• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.355-358
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• 2003

Recently, micro forming process technology have been developed since the size of machine parts become the crucial factor for minimizing of products in general electronic products. Most small machine parts consist of gear and rotation axis and the wear by mechanical contact is known as the primary factor for life reduction of high precision machine part. Lots of studies for mechanical wear and friction have been reported and many researches of MEMS technology have been studied recently. But just few studies for wear of micro or milli sized machine part have teen implemented. In this research, the wear equation is suggested according to the contact shape of axial part in micro or milli sized machine part. And wear analysis model which can predict the magnitude of wear through this suggested equation with numerical analysis program.

• 산업기술연구
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• 제28권B호
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• pp.81-89
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• 2008

This paper is results of investigating the dominant factors influencing to coefficient of consolidation in horizontal direction of Korean marine clays and their correlations through literature review. From the results of analyzing data obtained from field tests such as piezocone penetration and dilatometer tests as well as laboratory tests, coefficient of consolidation in the horizontal direction was found to increase with increase of stiffness index of soil while it decreases with the increase of dissipation time of pore pressure developed during field tests. In general, the coefficient of consolidation in the horizontal direction tends to increase with increase of undrained shear strength and preconsolidation pressure although correlation between them are relatively low. Friction ratio has a high correlation with coefficient of consolidation in the horizontal direction in case of friction ratio being greater than 1.0. For methods of estimating coefficient of consolidation in the horizontal direction with different testing device, values obtained from methods of P2-logt and DMT-A with dilatometer were quite similar to values from piezocone penetration test. Consistency of soil is quite proportional to coefficient of consolidation in the horizontal direction. Clear correlation between coefficients of consolidation in the horizontal and the vertical directions could not be found. coefficient of consolidation in the horizontal direction estimated from the results of field test tends to be 1.13~3.11 times greater than that obtained from laboratory tests.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.342-347
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• 2004

Excavation nearby the existing structures is being performed vigorously to get the greatest use of land along with fast economic growth in the downtown area. The application of soil nailing system gradually increases because of an advantage of soil nailing system adjacently constructed in the existing structures. In this study, friction resistance by pull-out is considered as main resistance except resistance formed by flexural rigidity of nail observing that resistance of flexural rigidity is about $0{\sim}15\;%$ of whole safety factor according to degree of flexural rigidity in general soil nail wall and application of geosynthetic fiber soil nailing system is evaluated through laboratory tensile strength test and field pull-out test.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 춘계학술발표회논문집(1)
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• pp.483-488
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• 1998

A pressure drop model for the PWR grids with and without mixing device is proposed at single phase based on the fluid mechanistic approach. Total pressure loss is expressed in additive way for form and frictional losses. The general friction factor correlations and form drag coefficients available in the open literatures are used to the model. As the results, the model shows better predictions than the existing ones for the non-mixing grids, and reasonable agreements with the available experimental data for mixing grids. Therefore it is concluded that the proposed model for pressure drop can provide sufficiently good approximation for grid optimization and design calculation in advanced grid development.

• East Asian Economic Review
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• 제27권2호
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• pp.89-114
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• 2023

This paper empirically examines how controlling strategic goods affects productivity by focusing on Korean industries from 2015 to 2019. We hypothesize that strategic goods control positively affects productivity because it promotes international trade by making up for market failures, building up national credibility, and stabilizing market environment; in turn, international trade contributes to productivity growth. The regression results are congruent with our hypothesis. The effects of strategic goods control on productivity were positive and statistically significant in general. These positive effects were more prominent in the group of industries that include strategic goods and, thus, are technologically intensive. The results also support that international trade is a key medium for the effects of strategic goods control on productivity. Consequently, our empirical results support government policy on strategic goods control, ensuring that strategic goods control can contribute to economic growth by reducing diplomatic friction and stabilizing the global market.

• 설비공학논문집
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• 제10권5호
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• pp.589-599
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• 1998

Air side heat transfer and pressure drop for fin-tube heat exchanger with wave and wave-slit fins were measured for various fin spacings and number of tube rows. Outer diameter of the tube including fin collar is 10.07mm, and experiments were done with dry surface condition. Longitudinal and transverse tube spacings of the heat exchangers are 21.65mm and 25mm respectively, and wave depth of the wave fin is 2mm. Experiments were conducted for 1, 2 and 3 rows and 3 different fin spacings, 1.3, 1.5 and 1.7mm. An attempt was made to demonstrate advantage of the enhanced fins over the plane fin by introducing the concept of fan power, Effect of the number of tube rows on heat transfer was discussed in connection with general mechanisms of heat transfer enhancement for fin-tube heat exchanger. Also the effect of hydrophilic coating was investigated. Lastly, correlations for Colburn j-factor and friction factor were developed.

• 한국농공학회지
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• 제38권5호
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• pp.140-154
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• 1996

In this study, displacement, deformation, and stability according to change of cohesion and internal friction angle were investigated through elasto-plastic method, finite-element method, and in-site experiment when excavating soft ground using sheet pile. The results of the study were as follows : 1. The horizontal displacement was 5.5% of the excavation depth by the elasto-plastic method and 3.9% of the excavation depth by the on-site experiment at the final excavation depth(GL-8.Om) on the condition of double stair strut after excavating GL-6.Om. 2. Relationships between cohesion(c) and internal friction angle $({\varphi})$ when safety factor to the penetration depth was 1.2 is shown in the following equations : (a) c= -O.0086$({\varphi})$+ O.3(D=3m) and (b) c=-0.00933$({\varphi})$+0.14(D=4m). 3. The results of elasto-plastic method and the experiment show that possible excavation depth was GL-6.Om after setting single stair strut in a short period in terms of possibility of carrying out on the condition of experimental site on the contrary general reinforcement method, setting double stair strut after excavating GL-4.0m. 4. After setting the strut, distribution of the horizontal displacement had concentrated on the excavation base and possible local failure which the shear strain caused decreased by the strut reinforced. 5. After setting strut, displacement of sheet pile was decreased by half, the limit of stable excavation depth of ground was GL-8.Om, and the maximum horizontal displacement at the GL-8.Om was 1.6% of excavation depth by the elasto-plastic method, 0.7% of excavation depth by the finite-element method.

• International Journal of Air-Conditioning and Refrigeration
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• 제16권3호
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• pp.100-107
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• 2008

The heat transfer and friction characteristics of heat exchangers having convex louver fins are experimentally investigated, and the results are compared with those of wave fin counterparts. Eighteen samples (nine convex louver fin samples and nine wave fin samples) which had different fm pitches (1.81 mm to 2.54 mm) and tube rows (one to four) were tested. The convex angle was $11.7^{\circ}$. The j factors are insensitive to fin pitch, while f factors increase as fin pitch increases. The effect of fin pitch on f factor is more significant for the wave fin compared with the convex louver fin. It appears that the complex fin pattern of the convex louver fin induces intense mixing of the flow, and thus reduces the effect of fin pitch. Both the j and f factors decrease as the number of tube row increases. However, as the Reynolds number increases, the effect of tube row diminishes. Comparison of the convex louver fin j factors with those of wave fin reveals that convex louver fin j factors are 18% to 29% higher than those of wave fin. The f factors are 16% to 34% higher for the convex louver fin. The difference increases as fin pitch decreases. Existing correlation fails to adequately predict the present data. More data is needed for a general correlation of the convex louver fin geometry.

• 대한기계학회논문집
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• 제11권3호
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• pp.425-436
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• 1987

본 연구에서는 강제대류가 있는 층류막비등유동을 벽면온도와 주수속도를 변 화시키며 수치해석하여 열전달계수와 유동특성을 구하였고, 열력학적 상태량들을 일정 하다고 가정하는 경우가 열전달계수에 어떠한 영향을 미치는가를 검토한 결과, 열전달 계수는 주수속도에는 큰 영향을 받지 않으나, 벽면온도와 열력학적 상태량의 변화에는 상당히 큰 영향을 받는 것으로 나타나고 있다.

• 한국수자원학회논문집
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• 제35권6호
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• pp.729-736
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• 2002

개수로의 설계에 있어서 등류수심의 산정은 가장 기본적인 요건이며, 인공수로를 구축할 경우 일반적으로 최량 수리단면은 가장 경제적인 단면이 된다. 따라서 최량 수리단면의 등류수심 산정은 거의 모든 수로 설계의 핵심적인 요소라 할 수 있다. 개수로 마찰력을 산정하기 위하여 일반성이 확보된 지수형 마찰계수 산정식을 도입하였다. 삼각형, 사각형 및 제형 등 거의 모든 형태의 수로에 대한 등류수심의 산정을 위하여 형식이 통일되고 양해적으로 해석이 가능한 산정식을 도출하였다. 또한 이들 등류수심 산정식은 관로설계에서 도출된 관경 산정식과 형식이 일치함을 확인하였다.