Interaction of seismic waves with a viscous liquid layer

1982 ◽  
Vol 72 (1) ◽  
pp. 55-72
Author(s):  
Michael Fehler
Keyword(s):  
Viscous Fluid ◽  
Physical Properties ◽  
Acoustic Impedance ◽  
Seismic Waves ◽  
Fluid Layer ◽  
Normal Incidence ◽  
Sh Wave ◽  
P Waves ◽  
Sh Waves ◽  
Hot Dry Rock

abstract The interaction of seismic waves with a layer filled with a viscous fluid is studied. This study is intended to provide the basis for designing active seismic experiments to detect the existence of hydraulically induced fractures in a Hot Dry Rock Geothermal energy system. We compute transmission and reflection coefficients for P, SV, and SH waves incident at arbitrary angles onto a fluid layer embedded between two homogeneous half-spaces. We find that coefficients for SH waves at normal incidence can be written in terms of two dimensionless parameters. One of these parameters, I, is the ratio of acoustic impedance of the fluid to the acoustic impedance of the solid. The other dimensionless parameter, γd, is a measure of the amount of energy the SH wave loses during one pass through the fluid layer. We find that the amplitude of the SH wave transmitted through the fluid layer is equal to the amplitude of the incident SH wave if I is nearly 1 and γd is small. As γd increases, energy is lost due to viscous dissipation in the fluid and transmitted wave amplitude diminishes. If I is not nearly 1, some energy is reflected by the fluid layer. Three dimensionless parameters are required for solution for the case of P waves normally incident on the fluid layer. One parameter, R, is the ratio of the bulk modulus to effective shear modulus of the fluid. The second parameter is the ratio of elastic impedance of the solid to the shear impedance of the fluid and the third is γd. We find that the value of R is a good measure of the importance of fluid viscosity on the propagation of P waves through the fluid. Detailed studies of the effects of fluid and solid physical properties on the amplitudes of transmitted and reflected waves when waves are normally incident provide valuable insight into the importance of physical properties in the calculations for non-normal incidence. Finally, reflection and transmission coefficients are computed for P and SV waves incident at arbitrary angle on a viscous fluid layer. Physical properties of fluid and rock are chosen to be those thought appropriate for the Los Alamos National Laboratory Hot Dry Rock Geothermal test site located at Fenton Hill, New Mexico.

Response of structures to nonvertically incident seismic waves

1982 ◽  
Vol 72 (1) ◽  
pp. 275-302 ◽  
Author(s):  
J. E. Luco ◽  
H. L. Wong
Keyword(s):  
Rayleigh Waves ◽  
Nuclear Power ◽  
Seismic Waves ◽  
Vertical Component ◽  
Wave Excitation ◽  
Sh Wave ◽  
Sh Waves ◽  
Torsional Response ◽  
Concrete Building ◽  
Incident Waves

abstract A study of the earthquake response of symmetric elastic structures subjected to SH-wave excitation with different angles of incidence and to Rayleigh waves is presented. For SH-wave excitation, particular emphasis is given to the study of the possible reduction of the response due to filtering by the foundation and the torsional response. For Rayleigh wave excitation, the effects of the additional rocking associated with the vertical component of the excitation are investigated. The results obtained for models of a 10-story reinforced concrete building and the containment structure of a nuclear power plant reveal that the response for nonvertically incident waves is significantly different from that obtained on the basis of the usual assumption of vertically incident SH waves.

Scattering of SH Wave on Periodic Cracks in an Infinite Plane of Piezoelectric/Piezomagnic Composite Materials

2012 ◽  
Vol 166-169 ◽  
pp. 3364-3368
Author(s):  
Wei Shi ◽  
Li Xia Ma
Keyword(s):  
Stress Intensity Factor ◽  
Integral Equation ◽  
Composite Materials ◽  
Piezoelectric Materials ◽  
Infinite Plane ◽  
Sh Wave ◽  
Scattering Problems ◽  
Sh Waves ◽  
Periodic Cracks ◽  
The Fourier Transform

In this paper, the scattering problems of SH waves on periodic cracks in an infinite of piezoelectric/piezomagnic composite materials bonded to an infinite of homogeneous piezoelectric materials is investigated, the Fourier transform techniques are used to reduce the problem to the solution of Hilbert singular integral equation, the latter is solved by Lobotto-Chebyshev and Gauss integral equation, at last, numerical results showed the effect of the frequency of wave, sizes and so on upon the normalized stress intensity factor.

A periodic seismic isolation foundation with an extremely broad low-frequency attenuation zone: Theoretical analysis and experimental verification

2021 ◽  
pp. 136943322110646
Author(s):  
Peng Zhou ◽  
Shui Wan ◽  
Xiao Wang ◽  
Yingbo Zhu ◽  
Muyun Huang
Keyword(s):  
Seismic Isolation ◽  
Seismic Waves ◽  
Periodic Structures ◽  
Finite Size ◽  
Low Frequency ◽  
Bridge Structure ◽  
Engineering Structures ◽  
P Waves ◽  
New Type ◽  
Dominant Frequencies

The attenuation zones (AZs) of periodic structures can be used for seismic isolation design. To cover the dominant frequencies of more seismic waves, this paper proposes a new type of periodic isolation foundation (PIF) with an extremely wide low-frequency AZ of 3.31 Hz–17.01 Hz composed of optimized unit A with a wide AZ and optimized unit B with a low-frequency AZ. The two kinds of optimized units are obtained by topology optimization on the smallest periodic unit with the coupled finite element-genetic algorithm (GA) methodology. The transmission spectra of shear waves and P-waves through the proposed PIF of finite size are calculated, and the results show that the AZ of the PIF is approximately the superposition of the AZs of the two kinds of optimized units. Additionally, shake tests on a scale PIF specimen are performed to verify the attenuation performance for elastic waves within the designed AZs. Furthermore, numerical simulations show that the acceleration responses of the bridge structure with the proposed PIF are attenuated significantly compared to those with a concrete foundation under the action of different seismic waves. Therefore, the newly proposed PIF is a promising option for the reduction of seismic effects in engineering structures.

Diffraction of elastic waves by a fluid-filled crack in a fluid-saturated poroelastic half-space

2021 ◽  
Author(s):  
Zhongxian Liu ◽  
Jiaqiao Liu ◽  
Sibo Meng ◽  
Xiaojian Sun
Keyword(s):  
Half Space ◽  
Seismic Waves ◽  
Incident Angle ◽  
Excitation Frequency ◽  
Vertical Displacement ◽  
Crack Model ◽  
P Waves ◽  
Amplification Effect ◽  
Resonance Frequencies ◽  
Angle Crack

Summary An indirect boundary element method (IBEM) is developed to model the two-dimensional (2D) diffraction of seismic waves by a fluid-filled crack in a fluid-saturated poroelastic half-space, using Green's functions computed considering the distributed loads, flow, and fluid characteristics. The influence of the fluid-filled crack on the diffraction characteristics is investigated by analyzing key parameters, such as the excitation frequency, incident angle, crack width and depth, and medium porosity. The results for the fluid-filled crack model are compared to those for the fluid-free crack model under the same conditions. The numerical results demonstrate that the fluid-filled crack has a significant amplification effect on the surface displacements, and that the effect of the depth of the fluid-filled crack is more complex compared to the influence of other parameters. The resonance diffraction generates an amplification effect in the case of normally incident P waves. Furthermore, the horizontal and vertical displacement amplitudes reach 4.2 and 14.1, respectively. In the corresponding case of the fluid-free crack, the vertical displacement amplitude is only equal to 4.1, indicating the amplification effect of the fluid in the crack. Conversely, for normally incident SV waves at certain resonance frequencies, the displacement amplitudes above a fluid-filled crack may be lower than the displacement amplitudes observed in the corresponding case of a fluid-free crack.

Reflection of SH waves from anisotropic transition layer

1974 ◽  
Vol 64 (6) ◽  
pp. 1979-1991 ◽  
Author(s):  
V. Thapliyal
Keyword(s):  
Reflection Coefficient ◽  
Incident Wave ◽  
Transition Layer ◽  
Seismic Energy ◽  
Considerable Effect ◽  
Anisotropy Factor ◽  
Sh Wave ◽  
Sh Waves ◽  
Obliquely Incident ◽  
Order Discontinuity

abstract The effects of anisotropy on the reflection of SH-waves (horizontally polarized shear waves) from a transition layer are studied. The transition layer is sand-wiched between two isotropic homogeneous half-spaces and is constituted by a medium which is both anisotropic and inhomogeneous. The SH-wave potentials are obtained for an anisotropic inhomogeneous medium in which both the anisotropy factor (ratio of the horizontal rigidity to the vertical rigidity) and vertical velocity vary with depth. An expression for the reflection coefficient of SH waves is obtained when the material mentioned above forms a finite transition zone between two isotropic homogeneous half-spaces. For further generalization, a second-order discontinuity along with the first-order on eis being assumed in the material properties, at the boundaries of the transition layer. The mathematical and numerical analyses show that the anisotropy factor, found at the top of the transition layer (N0/M0) produces considerable effect on the reflection coefficient for an obliquely incident SH wave. It has been noted that the greater the thickness of the transition layer, the greater is the dependence of the reflection coefficient upon the value of the anisotropy (N0/M0). The minima and maxima of the reflection of seismic energy are found dependent on the value of anisotropy. For greater values of the anisotropy, these maxima and minima shift toward the lower values of the wavelength of the propagating wave (or toward the higher values of the thickness of the transition layer). In fact, the values of the reflection coefficient at which these maxima and minima of seismic energy occur are found greater for the higher values of anisotropy. The effects of anisotropy are found more pronounced for the larger angles of incidence. This remains so until the angle of refraction becomes imaginary. However, no effects of the anistropy factor are found on the reflection coefficients for a normally incident wave. The results, mentioned above, are therefore discussed only for the obliquely incident wave. A geophysically interesting situation has been chosen for studying, quantitatively, the effects of the anisotropy factor on the reflection of SH waves.

Classification of Iron Meteorites with High Frequency Ultrasonic Waves

2019 ◽  
Vol 24 (2) ◽  
pp. 277-284
Author(s):  
Dris El Abassi ◽  
Bouazza Faiz ◽  
Abderrahmane Ibhi ◽  
Idris Aboudaoud
Keyword(s):  
Phase Velocity ◽  
Acoustic Impedance ◽  
Nickel Content ◽  
Normal Incidence ◽  
Ultrasonic Pulse ◽  
Ultrasonic Waves ◽  
Iron Meteorites ◽  
Acoustic Transducer ◽  
Pulse Echo ◽  
Non Destructive

We present the results of an ultrasonic pulse-echo technique and its potential to classify iron meteorites into hexahedrites, octahedrites and ataxites by determining their acoustic impedance and phase velocity. Our technique has been adapted from those used in the field of ultrasonic non-destructive investigation of a variety of materials. The main advantage of our technique is that it does not need any preparation of the meteorites like cutting and etching and therefore is rapid, easy and non-destructive. In essence, a broadband acoustic transducer is used in a monostatic pulse-echo configuration which means that both the transducer and the meteorite sample are located in a water bath and adjusted in the way that the ultrasonic pulse shit the meteorite sample at normal incidence. Then the reflected pulses from the front and rear faces of the meteorite sample are measured with the emitting transducer, digitally recorded and processed to analyze the signal. After Fourier transforming the echoed pulses from the front and the rear face of the meteorite sample, the calculated reflection coefficients yield the phase velocity and the acoustic impedance. Our study investigates a variety of iron meteorites collected in Morocco and other countries and it helps to understand how the nickel content of these meteorites affects the acoustic impedance. It reveals that the acoustic impedance of iron meteorites increases with increasing nickel content, so that a further refinement of our technique might have the potential to classify iron meteorites directly and reliably into hexahedrites, octahedrites and ataxites without destroying them.

On the Vibration Damping of a Plate by Means of a Viscous Fluid Layer

1987 ◽  
Vol 109 (2) ◽  
pp. 178-184 ◽  
Author(s):  
K. Uno Ingard ◽  
Adnan Akay
Keyword(s):  
Viscous Fluid ◽  
Frequency Response ◽  
Flow Resistance ◽  
Acoustic Radiation ◽  
Fluid Layer ◽  
Vibration Damping ◽  
Plate Motion ◽  
Flexible Plate ◽  
Dependent Flow ◽  
Rigid Plane

Vibration damping of a plate by means of a fluid layer is investigated. First, the frequency-dependent flow resistance of a fluid layer is explained with a simple illustration of the damping mechanism. Then, the vibration response of a plate is examined when it is backed by a rigid plane or another flexible plate with a fluid layer constricted in-between. Effects of the plate motion and acoustic radiation on the damping mechanism are also considered. The numerical results are presented in terms of frequency response of the plates.

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