Wave Angle Research Articles

Full-wave modeling of EMIC wave packets: ducted propagation and reflected waves

Electromagnetic ion cyclotron (EMIC) waves can scatter radiation belt electrons with energies of a few hundred keV and higher. To accurately predict this scattering and the resulting precipitation of these relativistic electrons on short time scales, we need detailed knowledge of the wave field’s spatio-temporal evolution, which cannot be obtained from single spacecraft measurements. Our study presents EMIC wave models obtained from two-dimensional (2D) finite-difference time-domain (FDTD) simulations in the Earth’s dipole magnetic field. We study cases of hydrogen band and helium band wave propagation, rising-tone emissions, packets with amplitude modulations, and ducted waves. We analyze the wave propagation properties in the time domain, enabling comparison with in situ observations. We show that cold plasma density gradients can keep the wave vector quasiparallel, guide the wave energy efficiently, and have a profound effect on mode conversion and reflections. The wave normal angle of unducted waves increases rapidly with latitude, resulting in reflection on the ion hybrid frequency, which prohibits propagation to low altitudes. The modeled wave fields can serve as an input for test-particle analysis of scattering and precipitation of relativistic electrons and energetic ions.

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.

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.

Numerical investigation on spray and flow field characteristics of elliptical nozzle in supersonic crossflow

ABSTRACT It has been suggested that using an elliptical nozzle could enhance the atomization and mixture quality. In order to explore the elliptical liquid jet on spray and flow field characteristics in supersonic airflow, the VOF-Spray one-way coupling model was adopted to study the nozzle exit patterns, size, and velocity distribution of droplets. The research also compared the flow field characteristics in Mach 2.85 air crossflow under the application of different orifices. The numerical results showed that elliptical 4 nozzle (Aspect ratio of 4) had better flow performance than circular nozzle. The cavitation area and turbulent disturbance of elliptical 4 nozzle were mainly concentrated in the major axis direction. The elliptical 4 jet always had a lower penetration depth than circular jet. At the flow range of 0 ~ 50 mm, the penetration depth of elliptical 4 jet is roughly 12% less than that of circular jet. Another finding was that the spanwise extension range of elliptical 4 spray was larger than the circular spray. The spanwise extension range of elliptical 4 spray increased by about 19.4% at most in the flow range of 0 ~ 50 mm. Additionally, the elliptical 4 spray had the smallest Santer Mean Diameter (SMD). The elliptical 4 jet had a 2.9% smaller Santer Mean Diameter than the circular jet. Due to the greater windward surface area of the elliptical 4 orifice, the gas streamwise velocity near the bottom wall was reduced. A reverse vortex pair with distinct characteristics could be observed under the application of elliptical 4 orifice. Furthermore, compared with the circular orifice, the shock wave angle generated by elliptical 4 orifice reduced by 9.7%, and the total pressure recovery coefficient rose by 2.3%.

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.

Nearshore wave angles and directional variability during storm events

Nearshore wave angles and directional variability during storm events

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 and analysis of quad-band polarization-insensitive infrared perfect metamaterial absorber with a wide-incident angle

There is a pressing demand to design simple absorber structures that support optimal absorption in multi-band to meet different applications. In this work, a novel quad-band infrared perfect metamaterial absorber (QPMA) is proposed and numerically investigated. The structure of the QPMA is composed of coaxial multi-layer dielectric (SiO2) disks of circular shape with different diameters where each disk is surrounded by a gold ring. All disks are placed on a SiO2 dielectric spacer and an impermeable gold ground layer. Simulation results reveal that the proposed absorber has four absorption peaks around wavelengths of 1064 nm, 1550 nm, 2080 nm, and 3000 nm. Since these wavelengths correspond to commercially available laser sources, the structure under investigation can be used in different applications such as laser stealth, infrared photodetection, and medical applications. Additionally, the QPMA structure enjoys a good absorption performance for a wide range of incident angles for both TE and TM waves. It achieves absorption greater than 85% at incident angles up to 40° at 1064 nm, and absorption greater than 90% for the other bands at incident angles up to 50°. Moreover, due to the symmetrical shape of the structure, the absorption is insensitive to wave polarization changes.

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.

Effect of Thermal Nonequilibrium on Captured Mass Flow Rate of Scramjet Inlets

The numerical simulation of a scramjet is often based on the thermal equilibrium model, but the flow inside the inlet and isolator is likely to be in thermal nonequilibrium due to shock-based compression. The objective of this study is to investigate the effect of thermal nonequilibrium on the mass flow rate captured by the scramjet inlet. Numerical simulations based on the thermochemical nonequilibrium model (thermal nonequilibrium) and the chemical nonequilibrium model (thermal equilibrium) were adopted to study the mass flow rate of the HyShot II scramjet with the incoming flow Mach numbers ranging from 6.0 to 8.0. The results show that the maximum difference of the mass flow rate between thermal nonequilibrium and equilibrium reaches 10.7% at with . The primary cause of the mass flow rate difference is the oblique shock wave angle difference between nonequilibrium and equilibrium. The relative magnitudes of oblique shock wave angles and flow parameter ratios across the wave under equilibrium and nonequilibrium are theoretically discussed in an intuitive way. A simplified model for the HyShot II is established to predict the mass flow rate difference between thermal nonequilibrium and equilibrium. The result shows that the expression of captured mass flow rate has a significant amplification effect on the slight difference of wave angles between thermal nonequilibrium and equilibrium, which means that the effect of thermal nonequilibrium cannot be ignored for scramjet in some cases.

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.

Global Empirical Models of Wave Amplitudes and Normal Angles of Banded Plasmaspheric Hiss Obtained From Van Allen Probes Observations

AbstractThe unique banded structure of plasmaspheric hiss with an upper band above ∼200 Hz and a lower band below ∼150 Hz has been recently reported. Based on observations from the twin Van Allen Probes from 15 September 2012 to 30 June 2019, we statistically investigate the global distributions of amplitude and power‐weighted wave normal angle (WNA) of banded hiss waves with respect to L, MLT, MLAT, and AE*. The results indicate that amplitudes of dayside banded hiss significantly depend on the substorm level (AE* index), while the variation of WNAs on the AE* index is slight. The WNAs of upper band hiss show a peak at L ∼ 3, while the WNAs of lower band hiss are relatively uniform at L &lt; 4. The WNAs of both bands decrease with increasing L values at L &gt; 4. We further develop the global empirical models of banded hiss wave amplitudes and WNAs to fit the statistical results, which show good agreement with satellite observations. These results can be essentially useful to evaluate the role of banded plasmaspheric hiss in the dynamic variations of Earth's radiation belt electrons.

Effects of Cold Plasma on the Mode Conversion From Fast Magnetosonic Wave to Electromagnetic Ion Cyclotron Wave in the Inner Plasmasphere

AbstractPrevious studies show that fast magnetosonic (MS) wave with frequency of tens of Hz may propagate to low L‐shells (L &lt; 2.0) in the inner plasmasphere and mode convert to electromagnetic ion cyclotron (EMIC) wave where its wave frequency is close to the local crossover‐cutoff‐resonance frequency triplet through different propagation paths. In this study, we investigate how this mode conversion process may depend on the ion composition and electron density by full‐wave simulation with various plasma density profiles and initial wave normal angles (WNAs) of incoming MS wave from magnetic equator and a higher latitude of 15°. We find that critical fraction of minority ion (He+ or M/Q = 2 ion − D+ or He++) exists during the mode conversion, over which the conversion from MS wave to H+ band right‐handedly polarized EMIC wave starts to become negligible. This critical fraction decreases with the incident WNA of MS wave from equator. The efficiency of this conversion process also decreases with the electron density. As incoming MS is from higher latitudes off equator, optimal fraction of minority ion exists, with which the efficiency of conversion from MS wave to H+ band left‐handedly polarized EMIC wave reaches a maximum. Moreover, this maximum conversion efficiency varies with the incident WNA and may approach 100% with WNA close to 90° at the magnetic latitude of 15°. We also find that localized wave structure may be formed when the converted H+ band EMIC wave is trapped between local H+ − D+(He++) bi‐ion resonance frequency and D+(He++) − He+ left‐handed polarization cut‐off frequency with a small M/Q = 2 ion fraction and a relatively larger He+ fraction as incoming MS wave is near equator.

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.

A New 3D Frequency-Selective Structure for 5G Communication

Background: In this paper, a new frequency-selective structure (FSS) for 3 to 4 GHz frequency band of fifth generation (5G) is proposed as a result of an analytical mode-matching method. Methods: A new periodic structure with stepped rods is designed using a closed-form equation derived by the analytical mode-matching method. Performance of the structure is simulated by different numerical packages. Results: The analytical and simulation results demonstrate that the designed structure transmits incident waves in 3.4 to 3.9 GHz frequency range with return loss lower than 10 dB and insertion loss of about 0.5 dB. The structure reflects the frequencies out of this range, especially wireless local area network (WLAN) 5 GHz, which is adjacent to this band. Furthermore, the performance of the proposed structure is independent of the TE and TM polarization of the incident wave and relative to the angle of the incident wave up to 60 degrees from perpendicular to the FSS surface, it has minor variations of about 8% in the transmitted frequency bandwidth. In addition, the average value of maximum field enhancement factor (MFEF) as the ratio of maximum field magnitude on the FSS surface to the magnitude of the incident field, used for assessing power handling capability of the structure, is about 4.5. Conclusion: Therefore, these features make the proposed structure suitable for 5G communication and high power systems.

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.

STABILITY OF RUBBLE MOUND STRUCTURES UNDER OBLIQUE WAVE ATTACK

Stability formulae for armour layers of rubble mound breakwaters are generally developed for perpendicular wave attack and do not include effects of oblique waves. Waves usually attack breakwater obliquely as the sea wave is three dimensional. Several studies have been performed to investigate the effect of wave angle (beta) on the armor stability. Galland (1994), Yu et al. (2002), Wolters and Van Gent (2010) and van Gent (2014) performed laboratory experiments to consider effects of oblique waves on the stability of armour layers. They performed tests with long-crested and/or short-crested waves on rock and concrete armours. The aim of this study is to find an appropriate and compatible reduction factor for EBV stability formulae.

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.