• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.6
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• pp.277-283
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• 2020

In order to improve the ground-motion prediction equation, which is an important factor in seismic hazard assessment, it is essential to obtain good quality seismic data for a region. The Korean Peninsula has an environment in which it is difficult to obtain strong ground motion data. However, because digital seismic observation networks have become denser since the mid-2000s and moderate earthquake events such as the Odaesan earthquake (Jan. 20, 2007, M_L 4.8), the 9.12 Gyeongju earthquake (Sep. 12, 2016, M_L 5.8), and the Pohang earthquake (Nov. 15, 2017, M_L 5.4) have occurred, some good empirical data on ground motion could have been accumulated. In this study, we tried to build a ground motion database that can be used for the development of the ground motion attenuation equation by collecting seismic data accumulated since the 2000s. The database was constructed in the form of a flat file with RotD50 peak ground acceleration, 5% damped pseudo-spectral acceleration, and meta information related to hypocenter, path, site, and data processing. The seismic data used were the velocity and accelerogram data for events over M_L 3.0 observed between 2003 and 2019 by the Korean National Seismic Network administered by the Korea Meteorological Administration. The final flat file contains 10,795 ground motion data items for 141 events. Although this study focuses mainly on organizing earthquake ground-motion waveforms and their data processing, it is thought that the study will contribute to reducing uncertainty in evaluating seismic hazard in the Korean Peninsula if detailed information about epicenters and stations is supplemented in the future.

• Journal of the Korean earth science society
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• v.27 no.4
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• pp.425-432
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• 2006

A seismic tomography using refraction waves is applied to provide information on depth of basement rocks and leachate distribution of the Noeun waste landfill site for the stage of preliminary environmental survey. This method is generally applied to civil and environmental areas. Three lines, apparently perpendicular to the potential leachate flow direction in this site, were installed to investigate the waste landfill site in pseudo three dimensional geometry. The results show that the site is composed of 3 layers and depth of basement becomes shallower at the upstream area of the landfill site than that of the downstream area. Moreover, some parts of the second layer and the basement at the down stream area are partially infiltrated by the leachate, probably related to the disturbed distribution of the different velocity materials within the second layer. In Conclusion, refraction wave tomography is found to be one of the most efficient way to investigate waste landfill site.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.9
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• pp.709-717
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• 2009

Heat transfer rate is a very important factor for the performance of a steam reformer because a steam reforming reaction is an endothermic reaction. Coaxial cylindrical reactor is the reactor design which can improve the heat transfer rate. Temperature, fuel conversion and heat flux in the coaxial cylindrical steam reformer are studied in this paper using numerical method under various operating conditions. Langmuir-Hinshelwood model and pseudo-homogeneous model are incorporated for the catalytic surface reaction. Dominant chemical reactions are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming (DSR) reaction. Although coaxial cylindrical steam reformer uses 33% less amount of catalyst than cylindrical steam reformer, its fuel conversion is increased 10 % more and its temperature is also high as about 30 degree. There is no heat transfer limitation near the inlet area at coaxial-type reactor. However, pressure drop of the coaxial cylindrical reactor is 10 times higher than that of cylindrical reactor. Operating parameters of coaxial cylindrical steam reformer are the wall temperature, the inlet temperature, and the Gas Hourly Space Velocity (GHSV). When the wall temperature is high, the temperature and the fuel conversion are increased due to the high heat transfer rate. The fuel conversion rate is increased with the high inlet temperature. However, temperature drop clearly occurs near the inlet area since an endothermic reaction is active due to the high inlet temperature. When GHSV is increased, the fuel conversion is decreased because of the heat transfer limitation and short residence time.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.75-75
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• 2011

본 논문에서는 진동중인 교량 거더에 작용하는 풍하중을 산정하고 그에 따른 플러터 발생풍속을 예측하기 위하여 분산형 전산환경을 활용한 수치해석 연구를 수행하였다. 분산형 전산환경은 웹 포탈을 기반으로 수치해석 환경을 제공하는 수치풍동 시스템으로서, 전산유체역학(CFD : Computational Fluid Dynamics)에 대한 전문지식이 부족한 사용자들도 격자생성, 수치해석자를 이용한 계산, 가시화 등의 전 과정을 편리하게 수행할 수 있는 차세대 토목분야 연구 환경이다. 본 시스템은 그리드스피어(GfidSphere)를 기반으로 구성되었으며, 기본적으로 사용자 관리, 세션 관리, 그룹 관리, 레이아웃 관리 등을 제공하여 사용자가 포탈을 통해서 다양한 서비스를 쉽게 사용할 수 있는 환경을 구축하도록 도와준다. 수치해석을 위한 유체 지배방정식은 2차원 비정상 비압축성 RANS(Reynolds-Averaged Navier-Stokes) 방정식이며, pseudo compressibility 방법을 적용하였다. 비정상 유동장을 해석하기 위하여 이중시간 전진법(dual time stepping)을 사용하였으며, 수렴가속화를 위해 Multi-grid 기법을 적용하였다. 또한 난류 유동장 해석을 위해서 $k-{\omega}$ SST 난류 모델을 사용하였으며, 난류 천이 과정에서의 유동을 모사하기 위하여 Total stress limitation 방법을 적용하였다. 교량 거더의 연직과 회전방향의 2자유도 움직임을 모사하기 위하여 동적격자 기법을 도입하였다. 교량 거더 주변의 비정상 유동해석 결과를 통해, 거더 표면에서 떨어져나가는 크고 작은 와류의 영향으로 양력 및 모멘트 계수 그래프가 중첩된 진폭과 주기를 갖고 주기적으로 나타나는 것을 확인할 수 있었다. 또한 계산된 비정상 공기력을 적용한 2자유도 플러터 방정식을 통하여 플러터 발생풍속을 산정하였다. 최종적으로 본 연구에서 계산된 결과의 타당성을 검증하기 위하여 수치적으로 구한 플러터 발생풍속과 기존의 실험 및 수치해석 결과를 비교하였으며, 결과는 잘 일치하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.347-355
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• 2016

This study presents a Lattice Boltzmann Method (LBM) coupled with a momentum-exchange approach/fictitious domain (MEA/FD) method for the simulation of particle suspensions. The method combines the advantages of the LB and the FD methods by using two unrelated meshes, namely, a Eulerian mesh for the flow domain and a Lagrangian mesh for the solid domain. The rigid body conditions are enforced by the momentum-exchange scheme in which the desired value of velocity is imposed directly in the particle inner domain by introducing a pseudo body force to satisfy the constraint of rigid body motion, which is the key idea of a fictitious domain (FD) method. The LB-MEA/FD method has been validated by simulating two different cases, and the results have been compared with those through other methods. The numerical evidence illustrated the capability and robustness of the present method for simulating particle suspensions.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1303-1308
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• 2007

Recently, precast concrete tracks are replacing ballast track for efficient and economic maintenance of track. Precast concrete railroad tracks are manufactured in factory, and transported to railroad construction site for installation. Therefore, quality of precast concrete track itself should be sufficiently good. On the contrary to the convenient manufacturing of precast concrete track, the installation of a precast concrete track requires careful steps. Typically, a precast concrete track is placed on an approximately 15-cm thick lean concrete layer. A mortar is filled between lean concrete layer and precast concrete track to adjust the sloping angle of a precast concrete track for a safe train operation at a curvy section. Then, the use of filled mortarproduces a void underneath a precast concrete track, which is harmful to structural safety of a precast concrete track undercyclic loading. Therefore, it is essential to make sure that there is no void left beneath a precast concrete track after mortar filling. In the continuous resonance method, the amplitude of frequency response measured using an instrumented hammer and an accelerometer is plotted against a pseudo-depth, which is half of the wave velocity divided by frequency. The frequency response functions are measured at consecutive measurement locations, 6-cm interval between measurement points, and then combined together to generate a 2-D plot of frequency response. The sections with strong reflections or large amplitude of frequency response are suspicious areas with internal voids and unfilled areas. The 2-D frequency response plot was efficient in locating problematic sections just by examining the color shade of a visualized plot in 2-D format. Some of the problematic sections were drilled to make a visual inspection of mortar filling. The visual image of interface between mortar and precast concrete track was verified using the validity of the continuous resonance technique adopted in this research.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.8
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• pp.799-807
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• 2010

Direct numerical simulations (DNS) of turbulent channel flow for which the drag is reduced by using polymer additives have been performed by a pseudo-spectral method. The Reynolds number based on the friction velocity and half-channel height is 395, and the polymeric stresses due to the polymer additives are evaluated using the FENE-P (finitely extensible nonlinear elastic-Peterlin) model. The numerical results show that the drag reduction rate is significantly affected by the parameters used in the FENE-P model, such as the maximum extensibility and relaxation time of the polymer molecules. The turbulence data for both low- and high-drag reduction regimes are analyzed. In addition, the effects of FENE-P model parameters on the flow characteristics have been investigated for the same drag reduction rate due to the polymer additives. Finally, the present DNS results have been used to verify the correlation between rheological parameters and the extent of drag reduction, which was suggested by Li et al. (2006).

• 한국석유지질학회:학술대회논문집
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• autumn
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• pp.57-72
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• 2000

The Murzuk Basin covers an area in excess of $350,000{\cal}km^2$, and is one of several intra-cratonic sag basins located on the Saharan Platform of North Africa. Compared with some of these basins, the Murzuk Basin has a relatively simple structure and stratigraphy, probably as a result of it's location on a the East Saharan Craton. The basin contains a sedimentary fill which reaches a thickness of about $4,000{\cal}m$ in the basin centre. This fill can be divided into a predominantly marine Paleozoic section, and a continental Mesozoic section. The principal hydrocarbon play consists of a glacial-marine sandstone reservoir of Cambro-Ordovician age, sourced and sealed by overlying Silurian shales. The present day borders of the basin are defined by tectonic uplifts, each of multi-phase generation, and the present day basin geometry bears little relation to the more extensive Early Palaeozoic sedimentary basin within which the reservoir and source rocks were deposited. The key to the understanding of the Cambro-Ordovician play is the relative timing of oil generation compared to the Cretaceous and Tertiary inversion tectonics which influenced source burial depth, reactivated faults and reorganised migration pathways. At the present day only a limited area of the basin centre remains within the oil generating window. Modelling of the timing and distribution of source rock maturity uses input data from AFTA and fluid inclusion studies to define palaeo temperatures, shale velocity work to estimate maximum burial depth and source rock geochemistry to define kinetics and pseudo-Ro. Migration pathways are investigated through structural analysis. The majority of the discovered fields and identified exploration prospects in the Murzuk Basin involve traps associated with high angle reverse faults. Extensional faulting occurred in the Cambro-Ordovician and this was followed by repeated compressional movements during Late Silurian, Late Carboniferous, Mid Cretaceous and Tertiary, each associated with regional uplift and erosion.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.64.2-64.2
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• 2019

HD 81817 is known as a hybrid star. Hybrid stars have both cool stellar wind properties and UV or even X-ray emission features of highly ionized atoms in their spectra. A white dwarf companion has been suggested as the source of UV or X-ray features. HD 81817 has been observed since 2004 as a part of our radial velocity (RV) survey program to search for exoplanets around K giant stars using the Bohyunsan Observatory Echelle Spectrograph (BOES) at the 1.8 m telescope of Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. We obtained 84 RV measurements between 2004 and 2018 for HD 81817 and found two periodic RV variations. The obtained amplitudes of RV periods are around 200 m/s, which are significantly lower than that expected from a white dwarf companion. Furthermore, our re-analysis of the IUE spectra used by Reimers (1984) shows that the excess in UV emission can easily be explained by a pseudo-continuum of unresolved emission lines originating in the extended chromosphere of the star. We thus conclude that there are no companions of stellar mass to HD 81817. Meanwhile, we analyzed two periodicities in RV measurements and conclude that the period of 627.9 days is caused by intrinsic stellar activities based on H alpha equivalent width (EW) variations of a similar period. On the other hand, the period of 1047.8 days is likely to be caused by substellar companion which has a minimum mass of 27.6 M_JUP, a semi-major axis of 3.3 AU, and an eccentricity of 0.17 assuming the stellar mass of 4.3 M_⊙ for HD 81817. The inferred mass puts HD 81817 b in the brown dwarf desert.

• Journal of English Language & Literature
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• v.58 no.5
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• pp.943-974
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• 2012

This paper aims to suggest the compromising vision of nature and technology as the solution to get out of the globally accelerated technology environment in Don DeLillo's Cosmopolis. This novel intends to emphasize on the importance of physical environment as a precondition for the survival of human. Eric wants to be a posthuman with the cybernetic idea, pursuing to be the digital self in a vast biosphere that integrates both the nature and the technology. His obsessive worship of technology through his quest for the futurity results in the effacement of the humanity and the insulation from the nature. Cosmopolis is DeLillo's first 9/11 novel, which describes a young-billionaire asset manager Eric's one-day life in New York in April 2000. Eric can be the third Twin Tower as a symbol of global economic hegemony. By the allusion of the 9/11 catastrophic event, it can be said that Eric's fall is caused by his hubris and avarice as a global capitalist. Crossing the 47th Street toward the West in his limousine, his journey is revealed as the environmental reflections on his desires to attain the futurity and transcendence by technology. This novel cautions that the abuse of technology can bring out the obsolescence and erasure of the humanity and the nature. DeLillo suggests that the best hope for the evolutionary possibility of posthuman can be realized through the correlation with nature and technology. This future-oriented novel warns that the excessive technology should not lead to the disappearance of community and humanity, and the separation of self and nature. It admonishes that they should not follow pseudo-cosmopolitanism as the greedy world citizens, devoting on the velocity of newest technology. This novel recommends that humans should be the world citizen of global ecosystem, making the ameliorative environment through the correlation with self/environment and technology/nature, and gardening the restorative biosphere and the younger planet.