• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1996년도 제24회 춘계학술대회
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• pp.86-93
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• 1996

The lubrication characteristics of high-speed ball bearings has been investigated empirically using 45mm bore split inner ring ball bearings employed in small industrial gas turbine engines with oil-jet lubrication method. For the close structural simulation, experiments carried out with bearing mounting supports of real engines, such as bearing housings and oil nozzle assemblies with squeeze film dampers. Thus the results of tests can be directly applied to the design and the development of gas turbine engines. Testing was done by varying operating speeds, axial load on bearings, and lubricant flowrates. During testing, the temperature of bearing at outer-ring face, the power consumption of the driving motor, and the rotating resistance of the bearing were measured. From this study, the representative factors for lubrication characteristics at high speed was found, and the most important one was not operating speed but axial load up to 1.95 million dmN speed and 303 kgf axial load. Furthermore, the detailed variation of the rotational resistance of the bearing could be visualized by measuring the change of the radial load under the bearing supports. The rotational resistance consists of the frictional resistance and the bearing-cavity oil resistance.

• 한국지열·수열에너지학회논문집
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• 제16권1호
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• pp.1-8
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• 2020

In this study, a new shape of wind turbine with horizontal axis has been proposed. The proposed wind turbine has two pairs of 3 tiltable blades which minimizes air resistance during the reverse rotational direction. Under a given wind speed, 3D numerical simulations on tiltable blades were performed for various TSRs(tip-speed-ratios). Four cases of rotational position was considered to analyze the torque and wind power generated on the blade surfaces. The results show that the maximum wind power occurs at the TSR of 0.2. Due to the blade tilting, the wind passes through the blade without air resistance at the reverse rotational direction. The torque is mainly caused by pressure differences between the front and rear surface of the blade, and it becomes maximum when the blade is located at the azimuth angle of 330°.

• 한국산학기술학회논문지
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• 제17권3호
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• pp.661-667
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• 2016

연약지반에 적용 가능한 앵커의 기술로 개발계획인 헬릭스 형태의 소형 앵커는 기존 앵커보다는 시공 단계가 단순하고 그라우트가 양생될 때까지 기다릴 필요가 없으므로 공기단축 및 연장 롯드 반복사용이 가능하며 비용 절감효과가 있다. 또한 배토가 없으며, 회전식으로 헬리컬 앵커를 삽입하기 때문에 시공성이 좋으며, 앵커의 제거도 설치만큼 쉬우므로 가시설의 제거용 앵커로도 활용 가능하며, 헬리컬 앵커 날개 수에 따라 인발저항이 달라, 효율적인 헬리컬 앵커 설계가 가능할 것으로 판단된다. 연약지반에 헬릭스 앵커를 시험시공하기 위하여 헬리컬 앵커와 토크드라이버를 제작하였으며 헬리컬 앵커를 삽입/인발하여 지지력을 산정하는 연구를 진행하였고 관입토크와 앵커의 인발력의 상관관계를 도출하였다. 대형토조를 활용하여 모형시험을 수행한 결과 지반이 단단할수록 회전관입 토크가 크게 측정되었으며 이에 따른 인발저항도 크게 나왔다. 이 연구에서 수행한 실험범위 내에서는 인발저항과 관입토크는 서로 비례관계에 있음을 알 수 있었다.

• Steel and Composite Structures
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• 제23권1호
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• pp.53-66
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• 2017

Structures submitted to Fire-After-Earthquake loading situations, are first experiencing inelastic deformations due to the seismic action and are then submitted to the thermal loading. This means that in the case of steel framed structures, at the starting point of the fire, plastic hinges have already been formed at the ends of the beams. The basic objective of this paper is the evaluation of the rotational capacity of steel I-section beams damaged due to prior earthquake loading, at increased temperatures. The study is conducted numerically and three-dimensional models are used in order to capture accurately the nonlinear behaviour of the steel beams. Different levels of earthquake-induced damage are examined in order to study the effect of the initial state of damage to the temperature-evolution of the rotational capacity. The study starts with the reference case where the beam is undamaged and in the sequel cyclic loading patterns are taken into account, which represent earthquakes loads of increasing magnitude. Additionally, the study extends to the evaluation of the ultimate plastic rotation of the steel beams which corresponds to the point where the rotational capacity of the beam is exhausted. The aforementioned value of rotation can be used as a criterion for the determination of the fire-resistance time of the structure in case of Fire-After-Earthquake situations.

• Structural Engineering and Mechanics
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• 제29권1호
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• pp.17-35
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• 2008

Neglecting the real joint behaviour in frame analysis may result in unrealistic predictions of the response and reliability of steel frames. The reliability of the prediction of main joint properties according to the component method (Eurocode 3-Part 1.8) still remains open to further investigation. The first step toward the solution is to compare the theoretical expressions given in EN 1993-1-8 and the experimental results. With that goal in mind six nominally the same, but really different specimens of welded beam-to-column joints subjected to static load were tested. The specimens present a combination of nominally identical structural elements produced in different European mills. This paper provides these tests, as well as their detailed evaulation and interpretation. All three joint structural properties (rotational stiffness, moment resistance and rotation capacity) have been considered. Four models for determining the plastic resistance out of experimental Mj-${\phi}$ curves have been applied. The results that have been discussed in detail, point to the fact that EN 1993-1-8 underestimates the real structural properties of the tested type of joint, as well as to the conclusion that detailed research of this problem needs to be conducted using the probabilistic reliability methods.

• Steel and Composite Structures
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• 제33권1호
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• pp.143-162
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• 2019

A number of desirable characteristics concerning excellent durability, aesthetics, recyclability, high ductility and fire resistance have made stainless steel a preferred option in engineering practice. However, the relatively high initial cost has greatly restricted the application of stainless steel as a major structural material in general construction. This drawback can be partially overcome by introducing composite stainless steel-concrete structures, which provides a cost-efficient and sustainable solution for future stainless steel construction. This paper presents a preliminary numerical study on stainless steel-concrete composite beam-to-column joints with bolted flush endplates. In order to ensure a consistent corrosion resistance within the whole structural system, all structural steel components were designed with austenitic stainless steel, including beams, columns, endplates, bolts, reinforcing bars and shear connectors. A finite element model was developed using ABAQUS software for composite beam-to-column joints under monotonic and symmetric hogging moments, while validation was performed based on independent test results. A parametric study was subsequently conducted to investigate the effects of several critical factors on the behaviour of composite stainless steel joints. Finally, comparisons were made between the numerical results and the predictions by current design codes regarding the plastic moment capacity and the rotational stiffness of the joints. It was concluded that the present codes of practice generally overestimate the rotational stiffness and underestimate the plastic moment resistance of stainless steel-concrete composite joints.

• Tribology and Lubricants
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• 제13권4호
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• pp.47-52
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• 1997

Friction torques, electrical contact resistances and bearing temperatures were measured on high speed angular contact ball beatings for the spindle of machine tools. The test bearings ran with oil-air lubrication at the thrust loads from 320 N to 1920 N and at the rotational speed of up to 12000 rpm. Electrical contact resistances between balls and races were measured to evaluate the formation of the lubricant film in the contact area. The test results with sufficient lubrication showed that the variations of friction torques were sensitive to the thrust loads and the rotational speeds, and that the friction torques were higher than those with insufficient lubrication. With insufficient lubrication and high thrust loads, the collapse of the lubricant film was detected even at a high rotational speed. It was concluded that these high speed beatings to run in condition of fluid lubrication should require monitoring not only the temperature increase of the bearing but also the lubricant film formation in contact areas resulting from the change in the applied load and the lubricant amount.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.694-697
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• 2003

Materials with specific micro-structural shape can exhibit negative Poisson's ratio. These materials can be widely used in structural applications because of their high resilience and resistance to impact. Specially, in the field of artificial implant's material, they have many potential applications. In this study, we investigated the Poisson's ratio and the ratio(E$_{e}$/E) of the elastic modulus of rotational particle structures based on structural design variables using finite element method. As the ratio of fibril's length to particle's diameter increased and the ratio of fibril's diameter to fibril's length decreased fixing the fibril's angle with 45 degree. the negative Poisson effect of rotational particle structures increased. The ratio of elastic modulus of these structures decreased with Poisson's ratio. The results show the reasonable values as compared with the previous analytical results.s.

• 한국도로학회논문집
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• 제14권5호
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• pp.67-74
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• 2012

PURPOSES: In this study the influence factors related to abrasion resistance of interlocking concrete block have been evaluated, and comparisons between various domestic and foreign abrasion test methods was also accomplished. METHODS: The modified rotational cutting method suggested in ASTM C 944 was applied. Surface materials with different types of fine aggregate such as crushed sand, sea sand, and mixture of crushed and sea sand were tested to compare the aggregate effect for abrasion resistance. RESULTS: The different surface mixtures with various W/C ratios, mortar and fly ash ratios have been investigated for functional and economical considerations. CONCLUSIONS: This study had obtained reliable results by changing diamond blade of rotating cutter. Therefore, in order to improve the abrasion resistance of interlocking concrete block for road, a new mix design was proposed.

• 한국지반환경공학회 논문집
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• 제19권9호
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• pp.5-12
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• 2018

연동비닐하우스의 기초는 주로 수직하중을 고려하여 소형의 얕은 콘크리트 기초로 설계 시공된다. 그러나 최근 강풍과 같은 이상기후로 인하여 기초에 설계 강도 이상의 수평하중 및 인발하중이 작용하여 온실기초의 안전성 문제를 야기하고 있다. 비닐하우스 기초의 안전성을 합리적으로 평가하기 위해 지반-기초의 상호작용에 의해 발현되는 회전 및 인발강성을 평가하여야 하며 이는 상부 구조재의 안전성에도 영향을 미치는 요소가 된다. 본 연구에서는 내재해형 연동비닐하우스 규격 기초를 형상에 따라 분류하여 3개의 대표 기초 유형을 선정하고, 기초 유형별 수평하중 가력실험 및 이론 해석을 수행하였다. 실험 및 해석의 비교 분석 결과, 기초-지반 접촉면의 성질과 지반의 역학적 성질이 동일할 경우 기초는 지반과의 접촉면적비에 따라 회전저항성능에 차이를 보이는 것으로 나타났다.