• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.135-139
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• 2001

This experimental study investigates the wake flow behind a pair of cylinders displaced normal to a free stream. In this experiment, the principal aim is to investigate the transition mechanism of the large vortex generating process in the wake having unique vortex shedding pattern. associated with the gap difference between the cylinders. The detailed visualization is carried out using the PIV measurement. The transition mechanism of the large generating vortex is clarified by showing the streak lines. the vorticity and the statistical fluctuating velocity distributions.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.1259-1263
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• 2006

The inter-coach spacing is one of the most important sources of the aero-acoustic noise of a high-speed train. When fluid at high speed flows over an open cavity, such as the inter-coach spacing, large acoustic pressure fields inside the cavity are produced by fluid/structure interactions at the downstream end of the cavity. In this study experiments were performed to investigate the characteristics the aero-acoustic noise generation from the inter-coach spacing of a high-speed train. Results of the measurement confirmed that the noise generated from the gap between mud-flaps are strongly dependent on the size of the gap.

• Journal of the Korean housing association
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• v.2 no.1
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• pp.77-92
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• 1991

This study is to investigate urban housing conditions in Seoul since 1945. The purposes of this study is to analyze the changes of housing conditions and the gap of average housing conditions and the housing norms longitudinally.For those purposes, the indicators that present the housing conditions are introduced, and the changes of average housing conditions are analyzed by social class, using Population and Housing Census and relateddata. Korean urban housing conditions has been better since 1970s in the aspect of quality. It is, however, relatively much worse than that of developed countries. The gap of housing conditions among social classes is large, especially in qualitative indicators, density and housing facilities. Comparing it with housing norm(as an ideal measurement), it is much worse.

• Journal of Ocean Engineering and Technology
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• v.19 no.1 s.62
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• pp.8-13
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• 2005

In a multiple array of vertical cylinders, flaw patterns are very complex and very interactive between cylinders. The patterns are turbulent and non-linear depending on various factors. The gap and flow incoming velocity of upstream can affect on the downstream cylinder. In this study, the flaw characteristics around two vertical cylinders are investigated numerically and experimentally. As the gap between cylinders is changed at fixed coming velocity, the pressure distributions around cylinders are observed and compared by experimental and numerical approaches. The F.D.M and multi-block method are applied in the study. The pressures at 12 points around the cylinder are measured in the experiment. The results can be applied in the understanding and design of multiple pile array structures.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1041-1042
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• 2007

This paper proposes a new method for detecting broken rotor bars in a squirrel-cage induction motor. The air-gap flux variation analysis was done using search coils inserted in stator slots when broken rotor bar occurs. An accurate modeling and analysis of air-gap flux variation in the induction motor are developed using finite-element (FE) software packages, and measurement of the flux are made using search coils. The simulation was done for the induction motor with 380 [V], 7.5 [kW], 4 Poles, 1,760 [rpm] ratings using the commercial FE analysis tool. The simulation and experiment results can be useful for detecting the broken rotor bar of an induction motor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.175-181
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• 1996

The magnetic levitation system is utilized in the magnetic bearing of high-speed rotor because of little friction, no lubrication, no noise and so on. The magnetic levitation system need the feedback controller for the stabilization of system, and gap sensors are usually used to measure the gap. The use of sensor is troublesome such as sensor trouble, discord between the measurement point and the control point etc. This paper presents the design of robust stabilizing controller by H$_{\infty}$ control theory using the sensorless method proposed already by authors in the magnetic levitation system. And we investigated both the validity of the designed controller and the usefulness of the sensorless method proposed by authors of magnetic levitation system through results of actual experiment..

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1729-1734
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• 2018

Organic-inorganic halide perovskite single crystals undergo phase transition of being cubic, tetragonal, or orthorhombic depending on the temperature. We investigated the $CH_3NH_3PbBr_{3-x}I_x$ single crystals grown by the inverse temperature crystallization method with temperature-dependent UV-Vis absorption and photoluminescence. From the temperature-dependent absorption measurement, the optical band gap is extracted by derivation of absorption spectrum fitting and Tauc plot. In our results, $CH_3NH_3PbBr_{3-x}I_x$ single crystals show that an abrupt change in optical band gap, PL peak position and intensity appears around 120 K - 170 K regions, indicating the phase transition temperature.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.16 no.4
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• pp.383-391
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• 1987

An experimental investigation has been conducted to determine the flow pattern for two-component , two-phase mixtures which flow vertically upwards in concentric annuli based on the measurement for the local void fraction and the distribution of the local void fraction in various radial locations in the annular gap. The annular test section consists of a lucite outer tube whose inside diameter is 38mm and a stainless steel rod, The rod diameter is either :2mm,16mm or 20mm. It is demonstrated that the probability density function of the fluctuations in void fraction may be used as an flow pattern indicator and the local void fraction distribution depends on the flow pattern and radial location in the annular passage.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.1
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• pp.79-84
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• 2007

Inventories of soluble elements in the gap and grain boundaries of domestic used PWR fuel pellets were measured to estimate the quantities of radionuclides that are liable to be rapidly released into the groundwater of a disposal site. The gap inventory of cesium for the pellets in the used fuel with a burn-up range of 45 to 66 GWD/MTU showed 0.85 to 1.7% of its total inventory, which was close to 1/6 to 1/3 of the fission gas release fraction (FGRF). However, the amounts of cesium released from the gaps of the pellets below 40 GWD/MTU of a burn-up and less than 1% FGRF were so erratic that the gap inventory could not be defined by ie FGRF. Strontium inventories in the gap and grain boundaries of the pellets in the same rod were not significantly varied, and the iodine inventory in the gap of the used PWR fuels was estimated to be less than or the same as the FGRF.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1343-1351
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• 2000

Thermally induced errors have been significant factors affecting the machine tool accuracy. In this paper, the spindle thermal error has been focused, where the 5 degree of freedom thermal error components are considered. An effective measurement system has been devised for the 5 DOF thermal errors, consisting of gap sensors and thermocouples around the micro-computer interfaced environment. Several thermal error modeling techniques are also implemented for the thermal error prediction: multiple linear regression, neural network and system identification methods, etc. The performance of the thermal error modeling techniques is evaluated and compared, giving the system identification method as the optimum model having the least deviation. The developed system for the thermal error measurement and modeling was practically applied to a CNC machining center, and the spindle thermal errors were effectively compensated around the micro computer-machine tool interfaced networks. The machine tool accuracy was improved about 4-5 times typically.