• International Journal of Fluid Machinery and Systems
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• 제6권1호
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• pp.33-48
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• 2013

If large pressure fluctuation is observed in the draft tube of a Francis turbine at part-load operation, we have generally called it draft-tube-surge. As occurrence of this phenomenon seriously affects the limit of turbine operating range, extensive studies on the surge have been made since proposal of surge-frequency criterion given by Rheingans. According to the literature survey of related topics in recent IAHR symposiums on hydraulic machinery and systems, in which state-of-the-art contributions were mainly presented, a certain review of them may be desirable for an outlook on the future studies in this research field. Thus, in this review paper, the authors' previous attempts for the last three decades to challenge the following topics: a rational method for component test of a draft tube, nature of spiral vortex rope and its behavior in a draft tube and cavitation characteristics of pressure fluctuations, are introduced together with other related contributions, expecting that more useful and significant studies will be accomplished in the future.

• International Journal of Fluid Machinery and Systems
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• 제8권4호
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• pp.230-239
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• 2015

The swirling flow in the draft tube of a Francis turbine can cause the flow instability and the cavitation surge and has a larger influence on hydraulic power operating system. In this paper, the cavitating flow with swirling flow in the diffuser was studied by the draft tube component experiment, the model Francis turbine experiment and the numerical simulation. In the component experiment, several types of fluctuations were observed, including the cavitation surge and the vortex rope behaviour by the swirling flow. While the cavitation surge and the vortex rope behaviour were suppressed by the aeration into the diffuser, the loss coefficient in the diffuser increased by the aeration. In the model turbine test the aeration decreased the efficiency of the model turbine by several percent. In the numerical simulation, the cavitating flow was studied using Scale-Adaptive Simulation (SAS) with particular emphasis on understanding the unsteady characteristics of the vortex rope structure. The generation and evolution of the vortex rope structures have been investigated throughout the diffuser using the iso-surface of vapor volume fraction. The pressure fluctuation in the diffuser by numerical simulation confirmed the cavitation surge observed in the experiment. Finally, this pressure fluctuation of the cavitation surge was examined and interpreted by CFD.

• 동력기계공학회지
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• 제13권6호
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• pp.88-94
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• 2009

In this paper, vibration characteristics after applying variable speed control to fans with a rated speed used in a power plant are studied by performing experiments and analyzing finite element models. Then the campbell diagram is presented to verify the reason of the abnormal vibration measured from fan structure during variable operation of Forced Draft Fan & Induced Draft Fan. According to results, it is found that amplitude of acceleration increases abruptly when a 2X harmonic component meets the natural frequency of fan rotor. Therefore it is very important thing that investigate exactly dynamic characteristics for the rotor at variable speed zone before applying variable speed control to a rotor with a rated speed.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1993년도 Proceedings of International Conference for Agricultural Machinery and Process Engineering
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• pp.307-315
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• 1993

A direct draft measurement system was developed based on the swingle tree- the rear component of the single-animal harnessing (or yoking) system . The prototype was made from a tube, on which four strain gages were attached. The pull of the draft animal through the flexible pull chains or ropes causes the beam to bend, The bending strain is sensed by the strain gages and the bridge converts this to a voltage signal. Counterweights keep the tube correctly oriented if the angle of pull changes , while end bearing follow the variations in the angle of pull. Hence, the voltage output is proportional to the draft. the device has highly linear response, acceptable sensitivity negligible error and hysteresis. It is suitable for electronic data acquisition, non-intrusive , easy to attach and detach and is reasonably priced.

• 한국미생물·생명공학회지
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• 제51권3호
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• pp.328-331
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• 2023

Genomic information of biotechnologically and industrially important microorganisms provides the basis for understanding their metabolic potential. Here, we report the draft genome sequence of the Neodothiora populina-like yeast strain JAF-11 capable of producing biosurfactant myo-inositol lipids. The draft genome contained genes associated with secondary metabolite biosynthesis, including transport and metabolism of lipids, which are a major component of fungal surfactants. Identification of myo-inositol and acyl chain synthesis genes in the draft genome corresponded to the specific biosurfactant produced by strain JAF-11. Further experimental studies could help to elucidate the genes responsible for the production of biosurfactant by strain JAF-11.

• 대한인간공학회지
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• 제22권3호
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• pp.45-56
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• 2003

This study was conducted to develop user interface design guidelines for those who design education software products (web sites or CD-ROM titles). To establish this guideline scheme, international standards, commercial design guidelines, and research papers were surveyed. Especially, ISO 9241 was referred as a basic model of a guideline scheme. First, the research group developed draft guidelines. After that, education software developers, designers, and a user group reviewed the draft and the draft was revised with their commentations. Five components were selected as a primary class of guideline scheme: general principle, dialogue design, user guidance, visual interface, and information presentation. Each component was divided several components as a secondary class. Finally, 45 items were selected as user interface design guidelines for the education software design.

• 아동학회지
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• 제31권1호
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• pp.101-111
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• 2010

The purpose of this study was to develop a scale to measure the life satisfaction of after-school classes. For this purpose, utilizing the theoretical background and the findings of previous studies, 147 questions from eight factors were selected for the 1st draft and 67 questions were selected for the 2nd draft by reviewing the validity of the contents after consulting with eleven professionals. A preparatory survey and factor analysis was then conducted using 291 people and a total of 32 questions were extracted from four sub-factors. Exploratory factor analysis by principal component analysis was conducted and orthogonal rotation was conducted by means of the VARIMAX method. The reliability of the class environment, operation management, program and teacher relationship sector were found to be very high. It is suggested that this study can be of great benefit in developing a child-centered scale and it's reliability was also found to be high.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.283-285
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• 2002

Boiler combustion systems are large, non-linear systems with numerous interactions between its component parts. In the analysis of such complex systems. dynamic simulation is recognized as a powerful method of keeping track of the myriad of interactions. This paper shows and discusses the developed analysis model, such as the forced draft fan the primary air fan, the furnace and burner system, pulverizer, air preheater and induced draft fan, etc. in accordance with BMCR condition of boiler using the Modular Modeling System(MMS) software.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 A
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• pp.392-394
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• 2001

Coal power plants are large, non-linear systems with numerous interactions between its component parts. In the analysis of such complex systems, dynamic simulation is recognized as a powerful method of keeping track of the myriad of interactions. This paper shows and discusses the developed analysis model, such as the forced draft fan the primary air fan, the furnace and burner system, air preheater and induced draft fan, etc. in accordance with BMCR condition of boiler using the Modular Modeling System(MMS) software.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 1987년도 제29회 수공학연구발표회논문초록집
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• pp.223-234
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• 1987

A weakly nonlinear solution is presented for the two-dimensional wave kinematics forced by a generic wavemaker of variable-draft. The solution is valid for both piston and hinged wavemakers of variable-draft that may be double articulated. The second-order propagating waves generated by a planar wave board are composed of two components; viz., a Stokes second-order wave and a second-harmonic wave forced by the wavemaker which travels at a different speed. A previously neglected time-independent solution that is required to satisfy a kinematic boundary condition on the wavemaker as well as a mixed boundary condition on the free surface is included for the first time. A component of the time-independent solution is found to accurately estimate the mean return current(correct to second-order) in a closed wave flume. This mean return current is usually estimated from kinematic considerations by a conservation of mass principle.