Peridynamic bond‐associated correspondence model: Wave dispersion property

Author(s):  
WaiLam Chan ◽  
Hailong Chen
2021 ◽  
Vol 9 (8) ◽  
pp. 840
Author(s):  
Yang Dong ◽  
Shengchun Piao ◽  
Lijia Gong ◽  
Guangxue Zheng ◽  
Kashif Iqbal ◽  
...  

Recent studies have illustrated that the Multichannel Analysis of Surface Waves (MASW) method is an effective geoacoustic parameter inversion tool. This particular tool employs the dispersion property of broadband Scholte-type surface wave signals, which propagate along the interface between the sea water and seafloor. It is of critical importance to establish the theoretical Scholte wave dispersion curve computation model. In this typical study, the stiffness matrix method is introduced to compute the phase speed of the Scholte wave in a layered ocean environment with an elastic bottom. By computing the phase velocity in environments with a typical complexly varying seabed, it is observed that the coupling phenomenon occurs among Scholte waves corresponding to the fundamental mode and the first higher-order mode for the model with a low shear-velocity layer. Afterwards, few differences are highlighted, which should be taken into consideration while applying the MASW method in the seabed. Finally, based on the ingeniously developed nonlinear Bayesian inversion theory, the seafloor shear wave velocity profile in the southern Yellow Sea of China is inverted by employing multi-order Scholte wave dispersion curves. These inversion results illustrate that the shear wave speed is below 700 m/s in the upper layers of bottom sediments. Due to the alternation of argillaceous layers and sandy layers in the experimental area, there are several low-shear-wave-velocity layers in the inversion profile.


Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1169-1179 ◽  
Author(s):  
J. L. Mari

When processing shear‐wave data it is often difficult to compute the static corrections using the same methods as for P-waves, because of the low velocities involved and of the interference with residual P-waves. A method especially tailored for static corrections of SH-waves is presented, which makes use of the dispersion property of Love waves. Assuming that the weathered zone of thickness H acts as a wave guide for the surface waves, their phase velocity ranges from [Formula: see text] at infinite frequency to [Formula: see text] at zero frequency, where [Formula: see text] and [Formula: see text] are the shear‐wave velocities into and below the weathered zone. For intermediate frequencies the phase velocity of Love waves is a known function of H, [Formula: see text] and [Formula: see text]. If the phase velocity of Love waves is measured on field records for a number of distinct frequencies, it is therefore possible to compute H, [Formula: see text], [Formula: see text], and the static corrections. In contrast with conventional techniques which require first arrivals to be picked manually, the computation of static corrections using the dispersion of Love waves is essentially based on velocity analysis efficiently performed by digital computers. Three field examples were conducted. The first of these was a noise analysis using 256 geophone positions ranging from 3 to 258 m. The two other examples are CDP lines obtained with polarized SH sources. The geophone group extension is 20 m and the distance between groups is 10 m. In all these examples, the upper layer thickness and velocity values resulting from the Love wave dispersion appeared to be in good agreement with those computed from the conventional methods.


2020 ◽  
Vol 11 (2) ◽  
pp. 26-49
Author(s):  
Narayan Roy ◽  
Aniket Desai ◽  
Ravi S. Jakka

Surface wave techniques are widely used to characterize a site based on shear wave velocity (Vs) or stiffness variation with depth. It utilizes the dispersion property of Rayleigh wave in a heterogeneous media. Dispersion curve is obtained from analyzing collected field test data and the final Vs profile is extracted from the inversion of the generated dispersion curve. The varying subsoil structures influence whether one or more Rayleigh modes will participate in the resulting wave propagation phenomenon. So, neglecting the higher mode participation may sometimes results in a completely different velocity profile than the actual existing one. In this paper, a detailed and comprehensive numerical study has been performed using finite element method for different types of soil profiles with different half-space impedances to assess how it affects the surface wave dispersion phenomenon. In addition to that, the effect of different data acquisition parameters on surface wave dispersion has also been studied.


Author(s):  
Chin H. Wu ◽  
Chih-Chieh Young

A novel approach that introduces the Boussinesq-type like equations into an implicit non-hydrostatic model, free of irrotational flow assumption, is presented. The basic concept is to obtain an analytical-based form of pressure distribution at the top layer by matching the reference velocity under a virtual grid system with the one under a non-hydrostatic model grid system. Locations of the references velocities are tuned to optimize the linear wave dispersion property in the model. Efficiency of this non-hydrostatic model with Boussinesq-type equations (NHM-BTE) is critically examined through several free-surface wave examples. Overall model results show that NHM-BTE using only a few vertical layers (i.e., two ∼ four) is capable of accurately simulating highly dispersive wave motion and wave transformation over irregular bathymetry.


Author(s):  
Ashish Kumar Agarwal ◽  
Daulat Singh Meena ◽  
Vijay Pathak ◽  
Anoop Jain ◽  
Rakesh Kumar Ola

Background: The aim of the present study was to study the effect of percutaneous balloon mitral  valvuloplasty (PBMV) on P wave dispersion and to test the correlation between P-maximum and  P-dispersion to right ventricular function and pulmonary artery pressure before and after PMBV. Also to study the impact of P-maximum and P-wave dispersion on the short term clinical outcome after successful PBMV in patients with mitral stenosis (MS) and sinus rhythm. Methods: 75 patients undergoing PMBV were enrolled in this study. We evaluated P-maximum, P-minimum and P-wave dispersion before and one month and one year after PBMV . We studied the changes in pulmonary arterial pressure (PAP), left atrial (LA) dimension, mitral diastolic gradient, and mitral valve area, in addition to the changes in right ventricular function utilizing tissue Doppler assessment both before and after PMBV, in addition the role of the P-wave dispersion in prediction of late cardiac events. Results: There were significant decrease in mean diastolic gradient, PAP, and LA size and significant improvement in right ventricular tissue Doppler indices after PMBV. Accompany these hemodynamic changes after PMBV. P-maximum and P-wave dispersion were found to be decreased (P < 0.001). Conclusion: Successful PBMV was associated with a decrease in Pmax and PWD. These simple electrocardiographic indices may predict the success of the procedure immediately after PBMV.  The P-maximum and P-wave dispersion changes were correlated with significant impairment of right dysfunction and the degree of pulmonary artery pressure. Keywords: PBMV.PAP,LA


2005 ◽  
Author(s):  
Jeffry L. Stevens ◽  
David A. Adams ◽  
G. E. Baker ◽  
Mariana G. Eneva ◽  
Heming Xu

2020 ◽  
Vol 222 (3) ◽  
pp. 1639-1655
Author(s):  
Xin Zhang ◽  
Corinna Roy ◽  
Andrew Curtis ◽  
Andy Nowacki ◽  
Brian Baptie

SUMMARY Seismic body wave traveltime tomography and surface wave dispersion tomography have been used widely to characterize earthquakes and to study the subsurface structure of the Earth. Since these types of problem are often significantly non-linear and have non-unique solutions, Markov chain Monte Carlo methods have been used to find probabilistic solutions. Body and surface wave data are usually inverted separately to produce independent velocity models. However, body wave tomography is generally sensitive to structure around the subvolume in which earthquakes occur and produces limited resolution in the shallower Earth, whereas surface wave tomography is often sensitive to shallower structure. To better estimate subsurface properties, we therefore jointly invert for the seismic velocity structure and earthquake locations using body and surface wave data simultaneously. We apply the new joint inversion method to a mining site in the United Kingdom at which induced seismicity occurred and was recorded on a small local network of stations, and where ambient noise recordings are available from the same stations. The ambient noise is processed to obtain inter-receiver surface wave dispersion measurements which are inverted jointly with body wave arrival times from local earthquakes. The results show that by using both types of data, the earthquake source parameters and the velocity structure can be better constrained than in independent inversions. To further understand and interpret the results, we conduct synthetic tests to compare the results from body wave inversion and joint inversion. The results show that trade-offs between source parameters and velocities appear to bias results if only body wave data are used, but this issue is largely resolved by using the joint inversion method. Thus the use of ambient seismic noise and our fully non-linear inversion provides a valuable, improved method to image the subsurface velocity and seismicity.


2021 ◽  
Vol 282 ◽  
pp. 122597
Author(s):  
Wallace W.L. Lai ◽  
Ray K.W. Chang ◽  
Christoph Völker ◽  
Bella W.Y. Cheung

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