Incident Direction Research Articles

Analysis on the split absorber integrated with taut-moored floating turbine

A new wave energy converter is proposed in this paper, consisting of three split heave point absorbers, combined with a taut-moored floating turbine. It is adapted to the waves in the China Sea area, which are characterized by short periods and small amplitudes. Based on a series of physical model tests in regular, irregular, and extreme waves, the hydrodynamic performance of the integrated device is systematically investigated under different damping forces and incident wave directions. The experimental results reveal that the split point absorber presents new hydrodynamic characteristics and that the wave energy capture efficiency of the new device is greatly improved for the short-period waves in low sea states. Moreover, due to the out-of-phase heave motion, as well as the induced shallow water effect, the submerged platform makes a contribution to improving the energy capture efficiency of the split floater, particularly pronounced in the case of a high damping force in the power takeoff system. Under the condition of incident wave direction being coincident with the horizontal projection of mooring lines, the energies of pitch motion and mooring force of the integrated system are increased as a result of the high-frequency oscillation, which needs to be solved by further optimizing the taut mooring system.

Phonon Focusing Effect in an Atomic Level Triangular Structure

The rise of artificial microstructures has made it possible to modulate propagation of various kinds of waves, such as light, sound and heat. Among them, the focusing effect is a modulation function of particular interest. We propose an atomic level triangular structure to realize the phonon focusing effect in single-layer graphene. In the positive incident direction, our phonon wave packet simulation results confirm that multiple features related to the phonon focusing effect can be controlled by adjusting the height of the triangular structure. More interestingly, a completed different focusing pattern and an enhanced energy transmission coefficient are found in the reverse incident direction. The detailed mode conversion physics is discussed based on the Fourier transform analysis on the spatial distribution of the phonon wave packet. Our study provides physical insights to achieving phonon focusing effect by designing atomic level microstructures.

Mechanical behavior and failure mechanism of composite layered rocks under dynamic tensile loading

To bolster the safety and efficacy of blasting and impact drilling for underground works in composite rock strata, the dynamic tension of composite rocks requires thorough examination. Given the challenges of composite rock sampling, cement mortars with varying mix ratios are utilized to create composite rock-like test blocks. These blocks are composed of two different strength materials, further processed into differently sized experimental samples as required. Using a split Hopkinson pressure bar (SHPB) test device, we conducted dynamic Brazilian splitting tests at varying incident angles α (the angle between the incident wave direction and the bedding plane) and strain rates on these composite rock-like samples. The modes of crack propagation in some samples were recorded with a high-speed camera. Laboratory tests and PFC2D simulation were used to analyze the dynamic tensile mechanical properties and failure mechanisms of composite rock samples. Findings indicate the dynamic tensile strength of a composite rock sample is governed by the bedding plane inclination angle. As the incident angle rises from 0° to 90°, the dynamic tensile strength of the composite rock sample first decreases, then increases, consistently reaching a minimum value at α = 30°. The damage model of composite rock samples is also influenced by the dip angle of the bedding planes. At α = 0°, the composite rock sample exhibits through-cracks along the incident wave direction and splitting tensile damage is observed. As α increases, the failure mode gradually transitions from splitting tensile damage to a combination of tensile and shear slip damage along the bedding. Tensile damage always manifests in materials of lower strength. When α surpasses 45°, the failure mode reverts from combined damage to splitting tensile damage. Cross-sectional tensile stress clouds generated by PFC software demonstrate that the tensile stress contours at the specimen's center are elliptically distributed, with the ellipse's long axis nearly parallel to the bedding plane.

Design, modeling, and initial testing of a multi-volume neutron spectrometer

A detector system for neutron spectroscopy and imaging was modeled in Monte Carlo N-Particle transport code (MCNP) to examine the possibility of incident neutron energy measurement (spectroscopy) from an incident direction (imaging) in a hand-held detector system. Experiments using a Pu–Be (plutonium beryllium) neutron source were also conducted. The system is composed of three separate scintillation materials; a hydrogenous neutron scintillation material (BC-501A) and Cs2LiYCl6:Ce (CLYC) separated by Lu2(1-x)Y2xSiO5(LYSO). Light production location and magnitude would be collected using multiple silicon-based photo-multiplier arrays, allowing for spectroscopy and imaging of incident neutrons. Modeled neutron interaction criteria are collected and cataloged through the particle tracking supplemental code (PTRAC) of MCNP 6.2 for analog interactions. Implementing classical neutron kinematics and capture-gated time-of-flight, simulations show that neutron energy is measurable in experiment and that there is position sensitivity to be realized in experiment with the proposed detection architecture. The modeled design was experimentally evaluated with a Pu–Be source, confirming that the spectroscopic capabilities of the detector are functional and closely match the modeled expectation. In this work, we direct our attention to neutron spectroscopy, but the imaging capabilities will be addressed in further work.

Analysis framework for the seismic performance of a concrete high-arch dam considering the incident direction and oblique incident angle of near-fault SV-waves

This study aims to develop an analytical framework to assess the seismic performance of high-arch dams by considering the incident direction and input angle of near-fault (NF) seismic waves. Based on this comprehensive analysis framework, we aim to accomplish the following objectives: (1) Comparison of the discrepancies in the variability of dynamic indices with increasing incident angles along different incident directions of seismic waves; (2) Estimation of the global damage responses based on the seismic characteristic parameters and incident angles; and (3) Assessment of the influences of the impulsive characteristics of NF earthquake waves with different incident directions on the correlations between the response indices. To this end, the effects of the incident direction and incident angle of NF SV-waves (including pulse-like waves and non-pulse-like waves) on the nonlinear responses and correlation of dynamic indicators of arch dams were investigated. The simulation results revealed that the changing pattern of the dynamic behavior of the dam with the incident angle differed significantly along the different incident directions of NF SV-waves. The peak ground velocity/peak ground acceleration was found to have a good correlation with the overall damage volume ratio. Further, along various input directions of NF SV-waves, the damage index was found to have a strong positive correlation with the upstream center joint opening, whereas the degree of correlation between the damage and displacement indices was not reduced owing to the impulsive characteristics of NF SV-waves. Finally, a two-variable damage model that considered both the input angle and seismic characteristic parameters was established and used to roughly predict the global damage index of the dam.

Numerical study on dynamic analysis of a nine-module floating aquaculture platform under irregular waves

A numerical study of the dynamics of a nine-module floating aquaculture platform in irregular waves is proposed, to examine the effect of the connector type between net cages and incident wave direction on the hydrodynamic response. A numerical model based on the coupled boundary element method and lumped-mass model was used to simulate the dynamic behavior of the aquaculture platform. Time-domain statistical analysis, and time-frequency analysis based on Hilbert-Huang transform on the motion responses of net cages and the mooring force responses of the platform were then carried out. The results indicate that the mooring system has a decisive influence on the frequency-domain characteristics of surge motion, while the influence of connector can be ignored. The surge motion under flexible hawser connector is less sensitive to wave incident direction, while the wave direction has a greater impact on surge motion under spherical joint connector. The amplitudes of pitch motion under two different connectors decrease significantly under oblique incident waves, compared with perpendicular incident wave condition. The wave incident direction has little effect on the overall mooring force response of the platform. The mooring force responses at different positions show completely different frequency characteristics when the cages are connected by spherical joints. The larger the pitch response of the cage, the smaller the mooring force response of the mooring chain connected to the net cage. There is a positive correlation between the gravity frequency of the mooring force response and the gravity frequency of the pitch response of the net cage.

Radial characteristics of laser-induced plasma under the influence of air pressure

Air pressure is one of the key factors affecting laser-induced breakdown spectroscopy (LIBS), and the mechanism of its influence on the spatial–temporal evolution of laser-induced plasma (LIP) is still not fully understood due to complex physical processes. In this study, the spatially and temporally resolved LIP’s spectra at different pressures were collected from the direction of laser incidence, and the radial distribution characteristics of LIP along the target surface under the influence of air pressure were studied. Furthermore, the spatial–temporal evolution of the radial distribution of the electron density n e and electron temperature T e was studied using Stark broadening and a Boltzmann plot. Finally, the radial distribution of LIP satisfying the McWhirter criterion and the influence of air pressure on its spatial–temporal evolution were studied. It was found that air pressure has a significant effect on the radial distribution of LIP. The spectral intensity, electron density n e, and the electron temperature T e of the LIP decrease faster against distance r from the LIP core and slower with the delay time T d in a higher air-pressure environment. Furthermore, the LIP will gradually fail to satisfy the McWhirter criterion with the increase in the radius r and delay time T d; in addition, the lifetime of LIP, which satisfies the McWhirter criterion, is longer at higher pressure. This study is helpful in clarifying the influence of air pressure on the spatial–temporal evolution of LIP, optimizing the experimental parameters of LIBS, and providing a reference for application of LIBS.

Dosimetric assessment in the brain for downlink EMF exposure in Korean mobile communication networks

Because the position and direction of the human body is not fixed in an actual environment, the incidence direction of the electromagnetic field (EMF) from mobile communication base stations, WiFi access points, broadcasting towers, and other far-field sources is arbitrary. To analyze the overall health effects of radio frequency EMF exposure, the dosimetric assessment for such environmental exposures created from an unspecified number of sources in daily life, along with exposures from specific EMF sources, must be quantified. This study is aimed at numerically evaluating the time-averaged specific absorption rate (SAR) of the human brain for environmental EMF exposure in the frequency range of 50–5800 MHz. Whole-body exposure to EMFs that are evenly incident spatially is considered. By comparing the results of several incidence directions and the number of polarizations, an optimal calculation condition has been derived. Finally, based on the results measured in Seoul at the end of 2021, the SAR and daily specific energy absorption (SA) in the brains of both a child and an adult for downlink exposures from 3G to 5G base stations are reported. Comparison results of the daily brain SA for exposure to DL EMF in all 3G to 5G mobile networks and exposure to a 10-min voice call (uplink EMF) using a mobile phone connected to a 4G network show that the SA from the downlinks is much higher than that from the uplinks.

Optical properties of N2/Ar plasma generated by electron beams with silicon nitride transmission window at high pressures

In this paper, we report the generation of nitrogen/argon electron beam plasmas with a 0.4 μm-thick silicon nitride transmission window. The measured transmittance of the electron beam is about 92% when the incident energy of electron beam is 40 keV. The optical properties of the electron beam plasma are investigated at high pressures. The luminescence intensity distribution of nitrogen and argon electron beam plasmas shows a good similarity with changing the gas pressure, suggesting that electron beam ionization is independent of background gas. At the same gas pressure, the nitrogen plasma with conical structure has a longer length along the incident direction of the electron beam and a smaller divergence cone angle compared with the argon plasma. In the nitrogen discharge, it is found that the intensities I380.4, I399.7, and I391.4 corresponding to characteristic lines at 380.4, 399.7, and 391.4 nm decrease along the incident direction of the electron beam, which is correlated with the reduction of the electron density along the incident direction of the electron beam. There is no change in the ratio of I399.7 to I380.4, indicating the spatial uniformity of the electron temperature. When the pressure increases, the ionization process induced by primary electron is enhanced, generating more plasma electrons, which is responding to the increase in the characteristic line intensity. At the same time, the neutral particle collision processes are enhanced and the electron temperature decreases with the increase in the pressure, which is believed to contribute to the observed reduction of the I399.7/I380.4 ratio.

First 3D reconstruction of a blast furnace using muography

The blast furnace (BF) is the fundamental tool used in the iron manufacture. Due to the difficulty of making direct measurements of the inner state of blast furnaces, we determined the density distribution of its internal volume in order to improve its productivity using muography. This is an imaging technique based on the differential absorption of a flux of incident particles, muons, by the target under study, similar to clinical X-ray imaging. Muons are elementary particles that have the property of passing through dense materials, up to hundreds of meters of rocks. Their relative absorption and deviation allows the generation of density distribution images of an object by tracking the number of muons received by a detector, before and after passing through a structure. The incident direction of the detected muons is reconstructed by means of a detector composed of 3 scintillator panels that we moved on 3 positions around the BF. With this technique, we obtained the first 3D image of the internal structure of a BF using a Markov Chain Monte Carlo (MCMC) inverse problem solving algorithm on muon flux data. We were also able to perform density monitoring of the BF and monitor some of its operating parameters. We distinguished the position and shape of the cohesive zone, a key element in the productivity of a furnace, validating this innovative measurement concept in the application to a BF and opening the field to a series of future experiments to gain both spatial and temporal resolution.

Rigorous Modal Analysis of Chiral Nanoparticles

AbstractThe physical origins of the chiroptical response from nanostructures are highly demanded for chiral photonics. The chiroptical response of a nanoparticle, whether measured along specific incident directions of exciting waves (when immobilized onto a substrate) or in solution through averaging responses across all structure orientations, is believed to stem from the interplay between three key factors: geometrical chirality, far‐field chirality, and near‐field chirality. This study aims to understand the relationship among these factors using a rigorous quasinormal mode (QNM) expansion method. By decomposing circular dichroism (CD) spectra into individual QNM contributions, it is observed that the chiroptical response with respect to incident directions depends on the extent of field overlapping between the QNM and light. In contrast, the near‐field optical chirality (OC) is determined by the QNMs of the nanoparticle, independent of external excitations. As a proof‐of‐concept, a nanohelix metasurface is proposed that employs lossless gold and exploits the physics of bound states in the continuum to maximize the CD signal.

Numerical Analysis of Wave Load Characteristics on Jack-Up Production Platform Structure Using Modified k-ω SST Turbulence Model

One of the important stages in the offshore structure design process is the evaluation of the marine hydrodynamic load in which the structure operates, this is to ensure an appropriate design and improve the safety of the structure. Therefore, accurate modeling of the marine environment is needed to produce good evaluation data, one of the methods that can accurately model the marine environment is through the Computational Fluid Dynamic (CFD) method. This research aims to analyze the ocean wave load of pressure and force characteristics on the jack-up production platform hull structure using the (CFD) method. The foam-extend 4.0 (the fork of the OpenFOAM) software with waveFoam solver is utilized to predict the free surface flow phenomena as its capability to predict with accurate results. The Reynold Averaged Navier Stokes (RANS) turbulence model of k-ω SST is applied to predict the turbulence effect in the flow field. Five variations of incident wave direction type are carried out to examine its effect on the pressure and force characteristics on the jack-up production platform hull. The wave model shows inaccurate results with the decrease in wave height caused by excessive turbulence in the water surface area. Excessive turbulence levels can be overcome by incorporating density variable and buoyancy terms based on the Standard Gradient Diffusion Hypothesis (SGDH) into the turbulent kinetic energy equation. The k-ω SST Buoyancy turbulence model shows accurate results when verified to predict wave run-up and horizontal force loads on monopile structures. Furthermore, test results of the wave load on the jack-up production platform hull structure shows that the most significant wave load is obtained in variations with the wave arrival direction relatively opposite to the platform wall. Especially in the direction of 90° because it also has the most expansive impact surface area. Meanwhile, the lower wave load is obtained in variations 45° and 135°, which have the relatively oblique direction of wave arrival to the surface.

A reactive molecular dynamics simulation of the atomic oxygen impact on poly(p-phenylene-terephthalamide)

Poly(p-phenylene-terephthalamide) (PPTA) is widely used in spacecraft structures due to its excellent mechanical properties and thermal stability. The space environment resistance of PPTA is the key factor affecting its service life. However, the mechanisms of the erosion process of PPTA during Atomic oxygen (AO) impact, which is one of the main factors for polymer degradation in the low earth orbit, remain unclear. In this study, the degradation mechanisms of PPTA under the AO impact are investigated by analyzing the morphology evolution, mass loss, the distribution of temperature, and the small molecules produced with simulation time using the ReaxFF reactive force field molecular dynamics simulations. The results show that the degradation mechanism of crystalline polymers due to the AO impact is closely related to the direction of the AO incidence. Throughout the simulation, the (010) surface has more mass loss and more CO and CO2 production, showing worse degradation than the (001) surface. This is due to the different temperature distributions of the two models caused by kinetic energy transfer in different crystal orientations. The extremely high local temperature on the surface of the (010) model leads to faster disintegration of the material. The simulation results can be used to provide atomic-scale insight into the design of crystalline polymers and their composites to resist atomic oxygen erosion.

A spectrally selective self-powered photodetector utilizing a ZnO/Cu2O heterojunction

Most heterojunction photodetectors (PDs) can detect single-band, dual-band, or even multi-band light. However, the ability to adjust the spectral response band of the PD remains a challenge. This study presents a self-powered PD based on a ZnO/Cu2O heterojunction that overcomes this limitation. Adjustable and selective detection bands were achieved within a single device by controlling the direction of the incident light. Under zero bias conditions, the PD exhibits a response exclusively in the 500–750 nm region when the light is incident from the ZnO side, with a responsivity of 1.27 mA W−1. Conversely, when the light is incident from the Cu2O side, responsivities of 10.63 and 52.42 mA W−1 are achieved in the 275–750 nm region. Remarkably, the ZnO/Cu2O PD enables tunable detection of the response region depending on the incident light direction. The dual-band response is attributed to the differential distribution of the width of the depletion layer and the built-in electric field. This study offers valuable insights into the potential applications of PDs with spectral selectivity in optical communication, sensing, and intelligent optoelectronic devices.

Effect of deposition angle on the deposition rate, microstructure, electrical and optical properties of magnetron sputtered ZrB2 thin films

The microstructure and properties of thin films prepared by magnetron sputtering are usually sensitive to not only sputtering power and working pressure, but also the incident direction. In this work, ZrB2 thin films were prepared by DC magnetron sputtering at same sputtering parameters but substrate inclined from 0° to 30°. The deposition rate, microstructure, electrical and optical properties were investigated in details. XPS analysis demonstrates that all the prepared ZrB2 films are B-rich in compositions. Microstructure characterization shows the ZrB2 films deposited at bigger oblique angles are with better crystallization and bigger surface roughness, the former leads to the films with lower resistivity, the latter leads to the films with stronger absorbing ability in the UV–vis-NIR wavelength band. Adjusting substrate to a suitable oblique angle is a promising method to achieve higher quality ZrB2 films..

Directional terahertz holography with thermally active Janus metasurface

Dynamic manipulation of electromagnetic (EM) waves with multiple degrees of freedom plays an essential role in enhancing information processing. Currently, an enormous challenge is to realize directional terahertz (THz) holography. Recently, it was demonstrated that Janus metasurfaces could produce distinct responses to EM waves from two opposite incident directions, making multiplexed dynamic manipulation of THz waves possible. Herein, we show that thermally activated THz Janus metasurfaces integrating with phase change materials on the meta-atoms can produce asymmetric transmission with the designed phase delays. Such reconfigurable Janus metasurfaces can achieve asymmetric focusing of THz wave and directional THz holography with free-space image projections, and particularly the information can be manipulated via temperature and incident THz wave direction. This work not only offers a common strategy for realizing the reconfigurability of Janus metasurfaces, but also shows possible applications in THz optical information encryption, data storage, and smart windows.

Seismic Response of a Rockfill Dam with an Asphalt–Concrete Core under P Waves with Arbitrary Incident Angles

The incident angles of seismic waves have a significant influence on the seismic response of asphalt–concrete core rockfill dams. This paper constructs the free field of elastic semispace under P waves with arbitrary incident angles and clarifies the variation law of the seismic intensity on the ground surface with incident angles γ and α. The free field on the foundation boundary under arbitrary combinations of angles γ and α are derived according to the wave-field superposition principle. Combined with the viscoelastic artificial boundary, the free field is transformed into the equivalent load on the boundary node, and the input method of the P wave with arbitrary incident angles is established. Finally, the seismic response of the asphalt–concrete core dam under P waves with arbitrary incident angles is studied. The results show that when the incident direction is perpendicular to the dam axis, the dynamic shear stress is the highest, and the local seismic safety factor of the dam is the largest. When the incident direction is parallel to the dam axis, the tensile stress of the asphalt core is the highest, there is a possibility of cracking at the contact part of the lower part of the asphalt core with the canyon, and the seismic subsidence rate of the dam crest is the highest. For the tensile stress of the asphalt core and the dam-crest subsidence rate, the most unfavorable incident angle α is 75° when the incident angle γ is the same.

Low-cost photoreactors for highly photon/energy-efficient solar-driven synthesis

Low-cost photoreactors for highly photon/energy-efficient solar-driven synthesis

Intelligent Prediction for Scattering Properties Based on Multihead Attention and Target Inherent Feature Parameter

In this communication, an artificial intelligent method based on the prevailing multi-head attention mechanism for prediction of scattering properties of 2D targets is presented. To make the predicting approach independent of the incident direction of an excitation plane wave, a kind of inherent feature parameters for a specific target are defined, and applied as the output of the artificial neural network. Two types of targets are experimented, one of which is composed of polygons and the other of smooth shapes. Numerical results show that the proposed method has satisfactory prediction accuracy and computing speed, as well as good generalization ability.

Terahertz near-field imaging of graphene disks

Due to the weak power of Terahertz sources, metal tips are often used to enhance the signal intensity of the Terahertz scattering scanning near-field optical microscope (THz s-SNOM). However, while enhancing the near-field, metal tips also affect the field distribution on the sample surface. In this paper, a home-built 97.8GHz sub-Terahertz near-field imaging system was used to image graphene disks with dozens of microns in diameter. It was found that the field distribution was significantly different from that without the tip, and was related to the incident direction of the terahertz wave.