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Artificial construction of a weakening zone over the roadway is an essential method for preventing coal bursts and rock bursts caused by strong mining tremors. However, concerning the seismic absorption and load reduction capabilities of an artificial structural weakening zone, the degree of rock mass damage to the roadway under weakening zone protection remains unclear. This study employed principles of elasticity and UDEC (Universal Distinct Element Code) to explore the seismic attenuation and load reduction capabilities of the weakening zone. The results indicate that the absorbing ability of the weakening zone increases exponentially with its weakening coefficient. Under the same dynamic load disturbance, when the weakening coefficient rises from 0.00 to 0.99, the sidewall displacement from the elastic wave source side changes from 0.400 m to 0.228 m. The total number of cracks in the roadway-surrounding rock, and the ranges of overstressed zones decreased linearly. The critical threshold of the roadway resisting the mining tremor disturbance increased. In particular, when the mining tremor is located directly above the roadway, the initial deformation of the roof is the largest, and the cumulative deformation of the rib is greater than the roof. By creating a weakening zone with a coefficient exceeding 0.95, the roadway remains unaffected by the 20 MPa dynamic loading. The study provides a theoretical basis for controlling coal burst that is triggered by mining tremors. [ABSTRACT FROM AUTHOR]

To understand crystal anisotropy effects on shock-induced elastic-plastic deformation of molybdenum (Mo), results from high-purity single crystals shocked along [110] and [111] orientations to an elastic impact stress of 12.5 GPa were obtained and compared with the [100] results previously reported [A. Mandal and Y. M Gupta, J. Appl. Phys. 121, 045903 (2017)]. Measured wave profiles showed a time-dependent response, and strong anisotropy was observed in the elastic wave attenuation with the propagation distance, elastic limits, shock speeds, and overall structure of the wave profiles. Resolved shear stresses on {110}〈111〉 and {112}〈111〉 slip systems provided insight into the observed anisotropy in elastic wave attenuation and elastic limits and showed that shear stresses, and not longitudinal stresses, are a better measure of strength in shocked single crystals. Under shock compression, resolved shear stresses at elastic limits were comparable to the Peierls stress of screw dislocations in Mo. Elastic wave attenuation was rapid when shear stresses were larger than the Peierls stress. Large differences in the elastic limits under shock and quasi-static loading are likely a consequence of the large Peierls stress value for Mo. Numerically simulated wave profiles, obtained using the dislocation-based plasticity model described in the [100] work, showed good agreement with all measured wave profiles but could not differentiate between the {110}〈111〉 and {112}〈111〉 slip systems. Overall, experimental results and corresponding numerical simulations for the three crystal orientations have provided a comprehensive insight into shock-induced elastic-plastic deformation of Mo single crystals, including the development of a continuum material model. [ABSTRACT FROM AUTHOR]

In this paper, a new type of low-frequency broadband elastic metamaterial is proposed, which is constituted of periodic I-shaped pillars arranged on a two-dimensional ground surface. The propagation of elastic waves through 3D samples of the seismic metamaterial is investigated in the harmonic regime by a combination of the finite element method and Bloch theory. In contrast, with two typical pillar structures consisting of circular and rectangle pillars, the proposed I-shaped seismic metamaterial can yield wider bandgaps and significantly attenuate the seismic surface waves at the frequencies ranging from 5.8 Hz to 8.8 Hz and from 9.2 Hz to 13.0 Hz, respectively. The generation mechanism of the bandgaps is further explored by computing the transmission spectra through a finite array and analyzing the displacement fields of the surface at 6.1 Hz and 10.2 Hz in two different bandgaps. The optimal geometric parameters of the I-shaped seismic metamaterial are also provided. Although we focus on the geophysical structure, the proposed metamaterial provides a possible alternative for various phenomena such as vibration and noise attenuation because the center frequencies of bandgaps can be easily achieved by modulating the material and geometrical parameters. [ABSTRACT FROM AUTHOR]

We present numerical simulations of elastic wave transport in two‐dimensional fractured media. Natural fracture systems, following a power‐law length scaling, are modeled by the discrete fracture network approach for geometrically representing fracture distributions and the displacement discontinuity method for mechanically computing fracture‐wave interactions. The model is validated against analytical solutions for wave reflection, transmission, and scattering by single fractures, and then applied to solve the wavefield evolution in synthetic fracture networks. We find that the dimensionless angular frequency ῶ = ωZ/κ plays a crucial role in governing wave transport, where ω, Z, and κ are the angular frequency, seismic impedance, and fracture stiffness, respectively. When ῶ is smaller than the critical frequency ῶc (≈5), waves are in the extended mode, either propagating (for small ῶ) or diffusing by multiple scattering (for intermediate ῶ); as ῶ exceeds ῶc, waves become trapped, entering either the Anderson localization regime (kl* ≈ 1) in well‐connected fracture systems or the weak localization regime (kl* > 1) in poorly‐connected fracture systems, where k is the incident wavenumber and l* is the mean free path length. Consequently, the inverse quality factor Q−1 scales with ῶ obeying a two‐branch power‐law dependence, showing significant frequency dependence when ῶ < ῶc and almost frequency independence when ῶ > ῶc. Furthermore, when ῶ < ῶc, the wavefield exhibits a weak dependence on fracture network geometry, whereas when ῶ > ῶc, the fracture network connectivity has an important impact on the wavefield such that strong attenuation occurs in well‐connected fracture systems. Key Points: Elastic wave propagation, scattering, and attenuation in fractured media are studied based on numerical simulationsWavefields are governed by the dimensionless angular frequency and show a transition from propagation to diffusion and to localizationThe inverse quality factor exhibits a two‐branch power‐law scaling as a function of the dimensionless angular frequency [ABSTRACT FROM AUTHOR]

In an effort to achieve higher‐resolution imaging as well as detailed lithology descriptions, it is important to consider attenuation as an aid in compensating for seismic wave amplitude and phase distortions due to the viscoelastic properties of natural rocks. We have evaluated elastic‐wave attenuation on a variety of Gulf of Mexico (GoM) rock salt samples (>95% halite by weight) in the laboratory using the ultrasonic pulse‐transmission technique and the spectral ratio (SR) method. Under conditions of 297 K (75°F) and relative humidity of 46%, the estimated P‐ and S‐wave quality factors QP and QS range from 26 to 74 and 29 to 44 in the unjacketed core samples, respectively. Increasing triaxial pressure elevates Q (decreases attenuation), possibly due to the crack closure and rock frame compaction. For example, a 40 MPa confining pressure increases QP to 275 at 297 K (75°F). Elevating temperature does not show a significant effect on Q values until raised from 339 to 366 K (150°F to 200°F), during which QP drops sharply (attenuation increases). The attenuation mechanisms may include thermal cracking and grain boundary condition changes. We have determined well‐constrained empirical relationships between Q and velocity (V) for both P‐ and S‐waves. These measurements and empirical relationships can further inform us about salt properties and assist with images of and through salt bodies. Key Points: We evaluate the elastic properties of a variety of Gulf of Mexico (GoM) coastal rock salt samples using the ultrasonic pulse‐transmission techniqueThe vibrational attenuation factor or quality factors (Q) of rock salt samples under varying pressures and temperatures are determined using the spectral ratio methodWe establish an empirical relationship between Q and the ultrasonic velocity (V) from the measurements of the GoM salt samples [ABSTRACT FROM AUTHOR]

The attenuation coefficients of sea waves in ice in the coastal zone of the Sea of Okhotsk with periods from 4 to 30 s were estimated as a function of their wavelength based on observations. We used the model dispersion relation for these waves in ice and calculated the theoretical attenuation coefficients. We compared them with those from the data of experiments based on the relation of the spectral energies of waves in ice-free water and in ice. It is possible to use the estimated attenuation coefficients for waves of different periods to calculate the distance of wave propagation in fast ice with the critical amplitude where ice breaking is possible. [ABSTRACT FROM AUTHOR]

Abstract This paper completes the thermodynamic characterization of normal and diabetic blood by the study of the propagation of electromagnetic waves. After a brief introduction on the thermodynamic approach in a biological system, the procedure used is briefly described. The problem of the propagation of electromagnetic waves is faced by deducing an expression of the propagation speed and attenuation of the wave as a function of the frequency. Comparison of results between normal and diabetic blood shows a greater number of permanent dipoles in diabetic blood than in the normal one. Diabetic blood tends to the insolubility because of conformational changes of blood proteins which cannot effectively respond to the stress of the electric field. Highlights • Diabetic blood shows several permanent dipoles in respect of the normal one. • In diabetic blood proteins cannot effectively respond to the stress of the electric field. • Macromolecular structures influence the electromagnetic waves propagation in normal and diabetic blood. [ABSTRACT FROM AUTHOR]

When ocean waves propagate over porous seabed, they cause variations of the pore pressure within seabed, leading to the possible wave attenuation and soil liquefaction. In order to advance and improve our understanding of the process of wave-induced seabed liquefaction and its impact on wave propagation, systematical experiments are carried out in a wave flume with a soil basin filled with silt. Both the pore pressures and water surface elevations are measured simultaneously, while the seabed liquefaction is videotaped using a high-speed camera. Laboratory measurements show that the pore pressure in surface layer mainly oscillates over time, while the wave period averaged pore pressure has little change. In the deep layer, however, the wave period averaged value of the pore pressure builds up dramatically. The results show that the wave height decreases rapidly along the direction of wave propagation when seabed liquefaction occurs. Such a wave attenuation is greatly enhanced when the liquefaction depth further increases. The experiments also demonstrate that the conditions (wave height and wave period) of incident waves have significant impacts on the wave-induced pore pressures, liquefaction depth and wave attenuation in a silt bed. [ABSTRACT FROM AUTHOR]

In this paper, we propose and study a single-phase elastic metamaterial with periodic chiral local resonator, which is composed of cylindrical central core surrounded by evenly distributed ligaments and embedded in the matrix in a square lattice. Based on the analytical and numerical analysis, we prove that the translational resonance of the unit cell can lead to negative effective mass density, and the rotational resonance of it can produce negative effective modulus. They can also work together to generate double-negative effective material properties. The wave attenuation of elastic waves in this elastic metamaterial is also demonstrated, which is owing to the negative effective mass density. In addition, the damping of the base material is also considered in the simulation. We finally examine the existence of negative band, and this leads to the physics of negative refraction, which is induced by simultaneous translational and rotational resonance of the unit cell. Our work can serve as the theoretical foundation for the design of single-phase elastic metamaterials. [ABSTRACT FROM AUTHOR]

The performance of GPS Klobuchar (GPSKlob), BDS Klobuchar (BDSKlob) and NeQuick Galileo (NeQuickG) ionospheric correction models are evaluated in the range delay and position domains over China. The post-processed Klobuchar-style (CODKlob) coefficients provided by the Center for Orbit Determination in Europe (CODE) and our own fitted NeQuick coefficients (NeQuickC) are also included for comparison. In the range delay domain, BDS total electrons contents (TEC) derived from 20 international GNSS Monitoring and Assessment System (iGMAS) stations and GPS TEC obtained from 35 Crust Movement Observation Network of China (CMONC) stations are used as references. Compared to BDS TEC during the short period (doy 010-020, 2015), GPSKlob, BDSKlob and NeQuickG can correct 58.4, 66.7 and 54.7% of the ionospheric delay. Compared to GPS TEC for the long period (doy 001-180, 2015), the three ionospheric models can mitigate the ionospheric delay by 64.8, 65.4 and 68.1%, respectively. For the two comparison cases, CODKlob shows the worst performance, which only reduces 57.9% of the ionospheric range errors. NeQuickC exhibits the best performance, which outperforms GPSKlob, BDSKlob and NeQuickG by 6.7, 2.1 and 6.9%, respectively. In the position domain, single-frequency stand point positioning (SPP) was conducted at the selected 35 CMONC sites using GPS C/A pseudorange with and without ionospheric corrections. The vertical position error of the uncorrected case drops significantly from 10.3 m to 4.8, 4.6, 4.4 and 4.2 m for GPSKlob, CODKlob, BDSKlob and NeQuickG, however, the horizontal position error (3.2) merely decreases to 3.1, 2.7, 2.4 and 2.3 m, respectively. NeQuickG outperforms GPSKlob and BDSKlob by 5.8 and 1.9% in vertical component, and by 25.0 and 3.2% in horizontal component. [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical studies of acoustic-structure interaction of selected helicoidal resonator with helicoidal profile made of an elastic material. Considered a well-recognized acoustic system for one representative type of acoustic helicoidal resonator with two resonant frequencies that correspond to previous studies of the author. Due to the large range of flexible materials to study, this work focuses on the change of material density, Poisson's ratio and Young's modulus as the basic parameters describing the properties of elastic materials. The results indicate a significant interaction between the acoustic attenuation performance of helicoidal resonator and elasticity of the helicoidal profile. These interactions are most evident in the frequency range in which the helicoidal resonator is revealed to be effective acoustic damper. [ABSTRACT FROM AUTHOR]

Compressional wave speed and attenuation were measured for water-saturated granular media employing five kinds of glass beads having unimodal and bimodal grain size distributions. Glass beads with grain sizes ranging from 250 to 850 μ m were used for the acoustic measurements at a frequency range from 350 kHz to 1.1 MHz, which includes the transition range where scattering and non-scattering losses co-exist. The compressional wave speed and attenuation data are presented as a function of frequency and grain size distribution. The compressional wave speed and attenuation data show a variety of frequency dependencies for varying grain size distribution. The observed acoustic properties are investigated for the volume ratio of larger and smaller sized grains in the mixed bimodal media. Also, the measured results are compared with the empirical multiple scattering formula as a function of Rayleigh parameter k d (product of wavenumber in the water k and mean grain diameter of the glass beads d ) using weighted mean grain size. The measured results are also discussed, focusing on the geophysical difference between unimodal and bimodal mixed grains. [ABSTRACT FROM AUTHOR]

Explicit expressions for bounds on the effective bulk and shear moduli of mixture of an elastic solid and Newtonian fluid are derived. Since in frequency domain the shear modulus of the Newtonian fluid is complex valued, the effective mixture moduli are, in general, also complex valued and, hence, the bounds are curves in the complex plane. From the general expressions for bounds of effective moduli of viscoelastic mixtures, it is shown that effective bulk and shear moduli of such mixtures must lie between the real axis and a semicircle in the upper half-plane connecting formal lower and upper Hashin-Shtrikman bounds of the mixture of the solid and inviscid fluid of the same compressibility as the Newtonian fluid. Furthermore, it is shown that the bounds on the effective complex bulk and shear moduli of the mixture are optimal; that is, the moduli corresponding to any point on the bounding curves can be attained by the Hashin sphere assemblage penetrated by a random distribution of thin cracks. The results are applicable to a variety of solid/fluid mixtures such as fluid-saturated porous materials and particle suspensions. [ABSTRACT FROM AUTHOR]

The double-porosity, dual-permeability theory is employed to predict the wave attenuation and phase velocity dispersion induced by wave-induced meso copic fluid flow. Instead of using an up-scaled, single-porosity approximation scheme proposed by previous researchers, we develop an analytical method to exactly solve the wave equations for double-porosity materials. We first propose a new form of wave equations formulated in terms of displacements. This new form of wave equations enables us to decouple the field equations into two second-order symmetric dynamic systems, namely, the P -system for compressional waves and the S -system for shear wave. We then implement Newton iteration for solving the cubic dispersion equation for compressional waves. Finally, to understand the loss mechanism caused by mesoscopic flow, we compare the attenuation curves of the first ( P 1-wave), the second ( P 2-wave), and the third compressional waves ( P 3-wave), as well as the shear wave ( S -wave), with the mesoscopic flow present to those with the mesoscopic flow absent. Furthermore, the effects of matrix porosity, pore-fluid viscosity, and values of fluid transport coefficient on wave attenuation are also investigated in numerical examples. [ABSTRACT FROM AUTHOR]

In this paper, we numerically and experimentally demonstrate the low-frequency broadband elastic wave attenuation and vibration suppression by using plate-type elastic metamaterial, which is constituted of periodic double-sides stepped resonators deposited on a two-dimensional phononic plate with steel matrix. The dispersion relations, the power transmission spectra, and the displacement fields of the eigenmodes are calculated by using the finite element method. In contrast to the typical phononic plates consisting of periodic stepped resonators deposited on a homogeneous steel plate, the proposed elastic metamaterial can yield large band gap in the low-frequency range, resulting in the low-frequency broadband elastic wave attenuation. The formation mechanisms of the band gap as well as the effects of material and geometrical parameters on the band gap are further explored numerically. Numerical results show that, the formation mechanism of opening the low-frequency band gap is attributed to the coupling between the local resonant Lamb modes of two-dimensional phononic plate and the resonant modes of the stepped resonators. The band gap can be significantly modulated by the material and geometrical parameters. The properties of broadband gaps of the proposed subwavelength scale elastic metamaterials can potentially be applied to vibration and noise reduction in the audio regime as well as broadband elastic wave confinement and modulation in ultrasonic region. [ABSTRACT FROM AUTHOR]

We investigate the effect of an electrical current on the attenuation length of a 900 nm wavelength spin-wave in a permalloy/Pt bilayer using propagating spin-wave spectroscopy. The modification of the spin-wave relaxation rate is linear in current density, reaching up to 14% for a current density of 2.3×1011 A/m2 in Pt. This change is attributed to the spin transfer torque induced by the spin Hall effect and corresponds to an effective spin Hall angle of 0.13, which is among the highest values reported so far. The spin Hall effect thus appears as an efficient way of amplifying/attenuating propagating spin waves. [ABSTRACT FROM AUTHOR]

Seismic coda represents a valuable source of information about the attenuation of the high-frequency waves in the studied region. The quality factor Q derived from coda is an integral parameter of the volume surrounding the hypocenter and seismic station and, according to the applied method, represents the total attenuation or the intrinsic and scattering parts. We analyzed records of 13 selected earthquakes in the magnitude range 1.7-2.9 of the 2011 swarm from West Bohemian/Vogtland area (central Europe), which were recorded at epicentral distances from 7 to 50 km. Two methods were applied: coda method for estimation of the Q and the Multiple Lapse Time Windows Analysis for separation of the scattering and intrinsic loss by estimation of Q and Q. Careful selection of the analyzed events was necessary due to the frequent contamination of coda decays by the running seismic swarm activity. The resulting coda Q is relatively high with respect to the geodynamic activity and varies between 100 and 2500 within the analyzed frequency range of 1-18 Hz. The intrinsic loss dominates over scattering attenuation with Q increasing from 100 and 1850 and Q from 300 to 3400 in the same frequency range, which is consistent with the geodynamic activity of the region. We find that the intrinsic attenuation in West-Bohemia/Vogtland is higher that in neighboring Germany, which could be attributed to the heterogeneity of the crust in central Europe. [ABSTRACT FROM AUTHOR]

Periodic pile barriers exhibit unique dynamic property, i.e., the frequency attenuation zones. When wave frequencies fall in the attenuation zones, the amplitude of the elastic waves could be reduced by the periodic pile barriers. In the present paper, out-of-plane waves propagating in two-dimensional periodic pile barriers are investigated. A novel numerical approach based on the weak form quadrature element method (WFQEM) is developed to study the effect of initial stress on the attenuation zones of the pile barriers. The proposed method is verified to be with significant advantages in both accuracy and convergence with regard to the lumped-mass method (LMM) in particular cases. The theoretical results show that the initial stress significantly alters the position and width of the attenuation zones, however, it does not affect the maximum attenuation coefficient. In addition, elastic waves propagating in periodic pile barriers with finite number of unit cells is simulated at the end of this paper. The results obtained in the present paper are very useful for the design and application of periodic pile barriers in ambient vibration reduction. [ABSTRACT FROM AUTHOR]

The attenuation and velocity dispersion of sonic waves contain valuable information on the mechanical and hydraulic properties of the probed medium. An inherent complication arising in the interpretation of corresponding measurements is, however, that there are multiple physical mechanisms contributing to the energy dissipation and that the relative importance of the various contributions is difficult to unravel. To address this problem for the practically relevant case of terrestrial alluvial sediments, we analyse the attenuation and velocity dispersion characteristics of broad-band multifrequency sonic logs with dominant source frequencies ranging between 1 and 30 kHz. To adequately compensate for the effects of geometrical spreading, which is critical for reliable attenuation estimates, we simulate our experimental setup using a correspondingly targeted numerical solution of the poroelastic equations. After having applied the thus inferred corrections, the broad-band sonic log data set, in conjunction with a comprehensive suite of complementary logging data, allows for assessing the relative importance of a range of pertinent attenuation mechanisms. In doing so, we focus on the effects of wave-induced fluid flow over a wide range of scales. Our results indicate that the levels of attenuation due to the presence of mesoscopic heterogeneities in unconsolidated clastic sediments fully saturated with water are expected to be largely negligible. Conversely, Monte-Carlo-type inversions indicate that Biot's classical model permits to explain most of the considered data. Refinements with regard to the fitting of the observed attenuation and velocity dispersion characteristics are locally provided by accounting for energy dissipation at the microscopic scale, although the nature of the underlying physical mechanism remains speculative. [ABSTRACT FROM AUTHOR]

The conventional piezoelectric metamaterials with operational-amplifier-based shunt circuits have limited application due to the voltage restriction of the amplifiers. In this research, we report a novel piezoelectric metamaterial beam that takes advantage of mechanical shunt resonators. The proposed metamaterial beam consisted of a piezoelectric beam and remote mechanical piezoelectric resonators coupled with electrical wires. The local resonance of the remote mechanical shunt resonators modified the mechanical properties of the beam, yielding an elastic wave attenuation capability. A finite-length piezoelectric metamaterial beam and mechanical shunt resonators were considered for conceptual illustration. Significant elastic wave attenuation can be realized in the vicinity of the resonant frequency of the shunt resonators. The proposed system has the potential in the application of wave attenuation under large-amplitude excitations. [ABSTRACT FROM AUTHOR]

In this work, the attenuation of ultrasonic elastic waves propagating through magnetorheological (MR) fluids is analysed as a function of the particle volume fraction and the magnetic field intensity. Non-commercial MR fluids made with iron ferromagnetic particles and two different solvents (an olive oil based solution and an Araldite-epoxy) were used. Particle volume fractions of up to 0.25 were analysed. It is shown that the attenuation of sound depends strongly on the solvent used and the volume fraction. The influence of a magnetic field up to 212mT was studied and it was found that the sound attenuation increases with the magnetic intensity until saturation is reached. A hysteretic effect is evident once the magnetic field is removed. [ABSTRACT FROM AUTHOR]

Cloaking is a challenging topic in the field of wave motion, and is of significant theoretical value. In this article, a type of carpet cloak has been theoretically designed for water waves by using the effective medium and transformation theory. This carpet cloak device, created by a three-dimensional printer, is composed of a periodic structure which realizes the equivalent anisotropic water depth. We demonstrate its excellent cloaking performance numerically and experimentally in a wide range of frequencies and angles of incidence, with low wave attenuation characteristics and simple device realization of this carpet cloak illustrating that water wave transformation is a powerful method with which to manipulate water waves. [ABSTRACT FROM AUTHOR]