowest frequency band. As a result, fast water waves can occur in the system, with both the phase and group velocities exceeding those in water without disks. Unusual effects, such as total reflection at oblique incidence and unidirectional transmission of water waves, are further realized.

Flared front pile supported breakwater in oblique waves

ABSTRACT Flared Front Pile Supported Breakwater (FPSB) is a new re-curved type of breakwater well suited for areas with a higher tidal variation. FPSB is expected to provide the required tranquility on its leeside as a significant amount of energy in the incoming waves will be dissipated while traversing over the re-curve. The hydrodynamic performance of FPSB in two water depths is experimentally studied under oblique wave incidence. The paper briefly explains the variation of the reflection coefficient, transmission coefficient, loss coefficient, non-dimensional pressures, and non-dimensional run-up as a function of the relative water depth and scattering parameter of the re-curve pile supported breakwater and that with a vertical front face (VPSB). The results obtained for FPSB shows that its hydrodynamic performance characteristics are better than that of VPSB in oblique wave fields.

A compact ultra-broadband metamaterial absorber for Ku-, K-, and Ka- band applications

Multiple electric resonators loaded with lumped resistors are usually constructed in a unit cell to design broadband metamaterial absorbers. In this paper, we propose a simple way to achieve ultra-broadband microwave absorption. Only one split ring resonator loaded with one lumped resistor in the absorber’s unit cell in our design. Its measured reflection coefficient is lower than −10 dB in the frequency range 14.20 GHz to 32.98 GHz. Its bandwidth is 18.78 GHz, and its absorption frequency covers the Ku-, K-, and Ka- bands. The absorber has a 1.524 mm dielectric layer, and the thickness of the copper foil on both sides of the dielectric layer is 0.035 mm. Therefore, the total thickness of the absorber is only 1.594 mm. The edge length of its unit cell is 1.8 mm, which is about 1/4 of the wavelength of 40 GHz, so the oblique incidence of electromagnetic waves will not excite higher-order modes below 40 GHz. In addition, we study its absorption mechanism in detail. It is discovered that besides selecting a suitable lumped resistance value, the construction of two magnetic resonances and an electric resonance between them is necessary to achieve broadband absorption.

Scattering of water waves by rectangular thick barriers in presence of surface tension

The influence of surface tension over an oblique incident waves in presence of thick rectangular barriers present in water of uniform finite depth is discussed here. Three different structures of a bottom-standing submerged barrier, submerged rectangular block not extending down to the bottom and fully submerged block extending down to the bottom with a finite gap are considered. An appropriate multi-term Galekin approximation technique involving ultraspherical Gegenbauer polynomial is employed for solving the integral equations arising in the mathematical analysis. The reflection and transmission coefficients of the progressive waves for two-dimensional time har- monic motion are evaluated by utilizing linearized potential theory. The theoretical result is validated numerically and explained graphically in a number of figures. The present result will almost match analytically and graphically with those results already available in the literature without considering the effect of surface tension. From the graphical representation, it is clearly visible that the amplitude of reflection coefficient decreases with increasing values of surface tension. It is also seen that the presence of surface tension, the change of width, and the height of the thick barriers affect the nature of the reflection coefficients significantly

Electromagnetic shielding effectiveness for A16061 metal matrix composite based mesh wire reinforced with Flyash for oblique incidence of EM wave

Nowadays, flywire is used exclusively in aeronautical applications. A plane’s complete control is dependent on electronic technology, yet it suffers from high-intensity radiated fields. An electromagnetic shield may be necessary to protect this equipment from external electromagnetic pollution. The current project attempts to create a protective barrier around the operating equipment to enhance its efficiency. AL6061 composite material was used to create a metal matrix mesh shield. It is reinforced with fly ash in various volume fractions, and the electrical characteristics and Shielding Effectiveness are determined (SE). The maximum SE is 45.36dB obtained, which can be effectively used as a shield for aerospace and other applications.

Explicit derivation of the Fraunhofer diffraction formula for oblique incidence

We have analytically explored the Rayleigh–Sommerfeld scalar diffraction for oblique incidence. We have explicitly derived the Fraunhofer diffraction formulae for oblique incidence of a plane scalar wave on various apertures, such as single-slit, circular aperture and diffraction grating. Such derivations in the background of Rayleigh–Sommerfeld scalar diffraction theory would be important for an undergraduate course on optics.

Analytical solution based on BEM to oblique waves scattering by thin arc-shaped permeable barrier applied for array of aquaculture cages

In this paper, linear oblique wave incident to a thin arc-shaped permeable barrier and an array of permeable circular cylinders was studied analytically. Two unique research objectives of this work include, considering the thickness for permeable material and the wavefield inside surrounded region by the permeable structure. The conventional boundary element method (BEM) is used to solve the governing equations of the problem. The mathematical relation between Bessel functions leads to representing the BEM-related integrals in the Fourier modes of Hankel function. This approach is useful as the singular integrals are accounted indirectly. Two basic geometries made by the permeable material are studied, including an arc-shaped and a circular geometry. The first geometry can represent a wave-breaking barrier in shallow water, while the latter can represent a floating fish farm in deep water. For the floating fish farm, the study is extended to the interaction between an array of cages. To quantify the amount of wave energy passed through the object, the Energy Transmission Index or ETI concept is introduced. ETI can be used as an indicator for permeable barriers performance.The results indicate that ETI is mostly a function of permeability rather than the wavenumber. In addition, the imaginary part of the permeability parameter plays an essential role in the problem of wave incident to permeable barrier, and it is necessary to be determined with enough accuracy. Furthermore, the shear force and bending moment on the base of the barrier and drift force and heeling moment on circular cylinders are studied. The results show, the drift force decreases as permeability and wavenumber increase. The results of this research are useful in the design of rigid circular offshore aquaculture fish cages and coastal barriers.

Evaluation of Ground Motion Amplification Effects in Slope Topography Induced by the Arbitrary Directions of Seismic Waves

The incident directions of seismic waves can change the ground motions of slope topography. To elaborate on the influences of the directions of seismic waves, a dynamic analysis of the slope topography was performed. Seismic waves were input using an equivalent nodal force method combined with a viscous-spring artificial boundary. The amplification of ground motions in double-faced slope topographies was discussed by varying the angles of incidence. Meanwhile, the components of seismic waves (P waves and SV waves), slope materials and slope geometries were all investigated with various incident earthquake waves. The results indicated that the pattern of the amplification of SV waves was stronger than that of P waves in the slope topography, especially in the greater incident angels of the incident waves. Soft materials intensely aggravate the acceleration amplification, and more scattered waves are produced under oblique incident earthquake waves. The variations in the acceleration amplification ratios on the slope crest were much more complicated at oblique incident waves, and the ground motions were underestimated by considering only the vertical incident waves. Therefore, in the evaluation of ground motion amplification of the slope topography, it is extremely important to consider the direction of incident waves.

Sediment pathways and morphodynamic response to a multi-purpose artificial reef – New insights

Multi-purpose Artificial Reefs (MPARs) are structures that may provide aesthetically acceptable coastal protection and improve recreational outcomes. Twenty years after construction of the first MPAR, Narrowneck Reef on the Gold Coast of Australia, most of the available literature is still focused on the planning, design and construction of such structures and peer-reviewed publications on their post-construction monitoring, interaction with sediment transport and impacts on coastal morphology are lacking. The aim of this paper is to evaluate how does Narrowneck Reef influence the sediment transport, and morphological changes around the anthropogenic structure, two decades after construction. To do so, a combination of ten high spatial resolution topo-bathymetric surveys from the top of the dune to the 10 m depth captured over 21 months and a series of 60 simulations using a calibrated numerical model were used. Our results demonstrate that: although not expected during design or reported in similar structures, sand can bypass the MPAR around its offshore end; under oblique waves, the longshore currents are deflected as they pass the reef, resulting in a shadow zone on the downdrift side where sand deposits; the bar crest tends to be higher on the reef's updrift side compared to downdrift, indicating that the MPAR can act as a store for sediments, as initially designed. Furthermore, the MPAR can act to stabilise the bar as it moves onshore with a downdrift offset of the inner bar as a result of low oblique wave incidence. The results presented here demonstrate that the short-term response to the MPAR twenty years after construction is more closely related to the updrift build up of sand and the deflection of longshore currents as they encounter the reef than to the dissipation of wave energy. This is because MPARs are designed to dissipate just enough wave energy so that they can achieve their recreational goal (surfing).

A 4-Bit Multistate Frequency-Selective Surface With Dual-Band Multifunction Response

In this letter, a novel 4 b multistate frequency-selective surface is proposed. Four p-i-n diodes are used to maneuver multifunction behavior of the structure with seven different functional states. The 4 b binary state operations 0000, 1100, 0011, and 1111 offer transverse electric (TE)/transverse magnetic (TM) waves both transmit, TE transmit/TM shield, TM transmit/TE shield, and TE/TM both shield, respectively, at 2 GHz frequency. The passband at 2 GHz frequency has <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-\text{10}$</tex-math></inline-formula> dB fractional bandwidth of 117%. The binary states 1101 and 1110 are symmetric, which select the TE wave transmit/TM wave shield to the passband at 3.45 GHz frequency with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-\text{10}$</tex-math></inline-formula> dB fractional bandwidth of 49%, whereas binary states 1011 and 0111 allow the TM wave to transmit at 3.45 GHz and shield the TE wave. The four symmetric binary states 0101, 0110, 1010, and 1001 provide transmission band at 3.45 GHz frequency for dual-polarized plane wave incidence. The transmission of both the passbands can be shielded by selecting the binary state equal to 1111. An equal circuit model is used to elaborate the contribution of different passive structural elements in terms of lumped components. A prototype of the structure is fabricated, and transmission coefficients for different states at normal and oblique incidence of the electromagnetic plane wave are measured, which verifies the simulated responses of the structure.

Shallow-water circulation on the northern coast of Rio Grande do Sul, Brazil: A wave-dominated system

Alongshore currents in the surf zone are formed after incident waves break. This process depends on the characteristics of the incident waves and can be altered by the wind, and to a lesser extent, by bathymetry and tide. In order to understand the behavior of the alongshore currents on the north coast of Rio Grande do Sul (Brazil), two datasets were obtained in the field. The first one was acquired during oceanographic moorings and is composed of long time series of wave data. The other database corresponded to direct measurements of vertical profiles of velocities and direction of alongshore currents in the surf zone, both simultaneously acquired for the first time in this coastal region. The analyses of these data sets enabled identification and quantification of the processes associated with incident waves and winds. Circulation by currents in the surf zone is induced by oblique incidence waves breaking as a result of radiation-stress energy flow. It was also noted that wind can influence alongshore currents to a lesser extent. The findings indicated that height and angle of incidence of waves was the main driving force of alongshore currents. A pattern has also been identified, in which waves that come from the southeast (SE) and northeast (NE) generate northeasterly and southwesterly fluxes, respectively.

Active meta-device for angular dispersion elimination of dual-polarized transmission windows.

Metasurface-based strategy of tailoring electromagnetic waves has aroused huge attention in both academic and engineering communities owing to great potential in a large portfolio of applications. Commonly, however, the artificially designed metasurfaces are sensitive to the oblique incident waves which results in the angular dispersion and inevitably deteriorates the performances. Here, we propose a paradigm of an active meta-device to effectively eliminate the angular dispersion in two orthogonal polarization states of transmission waves. By loading varactor diodes into a transmissive meta-atom, the transmission responses for traverse electric (TE) and traverse magnetic (TM) waves are actively tunable by a voltage-driven manner. Accordingly, the blue shifts of transmission windows can be ingeniously compensated via tailoring the corresponding dispersion characteristics of varactor diodes. A triple-layer meta-atom loaded with varactor diodes is designed as a dual-polarization proof-of-principle, in which the varactor diodes can be applied to independently control two polarization states. The numerical simulations and experimental verification are in good agreement, indicating the proposed paradigm possesses the potential in versatile applications, including radome, wireless communications, and other dispersionless systems.

Wideband and wide-angle radar cross section reduction using a hybrid mechanism metasurface.

In this paper, a hybrid mechanism metasurface (HMM) that incorporates absorption, polarization conversion and phase cancellation mechanisms is proposed for wideband and wide-angle radar cross section (RCS) reduction. The polarization conversion absorber (PCA) is proposed by embedding the lumped resistors into the polarization conversion structure, which integrates the absorption and polarization conversion mechanisms. Then, the phase cancellation mechanism is employed to redirect the scattering energy to the non-incident directions through the chessboard configuration, which exploits the opposite phase between the PCA and its mirror structure. Unlike previous HMMs that depended on nested or cascaded structures, the proposed strategy integrates the absorption and polarization conversion mechanisms in the same structure, and the two mechanisms are complementary to each other. Through the integration of multiple mechanisms, the HMM can achieve more than a 10 dB monostatic and bistatic RCS reduction in 8.7-32.5 GHz and 8.6-31.2 GHz, respectively. Furthermore, the specular and bistatic RCS reduction performances under oblique incident waves are also studied, and the stable scattering suppression performances are determined. The proposed hybrid mechanism strategy exhibits significant scattering suppression capability through the incorporation of multiple mechanisms, which have potential applications in the multifunctional metasurface.

Analysis of shielding effectiveness and mechanical properties of metal matrix composite AL6061 reinforced with Al2O3 and fly ash for oblique incidence of EM wave

PurposeFiber-reinforced polymers (FRP) contain critical electrical conductivity for high-intensity radiated fields such as lightning strike susceptibility, electromagnetic energy from radar, airborne radio frequency transmitter. To provide high-intensity radiated field protection (HIRFP) for the electric and electronic aircraft system and defied the EMI effect on it, metal matrix composite was conquered. To provide the dynamic ever-increasing requirement of industries, it is necessary that Al6061 metal matrix composite assisted with AL2O3 and fly ash is used to construct the aircraft to provide HIRFP. The thickness of the material can be maintained as low as possible to use it as a coating material for the aircraft surface. X-band for oblique incidence is used to measure electromagnetic and mechanical safeguarding properties of composites.Design/methodology/approachDay by day, the applications of aerospace are becoming digital and automated. Proper shielding techniques are required to operate digital electronic devices without electromagnetic interference. It leads to a rapid rise in temperature, thermal ablation, delamination, and adverse effects on the electric and electronic aircraft system. Fly ash, a metal matrix material composite AL6061 with different percentages of reinforcement of Al2O3, was contemplated and experimented with for mechanical properties like tensile strength, density and hardness.FindingsThe obtained results compared with adjusted values and an improvement of 0.19, 0.18, 0.14 g/cm3 for density of MMC-1, MMC-2, MMC-3.31, 11 MPa for tensile strength of MMC-1, MMC-2. 24, 27, 23 BHN for hardness of MMC-1, MMC-2, MMC-3. With regard to the shielding effectiveness the results compared with adjusted values and obtained 11.36, 14.56, 19.47 dB better value than it. According to the above results, fabricated MMC’s provide superior results for a defined application like HIRFP(Surface material of aircraft).Practical implicationsIt can be used to protect electronic devices under a high-intensity radiated field, mainly in aircraft design to protect from lightning effect.Originality/valueFor a better approximation of the signal toward the practical case, the oblique incidence was considered with a different combination of Al2O3 and fly ash, reinforced to pure AL6061 to get better shielding and mechanical properties.

Simulated seismic response analysis of subway tunnels under complex geological conditions of obliquely incident seismic SV waves

To investigate the seismic performance of simulated subway tunnels under complex geological conditions of obliquely incident earthquake excitations, a new input method for oblique incidence of SV waves with arbitrary incident angles in 3D space has been proposed. The method relies on explicit finite element method (EFEM) and viscous-spring artificial boundary (VSAB) condition, which simultaneously considers soil-structure interaction, surrounding soil characteristics, and seismic wave incident characteristics. It is applied and verified based on the seismic wave theory. The overall numerical model of subway tunnel and soil foundation is then established, and the dynamic response of subway tunnel in soft and hard interbedded soils under oblique incidence of SV waves is systematically analyzed. The obtained simulated results indicate that the dynamic response of each point in subway tunnel is decreased by increasing incident SV wave angle. It is also found that the dynamic responses of the site interbedded by soft and hard soils are significantly higher than that in other points of the site at the same incident angle, indicating that the mentioned zone has weak seismic resistance. In addition, the dynamic response of each point in tunnel structure tends to become closer when the bulk moduli of soft and hard soils are getting close. The displacement and moment of the site interbedded by soft and hard soils are reduced by increasing the thickness of lining structure, therefore improving the seismic resistance of the tunnel. The results of parametric study show that these factors could have significant influences on the seismic responses of tunnel structures during earthquake and should be considered during earthquake-resistant design of subway tunnels under complex geological conditions.

Wave energy dissipation by a floating horizontal porous plate in oblique incident waves

The interaction of oblique incident waves with a floating porous plate has been investigated using the matched eigenfunction expansion method (MEEM). The porous boundary condition based on Darcy’s law is applied at a floating porous plate (Zhao et al. (2009)). Depending on the presence of a vertical rear wall, the wave energy dissipation by a floating porous plate is evaluated with two analytical models: wave barrier and wave absorber. The nonlinear dispersion equation, derived from the porous boundary condition, is solved numerically by using Muller’s method to obtain the complex-number eigenvalues in the porous-plate covering region. Notably, it is confirmed that the real part of the first-mode eigenvalue is closely related to the energy dissipation due to the generation of vortices when waves propagate past a floating porous plate, and the porosity parameter b=5.0 (plate porosity P=0.1) is found to be the optimal value for the maximum energy dissipation. The analytical solutions are validated by means of the model test with a floating porous wave barrier.

Design investigation of mantle-cloak for a PEC cylindrical object under oblique incidence of TM and TE waves

In this paper, the possibility of cloaking a metallic cylinder is investigated for a wide range of angles of obliquely incidence TE and TM wave using the well-known mantle cloaking technique. Initially, the scattered field is formulated analytically using the circumferential waves in cylindrical coordinates. A full tensor is utilized for modeling the sheet impedance of an ideal metasurface wrapped around the cylinder to be cloaked. Then, a capacitive rectangular patch metasurface is designed and its parameters are optimized to suppress both the co- and cross-polarized components of the scattered fields. The analytical results are verified with those obtained using the full wave simulation investigation performed by CST Microwave Studio, and a very good agreement is observed between the obtained results.

Far-field characterization of wave oblique incidence on body channel for implant communication by using an analytical model

Characterization of human body channel is a necessity to pave way for the practical implementation of implant communication. Considering there are few investigations on the characterization of incident wave propagating at an arbitrary angle to human tissues, this paper applies an analytical model of wave oblique incidence onto multilayered planar lossy tissues to evaluate the far-field EMFs and PLs of body channel. With this model, EMFs and PLs of both TM and TE wave oblique incidence at different angles and frequencies in out-to-in and in-to-out propagations are calculated. A FEM model and a measurement on porcine tissues are also carried out. Comparing with simulation and experiment, the analytical results of PLs have the maximum differences of 0.03 and 1.0 dB, respectively, in out-to-in propagation and of 0.09 and 1.7 dB, respectively, in in-to-out propagation. Therefore, the analytical model is accurate and indicates the mechanism of EM wave propagation in body channel theoretically.

Numerical modelling of alongshore variability in waves and wave-driven currents during the morphodynamic change of a laboratory beach

A non-hydrostatic phase-resolving numerical model (SWASH) is used to investigate the wave-driven nearshore hydrodynamics corresponding to new observations from a three-dimensional physical model in a wave basin. In the physical model, waves from a passing storm are simulated by varying the energy and duration of waves generated by a paddle over time and the beach morphology is surveyed in high spatial-resolution using a 3D laser scanner after each segment of the storm. An oblique incident wave angle introduces spatially variability in wave energy along the beach and results in morphologic differences during the storm, with active transport of beach sand by the wave-driven circulation. SWASH is validated using wave and current observations at each stage of the storm, indicating low root-mean-squared errors between model results and wave measurements, where the high-resolution model is able to predict wave shoaling, breaking and generation of the alongshore current. Model-data agreement is not as high for the velocity, suggesting spatial variability in bottom friction and horizontal mixing, and evolution of the bed in the physical model, could explain the differences. The detailed numerical model results indicate that the alongshore current is generated by wave breaking in the nearshore zone, and it increases in speed across a wider surf zone for increasing wave energy during the storm. This is associated with a bottom shear stress that exceeds the critical bed shear stress, with the potential to initiate motion and transport sediment in agreement with the experimental observations.

Implementation of conformal digital metasurfaces for THz polarimetric sensing

Monitoring and controlling the state of polarization of electromagnetic waves is of significant interest for various basic and practical applications such as linear position sensing and medical imaging. Here, we propose the first conformal digital metamaterial absorber to detect the polarization state of THz incident waves. The proposed polarimeter is capable of characterizing four independent polarization states of (TE, TM, ±45° linear, and RCP/LCP) by observing the reflectivity of the structure with respect to the x- and y-direction. Besides, the proposed structure displays a strong absorptivity above 90% up to the incidence angle of 50° for oblique incident waves with different polarizations. By mere changing the bias voltage of two orthogonal VO2 microwires via two independent computer-programmed multichannel DC network, distinct conditions for reflected waves occurs under excitations of different polarizations, whereby the polarization state of the incident wave may readily be estimated. We believe that the proposed metasurface-based polarimeter can pave the way for polarization detection applications on curved surfaces.