Increase Of Incident Frequency Research Articles

Seismic Dynamic Response Analysis of Mountain Tunnels with Seismic Reduction and Isolation Measures

In this paper, the multi-domain indirect boundary element method (IBEM) is developed for the seismic response analysis of double-line mountain tunnels with seismic reduction and isolation measures. The dynamic response of the tunnel with seismic reduction and isolation measures under incident SV waves is analyzed, and the effect of the mountain topography on the tunnel is also investigated. Further, the effects of the isolation layer and the grouting reinforcement with different thicknesses on the seismic response of the tunnel are discussed in detail. The results show that the scattering of seismic waves by mountain topography significantly increases tunnel stress. In general, with the increase of incident frequency, the isolation layer will increase the peak displacement of the tunnel by about 12.7% at most, and the isolation ratio of the isolation layer on the tunnel stress exceeds 40%. The seismic reduction performance of the grouting reinforcement also depends on the incident frequency, and the amplitude decreases by approximately 20% at most frequencies. However, it is possible that the lining displacement under high-frequency waves becomes larger. This method can provide valuable insights and assessments for damage prediction.

Effective velocity of reflected wave in rock mass with different wave impedances of normal incidence of stress wave

AbstractThe effective velocity of the reflected wave in rock mass is of significance to the detection of crustal structure and the geophysical seismic exploration. In this paper, the modified characteristic method was introduced to solve P‐wave reflection in rock mass with different wave impedances on two sides of the joint. Effective velocity was defined to characterize the propagation velocity of the reflected wave in jointed rock mass. The effects of incident frequency, joint stiffness and wave impedance ratio on the effective velocity were discussed. The results show that when the stress wave propagation in "hard‐to‐soft" rock mass, the effective velocity increases firstly and then decreases as the incident frequency and the joint stiffness increase, while the effective velocity always decreases as the wave impedance ratio increases; when the stress wave propagation in "soft‐to‐hard" rock mass, the effective velocity decreases as the incident frequency increases, increases as the joint stiffness increases and decreases as the wave impedance ratio increases. The wave impedance ratio has an important influence on the effective velocity. The effective velocity without considering wave impedance ratio is smaller than that of stress wave propagation in "soft‐to‐hard" rock mass, but larger than that of stress wave propagation in "hard‐to‐soft" rock mass.

Scattering of Antiplane SH Waves by Complex Landforms

The multiple scattering of SH waves by isosceles triangular hill, semicircle depression, and isosceles trapezoidal hill in the solid half-space is studied. The complex model is divided into multiple subdomains by using the region matching method, then the wave functions in each subdomain are constructed by using the fractional-order Bessel function, and finally, the infinite algebraic equations for solving the unknown coefficients in the wave function are established by using the multipolar coordinate technique and the complex function method according to the boundary conditions. Fourier series is used to solve the unknown undetermined coefficients. The results show that due to the multiple reflections of the incident wave between complex landforms, surface displacement amplitude is affected by the incident angle, incident frequency, and the distance between the isosceles triangular hill, semicircle depression, and isosceles trapezoidal hill. It is found that when the incident frequency increases, there is a certain amplification effect between the hills and the depression. When the wave is incident horizontally, there is a certain “barrier” effect between hills and depression, and when the distance between the hills and depression reaches a certain level, the “barrier” effect will reach a stable value.

Investigation of wave reflection at the joint with different wave impedances on two sides

When the stress wave propagates through rock mass with different wave impedances on two sides. It shows different reflection tendencies compared with the traditional study of wave propagation. A characteristic line method combined with the displacement discontinuity model was proposed to study the wave reflection through such rock mass. The effects of incident frequency, joint stiffness and wave impedance ratio on the reflection coefficient were discussed. The results show that the reflection coefficient increases as the wave impedance ratio increases. The traditional study of wave reflection can be regarded as a special case of the present study when the wave impedance ratio equals 1.0. Moreover, the difference of reflection coefficients decreases as the incident frequency increases, while increases as the joint stiffness and wave impedance ratio increase when the wave impedance ratio is larger than 1.0. When the wave impedance ratio is smaller than 1.0, the difference of reflection coefficients increases firstly and then decreases with the increase of incident frequency and joint stiffness, while decreases as the wave impedance ratio increases. For the cases of large incident frequency or small joint stiffness, the effects of wave impedance ratio can be neglected for the approximated prediction of wave reflection.

Influence of Ancient River Covering Layer Shear-Wave Velocity Variation on Plane Primary Waves

While using the big circle method, Fourier Bessel series expansion technique, and the coordinate conversion of Graf's addition formula, an analytical solution for the scattering of non concentric arc layered alluvial valleys subjected to plane primary waves was derived. Then the precision of the numerical result was checked up and analyzed. Finally, by using the analytic solution, the surface displacement was analyzed at different shear wave velocity of covering layer. The analysis results show that shear wave velocity change has little effect on the crest value of displacement at lower frequency incidence, however the influence becomes significant with the increase of incident frequency. In general, lower the shear wave velocity is, higher the crest value of displacement will be. Compared with the existing conclusions, the covering thickness variation has little effect on the influence of shear wave velocity change on the scattering of elastic waves.

Effect of dust particle potential on plasma conductivity

In this paper, the concept of electrical potential influencing factor is proposed to describe the effect of electrical potential difference between the dust particle and background plasma on conductivity, based on which the conductivity model of dusty plasma is improved. The electrical potential influencing factor is directly proportional to the charge number, number density, radius of the dust particle, and the electron number density of the background plasma. Meanwhile, it is inversely proportional to the electron temperature of the background plasma. Taking rocket exhaust plume for example, the conductivities with and without considering potential difference are given both in the microwave and near infrared regions. In the given dusty plasma parameters condition, the influence of electrical potential difference on electrical conductivity reduces as the incident frequency increases. When the frequency increases to the near-infrared light region, the influence of electrical potential difference on the imaginary part of the conductivity can be ignored.

Diffraction of plane P waves by a canyon of arbitrary shape in poroelastic half-space (II): Numerical results and discussion

This paper investigates in detail the nature of diffraction of plane P waves around a canyon in poroelastic half-space, and studies the effects of incident frequency, drainage condition, porosity, etc, on the diffraction of waves. It is shown that the surface displacement amplitudes of the drained case are close to those of the undrained case, however, the surface displacement amplitudes of the dry case are very different from those of the saturated (either drained or undrained) cases. There are large phase shift between the dry case and the saturated cases, as well as slightly longer resultant wavelengths for the undrained case than those for the drained case and longer resultant wavelengths for the drained case than those for the dry case. For small porosity the surface displacement amplitudes for the saturated cases are almost identical to those for the dry case; while for large porosity, the effect of drainage condition becomes significant, and the surface displacement amplitudes for the undrained case are larger than those for the drained case. As the incident frequency increases, the effect of porosity becomes significant, and more significant for the undrained case than that for the drained case. As the porosity increases, the pore pressures increase significantly but their oscillations become smoother. As the incident frequency increases, the pore pressures become more complicated.

Phonon transport through a three-dimensional abrupt junction

By using the scattering matrix method, the authors investigate the transmission coefficient and thermal conductance of acoustic phonon through a three-dimensional abrupt junction at low temperatures. It is found that the transmission coefficient of long-wavelength phonon strongly depends on the geometrical parameters of the structure as the incident frequency ω→0, and there exist some dips in the transmission spectrum with an increase of incident frequency ω. In the meantime, as the temperature T→0, the thermal conductance is strongly influenced by the abrupt junction structure. These results are not in agreement with previous theoretical studies for the case of two-dimensional structure and can be used as a guideline for the thermal management of the various nanostructures.

Acoustic scattering from a hemicapped cylindrical shell with substructures

This paper extends the study on acoustic radiation of axisymmetric submerged shells of finite length to the scattering problem. A modal-based method is developed to determine the scattering from finite shells insounified by plane incident waves. A surface variational principle provides the acoustic impedance relationship between the surface pressure and displacement fields, which are expanded into a series of shape functions. Lagrange multipliers are introduced in a Lagrange formulation of the dynamic analysis to account for the interaction between the shell and internal substructures. Surface and far-field pressures scattered from the elastic shell are calculated. It is found that, at certain angles, the scattered pressure field has pronounced peaks, particularly as the incident frequency increases. A wave number domain analysis is performed on the surface displacement field. A dominant wave number is found which accounts for the high directivity pattern of the far field. The effect of substructures on the far field is also investigated.