• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.158-163
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• 2009

Titanium alloy sheets have excellent specific strength and corrosion resistance as well as good performance at high temperature. Recently, titanium alloys are widely employed not only aerospace parts but also bio prothesis and motorcycle. However, due to the low formability and large spring back at room temperature, titanium alloy sheets were usually formed by slow forming or hot forming with heating die and specimen. In the sheet metal forming area, FE simulation technique to optimize forming process is widely used. To achieve high accuracy FE simulation results, Identification of material properties and deformation characteristic such as yield function are very important. In this study, uniaxial tensile and biaxial tensile test of Ti-6Al-4V alloy sheet with thickness of 1.0mm were performed at elevated temperature of 873k. Biaxial tensile tests with cruciform specimen were performed until the specimen was breakdown to characterize the yield locus of Ti-6Al-4V alloy sheet. The experimental results for yield locus are compared with the theoretical predictions based on Von Mises, Hill, Logan-Hosford, and Balat's model. Among these Logan-Hosford's yield criterion well predicts the experimental results.

• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.44-48
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• 2021

In order to obtain ultra-high resolution MRI images, research and development of 11 T or higher superconducting magnets have been actively conducted in the world, recently. The high-temperature superconductor (HTS), first discovered in 1986, was very limited in industrial application until mid-2010, despite its high critical current characteristics in the high magnetic field compared to the low-temperature superconductor. This is because HTS magnets were unable to operate stably due to the thermal damage when a quench occurred. With the introduction of no-insulation (NI) HTS magnet winding technology that does not burn electrically, it could be expected that the HTS magnets are dramatically reduced in weight, volume, and cost. In this paper, a 6 T-class NI HTS magnet for basic characteristic analysis was designed, and a distributed equivalent circuit model of the NI coils was configured to analyze the charging current characteristics caused by excitation current, and the charge delay phenomenon and loss were predicted through the development of a simulation model. Additionally, the critical current of the NI HTS magnets was estimated, considering the magnetic field, its angle and temperature with a given current. The loss due to charging delay characteristics was analyzed and the result was shown. It is meaningful to obtain detailed operation technology to secure a stable operation protocol for a 6T NI HTS magnet which is actually manufactured.

• Nuclear Engineering and Technology
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• v.55 no.2
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• pp.780-791
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• 2023

To study oscillation characteristic of steam and non-condensable gas direct contact condensation through multi-hole sparger at low mass flux, a series of experiments of pure steam and mixture gas condensation have been carried out under the conditions of steam mass flux of 20-120kg/m²s, water temperature of 20-95 ℃ and mass fraction of non-condensable gas of 0-5%. The regime map of pure steam condensation through multi-hole sparger is divided into steam chugging, separated bubble, aggregated bubble and escaping aggregated bubble. The bubbles behavior of synchronization in the same hole columns and desynchronized excitation between different hole columns can be found. The coalescence effect of mixture bubbles increases with water temperature and non-condensable gas content increasing. Pressure oscillation intensity of pure steam condensation first increases and then decreases with water temperature increasing, and increases with steam mass flux increasing. Pressure oscillation intensity of mixture gas condensation decreases with water temperature and non-condensable gas content increasing, which is significantly weaker than that of pure steam condensation. The oscillation dominant frequency decreases with the rise of water temperature and non-condensable gas content. The correlations for oscillation intensity and dominant frequency respectively are developed in pure steam and mixture gas condensation at low mass flux.

• International Journal of Automotive Technology
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• v.8 no.6
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• pp.705-711
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• 2007

A rectangular fin with a fluid in the inside wall is analyzed and optimized using a two-dimensional analytical method. The influence of the fluid convection characteristic number in the inside wall and the fin base thickness on the fin base temperature is listed. For the fixed fin volumes, the maximum heat loss and the corresponding optimum fin effectiveness and dimensions as a function of the fin base thickness, convection characteristic numbers ratio, convection characteristic number over the fin, fluid convection characteristic number in the inside wall, and the fin volume are represented. One of the results shows that both the optimum heat loss and the corresponding fin effectiveness increase as the fin base thickness decreases.

• Progress in Superconductivity and Cryogenics
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• v.15 no.3
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• pp.9-12
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• 2013

Current-voltage characteristic models of superconducting material are suggested by many researchers. These current-voltage characteristic models are important because they can be used for design or simulation of superconductor devices. But widely used current-voltage models of superconductor wire still have some limitations. For example, a standard E-J power model has no parameters related with stabilizer's resistance in superconductor wire. In this paper, a current-voltage characteristic modeling method for high temperature superconductor (HTS) tape with considering the effect of stabilizer is introduced. And a current-voltage characteristic of a HTS tape is measured under different stabilizer conditions. Those measured current-voltage characteristics of the HTS tape modeled with proposed modeling method and the modeling results are compared.

• The KSFM Journal of Fluid Machinery
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• v.9 no.6 s.39
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• pp.22-28
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• 2006

Operation of a microturbine was simulated on the basis of component characteristic parameters obtained from performance test. Characteristic parameters, such as compressor and turbine efficiencies, recuperator effectiveness as well as turbine inlet temperature, were obtained for a wide operation range. Component characteristics including performance maps and characteristic curves were generated using measured data. Based on the component characteristics, a simulation program was constructed and operation of the microturbine was simulated, and the simulated results were compared with the measured data to verify the program. Also, influence of variation in the power control scheme on the operating characteristic and performance of the engine was simulated. The simulation program can be used for predicting operation of both healthy and degraded engine conditions.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.6
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• pp.81-87
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• 2008

A geometrically asymmetric trapezoidal fin with variable fin base thickness and height is optimized based on the fixed fin base height using a one-dimensional analytic method. The temperature profile along the normalized X position in the fin is presented. For the fixed fin base height, the optimum heat loss, fin length and efficiency as a function of inside fluid convection characteristic number, fin base thickness and height, fin shape factor, convection characteristic numbers ratio and ambient convection characteristic number are represented. One of the results shows that the effect of fin base height and ambient convection characteristic number on the optimum values is remarkable.

• Progress in Medical Physics
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• v.27 no.4
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• pp.224-231
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• 2016

The usefulness of Gel Bolus phantom was investigated by comparing the temperature distribution characteristic of the agar phantom produced to investigate the dose distribution characteristic of radiofrequency hyperthermia device with that of the Gel Bolus phantom under conditions similar to those of an agar phantom that can continuously carry out temperature measurement. The temperatures of the agar phantom and the Gel Bolus phantom were raised to $36.5{\pm}3^{\circ}C$ and a temperature sensing was inserted at depths of 5, 10, and 15 cm from the phantom central axis. The temperature increase rate and the coefficient of determination were analyzed while applying output powers of 100 W and 150 W, respectively, at intervals of 1 min for 60 min under conditions where the indoor temperature was in the range $24.5{\sim}27.5^{\circ}C$, humidity was 35~40%, internal cooling temperature of the electrode was $20^{\circ}C$, size of the upper electrode was 250 mm, and the size of the lower electrode was 250 mm. The coefficients of determination of 150 W output power at the depth point of 5 cm from the central axis of the phantom were analyzed to be 0.9946 and 0.9926 in the agar and Gel Bolus phantoms, respectively; moreover, the temperature change equation of the agar and Gel Bolus phantoms with time can be expressed as follows in the state the phantom temperature is raised to $36^{\circ}C:Y(G)$ is equation of Gel Bolus phantoms (in 5 cm depth) applying output power of 150 W. Y(G)=0.157X+36. It can be seen that if the temperature is measured in this case, the Gel Bolus phantom value can be converted to the measured value of the agar phantom. As a result of comparing the temperature distribution characteristics of the agar phantom of a human-body-equivalent material with those of the Gel Bolus phantom that can be continuously used, the usefulness of Gel Bolus phantom was exhibited.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.405-408
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• 2008

This study, as mock-up test for applying Polylon Fiber engineering method to the field, analyzed the fundamental characteristics and the fireproof characteristics of high strength concrete mixed with Polylon Fiber 0.05% and the results are summarized as followings. From the characteristic of the fresh concrete, both slump flow and air content were appeared to satisfy target range. And from the characteristic of hardened concrete, all compressive strengths according to the curing conditions were appeared to satisfy design standard strength of 60 MPa. From the fireproof characteristic, small scaling and spalling phenomenon were partially appeared on the surface part of specimens, but generally the excellent fireproof capacities were appeared. From the characteristic of temperature hysteresis, the highest temperature and the average temperature of reinforcing part after fire-resistant test for 3 hours were $531^{\circ}C$ and $405{\circ}C$, respectively and then satisfied fireproof standard of the Ministry of Land Transportation and Maritime Affairs.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.10
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• pp.100-106
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• 2009

In this study, methods of overheat detection at the coupling or wire in electrical facility are investigated, operating characteristic about the optic temperature sensor for continuous on-line temperature monitoring in diagnostics system of electrical facility is analyzed. Heating sources in the experiment for operating characteristics of optic temperature sensor use black body and hot plate, output voltage of optic temperature sensor in accordance with temperature variation is analyzed. Overheat generation due to poor contact at the circuit breaker in panel board detects using a thermocouple, infrared thermal camera and optic temperature sensor, and experiment results are analyzed. The effect of optic temperature sensor is the same that of other methods. These results expect to use basic research material for adjusting field of electrical diagnostics system using RFID type optic temperature sensor in the near future.