• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 C
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• pp.1856-1858
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• 2002

As the statistical data, the most of electrical shock accidents have been caused by human errors including those of mistake, carelessness, and so on during normal condition. But, there are currently no international standards for the determination of withstand distance to ensure safety of personnel form 22.9 kV electrical power facilities during their normal operation. Therefore, this paper describes the characteristics of flash-over voltage by moisture variation to establish the distance clearances in terms of electrical safety.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.400-408
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• 2009

Optimization of seal geometries can reduce significantly the energetic losses in a hydraulic seal [1], especially for high head runner turbine. In the optimization process, a reliable prediction of the losses is needed and CFD is often used. This paper presents numerical experiments to determine an adequate CFD model for straight, labyrinth and stepped hydraulic seals used in Francis runners. The computation is performed with a finite volume commercial CFD code with a RANS low Reynolds turbulence model. As numerical computations in small radial clearances of hydraulic seals are not often encountered in the literature, the numerical results are validated with experimental data on straight seals and labyrinth seals. As the validation is satisfactory enough, geometrical optimization of hydraulic seals using CFD will be studied in future works.

• 진공이야기
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• 제2권4호
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• pp.39-46
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• 2015

After stepping into a new field of vacuum 30 years ago, our company has grown up steadily as a specialized vacuum industry, and now we can provide vacuum devices covering most of the pressure range. We are planning to put out high level dry pump like a multistage Roots pump on the market in the near future. Procedures of technology development for designing, fabricating, and testing the multistage Roots pump of 600 L/min class will be briefly reported. Core items of the technical development on the multistage Roots pump are as follows; elaborated profile design of 3-lobe rotors using an involute curve, optimization of rotor dimensions, especially for clearances and rotor width, considering the pumping speed, compression ratio and heat load, and establishment of a standardized test system. At present, the multistage Roots pump is about to come into commercialization.

• Tribology and Lubricants
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• 제10권1호
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• pp.69-77
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• 1994

Oil flow pass of hermetic scroll compressor with back pressure chamber was described. Dynamic analysis was preceded in order to obtain the loads on the lubricating contacts. The mobility method of dynamically loaded journal bearings was applied to the crank jornal bearing and lower main bearing, and they could be designed to operate under fluid film lubrication. From the consideration of their film thicknesses and oil flow rates, optimal bearing clearances or other bearing dimensions could be assessed. The major friction loss was calculated to be from the axial force between the two scrolls. Therefore, it was suggested that the designers should be careful to reduce the over-turning moment on the orbiting scroll.

• Tribology and Lubricants
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• 제15권4호
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• pp.304-313
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• 1999

High-speed rotors set a lot of high vibration and stability problems especially when the speed of rotation is going through the first or the second critical speed. The aim of this paper is to investigate the possibility of an active control of a rigid rotor with squeeze film damper which has a good configuration of easily controlled end seal clearances and/or adjustment of a feed pressure. A theoretical method is presented and some numerical results are compared with test measurements. Both results show that the vibration or bit sizes are decreased when the end seal gap decreases with constant supply pressure, and when the supply oil pressure increases with constant seal gap. The experimental results show also a pleasing similarity on both orbit sizes and their decrement ratio compared with theoretical analysis. The possibility of an active control with the squeeze film damper was verified by adjusting the seal gap and the supply pressure.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.362-365
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• 2005

The hub hole is usually formed with a flanging process followed by a blanking process of a ]tole. Since the hole is made by blanking, the blanked surface is so rough that the formability in the region is rather poor. The emerging task is to identify the formability of the blanked region in the forming simulation and to relate the criterion to the real forming process by experiments. In this paper, hole expansion tests are carried out with respect to various hole conditions to verify the hole condition effect on the hole expansion ratio. The hole of specimens is made by machining or punching. In the case of punching, two different punching clearances are used for making the hole. From the results of test, fracture mechanism of the hole expansion is explained.

• 소성∙가공
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• 제19권5호
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• pp.290-295
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• 2010

Shaving technology is one of the significant metal forming technologies which can make the smooth and fine sheared surface of products after shearing process. The sheared surface on the side wall of the cutting edge is very important because it functions as a basic surface for measuring the dimensions of product. Effective sheared surface after shaving can be influenced by several working variables such as shaving allowance, shaving clearance, type of material and profile of cutting edge. The influence of these variables on shaving characteristics was investigated in this study. A cut-off die to make the simplified gear-shaped products was manufactured. Three kinds of sheet metals (AL5052, SPCC and SAPH440) of 3mm thickness were firstly sheared and then shaved for four shaving allowances and three sharing clearances. It was shown through experiments that the optimum working condition to give the maximum effective sheared surface in shaving was found ; Shaving allowance is 0.2mm and Shaving clearance is 0.01mm.

• International Journal of Automotive Technology
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• 제5권1호
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• pp.23-31
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• 2004

Secondary movements of piston in the bore clearance are closely related to the side impact to the engine block as well as many tribological problems. Some of the major parameters that influence these kinds of movements are piston profile shapes (barrel and flat), piston pin offsets and the magnitudes of bore clearances. In our study, computational investigations are performed about the piston movements in the bore clearance by changing the skirt profiles and piston offsets. In this work, it is found that curved profile and larger offset magnitude to thrust side provide better performance that has low side impact during the engine cycle.

• Journal of Pharmaceutical Investigation
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• 제5권1호
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• pp.28-40
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• 1975

Polyporus would used as diuretics. Then, for the purpose of experimentally certifying the above mention, the effect on the renal function of dog was investigated, utilizing clearance technique. Water and alcohol extracts, when injected intravenously, produced significant increases of urinary sodium and potassium, osmolar and free water clearances, and urine flow, while glomerular filtration rate and renal plasma flow remained unchanged. During diuresis produced by furosemide, addition of water extract reduced the action of furosemide and markedly renal plasma flow. It would appear that these compounds are capable of action by a different mechanism or a different site. water extract, when infused directly into a renal artery, reduced the urine flow of experimental kidney as well as renal plasma flow, and the contralateral kidney exhibited diuresis, whereas amounts of sodium and potassium excreted in urine increased on both kidney. It is surmised from those observations that Polyporus induces diuresis by inhibition the reabsorptive mechanism of renal tubules through some endogeneous humoral substances, in addition, directly reduces the renal plasma flow.

• 한국항공운항학회지
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• 제22권3호
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• pp.82-86
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• 2014

Modern Air Traffic Management has been shifted from the conventional vector- based clearances to trajectory based operations (TBO) concept which utilizes four-dimensional trajectory based on the internationally interoperable information using Globally Unique Flight Identifier (GUFI). This study reviews the development for TBO-related standards and Flight Information Exchange Model (FIXM), which has been discussed by the ICAO Air Traffic Management Requirements and Performance Panel (ATMRPP). In addition, plans for the next step with TBO and the Republic of Korea's participation on the Mini-Global Demonstration were also introduced.