Wave Attenuation Factor Research Articles

Experimental and numerical investigations on phase change thermal storage foam concrete based on CaCl2∙6H2O/silica aerogel composite phase change material

A new type of phase change thermal storage foam concrete was developed by effectively incorporating a composite phase change material (CPCM) into foam concrete. The CPCM was obtained by using 75 wt% CaCl2∙6H2O as PCM and 25 wt% silica aerogel as carrier, with a phase change temperature of 27.0 °C and an enthalpy value of 110.9 J/g. The mechanical and thermal properties of the obtained phase change thermal storage foam concrete blocks were investigated experimentally, along with a numerical analysis of their heat transfer characteristics. The experimental results demonstrated that after adding CPCM, the thermal performances of foam concrete blocks significantly increased, under the condition of their dry densities and compressive strengths met the specification requirements. Adding 20 wt% CPCM, the enthalpy value, specific heat capacity, thermal conductivity and thermal inertia of foam concrete block respectively reached 37.0 J/g, 1782.0 J/(kg∙K), 0.131 W/(m·K) and 770.9, with appropriate phase change temperature (27.2 °C). Numerical analysis for the heat transfer characteristics of the phase change thermal storage foam concrete wall revealed that optimal thermal insulation and thermal storage performances were achieved when the wall contained 20 wt% CPCM and thickness of 80 mm. In this case, the model exhibited a temperature wave attenuation factor of 6.66, the temperature amplitude of 5.84 K and a decline of 9.87 K for the highest temperature of the wall as well as delay time of 198,000 s, effectively regulating indoor temperature and saving energy. Therefore, the as-prepared phase change thermal storage foam concrete had great potential for application in building energy conservation.

Mangroves as Coastal Protection for Restoring Low-Energy Waterfront Property

Mangroves offer vital ecological advantages including air and water filtration, coastal and estuarine habitat provision, sediment stabilization, and wave energy dissipation. Their intricate root systems play a key role in safeguarding shorelines from tsunamis and erosive storms by dissipating wave energy. Moreover, mangroves shield against boat wakes and wind-waves, thus naturally bolstering shoreline defense. Wave dissipation is a function of forest width, tree diameter, and forest density. Restoration efforts of juvenile mangroves in Florida’s Indian River Lagoon (IRL) aim to reduce wave energy in areas vulnerable to erosion. Physical model testing of wave dissipation through mangroves is limited due to the complexity in representing the mangrove structure, where prop roots are non-uniform in both diameter and location. Previous studies have quantified wave-dissipating effects through the use of scaled and parameterized mangrove structures. This study measures the dissipation effects of live mangroves in a wave flume, forced by conditions representative of the IRL. These measurements are used to validate a parameterized dowel model. Error between wave attenuation factors for the live mangrove and dowel system was on average 2.5%. Validation of the modularized dowel system allowed for further parameterized testing to understand forest structure effects, such as sediment stabilization and wave attenuation. Maximum wave attenuation achieved in this study was 27–35% corresponding to a 40–60% reduction in wave energy depending on the configuration of the system. The wave reduction resulted in a 50–70% decrease in sediment erosion from the berm. The dowel tests indicate a target minimum thickness for mangrove root systems of 0.6 m for shoreline stabilization and restoration in the IRL.

Trans-scale dynamic shear-lag model for wave attenuation in staggered composites

In this study, we develop the trans-scale dynamic shear-lag model based on the strain gradient theory to investigate the wave propagation in staggered composites with architectures down to micro- and nano-scale. The model yields an analytical expression of the wave attenuation factor for nacre-like staggered composites with building blocks at the submicron scale for the first time. We show that when the matrix thickness reduces, the size effect on the wave attenuation performance becomes significant – the first bandgap of the composites shifts to higher frequencies, and the materials lose the efficiency to filter lower-frequency waves. Furthermore, parametric studies demonstrate that the first bandgap width and location are influenced greatly by many factors, such as the length scale parameter, the tablet volume fraction, and the overlap length. Particularly, the first bandgap width varies non-monotonically with the above parameters. Our study sheds light on the understanding of the wave attenuation mechanisms of biological and bio-inspired composites with microscopic architectures when the size effect is non-negligible. The findings here provide valuable guidance for designing advanced composites with sophisticated micro- and nano-structures to achieve exceptional dynamic properties.

Acoustothermoelasticity for Joint Effects of Stress and Thermal Fields on Wave Dispersion and Attenuation

AbstractThe stress field and thermal field are usually coupled in the Earth's subsurface. The mechanism of the joint effects of stress and thermal fields on wave propagation in rocks is not well understood. To fill this gap, this paper combines the acoustoelasticity theory with heat conduction theory to propose an acoustothermoelasticity mechanism to describe the joint effects of stress and thermal fields. The stress‐ and thermal‐dependent wave velocities and attenuation factors are formulated with 2‐D Fourier transform analysis for dynamic equations, which predict four wave modes of propagation including two longitudinal waves, namely, P wave and T (thermal) wave, and two shear waves, namely, fast S wave and second S wave. The stress‐induced anisotropy accounts for the S‐wave splitting phenomenon and T wave presents the thermal diffusive behavior, which depend on the magnitude and direction of stress and thermoelastic parameters. Stress and thermal effects on the wave velocity dispersion and attenuation are fully analyzed. Modeling results show that T wave is coupled with the P wave and fast S wave rather than the second S wave inducing the dissipation energy in the pre‐stressed thermoelastic rocks. The predicted wave velocities show reasonable agreement with ultrasonic laboratory measurements under uniaxial and triaxial stresses. Our model and results help to better understand mechanical properties and wave propagation in pre‐stressed thermoelastic rocks.

On the Kramers-Kronig relations

We provide a new derivation of the Kramers-Kronig relations on the basis of the Sokhotski-Plemelj equation with detailed mathematical justifications. The relations hold for a causal function, whose Fourier transform is regular (holomorphic) and square-integrable. This implies analyticity in the lower complex plane and a Fourier transform that vanishes at the high-frequency limit. In viscoelasticity, we show that the complex and frequency-dependent modulus describing the stiffness does not satisfy the relation but the modulus minus its high-frequency value does it. This is due to the fact that despite its causality, the modulus is not square-integrable due to a non-null instantaneous response. The relations are obtained in addition for the wave velocity and attenuation factor. The Zener, Maxwell, and Kelvin-Voigt viscoelastic models illustrate these properties. We verify the Kramers-Kronig relations on experimental data of sound attenuation in seabottoms sediments.

Effects of GPR antenna configuration on subpavement drain detection based on the frequency-shift phenomenon

The water and clay content of subsurface soil can significantly influence the detection results obtained from ground penetrating radar (GPR). Due to the variation of the material properties underground, the center frequency of transmitted GPR signals shifts to a lower range as wave attenuation increases. Examination of wave propagation in the subsurface employing an attenuation filter based on a linear system model shows that received GPR signals will be shifted to lower frequencies than those originally transmitted. The amount of the shift is controlled by a wave attenuation factor, which is determined by the dielectric constant, electric conductivity, and magnetic susceptibility of the transmitted medium. This paper introduces a receiver-transmitter-receiver dual-frequency configuration for GPR that employs two operational frequencies for a given test - one higher and one slightly lower - to take advantage of this phenomenon to improve subpavement drain detection results. In this configuration, the original signal is transmitted from the higher frequency transmitter. After traveling through underground materials, the signal is received by two receivers with different frequencies. One of the receivers has the same higher center frequency as the transmitter, and the other receiver has a lower center frequency. This configuration can be expressed as Rx(low-frequency)-Tx(high-frequency)-Rx(high-frequency) and was applied in both laboratory experiments and field tests. Results are analyzed in the frequency domain to evaluate and compare the properties of the signal obtained by both receivers. The laboratory experiment used the configuration of Rx(400MHz)-Tx(900MHz)-Rx(900MHz). The field tests, in addition to the configuration used in the lab tests, employed another configuration of Rx(270MHz)-Tx(400MHz)-Rx(400MHz) to obtain more information about this phenomenon. Both lab and field test results illustrate the frequency-shift phenomenon described by theoretical calculations. Based on the power spectrum for each signal, the signal received by the lower frequency antenna typically received more energy (higher density values) at its peak frequency than the energy received by the higher frequency antenna.

Stress‐Drop Variations and Source‐Scaling Relations of Moderate Earthquakes of the Indian Tectonic Plate

We investigate the source characteristics of 53 earthquakes in and around the Indian subcontinent through a grid‐search technique applied to the P ‐ and S ‐wave displacement spectra of regional waveforms registered at 42 broadband seismic stations. In addition, we estimate the P ‐ and S ‐wave attenuation factors representative of the various tectonic regions that constitute the Indian shield. We discuss the sensitivity of the displacement spectrum to various parameters and demonstrate that for a Brune‐type source model, the seismic moment is the best estimated parameter compared to others, such as the corner frequency. Our estimates of moment magnitudes are within the range of 1014–1020 (N·m), with the crack radii being less than ∼12 km. The nonuniform distribution of the static stress drop along the Himalaya, Burmese arc, and the western Indian regions indicates that the central Himalayas are prone to frequent failures owing to the lesser stress drop, in contrast with the northwestern Himalaya and Burmese arc regions. Our results suggest that median stress drops are independent of the earthquake mechanism. Online Material: List of events and associated estimated parameters.

Research status and development of laser shock peening

Laser shock peening (LSP) is a noncontact surface strengthening technology. It has been widely used because of its advantages in applied scope and strengthening effects. LSP has made considerable progress during the past four decades, but some technical issues affecting their applications remain to be resolved, for instance, the utilization rate of laser shock energy is only about 50%, the processing adaptability of rigid confinement layer is poor, and the thickness of the flexible confinement layer represented by a water layer is difficult to control. In this paper, the current research status of LSP technology was reviewed, and an outlook was given toward further development of this technology. On this basis, a method to form composite shock waves by designing a cavity to confine the water layer is presented in this paper, which is expected to address the issues mentioned above. A preliminary simulation for analyzing the relationship between the strengthening effect and the characteristic parameters of the composite shock wave was carried out, and the simulated results were discussed. The results show that the time interval between the adjacent waves and the wave attenuation factor have significant influence on the strengthening effects, which is helpful to the cavity design.

Effects of suspended solid particles on the propagation and attenuation of mud pressure pulses inside drill string

The attenuation of mud pressure pulses in the drilling fluid inside drill string has restricted the application of mud pulse telemetry systems in directional drilling operations. This paper aims to investigate the effects of suspended solid particles on the propagation and attenuation characteristics of pressure pulses. In this work, an analytical model estimating the wave speed and attenuation factor of pressure pulses has been proposed based on the solid–liquid two-fluid model by performing linear perturbation theory, with the interactions of the solid–liquid two phases being considered. The model calculations are compared with the results of the experiments, showing good agreement. Based on the model, the propagation behavior of pressure pulses has been analyzed to ascertain the important parameters affecting the wave speed and attenuation factor. The results indicate that the angular frequency of the pressure pulses, the volume fraction, size and density of the solid particles all exert significant influence on the pressure pulses propagation and attenuation. Lower angular frequency, solid particle size and density tend to reduce the attenuation of pressure pulses. The pressure pulses have maximum attenuation when the volume fraction falls within the range of 20%–30%. For different angular frequencies, the general effects of the volume fraction, size and density of the solid particles on the wave speed and attenuation factor are the same, although they differ in degree.

Towards a viscoelastic mechanical characterization of asphalt materials by ultrasonic measurements

This study focuses on the use of P-wave propagation measurements in order to evaluate the complex modulus, more specifically for the reversible and dissipated parts of asphalt materials. Both the wave velocity and attenuation factor have been measured by means of an ultrasonic transmission test, at frequencies between 200 and 300 kHz and temperatures ranging from −20 to 40 °C. Based on this wave velocity and attenuation factor, the high-frequency complex modulus and its components are computed by considering a 2D propagation of waves in an isotropic viscoelastic medium. Results are plotted with respect to the master curve, Cole–Cole and Black spaces. The ultrasonic test results agree with results obtained by complex modulus test and then fitted by the 2S2P1D rheological model. This paper shows in Cole–Cole space that ultrasonic data can facilitate the determination of important rheological parameters as one of the two parabolic dashpots (k) and the glassy modulus E0. The phase angle, which is also a key viscoelastic identification parameter, can be determined at high frequency in a Black space representation.

Description of mechanism of thermal conduction and internal damping by means of two-component Cosserat continuum

A new approach to the derivation of the theory of thermoviscoelasticity is proposed. Neither the hypothesis of fading memory nor rheological models are used within the framework of this approach. The proposed approach is based on the mechanical model of a one-rotor gyrostat continuum. In special cases, the mathematical description of this model is proved to reduce to the equations of the coupled problem of thermoelasticity, the self-diffusion equation, and the equation describing the flow of a viscous incompressible fluid. In the context of this model, we consider the original treatment of the physical nature of the mechanism of thermal conduction and internal damping. The first part of the paper contains the aforesaid theoretical results. The second part of the paper is devoted to the determination of some parameters of the model. On the base of the proposed theory, we obtain the dependence of the acoustic wave attenuation factor on a signal frequency. This dependence is in close agreement with the classical dependence in the low-frequency range and agrees with the dependence obtained on the base of the phonon theory in the hypersonic frequency range. We discuss some ways of determining of the volume and shear viscosities and the heat flow relaxation timescale by using known values of the sound velocity and the acoustic wave attenuation factor. The obtained values of the heat flow relaxation timescale are compared with the values derived from the phonon theory.

Use of site amplification and anelastic attenuation for the determination of source parameters of the Sikkim earthquake of September 18, 2011, using far-field strong-motion data

An earthquake of magnitude 6.9 (M w) occurred in the Sikkim region of India on September 18, 2011. This earthquake is recorded on strong-motion network in Uttarakhand Himalaya located about 900 km away from the epicenter of this earthquake. In this paper acceleration record from six far-field stations has been used to compute the source parameters of this earthquake. The acceleration spectra of ground motion at these far-field stations are strongly affected by both local site effects and near-site anelastic attenuation. In the present work the spectrum of S-phase recorded at these far-field stations has been corrected for anelastic attenuation at both source and site and the site amplification terms. Site amplifications at different stations and near-site shear wave attenuation factor have been computed by the technique of inversion of acceleration spectra given by Joshi et al. (Pure Appl Geophys 169:1821–1845, 2012a). For estimation of site amplification and shear wave quality factor [Q β (f)] at the recording sites, ten local events recorded at various stations between July 2011 and December 2011 have been used. The obtained source spectrum from acceleration records is compared with the theoretical source spectrum defined by Brune (J Geophys Res 76:5002, 1970) at each station for both horizontal components of the records. Iterative forward modeling of theoretical source spectrum gives the average estimate of seismic moment (M o), source radius (r o) and stress drop (Δσ) as (3.2 ± 0.8) × 1026 dyne cm, 13.3 ± 0.8 km and 59.2 ± 8.8 bars, respectively, for the Sikkim earthquake of September 18, 2011.

Effect of drop in pipe wall stiffness on water-hammer speed and attenuation

The effect of local drop of wall stiffness in pressurized waterways on the pressure wave speed and the wave attenuation during transients is investigated experimentally. A new signal-processing procedure to identify the presence of a weak reach is introduced and validated by physical experimentation based on assessing the pressure and vibration records acquired at both ends of a multi-reach steel test pipe. Water-hammer was generated by closing a downstream valve, whereas the weak reaches were simulated by replacing the steel portions with aluminium and PVC material. The wave speed and wave attenuation factor during transients are considered as global indicators of local and large changes in stiffness of the pipe wall. The method is capable of locating the stiffness weakness along the test pipe if one PVC reach is used. The error in estimating the position of such a reach relative to the real position of its mean value varies up to 23%.

Propagation of electroacoustic axial shear waves in a piezoelectric medium reinforced by continuous fibers

The propagation of electroacoustic axial shear waves in a fiber reinforced piezocomposites is studied in which matrix and fibers consist of piezoelectric transversely isotropic materials with symmetry axes parallel to the fiber axes. The effective medium method self-consistent variant as developed by Sabina and Willis is used to obtain explicit equations for the complex wave vector and it is solved numerically. Its real part determines the effective wave velocity and the imaginary part the attenuation factor. Integral equations expressed via dynamic Green’s function kernels are set up. The central problem of the method is the axial shear electroacoustic wave scattering on one isolated fiber in the medium having the effective piezoelectric properties. It is solved approximately by the Galerkin type method. The obtained expressions for the effective wave velocity and attenuation factor cover not only the long-wave region but the intermediate wave and it is valid for long wavelenghts up to the diameter of the inclusion. Wave velocity and attenuation coefficient coincide with ones obtained earlier in some other way. Some numerical examples are presented for real materials.

Frequency Dependence of Coda Q, Part I: Numerical Modeling and Examples from Peaceful Nuclear Explosions

Frequency-dependent coda attenuation values are often reported; however, such measurements usually depend on the types of the Q ( f ) models employed. We use numerical modeling of peaceful nuclear explosion (PNE) coda at far-regional to teleseismic distances to compare two such models, namely, the conventional frequency-dependent quality factor ( Q coda( f )= Q f η ) and frequency-independent coda attenuation ( Q c ) with geometrical attenuation ( γ ). The results favor strongly the ( γ , Q c ) model and illustrate the mechanisms leading to apparent Q coda( f ) dependencies. Tests for variations of the crustal velocity structures show that the values of γ are stable and related to lithospheric structural types, and the inverted Q c -values can be systematically mapped into the true S -wave attenuation factors within the crust. Modeling also shows that γ could increase in areas where relatively thin attenuating layers are present within the crust; such areas could likely be related to younger and active tectonics. By contrast, when interpreted by using the traditional ( Q , η ) approach, the synthetic coda shows a strong and spurious frequency dependence with η ≈0.5, which is also similar to the observations. Observed Lg coda from two PNEs located in different areas in Russia show similar values of γ ≈0.75×10-2 sec-1, which are also remarkably close to the independent numerical predictions. At the same time, coda Q c -values vary strongly, from 850 in the East-European platform to 2500 within the Siberian Craton. This suggests that parameters γ and Q c could provide stable and transportable discriminants for differentiating between the lithospheric tectonic types and ages and also for seismic coda regionalization in nuclear test monitoring research.

Effect of surface stress on magneto-elastic surface waves in finitely conducting media

This paper deals with the investigation of the effect of surface stress and conductivity on the propagation of surface wave in isotropic, homogeneous, elastic media under the action of a primary magnetic field. Formulation of the general surface wave propagation problem has been made, and the corresponding frequency equation has been derived. Frequency equations for Rayleigh wave, surface shear wave and Stoneley wave have been deduced from that of general surface wave as special cases. The effects of surface stress and magnetic field on the wave velocities and attenuation factors of Rayleigh wave and surface shear wave are shown by numerical calculations and graphs. Some important wave velocity equations, as obtained by other authors, have been deduced as special cases from the wave velocity equation for Stoneley wave. It is found that the combined effect of surface stress and magnetic field modulates the wave velocity ratios and attenuation factors of Rayleigh wave and surface shear wave to a considerable extent.

P20 浅間山構造探査記録におけるコーダ波減衰特性の空間分布(ポスターセッション,日本火山学会2007年秋季大会)

P20 浅間山構造探査記録におけるコーダ波減衰特性の空間分布(ポスターセッション,日本火山学会2007年秋季大会)

Waves propagation in turbulent superfluid helium in presence of combined rotation and counterflow

A complete study of the propagation of waves (namely longitudinal density and temperature waves, longitudinal and transversal velocity waves and heat waves) in turbulent superfluid helium is made in three situations: a rotating frame, a thermal counterflow, and the simultaneous combination of thermal counterflow and rotation. Our analysis aims to obtain as much information as possible on the tangle of quantized vortices from the wave speed and attenuation factor of these different waves, depending on their relative direction of propagation with respect to the rotation vector.

Intrinsic and scattering attenuation in western India from aftershocks of the 26 January, 2001 Kachchh earthquake

176 vertical-component, short period observations from aftershocks of the M w 7.7, 26 January, 2001 Kachchh earthquake are used to estimate seismic wave attenuation in western India using uniform and two layer models. The magnitudes ( M w ) of the earthquakes are less than 4.5, with depths less than 46 km and hypocentral distances up to 110 km. The studied frequencies are between 1 and 30 Hz. Two seismic wave attenuation factors, intrinsic absorption ( Q i − 1 ) and scattering attenuation ( Q s − 1 ) are estimated using the Multiple Lapse Time Window method which compares time integrated seismic wave energies with synthetic coda wave envelopes for a multiple isotropic scattering model. We first assume spatial uniformity of Q i − 1 , Q s − 1 and S wave velocity ( β). A second approach extends the multiple scattering hypothesis to media consisting of several layers characterized by vertically varying scattering coefficient ( g), intrinsic absorption strength ( h), density of the media ( ρ) and shear wave velocity structure. The predicted coda envelopes are computed using Monte Carlo simulation. Results show that, under the assumption of spatial uniformity, scattering attenuation is greater than intrinsic absorption only for the lowest frequency band (1 to 2 Hz), whereas intrinsic absorption is predominant in the attenuation process at higher frequencies (2 to 30 Hz). The values of Q obtained range from Q t = 118, Q i = 246 and Q s = 227 at 1.5 Hz to Q t ≈ 4000, Q i ≈ 4600 and Q s ≈ 33,300 at 28 Hz center frequencies, being Q t − 1 a measure of total attenuation. Results also show that Q i − 1 , Q s − 1 and Q t − 1 decrease proportional to f − ν . Two rates of decay are clearly observed for the low (1 to 6 Hz) and high (6 to 30 Hz) frequency ranges. Values of ν are estimated as 2.07 ± 0.05 and 0.44 ± 0.09 for total attenuation, 1.52 ± 0.21 and 0.48 ± 0.09 for intrinsic absorption and 3.63 ± 0.07 and 0.06 ± 0.08 for scattering attenuation for the low and high frequency ranges, respectively. Despite the lower resolution in deriving the attenuation parameters for a two layered crust, we find that scattering attenuation is comparable to or smaller than the intrinsic absorption in the crust whereas intrinsic absorption dominates in the mantle. Also, for a crustal layer of thickness 42 km, intrinsic absorption and scattering estimates in the crust are lower and greater than those of the mantle, respectively.

Propagation of axial shear magneto–electro-elastic waves in piezoelectric–piezomagnetic composites with randomly distributed cylindrical inhomogeneities

The integral equations of the scattering problem for piezoelectric–piezomagnetic composites with an inhomogeneity are derived. In the long-wave limit, the solutions of these integral equations for the composites containing a single inhomogeneous fiber are solved in close forms. The total scattering cross-section for the one-fiber composites is also obtained. By the so-called effective field method, the multi-fiber scattering problem is simplified to the one-fiber scattering problem, and the analytical expressions of magneto–electro-elastic fields for the multi-fiber composites are obtained in the long-wave limit. These solved magneto–electro-elastic fields are then used to solve the expressions of the static effective moduli, effective wave velocity and attenuation factor of piezoelectric–piezomagnetic composites with randomly distributed cylindrical inhomogeneities. Through numerical examples, it concludes that, if the random set of fiber cross-sections is homogeneous and isotropic, the effective field method is coincident with the Mori–Tanaka mean field method when the static effective moduli of piezoelectric–piezomagnetic composites are looked for. Moreover, the rules of the effective wave velocity versus the volume fraction of fibers are investigated for specific materials.