المؤلفون: Bin Liu, Yu Wu, Qijia Zheng, Lu Su, Yan Lu, Chenglin Miao, Jinyang Huang, Chang Wen Chen, Jianchun Liu

المصدر: IEEE Transactions on Mobile Computing. 22:2938-2954

مصطلحات موضوعية: Computer Networks and Communications, Computer science, business.industry, Real-time computing, Co-channel interference, Interference (wave propagation), Activity recognition, Robustness (computer science), Channel state information, Component (UML), Wireless, Electrical and Electronic Engineering, business, Wireless sensor network, Software

الوصف: Driven by a wide range of essential applications, significant achievements are made to explore WiFi-based Human Activity Recognition (HAR) techniques that utilize the information collected by commercial off-the-shelf WiFi infrastructures to infer human activities without the need for subjects to carry any devices. Although existing WiFi-based HAR systems achieve satisfactory performance in some instances, they are faced with a severe challenge that the impacts of ubiquitous Co-channel Interference (CCI) on WiFi signals are inevitable. This downgrades the performance of these HAR systems significantly. To address this challenge, we propose PhaseAnti, a novel WiFi-based HAR system to exploit the CCI-independent phase component, Nonlinear Phase Error Variation (NLPEV), of WiFi Channel State Information to cope with the negative effects of CCI. The stability of NLPEV data and the sensibility of this component to motions are rigorously analyzed. Furthermore, validated by extensive properly designed experiments, this phase component across subcarriers is invariant under various CCI scenarios while sufficiently distinct for different motions. Therefore, the NLPEV data can be used and processed effectively to perform HAR in CCI scenarios. Extensive experiments with various daily activities in different indoor rooms demonstrate the superior effectiveness and generalizability of the proposed PhaseAnti system under various CCI scenarios.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_________::d30d515bd8f7e40ee3d58ca609fb715aTest
https://doi.org/10.1109/tmc.2021.3127721Test

المؤلفون: Yiu-Wing Leung, Shuwei Qiu, Joseph Kee-Yin Ng, Xiaowen Chu

المصدر: IEEE Transactions on Mobile Computing. 22:2771-2788

مصطلحات موضوعية: Computer Networks and Communications, Computer science, business.industry, Quality of service, ComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKS, Fault tolerance, Interference (wave propagation), IEEE 802.11ax, Power (physics), Point (geometry), Electrical and Electronic Engineering, business, Greedy algorithm, Throughput (business), Software, Computer network

الوصف: IEEE 802.11ax is the standard for the new generation WiFi networks. In this paper, we formulate the problem of joint access point (AP) placement and power-channel-resource unit assignment for 802.11ax-based dense WiFi. The objective is to minimize the number of APs. Two quality-of-service (QoS) requirements are to be fulfilled: (1) a two-tier throughput requirement which ensures that the throughput of each station is good enough, and (2) a fault tolerance requirement which ensures that the stations could still use WiFi even when some APs fail. We prove that this problem is NP-hard. To tackle this problem, we first develop an analytic model to derive the throughput of each station under the OFDMA mechanism and a widely used interference model. We then design a heuristic algorithm to find high-quality solutions with polynomial time complexity. Simulation results under both fixed-user and mobile-user cases show that: (1) when the area is small (50 x 50 m2), our algorithm gives the optimal solutions; when the area is larger (80 x 60 m2), our algorithm can reduce the number of APs by 34.9-87.7% as compared to the Random and Greedy algorithms. (2) Our algorithm can always get feasible solutions that fulfill the QoS requirements.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_________::fd6aea2855c5b56cd304da98d0b0d139Test
https://doi.org/10.1109/tmc.2021.3129596Test

المؤلفون: Xun Li, Johan Robertsson, Dirk-Jan van Manen

المصدر: Geophysical Journal International, 233 (1)

مصطلحات موضوعية: Internal absorbing boundaries, Body waves, Wave propagation, Geophysics, Numerical modelling, Geochemistry and Petrology, Wave scattering and diffraction, Numerical solutions, Wave propagation experiments

الوصف: We describe an elastic wave propagation laboratory that enables a solid object to be artificially immersed within an extended (numerical) environment such that a physical wave propagation experiment carried out in the solid drives the propagation in the extended (numerical) environment and vice versa. The underlying method of elastic immersive wave experimentation for such a laboratory involves deploying arrays of active multicomponent sources at the traction-free surface of the solid (e.g. a cube of granitic rock). These sources are used to accomplish two tasks: (1) cancel outgoing waves and (2) emit ingoing waves representing the first-order interactions between the physical and extended domains, computed using, for example, a finite-difference (FD) method. Higher-order interactions can be built by alternately carrying out the processes for cancelling the outgoing waves and the FD simulations for generating the ingoing waves. We validate the proposed iterative scheme for realizing elastic immersive wave experimentation using 2-D synthetic wave experiments.
Geophysical Journal International, 233 (1)
ISSN:0956-540X
ISSN:1365-246X

وصف الملف: application/application/pdf

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::53afdf39588c263d1723d6f2f483f0a0Test
https://doi.org/10.1093/gji/ggac479Test

المؤلفون: Davide Raffaele, Emiliano Rustighi, Timothy Waters

المصدر: Vibration; Volume 6; Issue 2; Pages: 359-374

مصطلحات موضوعية: semi-analytical finite-element (SAFE) method, forced wave propagation, non-destructive evaluation techniques, structural health monitoring (SHM), General Medicine

الوصف: The Semi-Analytical Finite-Element (SAFE) method represents one of the most established numerical approaches for predicting the propagation of elastic waves in one-dimensional structures of arbitrary cross-sections. Its implementation in the commercial finite-element software COMSOL Multiphysics has been proposed in recent years; however, it is limited to only the free wave propagation for computing dispersion curves. To overcome this limitation, this paper proposes an extension of this approach that combines COMSOL and its Livelink for Matlab tool. This enables the extraction from COMSOL of the assembled mass and stiffness SAFE matrices to solve problems of both free and forced wave propagation in the Matlab environment. The resulting customised software takes advantage of both the potential of commercial FE software and the power of Matlab without worrying about compatibility issues. A model of a simply supported plate strip and that of a more complex geometry are implemented to validate, respectively, the SAFE matrix extraction procedure and the implemented forced response formulation. The results agree well with corresponding analytical and numerical results validating the proposed implementation of the SAFE method.

وصف الملف: application/pdf

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::6d230e004d96cd62be5661a831490fa2Test
https://doi.org/10.3390/vibration6020022Test

المؤلفون: Dan Keun Sung, Xinming Zhang, Hui Zhang

المصدر: IEEE Transactions on Mobile Computing. 22:1880-1893

مصطلحات موضوعية: Computer Networks and Communications, business.industry, Computer science, Retransmission, ComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKS, Latency (audio), Data_CODINGANDINFORMATIONTHEORY, Interference (wave propagation), law.invention, Relay, law, Metric (mathematics), Redundancy (engineering), Overhead (computing), Electrical and Electronic Engineering, business, Software, Selection (genetic algorithm), Computer network

الوصف: In VANETs, it is important to support fast and reliable multi-hop broadcast for safety-related applications. The performance of multi-hop broadcast schemes is greatly affected by relay selection strategies. However, the relationship between the relay selection strategies and the expected broadcast performance has not been fully characterized yet. Furthermore, conventional broadcast schemes usually attempt to minimize the waiting time difference between adjacent relay candidates to reduce the waiting time overhead, which makes the relay selection process vulnerable to internal interference, occurring due to retransmissions from previous forwarders and transmissions from redundant relays. In this paper, we jointly take both of the relay selection and the internal interference mitigation into account and propose a fast, reliable, opportunistic multi-hop broadcast scheme, in which we utilize a novel metric called the expected broadcast speed in relay selection and propose a delayed retransmission mechanism to mitigate the adverse effect of retransmissions from previous forwarders and an expected redundancy probability based mechanism to mitigate the adverse effect of redundant relays. The performance evaluation results show that the proposed scheme yields the best broadcast performance among the four schemes in terms of the broadcast coverage ratio and the end-to-end delivery latency.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_________::3edf7e5ffe048be6beec26d962c48309Test
https://doi.org/10.1109/tmc.2021.3119015Test

المؤلفون: Tatsuaki Kimura

المصدر: IEEE Transactions on Mobile Computing. 22:2205-2220

مصطلحات موضوعية: symbols.namesake, Computer Networks and Communications, Computer science, symbols, Statistical physics, Electrical and Electronic Engineering, Interference (wave propagation), Poisson distribution, Software

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_________::6764e15cc2a885b1240e43bbe21440d0Test
https://doi.org/10.1109/tmc.2021.3116314Test

المؤلفون: R Zhang, P Boué, M Campillo, J Ma

المساهمون: Institut des Sciences de la Terre (ISTerre), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Gustave Eiffel-Université Grenoble Alpes (UGA), Harbin Institute of Technology (HIT), Peking University [Beijing], ANR-20-CE49-0003,TerraCorr,Corrélation du Bruit Microsismique et de la Coda des Grands Séismes pour l'Imagerie de la Terre Profonde(2020), European Project: No. 742335,ERC F-IMAGE

المصدر: Geophysical Journal International
Geophysical Journal International, 2023, 234 (2), pp.933-947. ⟨10.1093/gji/ggad103⟩

مصطلحات موضوعية: Body waves, Wave propagation, Geophysics, Seismic noise, Numerical modelling, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Geochemistry and Petrology

الوصف: SUMMARY Secondary microseisms are caused by nonlinear interactions between ocean waves of approximately equal wavelengths and opposite propagation directions. This seismic forcing is evaluated using ocean sea-state hindcast data and further modulated by the bathymetric effect. The numerical ocean model provides a global activity representation of the secondary microseisms, from which we isolate major events. We backprojected teleseismic P-wave propagation into the Earth's mantle to validate these events as effective seismic sources. The ocean model provides spectral amplitude information for modelling microseisms generated seismic wavefield. A comparison of the backprojection for P and PP phases from observed and synthetic microseisms forcing indicates high reliability in the ocean model, at least for major sources. A combination of P and PP phases detected across a global network of stations enables global ocean coverage. We improve backprojection images even further by introducing a two-step stacking for the P phase to address the problem of unbalanced station distribution. Thresholds of microseisms events forces valuable for seismic imaging are determined by comparing backprojections and ocean models for the years 2015 and 2020. Finally, we extracted a catalogue of microseisms events every 3-hr from 1994 to 2020 from the ocean hindcast data set. This catalogue is an intriguing resource for future applications of interferometric imaging at large scale.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::267730072697fc8cab67281e89ad54b7Test
https://doi.org/10.1093/gji/ggad103Test

المؤلفون: Margherita Capriotti, Luis Waldo Escalona Galvis, Antonino Spada

المساهمون: Margherita Capriotti, Luis Escalona, Antonino Spada

المصدر: Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems. :1-24

مصطلحات موضوعية: Mechanics of Materials, aerospace structures, numerical analysis, wave propagation modeling, nondestructive evaluation, Settore ICAR/08 - Scienza Delle Costruzioni, Safety, Risk, Reliability and Quality, Civil and Structural Engineering

الوصف: As structures increase in complexity, in the use of high-performing materials and designs, their health assessment becomes increasingly challenging. Ultrasonic guided waves (UGWs) have shown to be very promising in the inspection of large (i.e. aerospace components) attenuating (i.e. composite materials) structures and have been successfully employed for damage detection in a variety of fields. The intrinsic complex nature of UGWs, due to their dispersive behavior, combined with the structural complexity of the applications, though, makes the interpretation of UGW inspections very challenging. Numerical simulations of UGW propagation become crucial to this end and have been addressed with fully numerical, semi-analytical and hybrid approaches. The capability of predicting UGW scattering can inform experimental testing in optimizing the sensitivity of UGW inspections to specific waveguides and defects, and in interpreting the acquired data for the non-destructive identification and quantification of damages. In this work, an improved computational tool for UGW scattering predictions is presented. The approach relies on the Global-Local method and leverages the efficiency of the semi-analytical finite element (SAFE) method and the parallelized implementation of the coupled solution. 2D applications of the Global-Local approach for UGW scattering predictions in composite structures over a wide range of frequencies will be presented, together with the demonstration of the improved computational performance. The computational efficiency promises feasible and reliable UGWs predictions in multi-layered complex assemblies and different damage scenarios, and enables virtual UGWs inspections and future integration in NDE testing.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::a16e69f124a05ea481e81cb489dc171dTest
https://doi.org/10.1115/1.4056897Test

المؤلفون: Thomas King, Luca De Siena, Philip Benson, Sergio Vinciguerra

المصدر: Geophysical Journal International. 232:1590-1599

مصطلحات موضوعية: Fracture and flow, Acoustic properties, Interface waves, Seismic attenuation, Wave propagation, Wave scattering and diffraction, Seismic attenuation, Interface waves, Wave propagation, Geophysics, Acoustic properties, Geochemistry and Petrology, Wave scattering and diffraction, Fracture and flow

الوصف: SUMMARY Seismic waves produced by stressed and deforming rocks lose coherence when they cross regions of high heterogeneity. The delay in the arrival of maximum seismic energy amplitude (peak delay), an essential attribute to model earthquake source characteristics, is increasingly used to map complex crustal geology, heterogeneous reservoirs and fault networks. However, no laboratory calibration for the sensitivity of this parameter to fractures is currently available due to both experimental challenges and the difficulty in modelling wavefields in the near field. In this study, peak delays have been measured and mapped in space in the frequency range 50 kHz to 1 MHz using acoustic emission data recorded during a triaxial deformation experiment of Darley Dale Sandstone. Peak delays can increase dramatically throughout the experiment, but their behaviour depends on frequency and, especially, anomalous azimuth-dependent scattering. The changes in frequency depend on strain. At low frequencies, peak delays are sensitive to surface waves generated at the sample boundaries, but they also mark the zones of shadow and intense/intermediate strains expected for an heterogeneous sample. At high frequencies, peak delays detect the zone of intense strain corresponding to the post-deformation shear zone. Temporal variations of peak delays show a frequency-dependent sensitivity to fracture nucleation, fault coalescence and sample failure. Scattering from these heterogeneities produces waves reverberating through seismic coda if the source–station path is close to an acoustic boundary, such as the fault zone or the sample boundaries. Our results confirm that peak delay has notable sensitivity to heterogeneity and can map and monitor structural- and deformation-induced changes in the near-field. The companion modelling paper tests this sensitivity and the corresponding imaging potential.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::be6c9bf6b938bcab639609450a5c9ee7Test
https://doi.org/10.1093/gji/ggac409Test

المؤلفون: Chao Xu, Zexing Yu, Fei Du, Jiaying Sun

المصدر: Chinese Journal of Aeronautics. 35:208-221

مصطلحات موضوعية: Physics, Guided wave testing, Fuselage, Wave propagation, Scattering, Mechanical Engineering, Acoustics, Aerospace Engineering, Sensitivity (control systems), Time domain, Interference (wave propagation), Finite element method

الوصف: Stiffened panels have been widely utilized in fuselages and wings as critical load-bearing components. These structures are prone to be damaged under long-term and extreme loads, and their health monitoring has been a common concern. The guided wave-based monitoring method is regarded as an efficient approach to detect the damage in stiffened plates because of its wide monitoring range and high sensitivity to micro-damage. Efficient simulation of wave propagation can theoretically demonstrate the detection mechanism of the method. In this study, a Time-Domain Spectral Finite Element Method (TD-SFEM) is adopted to study the wavefield in stiffened plates, where continuous Absorbing Layers with Increasing Damping (ALID) strategy is proposed to circumvent the disturbance of reflected waves on boundaries. After the convergence analysis, the developed TD-SFEM with ALID is validated by the finite element method first. Then, wave scattering and the influence of the stiffener are investigated in detail by comparing the results with the non-stiffened structure. Finally, the effects of the parameters of the stiffener, such as the height and width, on wave propagation are studied, respectively. The results illustrate that the proposed TD-SFEM with ALID is an efficient approach to study the wave propagation in the stiffened plate and can reveal the mechanism of influence of the stiffener. It is found that the height of the stiffener changes the interference of wavefield in the plate, while the effects of the width are mainly in wave scattering and mode conversion.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_________::9080aa0f944dab8132d91f29a43525bfTest
https://doi.org/10.1016/j.cja.2021.11.014Test