• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.94-100
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• 2021

To improve the productivity of cargo containment construction for a membrane LNG carrier, it is important to shorten the installation period and process of the scaffolding system, which is a construction workbench of a cargo containment for a membrane LNG carrier. As an effective method, opinions are being gathered to enlarge the lifting unit from the existing two stages to eight stages. On the other hand, the stresses around the pin and hole will increase significantly because of the increase in lifting load according to the large size of the module. The purpose of this study was to establish a new large module-lifting plan by introducing TRIZ to solve these problems. This study adopted a method to utilize 40 inventive principles, which is one of the various problem-solving tools of TRIZ. First, technical contradictions were derived, the engineering parameters were selected. Second, efficient inventive principles were selected to overcome the technical contradictions using a contradiction matrix. Finally, the general and specific solutions were derived through the selected inventive principle, and structural analysis confirmed that the stress generated in the structure was low. The utility of TRIZ was confirmed by the successful lifting of large modules using the established lifting method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.233-239
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• 2013

In this paper, a method of combining numerical analyses and experimental tests is used to evaluate fracture toughness of copper thin films of $15{\mu}m$ thickness. Far-field loadings of a global-local finite element model are inversely estimated by matching crack opening profiles in experiments with numerical results. The fracture toughness is then evaluated using the J-integral for cracks in thin films under far-field loadings. In experiments, Cu thin films attached to Aluminum sheets are loaded indirectly, and crack opening profiles are observed by microscope camera. Stress versus strain curves of Cu thin films are obtained through micro-tensile tests, and the grain size of Cu thin films is observed by TEM analysis. The results show that the fracture toughness of Cu thin films with $500nm{\sim}1{\mu}m$ sized grains is $6,962J/m^2$.

• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.169-176
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• 2011

In this study, the flexural test for reinforced high performance fiber reinforced cementitious composites (R/HPFRCC) members has been conducted in order to investigate the flexural behavior including the effect of an ordinary tensile reinforcing bar. Through the test, it was observed that the flexural strength increased due to the stable tensile stress transfer of HPFRCC, even up to the ultimate state. In addition, no localized crack appeared until the yielding of the reinforcement. From the layered section analysis of the tested members, it was found that the analysis with the tensile model obtained from the tension stiffening test showed better agreement with the flexural test results, whereas the analysis with direct tension test results overestimated the flexural capacity. Through the experimental and analytical studies, two flexural failure modes have been defined in this paper; concrete crushing at the top compression layer or tensile failure at the bottom tensile layer of the beam section. Based on these two flexural failure modes, a simple formula that estimates the ultimate flexural strength of the member has been proposed in this paper. The proposed equations can be useful in a design and an analysis of R/HPFRCC members.

• Journal of Korean Society of Steel Construction
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• v.11 no.2 s.39
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• pp.213-222
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• 1999

Elastic-plastic methods have been used for the better prediction of the actual behavior of continuous-composite plate girder bridges in the overload and maximum load analysis. The structural evaluation using ALFD(Alternate Load Factor Design) uses the elastic-plastic analysis. The plastic rotations that remain after the load is removed can be occurred by the yielding locations of the maximum moment section. This situation can occur due to the residual stresses even if the moment is below the theoretical yield moment. The local yielding causes positive automoments that assure elastic behavior under subsequent overloads. In this study, the automoments at the piers occurred due to the unit plastic rotations and other locations were calculated by the conjugate-beam method and three-moment equation, using the nine design span with progressively smaller pier sections. The automoments were determined by the developed computer programs in this study in which the moments and plastic rotations from the continuity and moment-inelastic rotation relationships must be equal. And also the ratings of 3-span continuous composite plate girder bridges with non-compact section were carried out according to the Korean Highway Bridge Specification.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.630-648
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• 1992

The minimum weight design for simply-supported isotropic or symmetrically laminated stiffened cylindrical shells subjected to various loads (axial compression or combined loads) is studied by a nonlinear mathematical search algorithm. The minimum weight design in accomplished with the CONMIN optimizer by Vanderplaats. Several types of buckling modes with maximum allowable stresses and strains are included as constraints in the minimum weight design process, such as general buckling, panel buckling with either stingers or rings smeared out, local skin buckling, local crippling of stiffener segments, and general, panel and local skin buckling including stiffener rolling. The approach allows the consideration of various shapes of stiffening members. Rectangular, I, or T type stringers and rectangular rings are used for stiffened cylindrical shells. Several design examples are analyzed and compared with those in the previous literatures. The unstiffened glass/epoxy, graphite/epoxy(T300/5208), and graphite/epoxy aluminum honeycomb cylindrical shells and stiffened graphite/epoxy cyindrical shells under axial compression are analyzed through the present approach.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.321-328
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• 2006

In this study, the deformation oi wall thinning elbow is measured and the position of the internal thinning defect is found out by shearography. Shearography is an optical method which has applied to nondestructive testing (NDT) and the strain/stress and deformation analysis. This technique has the merit of the directly measuring the first derivative of displacement with sensitivity which can be adjusted by handling the tilt mirror in the interferometer. In this paper, we tested carbon steel pipe locally wall thinned and loaded internal pressure and the shearography was applied to measure the out-of-plane deformation of wall thinning elbow and to investigate the internal thinning defect of it. From the results, it was confirmed that this technique is proper to the practical application on the pipe line system with internal defect.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.605-605
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• 2012

최근 통계자료에 의하면 국내 제방붕괴 유형 중 11.5%가 제체 불안정에 의한 붕괴로 보고되고 있다. 홍수시 노후화된 제방이 붕괴하여 발생하는 인명 및 재산피해는 점차 증가하고 있는 상황이어서, 이에 대한 제방 시설물의 보강 및 안전관리 대책이 필요한 상황이다. 하천시설물 주변의 흐름특성에 의하여 세굴이 발생할 수 있는 지점에는 보호공을 설치하여 시설물의 안정성을 확보하도록 하천설계기준 해설(2009)에서 제안하고 있다. 그러나 구조물을 보완하는 보호공의 공종 및 규격 등을 설계하기 위한 세부적인 설계지침이 미흡하여 외국의 연구 또는 설계사례를 참고하여 국내 하천에 적용하고 있는 상황이다. 해외의 연구사례를 살펴보면, 설계공식에 적용된 설계인자인 유속 및 수심 등을 1차원 단면평균값을 활용하는 경우가 많아서 복잡한 하천의 흐름특성을 반영하기에 미흡한 상황이다. 본 연구에서는 국내 하천해석에서 주로 활용되고 있는 수치모형을 이용하여 실험수로의 흐름을 재현하고 수리실험을 통하여 관측한 유속 및 수위분포 결과와 비교하였다. 2차원 수치모형으로는 RMA2, CCHE2D, FLUMEN 등의 상용모형과 최근 연구가 활발히 진행되고 있는 Approximate Riemann 기법을 적용하여 개발된 유한체적모형을 적용하였다. 제방 부근에서 형성되는 흐름을 상세하게 모의하기 위하여 국내 하천시설물 설계에서 많이 활용되고 있는 FLOW-3D 모형을 적용하여 3차원 모의결과와 수리실험결과를 비교하였다. 수리실험에서 관측된 사석호안공의 이탈시 흐름현상을 재현하여 호안공 이탈에 영향을 미치는 국부유속 및 전단응력을 산정하여 호안설계에 적합한 설계인자를 분석하였다. 연구결과를 활용하여 사석호안공 설계 기법에 적용되는 수치모형을 통하여 산정되는 설계인자의 정확성을 향상시킴으로써, 정량적이고 합리적인 사석호안공 설계기법개발에 도움이 될 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.251-251
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• 2021

최근 기후변화로 인한 집중호우의 영향으로 홍수 시 댐으로의 유입량이 설계 당시보다 증가하여 댐의 안전성 확보가 필요하다(감사원, 2003). 이에 건설교통부(2003)는 기후변화와 댐 노후화에 대비하여 치수능력증대사업을 추진하여 댐의 홍수배제능력을 확보하였고, 환경부(2020)에서는 40년 이상 경과된 댐을 대상으로 스마트 안전관리체계 구축을 통한 선제적 보수보강, 성능개선 및 자산관리로 댐의 장수명화를 목적으로 댐의 국가안전대진단을 추진하고 있다. 이에 본 연구에서는 댐 시설(여수로)의 노후도 평가 시 활용 될 수 있는 여수로 표면손상 원인규명에 대하여 3차원 수치모형(FLOW-3D 및 COMSOL Multiphysics)을 통해 검토하고자 한다. 연구대상 댐은 𐩒𐩒댐으로 지형 및 여수로를 구축하였으며, 계획방류량(200년 빈도) 및 최대방류량(PMF) 조건에서 모의를 수행하였다. 수치모의 계산의 정확도 검토를 위하여 Baffle의 설치를 통하여 시간에 따른 유량의 변화를 설계 값과 비교하였고 오차가 1.0% 이내를 만족하는 것을 확인하였다. 여수로 표면손상의 다양한 원인 중 기존연구(USBR, 2019)를 통하여 공동침식(Cavitation Erosion) 및 수력잭킹(Hydraulic Jacking)에 초점을 두었으며 방류조건 별 공동지수(Cavitation Index)산정을 통하여 공동침식 위험 구간을 확인하였다. 이음부의 균열 및 공동으로 인한 표층부 콘크리트의 탈락현상을 가속화시키는 수력잭킹 검토를 위하여 국부모형을 구축하였고 음압력(Negative Pressure), 정체압력(Stagnation Pressure), 양압력(Uplift Pressure)의 분포를 확인하였다. 최종적으로 COMSOL Multiphysics를 통하여 압력분포에 따른 구조해석을 수행하여 폰 미세스(Von Mises) 등가응력 및 변위를 검토하여 콘크리트의 탈락가능성을 확인하였다. 본 연구는 여수로 공동부 및 균열부에서의 손상메커니즘을 확인할 수 있는 기초적인 연구이지만 향후에는 다양한 지형조건 및 흐름조건에서의 압력분포 분석 및 유체-구조물 상호작용(Fluid-Structure Interaction, FSI)모의를 수행한다면 구조물 노후도 및 잔존수명 평가에 필요한 손상한계함수 도출이 가능할 것으로 기대된다.

• Composites Research
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• v.15 no.4
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• pp.23-31
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• 2002

The two dimensional size effect of specimen gauge section ($length{\;}{\times}{\;}width$) was investigated on the compressive behavior of a T300/924 $\textrm{[}45/-45/0/90\textrm{]}_{3s}$, carbon fiber-epoxy laminate. A modified ICSTM compression test fixture was used together with an anti-buckling device to test 3mm thick specimens with a $30mm{\;}{\times}{\;}30mm,{\;}50mm{\;}{\times}{\;}50mm,{\;}70mm{\;}{\times}{\;}70mm{\;}and{\;}90mm{\;}{\times}{\;}90mm$ gauge length by width section. In all cases failure was sudden and occurred mainly within the gauge length. Post failure examination suggests that $0^{\circ}$ fiber microbuckling is the critical damage mechanism that causes final failure. This is the matrix dominated failure mode and its triggering depends very much on initial fiber waviness. It is suggested that manufacturing process and quality may play a significant role in determining the compressive strength. When the anti-buckling device was used on specimens, it was showed that the compressive strength with the device was slightly greater than that without the device due to surface friction between the specimen and the device by pretoque in bolts of the device. In the analysis result on influence of the anti-buckling device using the finite element method, it was found that the compressive strength with the anti-buckling device by loaded bolts was about 7% higher than actual compressive strength. Additionally, compressive tests on specimen with an open hole were performed. The local stress concentration arising from the hole dominates the strength of the laminate rather than the stresses in the bulk of the material. It is observed that the remote failure stress decreases with increasing hole size and specimen width but is generally well above the value one might predict from the elastic stress concentration factor. This suggests that the material is not ideally brittle and some stress relief occurs around the hole. X-ray radiography reveals that damage in the form of fiber microbuckling and delamination initiates at the edge of the hole at approximately 80% of the failure load and extends stably under increasing load before becoming unstable at a critical length of 2-3mm (depends on specimen geometry). This damage growth and failure are analysed by a linear cohesive zone model. Using the independently measured laminate parameters of unnotched compressive strength and in-plane fracture toughness the model predicts successfully the notched strength as a function of hole size and width.

• Korean Journal of Agricultural Science
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• v.23 no.1
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• pp.25-38
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• 1996

To investigate the stability problem of irrigation-drainage channel excavation slope on soft ground, analyzed the behavior of the soft ground with excavation slope by the limit equilibrium method and the finite element method, and compared with field tests. The results of this study were summarized as follows; 1. When rapid drawdown the water level, the crack was occurred by the effect of the excess pore water pressure, and the pore water pressure was decreased slowly. 2. As the width of excavation was larger, the crack width was larger. And, excavated depth was deeper, the progressive failure was appeared. 3. When the soft ground excavation was small-scale, the minimum safety factor was more effected by cohesion(1.0, 1.5, 2.0, 2.5, 3.0) than excavated slope inclination(1:l, 1:1.5, 1:2). 4. As excavation was progressed, the settlement occurred on the top-slope due to plastic domain, and heaving was occurred at the bottom of excavation. 5. The maximum shear stress was appeared greatly as the base part of slope went down. Because of the increase of the maximum shear stress, tension area occurred and local failure possibility was increased. 6. As the excavation depth was increased, the maximum shear strain was appeared greatly at the base of slope and distribution pattern was concentrated beneath the middle of slope.