Dong Joo Min

We design a new frequency-domain, finite-difference approach, based on a displacement formulation, which correctly describes the stress-free conditions at a free surface. In the conventional, displacement-based finite-difference method, we assign both displacements and material properties such as density and Lame constants to nodal points (a node-based grid set), whereas in our new finite-difference method, displacements are still defined at nodal points but material properties within cells (a c

We present a weighted-averaging frequency-domain finite-element method for an accurate and efficient 2D elastic wave modeling technique. Our method introduces three kinds of supplementary element sets in addition to a basic element set that is used in the standard finite-element method. By constructing global stiffness and mass matrices for four kinds of element sets and then averaging them with weighting coefficients, we obtain a new global stiffness and mass matrix. With optimal weighting coef

Because of the limitations of conventional metal-oxide-based electrodes, studies on organic redox-active materials as alternative electrodes for secondary batteries are emerging. However, reported organic electrode materials are still limited to a few kinds of organic redox groups. Therefore, the development of new redox-active groups for high-performance electrode materials is indispensable. Here, we evaluate s-tetrazine derivatives as a new electrode material in Li-ion batteries and study thei

We propose a strategy to overcome the high sensitivity to early-time noise of the Laplace-domain waveform inversion. In deep-sea seismic data, this problem is particularly crucial to obtaining accurate velocity structures. To this end, rather than simply filtering or muting early-time data, we propose replacing the original, noise-contaminated direct waves with analytically computed noise-free waves. To reconstruct the noise-free direct waves, we compute Green′s functions for half-space media, e

Seismic data are often irregularly or insufficiently sampled along the spatial direction due to malfunctioning of receivers and limited survey budgets. Recently, machine learning techniques have begun to be used to effectively reconstruct missing traces and obtain densely sampled seismic gathers. One of the most widely used machine learning techniques for seismic trace interpolation is UNet with the mean-squared error (MSE). However, seismic trace interpolation with the UNet architecture suffers

The objective of the present study is to review and introduce R&D strategy, progress and plan focused on marine geological storage in Republic of Korea. Marine geological storage of CO2 is to transport and to store CO2 captured from major point sources into the offshore geologic formations. The present project focused on an investigation into potential CO2 storage in the Korean continental shelves. This technology development plan is to meet Korean Government's CCS demonstration plan to explore

Summary One of the most important issues in the multi-parametric full waveform inversion (FWI) is to find an optimal parameterization, which helps us recover the subsurface anisotropic parameters as well as seismic velocities, with minimal tradeoff. As a result, we analyze three different parameterizations for elastic VTI media in terms of the influence of the S-waves on the gradient direction for c13, the spatial coverage of gradient direction and the degree of trade-offs between the parameters

금속광산탐사에서 많이 이용되는 물리탐사 방법 중의 하나인 쌍극자-쌍극자 배열 전기비저항탐사의 실제 광산탐사에 대한 적용성을 평가하기 위하여 단순화된 광상구조에 대하여 현장자료 시뮬레이션 및 역산해석을 수행하였다. 실제 광상모형으로는 국내 여러 금속광상 중에서 가장 분포 빈도가 높은 맥상광상을 대상으로 하였다. 국내 맥상광상의 맥폭이 대부분 수십 cm에서 2 m 이내라는 점에 기초하여 맥폭을 변화시키고, 광맥의 물성을 변화시켰으며, 쌍극자-쌍극자 배열 전기비저항탐사의 전극간격은 40 m로 가정하였다. 맥폭이 1 m 이하일 경우 주변암과 광맥의 전기적 물성차가 300배이상 되는 경우에도 저비저항대가 나타나지 않았다. 맥폭이 커질수록 그리고 비저항의 차가 클수록 저비저항대가 뚜렷하게 나타났으나, 넓은 전극간격과 역산에 이용된 셀 크기가 심부로 갈수록 커져서 대체로 저 비저항대의 폭이 과장되게 나타났고, 깊이 또한 실제 깊이보다 깊게 나타났다. 실제 천열수광상 모형을 가정하고 현재 가행 중

We compare different regularization techniques of the steepest-descent directions appearing in waveform inversion using a backpropagation technique. In the waveform inversion using the steepest-descent method, we can have better convergence to a true velocity model by regularizing the steepest-descent directions properly. The regularization can be done by using the diagonal of pseudo Hessian matrix instead of using the approximate Hessian matrix that appears in Gauss-Newton method but is too exp

Seismic modeling is used to simulate wave propagation in the earth. Although the earth’s subsurface is usuallysemi-infinite, we cannot handle the semi-infinite model in seismic modeling because of limited computational resources.For this reason, we usually assume a finite-sized model in seismic modeling. In that case, we need to eliminate the edgereflections arising from the artificial boundaries introducing a proper boundary condition. In this study, we changed threekinds of boundary conditions