• Proceedings of the KIEE Conference
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• 2008.04c
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• pp.83-85
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• 2008

This paper deals with design and dynamic analysis of electromagnets for levitation applications. On the basis of equivalent magnetic circuit (EMC) method and 3-D finite element analysis (FEA) model, initial and detailed design for electromagnets are performed. Using the state equation for the closed-loop control, the dynamic analysis of electromagnets is also performed. Finally, this paper investigates the variation of levitation force according to current under fixed nominal air-gap, and the variation of required current according to load weight in order to maintain the nominal air-gap. From these results, the validation of design and dynamic analysis of electromagnets is confirmed. In particular, the influence of winding temperature on levitation control is discussed in detail.

• Proceedings of the KIEE Conference
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• 2004.04a
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• pp.62-64
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• 2004

This paper presents results of the finite-element(FE) analysis of air-gap flux variation in induction motor when rotor vibration conditions occur. Accurate modelling and analysis of rotor vibration in the machine are developed using FE software packages, and search coils are used for measuring the flux. In the FE analysis, the induction motor with 380 [V], 5 [HP], 4P, 1742 [rpm] ratings is used. The results of FE analysis can be useful for on-line vibration monitoring of the motor.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1201-1203
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• 2005

This paper presents results of the finite-element(FE) analysis and experiment of air-gap flux variation in induction motor when rotor eccentricity vibration conditions occur. An accurate modeling and analysis of rotor vibration in the machine are developed using commercial FE analysis tool and search coils are used for measuring the actual air-gap flux. In the FE analysis and experiment, the induction motor with 380[V], 5[HP], 4r, 1742[rpm] ratings is used. The simulation and experimental results can be useful for rotor vibration monitoring of the induction motor.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.9
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• pp.920-929
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• 2008

The main noise and vibration source of the BLDC rotary compressor for air conditioner was analyzed by using the measurement of noise and vibration, noise contour, and experimental modal analysis. The source is presumed to the mechanical resonance excited by the electromagnetic attractive force of the BLDC motor. To reduce the excessive noise of the BLDC rotary compressor due to the mechanical resonance, air-gap enlargement and structural dynamic modification were applied in this paper. Its validations were conducted by the analysis of the electromagnetic attractive force which is generated by the BLDC motor and by the measurement of noise and vibration of the BLDC rotary compressor. By enlarging the length of air-gap and conducting the structural dynamic modification, the noise and vibration in the compressor was significantly improved by 4.5 dB(A) and 56 percent, respectively.

• Fibers and Polymers
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• v.2 no.4
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• pp.203-211
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• 2001

Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait\`s state equation. Flow analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene.

• Proceedings of the KOR-KST Conference
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• 1998.10a
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• pp.236-244
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• 1998

When the capacity and traffic operation at signalized intersections are analyzed in Korea, the unprotected left-turn saturation flow rate, which is an important parameter for the analysis, is estimated form the USHCM model. thus, exact analysis of the left-turn is not possible because of the difference of traffic environments between two contries. In order to improve this problem, it is undertaken in this study to develop techniques for the estimation of unprotected left-turn saturation flows based on Korean drivers' data. As study intersections, signalized or unsignalized intersections on the 6, 4 and 2 lane streets are selected. the data for the saturation flow measurement and gap-acceptance behavior analysis are inputed in a notebook computer on the sites. The critical acceptance gaps of the 6, 4, and 2 lane streets are analyzed to be 6.0 secs, 4.6 secs, and 4.3 secs respectively. the average minimum headway of the left-turn vehicle was observed to be 2.6 secs. As the model to estimate unportected left-turn saturation flows, the drew model is recommended for 6 and 4 lane streets, and a graph is suggested for the 2-lane street. As the values of the parameters of the Drew model, the 2.6 secs of this study is recommended for the average minimum headway of the left-turn. But, the critical acceptance gap varies according to the approach speed of opposing traffic and driver population, it requires field survey to measure the gap of an intersection; however, the values of the gaps studied in this study may be used for the general intersections in urban area in Korean.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.341-349
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• 2001

Heat distortion of the non-contacting mechanical face seal is affected by friction heat between primary seal and seal sheet. The fluid or gas in mechanical face seal maintains operating gap, cooling friction heat and lubricates at the face of seal. So we designed face of seal for inclined face. inclined face of seal improves fluid or gas flow at the face of seal and it increases circumferential velocity at outer radius of the seal so temperature of the seal is decreased by low heat transfer coefficient at there. In this paper, inclined face seal are analysed numerically using finite element method for proof improve inclined face seal performance. Angle of the incline face used for FEA is from 50$^{\circ}$to 90$^{\circ}$and for explaining the effects of inclined face in seal, we get temperature, face distortion, and stress in the seal with variable operating gap and rotating speeds. Result of analysis shows that angle of the incline face is 60$^{\circ}$come to good thermal distortion characteristics.

• Journal of the Korean association of regional geographers
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• v.15 no.6
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• pp.774-788
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• 2009

This research analyzed the relative efficiency of 27 local governments' aged welfare institutions and facilities in Gyeonggi-do Province by using Data Envelopment Analysis. The results show that 12 local governments' aged welfare institutions are relatively inefficient as compare to their reference groups, meaning that there is efficiency gap among localities. It also appears that the most influential input and output elements are the budget for the aged and the number of the aged welfare institutions and facilities, relatively. However, the influential elements differ from one locality to another.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.119-122
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• 2005

A study on motor current signature analysis has been executed for monitoring the fault of journal bearing due to wear. The air gap eccentricity of motor produces specific frequencies in motor current, the supplied current frequency plus and minus rotational rotor frequency. The air gap eccentricity is simulated by the clearance of Journal bearing. The amplitudes of the specific frequencies increase with the increasing clearances. The amplitudes of the specific frequencies continue to increase over the wear limit that is used in the manufacturer of the test motor. Though clear relations between the amplitudes of the specific frequencies and the clearances are not obtained in this paper, the specific frequencies can be used as an indicator of a journal bearing fault. Further study is necessary to make out the quantitative relations between the specific frequencies and the clearances.

• Education of Primary School Mathematics
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• v.15 no.1
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• pp.13-29
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• 2012

This study is the analytic research of items having gender gap in 6th grade students in 'National Assessment of Educational Achievement(NAEA)'. For this problem solving, the following was investigated. First, items having gender gap were selected in NAEA for the past eight years. Then, the mathematical factors that cause gender gap were analyzed. Second, to do this the field test was developed using item concept map. Finally, after the analysis of field test result the reason of gender gap was deduced. Through this study the improvement of mathematics teaching and learning method in elementary school is expected.