• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.126-133
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• 2008

Geotechnical limit state design methods; LRFD of North America is an approach that estimates resistance using design model and then multiplies resistance factor by calculated resistance to reflect the uncertainty of geomaterials and design models; whereas, Eurocode of the Europe employs the partial resistance factor applied directly to each variable in the resistance equation that individual soil properties such as cohesion and angle of internal friction are applied. This discussion paper is a study on characteristic value which has globally been argued through processing of development of Eurocode 7 for geotechnical design even to the present. Estimating the characteristic value of soil properties affects not only determination of design value applied directly to design of geotechnical structures, but also economic feasibility and stability of the structures.

• 한국정밀공학회지
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• 제21권3호
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• pp.117-123
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• 2004

A brake disc with helical grooved vent in radial direction is proposed for the improvement of thermal dissipation. The heat transfer phenomenon is analyzed far both the proposed disc and the conventional one using finite element method. The thermal dissipation is considerably influenced by the geometrical differences of the brake discs. The results of the analysis show that the proposed brake disc with helical grooved vent has the improved performance to dissipate the thermal energy more effectively.

• Tribology and Lubricants
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• 제37권6호
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• pp.246-252
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• 2021

Among the engine components of an internal combustion engine, the valve train is a series of systems that supply intake gas to the combustion chamber and operate intake and exhaust valves that discharge exhaust gas. If excessive wear occurs in the valve train system, the suction and exhaust valves do not open and close on time, which leads to abnormal combustion and exhaust gas. In this study, we conduct experiments and analyses on friction and wear characteristics of the valve train system. Moreover, we experimentally study the correlation between the pinball and pinball cap on engine oil lubrication, friction experiment, wear amount analysis, and surface analysis. Specifically, we experiment using Ball on reciprocating tribo-tester and apply commercial engine oil sold on the market engine oil. We construct the experimental conditions for each new oil and oil. Accordingly, the completed specimen was subjected to a confocal microscope to check the wear volume, observe the surface of the specimen, and confirm the elemental components using a scanning microscope (SEM) and an energy dispersion X-ray spectrometer (EDS). Through this experiment, we analyze the friction and wear characteristics of valve train components according to engine oil grade, and the obtained data serve as an effective engine oil management method.

• 한국지반공학회논문집
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• 제25권4호
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• pp.39-54
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• 2009

대형직접전단시험기를 이용하여, 국내의 석산에서 생산된 쇄석재료들에 대한 전단거동을 분석하였다. 시료별로 전단강도를 산출하였으며, 최대입경, 수침조건, 밀도, 균등계수, 파쇄율 등의 변화에 따른 전단거동의 영향을 평가하여, 선행연구결과와 정성적으로 비교하였다. 아울러, 일의 원리를 응용하여, 쇄석재료의 응력-다일러턴시 관계를 규명하였으며, 한계상태의 마찰계수와 첨두마찰각 및 팽창각을 산출하였다. 실험결과 일축압축강도와 파쇄율이 쇄석의 내부마찰각에 가장 결정적인 영향을 미치며, 파괴시 다일러턴시도 연관성이 높은 것으로 밝혀졌다.

• 한국재난정보학회 논문집
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• 제16권4호
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• pp.712-722
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• 2020

연구목적: 최근 국내 규모 5.0이상의 지진으로 인한 피해 발생이 증가하고 있다. 지진이 발생하면 구조물 이외에도 내부설비, 전력기기 등에 피해를 주게 된다. 이에 본 논문에서는 지진으로 인한 배전반과 같은 전기기기의 피해를 저감시킬 수 있는 이중 슬립마찰면이 있는 면진장치를 개발하였으며, 이에 대한 면진성능을 평가하였다. 연구방법: 면진성능을 평가하기 위해 진동대 시험을 수행하였으며, 면진장치 유무에 따른 성능비교를 수행하였다. 다양한 주파수와 가속도 수준에 대한 응답가속도 및 변위를 비교하여 면진장치의 감쇠효과를 분석하였다. 연구결과: 시험결과, 면진장치가 설치되어 있는 경우가 면진장치가 설치되어 있지 않은 경우보다 가속도 증폭이 최대 42% 작았다. 이는 면진장치의 이중슬립마찰면 사이에서 발생한 변위가 지진에너지를 소산하는 역할을 하여 증폭에너지가 감소된 것으로 판단된다. 결론: 이중 슬립마찰면을 적용한 면진장치는 약진보다는 강진에서 지진감쇠효과가 더 컸으며, 주파수가 클수록 지진감쇠효과가 더 좋았다. 따라서, 배전반과 같은 전기기기에 적용하여 지진에너지를 감쇠하는 작용을 할 수 있을 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제48권6호
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• pp.809-822
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• 2013

Base isolation is widely used in seismic resisting buildings due to its low construction cost, high reliability, mature theory and convenient usage. However, it is difficult to design the isolation layer in high-rise buildings using the available bearings because high-rise buildings are characterized with long period, low horizontal stiffness, and complex re-distribution of the internal forces under earthquake loads etc. In this paper, a simple and innovative isolation bearing, named Teflon-based lead rubber isolation bearing, is developed to address the mentioned problems. The Teflon-based lead rubber isolation bearing consists of friction material and lead rubber isolation bearing. Hence, it integrates advantages of friction bearings and lead rubber isolation bearings so that improves the stability of base isolation system. An experimental study was conducted to validate the effectiveness of this new bearing. The effects of vertical loading, displacement amplitude and loading frequency on the force-displacement relationship and energy dissipation capacity of the Teflon-based lead rubber isolation bearing were studied. An analytical model was also proposed to predict the force-displacement relationship of the new bearing. Comparison of analytical and experimental results showed that the analytical model can accurately predict the force-displacement relationship and elastic shear deflection of the Teflon-based lead rubber isolation bearings.

• Geomechanics and Engineering
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• 제22권3호
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• pp.245-254
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• 2020

The interaction between the frozen soil and building structures deteriorates with the increasing temperature. A nuclear magnetic resonance (NMR) stratification test was conducted with respect to the unfrozen water content on the interface and a shear test was conducted on the frozen soil-structure interface to explore the shear characteristics of the frozen soil-structure interface and its failure mechanism during the thawing process. The test results showed that the unfrozen water at the interface during the thawing process can be clearly distributed in three stages, i.e., freezing, phase transition, and thawing, and that the shear strength of the interface decreases as the unfrozen water content increases. The internal friction angle and cohesive force display a change law of "as one falls, the other rises," and the minimum internal friction angle and maximum cohesive force can be observed at -1℃. In addition, the change characteristics of the interface strength parameters during the freezing process were compared, and the differences between the interface shear characteristics and failure mechanisms during the frozen soil-structure interface freezing-thawing process were discussed. The shear strength parameters of the interface was subjected to different changes during the freezing-thawing process because of the different interaction mechanisms of the molecular structures of ice and water in case of the ice-water phase transition of the test sample during the freezing-thawing process.

• 한국안전학회지
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• 제28권3호
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• pp.44-50
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• 2013

Process gas piping is one of the most basic components frequently used in the refinery and petrochemical plants. Many kinds of by-product gas have been used as fuel in the process plants. In some plants, natural gas is additionally introduced and mixed with the byproduct gas for upgrading the fuel. In this case, safety or design margin of the changed piping system of the plant should be re-evaluated based on a proper design code such as ASME or API codes since internal pressure, temperature and gas compositions are different from the original plant design conditions. In this study, series of piping stress analysis were conducted for a process piping used for transporting the mixed gas of the by-product gas and the natural gas from a mixing drum to a knock-out drum in a refinery plant. The analysed piping section had been actually installed in a domestic industry and needed safety audit since the design condition was changed. Pipe locations of the maximum system stress and displacement were determined, which can be candidate inspection and safety monitoring points during the upcoming operation period. For studying the effects of outside air temperature to safety the additional stress analysis were conducted for various temperatures in $0{\sim}30^{\circ}C$. Effects of the friction coefficient between the pipe and support were also investigated showing a proper choice if the friction coefficient is important. The maximum system stresses were occurred mainly at elbow, tee and support locations, which shows the thermal load contributes considerably to the system stress rather than the internal pressure or the gravity loads.

• Structural Engineering and Mechanics
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• 제64권2호
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• pp.195-204
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• 2017

Analytical and experimental studies of the innovative pipe in pipe damper have been recently investigated by the authors. In this paper, by adding lead or zinc infill or slit diaphragm inside the inner pipe, it is tried to increase the equivalent viscous damping ratio improving the cyclic performance of the recently proposed multi-level control system. The damper consists of three main parts including the outer pipe, inner pipe and added complementary damping part. At first plastic deformations of the external pipe, then the internal pipe and particularly the added core and friction between them make the excellent multi-level damper act as an improved energy dissipation system. Several kinds of added lead or zinc infill and also different shapes of slit diaphragms are modeled inside the inner pipe and their effectiveness on hysteresis curves are investigated with nonlinear static analyses using finite element method by ABAQUS software. Results show that adding lead infill has no major effect on the damper stiffness while zinc infill and slit diaphragm increase damper stiffness sharply up to more than 10 times depending on the plate thickness and pipe diameter. Besides, metal infill increases the viscous damping ratio of dual damper ranging 6-9%. In addition, obtained hysteresis curves show that the multi-level control system as expected can reliably dissipate energy in different imposed energy levels.

• 한국지반환경공학회 논문집
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• 제20권12호
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• pp.41-47
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• 2019

본 논문에서는 서남해 해상풍력 실증단지 해역을 대상으로 석션버켓기초의 지지력에 대한 신뢰성 분석에 대한 내용을 다루었다. 5MW급 해상풍력터빈의 콘크리트 석션버켓기초를 선정하여 기초 설치 후 연직지지력과 수평지지력에 대한 파괴확률을 계산하고 설계변수의 민감도를 분석하였다. AFOSM을 이용한 신뢰성해석을 수행한 결과, 기초-지반 분리거동 시 연직지지력에 대한 파괴확률이 가장 큰 것으로 나타났으며 기초지반의 단위중량과 내부마찰각이 지배적인 영향인자임을 확인하였다.