Incident Wave Angle Research Articles

Investigation on the effectiveness of transpiration cooling under the influence of shock wave

As an advanced active cooling method, transpiration cooling can be used for thermal protection of high-temperature wall. The change of cooling effect caused by the incident shock wave on the transpiration cooling boundary layer is sufficient to affect the safe flight of the aircraft. In this paper, the interaction mechanism between shock wave and transpiration cooling is studied based on the thermal equilibrium model. The effects of shock wave incident angle, coolant injection ratio, Mach number of high enthalpy airflow and coolant type on thermal protection effect were studied respectively. Shock wave incidence in the boundary layer of transpiration cooling can cause the change of coolant flow and heat sink distribution in porous media, and cause the fluctuation of fluid parameters in the boundary layer. The temperature inhomogeneity on the porous wall and the inhomogeneity of the total enthalpy difference are markedly affected by the shock wave intensity. The heat insulation effect of the coolant on the solid surface limits the improvement effect of the increase of the injection ratio on the effective heat absorption power. Hydrogen as a coolant can form a better cooling effect and has less resistance to the mainstream.

Terahertz bandwidth absorption metamaterial based on composite structure of single layer graphene

With the development of science and technology, people have realized the value of studying the terahertz band, in this paper, a terahertz bandwidth tunable metamaterial based on composite structure of single layer graphene is proposed, which can have an absorption higher than 0.9 at 3–6.7 THz and exhibit polarization insensitivity. By employing parameter inversion to calculate the relative impedance, the metamaterial adheres to the principles of impedance matching theory. The metamaterial exhibits considerable chemical and physical tuning capabilities, and it can be substantiated that the enhanced absorption rate of the metamaterial stems from a multitude of graphical configurations. Simultaneously, the metamaterial demonstrates a notable level of stability towards the incidence angle of electromagnetic waves and can function reliably at an incidence angle of 30°. In conclusion, the metamaterial holds promising potential for applications in radar stealth, communication, and other related domains.

Tunable terahertz multi-functional hybrid-patterned metasurface arrays based on vanadium dioxide

This study investigates a nine-layer multi-functional periodic array with active broadband tuning in the terahertz (THz) band. The device comprises symmetrical vanadium dioxide (VO2) films and polypropylene (PP) layers, along with silicon dioxide (SiO2) layers, hybrid-patterned metasurfaces, and a central VO2 layer. Through detailed analyses of the electric field distribution, equivalent circuit, and effective impedance, we have performed a thorough investigation of the resonance modes present in the device and meticulously optimized various parameters. Leveraging the insulator-to-metal transition of VO2, a remarkable device capable of seamlessly switching between extraordinary terahertz transmission and bi-directional perfect absorption was obtained. These characters exhibit limited susceptibility to incident angle of the incoming wave. By incorporating bow-tie apertures within the “vacuum region” of the hybrid-patterned metasurfaces, a significant improvement in field enhancement has been achieved, all while effectively eliminating any adverse effects on transmission and absorption performance. This device presents a novel and effective approach in the development of adjustable and multifunctional THz metasurface devices.

Multi-foci metalens based on all-dielectric metasurface with simultaneous amplitude and phase modulation

Metasurfaces provide a novel platform for designing high efficiency and multi-functional photonic devices with compact size. Multi-foci metalens have great potential in the applications of optical tomography technology, optical data storage, optical communication and photoelectric detection. Here, in order to broaden the functionality and applicability of multi-foci metalens, a scheme for designing multi-foci metalens based on all-dielectric metasurface with simultaneous amplitude and phase modulation is demonstrated. Based on this, a linear-polarization-dependent multi-foci metalens which can focus x-polarization and y-polarization incident wave into multiple focal points independently is designed and demonstrated numerically, the intensity ratio between the x-polarization foci and y-polarization foci can be tuned continuously by varying the polarization angle of incident wave. In addition, the polarization-independent multi-foci metalens and dual-frequency multi-foci metalens have also been demonstrated by utilizing this method, the intensity ratio among these foci can be designed at will. This work is of great significance for the practical applications of multi-foci metalens.

Theoretical investigation of hydrodynamic performance of multi-resonant OWC breakwater array

In this paper, we theoretically investigate a multi-resonant oscillating water column (OWC) breakwater array. Based on linear potential flow theory, an extension of semi-analytical solution for wave interaction with periodic OWCs was developed for periodic OWCs with arbitrary chamber number. Both the diffraction and radiation problem for periodic multi-chamber OWCs are solved and verified using Haskind relation and wave energy flux conservation law. Parametrical analysis was conducted to examine the hydrodynamic characteristics of the present OWC breakwater system. Results indicate that multiple resonance of OWCs in piston mode led to multiple peaks of hydrodynamic efficiency, therefore broaden the effective frequency bandwidth with significant wave power absorption and coastal protection capability. However, the resonance of OWCs in sloshing mode in along-shore direction significantly weakens the wave power extraction. The triggering of the sloshing mode resonance mainly depends on the along-shore length of OWC unit and the incident wave angle. For larger along-shore OWC unit length (2l > h, within the present calculations), the effective frequency bandwidth is significantly influenced by the incident wave angle. Notably, when the incident wave angle exceeds π/4, the effective bandwidth decreases by half approximately. However, for narrower lengths (2l < h), the hydrodynamic performance of the OWC array demonstrates reduced sensitivity to the variations of the incident wave angle.

Surface motion of P/SV wave scattering by a semicircular canyon in saturated half-space by complex function and conformal mapping

Based on the complex function theory of elastic dynamics, a complex function solution of P/SV-wave scattering by a semicircular canyon in an elastic porous saturated half-space is obtained. Firstly, through Biot theory and Helmholtz decomposition, the wave potential functions with unknown coefficients in the model are obtained based on the wave function expansion method. Secondly, the complex function expressions of stress and displacement in the model are obtained by using the complex function method and conformal mapping. According to the boundary conditions of the horizontal ground surface and semicircular canyon surface, this boundary value problem can be converted into a series of algebraic equations and solved numerically by truncation. Then, the correctness of the complex function solution in this paper is verified by comparing it with the published results through degenerating the scattering problem in the saturated porous elastic half-space in this paper into that in the elastic half-space. Finally, the influence of the boundary drainage conditions, the medium porosity, and the incident angle and frequency of the incident wave on the ground surface displacement is investigated. Although the P/SV-wave scattering problem is a traditional problem, there is currently no accepted analytical solution that strictly satisfies the zero-stress condition on the horizontal ground surface. This paper is an attempt at this problem, which may provide insight into the search for the strictly analytical solution for P/SV-wave scattering.

Numerical modelling of a catamaran float-over deck installation for a spar platform with complex hydrodynamic interactions and mechanical couplings

Multi-body system is becoming common in engineering practice, such as the catamaran float-over installation for a Spar platform, one of the most complex marine systems. Gap resonance phenomenon occurs in the catamaran float-over system due to strong hydrodynamic interactions, inducing inaccuracy in evaluations of the hydrodynamic coefficients. To obtain reasonable hydrodynamic coefficients, the damping lid method in AQWA, which provide viscous correction for the potential flow theory, is first validated and then applied to the model in this study. It is found that the damping lid is capable of dealing with the gap resonance phenomenon. With the introduction of the damp lid method in the catamaran float-over system with α = 0.20, the relative error between frequency-domain and time-domain declined from 690% to 1.7%. Based on the corrected frequency-domain results, a time-domain model, considering various types of mechanical coupling components in the float-over system, including LMUs, DSUs, steel-to-steel impacts on LMUs, lateral constrains of LMUs and DSUs, sway fenders, hawsers and the mooring system. Simulations for first contact stage and last contact stage under different incident wave angle are performed. It is observed that the relative motions under quartering sea in first contact stage are the largest. Furthermore, in order to reveal the coupling mechanism, different configurations of the barges and Spar are investigated for the first contact stage under irregular waves. It is found that the relative heave motions on the LMUs are larger when the deck and barges are rigidly connected to form a catamaran-barge.

A tunable broadband absorber in the terahertz band based on the proportional structure of a single layer of graphene

This paper presents a novel graphene-based proportional structure for a tunable wideband absorber in the terahertz (THz) frequency range. In order to achieve the ideal design structure, we make the distance between the top graphene structure and the periodic edge remains proportional, enabling excellent absorption with an absorption rate exceeding 90 % within the frequency range of 3.1–6.97 (3.87)THz. Notably, a perfect absorption is achieved at f = 6.5 THz. At f = 4.2 THz, the absorption rate is close to 97 %, and at f = 5.2 THz, the absorption rate is about 91 %. The average absorption rate is 94.6 % in the range of 3.1–6.97 THz. The absorber's impedance is calculated to demonstrate its favorable absorption band. Furthermore, an analysis of the electric field within the absorber reveals the coupling effect of strong electric fields between different regions, leading to the overlapping of absorption peaks and the formation of a wideband response. This allows us to choose regions to combine according to the needs of the application. By adjusting the parameters of the absorber, it exhibits coordinated performance and manufacturing tolerance. Additionally, the absorber shows a certain degree of tolerance to the incident angle of electromagnetic waves. These findings highlight the potential applications of this absorber in optoelectronic devices, THz detection, and stealth technology.

Eigenfunction expansion solution for wave diffraction from a uniform cylinder in front of a partially reflective wall

In this work, wave diffraction from a uniform circular cylinder in front of a partially reflective wall is solved with the aid of its mirror image cylinder arranged symmetrically about the wall. The mirror image cylinder generates a scattering potential with its value being decreased by the wave reflection from the partially reflective wall. The eigenfunction expansion method is applied to solve this wave diffraction problem, and the Graf's addition theorem is applied to transform the scattering potential back from the imaginary to the original cylindrical coordinate system. Numerical simulations were carried out to examine the effects of the wave reflection of the partially reflective wall, the wave incidence direction, and the distance between the cylinder and the wall. It shows that the non-dimensional wave forces oscillate with the incident wave number, and the oscillation amplitude increases with the increasing reflection coefficient of the wall. In addition, the wave numbers at which the force peaks/troughs occur change significantly with the wave incidence angle and the distance between the cylinder and the wall.

A robust design strategy for active control of scattered sound based on virtual sensing.

Combining virtual sensing (VS) with scattered sound control enables active acoustic cloaking when there are limitations in sensor configurations. The remote microphone method and additional filter method (AFM) are two common VS methods, and both can be divided into the training and control stages; the consistency of the environments in these two stages is essential for the control system. This paper investigates the effects of uncertainties in the incidence angle of the detection wave on these two VS-based scattered sound control methods. Following the analysis, we propose a robust design strategy based on the optimal layout of physical sensors, and the placement scheme is chosen by minimax optimization. The feasibility of the proposed strategy is verified by numerical simulations of a finite-length cylindrical scattering model. The results demonstrate that the proposed strategy can effectively reduce the degradation of system performance over the examined range of variations in the detection waves. In particular, the AFM-based method, combined with optimal placement, shows a remarkable improvement in robustness. It improves the worst noise reduction by approximately 14.5 and 10.8 dB on average, respectively, compared with the uniform placement and the direct control method based on the Wiener solution.

Three-dimensional shape optimization of a submerged body under wave diffraction

This study explores the use of shape optimization to reduce wave forces on a submerged floating body subjected to wave diffraction. To this end, gradient-based shape optimization is adopted, in which dimensionless wave excitation forces are the optimization objective. A shape parameterization method based on the Fourier-series expansion is developed that permits the representation of an arbitrary three-dimensional floating body. The discrete adjoint method is utilized to calculate the gradient of the objective function with respect to the shape parameters. Using three-dimensional shape optimization, taking the initial shape to be a hemisphere, a significant reduction in surge, heave, and pitch wave forces is achieved, with a maximum reduction of 48.40%, 68.43%, and 46.22%, respectively. Furthermore, optimization effectively suppresses wave run-up, with a maximum reduction of 15.62%. A comprehensive analysis of parameters is performed to reveal the effects of wave number, incident angle, and shape parameters on the final optimized shape and wave load characteristics. This study provides a solid guide to the optimization of floating offshore platforms and the development of innovative structural systems.

Theoretical proposal of a sensor based on the comb-shaped coherent absorption realized by the magnetized plasma photonic crystals

The study presents a theoretical framework outlining a sensor capable of realizing comb-shaped coherent absorption peaks in magnetized plasma photonic crystals. The proposed model enables simultaneous measurement of alterations in the applied magnetic induction intensity, thickness of the dielectric layer, incident angle of electromagnetic waves, and the refractive index. The nascent stage of coherent absorption theory's application to photonic crystals is currently under scrutiny. Enabling interaction between both forward and backward propagating electromagnetic waves at either end of the photonic crystals creates comb-shaped absorption peaks for detecting variances in physical quantities. The sensor model utilized the transfer matrix method for computation of the transmission and reflection coefficients, linear range, sensitivity, and further linear fitting equations across all physical quantities when employed for multi-physics measurements. The present study entailed an analysis of linear range, the figure of merit, and the sensitivity of a sensor designed to detect magnetic induction intensity. Results demonstrate that the linear range from 0.7 T–1.3 T, while the figure of merit equals 50.2189 T⁻1 and sensitivity equals 4.3535 × 10⁻8 (ωd/2πc)/T. Conversely, when measuring thickness, the corresponding linear range extends from 0.4–0.85 mm, with figure of merit reaching 481.06 mm⁻1 and sensitivity equating to 3.5567 × 10⁻4 (ωd/2πc)/mm. Additionally, the sensor's application to the measurement of both incident angle and refractive index revealed parameters for linear range that ranged from 2 to 4.1, while figure of merit was calculated at 124.00 RIU⁻1 and sensitivity at 15.54952 (ωd/2πc)/RIU. Regarding incident angle, related values for linear range spanned from 15°–44°, with figure of merit established at 4.2157°⁻1 and sensitivity at 0.8661 (ωd/2πc)/degree.

Nonlinear analysis of sound transmission loss through cylindrical shell considering companion modes

This paper investigates the nonlinear vibro-acoustic performance of simply supported cylindrical shell under oblique incident plane sound wave including companion modes participation. The cylindrical shell equation of motion is obtained employing Donnell’s nonlinear shallow shell theory. The Galerkin method is applied to the equations of motion in order to obtain the system of nonlinear nonhomogeneous second order ordinary differential equations. The considered mode shapes are two asymmetric driven and companion modes and one axisymmetric mode. Multiple Scales Method is used to determine the response of resultant nonlinear differential equations. Next, the effects of incident sound characteristics on the transmission loss factor are studied. According to the results, effect of companion mode on the transmission loss (TL) through the shell can be seen only in high frequency of the incident sound wave. In addition, at high incident angle of acoustic wave, the companion mode effect on the TL of the system is very small.

Design of dual-layer serpentine-shaped metamaterial with tunable resonant infrared wavelength and spectra intensity

We present a design of dual-layer serpentine-shaped metamaterials (SSM) in the infrared (IR) wavelength range. It is composed of one serpentine-shaped gold (Au) nanostructure array on silicon (Si) substrate and another serpentine-shaped Au nanostructure array suspended atop. SSM device shows multi-resonance in the wavelength range from 1 μm to 3 μm in transverse electric (TE) and transverse magnetic (TM) modes. By changing the gap of top SSM layer, the resonance at the wavelength of 1.15 μm can be modulated from 23% to 47% and that at the wavelength of 1.78 μm can be modulated from 82% to 2% in TE mode. In TM mode, the tuning ranges of two resonances are over 80%. Moreover, the proposed SSM design is sensitive to the polarization angle of incident wave, which shows switching characteristics at resonant wavelengths under the conditions of different polarization angles. To increase the flexibility and applicability of SSM device, it is exposed on the ambient environment with different refractive indexes. The relationships of resonances and refractive indexes are quite linear. Hence, the SSM device exhibits the potential application to be used to realize logic devices, switchable optic devices, environmental detectors, tunable filters and so on.

Hydrodynamic analysis of a floating platform coupled with an array of oscillating bodies

In this paper, based on multi-body dynamics and beam bending theory, a frequency-domain model is developed to investigate the hydrodynamic performance of a hybrid floating platform (HFP). The HFP investigated here is characterized by hydroelasticity and complex interconnection conditions. The constraint matrix is derived to handle the couple response of an elastic platform and an array of rigid bodies, representing wave energy converters. The hydroelasticity and coupled dynamics of the floating platform in waves and the wave power extraction performance is analyzed. The numerical results reveal that the platform deformations have a significant impact on the relative pitch response between the buoy array and the platform. Neglecting hydroelasticity leads to an overestimation of the hydrodynamic efficiency of the buoy array when 0.4 < λ/L < 1.0, as demonstrated in our calculations. Influence of key parameters such as spacing and incident wave angle is examined numerically. As a result of these investigations, suggestions are identified for an improved design of such kind of multi-use floating platform.

Terahertz metamaterials for broadband, high modulation depth modulator, and tunable dual-band absorber based on metal-vanadium dioxide hybrid structure

Terahertz metamaterials for broadband, high modulation depth modulating, and tunable dual-band absorbing are designed based on the similar composite structure of metal and vanadium dioxide film arrays. By using external excitation to induce the insulator-metal phase transition of the vanadium dioxide layer, the transmission characteristics of the metamaterial can be manipulated. High modulation depths of more than 80% are achieved in the range of 0.2–0.8 THz, and the bandwidth width with modulation depths exceeding 60% is up to 140%. By increasing the dielectric thickness and adding a metal ground, the initial broadband modulator can be switched to a dual-band absorber when the vanadium dioxide is in the metal phase. Furthermore, the modulation effect and the absorption performance exhibit insensitive characteristics to the polarization angle of incident waves. This work provides potential applications in broadband modulation of terahertz communication as well as dual-band absorption for terahertz detection.

EXPERIMENTAL AND NUMERICAL STUDY ON OBLIQUE WAVE-IN-DECK LOADS

Most studies on wave-in-deck loads focus on head-on wave impingement whereas wave-in-deck loads due to waves incident from oblique directions are rarely reported. Numerical simulations for oblique wave-in-deck loads were presented in Iwanowski et al. (2002), Brodtkorb (2008) and Chen et al. (2018). However, in these studies, only numerical validations were performed against either two-dimensional experiments or empirical formulations due to a lack of experimental results. In light of this, we present the experimental results for wave impacts on a solid deck model due to a transient focused wave group incident from oblique direction in this study. The oblique experimental data is compared with the head-on counterpart by Santo et al, (2020) to investigate the incident wave angle effect on wave-in-deck loads. Numerical simulations are carried out to reproduce both the head-on and oblique wave-in-deck experiments using a three-dimensional (3D) numerical wave tank (NWT), and flow field information is interrogated to derive physical insights into complex wave-deck interactions. The solid deck model is a representative of a typical 2nd generation North Sea topside structures commonly exposed to severe winter weather. The configuration is also applicable to coastal structures such as bridges, piers, jetties or docks.

Hydrodynamic investigation of a parabolic breakwater for wave energy focusing

The integration of wave energy converters (WECs) with a breakwater can reduce construction and maintenance costs and enhance the energy conversion performance of WECs. Intelligent use of a parabolic breakwater to focus water waves to a specific region can significantly increase the available wave energy. However, the theoretically calculated focal point of a parabolic breakwater may not always coincide with the observed wave focusing position. To determine the actual position of the focal point for installing the WEC, both numerical simulations and experimental research are conducted to investigate hydrodynamic characteristics of the parabolic breakwater. The realized focal point is found to be located at a position separated from the theoretical position, and its location varies with the incident wavelength. The underlying cause of this behavior is identified and investigated. The effects of chord length, parabolic wall aspect ratio, and incident wave directions on the wave amplitude at the focal point are examined. It is found that the shift in the actual focusing position exhibits a cyclic configuration as the incident wavelength changes, with the observed focal point revolving around the theoretical focal point. The position of the recorded focal point is determined by the interaction between the incident and reflected wave crests. The wave amplitudes at the theoretical focal point reaches their maxima when the focal lengths are nearly equal to integer multiples of half incident wavelength. The wave amplitudes at both the theoretical and observed focal points are shown to magnify with increasing chord length and with decreasing focal length. The parabolic wall is demonstrated to consistently maintain a substantial focusing effect for incident wave angles up to 15°.

Substrate Comparison on Multiband Reflector Performance for Intelligent Reflecting Surfaces (IRSs)

This paper presents the substrate comparison on the multiband reflector performance at X-band frequency for an Intelligent Reflecting Surface (IRS). Functioning as a multiband reflector, the proposed reflector is using a circular multi-ring resonator on several substrates such as RO5880, F4BMX220, RO4003C, and FR4, with slightly different substrate thicknesses based on the available market, that can be operated at X-band frequency. The simulated results have shown in the graph of S-parameters and reflection phase among the substrates. In addition, the bandwidth of the proposed reflector is calculated based on the simulation results. Also, the incident wave angle effect against the proposed reflector is shifted along the horizontal axis. For the overall simulation results, the reflector that uses a RO5880 substrate has slightly better results and a wider bandwidth than the F4BMX220 substrate.

Surface Motion for P-Wave Scattering by an Arbitrary-Shaped Canyon in Saturated Half-Space

This paper obtained a semianalytical solution for the P-wave scattering problem by an arbitrary-shaped canyon in a saturated half-space by using Biot’s theory, the wave function expansion method, and the moments method. Firstly, based on the Biot fluid-saturated porous media theory and the wave function expansion method, the wave potentials which automatically satisfy the zero-stress boundary condition on the surface of the half-space are obtained. Then, the boundary value problem is transformed into an algebraic problem by the method of moments according to the boundary conditions, and then solved numerically by truncation. By adjusting the parameters, the saturated medium in the original model approximately degenerates into a single-phase elastic medium, and the correctness of the proposed method is verified by comparing it with published results. Finally, the effects of the canyon shape, the porosity of the soil, and the incidence angle and frequency of the incident wave on the amplitude of ground surface motion are investigated. The results show that the incidence angle has a significant effect on the ground surface motion, while the porosity of the soil has little influence on the amplitude of surface motion. The influence of canyon shape on surface motion is mainly reflected in the shielding effect on the incident wave. Although P-wave scattering by a canyon is a traditional problem, most of the analytical solutions are limited to solving the scattering of seismic waves in geometric regular canyons. However, the actual shape of the canyon is not regular, which limits the application of closed analytical solutions in practical engineering. In this paper, the scattering of P-waves in arbitrary-shaped canyons is successfully solved by using a semianalytical method combined with a numerical method-moments method, which provides a possibility for engineering application.