Transient elastic waves in an inhomogeneous layer

1970 ◽  
Vol 60 (2) ◽  
pp. 383-392 ◽  
Author(s):  
R. A. Scott
Keyword(s):  
Elastic Waves ◽  
Harmonic Wave ◽  
Low Frequency ◽  
Field Approximation ◽  
Inhomogeneous Layer ◽  
Far Field ◽  
Lateral Loads ◽  
Wavelength Approximation ◽  
Formal Solutions ◽  
Large Wavelength

abstract The excitation, by lateral loads, of transients in a layer of a transversely inhomogeneous solid with constant speeds of propagation is considered. Formal solutions in terms of the modes of harmonic wave propagation are developed, and from these and a low frequency, large wavelength approximation a far-field approximation to the response is derived.

A far-field scattering model in textured polycrystals with ellipsoidal grains of arbitrary crystal symmetry

2020 ◽  
Vol 25 (5) ◽  
pp. 1155-1171
Author(s):  
Gaofeng Sha
Keyword(s):  
Elastic Waves ◽  
Field Approximation ◽  
Crystal Symmetry ◽  
Polycrystalline Materials ◽  
Far Field ◽  
Efficient Tool ◽  
Practical Applications ◽  
Full Wave ◽  
Non Destructive ◽  
High Computational Efficiency

Modeling the scattering-induced attenuation of elastic waves in heterogeneous polycrystals has practical applications in seismology and non-destructive evaluation. However, attenuation modeling for polycrystals with preferred crystallographic orientation (statistically anisotropic or textured polycrystals) has not been well studied. The far-field approximation (FFA) model, which is applicable for arbitrary crystal (triclinic) symmetry and valid for the whole frequency range (Rayleigh region, stochastic regime, and geometric region), has been reported for texture-free polycrystalline materials. This paper extends the FFA model to textured polycrystals with ellipsoidal grains of arbitrary crystal symmetry. This FFA model for textured polycrystals encompasses two advantages: a simple form of dispersion equation and high computational efficiency. Furthermore, this FFA model can predict both the attenuation and phase velocity of elastic waves in textured polycrystals. The FFA model in this study has also been validated by comparison with the full-wave second-order attenuation model on textured polycrystals of triclinic grains. This work provides a simple and efficient tool to predict the elastic wave behavior in heterogeneous polycrystalline materials.

Transient Elastic Waves in Anisotropic Plates

1967 ◽  
Vol 34 (1) ◽  
pp. 104-110 ◽  
Author(s):  
R. A. Scott ◽  
Julius Miklowitz
Keyword(s):  
Elastic Waves ◽  
Equations Of Motion ◽  
Low Frequency ◽  
Elastic Solid ◽  
Field Analysis ◽  
Material Symmetry ◽  
Anisotropic Plates ◽  
Linear Elastic ◽  
Isotropic Media ◽  
Wavelength Approximation

The equations of motion of a linear elastic solid have been used to study the propagation of transient compressional disturbances in anisotropic plates, generated by several types of surface and edge loadings. A particular orientation of the axes of material symmetry was chosen, and several classes of anisotropic media have been considered. From the exact solutions obtained, a far-field analysis based on a low-frequency, large-wavelength approximation is given; and numerical results are presented for copper, ice, zinc, beechwood, and several isotropic media for comparison purposes.

scholarly journals Numerical Modelling and Optimization of Two-Dimensional Phononic Band Gaps in Elastic Metamaterials with Square Inclusions

2021 ◽  
Vol 11 (7) ◽  
pp. 3124
Author(s):  
Alya Alhammadi ◽  
Jin-You Lu ◽  
Mahra Almheiri ◽  
Fatima Alzaabi ◽  
Zineb Matouk ◽  
...  
Keyword(s):  
Elastic Wave ◽  
Tungsten Carbide ◽  
Composite Structure ◽  
Elastic Waves ◽  
Wave Attenuation ◽  
Low Frequency ◽  
Filling Fraction ◽  
Carbide Composite ◽  
Elastic Metamaterials ◽  
Tungsten Carbide Composite

A numerical simulation study on elastic wave propagation of a phononic composite structure consisting of epoxy and tungsten carbide is presented for low-frequency elastic wave attenuation applications. The calculated dispersion curves of the epoxy/tungsten carbide composite show that the propagation of elastic waves is prohibited inside the periodic structure over a frequency range. To achieve a wide bandgap, the elastic composite structure can be optimized by changing its dimensions and arrangement, including size, number, and rotation angle of square inclusions. The simulation results show that increasing the number of inclusions and the filling fraction of the unit cell significantly broaden the phononic bandgap compared to other geometric tunings. Additionally, a nonmonotonic relationship between the bandwidth and filling fraction of the composite was found, and this relationship results from spacing among inclusions and inclusion sizes causing different effects on Bragg scatterings and localized resonances of elastic waves. Moreover, the calculated transmission spectra of the epoxy/tungsten carbide composite structure verify its low-frequency bandgap behavior.

Far-field, extremely-low-frequency propagation measurements, 14 March to 9 April 1971

Radio Science ◽  
1973 ◽  
Vol 8 (7) ◽  
pp. 623-631 ◽  
Author(s):  
Peter R. Bannister ◽  
Edwin A. Wolkoff ◽  
J. Robert Katan ◽  
Frederick J. Williams
Keyword(s):  
Low Frequency ◽  
Far Field ◽  
Extremely Low Frequency

scholarly journals Energy Reflection of Elastic Waves from an Inhomogeneous Layer.

1993 ◽  
Vol 59 (561) ◽  
pp. 1238-1243
Author(s):  
Kimihisa Miura ◽  
Tadashi Ohyoshi ◽  
Toshihiro Hara ◽  
Masafumi Okazaki
Keyword(s):  
Elastic Waves ◽  
Inhomogeneous Layer

Control of low frequency noise from an environmental test facility

2021 ◽  
Vol 263 (3) ◽  
pp. 3488-3497
Author(s):  
Malcolm Smith ◽  
Erika Quaranta
Keyword(s):  
Low Frequency ◽  
Building Design ◽  
Test Facility ◽  
Successful Outcome ◽  
High Mountain ◽  
Frequency Noise ◽  
Mountain Range ◽  
Far Field ◽  
Low Frequency Noise ◽  
Environmental Test

Environmental test chambers are used in the automotive industry to verify the resilience of vehicles. In just a few hours it is possible to take a car from mid-winter in the artic, via a high mountain range, to mid-summer in a desert. Powerful ventilation systems are used to change the temperature, pressure and humidity of the air in the chamber, and the variable speed blowers are a major source of low frequency noise, which can cause significant disturbance at neighbouring properties if there are gaps in silencer performance. This paper details a study to assess the attenuation requirements for a system to meet a standard criterion for low frequency far-field noise levels, and to select a reactive silencer system to achieve that specification under all circumstances. The system used standard silencer components where possible, but needed to take account of long pipe runs through the facility, with tailpipe resonances being a particular issue, and was further constrained by space and loading limits for the building. Design layouts were verified using the Actran FE code, taking account of interactions with existing silencers and transfer functions to the far-field, in order to have very high confidence of a successful outcome.

scholarly journals Pre-selection of the candidate fields for deep imaging of the epoch of reionization with SKA1-low

2020 ◽  
Vol 499 (3) ◽  
pp. 3434-3444
Author(s):  
Qian Zheng ◽  
Xiang-Ping Wu ◽  
Quan Guo ◽  
Melanie Johnston-Hollitt ◽  
Huanyuan Shan ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Low Frequency ◽  
Far Field ◽  
Frequency Range ◽  
High Quality ◽  
Average Surface ◽  
Square Kilometre Array ◽  
Broad Frequency Range ◽  
Deep Imaging ◽  
Selection Of

ABSTRACT The Square Kilometre Array (SKA) will be the first low-frequency instrument with the capability to directly image the structures of the epoch of reionization (EoR). Indeed, deep imaging of the EoR over five targeted fields of 20 sq deg each has been selected as the highest priority science objective for SKA1. Aiming at preparing for this highly challenging observation, we perform an extensive pre-selection of the ‘quietest’ and ‘cleanest’ candidate fields in the southern sky to be suited for deep imaging of the EoR using existing catalogues and observations over a broad frequency range. The candidate fields should meet a number of strict criteria to avoid contaminations from foreground structures and sources. The candidate fields should also exhibit both the lowest average surface brightness and smallest variance to ensure uniformity and high-quality deep imaging over the fields. Our selection eventually yields a sample of 7 ‘ideal’ fields of 20 sq deg in the southern sky that could be targeted for deep imaging of the EoR. Finally, these selected fields are convolved with the synthesized beam of SKA1-low stations to ensure that the effect of sidelobes from the far-field bright sources is also weak.

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