Incident Wave Angle Research Articles

Nonlinear Seismic Response of SV Wave Incident Angle and Direction to Concrete Gravity Dam

Nonlinear Seismic Response of SV Wave Incident Angle and Direction to Concrete Gravity Dam

Torsional effect of the single-bay masonry building considering seismic wave incident angle

Single-bay masonry building is the main structure form of rural houses in Southwest China. In the investigation of earthquake damage in Lushan earthquake, it is found that this type of structure has serious torsional damage. In this paper, the torsional effect was verified with 1/6 scale model while the torsional responses of some actual size models were simulated by self-compiled program. Under the coupling action of translation and torsion, the effects of seismic wave incident angle and structural geometric dimension on the torsional response of structure were analyzed. The results showed that the incident angle of seismic wave and the structural irregularity were the important reasons which caused the torsional failure of the structure. When the incident angle of the seismic wave was about 60°, the torsional response of the structure was the strongest. Besides, in order to reduce the influence of torsional effect, the eccentricity ratio should be smaller than 6%, and the number of storey should better be three or less.

Realization of Multifunctional Metamaterial Structure Based on the Combination of Vanadium Dioxide and Graphene.

Combining tunable properties and various functionalities into a single metamaterial structure has become a novel research hotspot and can be used to tackle great challenges. The multifunctional metamaterial structure that combines absorption, linear-to-circular (LTC) polarization conversion, filtering and switching functions into a single metamaterial device was designed and investigated in this study. The switching of different functions can be achieved based on the phase transition of vanadium dioxide (VO2) and change of graphene chemical potential. When VO2 is in a metal state, the multi-frequency absorption and LTC polarization conversion can be achieved with different chemical potentials. When VO2 is in the insulator state and the polarization angle of incident wave is 45°, the device can be used to select or isolate the incident waves with different polarization states in the frequency region of 1.2–1.8 THz. Furthermore, when the chemical potentials are 0.05 eV and 1.2 eV, the corresponding transmissions of the TE-polarized wave demonstrate the opposite results, realizing the switching functions in the frequency region of 0.88–1.34 THz. In the frequency region above 2 THz, the multi-frequency rejection filter can be achieved. The designed switchable multifunctional metamaterial device can be widely implemented in radar monitoring and communication systems.

Independently tunable bifunctional terahertz metasurface based on double-layer graphene

Artificial metasurfaces are one of the most promising candidates for realizing flexibly tunable devices. Here we propose a tunable bifunctional metasurface (TBM), which incorporates two layers of independently controllable hollow-patterned graphene that contribute to wideband linear polarization conversion mode and dual-band absorption mode, respectively. When working in linear polarization conversion mode, it can achieve the polarization conversion ratio (PCR) of over 96.1% and the relative bandwidth of about 42.2% in 3.98–6.11 THz; when operating in dual-band absorption mode, the absorptivity can reach 97.1% and 99.9% at 3.55 THz and 4.98 THz, respectively. The working mechanisms are elucidated through the eigenmode decomposition, transmission line model, surface current and field distributions. In addition, the influences of the chemical potential and relaxation time of graphene, main geometric parameters of the TBM, and incident angle of terahertz waves are discussed, implying that the TBM has excellent tunability and tolerance, and may provide a scheme for designing terahertz devices such as isolators, modulators and rotators.

A vanadium dioxide-based metamaterial with quatrefoil and circle loaded structure on flexible polyamide substrate for terahertz applications

In this study, a novel broadband metamaterial (MTM) absorber is proposed, which is based on vanadium dioxide (VO2) resonators coated onto a flexible polyamide substrate. The VO2 resonator is in the form of a quatrefoil and circle-loaded complementary square split ring resonator (CSSRR), which is fine tuned to operate in the terahertz range. The MTM design and simulation were carried out using Computer Simulation Technology (CST) software, by which different layouts were investigated to achieve the optimum structure. The results showed the presence of two pronounced peaks for the proposed MTM structure at 0.88 and 1.42 THz. The absorption peaks were found to be insensitive to the wave polarization and incident angle from 0° to 90°. The absorption mechanism of the MTM was investigated considering the insulating and metallic states of VO2. The results were in a good agreement with those calculated using high frequency simulated structure (HFSS) software. The flexible nature of the proposed MTM design makes it a viable candidate for non-planar and conformal geometry applications in stealth technology, and terahertz imaging.

Kathmandu Basin as a local modulator of seismic waves: 2-D modelling of non-linear site response under obliquely incident waves

SUMMARYThe 2015 Mw 7.8 Gorkha, Nepal earthquake is the largest event to have struck the capital city of Kathmandu in recent times. One of its surprising features was the frequency content of the recorded ground motion, exhibiting a notable amplification at low frequencies (<2 Hz) and a contrasting depletion at higher frequencies. The latter has been partially attributed to the damper behaviour of the Kathmandu basin. While such weak high-frequency ground motion helped avoiding severe damage in the city, the catastrophic outcomes of earlier earthquakes in the region attest to a contrasting role of the Kathmandu basin as a broad-band amplifier, in addition to possible source effects. Given the possibility of future strong events in the region, our main objective is to elucidate the seismic behaviour of the Kathmandu basin by focusing on site effects. We numerically model 2-D P–SV wave propagation in a broad frequency band (up to 10 Hz), incorporating the most recent data for the Kathmandu basin geometry, soil stratigraphy and geotechnical soil properties, and accounting for the non-linear effect of multidimensional soil plasticity on wave propagation. We find that: (1) the Kathmandu basin generally amplifies low frequency ground motion (<2 Hz); (2) waves with large incidence angles relative to vertical can dramatically amplify the high frequency ground motion with respect to bedrock despite the damping effect of soil non-linearity and (3) the spatial distribution of peak ground motion amplitudes along the basin is highly sensitive to soil non-linearity and wave incidence (angle and direction), favouring larger values near the basin edges located closer to the source, as observed during the 2015 event. Our modelling approach and findings can support the ongoing resilience practices in Nepal and can guide future seismic hazard assessment studies for other sites that feature similar complexities in basin geometry, soil stratigraphy and dynamic soil behaviour.

Dynamic SV‐Wave Signatures of Fluid‐Saturated Porous Rocks Containing Intersecting Fractures

AbstractDetecting fracture intersections is crucial for understanding rock hydraulic properties. For this purpose, we study the dynamic SV‐wave signatures of fluid‐saturated porous rocks containing intersecting fractures. A theoretical model is derived using the dynamic Biot's poroelasticity equations. Using this model, we analyze the features of SV‐waves and compare to those of previously studied P‐waves. The results show that the dispersion and attenuation of SV‐waves caused by elastic scattering and FF‐WIFF (Fracture‐Fracture Wave‐induced Fluid Flow) have a similar dependence on properties of intersecting fractures and fluid as those of P‐waves. However, the FB‐WIFF (Fracture‐Background Wave‐induced Fluid Flow) causes much smaller dispersion and attenuation for SV‐waves than for P‐waves. In particular, such dispersion and attenuation of SV‐waves are negligibly small for the orthogonally intersecting fractures regardless of wave incidence angles. In addition to the dispersion and attenuation, the WIFF and elastic scattering also greatly affect the anisotropy properties, which gives rise to frequency‐dependent velocity and attenuation anisotropies for both SV‐ and P‐ waves. Such anisotropy properties are sensitive to fracture intersection angles and are quite different between SV‐ and P‐ waves. These complementary features of SV‐ and P‐ waves provide the basis for fracture intersection detection using the combined features of these two waves. By comparing our model to the known results for the limiting cases, we validate our model.

Effect of Considering Wave Angles on the Motion Response of Oversized Floating Bodies in Offshore Airports under Irregular Wind and Wave Loads

Most existing studies are based on the hydroelastic response of oversized floating bodies under regular waves, ignoring the effect of wave conditions and incident wave angle on the vibration response of oversized floating bodies in real sea conditions. In this paper, the stability performance of a single module of a mega-floating body at an offshore airport was investigated by using STAR-CCM + numerical simulations based on a specific model, with the introduction of parameters under extreme random wind and wave combined sea conditions. By comparing and analyzing the distribution characteristics of the single module floating body under the action of regular waves and irregular waves, wind, and wave load, and by considering the wave angle along the flow direction, as well as the spreading direction and vertical displacement value under the action of mooring, the overall displacement amplitude of rigid displacement, elastic deformation displacement and considering the influence of both, and the distribution law of motion response along the length of the floating body, we summarize the influence of the wave angle on the dynamic response of an oversized floating body of an offshore airport. The results show that the maximum value of the hydro-elastic response tends to appear at the head and tail of the floating body, the rigid body vertical displacement dominates the role, the amplitude of all displacements of the floating body under the action of the cross wave is larger, and the stress area along the floating body is larger when the wave angle is between 15–30°. The floating body stress value is smaller with angles of 30–65°, and the ability to bear the load is stronger. The hydroelastic response under irregular wave conditions is more sensitive to the wave direction angle, and the elastic deformation has less influence.

A Symmetrical Terahertz Triple-Band Metamaterial Absorber Using a Four-Capacitance Loaded Complementary Circular Split Ring Resonator and an Ultra-Thin ZnSe Substrate

In this research work, a symmetrical four-capacitance loaded complementary circular split ring resonator is proposed, which uses an ultra-thin Zinc Selenide (ZnSe) substrate to realize a low-profile triple-band metamaterial (MTM) perfect absorber for application in the terahertz (THz) frequency range. The electromagnetic properties of the proposed structure were calculated and investigated using the Finite Integration Technique (FIT). The proposed structure exhibited three highly absorptive (nearly perfect) peaks at the resonance frequencies of 15.68 THz, 37.48 THz, and 39.55 THz. Furthermore, the absorber was found to be insensitive to the polarization and incident wave angles, due to its symmetrical design. The effects of the conductor type, substrate thickness, unit cell dimension, resonator gap, and substrate type on the reflection and absorption spectra were investigated. To validate the numerical results, the proposed design was analyzed using High-Frequency Simulation Software (HFSS) and Advanced Design System (ADS). The surface current, electric field, and magnetic field distributions at the three-resonance frequency were analyzed. It was concluded that the overall performance of the proposed MTM structure was superior compared to those reported in the literature. The proposed design could be a good candidate for application in stealth technology, imaging, and thermal energy harvesting.

Analysis of AVAZ Seismic Forward Modeling of Fracture-Cavity Reservoirs of the Dengying Formation, Central Sichuan Basin

For the purpose of clarifying the seismic response characteristics of fractured-cavity reservoirs of Dengying Formation in the central Sichuan Basin, the paper first intends to establish three geological models of fracture cave reservoirs based on drilling, logging, and core data of the Dengying Formation in the central Sichuan Basin. Then, the formation reflection is calculated with reference to anisotropic Horizontal Transverse Isotropy (HTI) medium. Finally, further research on Amplitude Variation with Azimuth (AVAZ) seismic forward modeling has been conducted to clarify the seismic response characteristics of different reservoir types in the study area. The results suggest that: Seismic response characteristics of fractured-cavity reservoirs are controlled by incident angle and azimuth angle of seismic waves in different types of reservoirs. The incident angle of the seismic wave controls the difference in amplitude caused by different micro-fracture densities, and the azimuth angle controls the identification ability of the micro-fracture direction. The increase in incident angle brings about a gradual decline in amplitude. The magnitude reaches the highest when the azimuth is parallel to the normal direction of the fracture surface; however, it’ll come down to the lowest as the azimuth is perpendicular to the normal direction of the fracture surface. The fracture density fails to affect the amplitude as long as the azimuth angle is parallel to the direction of the fracture. However, the decreased amplitude reflects the increasing fracture density as the azimuth angle is identical to the normal direction of the fracture surface. The comparison between the theoretical model of three different types of fractured-cavity reservoirs and the actual uphole trace shows that the model has high accuracy. The prospect of seismic identification of fractured-cavern reservoirs, based on the results, can provide us with feasible and applicable evidence for future research on seismic identification of reservoirs and prediction of fracture distribution in the Dengying Formation of central Sichuan.

Impact of Wedge Parameters on Ultrasonic Lamb Wave Liquid-Level Sensor.

The ultrasonic Lamb wave detection principle can realize the noncontact measurement of liquid level in closed containers. When designing an ultrasonic Lamb wave sensor, it is vital to thoroughly study and select the optimal wedge size at the front of the sensor. In this paper, firstly, we select the best working mode of Lamb waves according to their propagation dispersion curve in aluminum alloy, and we obtain the best angle of wedge through experiments. Secondly, we study the impact of the size of the wedge block on the results, and we obtain the selection method of wedge block parameters. The evaluations show that, when the frequency–thickness product is 3 MHz·mm, the Lamb waves work in the A1 mode, and the experimental effect is the best. At this time, the incident angle of the ultrasonic wave is 27.39°. The wedge thickness should be designed to avoid the near-field area of the ultrasonic field, and we should choose the length as odd multiples of 1/4 wavelength. The rules obtained from the experiment can effectively select the best working mode for ultrasonic Lamb waves, while also providing a basis for the design of the wedge block size in a Lamb wave sensor.

Theoretical Evaluation of Angle-Dependent Optical Properties of a Thin Film Solar Cell Including One-Dimension Photonic Crystals

The effective use of photonic-based integrated systems, whose optical properties can be tuned through light management engineering in optoelectronic devices, constitutes the backbone of today's technology. Especially in systems such as CdTe-based solar cells with well-known and high efficiency, one-dimensional photonic crystal designs emerge as an effective way to provide an electronic or optical improvement. With this intention, in this study, the optical spectra of the MgF2/MoO3 one-dimensional photonic crystal integrated into the CdTe solar cell to improve photon harvesting were investigated theoretically under both bottom and top illumination according to the incidence angle of the electromagnetic wave. The transfer matrix method was used to calculate the angle dependent optical spectra. Since the electromagnetic wave interacts directly with the photonic crystal, it has been observed that the optical properties are more dependent on the angle under the top illumination compared to the bottom one. For top illumination, up to 30°, there is no significant change in reflection in the photonic band gap, but reflection drops significantly at incidence angles greater than 30°. Also, increasing the angle indicates that the low wavelength tail of the photonic band gap shifts to shorter wavelengths and enters the visible region. In the photonic band gap, for angles greater than 45°, the probability of absorption increases significantly as more electromagnetic waves enter the structure. For the bottom illumination, there is no serious dependence on the angle of incidence. For 75°, there is an increase in reflection for all wavelengths and, therefore, a decrease in absorption.

Study on the enhancement mechanism of terahertz molecular fingerprint sensing

THz-time domain spectroscopy is an effective method of label-free molecular detection, but it is limited by the size of the measured samples. Traditional detection approaches will have to overcome challenges when the analyte are in trace amounts. Here, we propose an enhanced mechanism for terahertz molecular fingerprint sensing, involving an all-dielectric metasurface. Based on incident wave angle scanning under light polarization, the broadband light–matter interaction is effectively enhanced, significantly improving the fingerprint signal of the molecule to be detected. The results demonstrate a new method for trace molecular detection in the terahertz region and large-scale molecular screening.

Switchable Multifunctional Terahertz Metamaterials Based on the Phase-Transition Properties of Vanadium Dioxide.

Currently, terahertz metamaterials are studied in many fields, but it is a major challenge for a metamaterial structure to perform multiple functions. This paper proposes and studies a switchable multifunctional multilayer terahertz metamaterial. Using the phase-transition properties of vanadium dioxide (VO2), metamaterials can be controlled to switch transmission and reflection. Transmissive metamaterials can produce an electromagnetically induced transparency-like (EIT-like) effect that can be turned on or off according to different polarization angles. The reflective metamaterial is divided into I-side and II-side by the middle continuous VO2 layer. The I-side metamaterials can realize linear-to-circular polarization conversion from 0.444 to 0.751 THz when the incident angle of the y-polarized wave is less than 30°. The II-side metamaterials can realize linear-to-linear polarization conversion from 0.668 to 0.942 THz when the incident angle of the y-polarized wave is less than 25°. Various functions can be switched freely by changing the conductivity of VO2 and the incident surface. This enables metamaterials to be used as highly sensitive sensors, optical switches, and polarization converters, which provides a new strategy for the design of composite functional metamaterials.

3D Numerical Modeling and Quantification of Oblique Wave Forces on Coastal Bridge Superstructures

Simply supported bridges comprise the majority of bridge systems in coastal communities and are susceptible to severe damage from extreme waves induced by storms or tsunamis. However, the effects of oblique wave impacts have been less investigated due to the lack of appropriate numerical models. To address this issue, this study investigates the effects of wave incident angles on coastal bridge superstructures by developing an advanced computational fluid dynamics (CFD) model. Different wave scenarios, including wave height, relative clearance, incident angle, and wavelength are tested. It is found that the maximum wave forces in the horizontal and longitudinal directions could reach 1901 and 862 kN under extreme conditions, respectively, destroying bearing connections. Three surrogate models, i.e., the Gaussian Kriging surrogate model, the Artificial Neural Network (ANN), and the Polynomial Chaos Expansion (PCE), are established by correlating the wave parameters with the maximum wave forces. Through comparisons among the three surrogate models, it is found that the 3-order PCE model has better performance in predicting loads in vertical and horizontal directions, while the ANN model is more suitable for results in the longitudinal direction. This study contributes to the optimized design of coastal bridges and also offers an opportunity for future studies to investigate hazard damage-mitigation measures.

Parametric study of wave impact pressure impulse and characteristic pressure on a square column with overhanging deck

Semi-submersible platforms may suffer safety accidents due to severe wave impacts on the decks and columns in extreme ocean environment. The pressure impulse considering the cumulative effect of time is significant for the dynamic response analysis of offshore and coastal structures, and has attracted attentions in recent years. In this study, wave impact tests on a square column with overhanging deck were carried out under a series of fifth-order Stokes waves with large steepness to investigate the influence parameters on the impact pressure impulse. A novel definition of characteristic pressure is proposed from the perspective of pressure impulse, meanwhile, its dimensionless relation with the peak impact pressure is presented. The spatial distributions of the pressure impulse and characteristic pressure on the square column with overhanging deck, as well as the influences of several environmental and model parameters are discussed in detail. The results show that the spatial distributions and vertical variations of wave pressure impulse are affected significantly by the wave parameters, initial air gap, column incline angle and wave incidence angle. In general, the wave impact on the overhanging deck and the upper part of column is severer, and the inclination of column can reduce the pressure impulse to some extent. The research findings may provide references for further research and the predesign of the column–deck structure of semi-submersibles.

Simulation and Design of HgSe Colloidal Quantum-Dot Microspectrometers

In recent years, colloidal quantum dots (CQD) have been intensively studied in various fields due to their excellent optical properties, such as size-tunable absorption features and wide spectral tunability. Therefore, CQDs are promising infrared materials to become alternatives for epitaxial semiconductors, such as HgCdTe, InSb, and type II superlattices. Here, we report a simulation study of a microspectrometer fabricated by integrating an intraband HgSe CQD detector with a distributed Bragg reflector (DBR). Intraband HgSe CQDs possess unique narrowband absorption and optical response, which makes them an ideal material platform to achieve high-resolution detection for infrared signatures, such as molecular vibration. A microspectrometer with a center wavelength of 4 µm is studied. The simulation results show that the optical absorption rate of the HgSe CQD detector can be increased by 300%, and the full-width-at-half-maximum (FWHM) is narrowed to 30%, realizing precise regulation of the absorption wavelength. The influence of the incident angle of light waves on the microspectrometer is also simulated, and the results show that the absorption rate of the HgSe quantum dot detector is increased 2–3 times within the incident angle of 0–23 degrees, reaching a spectral absorption rate of more than 80%. Therefore, we believe that HgSe CQDs are a promising material for realizing practical HgSe microspectrometers.

Multilayer metamaterial graphene sensor with high sensitivity and independent on the incident angle

A new metamaterial refractive index sensor in terahertz frequency band is proposed. The designed structure is multilayer and periodic. It consists of two SiO2 layers separated by an air gap. On the upper SiO2 layer, a unit cell of a graphene circular ring as well as four graphene elliptical half rings are placed while, a graphene circular disk is located on the lower SiO2 layer. By changing the Fermi level of graphene, selection of the optimized dimensions of the structure and the embedded air gap between the two SiO2 layers, a high sensitivity sensor by suitable figure of merit is provided. The maximum sensitivity of 36.7 μm/RIU and figure of merit of 6.43, with refractive index variations of the sensing environment from 1 to 2, is obtained. The symmetric sensor is independence from the incident wave polarization and angle. Electric field and surface current distribution of the structure is investigated and strong interaction of the incident wave with the graphene pattern is illustrated. The performance of the designed structure is compared with recent similar works and it is shown that sensitivity improvement is achieved. The proposed structure is suggested for biosensing applications.

Performance evaluation of crack identification using density-based topology optimization for experimentally visualized ultrasonic wave propagation

Although techniques to visualize ultrasonic wave propagation help to detect defects, quantitative evaluation using these techniques remains a significant challenge. In this study, a topology-optimization-based damage identification method combined with an ultrasonic wave visualization technique is applied to the experimental results, and its performance is evaluated. This method estimates the target crack as the distribution of ‘damage parameters’ that reproduces the experimentally visualized ultrasonic wave propagation in an inverse analysis model. The objective function of the optimization was the sum of the squared error between the maximum amplitude distribution obtained in the experiment and finite element analysis. Our results suggest that the crack identification results depend on the incidence angle of the ultrasonic wave to the target crack. This is because the low amplitude in the downstream region of the ultrasonic wave to the crack causes low sensitivity of the objective function. Crack identification was performed using the dataset of ultrasonic wave propagation incident from two directions. The crack could be identified with high accuracy provided the sensitivity of the objective function was high in the entire design domain. Based on this mechanism of crack identification, this study proposes two indices to evaluate the validity of crack identification results in actual inspections.

Energy reflection and transmission characteristics of acoustic waves in a functionally graded piezoelectric plate immersed into non-viscous fluid

In this work, the reflection and transmission coefficients characteristics of plane waves in a functionally graded (FG) piezoelectric plate immersed in non-viscous liquid (water) are investigated using the stiffness matrix method (SMM). The general solutions of the displacement and the stress are expressed in terms of the eigenvalues and eigenvectors. These are derived from a system of first-order ordinary differential equations with variable coefficients of eight ranks. The SMM is employed to find the relation between the displacements and the tractions on the upper and lower interfaces of the multilayer. Subsequently, the reflection and transmission coefficients of a plane acoustic wave propagating in the FG piezoelectric plates are derived by computing the Poynting vector of each partial wave. The convergence of the SMM is studied through several numerical examples. The effects of the wave incident angle and the gradient coefficients of FG plate on the reflection/transmission characteristics and critical angle are discussed. It is found that the critical angle of incidence is strongly affected by the variation of the linear and the exponential gradient coefficient as well, the resonance frequency shifts to the lower frequency range with the increase of the gradient coefficient.