• International Journal of Aeronautical and Space Sciences
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• 제10권1호
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• pp.20-29
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• 2009

There are concerns about the influence of the gust wind caused by helicopters affecting the moving vehicles while hovering over the road during rescue activities. For the understanding of such complicated flow. numerical simulation of a rotor hovering above the ground has been carried out, changing the rotor/ground clearances. The rotor thrust is kept constant. and the rotor control is determined by trim adjustments incorporated into the CFD algorithm. Collective pitch angle and the required power decreases with the rotor/ground clearance which agrees with experience. Changes of the flowfield near the rotor with regard to the rotor height are investigated based on the calculated results.

• 한국정밀공학회지
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• 제21권1호
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• pp.173-180
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• 2004

This paper presents the effect of varying boundary conditions such as ground subsidence, internal pressure and temperature variation for buried pipelines on failure prediction by using a failure probability model. The first order Taylor series expansion of the limit state function incorporating with von-Mises failure criteria is used in order to estimate the probability of failure mainly associated with three cases of ground subsidence. Using stresses on the buried pipelines, we estimate the probability of pipelines with von-Mises failure criterion. The effects of varying random variables such as pipe diameter, internal pressure, temperature, settlement width, load for unit length of pipelines, material yield stress and pipe thickness on the failure probability of the buried pipelines are systematically studied by using a failure probability model for the pipeline crossing ground subsidence regions which have different soil properties.

• 한국안전학회지
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• 제13권2호
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• pp.54-64
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• 1998

This study was initiated to examine the stress and deformation characteristics of the pipelines which were subjected to various environmental conditions in order to confirm their integrity. As the part of them, this paper presents the analysis results for the effect of ground subsidence combined with main loads on buried natural gas pipelines. The ground subsidence which can occur for buried gas pipeline has been classified to the three cases. Finite element method was used to analyze the effect of ground subsidences on pipeline of 26 inch(0.660 m) and 30 inch(0.762 m) diameter used as high pressure ($70 kg_f/cm^2(6.86 MPa)$) main pipelines of KOGAS. This paper shows the result of stress analysis for the pipelines subjected to those three case ground subsidence. Comparing these results with safety criterion of KOGAS(0.9 $\sigma_y$), maximum allowable settlement and loads have been calculated.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.63-65
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• 2003

The purpose of the study is to produce the surface ground temperature diagnostically using surface EBM with the use of GRID model in Geographic Information Systems (GIS). Certain characteristics have been analyzed for local slope effect, coastal effect and influence of high orographic aspect on the surface ground temperature. We present discussions on the meteorological responsibility for their temperature. The derived surface ground temperatures can be provided for comparison with those from satellite-based observ ation.

• 한국지반환경공학회 논문집
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• 제7권2호
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• pp.5-14
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• 2006

풍화토나 풍화암 지반의 경우 집중호우에 의한 사면붕괴는 주로 지표면부근 2.0m 이내에서 발생되며, 강우발생 전에 사면 내 지하수위가 높지 않다면 강우가 지하수위 상승에 미치는 영향은 크지 않은 것으로 보고되고 있다. 그러나 국내 사면설계에 적용되고 있는 우기시 지하수위 조건은 강우에 의해 지하수위가 지표면까지 상승하는 것으로 보고 있어, 사면의 활동 파괴면이 지표부근 보다는 사면 심부에서 발생되는 것으로 검토 되고 있다. 본 연구는 사면 안정에 주된 영향을 미치는 지하수위 조건의 적정성 여부를 검토하기 위하여 서울지역 30년 평균일강우량을 적용하여 실제 우기시 지하수위 상승 및 사면안정성을 검토하였다. 그 결과 지하수위 상승량은 사면 높이의 6.0~41.0%로 나타나 현재 통용되고 있는 우기시 지하수위 적용 기준이 과대평가되고 있음을 알 수 있었다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 1999년도 추계학술대회 논문집
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• pp.407-414
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• 1999

Sand drain as a vertical drainage is widely used in soft ground improvement. Recently, sand, the principal source of sand drain, is running out. A laboratory model test was carried out to utilize gravel as a substitute for sand. Though which the characteristics of gravel are compared to those of sand for engineering purpose. According to the test, the settlement was found to be smaller in gravel drain than in sand drain. The increase in bearing capacity by gravel rile explains the result. The clogging effect was not found in gravel column. As a result, it is assumed that gravel is relatively acceptable as a drainage material. Gravel material seems better than sand material in bearing capacity and it is found that bearing capacity is larger when gravel is used as compaction pile than as drain from in-situ test on bearing capacity. Increase of bearing capacity with gravel pile means an effect of composite ground by stiffness of gravel material. It can lie supposed to use gravel pile instead of sand pile in view of consolidation effect and bearing capacity.

• Earthquakes and Structures
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• 제17권6호
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• pp.635-647
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• 2019

Tests and theoretical studies for seismic responses of a transmission tower-line system under coupled horizontal and tilt (CHT) ground motion were conducted. The method of obtaining the tilt component from seismic motion was based on comparisons from the Fourier spectrum of uncorrected seismic waves. The collected data were then applied in testing and theoretical analysis. Taking an actual transmission tower-line system as the prototype, shaking table tests of the scale model of a single transmission tower and towers-line systems under horizontal, tilt, and CHT ground motions were carried out. Dynamic equations under CHT ground motion were also derived. The additional P-∆ effect caused by tilt motion was considered as an equivalent horizontal lateral force, and it was added into the equations as the excitation. Test results were compared with the theoretical analysis and indicated some useful conclusions. First, the shaking table test results are consistent with the theoretical analysis from improved dynamic equations and proved its correctness. Second, the tilt component of ground motion has great influence on the seismic response of the transmission tower-line system, and the additional P-∆effect caused by the foundation tilt, not only increases the seismic response of the transmission tower-line system, but also leads to a remarkable asymmetric displacement effect. Third, for the tower-line system, transmission lines under ground motion weaken the horizontal displacement and acceleration responses of transmission towers. This weakening effect of transmission lines to the main structure, however, will be decreased with consideration of tilt component.

• 한국항공우주학회지
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• 제33권6호
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• pp.1-7
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• 2005

비압축성 평균 Navier-Stokes 방정식에 $\varepsilon{-SST}$ 난류 모델을 적용하여 정사각주 주위 유동과 지면의 간극 유동을 해석하였다. 지면이 운동할 경우에는 지면의 박리 전단층의 강도가 약화되어 사각주 상/하부의 박리 전단층 상호 작용을 촉진시키므로 고정 지면에 비하여 더 낮은 간극에서도 와류 배출이 발생한다. 지면 효과를 고려할 경우 고정 지면의 경우와는 달리 지면의 박리 거품이 존재하지 않게 되고, 이로 인하여 2차 박리 주파수는 나타나지 않는다. 이와 더불어 지면이 운동할 경우 고정 지면에 비해 더 높은 와류 배출 주파수와 공력 계수가 나타남을 확인하였다.

• 한국지반신소재학회논문집
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• 제8권1호
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• pp.19-24
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• 2009

본 논문에서는 연약지반개량공법 중의 하나인 PVD공법에 의한 연약지반개량효과를 파악하기 위하여 일련의 수치해석을 실시하였다. 본 연구에서는 기존에 수행된 실내모형실험 결과와의 비교를 통하여 그 신뢰성이 검증된 탄점소성 3차원압밀 유한요소해석 방법을 사용하였다. 수치해석에서는 PVD의 폭과 상재하중의 크기를 다양하게 변화시키며 개량된 점토지반의 압밀거동을 재현하였으며 그 결과를 이용하여 개량된 연약점토지반의 압밀촉진효과에 미치는 PVD의 폭과 상재하중 크기의 영향에 대하여 고찰하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 봄 학술발표회 논문집
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• pp.357-364
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• 1998

In this paper, ground vibration analysis methods for train transit on bridges are studied. Train loads acting on the piers are evaluated considering the interactions between the trains and the bridge. The 2D in-plane wave propagation method and the axisymmetric wave propagation method are used in the ground vibration analysis, and then the results of the ground vibration are compared. A modified axisymmetric method is presented, which can consider the effect of the train loadings on a series of piers as the train moves.