المؤلفون: Zhang, Zhennan¹ (AUTHOR), Jiang, Huan¹ (AUTHOR), Bednarcyk, Brett A.² (AUTHOR), Chen, Yanyu¹ (AUTHOR) yanyu.chen@louisville.edu

المصدر: Advanced Materials Technologies. 11/10/2023, Vol. 8 Issue 21, p1-14. 14p.

مصطلحات موضوعية: *ELASTIC wave propagation, *BRITTLE materials, *FRACTALS, *POISSON'S ratio, *METAMATERIALS, *ELASTIC waves

مستخلص: Stretchable materials that can sustain a large deformation are in high demand, because they find broad applications ranging from stretchable energy storage devices to tunable noise and vibration devices. One main challenge is creating strain‐releasing mechanisms from inherently brittle materials. This work explores a new approach to designing stretchable metamaterials, using a "kerfing" pattern inspired by the ancient Greek Key configuration. The kerfing architecture allows for substantial in‐plane elongation. In‐plane tensile experiments show an ≈8‐times increase in stretchability when the kerfing width is enlarged four times. With higher‐order fractal patterns, the fractal lattice exhibits a stretchability of up to ≈520%, far beyond the inherent deformability of the brittle constituent. Moreover, this design also enables the tunability of various mechanical properties, including stiffness, strength, toughness, and Poisson's ratio. Ashby‐type plots are presented, revealing the relationships between stretchability and other mechanical properties to aid in the design and fabrication of advanced engineering materials. To demonstrate a vital application of the achieved stretchability, elastic wave propagation in the proposed kerfing metamaterials is studied. Simulations indicate that multiple broad phononic bandgaps arise in these structures as the fractal order increases. These bandgaps prove to be adjustable not only through the fractal lattice geometry but also by means of applied mechanical loading. This investigation highlights the potential of fractal‐based layouts as a promising avenue for designing cutting‐edge stretchable metamaterials with customizable mechanical properties and functionalities. [ABSTRACT FROM AUTHOR]

المؤلفون: Tsironis, Christos¹ (AUTHOR) ctsiron@mail.ntua.gr, Papadopoulos, Aristeidis¹ (AUTHOR)

المصدر: Journal of Electromagnetic Waves & Applications. Nov2023, Vol. 37 Issue 16, p1366-1393. 28p.

مصطلحات موضوعية: *ELECTROMAGNETIC wave propagation, *FINITE difference time domain method, *PHYSICS, *MAXWELL equations, *THEORY of wave motion

مستخلص: Numerical codes for electromagnetic wave propagation in magnetized plasmas are mainly based on frequency-domain asymptotic methods, which provide a fast solution and are thus valuable for experiment design and control applications. However, in several cases of practical interest (e.g. mode conversion), these tools run close to their limits of validity and should be compared to full-wave solutions. The code RFFW solves Maxwell's equations with the finite-difference time-domain method in 3D geometry, for scenarios involving high-frequency waves with arbitrary electric field spectrum in plasmas with axisymmetric equilibrium. In fusion-related problems, the code may conduct investigations of wave propagation and absorption relevant to auxiliary plasma heating and current drive, reflectometry and instability control. The code has been parallelized with a hybrid OpenMP-MPI scheme, which has allowed exploiting the much larger processing power and memory of current-day supercomputers. In this work, we present the main aspects of the physics implemented in the code, and also refer shortly to the parallelization scheme. Furthermore, we show results that exhibit the strong scaling performance of the code, and examine cases of electron-cyclotron heating application in medium-sized tokamaks. [ABSTRACT FROM AUTHOR]

المؤلفون: Qi, Yubo¹ (AUTHOR) qyb@mail.ioa.ac.cn, Zhou, Shihong¹ (AUTHOR), Liu, Changpeng¹ (AUTHOR)

المصدر: Journal of the Acoustical Society of America. Nov2023, Vol. 154 Issue 5, p2800-2811. 12p.

مصطلحات موضوعية: *ACOUSTIC wave propagation, *ANGLES, *BEAMFORMING, *SPEED of sound

مستخلص: A publication by McCargar and Zurk [J. Acoust. Soc. Am. 133(4), EL320–EL325 (2013)] introduced a passive source depth estimation method for a moving tonal source with a vertical line array (VLA), utilizing the depth-dependent modulation in the arrival angle domain caused by the interference between the direct and surface-reflected acoustic arrivals. Under the isovelocity approximation, this method can estimate the depth of sources at close ranges, but the depth estimation error will increase with the increase in source range, as the impact of the sound speed profile on sound propagation is ignored. This paper presents a theoretical formula for calculating the modeled interference structure in the arrival angle domain with the knowledge of the sound speed profile. By matching the measured interference structure obtained from the beamforming of the acoustic data received by the VLA with the modeled structure under different assumed source depths, the tonal source depth estimation is achieved, even for sources at the remote part of the direct arrival zone. The performance of this method is verified by simulation data, as well as experimental data radiated from a towed source and a non-cooperative passing ship. [ABSTRACT FROM AUTHOR]

المؤلفون: Chesnel, Lucas¹ lucas.chesnel@inria.fr, Heleine, Jérémy², Nazarov, Sergei A.³, Taskinen, Jari⁴

المصدر: ESAIM: Mathematical Modelling & Numerical Analysis (ESAIM: M2AN). Nov/Dec2023, Vol. 57 Issue 6, p3585-3613. 29p.

مصطلحات موضوعية: *WAVEGUIDES, *ACOUSTIC wave propagation, *ASYMPTOTIC expansions, *S-matrix theory, *REFLECTANCE, *INVERSE scattering transform

مستخلص: We consider the propagation of acoustic waves in a waveguide containing a penetrable dissipative inclusion. We prove that as soon as the dissipation, characterized by some coefficient η, is non zero, the scattering solutions are uniquely defined. Additionally, we give an asymptotic expansion of the corresponding scattering matrix when η → 0+ (small dissipation) and when η → +∞ (large dissipation). Surprisingly, at the limit η → +∞, we show that no energy is absorbed by the inclusion. This is due to the so-called skin-effect phenomenon and can be explained by the fact that the field no longer penetrates into the highly dissipative inclusion. These results guarantee that in monomode regime, the amplitude of the reflection coefficient has a global minimum with respect to η. The situation where this minimum is zero, that is when the device acts as a perfect absorber, is particularly interesting for certain applications. However it does not happen in general. In this work, we show how to perturb the geometry of the waveguide to create 2D perfect absorbers in monomode regime. Asymptotic expansions are justified by error estimates and theoretical results are supported by numerical illustrations. [ABSTRACT FROM AUTHOR]

المؤلفون: Xiaofang Sun¹, Shisong Zhang¹, Xunxian Nian² 869712454@qq.com

المصدر: AIP Advances. Nov2023, Vol. 13 Issue 11, p1-8. 8p.

مصطلحات موضوعية: *MESOSCALE eddies, *ACOUSTIC wave propagation, *UNDERWATER acoustics, *ACOUSTIC field, *DEPTH sounding, *SOUND waves, *PARABOLIC troughs

مستخلص: Mesoscale vorticity is an important factor that affects the non-uniform horizontal and vertical distribution of hydrologic elements in the ocean. In this paper, temperature and salinity data from measured mesoscale cold-core eddies during a voyage within a certain sea area are studied, and a synchronous sound field test was conducted on the mesoscale vorticity. Based on the temperature and salinity data, the parabolic equation (PE) method was selected to predict the acoustic field, and the results were compared with the measured propagation loss data of the acoustic field to verify the accuracy and effectiveness of the PE model. The underwater sound propagation characteristics in the mesoscale cold-core eddy environment were then analyzed using the temperature and salinity data retrieved from the voyage. It was found that the convergence area of the acoustic field gradually dispersed with an increase in the depth of the sound source. In a mesoscale eddy environment, when sound waves propagate from inside to outside the eddy, the presence of a cold-core eddy causes the convergence area to shift toward the edge of the eddy, and the deviation gradually decreases with an increase in the depth of the sound source. [ABSTRACT FROM AUTHOR]

المؤلفون: Hong Li¹, Qingfeng Wang¹ qingfengwang76910@gmail.com

المصدر: AIP Advances. Nov2023, Vol. 13 Issue 11, p1-4. 4p.

مصطلحات موضوعية: *ELASTIC wave propagation, *FINITE element method, *CONVOLUTIONAL neural networks, *ELASTIC waves, *COMPOSITE materials, *SOLID mechanics, *DEEP learning

مستخلص: Deep learning surrogate models can be employed in solid mechanics to forecast the behavior of structures subjected to various loading conditions, substantially decreasing the computational costs associated with simulations. In this letter, we have utilized convolutional neural networks and Fourier transform to predict the elastic wave output from composite bars. The microstructures of the bar are utilized as inputs to the deep learning model, while the output is the elastic wave response. The convolutional neural network learns to identify crucial input composite features and utilizes this information to predict the output elastic waves. Finally, the mean squared error of the predicted output signals is compared to the actual output signals, which was used to evaluate the model. The outcomes of this study demonstrate that the deep learning model can precisely and swiftly predict the output elastic waves of the composites, thus serving as a surrogate model for time-consuming finite element simulations. [ABSTRACT FROM AUTHOR]

المؤلفون: Luís, Diana^1,2 (AUTHOR) diana.luis@vki.ac.be, Giangaspero, Vincent^1,3 (AUTHOR), Viladegut, Alan¹ (AUTHOR), Lani, Andrea³ (AUTHOR), Camps, Adriano^2,4,5 (AUTHOR), Chazot, Olivier¹ (AUTHOR)

المصدر: Acta Astronautica. Nov2023, Vol. 212, p408-423. 16p.

مصطلحات موضوعية: *ELECTRON density, *ELECTROMAGNETIC wave propagation, *PLASMA flow, *TRANSMITTING antennas, *HORN antennas, *ANECHOIC chambers

مستخلص: Spacecraft entering a planetary atmosphere are surrounded by a plasma layer containing high levels of ionization, due to the extreme temperatures in the shock layer. The high electron number densities cause attenuation of the electromagnetic waves emitted by the on-board antennas, leading to communication blackout for several minutes. This work presents experimental measurements of signal propagation through an ionized plasma flow. The measurements are conducted at the VKI plasma wind tunnel (Plasmatron) using conical horn antennas transmitting in the Ka-band, between 33 and 40 GHz. Testing conditions at 15, 50 and 100 mbar, and powers between 100 and 600 kW cover a broad range of the testing envelope of the Plasmatron as well as a broad range of atmospheric entry conditions. The transmitting antenna is characterized at the UPC anechoic chamber, obtaining the radiation patterns, beamwidth, and gain at the boresight direction; and an optical ray tracing technique is used to describe the electromagnetic waves propagation in the plasma flowfield inside of the Plasmatron chamber. The signal propagation measurements show clear attenuation when the signal is propagating through the plasma, varying between 2 and 15 dB depending on the testing conditions. This attenuation increases with electron number densities, which are driven by the Plasmatron power and pressure settings. Preliminary evidence of Faraday rotation effects caused by the plasma is also observed. • Signal attenuation due to plasma between 2 and 15 dB depending on the flow condition. • Similar evolution of the signal attenuation and electron number density. • Ray tracing simulations of the radio signal bending due to an ionized medium. • Preliminary experimental evidence of Faraday rotation of a radio signal due to plasma. [ABSTRACT FROM AUTHOR]

المؤلفون: Kamel, Omar A.¹ (AUTHOR) oalaaeldein@mun.ca, Abouhussien, Ahmed A.² (AUTHOR) aabouhussien@mun.ca, Hassan, Assem A. A.³ (AUTHOR) ahassan@un.ca, AbdelAleem, Basem H.⁴ (AUTHOR) b.abdelaleem@mun.ca

المصدر: Journal of Materials in Civil Engineering. Nov2023, Vol. 35 Issue 11, p1-11. 11p.

مصطلحات موضوعية: *ACOUSTIC emission, *ACOUSTIC wave propagation, *RUBBER powders, *COLD (Temperature), *CRUMB rubber, *CONCRETE testing, *RUBBER

مستخلص: This study investigates the change in the acoustic emission (AE) parameters emitted in rubberized concrete under abrasion action at a sub-freezing temperature (−20°C). Seven concrete mixtures were developed with two coarse-to-fine aggregate ratios (C/F) (2.0 and 0.7), various crumb rubber (CR) content (0%, 10%, 20%, and 30%), and different rubber particle sizes [4.5 mm CR and 0.4 mm powder rubber (PR)]. Rotating cutter tests were conducted on three 100 mm cubic samples from each mixture at −20°C and 25°C while monitored via an AE system. AE parameters such as amplitude, number of hits, and signal strength were collected and underwent two parameter-based analyses: b -value and intensity analysis approaches, resulting in three additional parameters: b -value, severity (Sr), and the historic index [ H(t) ]. Results showed that testing concrete samples under abrasion at cold temperature, −20°C , resulted in a decrease in the emitted number of hits, cumulative signal strength (CSS), Sr , H(t) , and an increase in b -values compared to testing at 25°C. Furthermore, incorporating rubber particles was found to decrease the AE signals' amplitudes significantly at 25°C and slightly at −20°C , which manifested the higher wave attenuation occurrence at ambient temperature compared to cold temperature. AE analysis also showed a decrease in the abrasion resistance for mixtures with higher C/F, higher CR content, and larger rubber particle size. These decreases were more noticeable at 25°C compared to −20°C. Finally, the study developed two damage classification charts to estimate the ranges of abrasion mass loss percentage and wear depth in terms of the intensity analysis parameters: Sr and H(t). [ABSTRACT FROM AUTHOR]

المؤلفون: Marvasti, Mohammad¹, Boutayeb, Halim¹ halim.boutayeb@uqo.ca

المصدر: Applied Computational Electromagnetics Society Journal. Nov2023, Vol. 38 Issue 11, p829-840. 12p.

مصطلحات موضوعية: *FINITE difference time domain method, *ELECTROMAGNETIC wave propagation, *METALLIC wire, *PLANE wavefronts, *ELECTROMAGNETIC waves, *SPECIAL relativity (Physics)

مستخلص: This paper proposes an original and thorough analysis of the behavior of electromagnetic waves in the presence of moving bodies by using the finite difference time domain (FDTD) method. Movements are implemented by changing positions of the objects at each time step, through the classical FDTD time loop. This technique is suitable for non-relativistic speeds, thus for most encountered problems in antennas and propagation domain. The numerical aspects that need to be considered are studied. Then, different bodies in motion are examined: plane wave source with matching resistors, observation point, inclined partially reflecting surface (PRS), line source, and metallic cylinder illuminated by a plane wave. The results are compared with those of special relativity which are considered as the references. Some aspects of special relativity are present in the direct FDTD approach, such as the independence of the velocity of electromagnetic wave propagation with the speed of the source and Lorentz local time (with a different physical interpretation). It is shown that the amplitude of the electric field for a moving plane wave source does not increase with the speed of motion, if the impedance of the source is small. Moreover, for a moving scattering metallic wire, one can observe a phenomenon similar to shock waves. [ABSTRACT FROM AUTHOR]

المؤلفون: Raghib, R.¹ (AUTHOR) rababraghib97@gmail.com, Khalfi, H.¹ (AUTHOR), Naciri, I.¹ (AUTHOR), Elmaimouni, L.¹ (AUTHOR) la_elmaimouni@yahoo.fr, Yu, J.² (AUTHOR), Belkassmi, Y.¹ (AUTHOR), Maimouni, Lahcen. El³ (AUTHOR)

المصدر: AIP Conference Proceedings. 2023, Vol. 2761 Issue 1, p1-11. 11p.

مصطلحات موضوعية: *THEORY of wave motion, *ACOUSTIC wave propagation, *FUNCTIONALLY gradient materials, *EQUATIONS of motion, *FOURIER series, *POWER law (Mathematics)

مستخلص: The study presented in this paper deals with the acoustic wave propagation modeling in a composite cylinders of infinite lengths, made of a functionally graded materials (FGM), using a semi-analytical method. The theory of three-dimensional elasticity is used to formulate this method. The effective material properties of FGM cylinders are supposed to change continuously in the radial direction accordance to the volume fraction's power-law distribution. The displacement components developed in a series of trigonometric functions, Legendre polynomials are embedded into the motion equations using elastic constants depending on the position, and the rectangular window function, with the advantage that the wave equation's solution is simplified to an eigenvalue/eigenvector problem. The dispersion curves in two types of FGM cylinders are calculated using a mathematical formula for longitudinal, torsional, and flexural modes. The dispersion curves with diverse graded index are depicted. These results imply that the graded-index has a major impact on the variations in material properties following the radial direction. Furthermore, the graded index has a considerable impact on the dispersion curves. The obtained numerical results are compared with those reported in theory in order to verify the efficiency and accuracy of this approach. [ABSTRACT FROM AUTHOR]