• 한국산림과학회지
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• 제108권1호
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• pp.50-58
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• 2019

우리나라에서 발생된 땅밀림지의 지형특성을 분석하여 땅밀림지에 대한 지형적인 기초자료를 제공하기 위하여 실시하였다. Aspect ratio가 1.00 미만인 땅밀림지는 전체 37개소 중 17개소(약 46.0 %)로 0.37 ~ 0.92의 범위를 나타내었다. 또한 Aspect ratio가 2.00 미만인 경우는 전체 37개소 중 36개소(약 97.0 %)이었다. 종단형상비가 1.00 미만인 땅밀림 지역은 총 37개소 중 15개소(약 41.0 %)이었으며, 1.00 이상인 땅밀림지는 22개소(약 59.0 %)이었다. 우리나라에서 발생한 전체 37개소의 땅밀림지 중 평면형지형은 말발굽형이 가장 많은 것으로 나타났다. 또한 미세지형은 철(凸)상대지상 지형이 가장 많은 것으로 나타났다. 땅밀림지역의 미세지형의 등고선 간격을 평균한 결과 29.4(9.5 ~ 83.2)m이었으며, 땅밀림지 내에서 미세지형을 제외한 땅밀림지 내의 평균등고선 간격은 24.3(14.4 ~ 59.4)m로 미세지형이 5.1(4.9 ~ 23.8)m 더 넓게 나타났다. 우리나라에서 발생한 땅밀림지 내에서 미세지형의 평균 등고선 간격과 미세지형을 제외한 평균 등고선 간격의 T-test 분석 결과 5 % 수준에서 유의한 것으로 나타났다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.112-117
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• 2003

The purpose of this work is to general approach to numerically simulating wear in rolling and sliding contact area between wheel and rail interface based on the analysis of dynamics with general MBS package. A simulation scheme is developed that calculates the wear at a detailed level. The estimation of material removal follows Archard's wear equation which states that the reduction of volume is linearly proportional to the sliding distance, the normal applied load and the wear coefficient and inverse proportional to hardness. The main research application is the wheel-rail contact of Korea High Speed Railway.

• 비파괴검사학회지
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• 제19권2호
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• pp.110-117
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• 1999

크리프 손상을 단계적으로 받은 순수 구리 시편에 대하여 손상 진전에 따른 기공의 미시구조 변화를 관찰하고 초음파 속도와 주파수 의존 진폭 스펙트럼 및 감쇠를 측정하였다. 손상 진전에 따른 입계기공의 비등방적 성장으로 인하여 하중축에 대하여 세 방향으로 측정한 속도는 이방성 거동을 보였다. 최대 2%의 기공에 대하여 종파와 횡파는 각각 11%와 4%의 속도 감소를 보였으며, 기공량의 증가와 함께 비선형적인 감소 경향을 보였다. 진폭 스펙트럼은 기공량이 증가함에 따라 고주파수 성분이 감소하고 중심 주파수가 저주파수로 이동하였으며, 감쇠는 사용 주파수 범위에서 거의 선형적인 거동을 보였다. 기공량의 정량적 비파괴평가 파라미터로서 정규화 속도, 진폭 스펙트럼의 중심 주파수, 감쇠 기울기를 선정하였으며 기공량과의 상관관계를 제시하였다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2005년도 춘계학술발표회
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• pp.521-522
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• 2005

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.355-358
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• 2005

In this paper, an actual behavior of the pylon of Seohae Grand Bridge which is a cable stayed bridge and has been constructed 4 years ago was analyzed by using data acquisition system. As a result, the pylon of cable stayed bridge behaved normally with respect to the change of temperature. The annual displacement of the top of pylon(PY1) ranged from -71.4mm to +181.7mm in the longitudinal direction of the bridge. In the case of the longitudinal displacement, the displacement of PY1 was bigger than that of PY2 because PY1 is movable and PY2 is fixed in terms of the constraint condition of super structure. For the long term, PY1 will be sloped gently to the direction of Dangjin and PY2 will be also sloped gently to the direction of Pyongtaek by the effect of creep and shrinkage in the case of the longitudinal direction. The result of structural analysis showed good agreement with the result mentioned above.

• Structural Engineering and Mechanics
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• 제61권1호
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• pp.143-160
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• 2017

The paper studies the attenuation of the axisymmetric longitudinal waves propagating in the bi-layered hollow cylinder made of linear viscoelastic materials. Investigations are made by utilizing the exact equations of motion of the theory of viscoelasticity. The dispersion equation is obtained for an arbitrary type of hereditary operator of the materials of the constituents and a solution algorithm is developed for obtaining numerical results on the attenuation of the waves under consideration. Specific numerical results are presented and discussed for the case where the viscoelasticity of the materials is described through fractional-exponential operators by Rabotnov. In particular, how the rheological parameters influence the attenuation of the axisymmetric longitudinal waves propagating in the cylinder under consideration, is established.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.1326-1331
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• 2006

The precast concrete deck is one of suitable solutions for replacement and new construction in urban area. However, the precast concrete deck could be a weak point of the steel plate girder bridges structurally due to the connections between precast panels in the longitudinal direction. Thereafter, it is necessary for improvement of durability and load carrying capacity to introduce the prestress force in the longitudinal direction Some cracks of connections at the precast concrete deck may be occurred due to live loads, the difference of temperature and long-term effects. The shrinkage and creep of concrete may significantly affect long-term behaviors which occur tensile stresses at the precast concrete deck of steel plate girder bridges. In this study, the time-dependant analysis program has been developed to determine the initial prestress force in the longitudinal direction considering loss of stress at the precast concrete deck. Also it has been estimated the initial prestress force by construction stages and shapes of girder.

• 대한기계학회논문집A
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• 제34권1호
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• pp.61-65
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• 2010

두께방향으로 분극처리되어 있는 상업용 PZT 웨이퍼가 폐쇄회로와 개방회로의 두 가지 전기적 경계조건에서 길이 방향으로 일정한 크기의 인장하중을 받는다. 하중과정 동안 두께 방향으로의 전기밀도와 평면내 변형률의 시간에 따른 변화를 측정한다. 두 가지 전기적 경계조건에서의 서로 다른 거동 특성을 시편 내부에서 발생하는 전기장과 분극역전 현상으로 설명한다. 마지막으로 관측된 크립 거동을 예측하기 위한 정규분포 형식을 가지는 자유 에너지 함수를 도입하고 모델의 예측과 실험결과를 비교한다.

• Steel and Composite Structures
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• 제6권3호
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• pp.237-255
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• 2006

This paper presents a novel analytical formulation for the analysis of composite beams with partial shear interaction stiffened by a bolted longitudinal plate accounting for time effects, such as creep and shrinkage. The model is derived by means of the principle of virtual work using a displacement-based formulation. The particularity of this approach is that the partial interaction behaviour is assumed to exist between the top slab and the joist as well as between the joist and the bolted longitudinal stiffening plate, therefore leading to a three-layered structural representation. For this purpose, a novel finite element is derived and presented. Its accuracy is validated based on short-and long-term analyses for the particular cases of full shear interaction and partial shear interaction of two layers for which solutions in closed form are available in the literature. A parametric study is carried out considering different stiffening arrangements to investigate the influence on the short-and long-term behaviour of the composite beam of the shear connection stiffness between the concrete slab and the steel joist, the stiffness of the plate-to-beam connection, the properties of the longitudinal plate and the concrete properties. The values of the deflection obtained from the finite element simulations are compared against those calculated using the effective flexural rigidity in accordance with EC5 guidelines for the behaviour of elastic multi-layered beams with flexible connection and it is shown how the latter well predicts the structural response. The proposed numerical examples highlight the ease of use of the proposed approach in determining the effectiveness of different retrofitting solutions at service conditions.

• 한국안전학회지
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• 제24권2호
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• pp.17-22
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• 2009

Thermal stress and elastic creeping stress analysis was conducted by finite element method to simulate start-up process of a boiler header of 500MW standard fossil power plant. Start-up temperature and operating pressure history were simplified from the real field data and they were used for the thermal stress analysis. Two kinds of thermal stress analysis were considered. In the first case only temperature increase was considered and in the second case both of temperature and operating pressure histories were considered. In the first analysis peak stress was occurred during the temperature increase from the room temperature. Hence cracking or fracture may occur at the temperature far below the operating maximum temperature. In the results of the second analysis von Mises stress appeared to be higher after the second temperature increase. This is due to internal pressure increase not due to the thermal stress. When the stress components of radial(r), hoop($\theta$) and longitudinal(z) stress were investigated, compression hoop stress was occurred at inner surface of the stub tube when the temperature increased from room temperature to elevated temperature. Then it was changed to tension hoop stress and increased because of the operating pressure. It was expected that frequent start-up and shut-down operations could cause thermal fatigue damage and cracking at the stub tube hole in the header. Elastic-creeping analysis was also carried out to investigate the stress relaxation due to creep and stabilized stress after considerable elapsed time. The results could be used for assessing the creep damage and the residual life of the boiler header during the long-tenn service.