• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2003년도 춘계학술대회논문집
• /
• pp.199-203
• /
• 2003

Idler of excavator are large product with diameter 500 - 600 mm and parts of a power transmit device. The object of the paper is developed large products by hot closed-die forging. The forging process which is proposed from numerical analysis and various tests is developed a large products with good quality. To estimate the design process parameters such as working load, temperature and flash thickness so on, numerical analysis are used by DEFORM 2D. To obtain a flow stress data and optimal forging temperature is carried out hot compression and tensile test at a various temperature range. Developed product is tested mechanical properties of elongation, hardness and tensile strength so on. Test results are presented excellent mechanical properties.

• 대한기계학회논문집
• /
• 제17권12호
• /
• pp.2970-2981
• /
• 1993

In hot closed-die forging the load increases rapidly near the final stage. Preforming operation is important to both the sound final forging and die-service life. In this study, the material flows during preforming and final forging are investigated. The physical modeling with Plasticine as a model material showed clear flow patterns. The forging process were numerically simulated by the finite element method with the isothermal and the non-isothermal models. The flow patten of the isothermal simulation showed good agreements with the experiments. Temperature changes and pressure distributions on the die surfaces during one cycle of the forging process were obtained from the non-isothermal simulation. High pressure and temperature were developed at certain areas of the die surfaces. It was concluded that those areas usually coincide with each other and should be distributed by the preforming operations to enhance the die life.

• 농촌계획
• /
• 제19권4호
• /
• pp.293-306
• /
• 2013

According to the increase of rural experience, that is important in satisfying needs of green tourism and vitalizing rural economy to use closed school in rural area as experience facility. For using closed school as experience facility, political and institutional assistants are needed in effective equipments and stable operation based on multi-perspective approach and analysis. In this study, we try to evaluate green-tourism accessibility of rural experience facility remodeled from closed school considering regional population and spatial characteristics. In evaluating process, gravity potential model are adapted with considering group size of customer and distance-friction coefficient. Distance-friction coefficient is a function of user restriction which depend on possible activity in each experience facility. Green tourism accessibility of experience facility is calculated with summation of accessibility to each region, and we analyzed it as a group by closed school type and location with application in Chungcheongnam-do. We found a correlation between green tourism accessibility of rural closed school and their income.

• 소성∙가공
• /
• 제22권5호
• /
• pp.269-274
• /
• 2013

Experiments and numerical simulations of the incremental upsetting test were carried out to investigate void closure behavior and mechanical characteristic of a 1.5wt%C ultra-high carbon steel. The experimental results showed that the voids become quickly smaller as the reduction ratio increases. The simulation results confirmed this behavior and indicated that the voids were completely closed at a reduction ratio of about 40~45% during incremental upsetting. After the completion of the incremental upsetting tests, the process of diffusion bonding was employed to heal the closed voids in the deformed specimens. To check the appropriate temperature for diffusion bonding, deformed specimens were kept at 800, 900, 1000 and $1100^{\circ}C$ for an hour. In order to investigate the effect of holding time for diffusion bonding at $1100^{\circ}C$, specimens were kept at 10, 20, 30, 40, 50 and 60minutes in the furnace. A distinction between closed and healed voids was clearly established using microstructural observations. In addition, subsequent tensile tests demonstrated that complete healing of a closed void was achieved for diffusion bonding temperatures in the range $900{\sim}1100^{\circ}C$ with a holding time larger than 1 hour.

• 동력기계공학회지
• /
• 제9권2호
• /
• pp.88-92
• /
• 2005

The experiment of thermal performance about closed-wet cooling tower was conducted in this study. A closed cooling tower is a device similar to a general cooling tower, but with cooling tower replaced by a heat exchanger. The test section for this experiment has the process that the cooling water flows from the top of the heat exchanger to the bottom side in the inner part of the tube, and spray water flows in the gravitational direction in the outer side. Air comes in direct contact with the spray water at the outer side of the tube while passing from the lower the upper part having a counterflow to the spray water. The heat transfer pipe used in this experiment is a bare-type tube having an outer diameter of 15.88mm. The heat exchanger is consisted of seven rows and fifteen columns. In this experiment, thermal performance of the cooling tower is derived from overall heat transfer coefficients between the process fluid and sprayed water and volumetric overall mass transfer coefficient between sprayed water and air.

• 한국마린엔지니어링학회:학술대회논문집
• /
• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
• /
• pp.1096-1101
• /
• 2005

In this study, the experiment of thermal performance about closed-type hybrid cooling tower was conducted. A closed type cooling tower is a device similar to a general cooling tower, but with cooling tower replaced by a heat exchanger. The test section for this experiment has the process that the cooling water flows from top part of heat exchanger to bottom side in the inner side of tube, and spray water flows gravitational direction in the outer side of it. Air contacts of tube outer side are counterflow. The heat transfer pipe used in this experiment is a bare type tube having an outside diameter of 15.88mm. In this experiment, heat performances of the cooling tower are calculated such as overall heat transfer coefficient of between the process fluid and air, cooing capacity and pressure drop.

• 펄프종이기술
• /
• 제43권1호
• /
• pp.65-73
• /
• 2011

The fibrous raw materials in packaging-grade paper production in Korea were mainly obtained from waste paper. The use of recycled paper has both positive and negative impacts in papermaking process. The primary positive impacts are the environmental protection and manufacturing cost reduction, and the negative impacts are the quality reduction in paper quality and the accumulation of heavy metals and other pollutants in wet- and dry-end process. This study was carried out to consider the optimum acid decomposition system with the highest recovery rate for the analysis of heavy metals in packaging-grade paper. The open digestion system using Kjeldahl apparatus and the closed digestion system using microwave oven for decomposing the organic materials in paper were compared. In both open and closed digestion method, the combination of nitric acid, hydrochloric acid and hydrogen peroxide showed higher recovery rate than using only nitric acid alone because the presence of Cl- ions in hydrochloric acid stabilizes ligand formation with metal ions. KOCC was observed to have the highest heavy metal content among the recycled paper samples. The heavy metal contents decomposed with the closed digestion system were relatively higher than with open digestion system.

• 펄프종이기술
• /
• 제38권2호
• /
• pp.1-8
• /
• 2006

In this study a process simulation method was used to analyze the accumulation phenomena of anionic starch in the process white water as the closure level of a fine paper making process is increased. A pilot paper machine was used as a model process. Dynamic simulations of the influence of white water usage ratio and uncoated broke addition ratio on the variation of process variable was monitored as a function of time. Results from the dynamic simulations showed that the volume of reservoirs affected the dynamic behavior of the process. The dynamic behavior of flow rate and dissolved starch concentration in process units were different from each other. The speed of the change of dissolved starch concentration in process units was depend on the starting point of the change of dissolved starch concentration, the length of circulation loop, and the volume of reservoirs.

• Journal of the Korean Statistical Society
• /
• 제36권2호
• /
• pp.237-256
• /
• 2007

This paper studies the problem of option pricing in an incomplete market. The market incompleteness comes from the discontinuity of the underlying asset price process which is, in particular, assumed to be a compound Poisson process. To find a reasonable price for a European contingent claim, we first find the unique minimal martingale measure and get a price by taking an expectation of the payoff under this measure. To get a closed-form price, we use an asymptotic expansion. In case where the minimal martingale measure is a signed measure, we use a sequence of martingale measures (probability measures) that converges to the equivalent martingale measure in the limit to compute the price. Again, we get a closed form of asymptotic option price. It is the Black-Scholes price and a correction term, when the distribution of the return process has nonzero skewness up to the first order.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2003년도 춘계학술대회논문집
• /
• pp.143-147
• /
• 2003

Despite of outstanding optical performance of glass lens, glass lens have not been widely used because of poor productivity and high cost due to manufacturing process i.e. grinding, polishing. However, press-forming method of glass lens overcomes this disadvantage because of mass production. When glass lens is produced by press-forming method using closed die, it is needed that the volume of glass lens preform precisely measured in order to prevent incomplete products and to increase in life of die. The present paper shows the shortcoming of forming process with closed die, and performs FEM simulation of forming process with open die in order to overcome this shortcoming. The design parameter of open die is selected in standard of assembly with optical module and maintenance of optical performance. FEM simulation is carried out with selected parameter of open die and two basic preform. According to distribution of effective strain in glass lens, optical property of glass lens formed at each set of die and preform is compared.