The Experts below are selected from a list of 20049 Experts worldwide ranked by ideXlab platform
Alexey Stovas - One of the best experts on this subject based on the ideXlab platform.
-
reflection and transmission responses in a layered transversely Isotropic Medium with horizontal symmetry axis
81st EAGE Conference and Exhibition 2019, 2019Co-Authors: Song Jin, Alexey StovasAbstract:ABSTRACTSeismic wave reflection and transmission (R/T) responses characterize the subsurface local property, and the widely spread anisotropy has considerable influences even at small incident angl...
-
caustics in a periodically layered transversely Isotropic Medium with vertical symmetry axis
Geophysical Prospecting, 2011Co-Authors: Yuriy Roganov, Alexey StovasAbstract:Wave propagation in a finely layered Medium is a very important topic in seismic modelling and inversion. Here we analyse non-vertical wave propagation in a periodically layered transversely Isotropic (VTI) Medium and show that the evanescent (attenuation) zones in the frequency-horizontal slowness domain result in caustics in the group velocity domain. These caustics, which may appear for both the quasi-compressional (qP) and quasi-shear (qSV) wave surfaces are frequency dependent but display weak dependence at low frequencies. The caustics computed for a specific frequency differ from those observed at the low- and high-frequency limits. We illustrate these caustics with a few numerical examples and snapshots computed for both qP- and qSV-wave types.
-
generalized moveout approximation for qp and qsv waves in a homogeneous transversely Isotropic Medium
Geophysics, 2010Co-Authors: Alexey StovasAbstract:The moveout approximations can be used in kinematic modeling, velocity analysis, and time migration. The generalized moveout approximation involves five approximation parameters and has several known approximations as special cases. A method is demonstrated for determining parameters of the generalized nonhyperbolic moveout approximation for qP- and qSV-waves in a homogeneous transversely Isotropic Medium with vertical symmetry axis (VTI Medium). The additional parameters for the generalized approximation are computed from the hyperbolic asymptote at infinite offset. Comparison with a few well-known moveout approximations for higher-order terms in the Taylor series and asymptotic behavior shows that the generalized moveout approximation is superior to other nonhyperbolic approximations. A few numerical examples for qP- and qSV-waves in a VTI Medium also indicate that the generalized approximation performs the best.
-
On shear-wave triplications in a multilayered transeversely Isotropic Medium with vertical symmetry axis
Geophysical Prospecting, 2009Co-Authors: Yuriy Roganov, Alexey StovasAbstract:ABSTRACT The presence of triplications (caustics) can be a serious problem in seismic data processing and analysis. The traveltime curve becomes multi‐valued and the geometrical spreading correction factor tends to zero due to energy focusing. We analyse the conditions for the qSV‐wave triplications in a homogeneous transversely Isotropic Medium with vertical symmetry axis. The proposed technique can easily be extended to the case of horizontally layered vertical symmetry axis Medium. We show that the triplications of the qSV‐wave in a multilayered Medium imply certain algebra. We illustrate this algebra on a two‐layer vertical symmetry axis model.
-
traveltime approximations for a layered transversely Isotropic Medium
Geophysics, 2006Co-Authors: Bjørn Ursin, Alexey StovasAbstract:We consider multiple transmitted, reflected, and converted qP-qSV-waves or multiple transmitted and reflected SH-waves in a horizontally layered Medium that is transversely Isotropic with a vertical symmetry axis (VTI). Traveltime and offset (horizontal distance) between a source and receiver, not necessarily in the same layer, are expressed as functions of horizontal slowness. These functions are given in terms of a Taylor series in slowness in exactly the same form as for a layered Isotropic Medium. The coefficients depend on the parameters of the anIsotropic layers through which the wave has passed, and there is no weak anisotropy assumption. Using classical formulas, the traveltime or traveltime squared can then be expressed as a Taylor series in even powers of offset. These Taylor series give rise to a shifted hyperbola traveltime approximation and a new continued-fraction approximation, described by four parameters that match the Taylor series up to the sixth power in offset. Further approximations give several simplified continued-fraction approximations, all of which depend on three parameters: zero-offset traveltime, NMO velocity, and a heterogeneity coefficient. The approximations break down when there is a cusp in the group velocity for the qSV-wave. Numerical studies indicate that approximations of traveltime squared are generally better than those for traveltime. A new continued-fraction approximation that depends on three parameters is more accurate than the commonly used continued-fraction approximation and the shifted hyperbola.
A A Rukhadze - One of the best experts on this subject based on the ideXlab platform.
-
negative group velocity electromagnetic waves and the energy momentum tensor
Physics-Uspekhi, 2011Co-Authors: Vyacheslav P Makarov, A A RukhadzeAbstract:V G Veselago's results (Usp. Fiz. Nauk 179 689 (2009) [Phys. Usp. 52 649 (2009)]) on the electromagnetic (EM) energy–momentum tensor in a Medium are analyzed. It is shown that Veselago's statements on the Abraham tensor are wrong (this is not actually a tensor, and the Abraham force was introduced into the theory as an artificial auxiliary device). In discussing the EM energy–momentum tensor in a dispersive Medium, it seems to have escaped the author's attention that the problem was resolved a long time ago: the electromagnetic energy–momentum tensor for a dispersive Isotropic Medium at rest is a symmetric 4-tensor which includes the Brillouin energy density, the energy flux density (Umov–Poynting vector), the momentum density (the Umov–Poynting vector divided by ), and the Pitaevskii tension tensor. For a mechanically and thermally equilibrium Medium, it is shown that the spatial components of the Polevoi–Rytov tensor which is discussed in the analyzed paper cannot be interpreted as the field-dependent part of the Pitaevskii total tension tensor, unless for quasimonochromatic plane wave propagation. It is also shown that for arbitrary (not necessarily zero) reflection, the force an EM wave in an Isotropic Medium exerts on a solid can be expressed in terms of an appropriate component of the Polevoi–Rytov tension tensor.
V N Bastun - One of the best experts on this subject based on the ideXlab platform.
-
deformation of damaged elastic brittle Isotropic materials with a fixed concentration of microdefects in a complex stress state
Journal of Strain Analysis for Engineering Design, 2011Co-Authors: D V Babich, V N BastunAbstract:The character of deformation of elastic—brittle Isotropic materials weakened by flat microdefects in the form of circular or elliptic microcracks randomly dispersed over volume is studied in the complex stress state. It is assumed that concentration of the microcracks under loading remains constant. Equations of state for such materials are derived depending on the stress state mode and sign of applied stresses. The damaged material is simulated by a linear elastic Isotropic Medium under all-round compression or tension and under biaxial compression, by a linear elastic transversally Isotropic Medium under biaxial tension, and by a non-linear orthotropic Medium under compression along one axis and tension along another axis. To determine compliance characteristics entering into the equations of state, the continual model of a cracked Medium and a method based on the equivalence principle of deformation energy of this Medium are used. A numerical example is presented.
-
deformation of damaged elastic brittle Isotropic materials with a fixed concentration of microdefects in a complex stress state
Journal of Strain Analysis for Engineering Design, 2011Co-Authors: D V Babich, V N BastunAbstract:The character of deformation of elastic—brittle Isotropic materials weakened by flat microdefects in the form of circular or elliptic microcracks randomly dispersed over volume is studied in the complex stress state. It is assumed that concentration of the microcracks under loading remains constant. Equations of state for such materials are derived depending on the stress state mode and sign of applied stresses. The damaged material is simulated by a linear elastic Isotropic Medium under all-round compression or tension and under biaxial compression, by a linear elastic transversally Isotropic Medium under biaxial tension, and by a non-linear orthotropic Medium under compression along one axis and tension along another axis. To determine compliance characteristics entering into the equations of state, the continual model of a cracked Medium and a method based on the equivalence principle of deformation energy of this Medium are used. A numerical example is presented.
Wennan Zou - One of the best experts on this subject based on the ideXlab platform.
-
Revisiting the problem of a 2D infinite elastic Isotropic Medium with a rigid inclusion or a cavity
International Journal of Engineering Science, 2018Co-Authors: Wennan ZouAbstract:Abstract The problem of analytically finding the elastic fields inside a 2D infinite elastic Isotropic Medium containing a rigid inclusion or a cavity and subjected to uniform remote loading is a classical elasticity problem of theoretical and practical interest. In the present work, we revisit the Kolosov–Muskhelishvili potential theory which is a powerful tool for solving the problem in question. In particular, a novel strategy is proposed to deal with the rigid-body displacements that the rigid inclusion or cavity may undergo. When the shape of the rigid inclusion or cavity is described by a Laurent polynomial, a general method is elaborated to solve the problem. The results obtained by using our method include as special cases all the relevant results reported in the literature. In light of our results, some errors in the literature are corrected. Finally, the cases of a rhombus rigid inclusion and a pentagonal cavity saturated with a fluid are studied in detail and some general properties are discussed.
Long Chang - One of the best experts on this subject based on the ideXlab platform.
-
a porothermoelastic solution for the inclined borehole in a transversely Isotropic Medium subjected to thermal osmosis and thermal filtration effects
Geothermics, 2017Co-Authors: Jiajia Gao, Jingen Deng, Kai Lan, Zhicong Song, Yutian Feng, Long ChangAbstract:Abstract Given that the hydraulic boundary conditions at the wellbore wall are identified as permeable (PBC) and impermeable (IMPBC) and that the assumption of plane strain holds, the present paper formulates an analytical solution, which is based on fully coupled linear porothermoelastic model with the thermal osmosis and thermal filtration effects, in Laplace space domain. The solution is available for the cases that the wellbore axis of inclined wellbore is perpendicular to the Isotropic plane of the transversely Isotropic Medium under non-hydrostatic stress condition. The wellbore problem is decomposed into axisymmetric and deviatoric loading cases. The numerical results of the time-dependent distributions of field variables are obtained by virtue of performing the inversion technique for Laplace transforms. The sensitivity analyses are performed on the key parameters to thermal osmosis and thermal filtration effects. The effect of thermal filtration on temperature is also illustrated. The numerical comparative analyses in the present paper examine the influence of material anisotropy of poromechanical parameters and thermal properties, which embody in porothermoelastic-osmosis-filtration model and common porothermoelastic one, on the thermally induced pore pressure and stresses. Finally, an integrated geomechanical wellbore stability model is developed to investigate the compressive and tensile failure extents of horizontal wells. The model is involved with three aspects, i.e. the coordinates transformations pertaining to wellbore and weak plane systems, the criteria to evaluate the shear failure (including intact rock and weak plane) as well as tensile fracture, and the fully coupled porothermoelastic analytical solution. The developed porothermoelsatic analytical solution can provide a theoretical basis for multiple of aspects including the inversion of in-situ stress, geothermal reservoir stimulation and petroleum drilling design.
