المؤلفون: Zhou, Yiheng¹ (AUTHOR), Tan, Ye² (AUTHOR), Zhang, Ruizhi^1,2 (AUTHOR) zhangrz1991@gmail.com, Li, Zhiguo² (AUTHOR), Chen, Han² (AUTHOR), Bai, Jingsong² (AUTHOR), Li, Lei² (AUTHOR), Shen, Qiang¹ (AUTHOR), Luo, Guoqiang^1,3 (AUTHOR) luogq@whut.edu.cn

المصدر: Journal of Applied Physics. 12/14/2023, Vol. 134 Issue 22, p1-15. 15p.

مصطلحات موضوعية: *STRESS waves, *ELASTIC wave propagation, *THEORY of wave motion, *CASCADE impactors (Meteorological instruments), *EQUATIONS of state, *LOADING & unloading

مستخلص: Quasi-isentropic loading and unloading, employing graded density impactors (GDIs) as flyers in gas gun-driven plate impact experiments, can provide novel and valuable insights into the equation of state and strength properties of the loaded material. However, the internal ballistic process may lead to spalling or debonding of the GDI due to the intricate interactions between stress waves and interfaces. In this study, the wave propagation in the GDI was analyzed using the multimaterial Lagrangian elastic-plastic model and elastic wave propagation theory. The impact of gradient direction, power-law constant p, and thickness of the first and last layers on the tensile stress was investigated. The outcomes reveal that the mechanism of generating tensile stress varies for two gradient directions. Moreover, adjusting the constant p and the layer thickness may decrease the maximum tensile stress by 74.1% (forward graded) and 95.8% (reverse graded), respectively. The outcomes of this research provide a theoretical and simulation basis for designing and fabricating GDIs to be utilized in quasi-isentropic experiments. [ABSTRACT FROM AUTHOR]

المؤلفون: Hao Qin¹, Xingqi Zhang^1,2 xingqi.zhang@ucd.ie

المصدر: IET Microwaves, Antennas & Propagation (Wiley-Blackwell). Feb2024, Vol. 18 Issue 2, p59-72. 14p.

مصطلحات موضوعية: *TELECOMMUNICATION systems, RADIO wave propagation, TUNNELS, COMPARATIVE studies, ELECTROMAGNETIC wave propagation

مستخلص: Radio wave propagation modelling in railway environments is of fundamental importance in designing reliable train communication systems. Parabolic equation (PE) methods have been widely applied to the modelling of wave propagation in tunnels due to their high computational efficiency and fidelity. The finite-difference parabolic equation (FDPE) and the split-step parabolic equation (SSPE) methods are two commonly used approaches to solve PE numerically. However, the relevant literature is still missing a comprehensive study of their performance, including the selection of parameters such as discretisation steps and the tradeoffs involved in terms of their accuracy and efficiency, especially as current wireless systems shift to high frequencies. In this study, a systematic analysis of the error and computational complexity of the FDPE and SSPE methods for radio wave propagation modelling in tunnels is provided. Guidelines for the choice of their parameters are provided, and their performance is demonstrated through both numerical examples and experimental measurements in actual tunnel cases. [ABSTRACT FROM AUTHOR]

: Copyright of IET Microwaves, Antennas & Propagation (Wiley-Blackwell) is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Falletta, S.¹ (AUTHOR) silvia.falletta@polito.it, Monegato, G.¹ (AUTHOR) giovanni.monegato@polito.it, Scuderi, L.¹ (AUTHOR) letizia.scuderi@polito.it

المصدر: AIP Conference Proceedings. 2024, Vol. 3094 Issue 1, p1-4. 4p.

مصطلحات موضوعية: *ELASTIC wave propagation, *ELASTODYNAMICS, *BOUNDARY element methods, *FINITE element method, *ELASTIC scattering, *COLLOCATION methods, *INTEGRAL representations

مستخلص: We consider the decomposition into scalar potentials for the simulation of transient 2D soft scattering elastic wave propagation problems in unbounded isotropic homogeneous media. The vector elastodynamic equation is reformulated in terms of two scalar wave equations, that are coupled by the Dirichlet boundary conditions. These are successively solved by using their associated space-time Boundary Integral Equation (BIE) representations. The corresponding Boundary Element Method (BEM) is obtained by combining a time convolution quadrature formula with a classical space collocation method. Then, the same boundary integral representation and its discretization are used to define a non-reflecting condition to be imposed on an artificial boundary delimiting the exterior computational domain of interest. In this latter a Finite Element Method (FEM) is applied. [ABSTRACT FROM AUTHOR]

المؤلفون: Pomerleau-Perron, Patrick¹ (AUTHOR) pomerlep@uwindsor.ca, Rankin, Gary W.^1,2 (AUTHOR) rankin@uwindsor.ca

المصدر: AIP Conference Proceedings. 2024, Vol. 3094 Issue 1, p1-4. 4p.

مصطلحات موضوعية: *MACH number, *ACOUSTIC wave propagation, *FREQUENCIES of oscillating systems, *SURFACE pressure, *NAVIER-Stokes equations, *ATMOSPHERIC turbulence

مستخلص: A numerical model is used to explain the high-frequency surface pressure fluctuations experimentally observed during the transient impact of a supersonic jet onto a substrate. The observations are made during experiments associated with the Shockwave-Induced Spray Process. Various approximations of the experimental arrangement and operating conditions are made to simplify the model and maintain a reasonable computational cost. The model geometry is axially symmetric, and a single mean jet Mach number value is used. The selected Mach number corresponds to the transient value that occurs during the high-frequency oscillation. The steady Reynolds-Averaged Navier-Stokes equations are first solved to establish the mean velocity field, followed by an unsteady Reynolds-Averaged Navier-Stokes solution to resolve the fluctuations. Due to the presence of acoustic wave propagation, non-reflecting boundary conditions are employed on the atmospheric boundaries of the solution domain. The numerical results indicate that the substrate pressure fluctuations are due to an instability of the bow shockwave that forms ahead of the substrate. The shock experiences an axially pulsing oscillation which is consistent with that previously described in the literature. The predicted frequency of oscillation however does not agree with the experiment. This is explained by the differences in the current model geometry compared to that of the actual experimental equipment. [ABSTRACT FROM AUTHOR]

المؤلفون: Petrover, Kayla, Baz, A.

المصدر: Journal of Applied Physics; 6/21/2024, Vol. 135 Issue 23, p1-15, 15p

مصطلحات موضوعية: BLACK holes, TRANSFER matrix, ACOUSTIC wave propagation, ENERGY dissipation, WAVEGUIDES, ABSORPTION

مستخلص: A new class of acoustic black hole (ABH) waveguides is presented, which relies in its operation on an array of optimally designed functionally graded perforated rings (FGPRs). In this manner, the developed ABH is provided with built-in energy dissipation characteristics generated by virtue of the flow through perforations, which enhances its acoustic absorption behavior and makes the speed of the propagating waves vanish faster when reaching the end of the waveguide. Furthermore, the particular design of the rings enables sandwiching of additional porous absorbing layers between the rings to further boost the absorption characteristics of the proposed ABH. Accordingly, the operating principle of the new class of ABH is radically different from that of the conventional ABH that employs sequential solid-flat rings of decreasing inner radii to create a virtual power law taper necessary for generating the black hole effect, but through reactive means rather than the effective dissipative means of the proposed ABH. Therefore, this paper develops a transfer matrix modeling (TMM) approach to model the absorption and reflection characteristics of the new class of ABH, in an attempt to predict its behavior, optimize the selection of its design parameters, and more importantly, demonstrate its merits as effective means for controlling sound propagation. Numerical examples are presented to highlight the merits and behavior of the proposed ABH. Predictions of the TMM are validated against experimental results that are available in the literature for one and two micro-perforated plates. Comparisons are also established between the ABH with FGPR and the conventional ABH in order to distinguish the behavior and underlying principles of their operations. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Applied Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Sabiru, Aminu Yaradua¹ (AUTHOR) aminu.sabiru@umyu.edu.ng, Akinbolati, Akinsanmi^1,2 (AUTHOR) aakinbolati@fudutsinma.edu.ng, Ikechiamaka, Florence N.² (AUTHOR) fosuagwu@fudutsinma.edu.ng, Abe, Bolanle T.³ (AUTHOR) abebt@tut.ac.za

المصدر: Advances in Space Research. Jul2024, Vol. 74 Issue 2, p890-898. 9p.

مصطلحات موضوعية: *RADIO wave propagation, *CITIES & towns, *WIRELESS communications, *RADIO (Medium)

مصطلحات جغرافية: KADUNA (Nigeria), SOKOTO (Nigeria), KATSINA (Nigeria)

مستخلص: A good understanding of the behavior of the atmosphere is a key factor in radio wave propagation and link's design. This study investigated the influence of refractivity gradient, effective earth radius factor (k-factor) and geo-climatic factor (K-factor) on radio communication over the cities of Kaduna, Katsina and Sokoto, in Northwestern parts of Nigeria. Forty-one year's secondary data (1980–2020) of temperature, pressure and humidity at the surface 12, 100 and 250 m above ground level retrieved from European Centre for Medium-Range Weather Forecasts (ECMRWF) ERA-5 reanalysis were used for the study. The three secondary radio-climatic parameters under investigation were computed and analyzed using latest ITU-R (Rec.P.453-14 (08/2019)) Models. It was observed that secondary radio-climatic variables exhibit seasonal type dependence. The research also reveals that the secondary radio-climatic variables depend on location, with all the study locations having different values. The highest value of refractivity gradient obtained is about −75.06 (N-units / km) in the month of February in Sokoto while the least of about −162.65 (N-units/km) was recorded in Kaduna in September. The value of the refractivity gradient is higher during the dry season compared to the wet season months with Sokoto recording the highest values for more than half of the months, followed by Katsina. Kaduna recorded highest number of lowest values of refractivity gradient. For the geoclimatic factor, it was revealed that Kaduna has an average maximum geoclimatic factor of 14.0000E-5 in September and an average minimum of 9.6677E-05 in February. Furthermore, the obtained values of k factor values for the study areas are higher than the standard value of, 4 3 (1.33). The k-factor in Kaduna ranges from 1.69 to 2.16 with mean value of 1.85 for dry season while for the wet season it ranges from 2.66 to 4.12 with a mean value of 3.74; the overall mean value for Kaduna is 2.80. In Katsina, it ranges from 1.66 to 2.20 with mean value of 1.81 for dry season while for the wet season it ranges from 1.95 to 4.00 with a mean value of 3.27; the overall mean value is 2.54. In Sokoto it ranges from 1.60 to 2.30 with mean value of 1.78 for dry season while for the wet season it ranges from 1.72 to 3.45 with a mean value of 2.59; the overall mean value is 2.19. The interpretation of this is that, radio signal propagation in the Northwest region of Nigeria is super-refractive. The overall findings of this research are essential for estimating location-dependent fade margins, which are useful for the design of wireless communication links for the region. [ABSTRACT FROM AUTHOR]

المؤلفون: Simon, Alverède¹ (AUTHOR), Baudis, Quentin¹ (AUTHOR), Wunenburger, Régis¹ (AUTHOR), Valier-Brasier, Tony¹ (AUTHOR) tony.valier-brasier@sorbonne-universite.fr

المصدر: Journal of the Acoustical Society of America. Jun2024, Vol. 155 Issue 6, p3627-3638. 12p.

مصطلحات موضوعية: *ELASTIC waves, *ELASTIC wave propagation, *ROTATIONAL motion, *SHEAR waves, *MULTIPLE scattering (Physics), *TRANSLATIONAL motion, *LONGITUDINAL waves

مستخلص: The propagation of coherent longitudinal and transverse waves in random distributions of spherical scatterers embedded in an elastic matrix is studied. The investigated frequency range is the vicinity of the resonance frequencies of the translational and rotational motion of the spheres forced by the waves, where strong dispersion and attenuation are predicted. A technique for making samples made of layers of carbide tungsten beads embedded in epoxy resin is presented, which allows control of the scatterers distribution, induce short-range positional correlations, and minimize the anisotropy of samples. Comparison between phase velocity and attenuation measurements and a model based on multiple scattering theory (MST) shows that bulk effective properties accurately described by MST are obtained from three beads layers. Besides, short-range correlations amplify the effect of mechanical resonances on the propagation of longitudinal and transverse coherent waves. As a practical consequence, the use of short-range positional correlations may be used to enhance the attenuation of elastic waves by disordered, locally resonant, elastic metamaterials, and MST globally correctly predicts the effect of short-range positional order on their effective properties. [ABSTRACT FROM AUTHOR]

المؤلفون: Reyes-Romero, Arturo¹ (AUTHOR) artrero77@gmail.com, Adrian Reyes, J.² (AUTHOR)

المصدر: Waves in Random & Complex Media. Jun2024, Vol. 34 Issue 3, p1702-1725. 24p.

مصطلحات موضوعية: *ELECTROMAGNETIC wave propagation, *CHOLESTERIC liquid crystals, *MAXWELL equations, *CONSTRUCTION slabs, *STOCHASTIC analysis, *PLANAR waveguides, *FILLER materials

مستخلص: A stochastic theoretical analysis of electromagnetic wave propagation inside a planar slab waveguide filled with a cholesteric material, whose azimuthal angular component on its director n is randomly fluctuating is presented in this article. By means of van Kampen systematic expansion method, Maxwell's electromagnetic equations with random dielectric tensor and appropriate boundary conditions are obtained. As numerical examples, the effects of the randomness on the propagating constant, on the ratio between magnetic and electric modes, on the field profiles, and on the energy flow are presented and discussed. The results in this paper are consistent with those corresponding to the deterministic conventional waveguide. [ABSTRACT FROM AUTHOR]

المؤلفون: Faber, Marthe¹ (AUTHOR) M.Faber@sms.ed.ac.uk, Curtis, Andrew¹ (AUTHOR)

المصدر: Geophysical Journal International. Jun2024, Vol. 237 Issue 3, p1459-1489. 31p.

مصطلحات موضوعية: *WAVE equation, *ACOUSTIC wave propagation, *SEISMIC waves, *SURFACE of the earth, *SEISMIC wave velocity, *IMAGING systems in seismology, *SURFACE waves (Seismic waves)

مستخلص: Material density remains poorly constrained in seismic imaging problems, yet knowledge of density would provide important insight into physical material properties for the interpretation of subsurface structures. We test the sensitivity to subsurface density contrasts of spatial and temporal gradients of seismic ambient noise wavefields, using wave equation inversion (WEI), a form of seismic gradiometry. Synthetic results for 3-D acoustic media suggest that it is possible to estimate relative density structure with WEI by using a full acoustic formulation for wave propagation and gradiometry. We show that imposing a constant density assumption on the medium can be detrimental to subsurface seismic velocity images. By contrast, the full acoustic formulation allows us to estimate density as an additional material parameter, as well as to improve phase velocity estimates. In 3-D elastic media, severe approximations in the governing wave physics are necessary in order to invert for density using only an array of receivers on the Earth's free surface. It is then not straightforward to isolate the comparatively weak density signal from the influence of phase velocity using gradiometric WEI. However, by using receivers both at the surface and in the shallow subsurface we show that it is possible to estimate density using fully elastic volumetric WEI. [ABSTRACT FROM AUTHOR]

المؤلفون: Luo, Yuqin¹ (AUTHOR), Wang, Tao¹ (AUTHOR) cugbwt@163.com, Li, Yongdong¹ (AUTHOR), Cai, Ji¹ (AUTHOR), Wang, Ying¹ (AUTHOR), Fang, Guangyou¹ (AUTHOR)

المصدر: Acta Geophysica. Jun2024, Vol. 72 Issue 3, p1561-1573. 13p.

مصطلحات موضوعية: *ELASTIC wave propagation, *DIFFERENTIAL equations, *SEISMIC waves

مستخلص: Absorbing boundary conditions are often utilized to eliminate spurious reflections that arise at the model's truncation boundaries. The perfectly matched layer (PML) is widely considered to be very efficient artificial boundary condition. A new alternative implementation of the PML is presented. We call this method residual perfectly matched layer (RPML) because it is based on residual calculation between the original equations and the PML formulations. This new approach has the same form as the original governing equations, and the auxiliary differential equation has only one partial derivative with respect to time, which is the simplest compared to other PMLs. Therefore, the RPML shows great advantages of implementation simplicity and computational efficiency over the standard complex stretched coordinate PML. At the same time, the absorption performance is improved by adopting the complex frequency shifted stretching function; the stability of the boundary is enhanced by applying the double damping profile. [ABSTRACT FROM AUTHOR]