• Journal of Ocean Engineering and Technology
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• v.16 no.6
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• pp.55-59
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• 2002

Delamination means that cracking occurs on the interface layer between composite laminates. In this paper, to predict the delamination growth in composite laminates subjected to low-velocity impact, the unit load method was introduced, and an eighteen-node 3-D finite element analysis, based on assumed strain mixed formulation, was conducted. Strain energy release rate, necessary to determine the delamination growth, was calculated by using the virtual crack closure technique. The unit load method saves the computation time more than the re-meshing method. The virtual crack closure technique enables the strain energy release rate to be easily calculated, because information of the singular stress field near the crack tip is not required. Hence, the delamination growth in composite laminates that are subjected to low-velocity impact can be efficiently predicted using the above-mentioned methods.

• Composites Research
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• v.13 no.1
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• pp.11-24
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• 2000

In this paper, finite thickness and tow phase effects on the mechanical behavior were studied numerically for plain weave textile composites. Unit cell analysis based on a superposition method was employed to simulate uniaxial tensile loading condition and macro-element post-processor was used to reduce computer resource requirement. The effective moduli and micro-stress distribution were calculated for finite thick plain weave composites with phase shifts. Single layer and infinitely thick configurations were also considered for comparison.

• Bulletin of the Society of Naval Architects of Korea
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• v.33 no.4
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• pp.13-20
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• 1996

해양공간 활용을 위해 예상되는 부유식 해양구조물은 단위구조들이 결합된 형태의 초대형 구조물로서 단위 구조물간의 탄성변형 문제가 매우 중요시되고 있으며 이에 따라 단위구조물간의 상호작용이 고려된 유체력 산출과 탄성응답이 고려된 해석법의 개발이 전세게적으로 활발히 이루어지고 있다. 독립 부유구조물 자체의 크기가 대형화될 때 발생하는 탄성 변형 또한 구조 해석 및 진동관점에서 중요한 고려사항이며, 이는 조선공학분야에서 유탄성 해석기법에 바탕을 두고 연구가 활발히 진행중이다. 본 고에서는 부유구조물의 설계에 있어 핵심기술중 하나인 파랑응답 해석기술의 현황에 대해 살펴보고 현재 한국기계연구원에서 수행중인 국책연구개발사업 "해양공간이용 대형 복합플랜트 개발"의 세부과제인 "부유구조물 파랑응답 해석기법 개발"의 추진내용에 대해 환경 하중/응답해석기술, 계류시스템 설계/해석기술, 유탄성응답 해석기술로 나누어 소개하고자 한다. 해석기술로 나누어 소개하고자 한다.

• Composites Research
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• v.30 no.6
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• pp.331-337
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• 2017

The composite lattice structures have advantages of high specific stiffness and strength and are mainly applied to the structures of launch vehicles that carry the compressive load. However, since these structures are manufactured by filament winding technology, there are some defects and voids found in the knots. For these reasons, the stiffness and strength of the lattice structures have to be compared with finite element model for predicting design load. But, the full scale test is difficult because time and space are limited and the shape of structure is complex, and hence the simple and reliable test methods for examination of stiffness are needed. In this paper, subelements of composite lattice structures were prepared and compressive and bending test were conducted for examination of stiffness of helical and hoop rib. Test methods for subelements of composite lattice structures that has curved and twisted shape were supposed and compared with finite element analysis results.

• Journal of the Korean Geotechnical Society
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• v.27 no.9
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• pp.77-86
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• 2011

The stress condition mainly dominates the thermal conductivity of soils whereas governing factors such as unit weight and porosity suggested by empirical correlations are still valid. The 3D thermal network model enables evaluation of the stress-dependent thermal conductivity of particulate materials generated by discrete element method (DEM). The relationship among dominant factors is analyzed based on the coordination number and porosity determined by stress condition and thermal conductivity of pore fluid. Results show that the variation of thermal conductivity is strongly attributed to the enlargement of inter-particle contact area by loading history and pore fluid conductivity. This study highlights that the anisotropic evolution of thermal conductivity depends on the directional load and that the particle-scale mechanism mainly dictates the heat transfer in soils.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.3
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• pp.87-95
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• 1998

This paper presents the method for the automatic tuning of a design weighting polynomial parameter of a generalized minimum-variance stochastic self tuning controller which adapts to changes in the system parameters with time delays and noises. The self tuning effect is achieved through the recursive least square algorithm at the parameter estimation stage and also through the Robbins-Monro algorithm at the stage of optimizing a design weighting polynomial parameters. The proposed self tuning method is simple and effective compared with other existing self tuning methods. The computer simulation results are presented to illustrate the procedure and to show the performance of the control system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.3
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• pp.311-321
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• 2020

In this study, coefficient of variation for the seismic load effect on the segment lining was calculated. The statistical characteristics of the soil property were analyzed for the probability characteristics of domestic soil. In order to calculate the coefficient of variation for the seismic load effect, the MCS technique was applied, and the closed-form equation was applied to calculate the seismic load effect. As a result of calculating the coefficient of variation, the coefficient of variation of the seismic load effect on the weathered soil was analyzed in the range of 0.06~0.15, and the coefficient of variation was judged to be used as basic data for designing the limit state of the shield tunnel on seismic condition.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.2
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• pp.245-256
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• 2000

A moment-curvature relationship to simulate the behavior of reinforced concrete beam under cyclic loading is introduced. Unlike previous moment-curvature models and the layered section approach, the proposed model takes into consideration the bond-slip effect by using monotonic moment-curvature relationship constructed on the basis of the bond-slip relation and corresponding equilibrium equation at each nodal point. In addition, the use of curved unloading and reloading branches inferred from the stress-strain relation of steel gives more exact numerical result. The advantages of the proposed model, comparing to layered section approach, may be on the reduction in calculation time and memory space in case of its application to large structures. The modification of the moment-curvature relation to reflect the fixed-end rotation and pinching effect is also introduced. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed model.

• 어항어장
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• s.2
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• pp.86-127
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• 1988

버트리스 푸팅 케슨(Buttress footing caisson) 및 상형 푸팅 케슨의 역학특성을 해명하고 구조설계법을 검토할 목적으로 재하실험을 실시했다. 재하실험에는 배근의 제약등을 고려해서 실구조물의 1/4정도의 대형모형공시체를 사용해서 푸팅부를 중심으로 해석하기위해 푸팅에 선분포하중을 재하했다. 유한요소법에 따른 선형구조해석을 실시하여 변위, 단면력과 한계상황설계법에서의 산정식에서 얻어진 단면내력과를 비교하여 동설계법의 케슨구조물에 대한 적용성에 관하여 고찰했다. 이 보고로써 얻어진 주요한 결론은 아래와 같다. (1) 재하실험에 의하면 버트리스 푸팅공시체의 파괴형식은 버트리스부의 철근에 연한 부착할열파괴였다. 또 상형푸팅공시체에서는 푸팅부의 내면전단파괴였다. 양구조물을 설계할 때는 종래의 면외력만의 검토뿐아니라 면내력도 적절히 평가할 필요가 있다. (2) 양공시체 함께 푸팅 케슨본체와의 접합부 및 푸팅과 상자옆쪽의 벽과의 접합부에 변형이 일어나 종래의 판구조설계에서 가정하고 있는 판주변의 고정조건이 만족되지 않았다. 따라서 케슨구조물의 구조해석에서 구조전체계를 취급할 필요가 있고 부재단위에서는 단면력을 과대 또는 과소로 산정할 우려가 있다. (3) 철근강복시정도까지는 구조전체계를 모델화한 유한요소법에 의한 선형구조해석결과와 실험결과가 잘 일치했다. (4) 한계상태설계법에서의 굽음내력, 전단내력 및 구열폭의 산정식은 실험결과와 비교해서 어느쪽이나 안전측의 치를 부여했다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.5
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• pp.1421-1433
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• 2014

In this study, appropriate probability distribution and parameter estimation method were selected to perform snowfall frequency analysis. Generalized Extreme Value (GEV) and Probability Weighted Moment Method (PWMM) appeared to be the best fit for snowfall frequency analysis in Korea. Snowfall frequency analysis applying GEV and PWMM were performed for 69 stations in Korea. Peak snowfall corresponding to recurrence intervals were estimated based on frequency analysis while snow loads were calculated using the estimated peak snowfall and specific weight of snow. Design snow load map was developed using 100-year recurrence interval snow load of 69 stations through Kriging of ArcGIS. The 2009 Korean Building Code and Commentary for design snow load was assessed by comparing the design snow loads which calculated in this study. As reflected in the results, most regions are required to increase the design snow loads. Thus, design snow loads and the map were developed from based on the results. The developed design snow load map is expected to be useful in the design of building structures against heavy snow loading throughout Korea most especially in ungaged areas.