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1دورية أكاديمية
المؤلفون: Fichtner A., Bogris A., Bowden D., Lentas K., Melis N.S., Nikas T., Simos C., Simos I., Smolinski K.
المصدر: Geophysical Journal International ; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85135220940&doi=10.1093%2fgji%2fggac238&partnerID=40&md5=e25975de7fa78c4a0273d2499522cf32Test
مصطلحات موضوعية: Fibers, Light transmission, Seismology, Computational seismologies, Distributed measurements, Fiber-optics, Optical phasis, Phase delay, Seismic instruments, Seismic tomography, Sensitivity kernels, Theoretical seismologies, Transmission fibers, Wave propagation, remote sensing, satellite imagery, seismic data, seismic source, sensitivity analysis, Oxford University Press
الوصف: Fibre-optic sensing based on transmission offer an alternative to scattering-based distributed acoustic sensing (DAS). The ability to interrogate fibres that are thousands of kilometres long opens opportunities for studies of remote regions, including ocean basins. However, by averaging deformation along the fibre, transmission systems produce integrated instead of distributed measurements. They defy traditional interpretations in terms of simple seismic phases, thereby inherently requiring a full-waveform approach. For this, we develop a formalism to calculate sensitivity kernels of transmitted optical phase changes with respect to (Earth) structure using optical phase delay measurements. We demonstrate that transmission-based sensing can effectively provide distributed measurements when optical phase delays are analysed in different time windows. The extent to which a potentially useful sensitivity coverage can be achieved depends on the fibre geometry, and specifically on its local curvature. This work establishes a theoretical foundation for tomographic inversions and experimental design using transmission-based optical sensing. © 2022 The Author(s).
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2دورية أكاديمية
المؤلفون: Cantero-Chinchilla S., Papadimitriou C., Chiachío J., Chiachío M., Koumoutsakos P., Fabro A.T., Chronopoulos D.
المصدر: Structural Control and Health Monitoring ; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85142180759&doi=10.1002%2fstc.3143&partnerID=40&md5=bad26313872d2dc3ea37e6b1f46d74e7Test
مصطلحات موضوعية: Cost benefit analysis, Guided electromagnetic wave propagation, Plates (structural components), Structural dynamics, Structural optimization, Uncertainty analysis, Health monitoring, Model errors, Optimal sensor, Optimal sensor configuration, Prediction model error, Prediction modelling, Robust optimization, Sensor configurations, Uncertainty, Value of information, Structural health monitoring, John Wiley and Sons Ltd
الوصف: Sensing is the cornerstone of any functional structural health monitoring technology, with sensor number and placement being a key aspect for reliable monitoring. We introduce for the first time a robust methodology for optimal sensor configuration based on the value of information that accounts for (1) uncertainties from updatable and nonupdatable parameters, (2) variability of the objective function with respect to nonupdatable parameters, and (3) the spatial correlation between sensors. The optimal sensor configuration is obtained by maximizing the expected value of information, which leads to a cost-benefit analysis that entails model parameter uncertainties. The proposed methodology is demonstrated on an application of structural health monitoring in plate-like structures using ultrasonic guided waves. We show that accounting for uncertainties is critical for an accurate diagnosis of damage. Furthermore, we provide critical assessment of the role of both the effect of modeling and measurement uncertainties and the optimization algorithm on the resulting sensor placement. The results on the health monitoring of an aluminum plate indicate the effectiveness and efficiency of the proposed methodology in discovering optimal sensor configurations. © 2022 The Authors. Structural Control and Health Monitoring published by John Wiley & Sons Ltd.
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3دورية أكاديمية
المؤلفون: Cantero-Chinchilla S., Fabro A.T., Meng H., Yan W.-J., Papadimitriou C., Chronopoulos D.
المصدر: Journal of Sound and Vibration ; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85127366673&doi=10.1016%2fj.jsv.2022.116896&partnerID=40&md5=5ef2173f7c7899c086e5b9871c928e56Test
مصطلحات موضوعية: 3D printers, Cost functions, Economic and social effects, Elastic moduli, Laser heating, Optimal systems, Optimization, Resonators, Wave propagation, Mechanical, Metastructures, Optimal design, Optimized designs, Parallel plates, Robust optimization, Shaped beam, Trade off, Uncertainty, Vibration attenuation, Sintering, Academic Press
الوصف: In this work, a strategy for optimal design of mechanical metastructure is proposed taken into account uncertainties arising from additive manufacturing. A locally resonant Π-shaped beam with parallel plate-like insertions and two cantilever mass resonators at each unit cell is manufactured through a selective laser sintering process. The variability of the material properties introduced by the additive manufacturing procedure is experimentally obtained. Given that such manufacturing approaches are predominantly employed for producing complex metastructure architectures, it can significantly compromise the optimality of the design. A transfer matrix approach is employed to propagate variability at a structural level and predict the structural receptance due to a point harmonic force in the finite length metastructure. Then, the mass ratio of the metastructure is optimised for maximising vibration attenuation considering different numbers of added resonators and relative masses. A cost function is introduced in the classical robust design approach in order to favour designs with least complexity, represented by the number of added resonators. It is exhibited in several cases that the robustly optimal design is away from the deterministic optimal one, emphasising the relevance of the proposed approach in the optimisation of complex and locally resonant structures. Moreover, it is shown that the frequency range of interest plays a major role on the derived optimal design for each number of implemented resonators. The presented results show that even small variability in the Young's modulus of up to 3% and in the mass density of up to 1% can still affect the robustness of the optimal design for locally resonant metastructure as due to the consequent mistuning of the added resonators. © 2022 Elsevier Ltd
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4دورية أكاديمية
المؤلفون: Fichtner A., Bogris A., Nikas T., Bowden D., Lentas K., Melis N.S., Simos C., Simos I., Smolinski K.
المصدر: Geophysical Journal International ; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85136132368&doi=10.1093%2fgji%2fggac237&partnerID=40&md5=de1fd93b26dca8ac51b8ea17744349baTest
مصطلحات موضوعية: Computation theory, Deformation, Fiber optics, Fibers, Seismic waves, Seismology, Strain measurement, Tensors, Wave propagation, Computational seismologies, Deformation tensors, Fiber optic deformation, First order, Higher order effects, Ordering relations, Phase Change, Seismic instruments, Seismic tomography, Theoretical seismologies, Refractive index, acoustic method, laboratory method, seismic wave, sensor, Oxford University Press
الوصف: We present a theory and conceptual examples for fibre-optic deformation sensing based on phase changes of transmitted light. As a first result, we establish an exact relation between observable phase changes and the deformation tensor along the fibre. This relation is nonlinear and includes effects related to both local changes in fibre length and deformation-induced changes of the local refractive index. In cases where the norm of the deformation tensor is much smaller than 1, a useful first-order relation can be derived. It connects phase changes to an integral over in-line strain along the fibre times the local refractive index. When spatial variations of the refractive index are negligible, this permits the calculation of phase change measurements from distributed strain measurements, for instance, from distributed acoustic sensing (DAS). An alternative form of the first-order relation reveals that a directional sensitivity determines the ability of a point along the fibre to measure deformation. This directional sensitivity is proportional to fibre curvature and spatial variability of the refractive index. In a series of simple conceptual examples, we illustrate how a seismic wavefield is represented in a phase change time-series and what the role of higher-order effects may be. Specifically, we demonstrate that variable curvature along the fibre may lead to a multiplication of seismic waves, meaning that a single seismic wave appears multiple times in a recording of optical phase changes. Furthermore, we show that higher-order effects may be observable in specific scenarios, including deformation exactly perpendicular to the fibre orientation. Though higher-order effects may be realized in controlled laboratory settings, they are unlikely to occur in seismic experiments where fibre geometries are irregular and waves asymptotically propagate in all directions with all possible polarizations as a consequence of 3-D heterogeneity. Our results provide the mathematical foundation for the analysis of emerging ...
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5دورية أكاديمية
المؤلفون: Yan W.-J., Chronopoulos D., Cantero-Chinchilla S., Yuen K.-V., Papadimitriou C.
المصدر: Mechanical Systems and Signal Processing ; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85082796568&doi=10.1016%2fj.ymssp.2020.106802&partnerID=40&md5=6d24436f772b2ecdbc3be7a3ac71ee31Test
مصطلحات موضوعية: Bayesian networks, Composite structures, Computation theory, Computational efficiency, Cost benefit analysis, Finite element method, Guided electromagnetic wave propagation, Inference engines, Markov chains, Mechanical properties, Probability density function, Probability distributions, Structure (composition), Ultrasonic waves, Uncertainty analysis, Bayesian Analysis, Local structural properties, Markov Chain Monte-Carlo, Metamodeling, Periodic structure theory, Ultrasonic guided wave, Uncertainty quantifications, Wave propagation characteristics, Parameter estimation, Academic Press
الوصف: Reliable verification and evaluation of the mechanical properties of a layered composite ensemble are critical for industrially relevant applications, however it still remains an open engineering challenge. In this study, a fast Bayesian inference scheme based on multi-frequency single shot measurements of wave propagation characteristics is developed to overcome the limitations of ill-conditioning and non-uniqueness associated with the conventional approaches. A Transitional Markov chain Monte Carlo (TMCMC) algorithm is employed for the sampling process. A Wave and Finite Element (WFE)-assisted metamodeling scheme in lieu of expensive-to-evaluate explicit FE analysis is proposed to cope with the high computational cost involved in TMCMC sampling. For this, the Kriging predictor providing a surrogate mapping between the probability spaces of the model predictions for the wave characteristics and the mechanical properties in the likelihood evaluations is established based on the training outputs computed using a WFE forward solver, coupling periodic structure theory to conventional FE. The valuable uncertainty information of the prediction variance introduced by the use of a surrogate model is also properly taken into account when estimating the parameters’ posterior probability distribution by TMCMC. A numerical study as well as an experimental study are conducted to verify the computational efficiency and accuracy of the proposed methodology. Results show that the TMCMC algorithm in conjunction with the WFE forward solver-aided metamodeling can sample the posterior Probability Density Function (PDF) of the updated parameters at a very reasonable cost. This approach is capable of quantifying the uncertainties of recovered independent characteristics for each layer of the composite structure under investigation through fast and inexpensive experimental measurements on localized portions of the structure. © 2020 Elsevier Ltd
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6دورية أكاديمية
المؤلفون: Tsimpoukis A., Valougeorgis D.
المصدر: Sensors and Actuators A: Physical ; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85112785985&doi=10.1016%2fj.sna.2021.112997&partnerID=40&md5=737ae214be3aae25f6790c612a56b003Test
مصطلحات موضوعية: Acoustic wave propagation, Damping, Flow of gases, Oscillating flow, Shear flow, Shear stress, Antiresonance and resonance, Antiresonance frequencies, Comb finger element, Comb fingers, Normal and shear stress, Oscillation parameters, Oscillatory rarefied gas flow, Resonance frequencies, Slide film damping, Squeeze-film damping, Gases, Elsevier B.V
الوصف: The linear oscillatory two-dimensional rarefied gas flow in the zig-zag channel between the shuttle and stator fingers of typical comb elements, due to the harmonic motion of the shuttle finger with arbitrary frequency, is numerically investigated, via the linearized unsteady Shakhov kinetic model equation, subject to purely diffuse boundary conditions. The amplitude and phase distributions of the velocity components, normal and shear stresses, density and temperature are thoroughly investigated in the whole range of the gas rarefaction and oscillation parameters, characterizing the flow. The low, moderate and high flow oscillation regimes are defined by the ratio of the gas rarefaction over the oscillation parameters. It is shown that in the low oscillation regime the flow may be approximated by the corresponding steady-state analysis, while in the high oscillation one by the superposition of the associated oscillatory one-dimensional normal sound propagation and Couette flows. In the former case edge and compressibility effects are considerable and in the latter one the flow is characterized by gas trapping along the shuttle finger. In the moderate oscillation regime the fully oscillatory two-dimensional flow must be analysed. Here, the antiresonance and resonance states of the flow are considered. The ratios of the gas rarefaction over the oscillation parameters, where the average normal and shear stresses acting on the shuttle finger are minimized are computationally specified. Changing the main geometry parameters of the comb finger block, significantly affects the normal and shear stresses acting on the shuttle finger, mainly in the low oscillation regime. The present work may be applied to minimize the damping forces in comb finger blocks, as well as to optimize the design of new generation devices operating in moderate and high frequencies. © 2021 Elsevier B.V.
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7مؤتمر
المؤلفون: Yan W., Chronopoulos D., Papadimitriou C., Cantero-Chinchilla S., Zhu G.-S.
المصدر: COMPDYN Proceedings ; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85079054364&partnerID=40&md5=e81622a57ef37f704630bd321ae0d338Test
مصطلحات موضوعية: Computation theory, Computational methods, Damage detection, Earthquake engineering, Engineering geology, Frequency domain analysis, Geophysics, Guided electromagnetic wave propagation, Markov processes, Probability density function, Probability distributions, Structural dynamics, Ultrasonic waves, Uncertainty analysis, Bayesian Analysis, Damage Identification, Ultrasonic guided wave, Uncertainty quantifications, Wave finite element, Finite element method, National Technical University of Athens
الوصف: Ultrasonic Guided Wave(GW) has been proven to be sensitive to small damage. Motivated by the fact that the quantitative relationship between wave scattering and damage intensity can be described by scattering properties, this study aims at proposing a new probabilistic damage characterization method based on the scattering coefficients in tandem with hybrid wave finite element model (WFEM) scheme. The probabilistic distribution properties of the scattering coefficients estimated using measured ultrasonic guided waves in the frequency domain are inferred based on absolute complex ratio statistics. The theoretical scattering coefficients can be efficiently calculated using WFEM which combines conventional finite element analysis with periodic structure theory. Based on the probabilistic distribution of reflection/transmission coefficients, the likelihood function connecting the theoretical model responses containing the parameters to be updated and the measured responses are formulated within a unified Bayesian system identification framework to account for various uncertainties. The transitional Monte Carlo Markov Chain (TMCMC) is used to sample the posterior probability density function of the updated parameters. A numerical example is utilized to verify the accuracy of the proposed algorithm. Results indicate that the strategies proposed in this study can quantify the uncertainties of damage characterization © 2019 The authors.
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8دورية أكاديمية
المؤلفون: Yan W.-J., Chronopoulos D., Papadimitriou C., Cantero-Chinchilla S., Zhu G.-S.
المصدر: Journal of Sound and Vibration ; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85075544985&doi=10.1016%2fj.jsv.2019.115083&partnerID=40&md5=94134c570078151b6dce261f6216a939Test
مصطلحات موضوعية: Bayesian networks, Computation theory, Computational efficiency, Damage detection, Efficiency, Function evaluation, Guided electromagnetic wave propagation, Inference engines, Markov processes, Probability density function, Ultrasonic waves, Uncertainty analysis, Bayesian Analysis, Damage Identification, Surrogate model, Ultrasonic guided wave, Uncertainty quantifications, Wave finite element, Parameter estimation, Academic Press
الوصف: Ultrasonic Guided Waves (GW) actuated by piezoelectric transducers installed on structures have proven to be sensitive to small structural defects, with acquired scattering signatures being dependent on the damage type. This study presents a generic framework for probabilistic damage characterization within complex structures, based on physics-rich information on ultrasound wave interaction with existent damage. To this end, the probabilistic model of wave scattering properties estimated from measured GWs is inferred based on absolute complex-valued ratio statistics. Based on the probabilistic model, the likelihood function connecting the scattering properties predicted by a computational model containing the damage parametric description and the scattering estimates is formulated within a Bayesian system identification framework to account for measurement noise and modelling errors. The Transitional Monte Carlo Markov Chain (TMCMC) is finally employed to sample the posterior probability density function of the updated parameters. However, the solution of a Bayesian inference problem often requires repeated runs of “expensive-to-evaluate” Finite Element (FE) simulations, making the inversion procedure firmly demanding in terms of runtime and computational resources. To overcome the computational challenges of repeated likelihood evaluations, a cheap and fast Kriging surrogate model built and based on a set of training points generated with an experiment design strategy in tandem with a hybrid Wave and Finite Element (WFE) computational scheme is proposed in this study. In each “numerical experiment”, the training outputs (i.e. ultrasound scattering properties) are efficiently computed using the hybrid WFE scheme which combines conventional FE analysis with periodic structure theory. By establishing the relationship between the training outputs and damage characterization parameters statistically, the surrogate model further enhances the computational efficiency of the exhibited scheme. Two case studies including ...
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9مؤتمر
المؤلفون: Kouroussis G., Vogiatzis K.E., Connolly D.P.
المصدر: 24th International Congress on Sound and Vibration, ICSV 2017
https://www.scopus.com/inward/record.uri?eid=2-s2.0-85029414219&partnerID=40&md5=1f3f10ffc361c39baf77829e6f2cdb80Testمصطلحات موضوعية: Railroad rolling stock, Railroad tracks, Railroads, Rails, Soil structure interactions, Surface defects, Transportation, Trolley cars, Urban transportation, Vehicles, Vibrations (mechanical), Wave propagation, Building vibrations, Ground wave propagation, Multibody vehicle model, Railway ground vibrations, Structural response, Tram, Vibration predictions, Wheel/rail contact, Light rail transit, International Institute of Acoustics and Vibration, IIAV
الوصف: With the development of light rail transit in urban areas, the effect of railway vibrations on buildings and people inside buildings is a growing problem. In particular, urban transit commonly generates large vibration levels at rail discontinuities, and thus this paper presents a 2-stage numericalexperimental vibration prediction methodology. The first step is purely numerical and focuses on the vehicle-track dynamics by analysing the effect of local defects at the rail surface during train passage. A multibody vehicle model and a flexible two-dimensional track are coupled using Herzian contact theory, which includes the geometry of the studied defect. The results obtained capture the interaction between the railway vehicle and the track, which serves as input for the second step. The latter uses experimental source transfer mobilities obtained on-site. This offers a way to accurately evaluate the soil-structure interaction which occurs in a complex medium such as the ground in urban areas. Structural response is then calculated by combining the two approaches. An illustrative example is presented, where the effect of various rail defects in the tram Brussels network is analysed. It is shown that it is possible to quantify vibration levels on light rail transit lines, where tramway networks interact with local rail defects and where railway ground vibration are problematic.
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10مؤتمر
المؤلفون: Stocker A.J., Argyriou A., Giorgetti A., Paolini E., Siddle D.R., Tortora P., Zeqaj A., De Vicente J., Abello R., Mercolino M.
المصدر: IET Conference Publications ; https://www.scopus.com/inward/record.uri?eid=2-s2.0-85057338804&partnerID=40&md5=5e4d27d892a2f5316dbc89a902b01b50Test
مصطلحات موضوعية: Earth (planet), Scintillation, Solar wind, Wave propagation, Channel measurements, Channel model, Deep space communications, Error correcting code, Solar plasma, Radio links, Institution of Engineering and Technology
الوصف: Some results so far achieved in the framework of the HELIOS (Highly rEliable LInks during sOlar conjunctionS) Project, founded by the European Space Agency (ESA), are presented. The purpose of the project is the definition of a TT&C communication subsystem architecture (including both ground and space segments, as well as operational methods) being robust to impairments due to superior solar conjunction, especially when the Sun-Earth-Probe angle is below 5 degrees. © Institution of Engineering and Technology.All Rights Reserved.
