• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.251-257
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• 1999

Smart structure that contains sensors, which are either embedded in a composite material or attached to a structure, is currently receiving considerable attention. Fiber Bragg grating sensor, one of the optical fiber sensors, has been widely used to sense strain and temperature for smart structures since both parameters change the resonant frequency of the grating. In this paper, according to the various heating and cooling conditions the thermal behavior of unidirectional composite material was monitored by embedding the fiber Bragg grating sensors in the longitudinal and transverse directions of unidirectional composites. The thermal behavior of unidirectional composite material was monitored for various heating and cooling rates and applied pressure. It was found that the thermal behavior was unaffected by pressure variations and heating and cooling rates applied to the composites. The thermal strains were measured by considering the shift in Bragg wavelength that was generated by the thermal expansion of composite specimen. The longitudinal and transverse C.T.E.'s were also obtained from the corresponding temperature-thermal strain curves.

• 설비공학논문집
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• 제12권4호
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• pp.381-387
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• 2000

An experimental study on the stratified fluids was carried out to investigate the flow characteristics, heat transfer through the interface of fluids, and the applications of thermal behaviors in the square cavity. The same volume of water and silicon oil was filled in it. The experiments were performed with the variations of initial temperatures and cooling surface temperatures. And the effect of vertical or horizontal cooling surface positions in the square cavity was investigated. When the cooling surface temperatures were $-4^{\circ}C$ , the supercooling phenomena were observed for both cases of cooling surface positions in the full region regardless of the initial temperature of fluid. In the square cavity with horizontal cooling surfaces, the lower the initial temperatures were, the longer the supercooling durations were, and with vertical cooling surface the lower the initial temperatures were, the shorter the supercooling durations were.

• 열처리공학회지
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• 제29권1호
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• pp.15-23
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• 2016

The effects of austenitizing temperature and cooling rate on precipitation behavior and tensile properties were investigated in an Mn-Mo-Nb-V pressure vessel steel. During austenitizing, it was shown that the austenite coarsening was somewhat suppressed by undissolved NbC. After cooling from austenitizing, the microstructure of all the steels mainly consisted of upper bainite. However, the steel comprised a little lower bainite and martensite in the case of aqua oil quenching from $1000^{\circ}C$, which would be due to increased hardenability by partly dissolved Nb and comparatively large austenite grains. The average size of NbC in austenite at higher temperature was analyzed to be smaller than that at lower temperature because of the more dissolution. It was found that the NbC did not grow much during fast cooling from austenitizing. Meanwhile, the NbC grew much during slow cooling, probably due to wide temperature range of cooling and sufficiently long time for NbC to grow. It was conjectured the V precipitates newly formed and/or grew during cooling from austenitizing and during tempering. On the other hand, the formation of NbC was almost completed before tempering and little more precipitated during tempering. Among the tempered steels, the steel which was fast cooled from $1000^{\circ}C$ showed the highest tensile strength, which seemed to come from the microstructure of fine upper bainite and some low temperature phases as well as the comparatively fine NbC precipitates.

• 한국전산구조공학회논문집
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• 제13권1호
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• pp.147-158
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• 2000

철근콘크리트 냉각탑은 대형의 구조물로서 건설과정중의 오류와 콘크리트의 장기 거동에 의하여 기하학적 형상이 설계에서 목적하는 형상에서 벗어난 형상불완전을 가질 수 있다. 형상불완전의 구조거동에의 영향은 완전쉘에 나타나는 응력 이외에 추가적인 응력의 발생을 들 수 있다. 본 논문에서는 몬테카를로 방법을 사용하여 냉각탑 쉘의 형상불완전에 의한 확률론적 거동에 대하여 고찰하였다. 냉각탑에 형상불완전을 유발하는 기하인수로는 냉각탑의 반지름과 쉘의 두께를 택하였다. 이들 기하인수는 기존에 사용되던 모델인 축대칭 모델과 볼록형상의 모델과는 달리 특정 통계특성치를 가지는 추계장으로 가정하였다. 해석 결과는 냉각탑의 반지름에 나타나는 불확실성은 쉘의 두께에서의 불확실성보다 구조거동의 반응변화도에 매우 큰 영향을 미친다는 사실을 보여주었다. 기하학적 인수의 불확실성에 더하여 재료탄성계수의 공간적 불확실성에 의한 구조 반응변화도를 고찰하여 비교하였다.

• 한국정밀공학회지
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• 제28권4호
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• pp.505-512
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• 2011

Linear permanent magnet synchronous motors utilize high-energy product permanent magnet to produce high thrust, velocity and acceleration. Such motors are finding applications requiring high positioning accuracy and speed response, for example, machine tools, in the absence of mechanical gears and ball screw systems. A disadvantage of the linear motors is high power loss in comparison with rotary motors. For the application of the linear motors to machine tools, it is required to use water coolers and to improve the thermal behavior through insulation and structure optimization or control strategies. This paper presents the function of the secondary part of the linear synchronous motor as to the thermal behavior and the improving method. The result shows cooling pipe combined with an insulation layer is a suitable design for improving of the thermal behavior.

• 한국자동차공학회논문집
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• 제2권2호
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• pp.103-116
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• 1994

In this study the behavior of engine cooling loss and overall heat transfer coefficient were studied experimentally using naturally aspirated engine and turbo charged engine. Using turbo charging, heat dissipation was increased because of the density of the mixture was increased with increment of inlet air flow rate. Therefore, cooling loss of turbo charged engine is larger than naturally aspirated engine. As taking the measurement of surface temperature of combustion chamber, gas heat transfer coefficient was calculated and found that it has greatly affected to overall heat transfer coefficient. The empirical formula of overall heat transfer coefficient established in order to predict of engine cooling loss and express only as a function of mean piston velocity.

• Structural Engineering and Mechanics
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• 제5권5호
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• pp.541-552
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• 1997

In this paper the ultimate strength of the R/C cooling towers, which have initial imperfection and pre-cracked elements, is analyzed. The initial geometric imperfections arise from the unavoidable inaccuracies under the construction and the pre-cracks are assumed to be produced by the temperature stress gradients or cyclic loading under wind pressure and/or earthquake load. Both effects are strongly influenced on the strength of the R/C cooling tower shell structures. The reinforcing ratio is also the important factor to evaluate the ultimate strength of the R/C cooling tower shells. However we could not analyze these structures experimentally because of their large, analyses are the powerful schemes to evaluate the safety and reliability of these structures. The analyzed model is Port Gibson cooling tower shell. In the numerical analysis the geometric and material nonlinearities are taken into account.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.955-960
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• 2009

In order to improve the efficiency of the main transformer in a tilting train, the optimal operation of a cooling system is necessary. Mathematical models of a main transformer cooling system were developed. These include models for the main transformer, the oil pump, the oil cooler, and the blower. The optimal oil temperature algorithm was also developed. This consists of the optimal setpoint algorithm and the control algorithm. A simulation program was developed by using mathematical models and the optimal oil temperature algorithm. Simulation results showed that the dynamic behavior of a main transformer cooling system was predicted well by mathematical models and a main transformer cooling system was controlled effectively by the optimal oil temperature algorithm.

• Wind and Structures
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• 제2권2호
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• pp.105-117
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• 1999

The various spectral density functions of wind are applied in the wind process simulation by the spectral representation method. In view of the spectral density functions, the characteristics of the simulated processes are compared. The ensemble spectral density functions constructed from the simulated sample processes are revealed to have the similarity not only in global shape but also in the maximum values with the target spectral density functions with a high accuracy. For the correlation structure to be satisfied in the circumferential direction on the cooling tower shell, a new formula is suggested based on the mathematical expression representing the circumferential distribution of the wind pressure on the cooling tower shell. The simulated wind processes are applied in the dynamic analysis of cooling tower shell in the time domain and the fluctuating stochastic behavior of the cooling tower shell is investigated.

• Computational Structural Engineering : An International Journal
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• 제2권1호
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• pp.25-32
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• 2002

Natural draught cooling towers often develop visible crack structures as consequences of progressive damage processes over their life-time. The aim of this paper is a numerical demonstration of the progressive damage process of cooling towers, representatively for the reinforced concrete structures, in order to improve the durability and extend the life-time of structures subjected to such damage processes. For the analyses, the applied material model for reinforced concrete will be briefly introduced. An existing natural draught cooling tower with a pronounced crack structure, in which this crack structure indicates the typical damage pattern of large cooling towers will be numerically simulated. The change of dynamical behavior of the structure with regard to natural frequencies, reflecting the global damage process due to the degrading stiffness of the structure in dependence of the load type and intensity, will be presented and discussed.