scholarly journals Numerical experiments on wave propagation towards a 3D null point due to rotational motions

2003 ◽  
Vol 108 (A1) ◽  
Author(s):  
K. Galsgaard
Keyword(s):  
Wave Propagation ◽  
Numerical Experiments ◽  
Null Point ◽  
Rotational Motions

scholarly journals MHD wave propagation in the neighbourhood of a two-dimensional null point

2004 ◽  
Vol 420 (3) ◽  
pp. 1129-1140 ◽  
Author(s):  
J. A. McLaughlin ◽  
A. W. Hood
Keyword(s):  
Wave Propagation ◽  
Null Point ◽  
Two Dimensional

scholarly journals The imprint of crustal density heterogeneities on regional seismic wave propagation

Solid Earth ◽  
2016 ◽  
Vol 7 (6) ◽  
pp. 1591-1608 ◽  
Author(s):  
Agnieszka Płonka ◽  
Nienke Blom ◽  
Andreas Fichtner
Keyword(s):  
Wave Propagation ◽  
Travel Time ◽  
Correlation Length ◽  
Seismic Wave ◽  
Numerical Experiments ◽  
Seismic Wave Propagation ◽  
Travel Times ◽  
Full Waveform ◽  
Seismic Waveform ◽  
Crustal Density

Abstract. Density heterogeneities are the source of mass transport in the Earth. However, the 3-D density structure remains poorly constrained because travel times of seismic waves are only weakly sensitive to density. Inspired by recent developments in seismic waveform tomography, we investigate whether the visibility of 3-D density heterogeneities may be improved by inverting not only travel times of specific seismic phases but complete seismograms.As a first step in this direction, we perform numerical experiments to estimate the effect of 3-D crustal density heterogeneities on regional seismic wave propagation. While a finite number of numerical experiments may not capture the full range of possible scenarios, our results still indicate that realistic crustal density variations may lead to travel-time shifts of up to  ∼ 1 s and amplitude variations of several tens of percent over propagation distances of  ∼ 1000 km. Both amplitude and travel-time variations increase with increasing epicentral distance and increasing medium complexity, i.e. decreasing correlation length of the heterogeneities. They are practically negligible when the correlation length of the heterogeneities is much larger than the wavelength. However, when the correlation length approaches the wavelength, density-induced waveform perturbations become prominent. Recent regional-scale full-waveform inversions that resolve structure at the scale of a wavelength already reach this regime.Our numerical experiments suggest that waveform perturbations induced by realistic crustal density variations can be observed in high-quality regional seismic data. While density-induced travel-time differences will often be small, amplitude variations exceeding ±10 % are comparable to those induced by 3-D velocity structure and attenuation. While these results certainly encourage more research on the development of 3-D density tomography, they also suggest that current full-waveform inversions that use amplitude information may be biased due to the neglect of 3-D variations in density.

scholarly journals Multi-Symplectic Method for the Logarithmic-KdV Equation

Symmetry ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 545
Author(s):  
Yu Zhang ◽  
Shaohua Li
Keyword(s):  
Numerical Simulation ◽  
Wave Propagation ◽  
Numerical Experiments ◽  
Kdv Equation ◽  
Symplectic Method ◽  
Symplectic Integrator ◽  
Fully Implicit ◽  
Box Scheme ◽  
Integration Approach ◽  
Intermediate Variables

The multi-symplectic integrator, as a numerical integration approach with symmetry, is known to have the characteristic of preserving the qualitative features and geometric properties of certain systems. Using the multi-symplectic integrator, the numerical simulation of the Gaussian solitary wave propagation of the logarithmic Korteweg–de Vries (logarithmic-KdV) equation was investigated. The multi-symplectic formulation of the logarithmic-KdV equation was explored by introducing some intermediate variables. A fully implicit version of the centered box scheme was used to discretize the multi-symplectic equations. In addition, numerical experiments were carried out to show the conservative properties of the proposed scheme.

Systematic forcing of large-scale geophysical flows by eddy-topography interaction

1987 ◽  
Vol 184 ◽  
pp. 463-476 ◽  
Author(s):  
Greg Holloway
Keyword(s):  
Wave Propagation ◽  
Continental Shelf ◽  
Numerical Experiments ◽  
Antarctic Circumpolar Current ◽  
Large Scale ◽  
Geophysical Flows ◽  
Dominant Mechanism ◽  
Coastal Oceans ◽  
Circumpolar Current ◽  
Closure Theory

The interaction of eddies with variations in topography, together with a tendency for large-scale wave propagation, generates a systematic stress which acts upon large-scale mean flows. This stress resists the midlatitude tropospheric westerlies, resists the oceanic Antarctic Circumpolar Current, and may be a dominant mechanism in driving coastal undercurrents. Associated secondary circulation provides a systematic upwelling in coastal oceans, pumping deeper water onto continental shelf areas. The derivation rests in turbulence closure theory and is supported by numerical experiments.

Infinite boundary element absorbing boundary for wave propagation simulations

Geophysics ◽  
2000 ◽  
Vol 65 (2) ◽  
pp. 596-602 ◽  
Author(s):  
Li‐Yun Fu ◽  
Ru‐Shan Wu
Keyword(s):  
Wave Propagation ◽  
Boundary Element ◽  
Numerical Experiments ◽  
Computing Time ◽  
Computational Effort ◽  
Shape Functions ◽  
Absorbing Boundary ◽  
Perfect Absorption ◽  
Memory Space ◽  
Absorbing Elements

In the boundary element (BE) solution of wave propagation, infinite absorbing elements are introduced to minimize diffractions from truncated edges of models. This leads to a significant simplification and reduction of computational effort, especially for 3-D problems. The infinite BE absorbing boundary condition has a general form for both 2-D and 3-D problems and for both acoustic and elastic cases. Its implementation is facilitated by the introduction of the corresponding shape functions. Numerical experiments illustrate a nearly perfect absorption of unwanted diffractions. The approach overcomes some of the difficulties encountered in conventional absorbing techniques and takes less memory space and less computing time.

White's model for wave propagation in partially saturated rocks: Comparison with poroelastic numerical experiments

Geophysics ◽  
2003 ◽  
Vol 68 (4) ◽  
pp. 1389-1398 ◽  
Author(s):  
José M. Carcione ◽  
Hans B. Helle ◽  
Nam H. Pham
Keyword(s):  
Wave Propagation ◽  
Numerical Experiments ◽  
Water Saturation ◽  
Relaxation Mechanism ◽  
P Wave ◽  
Fluid Interfaces ◽  
Differential Motion ◽  
Theoretical Predictions ◽  
Flow Effects ◽  
Rock Skeleton

We use a poroelastic modeling algorithm to compute numerical experiments of wave propagation in White's partial saturation model. The results are then compared to the theoretical predictions. The model consists of a homogeneous sandstone saturated with brine and spherical gas pockets. White's theory predicts a relaxation mechanism, due to pressure equilibration, causing attenuation and velocity dispersion of the wavefield. We vary gas saturation either by increasing the radius of the gas pocket or by increasing the density of gas bubbles. Despite that the modeling is two dimensional and interaction between the gas pockets is neglected in White's model, the numerical results show the trends predicted by the theory. In particular, we observe a similar increase in velocity at high frequencies (and low permeabilities). Furthermore, the behavior of the attenuation peaks versus water saturation and frequency is similar to that of White's model. The modeling results show more dissipation and higher velocities than White's model due to multiple scattering and local fluid‐flow effects. The conversion of fast P‐wave energy into dissipating slow waves at the patches is the main mechanism of attenuation. Differential motion between the rock skeleton and the fluids is highly enhanced by the presence of fluid/fluid interfaces and pressure gradients generated through them.

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