• 소성∙가공
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• 제8권4호
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• pp.364-373
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• 1999

For material characterization of semi-solid materials, backward extrusion process, which has been used in forming of hollow-sectioned products, was analyzed by the upper bound analysis in the current study. The existing kinematically admissible velocity field was applied to steady state at which there was no change in the assumed regions of velocity field. For unsteady state, new velocity field, as a function of dead zone angle, was proposed. Through the whole analysis, fiction between die and workpiece was also considered. It has been studied how the process variables, such as friction factor and punch velocity, and material parameters, such as strength coefficient, strain rate sensitivity could affect on analysis results. Finally, by the comparison with the finite element analysis, the reliability and efficiency of the proposed velocity field were discussed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.115-118
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• 1991

The temperature distribution on the superconducting thin-film is analyzed as moving constant field is applied above upper critical field. The distribution of magnetic field is derived in the normal spot. Governing equation is obtained with the help of the equation of conservation of energy. The temperature distribution and the heat dissipation are obtained through computer simulation by the method of numerical analysis. Maximum temperature is occured in the most right side inside normal spot. The temperature is increased abruptly inside the normal spot, and decreased more gradually outside normal spot in the direction of moving field as velocity is increased. Increasing the velocity rather than increasing magnitude of the normal spot and the applied field makes maximum temperature larger. Heat dissipation is affected by the velocity rather than the magnitude of normal spot and the applied field.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.572-575
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• 2008

Flow-field design has much influence over the performance of proton exchange membrane fuel cell (PEMFC) because it affects the pressure magnitude and distribution of the reactant gases. To obtain the pressure magnitude and distribution of reactant gases in four kinds of flow-field designs without additional measurement equipment, computational fluid dynamics (CFD) analysis was performed. After the CFD analysis, the performance values of PEMFC according to the flow-field configurations were measured via a single cell test. As expected, the pressure differences due to different flow-field configurations were related to the PEMFC performance because the actual performance results showed the same tendency as the results of the CFD analysis. A large pressure drop resulted in high PEMFC performance. So, the single serpentine configuration gave the highest performance. On the other hand, the parallel flow-field configuration gave the lowest performance because the pressure difference between inlet and outlet was the lowest.

• 천문학회지
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• 제8권1호
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• pp.29-34
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• 1975

Solar electrical conductivity has been calculated, making use of Yun and Wyller's formulation. The computed results arc presented in a tabulated form as functions of temperature and pressure for given magnetic field strengths. The results of the calculation show that the magnetic field does not play any important role in characterizing the electrical conductivity of the ionized gas when the gas pressure is relatively high (e.g., $P{\geq}10^4\;dynes/cm^2$). However, when the gas pressure is low (e.g., $P{\leq}10\;dynes/cm^2$), the magnetic field becomes very effective even if its field strength is quite small (e.g., $B{\leq}0.01$ gauss). It is also found that, except for lower temperature region (e.g., $T{\leq}10^{4^{\circ}}K$), there is a certain linear relationship in a log- log graph between the pressure and the critical magnetic field strength, which is defined as a field strength capable of reducing the non-magnetic component of the electrical conductivity by 20%.

• Nuclear Engineering and Technology
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• 제30권3호
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• pp.202-211
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• 1998

Interfacial stresses at two-material interfaces and initial displacement field over the entire domain are obtained by modifying the potential energy functional with a penalty function, which enforces continuity of the stresses at the interface of two materials. Based on the initial displacement field and interfacial stresses, a new methodology to generate a continuous stress field over the entire domain has been proposed by combining the modified projection method of stress-smoothing and Loubignac's iterative method of improving the displacement field. Stress analysis is carried out on two examples made of dissimilar materials : one is a two-material cantilever composed of highly dissimilar materials and the other is a zirconium-lined cladding tube made of slightly dissimilar materials. Results of the analysis show that the proposed method provides an improved continuous stress field over the entire domain, and accurately predicts the nodal stresses at the interface, while the conventional displacement-based finite element method produces significant stress discontinuities at the interface. In addition, the total strain energy evaluated from the improved continuous stress field converges to the exact value in a few iterations.

• 대한의용생체공학회:의공학회지
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• 제17권1호
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• pp.93-98
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• 1996

The purpose of this paper is to propose a new localized imaging method of reduced imaging time luting a locally-linear gradient. Since most fast MR(Magnetic Resonance) imaging methods need the whole $\kappa$-space(Spatial frequency space) data corresponding to the whole imaging area, there are limitstions in reducing the minimum imaging time. The imaging method proposed in this paper uses a specially-made gradient coil generating a local ramp-shape field and uniform field outside of the imaging areal Conventional imaging sequences can be used without any RF/gradient pulse sequence modifiestions except the change in the number of encoding steps and the field of view.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권7호
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• pp.305-309
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• 2003

This paper was shown the simulation of electric field distribution of globular dielectric for design of ideal packed-bed plasma reactor. When discharge gap between the electrodes and input voltage are each 20[mm]. 10000[V] in the atmosphere, the results of simulation to the electric field was measured stronger at globular dielectric of $\phi$5[mm] than 1$\phi$[mm] and 3.33$\phi$[mm]. And the maximum electric field or globular dielectric with $\phi$10[mm] was increased about 5[%] to maximum electric field of globular dielectric with $\phi$5[mm] in the atmosphere. when dielectric constant of globular dielectric is 100, it was simulated about 90[%] of maximum electric field of globular dielectric over 1000 dielectric constant. Ana the highest electric field appeared as globular electric was parallel structure with the other globular dielectric side by side of the globular dielectric and connected to electrodes.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 추계학술대회 논문집
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• pp.237-241
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• 1997

It is necessary to know the accurate field distribution around the high power apparatus, in designing it. To calculate the field around electrodes, we use the Charge Simulation Method(CSM) among several numerical methods and develop the new \"Field Analysis System\", by which we can draw the shape of electrodes, save the drawing in ascii code and apply CSM on the data. In the Field Analysis System, we try several rules for arrangement of simulation charge on CSM and consider their accuracy. At firs we simulate the case with simple electrode geometry and consider the adequacy of the rules. With tole field Analysis System applied the rules, we simulate the main electrode of load switchgear. As a result of the simulation, equipotential line, flux line and field strength on male electrode are drawn.

• 전기학회논문지
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• 제67권9호
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• pp.1165-1173
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• 2018

Recently, owing to environmental problems and instability of rare earth resources market, non-rare earth electric motors are attracting attention. As a non-rare earth motor type, a wound rotor synchronous motor(WRSM) has high power density and wide driving range further it can reduce loss by field current control during field weakening control at high speed. However, since the d-axis flux of the WRSM is coupled with the rotor circuit, the fluctuation in the d-axis flux linkage affects the rotor circuit, which causes ripple of the field current and torque. In this paper, we propose the field current ripple compensation method by injecting the feedforward voltage. the proposed compensating method was demonstrated by simulation and experiments.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.252-254
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• 2003

A magnetic field sensor is fabricated with superconducting ceramics system. The sensor at liquid nitrogen temperature shows the increase in electrical resistance by applying magnetic field. Actually, the voltage drop across the sensor is changed from zero to a value more than $100{\mu}V$ by the applied magnetic field. The change in electrical resistance depends on magnetic field. The sensitivity of this sensor is 2.9 ohm/T. The increase in electrical resistance by the magnetic field is ascribed to a modification of the Josephson junctions due to the penetrating magnetic flux into the superconducting material.