• Title/Summary/Keyword: 이방성 모델

Search Result 191, Processing Time 0.029 seconds

Seismic First Arrival Time Computation in 3D Inhomogeneous Tilted Transversely Isotropic Media (3차원 불균질 횡등방성 매질에 대한 탄성파 초동 주시 모델링)

  • Jeong, Chang-Ho;Suh, Jung-Hee
    • Geophysics and Geophysical Exploration
    • /
    • v.9 no.3
    • /
    • pp.241-249
    • /
    • 2006
  • Due to the long tectonic history and the very complex geologic formations in Korea, the anisotropic characteristics of subsurface material may often change very greatly and locally. The algorithms commonly used, however, may not give sufficiently precise computational results of traveltime data particularly for the complex and strong anisotropic model, since they are based on the two-dimensional (2D) earth and/or weak anisotropy assumptions. This study is intended to develope a three-dimensional (3D) modeling algorithm to precisely calculate the first arrival time in the complex anisotropic media. Considering the complex geology of Korea, we assume 3D TTI (tilted transversely isotropy) medium having the arbitrary symmetry axis. The algorithm includes the 2D non-linear interpolation scheme to calculate the traveltimes inside the grid and the 3D traveltime mapping to fill the 3D model with first arrival times. The weak anisotropy assumption, moreover, can be overcome through devising a numerical approach of the steepest descent method in the calculation of minimum traveltime, instead of using approximate solution. The performance of the algorithm developed in this study is demonstrated by the comparison of the analytic and numerical solutions for the homogeneous anisotropic earth as well as through the numerical experiment for the two layer model whose anisotropic properties are greatly different each other. We expect that the developed modeling algorithm can be used in the development of processing and inversion schemes of seismic data acquired in strongly anisotropic environment, such as migration, velocity analysis, cross-well tomography and so on.

S-wave Velocity Structure and Radial Anisotropy of Saudi Arabia from Surface Wave Tomography (표면파 토모그래피를 이용한 사우디아라비아의 S파 속도구조 및 이방성 연구)

  • Kim, Rinhui;Chang, Sung-Joon;Mai, Martin;Zahran, Hani
    • Geophysics and Geophysical Exploration
    • /
    • v.22 no.1
    • /
    • pp.21-28
    • /
    • 2019
  • We perform a 3D tomographic inversion using surface wave dispersion curves to obtain S-velocity model and radial anisotropy beneath Saudi Arabia. The Arabian Peninsula is geologically and topographically divided into a shield and a platform. We used event data with magnitudes larger than 5.5 and epicentral distances shorter than $40^{\circ}$ during 2008 ~ 2014 from the Saudi Geological Survey. We obtained dispersion curves by using the multiple filtering technique after preprocessing the event data. We constructed SH- and SV-velocity models and consequently radial anisotropy model at 10 ~ 60 km depths by inverting Love and Rayleigh group velocity dispersion curves with period ranges of 5 ~ 140 s, respectively. We observe high-velocity anomalies beneath the Arabian shield at 10 ~ 30 km depths and low-velocity anomalies beneath the Arabian platform at 10 km depth in the SV-velocity model. This discrepancy may be caused by the difference between the Arabian shield and the Arabian platform, that is, the Arabian shield was formed in Proterozoic thereby old and cold, while the Arabian platform is covered by predominant Paleozoic, Mesozoic, and Cenozoic sedimentary layers. Also we obtained radial anisotropy by estimating the differences between SH- and SV-velocity models. Positive anisotropy is observed, which may be generated by lateral tension due to the slab pull of subducting slabs along the Zagros belt.

Reverse-time Migration for VTI and TTI Media (VTI 및 TTI 매질에서의 역시간 구조보정)

  • Kwak, Na-Eun;Min, Dong-Joo;Bae, Ho-Seuk
    • Geophysics and Geophysical Exploration
    • /
    • v.14 no.3
    • /
    • pp.191-202
    • /
    • 2011
  • Reserve-time migration (RTM) using a two-way wave equation is one of the most accurate migration techniques. RTM has been conducted by assuming that subsurface media are isotropic. However, anisotropic media are commonly encountered in reality. Conventional isotropic RTM may yield inaccurate results for anisotropic media. In this paper, we develop RTM algorithms for vertical transversely isotropic media (VTI) and tilted transversely isotropic media (TTI). For this, the pseudo-acoustic wave equations are used. The modeling algorithms are based on the high-order finite-difference method (FDM). The RTM algorithms are composed using the cross-correlation imaging condition or the imaging condition using virtual sources. By applying the developed RTM algorithms to the Hess VTI and BP TTI models, we could obtain better images than those obtained by the conventional isotropic RTM.

Three-dimensional S-wave Velocity Structure and Radial Anisotropy of Crust and Uppermost Mantle Beneath East Asia (동아시아 지각과 최상부맨틀의 3차원 S파 속도구조 및 이방성 연구)

  • Lim, DoYoon;Chang, Sung-Joon
    • Geophysics and Geophysical Exploration
    • /
    • v.21 no.1
    • /
    • pp.33-40
    • /
    • 2018
  • We investigate the crustal and uppermost mantle SV- and SH-wave velocity structure and radial anisotropy beneath East Asia including Korea, China and Japan. Rayleigh waves and Love waves were extracted from the seismic data recorded at broadband seismic stations in East Asia. Using the MFT (Multiple Filter Technique), we obtained group velocity dispersion curves of Rayleigh and Love waves with a period range of 3 to 200 s. We obtained 62466 Rayleigh-waves dispersion-curve measurements in vertical components and 54141 Love-waves dispersion-curve measurements in transverse components, respectively. The inverted models using these data sets provide SV- and SH-wave velocity structure of crust and uppermost mantle down to 100 km depth. In both cases of the S-wave velocity structures, strong high-velocity anomalies are observed down to 30 km depth beneath the East Sea, and deeper than 30 km depth, strong low-velocity anomalies are found beneath the Tibetan plateau. In the case of the SH-wave velocity structure, strong low-velocity anomalies are observed beneath the East Sea deeper than 30 km depth, leading to negative anisotropy. On the other hand, positive anisotropy is usually observed beneath the Tibetan plateau.

Realistic Rendering of Woven Surface using Procedural Bump Mapping (절차적 범프 매핑을 이용한 직물표면의 사실적 렌더링)

  • Kang, Young-Min
    • Journal of Korea Game Society
    • /
    • v.10 no.3
    • /
    • pp.103-111
    • /
    • 2010
  • In this paper, an procedural approach to photorealistic rendering of woven fabric material is proposed. Previously proposed procedural approaches to fabric rendering have the disadvantage that the rendering result is not sufficiently realistic. In order to enhance the realism, researchers employed example-based approaches. However, those methods have serious disadvantage that they require huge amount of storage for the various reflectance properties of diverse materials. The proposed method can express the reflectance on weft and warp yarns by alternating the anisotropic reflectance on yarns. In addition, we propose the proposed method procedurally models the bumpy yarn structure of woven fabric to obtain plausible rendering results. The proposed method can efficiently reproduce realistic virtual fabric without any reflectance data sets.

Nonlinear FE Analysis of RC Shear Walls (철근콘크리트 전단벽의 비선형 유한요소해석)

  • 곽효경;김도연
    • Journal of the Computational Structural Engineering Institute of Korea
    • /
    • v.12 no.3
    • /
    • pp.293-308
    • /
    • 1999
  • 이 논문에서는 패널, 깊은 보 그리고 전단벽과 같이 평면응력상태하에 있는 철근콘크리트 구조물의 비선형 유한요소해석에 있어서의 직교이방성 콘크리트 구성 모델의 적용성을 보여준다. 등가의 일축 변형을 개념을 토대로 콘크리트의 구성 관계가 주변형률 축과 일치하고 하중이력에 따라 회전하는 직교하는 축에 대해 제시된다. 제안된 모델은 이축 압축응력상태와 인장-압축 응력상태에서 각각 압축강도의 증가와 인장 저항력의 감소효과를 보여주는 이축 파괴영역의 정의를 포함한다. 인장균열이 발생한 후, 콘크리트의 압축강도의 감소효과가 제시되고, 인장강화효과로 알려진 철근에 의해 지지되는 콘크리트의 인장응력이 고려된다. 평균응력과 평균변형률 개념을 사용하여 힘의 평형, 적합조건 그리고 철근과 철근을 둘러싼 콘크리트 사이의 부착응력-슬림 관계를 토대로 인장강화효과를 모사하기 위한 모델이 제안된다. 유한요소 모델에 의한 예측은 유용한 실험자료와의 비교에 의해 입증된다. 이 논문에서는 해석결과와 이상화한 전단 패널실험으로부터 얻어진 실험값의 비교연구가 수행되고, 제안된 모델의 타당성을 보여주기 위해 서로 다른 응력상태하의 전단 패널 보와 벽체의 힘-변위 관계를 평가하였다.

  • PDF

The Anisotropic and Viscoelastic Properties of Bone Tissue (근골격계의 골조직이 가지는 이방성 및 점탄성 특성)

  • Kim, Jin-Sung;Kwon, Jung-Sik;Roh, Jin-Ho;Lee, Soo-Yong
    • Composites Research
    • /
    • v.25 no.1
    • /
    • pp.9-13
    • /
    • 2012
  • In this research, biomechanical characteristics of the bone tissue are experimentally investigated. By using specimens of the bovine bone, the mechanical properties are obtained through tension and shear tests. In experiments, non-homogeneous and anisotropic properties with respect to longitudinal and transversal directions are observed. Moreover, the viscoelastic behavior in which modulus and strength properties are dependent on strain rates is analyzed. It is expected that a numerical damage model of the bone be efficiently established based on the results.

Relation Between Magnetization Easy Axis and Anisotropic Magnetoresistance in Permalloy Films (퍼멀로이 박막의 자화 용이축과 자기저항 변화와의 상관관계에 대한 연구)

  • Hwang, Tae-Jong;Ryu, Yeung-Shik;Kwon, Jin-Hyuk;Kim, Ki-Hyeon;Kim, Dong-Ho
    • Journal of the Korean Magnetics Society
    • /
    • v.18 no.1
    • /
    • pp.28-31
    • /
    • 2008
  • We studied the effect of easy magnetization axis orientation with respect to the strip direction by measuring the magnetoresistance(MR), the magneto-optic Kerr effect(MOKE), and real-time domain evolution. The five strips were patterned on a single chip with the easy axis orientation of each strip relative to the longitudinal direction by around $0^{\circ}$, $18^{\circ}$, $36^{\circ}$, $54^{\circ}$ and $72^{\circ}$, respectively. The overall shape of field dependent MR was mostly governed by the anisotropy magnetoresistnace. The relative change of the longitudinal MR was significantly increased with increasing angle between the easy axis and strip direction, whereas, the transverse MR variation rate was decreased with increasing angle. Several MR steps were observed during the magnetization reversal, and the simultaneous measurement of the MOKE and the domain images identified that the MR steps were associated with evolution of the oppositely directed magnetic domain.

Prediction of Strength for Transversely Isotopic Rock Based on Critical Plane Approach (임계면법을 이용한 횡등방성 암석의 강도 예측)

  • Lee, Youn-Kyou
    • Tunnel and Underground Space
    • /
    • v.17 no.2 s.67
    • /
    • pp.119-127
    • /
    • 2007
  • Based on the critical plane approach, a methodology far predicting the anisotropic strength ot transversely isotropic rock is Proposed. It is assumed that the rock failure is governed by Hoek-Brown failure criterion. In order to establish an anisotropic failure function, Mohr envelope equivalent to the original Hoek-Brown criterion is used and the strength parameters m, s are expressed as scalar functions of orientation. The conjugate gradient method, which is one of the robust optimization techniques, is applied to the failure function for searching the orientation giving the maximum value of the anisotropic function. While most of the existing anisotropic strength models can be applied only when the stress condition is the same as that of conventional triaxial compression test, the proposed model can be applied to the general 3-dimensional stress conditions. Through the simulation of triaxial compression tests for transversely isotropic rock sample, the validity of the proposed method is investigated by comparing the predicted triaxial strengths and inclinations of failure plane.

Study on Hydraulic Fracturing in Transverse Isotropic Rock Using Bonded Particle Model (입자결합모델을 이용한 횡등방성 암석에서의 수압파쇄 특성 연구)

  • Jung, Jaewoong;Heo, Chan;Jeon, Seokwon
    • Tunnel and Underground Space
    • /
    • v.23 no.6
    • /
    • pp.470-479
    • /
    • 2013
  • Hydraulic fracturing is used as a method for promoting the fluid flow in the rock and, in the energy field such as geothermal development and the development of sales gas, many studies has been actively conducted. In many cases, hydraulic fracturing is not performed in isotropic rock and especially in the case of sedimentary rocks, hydraulic fracturing is conducted in the transverse isotropic rock. The direction of the crack growth on hydraulic fracturing does not necessarily coincides with the direction of maximum principal stress in the transverse isotropic rock. Therefore, in this study, bonded particle model with hydro-mechanical coupling analysis was adopted for analyzing the characteristics of hydraulic fracturing in transverse isotropic rock. In addition, experiments of hydraulic fracturing were conducted in laboratory-scale to verify the validity of numerical analysis. In this study, the crack growth and crack patterns showed significant differences depending on the viscosity of injection fluid, the angle of bedding plane and the influence of anisotropy. In the case of transverse isotropic model, the shear crack growth due to hydraulic fracturing appeared prominently.