• 한국세라믹학회지
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• 제41권1호
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• pp.1-8
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• 2004

The microstructural features and mechanical behavior of directionally solidified $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fibers after extended beat treatment in oxidizing environment were investigated. The fiber was grown continuously by an Edge-defined Film-fed Growth (EFG) technique. The microstructure was characterized using X-Ray Diffraction (XRD) and Scanning Electron Microscopy(SEM). The microstructure of the fiber in the as-fabricated state consists of highly oriented colonv and fine lamellar microstructure along the fiber axis. Tensile strength of the $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber remained unchanged with heat treatment at temperatures between $1200^{\circ}C$ and $1500^{\circ}C$ up to 300h. The weibulls modulus remained fairly constant after extended thermal exposure. The fracture toughness and crack propagation behavior were investigated. The fracture toughness ($K_{1C}$) of the $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber in the as-fabricated state were measured to be 3.6 ${\pm}$ 0.5 MPa${\cdot}m^{1/2}$ by an indentation technique and 2.2 ${\pm}$ 0.2 MPa${\cdot}m^{1/2}$ by assuming elliptical flaw of a semi-infinite solid, respectively. The $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber showed a radial (Palmqvist) crack type and exhibited an orthotropic crack growth behavior under 100 g load.

• Computers and Concrete
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• 제26권1호
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• pp.75-94
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• 2020

The aim of this research is to investigate free vibration of a novel five layer Timoshenko microbeam which consists of a transversely flexible porous core made of Al-foam, two graphen platelets (GPL) nanocomposite reinforced layers to enhance the mechanical behavior of the structure as well as two piezo-magneto-electric face sheets layers. This microbeam is subjected to a thermal load and resting on Pasternak's foundation. To accomplish the analysis, constitutive equations of each layer are derived by means of nonlocal strain gradient theory (NSGT) to capture size dependent effects. Then, the Hamilton's principle is employed to obtain the equations of motion for five layer Timoshenko microbeam. They are subsequently solved analytically by applying Navier's method so that discretized governing equations are determined in form of dynamic matrix giving the possibility to gain the natural frequencies of the Timoshenko microbeam. Eventually, after a validation study, the numerical results are presented to study and discuss the influences of various parameters such as nonlocal parameter, strain gradient parameter, aspect ratio, porosity, various volume fraction and distributions of graphene platelets, temperature change and elastic foundation coefficients on natural frequencies of the sandwich microbeam.

• Structural Engineering and Mechanics
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• 제58권5호
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• pp.757-781
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• 2016

The results of diagnostics and analysis of an industrial hall located on the premises of a thermal power plant severely damaged by fire are presented in the paper. The comprehensive failure-related diagnostics, non-destructive and destructive tests of steel and concrete materials, geodetic surveying of selected structural members, numerical modelling, static analysis and reliability assessment were focused on two basic goals: The determination of the current technical condition of the load bearing structure and the assessment of its post fire resistance as well as assessing the degree of damage and subsequent design of reconstruction measures and arrangements which would enable the safe and reliable use of the building. The current mechanical properties of the steel material obtained from the tests and measured geometric characteristics of the structural members with imperfections were employed in finite element models to study the post-fire behaviour of the structure. In order to compare the behaviour of the numerically modelled steel roof truss, subjected to the effects of fire, with the real post-fire response of the damaged structure theoretically obtained resistance, critical temperature and the time at which the structure no longer meets the required reliability criteria under its given loading are compared with real values. A very good agreement between the simulated results and real characteristics of the structure after the fire was observed.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.1347-1352
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• 2008

The SCW ground heat pump system releases ground energy from the ground water of ground heat exchanger. In other word, ground water is used to heating through releases ground energy which oneself has. But the thermal efficiency of system is going to down because repetitive process of ground water will lost ground energy in standing column well system and if heating load is continually increase, energy of ground water may be frozen or there are no benefits to use ground energy as it owes just little energy. To solve these problems, there are need to exchange water to the ground heat exchanger then the way will be used to maintain Efficiency continually as the way of to be supplied with fresh ground water into ground heat exchanger. However, this type causes waste of ground water. Therefore it is essential to discharge water to outside timely on a heat exchanger. Therefor through a study, find out the best time to discharge water to outside and exchange water to ground heat exchanger, and propose to the DB of design of the ground heat exchanger.

• 한국전산구조공학회논문집
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• 제17권4호
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• pp.365-374
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• 2004

강구조물에 있어서 여러 가지 환경요인에 의해 균열 및 부식 등의 문제가 발생되고 있다. 이는 구조물의 내구성을 저하시키는 요인이 된다. 이와 같은 문제를 해결하기 위해 용접 보수${\cdot}$보강방법을 사용할 수 있다. 이러한 보수용접은 전단 및 용접과 같은 입열 과정을 필연적으로 수반하고 있다. 따라서 이러한 입열과정에 있어서 발생되는 잔류응력 및 변형의 예측${\cdot}$제어${\cdot}$방지는 구조물의 안전이라는 측면에서 볼 때 중요하다고 할 수 있다. 본 연구에서는 2차원 및 3차원 유한요소 해석을 수행하여 가스전단 및 아크용접에 의해 얻어진 절단 및 용접 잔류응력과 변형을 구하였으며, 2차원 및 3차원 해석기법에 따른 그 값의 정도를 명확히 하였다. 해석기법에 따라 2차원 및 3차원 해석을 수행하여 얻은 절단 및 용접 잔류응련의 분포 및 그 절대치는 유사한 값을 나타내었다.

• 설비공학논문집
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• 제18권12호
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• pp.1007-1016
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• 2006

Although the advance in electronic technology enables a large number of circuity to be packed in a small volume, it is simultaneously required to remove the high heat load produced by them. In this study, the heat transfer and pressure drop characteristics of a mini-channel heat exchanger, which is designed for liquid cooling of electronic components, are investigated by varying operating conditions. Water and FC-72 were used as working fluids. The mini-channel heat exchanger was made with circular shape channels having din-meters of 2, 3, and 4 mm in regular intervals, and the channel length was 100 mm. The header and inlet guide pathway to provide uniform inflow were attached at the inlet of the test section. Copper block including the heaters was attached at the sidewall of the test section as a heat source, which provided the heat flux from 5 to $15W/cm^2$. The entrance effects enhanced the heat transfer coefficient in the mini-channel significantly. In addition, the single-phase pressure drop in the mini-channel was very similar to that predicted by the laminar flow correlation except that the transition Re decreased due to flow instability in the entrance region.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.761-764
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• 2008

본 연구는 40, 60, 80MPa급 고강도콘크리트의 변형특성에 있어서 $20{\sim}700^{\circ}C$ 범위로 상승되는 온도의 영향을 연구하는데 그 목적이 있다. 본 연구에서 시험의 종류는 설계하중 사전재하 및 잔존 강도 시험방법으로서 시험체를 가열하기 전에 극한강도의 25%하중을 사전재하한 후 가열을 실시하고, 가열하는 동안 하중을 유지하며, 목표온도에 도달한 후 고온상태 및 상온에서 24시간 냉각상태에서 시험체가 파괴될 때까지 재하를 실시했다. 시험은 W/B 46%, 32% 및 25%로 이루어진 콘크리트 시험체에 대하여 $20{\sim}700^{\circ}C$의 다양한 온도하에서 실시하였다. 시험결과 콘크리트 강도가 증가할수록 고온에서의 상대적인 탄성계수는 감소하였으며, 최대하중에서의 축방향 변형은 설계하중 사전 재하와 상관성이 높은 것으로 나타났다. 또한 온도상승에 따른 콘크리트의 열팽창변형은 압축강도뿐만 아니라 초기사전재하의 영향을 받는 것으로 나타났다.

• 한국전기전자재료학회논문지
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• 제29권12호
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• pp.769-775
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• 2016

Characteristics of a wireless sensor powered by the IDE (interdigitated electrode) embedded piezoelectric cantilever generator were analyzed in order to evaluate its potential for use in wireless sensor applications. The IDE embedded piezoelectric cantilever was designed and fabricated to have a self-resonance frequency of 126 Hz and acceleration of 1.57 G, respectively, for the mechanical resonance with a practical conveyor system in a thermal-power plant. It produced maximum output power of 2.81 mW under the resistive load of $160{\Omega}$ at 126 Hz. The wireless sensor module is electrically connected to a rectifier capacitor with capacity of 0.68 farad and 3.8 V for power supply by the piezoelectric cantilever generator. The unloaded capacitor could be charged as a rate of approximately $365{\mu}V/s$ while the capacitor exhibited that of 0.997 mV/min. during communication under low duty cycle of 0.2%. Therefore, it is considered that the fabricated IDE embedded piezoelectric cantilever generator can be used for wireless sensor applications.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2017년도 춘계학술대회
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• pp.735-737
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• 2017

An Off grid or remote solar electric systems are an energy supply to our home or to our companies without the utility of Grid at all. Off grid solar systems are very important for those who live in remote locations especially for developing countries where getting the electric grid is extremely expensive, inconvenient or for those who doesn't need to pay a monthly bill with the electric bill in general. The main critical components of any solar power system or renewable energy harvesting systems are the energy storage systems and its charge controller system. Energy storage systems are the essential integral part of a solar energy harvesting system and in general for all renewable energy harvesting systems. To provide an optimal solution of both high power density and high energy density at the same time we have to use hybrid energy storage systems (HESS), that combine two or more energy storage technologies with complementary characteristics. In this present work, design and simulation we use two storage systems supercapacitor for high power density and lithium based battery for high energy density. Here the system incorporates fast-response supercapacitors to provide power to manage solar smoothing and uses a battery for load shifting. On this paper discuss that the total energy throughout of the battery is much reduced and the typical thermal stresses caused by high discharge rate responses are mitigated by integrating supercapacitors with the battery storage system. In addition of the above discussion the off grid solar electric energy harvesting presented in this research paper includes battery and supercapacitor management system, MPPT (maximum power point tracking) system and back/boost convertors. On this present work the entire model of off grid electric energy harvesting system and all other functional blocks of that system is implemented in MATLAB Simulink.

• Composites Research
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• 제16권1호
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• pp.26-33
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• 2003

열-음향방출(thermo-acoustic emission)기법을 이용함으로써, 직교형 복합재료적층판의 저온냉각 시에 형성되는 미세손상을 검출하고 평가하여 그 유효성을 검토하였다. 액체질소에 의한 저온냉각($-191^{\circ}C$)으로 생성된 미세손상은 가열-냉각 열부하사이클 시에 발생하는 음향방출(AE)거동의 해석을 통해 평가되었다. 저온냉각에 따른 섬유파단과 모재파손은 초음파 C스캔, 광학현미경, 주사형 전자현미경을 통해 관찰되었으며, 이들 미세파손 모드는 AE신호의 퓨리에 변환(FFT)처리해석, 단시간 퓨리에 변환(STFT)처리해석으로 분류되는 3종류의 서로 다른 특징을 갖는 AE신호로 검출될 수 있었다. 이들 AE신호특성을 시간 단계별로 검출하여 저온냉각시에 형성되는 복합재료 미세파괴의 과정을 실시간으로 평가할 수 있었으며, 또한 열부하 사이클시의 AE신호해석을 통해서 저온 냉각으로 생성된 미세파손의 정도를 추정할 수 있었다.