• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.301-304
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• 2004

Friction welding was used to weld the turbine wheel and shaft and have a good welding quality. Friction welding was conducted an the two dissimilar material, Nimonic 80A and SNCrW. The control of friction welding process parameter such as flywheel energy, interface temperature, amount of upset have an effect on the mechanical properties of the welded joint. FE simulation can be a useful tool to optimize the weld geometry and process parameters. Flash shape and thickness weld is consistent with the simulated results. Process analysis was performed by the commercial code DEFORM 2D. Mechanical property of weld joints was evaluated by microstructure, chemical component, tensile, impact, hardness test so on.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.406-409
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• 2005

In the forging operation of large ingot two break-down process are upsetting and cogging. The first purpose of upsetting is to ensure sufficient forging ratio for subsequent cogging operations and consolidate the voids along the centerline. The second purpose is related to improve the physical properties for a final product. Voids which are generated during the casting process can be one of the decisive defects of materials. So it is necessary to know the standard of Judgment for void-closure in upsetting operation. In practical conditions, FEM analysis(DEFORM 2D 8.1) was carried out to decide how much effective strain has influence on void-closure. It is finally suggested that the function consists of the effective strain of analysis data and the area rate of void.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.277-280
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• 2005

A shape optimization is applied to achieve a design objective in three-dimensional forging processes. In multi-stage forging processes, among the important design aspects, the die shape fur preforming is regarded as the design variable since it influences the forged part relatively higher than the others. The rigid-plastic finite element method and the sensitivity method are employed and formulated to solve a formulated optimization problem. An approximation scheme is also used for the direction search during the optimization. The upset forging of a square box is selected as a test example in order to demonstrate and verify the optimization process of this study. After the optimization, the optimized shape of the die yields a finial product of desire shape.

• Journal of Welding and Joining
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• 제3권2호
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• pp.1-9
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• 1985

In this study, the influence of carbon equivalents on friction welds of similar steels was investigated. Four types of steels with 15mm diameter tested in the wide range of carbon equivalents from 0.3 to 1.1 Main experimental results are summarized as follows : (1) Under the constant burn-off length, the friction time becomes longer with the increasing carbon equivalent, but the upset length shows no consistent tendencies. (2) Due to the recrystallization in the contact area, the maximum hardness occurs some away from the contact surface. And it increases almost linearly with the increasing carbon equivalent. (3) Even a steel with 1.1 C.E. can be friction welded to make defect-free welds. (4) With the increasing carbon equivalent, the bend angle and charpy impact value decrease very rapidly in the range from 0.3 C. E., but remain nearly unchanged for C. E. higher than 0.6. (5) Heat treatment of the base metals before welding has very little influence on the mechanical properties of welds. On the other hand, normalizing of the welds improves the bend angle and charpy impact value, but its effect becomes almost negligible, when the carbon equivalents are higher than 0.6.

• International Journal of Aeronautical and Space Sciences
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• 제5권2호
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• pp.28-34
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• 2004

One of the major problem encountered in nuclear plants and satellites design isEMI (Electro-Magnetic Interference) and EMC (Electro-Magnetic Compatibility).Here, our focus is to implement the test board for checking SEU (Single EventUpsets); the effects of protons on the electronic system. The SEU results from thelevel change of stored information due to photon radiation and temperature in thespace environment. The impact of SEU on PLD (Programmable Logic Devices)technology is most apparent in ROM/SRAM/DRAM devices wherein the state ofstorage cell can be upset. In this paper, a simple and powerful test techniques issuggested, and the results are presented for the analysis and future reference. In ourexperiment, the proton radiation facilitv (having the energy of 50 MeV with a beamcurrent of 60 uA of cyclotron) available at KIRAMS (Korea Institute of RadiologicalMedical Sciences) has been applied on a commercially available SRAM manufacturedby Hynix Semiconductor Company.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 E
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• pp.1645-1647
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• 1997

Electronic circuits are becoming more vulnerable owing to the development of integrated circuit. Computer and info-communication facilities are very sensitive to surges caused by lightning, and they can suffer a malfunction and damage. Recent concern about damage and upset caused by transient overvoltages has focused on surge protection. The most important parameter in surge protection is the transient grounding impedance. In this paper, the transient grounding impedances of a rod electrode have been measured under impulse current waves. Z-t, Z-i and V-i characteristics of the grounding electrode in according to the length of the grounding lead wire were obtained and analyzed.

• 한국GIS학회:학술대회논문집
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• 한국GIS학회 2004년도 GIS/RS 공동 춘계학술대회 논문집
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• pp.247-250
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• 2004

OSMI/KOMPSAT-I 위성의 Level-0 영상자료의 줄무늬 제거에 대한 연구가 수행되었다. 이 줄무늬 원인은 크게 2가지로 구분되었다. 하나는 96 pixel CCD의 전반부와 후반부에 따라 얻어지는 신호크기 차이 있으며, 다른 하나는 pixel간의 감도의 차이가 있는 것으로 나타났다. 문제는 각 영상자료마다 이들의 보정계수가 일치하지 못하여 매 영상으로부터 새로운 보정계수가 필요하다는 것이다. 줄무늬 제거의 근본적인 접근은 바로 2가지 문제를 해결하는 방향으로 접근하였다. 즉, 첫 번째 문제인 전후반부의 CCD pixel에서 얻어지는 신호의 크기 차이가 감도의 차이인지 아니면 upset 값의 차이인지가 규명되었고, 동시에 각 센서 pixel의 감도 역시 신호의 세기에 따라 감도가 다른 것으로 나타났다. 본 연구에서는 이러한 모든 줄무늬 보정 정보를 매 영상마다 독립적으로 얻게 하여 OSMI 위성영상의 질을 보다 높일 수 있었다.

• 한국안전학회지
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• 제14권1호
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• pp.150-157
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• 1999

Developed in the study is the analysis of human factors involved in accidents of Korean Construction Projects. The 556 cases are sampled from a survey material 'Serious Accident Cases in the Construction Projects' edited by Korea Industrial Safety Corporation in 1995 through 1997. The analysis of these cases shows that existing classification system is not good for practical applications in real spots since they are difficult for engineers to understand. In this paper, human factors are classified into three groups by extracting the analysis and arrangement of the cases. Futhermore, We'll propose here a new type of accident which is subdivided. If engineers use this type of accident, they will be probably able to analyze efficiently human factors which are involved in accidents and relatied with how it happen. In the case of fall and upset accidents, personal factors seem to be critical when workers are horizontally moving in an unstable manner, and vertically moving without boarding facilities. Futhermore work environmental factors are important when workers release some materials and are performing building and dismantling tasks.

• 한국공작기계학회논문집
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• 제10권6호
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• pp.63-70
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• 2001

This study is concerned with Finite Element Analysis on welded part of control link fur automobile. For analysis, control link was modeled into two parts, ring and rod. Heating condition, temperature distributions and fatigue fracture strength were analyzed using "HEAT III" and "NDURE" module of NISA II. Metal flow in the process of welding was simulat- ed by $DEFORM^{TM}2D$.The analyzed results were compared with experimental inspection. Quality of welded part was able to be improved by controlling metal flow in the process of welding by increase the friction constant of ring part. Heat transfer analysis and flow simulations were in good agreement wish welding experiments.

• 설비공학논문집
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• 제13권12호
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• pp.1255-1265
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• 2001

A numerical study has been conducted to characterize the transient flow in a utility gas turbine burning natural gas. The solution domain encompasses the supply gas pressure regulator to the combustor of the gas turbine that employs multi-nozzle fuel injectors. Some results produced for verification in the present study agree suite well with the experimental ones. It is found that the total gas flow may decrease noticeably during its combustion mode change, which would be the reason of momentary combustion upset, when a reference case of opening ratios of control valves in the system is applied. Several parameters are then varied in order to make the total gas flow stable over that period of time. Results of this study may be useful to understand the unsteady behavior of combustion system burning natural gas.