• 한국환경과학회지
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• 제7권3호
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• pp.349-360
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• 1998

Effects of uniform flow on a two-dimensional mesoscale horizontal convection were investigated by using the vorticity and thermodynamic equations. For thins purpose, We simulated properties of a thermal convection m a stably stratified Boussinesq flued caused by partial heating at the center of a lower boundary If we don't consider effects of the uniform flow, the convection takes the form of aidsymmetrlc with respect to the z-alds. But when uniform flow Is strong, velocity field and temperature field consist of a sin91e cell structure which spreads upstream side of the partial heating area. The flow pattern for strong uniform flows takes the form of positive temperatue near the ground and negative temperature perturbation soft over the partial heating area, and downward motion directly over the upwind portion of the partial heating area and upward motion on the downstream side. The downstream edge of the upstream cell Is shifted in the downstream direction with the Increase of uniform flow almost linearly.

• Earthquakes and Structures
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• 제20권2호
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• pp.175-185
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• 2021

This study strives to highlight the importance of considering the vertical ground motions (VGM) in the seismic evaluation of RC buildings. To this aim, IDA (Incremental Dynamic Analysis) is conducted on three code-based designed high-rise RC frame-core wall buildings using a suite of earthquake records comprising of significant VGMs. To unravel the significance of the VGM inclusion on the performance of the buildings, IDAs are conducted in two states (with and without the vertical component), and subsequently based on each analysis, fragility curves are developed. Non-simulated collapse criteria are used to determine the collapse state drift ratio and the area under the velocity spectrum (SIm) is taken into account as the intensity measure. The outcome of this study delineates that the inclusion of VGM leads to the increase in the collapse vulnerability of the structures as well as to the change in the pattern of inter-story drifts and failure mode of the buildings. The results suggested that it would be more conservative if the VGM is included in the seismic assessment and the fragility analysis of RC buildings.

• Geomechanics and Engineering
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• 제31권2호
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• pp.183-195
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• 2022

Under the effects of the near-field earthquakes, the incident angle of the incoming wave could be different. In this study, the influences of some parameters such as incident angle, basin edge, peak ground acceleration level of the bedrock motion as well as different clay types with different consistency on the amplification behavior of the shallow basins are investigated. To attain this goal, the numerical analyses of the basins filled with three different clay types are performed using a fully nonlinear method. The two dimensional models of the basins are subjected to a set of strong ground motions with different peak ground acceleration levels and three different incident angles of 30◦, 45◦ and 90◦ with respect to the horizontal axes. The results show the dominant effect of the obliquely subjected waves at most cases. The higher effect of the 45◦ incident angle on the basin response was concluded. In the other part of this study, the spectral amplification curves of the surface points were compared. It was seen that the maximum spectral amplification of different surface points occurs at different periods. Also, it is affected by the increase in the peak acceleration level of the incoming motions.

• Structural Engineering and Mechanics
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• 제51권2호
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• pp.277-297
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• 2014

Since the isolation bearings undergo large displacements in base-isolated structures, impact with adjacent structures is inevitable. Therefore, in this investigation, the effect of impact on seismic response of isolated structures mounted on double concave friction pendulum (DCFP) bearings subjected to near field ground motions is considered. A non-linear viscoelastic model of collision is used to simulate structural pounding more accurately. 2-, 4- and 8-story base-isolated buildings adjacent to fixed-base structures are modeled and the coupled differential equations of motion related to these isolated systems are solved in the MATLAB environment using the SIMULINK toolbox. The variation of seismic responses such as base shear, displacement in the isolation system and superstructure (top floor) is computed to study the impact condition. Also, the effects of variation of system parameters: isolation period, superstructure period, size of seismic gap between two structures, radius of curvature of the sliding surface and friction coefficient of isolator are contemplated in this study. It is concluded that the normalized base shear, bearing and top floor displacement increase due to impact with adjacent structure. When the distance between two structures decreases, the base shear and displacement increase comparing to no impact condition. Besides, the increase in friction coefficient difference also causes the normalized base shear and displacement in isolation system and superstructure increase in comparison with bi-linear hysteretic behavior of base isolation system. Totally, the comparison of results indicates that the changes in values of friction coefficient have more significant effects on 2-story building than 4- and 8-story buildings.

• 대한토목학회논문집
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• 제30권2A호
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• pp.93-102
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• 2010

시공단계별 수치해석 및 안전성 평가는 장경간 교량의 시공 중 불안전성을 해결하기 위한 주요 검토사항으로 고려되어야 한다. 장경간 교량의 시공단계해석에 따른 구조응답특성 평가 시, 근거리지진(NFGM)의 영향은 기존 입력지진동 데이터와는 확연히 다른 특성을 가지고 있기 때문에 내진설계를 위한 주요 변수로 평가되어야 한다. 따라서 이 연구에서는 응답스펙트럼 해석결과를 바탕으로 NFGM 특성에 따른 장경간 교량의 응답양상을 재검토하였으며, 장경간 교량의 시공단계해석 및 신뢰성평가를 효율적으로 수행하기 위해 관련연구에서 제시된 수치해석 프로그램을 개선하였다. NFGM 특성을 고려한 다양한 시공방안의 우수성은 주요 부재의 시간이력해석 결과를 이용하여 평가하였다. 정량적인 안전수준 평가를 위해 확률변수에 포함된 External Uncertainty의 영향을 고려하여 신뢰성해석을 수행하였으며, NFGM 특성에 따른 주요 시공단계의 안전지수 및 파괴확률을 제시하였다. 아울러, 몬테카르로 시뮬레이션(MCS)을 이용하여 신뢰성해석 결과에 대해 Internal Uncertainty의 영향을 검토하였으며, 주요 해석결과의 분포양상을 평가하였다. 이 연구는 NFGM 특성을 고려한 장경간 교량의 내진설계 시, 시공안전성 향상을 위한 기초자료를 제공할 것으로 기대된다.

• Steel and Composite Structures
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• 제39권4호
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• pp.353-366
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• 2021

Cored moment resisting stub column (CMSC) was previously developed by the features of adopting a core segment which remains mostly elastic and reduced column section (RCS) details around the ends to from a stable hysteretic behavior with large post-yield stiffness and considerable ductility. Several full-scale CMSC components with various length proportions of the RCSs with respect to overall lengths have been experimentally investigated through both far-field and near-fault cyclic loadings followed by fatigue tests. Test results verified that the proposed CMSC provided very ductile hysteretic responses with no strength degradation even beyond the occurrence of the local buckling at the side-segments. The effect of RCS lengths on the seismic performance of the CMSC was verified to relate with the levels of the deformation concentration at the member ends, the local buckling behavior and overall ductility. Estimation equations were established to notionally calculate the first-yield and ultimate strengths of the CMSC and validated by the measured responses. A numerical model of the CMSC was developed to accurately capture the hysteretic performance of the specimens, and was adopted to clarify the effect of the surrounding frame and to perform a parametric study to develop the estimation of the elastic stiffness.

• Smart Structures and Systems
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• 제16권4호
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• pp.701-723
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• 2015

Friction isolators are one of the most important types of bearings used to mitigate damages of earthquakes. The adaptive behavior of these isolators allows them to achieve multiple levels of performances and predictable seismic behavior during different earthquake hazard levels. There are three main types of friction isolators. The first generation with one sliding surface is known as Friction Pendulum System (FPS) isolators. The double concave friction pendulum (DCFP) with two sliding surfaces is an advanced form of FPS, and the third one, with fully adaptive behavior, is named as triple concave friction pendulum (TCFP). The current study has been conducted to investigate and compare seismic responses of these three types of isolators. The structure is idealized as a two-dimensional single degree of freedom (SDOF) resting on isolators. The coupled differential equations of motion are derived and solved using state space formulation. Seismic responses of isolated structures using each one of these isolators are investigated under seven near fault earthquake motions. The peak values of bearing displacement and base shear are studied employing the variation of essential parameters such as superstructure period, effective isolation period and effective damping of isolator. The results demonstrate a more efficient seismic behavior of TCFP isolator comparing to the other types of isolators. This efficiency depends on the selected effective isolation period as well as effective isolation damping. The investigation shows that increasing the effective isolation period or decreasing the effective isolation damping improves the seismic behavior of TCFP compared to the other isolators. The maximum difference in seismic responses, the base shear and the bearing displacement, for the TCFP isolator are calculated 26.8 and 13.4 percent less than the DCFP and FPS in effective isolation damping equal to10%, respectively.

• 천문학회보
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• 제36권2호
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• pp.91-91
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• 2011

The passage of the interplanetary discontinuity (i.e., sudden increases in the solar wind speed, density, and IMF strength) was detected by ACE near GSE (x, y, z) ~ (222, -36, 3) Re upstream of Earth around 22:48 UT on November 24, 2008. About 55 min later, this solar wind discontinuity was observed by Geotail near GSE (x, y, z) ~ (23, 18, -7) Re in front of Earth's bow shock. From the propagation time of the solar wind discontinuity between ACE and Geotail, it is expected that the discontinuity front is aligned with the Parker spiral and strikes the postnoon dayside magnetopause first. Using coordinated multi-point measurements (THEMIS and GOES) at or in geosynchronous orbit, we observed a tailward propagating sudden impulse (SI), excited by the interplanetary discontinuity, around 23:50 UT with its front retaining alignment similar to that of solar wind discontinuity. The SI event appears a negative-then-positive variation in the H component at high latitude Chokurdakh (CHD: MLAT ~ 64.7 deg) in the prenoon sector, which is opposite sense of normal SI event. During the positive deflection at CHD, the SuperDARN Hokkaido radar detected the downward motion of the ionosphere, implying westward electric field enhancement, at subauroral latitudes near CHD meridian. In our study we will discuss magnetospheric and ionospheric responses to the passage of the solar wind discontinuity using multi-point observations in space and on the ground.

• 지적과 국토정보
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• 제48권1호
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• pp.71-91
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• 2018

최근 영농분야에서 종자파종, 병충해 방제 등에 무인항공기(UAV ; Unmanned Aerial Vehicle)를 활용한 응용이 활발히 진행되고 있다. 본 연구는 UAV에 다양한 파장대의 영상센서를 탑재하고 SfM(Structure from Motion) 영상해석기법과 연계한'고해상 저고도 원격탐측시스템(UAS ; Unmanned Aerial System)'를 구성, UAS 기반 식생조사의 효용성을 고찰하여 정밀영농의 활용성을 검토하였다. 이를 위해 저가 UAV에 가시 컬러(VIS_RGB ; Visible Red, Green, and Blue) 영상센서, 수정된 BG_NIR(Blue Green_Near Infrared Red) 근적외 영상 센서, $7.5{\sim}13.5{\mu}m$ 분광대역의 열적외 영상(TIR ; Thermal Infrared Red)센서를 조합 연계한 UAS를 구성하였다. 또한, 가시 근적외 및 열적외 파장대를 기본요소로 광합성에 따른 식물의 엽록소, 질소 및 수분 함유량 등을 검토할 수 있는 총 10종의 식생지수를 선정, 식생상태 검출에 활용하였다. 시험대상지에 대한 각 파장대역의 영상을 획득하고 사전에 조사된 지상 피복현황을 기준으로 각 식생지수의 분포도 및 식생지수 간 상관성(결정계수 R2) 등을 비교 고찰하여 무인항공기를 활용한 가시 컬러, 근 적외 및 열 적외 영상에 의한 식생상태의 검측 수행능력을 검토하였다. 저가 무인항공기에 VIS_RGB, BG_NIR 및 TIR 영상 센서를 탑재, 식생조사의 효용성을 종합적으로 검토한 결과, 인공위성과 항공영상에 의존한 과거의 식생조사방식 대비, 영상해상도, 경제성 및 운용성 면에서 UAV기반 고해상 저고도 원격탐측시스템(UAS)의 효용성을 입증할 수 있었으므로 정밀농업, 수계 및 산림조사 등의 분야에 그 활용이 기대된다.

• 터널과지하공간
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• 제7권2호
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• pp.116-129
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• 1997

The objective of this study is to predict the minimization effect of the noise and vibration during the construction and the train operation regarding to the design modification of the Taegu Subway Line No. 1. It was suggested optimal control blasting methods to reduce the causing vibration Nuance to the resident in City Taegu and also proposed the better governing method to decrease the environmental hazard to the near buildings and residents during the train operation. When the high-density gaseous reaction of explosion products exerts a high pressure in motion outward, a dynamic stress field will be created in the surrounding buildings. Therefore, in the region close to the charge, permanent damage begins to occur at a great critical level of partial velocity, that is difficult from different structure as working conditions. It is reliable to predict that the damages could be reduced if we know the peak velocity and the exact reasons through the conducting of detail studies of structural analysis of the related buildings with the optimal blasting designs. A blasting technique should be deemed to take advantage of the reduction of damage of the surrounding rocks and structures to improve the in-city blasting. This is a typical in-city blasting operation where success depends on closely controlling the ground vibrations in case of better designed blasting methods. There are techniques that can be applied to prevent large vibrations from damaging the important buildings through the Route Modification of the Taegu Subway Line No. 1.