• 한국전산구조공학회논문집
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• 제12권3호
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• pp.353-362
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• 1999

본 연구에서는 콘크리트 중력식 댐의 임계균열길이가 계산되었으며 또한 복합균열의 균열선단에서 유효응력 확대계수의 변화량이 조사되었다. 작용하중으로는 댐 상부면에 작용하는 정수압과 댐의 균열면에 작용하는 수압 및 자중으로 구성된 정하중, 그리고 댐 주위에서 발파작업이 수행되는 경우에 고려될 수 있는 발파진동 및 동수압으로 구성된 동하중이 사용되었다. 균열이 발생한 위치와 방향 및 발파진동의 크기에 따라 임계균열길이가 계산되었으며, 또한 복합균열의 형태 및 균열선단 간의 이격거리에 따른 유효응력확대계수의 변화량이 검토되었다.

• 한국전산구조공학회논문집
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• 제16권1호
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• pp.77-86
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• 2003

비행체의 선회운동 시 액체연료 저장탱크의 동응답을 ALE(arbitrary Lagrangian-Eulerian) 유한요소법을 이용하여 해석하였다. 연료탱크는 선회운동 시 내부 연료의 관성력에 의해 상당한 양의 충격하중을 받게 된다. 또한 이로 인해 유발된 큰 동 하중과 모멘트는 구조물의 안정성과 제어시스템에 영향을 미친다. 본 논문에서는 내부연료의 동적 영향력을 억제하기 위하여 링형배플을 채용하였다. 배플개수와 배플위치에 따른 연료탱크의 파라메트릭 해석을 통하여 연료탱크의 동응답 특성에 미치는 배플의 영향을 분석하였다. 유체와 구조물 사이의 연계는 ALE 유한요소법을 통하여 정확하고 효과적으로 처리되었다.

• 국제강구조저널
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• 제18권4호
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• pp.1431-1439
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• 2018

For floating buildings may fl oat on the water for a long time, they are constantly affected by various environmental loads such as wind and wave loads. In this study to find the wave effect on the floating building, five models are designed using steel moment resisting frame. It is assumed that the lower part of the floating building is a reinforced concrete pontoon, while the upper part is a three-story steel frame. To analyze floating buildings affected by wind and wave loads, hydro-dynamic and substructure analysis are performed. As input loads, this study set limits that the mean wind velocity is 35 m/s and the significant wave height is 0.5 m for the residential building. From the hydrodynamic analysis, the time-history acceleration of building is obtained and transformed into a base ground input for a substructure analysis of the superstructure of the building. Finally the mean of the maximum from 30 dynamic analysis of the floating buildings are used to be compared with the results of the same model on the ground. It was shown that the dynamic results with wind and wave loads are not always lesser than the static results which are calculated with static equivalent wind load for a building that is located on the ground.

• 한국해양공학회지
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• 제36권6호
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• pp.390-402
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• 2022

Offshore wind energy has become a major energy source, and various studies are underway to increase the economic feasibility of floating offshore wind turbines (FOWT). In this study, the characteristics of wave-induced motion of a combined wind-wave energy platform were analyzed to reduce the variability of energy extraction. A user subroutine was developed, and numerical analysis was performed in connection with the ANSYS-AQWA hydrodynamic program in the time domain. A platform combining the TLP-type FOWT and the Wavestar-type wave energy converter (WEC) was proposed. Each motion response of the platform on the second-order wave load, the effect of WEC attachment and Power take-off (PTO) force were analyzed. The mooring line tension according to the installation location was also analyzed. The vertical motion of a single FOWT was increased approximately three times due to the second-order sum-frequency wave load. The PTO force of the WEC played as a vertical motion damper for the combined platform. The tension of the mooring lines in front of the incident wave direction was dominantly affected by the pitch of the platform, and the mooring lines located at the side of the platform were mainly affected by the heave of the platform.

• 한국해양환경ㆍ에너지학회지
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• 제2권1호
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• pp.63-73
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• 1999

3파원 해수유동모델을 이용하여 황해의 잔차류를 시뮬레이션한 결과, 북위 34° 25' 위도선을 통한 잔차류량은 조석주기당 약 4km³, 체류시간은 약 6년으로 산성되었고, 황해의 남동 경계선을 통한 잔차류량은 조석주기당 약 13km³, 체류시간은 약 2.5년으로 산정되었다. 황해의 용존산소량은 하계의 해수중 용존산소를 5.0mg/ℓ이상으로 유지하면서, 약 58×10/sup 6/ton의 화학적 산소요구량(COD)윽 수용할 수 있으므로, 유기오염 부하량의 한계로 표현한 황해의 환경용량은 황해고 유입하는 주요 하천들의 연간 유기오염 부하량의 약 8배에 해당한다. 하계에 있어서, 북위 34ℓ 25' 위도선의 전체 수층을 통한 잔차류량은 하루에 약 57×10³ton의 용존산소를 수송하고, 또한 황해의 남동 경계선의 전체 수층을 통한 잔차류량은 하구에 약 203×10³ton의 용존산소를 수송하는 것으로 산정되었다. 따라서 황해가 해수중의 용존산소를 전혀 감소시키지 않고, 유입 하천의 유기오염 부하량을 수용할 수 있는 환경용량은, 북위 34° 25' 위도선을 통한 잔차류에 의한 용존산소 수송량을 기준으로 표현할 경우에는 황해고 유입하는 주요 하천들의 화학적 산소요구량(COD) 부하의 약 3배에 해당하고, 또한 황해의 남동 경계선을 통한 잔차류에 의한 용존산소 수송량을 기준으로 표현하면, 황해로 유입하는 주요 하천들의 화학적 산소요구량(COD) 부하의 약 10배에 해당한다.

• Tribology and Lubricants
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• 제40권3호
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• pp.103-110
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• 2024

Gas foil thrust bearings (GFTBs) are oil-free self-acting hydrodynamic bearings that support axial loads with a low friction during airborne operation. They need solid lubricants to reduce dry-friction between the runner and top foil and minimize local wears on their surfaces during start-up and shutdown processes. In this study, we evaluate the lift-off speeds and load capacity performance of a GFTB with Polytetrafluoroethylene (PTFE) surface coating by measuring drag torques during a series of experimental tests at increasing ambient temperatures of 25, 75 and 110℃. An electric heat gun provides hot air to the test GFTB operating in the closed booth to increase the ambient temperature. Test results show that the increasing ambient temperature delays the lift-off speed and decreases the load capacity of the test GFTB. An early developed prediction tool well predicts the measured drag torques at 60 krpm. After all tests, post inspections of the surface coating of the top foil are conducted. Scanning electron microscope (SEM) images imply that abrasive wear and oxidation wear are dominant during the tests at 25℃ and 110℃, respectively. A quantitative energy dispersive spectroscopy (EDS) microanalysis reveals that the weight percentages of carbon, oxygen, and nitrogen decrease, while that of fluorine increases significantly during the highest-temperature tests. The study demonstrates that the increasing ambient temperature noticeably deteriorates the static performances and degrades the surface coating of the test GFTB.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.478-483
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• 2005

This paper presents the comparison analysis of a Journal and thrust FDB (fluid dynamic bearing) and a conical FDB in a HDD spindle motor. The Reynolds equation is appropriately transformed to describe journal, thrust and conical bearing. Finite element method is applied to analyze the FDB by satisfying the continuity of mass and pressure at the interface between the hearings. The pressure field of the bearings is numerically approximated by applying the Reynolds boundary condition. The load and friction torque are obtained by integrating the pressure and the velocity gradient along the fluid film. The flying height of the spindle motor is measured to verify the proposed analytical result. This research shows that the conical bearing generates bigger load capacity and less friction torque than the journal and thrust bearing in a HDD spindle motor.

• Journal of Advanced Research in Ocean Engineering
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• 제3권2호
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• pp.53-58
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• 2017

This study introduces the case of pipelines installed in subsea conditions and buried offshore. Such installations generate pore water pressure under the seabed because of cyclic wave excitation, which is an environmental load, and consistent cyclic wave loading that reduce the soil shear strength of the seabed, possibly leading to liquefaction. Therefore, in view of the liquefaction of the seabed, stability of the subsea pipelines should be examined via calculations using a simple method for buried subsea pipelines and floating structures. Particularly, for studying the possible liquefaction of the seabed in regard to subsea pipelines, high waves of a 10- and 100-year period and the number of occurrences that are affected by the environment within a division cycle of 90 s should be applied. However, when applying significant wave heights (HS), the number of occurrences within a division cycle of 3 h are required to be considered. Furthermore, to research whether dynamic vertical load affect the seabed, mostly a linear wave is used; this is particularly necessary to apply for considering the liquefaction of the seabed in the case of pile structure or subsea pipeline installation.

• Tribology and Lubricants
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• 제30권1호
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• pp.1-8
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• 2014

In this study, a three-pad gas foil journal bearing with a diameter of 40 mm and an axial length of 35 mm was modeled to predict the static and dynamic performances with regard to an increasing mechanical preload. The Reynolds equation for an isothermal and isoviscous ideal gas was coupled with a simple elastic foundation foil model to calculate the hydrodynamic pressure solution iteratively. In the prediction results, the journal eccentricity, journal attitude angle, and minimum film thickness decreased, but the friction torque increased with the preload. A quick comparison implied a lower load capacity but higher stability for a three-pad gas foil bearing compared to a one-pad gas foil journal bearing. The direct stiffness coefficients increased with the preload, but the cross-coupled stiffness coefficients decreased. The direct damping coefficient increased in the horizontal direction but decreased in the vertical direction as the preload increased. These model predictions will be useful as a benchmark against experimental test data.

• 한국생산제조학회지
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• 제25권4호
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• pp.301-306
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• 2016

High speed polishing can kinematically increase the polishing removal rate by using the conventional Preston equation, especially for hard substrates such as sapphire or diamond. However, high speed effects should be clarified beforehand considering the lubrication state and process parameter variations. In this paper, we developed a polishing experimental method and apparatus to determine the lubrication state by measuring the real time friction coefficient using two load cells. Through experiments, we obtained a boundary lubrication state above 0.35 of the friction coefficient by using low table speed and high polishing load, indicating a synchronized stable behavior in polishing head rotation. However, larger Stribeck indexes by a high speed above 200 rpm can generate a hydrodynamic lubrication state below 0.25 of the low friction coefficient. This causes the polishing head rotation to stop. A forced and synchronized head rotation is required for high speed polishing.