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1دورية أكاديمية
المؤلفون: Costa, Mirella B., Siegle, Eduardo
المصدر: Ocean and Coastal Research. January 2022 70
مصطلحات موضوعية: Wave propagation, Reef wave transformation, Rocas Atoll
الوصف: Processes on atolls and coral reef lagoons are defined by local wave and tide climates. Based on the reconstruction of lagoon wave climate by downscaling offshore historical wave information, this study aims to assess the wave climate and wave extremes on a mesotidal atoll lagoon (Rocas Atoll, Brazil). Results show that the transformation of offshore waves, when propagating into the lagoon, results in a different and far more homogeneous wave climate. Atoll morphology and tides play a key role in controlling the directional and energy characteristics of the lagoon wave climate. Refraction processes and the reef passage make the side protected from the dominant SE waves the most energetic zone for lagoon wave propagation. Lagoon waves tend to propagate in opposite directions to offshore wind waves, showing the refraction effect of approaching waves when crossing the atoll rim and the channel. The tidal effect on the dissipation process is also a filter for extreme wave conditions. We highlight the dependence of the resulting lagoon wave climate on atoll morphology, thereby addressing its implications to geomorphological process inside the atoll.
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2دورية أكاديمية
المؤلفون: Regupathi, R., Jayaguru, C.
المصدر: Latin American Journal of Solids and Structures. January 2022 19(3)
مصطلحات موضوعية: Lap Splices, PZT Transducers, Wave propagation, Damage Index, Pull-out bond, wavelet Packet
الوصف: Using bonded piezoelectric transducers (PZT), this study evaluates damage to reinforced concrete beams at lap splices of tensile rebars. Four reinforced concrete beams with a span of 2700mm and a cross-section of 200 x 250mm were cast and simply edge-supported on roller supports 2250mm apart. In the zone of constant moment, the tensile reinforcements of the beams were spliced with varying lap lengths (10ϕ, 20ϕ, 30ϕ and 40ϕ). Two PZT patches (one to operate as an actuator and the other as a receiver) were bonded on steel rebars and placed 50mm apart from their lapping edges. The wave propagation technique was used to record the signals experimentally, and the signals were processed further using wavelet packet analysis. By setting the time lag results of waves under pulse excitation, the damage of beams were identified. Damage indices were calculated based on the wavelet packet energy to ascertain the damage levels. The PZT was very sensitive to detect the pull-out bond failure and ductile flexural failure at the lap slices of steel rebars in the beam and it gives an advance indication before the structural collapse due to brittle failure.
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3دورية أكاديمية
المؤلفون: Barreto, Lucas S., Machado, Marcela R., Santos, Juliana C., Moura, Braion B. de, Khalij, Leila
المصدر: Latin American Journal of Solids and Structures. January 2021 18(2)
مصطلحات موضوعية: Damage quantification, Spectral Element Method, Wave propagation, Damage Index
الوصف: Damage detection in structures and systems is essential for monitoring parameters that can affect their integrity. This paper evaluates the efficiency of four damage indices (DIs) commonly used with temporal wave signals. The root mean square deviation, mean absolute percentage deviation, covariance, and correlation coefficient deviation DIs are presented, and a normalization is then proposed. An Euler-Bernoulli beam is used as a guided wave modelled with the spectral element method and excited by a toneburst signal. It includes the theoretical background of the throw-off beam, undamaged and cracked beam spectral elements. The DIs for a single crack position and a map varying crack depth and positions are calculated with deterministic and random temporal signal responses derived from noise addition. Results showed that DIs could identify and quantify the damage conditioned to the pulse location point and the influence of noise in the estimation, which leads in an analysis comparable to practical applications.
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4دورية أكاديمية
المؤلفون: Fallah, Mahmoud, Nazeri, Amir. H
المصدر: Journal of Microwaves, Optoelectronics and Electromagnetic Applications. October 2018 17(4)
مصطلحات موضوعية: Electromagnetic wave propagation, Groundwaves, Surface wave propagation, Terrain modeling, Consecutive windows, Finite-difference time-domain (FDTD), Time-domain wave propagation (TDWP)
الوصف: Researchers have always been in face of path loss calculation in different media for applications such as telecommunication link design. Wave propagation calculations in large spaces using the FDTD method is time-consuming and imposes a great computational burden. For this reason, to replace the classical FDTD method for wave propagation simulation and path loss calculation in large spaces, optimized methods, namely TDWP, have been provided. In this paper, the use of the TDWP method for wave propagation simulation and path loss calculation above a terrain is investigated. Longitudinal components of ground-waves are taken into account (including direct waves, ground reflections, and surface waves). Propagation space is longitudinally divided into smaller FDTD windows with finite length. The electromagnetic pulse travels through these windows from left to right to the desired point. But despite its capability in reducing computational burden and increasing processing speed, TDWP has lower precision in instantaneous field simulation and calculation of propagation coefficients, so that results obtained from FDTD and TDWP are clearly different. In this paper, some efficient methods are proposed, which yield an increase in method accuracy.
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5دورية أكاديمية
المؤلفون: Almeida, M.P.C., Mello, L. da Silva, Braz, J.A.C., David, R.P., Castellanos, P.V.G., Lima, F.F.
المصدر: Journal of Microwaves, Optoelectronics and Electromagnetic Applications. September 2017 16(3)
مصطلحات موضوعية: Digital broadcasting, HD Radio, Medium wave propagation, Radio propagation
الوصف: This paper presents the results of measurements of medium wave received field strength, HD Radio audio quality and maximum coverage distances in a dense urban region. Analog AM and digital HD Radio signals broadcasting the same content were simultaneously transmitted in São Paulo, the largest city in Brazil. The received signal intensity and the reception quality were recorded along radial routes of up to 45 km from the transmitter under both mobile and static conditions, enabling the comparative assessment of the digital and analog system performances.
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6دورية أكاديمية
المصدر: Latin American Journal of Solids and Structures. January 2016 13(14)
مصطلحات موضوعية: Damage quantification, Wave propagation, Meshfree method, Radial basis function, Hermite Radial point interpolation
الوصف: This paper investigates the numerical modeling of the flexural wave propagation in Euler-Bernoulli beams using the Hermite-type radial point interpolation method (HRPIM) under the damage quantification approach. HRPIM employs radial basis functions (RBFs) and their derivatives for shape function construction as a meshfree technique. The performance of Multiquadric(MQ) RBF to the assessment of the reflection ratio was evaluated. HRPIM signals were compared with the theoretical and finite element responses. Results represent that MQ is a suitable RBF for HRPIM and wave propagation. However, the range of the proper shape parameters is notable. The number of field nodes is the main parameter for accurate wave propagation modeling using HRPIM. The size of support domain should be less thanan upper bound in order to prevent high error. With regard to the number of quadrature points, providing the minimum numbers of points are adequate for the stable solution, but the existence of more points in damage region does not leads to necessarily the accurate responses. It is concluded that the pure HRPIM, without any polynomial terms, is acceptable but considering a few terms will improve the accuracy; even though more terms make the problem unstable and inaccurate.
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7دورية أكاديمية
المؤلفون: Rodrigues, André, Dimitrovová, Zuzana
المصدر: Latin American Journal of Solids and Structures. August 2015 12(8)
مصطلحات موضوعية: Elastic wave propagation, finite element method, absorbing boundary layer, unbounded domains
الوصف: his paper addresses the Caughey Absorbing Layer Method (CALM) performance in the one-dimensional problem and its implementation in commercial software, with possibility of direct extension to two-dimensions. The adequacy and numerical efficiency is evaluated using three different error measures and five different variations of the damping profile. Other parameters that are subjected to evaluation are the length of the absorbing layer in relation to the wavelength to absorb, the value of the loss factor at the end of the absorbing layer, and the ratio of the load to layer frequency. The problem is firstly analysed theoretically, resulting in estimates for the wave reflection due to transition and truncation of the model. In order to confirm that no spurious waves will be present in the finite element solution, the numerical implementation is validated by comparison with the analytical solution. The analysis of the error measures on the numerical results obtained for various combinations of the model's parameters lead to the conclusion that CALM is effective at mitigating waves reflected from the boundaries. The optimum loss factor as a function of the ratio of the length of the absorbing layer to the wavelength to absorb is determined through parametric analyses. Although the optimal damping is frequency dependent, it was shown that the CALM's effectiveness can be extended to a wider range of frequencies by increasing the smoothness of the damping profile.
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8دورية أكاديمية
المؤلفون: Rahimzadeh, Mohammad, Daneshjoo, Kamran
المصدر: Latin American Journal of Solids and Structures. January 2014 11(9)
مصطلحات موضوعية: Particulate composite, Random media, Wave propagation, Spherical inclusion
الوصف: This paper aims to conduct a comparative study on four different models of effective field and effective medium for modeling propagation of plane elastic waves through the composites containing spherical particles with random distribution. Effective elastic properties along with the normalized phase velocity and attenuation of the average wave was numerically evaluated by the models. The plane incident wave was considered longitudinal to get the results. The numerical analyses were performed on four types of composites in the range of low to intermediate frequency and different volume fractions. Judgment about this comparative study is done based on physical and theoretical concepts in the wave propagation phenomenon. The obtained results provide a good viewpoint in using different models for studying propagation of the plane elastic waves in various particulate composites.
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9دورية أكاديمية
المؤلفون: Chung, Ie-Lung, Liou, Gin-Show
المصدر: Latin American Journal of Solids and Structures. November 2013 10(6)
مصطلحات موضوعية: Wave propagation, Impedance matrix, Dynamic stiffness and Soil-structure Interaction
الوصف: The paper is devoted to develop a new scheme to calculate impedance matrices for axial-symmetric foundations embedded in half-space medium. The half-space medium can be approximated by increasing thickness of one layer stratum on rigid bedrock due to the effect of material damping. However, as thickness increases, the numerical problem will arise. This problem is caused by the numerical contamination by some negligible reflection waves from rigid bedrock. In reality, the effect of these reflection waves on impedance is getting small as the thickness of the one layer stratum increases. Therefore, the scheme will employ the solutions for one layer stratum with suppressing these reflection waves to generate the impedance for the case of half-space. The numerical results by the presented scheme are compared with the results by other scheme in order to show that the new numerical scheme is effective and the solutions in layered medium can be extended to obtain the results for the cases of layered half-space medium. Some numerical results of torsional, vertical, horizontal, coupling and rocking impedances with different embedded depths will be presented and comments on the numerical scheme will be given.
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10دورية أكاديمية
المؤلفون: Kumar, Rajneesh, Garg, S.K., Ahuja, Sanjeev
المصدر: Latin American Journal of Solids and Structures. November 2013 10(6)
مصطلحات موضوعية: Microstretch, thermoelastic diffusion solid, plane wave, wave propagation, amplitude ratios, energy ratios
الوصف: The problem of reflection and refraction phenomenon due to plane waves incident obliquely at a plane interface between uniform elastic solid half-space and microstretch thermoelastic diffusion solid half-space has been studied. It is found that the amplitude ratios of various reflected and refracted waves are functions of angle of incidence, frequency of incident wave and are influenced by the microstretch thermoelastic diffusion properties of the media. The expressions of amplitude ratios and energy ratios are obtained in closed form. The energy ratios have been computed numerically for a particular model. The variations of energy ratios with angle of incidence are shown for thermoelastic diffusion media in the context of Lord-Shulman (L-S) (1967) and Green-Lindsay (G-L) (1972) theories. The conservation of energy at the interface is verified. Some particular cases are also deduced from the present investigation.
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