Estimation of Near‐Surface Quality Factors by Constrained Inversion of Rayleigh‐Wave Attenuation Coefficients

2011 ◽  
Author(s):  
Jianghai Xia ◽  
Richard Miller ◽  
Julian Ivanov ◽  
Shelby Peterie
Keyword(s):  
Rayleigh Wave ◽  
Surface Quality ◽  
Wave Attenuation ◽  
Quality Factors ◽  
Attenuation Coefficients ◽  
Near Surface

Broadband Rayleigh wave attenuation by gradient metamaterials

2021 ◽  
pp. 106592
Author(s):  
Xinyue Wu ◽  
Zhihui Wen ◽  
Yabin Jin ◽  
Timon Rabczuk ◽  
Xiaoying Zhuang ◽  
...  
Keyword(s):  
Rayleigh Wave ◽  
Wave Attenuation

Application of bandlimited anelastic models to wave propagation in highly attenuative media

1995 ◽  
Vol 85 (5) ◽  
pp. 1359-1372
Author(s):  
Hsi-Ping Liu
Keyword(s):  
Wave Propagation ◽  
Quality Factor ◽  
Lower Limit ◽  
Relaxation Function ◽  
Function Approach ◽  
Creep Function ◽  
Frequency Range ◽  
Quality Factors ◽  
Low Frequencies ◽  
Near Surface

Abstract Because of its simple form, a bandlimited, four-parameter anelastic model that yields nearly constant midband Q for low-loss materials is often used for calculating synthetic seismograms. The four parameters used in the literature to characterize anelastic behavior are τ1, τ2, Qm, and MR in the relaxation-function approach (s1 = 1/τ1 and s2 = 1/τ2 are angular frequencies defining the bandwidth, MR is the relaxed modulus, and Qm is approximately the midband quality factor when Qm ≫ 1); or τ1, τ2, Qm, and MR in the creep-function approach (s1 = 1/τ1 and s2 = 1/τ2 are angular frequencies defining the bandwidth, and Qm is approximately the midband quality factor when Qm ≫ 1). In practice, it is often the case that, for a particular medium, the quality factor Q(ω0) and phase velocity c(ω0) at an angular frequency ω0 (s1 < ω0 < s2; s1 < ω0 < s2) are known from field measurements. If values are assigned to τ1 and τ2 (τ2 < τ1), or to τ1 and τ2 (τ2 < τ1), then the two remaining parameters, Qm and MR, or Qm and MR, can be obtained from Q(ω0). However, for highly attenuative media, e.g., Q(ω0) ≦ 5, Q(ω) can become highly skewed and negative at low frequencies (for the relaxation-function approach) or at high frequencies (for the creep-function approach) if this procedure is followed. A negative Q(ω) is unacceptable because it implies an increase in energy for waves propagating in a homogeneous and attenuative medium. This article shows that given (τ1, τ2, ω0) or (τ1, τ2, ω0), a lower limit of Q(ω0) exists for a bandlimited, four-parameter anelastic model. In the relaxation-function approach, the minimum permissible Q(ω0) is given by ln [(1 + ω20τ21)/(1 + ω20τ22)]/{2 arctan [ω0(τ1 − τ2)/(1 + ω20τ1τ2)]}. In the creep-function approach, the minimum permissible Q(ω0) is given by {2 ln (τ1/τ2) − ln [(1 + ω20τ21)/(1 + ω20τ22)]}/{2 arctan [ω0(τ1 − τ2)/(1 + ω20τ1τ2)]}. The more general statement that, for a given set of relaxation mechanisms, a lower limit exists for Q(ω0) is also shown to hold. Because a nearly constant midband Q cannot be achieved for highly attenuative media using a four-parameter anelastic model, a bandlimited, six-parameter anelastic model that yields a nearly constant midband Q for such media is devised; an expression for the minimum permissible Q(ω0) is given. Six-parameter anelastic models with quality factors Q ∼ 5 and Q ∼ 16, constant to 6% over the frequency range 0.5 to 200 Hz, illustrate this result. In conformity with field observations that Q(ω) for near-surface earth materials is approximately constant over a wide frequency range, the bandlimited, six-parameter anelastic models are suitable for modeling wave propagation in highly attenuative media for bandlimited time functions in engineering and exploration seismology.

Attenuation of Rayleigh-wave amplitudes across Eurasia

1977 ◽  
Vol 67 (3) ◽  
pp. 751-769
Author(s):  
Nazieh K. Yacoub ◽  
Brian J. Mitchell
Keyword(s):  
Rayleigh Wave ◽  
Regional Variation ◽  
Wave Amplitude ◽  
Period Range ◽  
Attenuation Coefficients ◽  
Nuclear Explosions ◽  
Amplitude Data ◽  
Standard Deviations ◽  
Data Yield ◽  
Rayleigh Mode

abstract Surface waves generated by six earthquakes and two nuclear explosions are used to study the attenuation coefficients of the fundamental Rayleigh mode across Eurasia. Rayleigh-wave amplitude data yield average attenuation coefficients at periods between 4 and 50 sec. The data exhibit relatively large standard deviations and in some cases the average attenuation coefficients take on negative values which may be due to regional variations of the attenuative properties of the crust, lateral refraction, multipathing and scattering. A method has been developed to investigate the regional variation in the attenuative properties of the Eurasian crust and its effect on surface-wave amplitude data, employing the evaluated average attenuation coefficients for the fundamental Rayleigh mode. For this investigation, Eurasia is divided into two regions, one considered to be relatively stable, and the other considered to be tectonic in nature. This regionalization shows that the tectonic regions exhibit higher attenuation than the stable regions in the period range below about 20 sec, whereas in the period range above about 20 sec, no clear difference can be observed for the two regions. Although the effects of lateral refraction and multipathing may still significantly affect the observations, the regionalization lowers the standard deviations considerably and eliminates the negative values which were obtained in the unregionalized determinations.

scholarly journals MULTI-WAVE ULTRASONIC CONTROL OF CONCRETE

2017 ◽  
Vol 16 (4) ◽  
pp. 289-297
Author(s):  
D. Yu. Snezgkov ◽  
S. N. Leonovich
Keyword(s):  
Rayleigh Wave ◽  
Pulse Propagation ◽  
Ultrasonic Method ◽  
Physical And Mechanical Properties ◽  
Pulse Velocity ◽  
Energy Localization ◽  
Near Surface ◽  
In Situ Conditions ◽  
Selection Of

The existing non-destructive testing system of structure concrete is actually orientated on the usage of longitudinal acoustical waves. This is due to simplicity of technical realization for measuring velocity (time) of acoustical pulse propagation in bulk concrete. But a reverse side of simple measuring procedure is a loss of additional information on concrete which is contained in the accepted acoustical signal. Therefore usage of an ultrasonic concrete testing method is limited by assessment of its strength. Joint usage of several wave types, so-called multi-wave testing, allows to refine metrology parameters of the ultrasonic method and to gain more information while determining physical and mechanical properties of concrete in laboratory and in situ conditions. The paper considers testing of elongated concrete elements and structures by an ultrasonic pulsing method on the basis of longitudinal subsurface and Rayleigh waves. It has been proposed to use methodology for time selection of wave components according to amplitude parameter and it has been applied for standard acoustical transformers with considerable reverberation time and not possessing spatial selectivity Basic principle of the proposed methodology is visual (according to oscillogram of the received signal) determination of characteristic time moments which are used for calculation of differential value of a propagation velocity in the Rayleigh wave impulse. The paper presents results pertaining to simulation of acoustical pulse propagation on the basis of 0.15 m and data of concrete ultrasonic in situ testing on measuring bases from 0.25 to 1.75 m. Advantage of large baseline for sonic test is a possibility for execution of a hundred percent inspection for surface of large-sized elements and structures, and so there is no need to make a selective inspection in some control areas as it is stipulated by provided by existing regulations. Responsivity of the Rayleigh wave parameters to near surface concrete defects permits quickly and efficiently to detect crack areas in a reinforced structure. Energy localization of a surface wave in a layer having width λ/2–λ provides a possibility to ignore reinforcement availability under appropriate selection of oscillation frequency. In addition to this, large measuring baseline makes it possible to lower effect of concrete structural inhomogeneity on statistical stability for pulse velocity assessment that ultimately reveals a possibility to register an appearance of concrete acoustical elasticity effect under in situ conditions.

Surface Quality of Pulsed Laser Cutting of Difficult to Machine Steel

2011 ◽  
Vol 299-300 ◽  
pp. 1016-1019
Author(s):  
Tie Jun Li ◽  
Jing Tang ◽  
Li Jun Yan ◽  
Yang Wang
Keyword(s):  
Surface Quality ◽  
Laser Cutting ◽  
Pulsed Laser ◽  
Cutting Parameters ◽  
Quality Factors ◽  
Good Separation ◽  
Machine Steel ◽  
Optimum Cutting ◽  
Super Alloy

This paper presented the experiments of Nd:YAG pulsed laser cutting of titanium alloy, super-alloy and stainless steel sheet, and investigated the influences of different laser cutting parameters on the surface quality factors focusing surface morphology. In comparison with air-, argon- and nitrogen-assisted laser cutting, argon-assisted laser cutting comes with unaffected surface quality and is suitable for laser cutting with subsequent welding requirement. With analyzing the interaction between pulses overlapping rate and energy, the results show that medium pulse overlapping rate and lower pulse rate helps to improve the surface roughness with pulsed laser cutting. And the results would be beneficial to find optimum cutting parameters for good separation surface.

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