• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.4
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• pp.351-359
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• 2011

In a structure, damage can occur at several scales from micro-cracking to corrosion or loose bolts. This makes the identification of damage difficult with one mode of sensing. Hence, a multi-mode actuated sensing system is proposed based on a self-sensing circuit using a piezoelectric sensor. In the self sensing-based multi-mode actuated sensing, one mode provides a wide frequency-band structural response from the self-sensed impedance measurement and the other mode provides a specific frequency-induced structural wavelet response from the self-sensed guided wave measurement. In this study, an experimental study on the pipeline system is carried out to verify the effectiveness and the robustness of the proposed structural health monitoring approach. Different types of structural damage are artificially inflicted on the pipeline system. To classify the multiple types of structural damage, a supervised learning-based statistical pattern recognition is implemented by composing a two-dimensional space using the damage indices extracted from the impedance and guided wave features. For more systematic damage classification, several control parameters to determine an optimal decision boundary for the supervised learning-based pattern recognition are optimized. Finally, further research issues will be discussed for real-world implementation of the proposed approach.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10d
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• pp.697-699
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• 2002

본 논문에서는 복합명사에 대한 색인 방법을 다각적으로 적용하여 계층적 결함 문서 클러스터링 시스템의 결과를 분석하고자 한다. 우선 한글 색인 엔진과 HAC(Hierarchical Agglumerative Clustering) 엔진에 대해서 설명하고 한글 색인엔진에서 제공되는 세가지 복합명사 분석 모드에 대해서 설명한다. 또한 구현된 클러스터링 엔진의 특징과 속도 향상을 위한 기법 등을 설명한다. 실험에서는 다양한 요소를 가지고 클러스터링된 문서 집합에 대한 분석 결과를 보인다. 실험 결과에 대한 분석에서 복합명사에 대한 색인 방법이 문서 클러스터링의 결과에 직접적인 영향을 준다는 것을 보여준다.

• Journal of the KSME
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• v.34 no.5
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• pp.372-383
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• 1994

복합재료의 피로특성과 해석방법에 대하여 간략하게 살펴보았다. 복합재료의 피로현상에 대한 이해의 폭이 넓어짐에 따라 앞에서 소개한 방법외에 파단모드별 연구, 역학에 기초를 둔 해석법, 유한요소법의 적용, 혼성복합재료(hybrid composites)의 피로수명 예측 등의 다양한 연구가 진 행중이나, 아직 정립된 피로수명 예측식은 없다고 말할 수 있다. 재료의 손상을 나타내는 매개 변수로서 강성변화의 유용성이 밝혀진 상태이므로 앞으로 이를 이용하여 실제의 현상을 표현할 수 있는 손상함수의 구성과 피로수명 예측에 관한 연구가 수행되어야 한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.83-90
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• 2016

Ramjet mode combustion test was performed for a dual-mode ramjet engine model. The engine model consists of an air intake, a combustor and a nozzle. The combustor in the model has a large backward-facing step, designed to be used as a part of a rocket-based combined cycle engine. The test was performed at the flight speed of Mach 5 and the altitude of 24 km. Strong combustion was established only when the fuel was injected from both of the bottom-side and cowl-side wall. When the total fuel stoichiometric ratio was 1.0, distributed as 0.5 on the cowl side and 0.5 on the bottom side, the flow became subsonic at some portion in the combustor by thermal choking, i.e., ramjet mode was established for this condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.457-464
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• 2006

Fiber-reinforced composite materials due to their high specific strength, high stiffness and light weight are becoming increasingly used in many engineering industry, especially in the aerospace, marin and civil, etc. In this paper, the buckling load and mode shapes of composite laminates with elliptical cross-section including transverse shear deformations are analyzed. For solving this problems, a versatile flat shell element has been developed by combining a membrane element with drilling degree-of-freedom and a plate bending element. Also, an improved shell element has been established by the combined use of the addition of enhanced assumed strain and the substitute shear strain fields. The combined influence of shell geometry and elliptical cross-sectional parameter, fiber angle, and lay-up on the buckling loads of elliptical cylinder is examined. The critical buckling loads and mode shapes analyzed here may serve as a benchmark for future investigations.

• Magazine of the Korea Concrete Institute
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• v.9 no.4
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• pp.187-196
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• 1997

시멘트를 기초로하는 복합재료의 파괴거동은 주균열이 진행하기 이전에 파괴진행영역이라고 하는 미세균열대가 콘크리트 내부에 형성고기 때문에 선형파괴역하게 입각하여 해석하게 되면 실험치와 상당한 차이를 나타낸다. 이러한 문제점을 해결하기 위해 가상균열모델이나 균열띠 모델, 두 파라메터 파괴모델 등 비선형해석에 따른 여러 파괴역학모델들이 제안되었으나 이들 모델들은 2차원 해석에 근거를 두고 있기 때문에 구조체의 두께 방향으로 동일한 균열이 형성되며, 특히 콘크리트 실험에서 관찰되는 비연속적 균열발생에 대해서 설며이 어려웠다. 이에 본 연구는 콘크리트를하나의 다종복합체로 가정하고 연립변형모드 및 진행파괴모드 방향으로 구성재료를 배열한 상태에서 가상균열 이론에 근거한 비선형해석방법으로 모델링하였다. 진행파괴모드로 구성재료를 배열하면 강성이 높은 구성재료를 통과하여 균열이 진행될 때 균열선단으로부터 분포된 응력이 상층의 허용인장강도를 초과하게 되어 균열이 발생되며 이러한 균열은점진적인 균열진행과는 달리 비연속 동시 발생 균열ㄹ로 나타났다. 본 연구는 진행파괴모드에서의 파괴 해석 방법과연립변형모드에서의 해석 방법을 제시하였으며, 해석결과를 실험결과와 비교함으로써 검증하였다.

• Journal of Climate Change Research
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• v.2 no.3
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• pp.175-189
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• 2011

In this research, we describe the methodology and the quantification about GHG reduction effects, expected by optimization of operation mode according to establishing additional heat storage system of Bundang Combined Cycle Power Plant. As an intermediate form of General Combined Cycle Power Plant and Heat supply only district heating plant, Bundang Combined Cycle Power Plant(and Ilsan, Anyang, Bucheon) is possible to satisfy demand for the electrical load and thermal load capacity at the same time through changes to the operation mode itself. Therefore, through the operating transition of high-efficiency mode that the condenser cooling water is recovered and supplied to district heat and cooling, establishing additional heat storage system have flexible supply ability at the power and heat market. In this research, We calculated using the operating performance for the last three years(2008~2010) and efficiency of each mode-specific values. As a result, GHG reduction effects were calculated as $97.95kg_{-}CO_2/Gcal$ per heat energy 1 Gcal supplied at the heat storage system and we expected emmision reduction effect about $13,500Ton_{-}CO_2/yr$.

• Journal of the Korean Society for Advanced Composite Structures
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• v.1 no.2
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• pp.36-43
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• 2010

In this study, the buckling loads and mode shapes characteristic of circular and non-circular(elliptical) closed composite shells were analyzed. To analyses the buckling behaviors, we develop and report an improved generalized shell element called 4EAS-FS through a combination of enhanced assumed strain and the substitute shear strain fields. A flat shell element has been developed by combining membrane element with drilling degree-of-freedom and a plate bending element. The combined influences of length, thicknesses, cross-sectional parameters, and fiber-angle on the critical buckling loads and mode shapes of circular and non-circular(elliptical) closed shells are examined.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.2
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• pp.115-128
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• 2006

A technical analysis of current scramjet and combined-cycle engine is presented. Substantial research has been pursued to characterize the operation mechanism of scramjet propulsion, especially in the areas of flame stabilization and system integration, dramatically over the years in support of both military and space access application. Major technology that had significant impact on the maturation of scramjet propulsion technology are dual combustion ramjet, dual mode ramjet, and combined cycle engine to cover a typical wide rage of flight, up to flight Mach number 10. Notable are the fundamental and practical techniques, for instance, scram propulsion itself, thermal relaxation and protection using endothermic fuel and/or CSiC composit materials, and design/manufacture of movable intake and nozzle, to realize high speed propulsion system in near future.

• Journal of Korean Society of Steel Construction
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• v.18 no.1
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• pp.93-100
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• 2006

A simple but precise method of calculating the natural vibration frequencies of composite laminated plates with all-simple support and under axial loadings is presented herein. This method uses deflection influence surfaces, which can be obtained by any method for vibration analysis and member due to the inertia force under resonance condition. Beginning with an initially guessed mode shape, the exact mode shape is obtained by the process similar to iteration. In this paper, equations are given for the case of special orthotropic laminates. The same equations, however, can be used for any laminate as long as ${B_1_6}$, ${B_2_6}$, ${D_1_6}$, and ${D_2_6}$ are negligible as the number of plies increases. Some laminates that possess such properties are presented in the paper.