• Journal of Industrial Technology
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• v.20 no.B
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• pp.15-20
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• 2000

High pressure, pressure ratio, refrigerating effect, heat transfer from the condenser and the power of the compressor etc. of a self-made refrigeration equipment for R-12 are investigated when R-12 and R-134a are used as the coolants. The comparison between the performance for R-12 and that for R-134a is made. As a result, R-134a is better than R-12 in the view of high pressure, refrigerating effect and the coefficient of performance and vice versa in the view of pressure ratio, exit gas temperature from the compressor and heat transfer from the condenser.

• Tribology and Lubricants
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• v.15 no.1
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• pp.98-107
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• 1999

In this work the effect of pressure drop at inner film due to centrifugal forces acting on the lubricating fluid is investigated for static and dynamic characteristics of floating ring journal bearing. The momentum effect of oil supply into a inner film through oil feeding holes of floating ring on the bearing performance is also studied. It is compared the pressure drop effects and the momentum effect of oil supply into a inner film fur all bearing performance parameters. It is shown that some performance of floating ring bearings can be controled by the momentum of oil supply into a inner film.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.238-244
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• 2003

An experimental study was performed to examine the heat transfer performance of individual rows of fin-tube heat exchangers. The heat transfer performance was measured using air-enthalpy type calorimeter. The examined heat exchangers consists of $7{\Phi}$ tube and fin patterns of them are slit and louver types. Equivalent fin spacing are 18 FPI for all samples, and the number of tube rows were 2. In order to confirm that thermal boundary condition on fins of each row are the same, physically separated between two rows as well as connected heat exchangers were used. The frontal air velocity varied from 0.7 to 2.5 m/s. Heat transfer performance for each row are measured. It was observed that the heat transfer coefficient of the 2nd row were smaller than that of the 1st row at low Reynolds number while larger at high Reynolds number.

• Ocean Systems Engineering
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• v.14 no.2
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• pp.141-156
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• 2024

The turbine system converts the kinetic energy of water flow to electricity by rotating the rotor in a restricted waterway between the seabed and free surface. A turbine system's immersion depth and rotation direction are significantly critical in the turbine's performance along with the shape of the rotor. This study has investigated the hydrodynamic performance of the Savonius hydrokinetic turbine (SHT) according to the immersion depth and rotation direction using computational fluid dynamics (CFD) simulations. The instantaneous torque, torque coefficient, and power coefficients are calculated for the immersion ratios Z/D ranging [0.25, 3.0] and both clockwise (CW) and counterclockwise (CCW) rotations. A flow visualization around the rotor is shown to clarify the correlation between the turbine's performance and the flow field. The CFD simulations show that the CCW rotation produces a higher power at shallow immersion, while the CW rotation performs better at deeper immersion. The immersion ratio should be greater than the minimum of Z/D=1.0 to obtain the maximum power production regardless of the rotation direction.

• Proceedings of the KIEE Conference
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• 2006.10c
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• pp.588-590
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• 2006

Recently, many on-line approaches to instrument channel surveillance (drift monitoring and fault detection) have been reported worldwide. On-line monitoring (OLM) method evaluates instrument channel performance by assessing its consistency with other plant indications through parametric or non-parametric models. The heart of an OLM system is the model giving an estimate of the true process parameter value against individual measurements. This model gives process parameter estimate calculated as a function of other plant measurements which can be used to identify small sensor drifts that would require the sensor to be manually calibrated or replaced. This paper describes an improvement of auto-associative kernel regression by introducing a correlation coefficient weighting on kernel distances. The prediction performance of the developed method is compared with conventional auto-associative kernel regression.

• Journal of Aerospace System Engineering
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• v.10 no.1
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• pp.35-42
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• 2016

Bearing friction and disturbance are the important parameters in control spacecraft using reaction wheel. In this paper, those parameters are estimated by preload and oil quantity. In order to determine the bearing preload's impact on performance, measure the disturbance and the bearing friction coefficient with increasing the preload to the allowed amount. And, find the relationship between oil quantity and bearing friction coefficient, measure it with increasing the oil amount in the bearing. With these results as a reference, find the appropriate amount of preload and oil quantity.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.2
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• pp.415-419
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• 2007

Data compression is very important for the storage and transmission of informations. EZW image compression algorithm has been widely used in real application due to its high compression performance. In the EZW algorithm, when a new significant coefficient is generated, its children are all encoded, although its all descendants may be insignificant, and thus its performance is declined. In this paper, we proposed an improved EZW algorithm using IS(Isolated Significant) symbol, which checks all descendants of significant coefficient and avoids encoding the children of each newly generated significant coefficient if it has no significant descendant.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.733-736
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• 2002

This study was carried out to investigate the braking performances associated with the friction coefficients and temperature fluctuations. Friction coefficient stability and maximum temperature of brake drums, made of an Al-MMC and conventional cast iron, were tested by the inertial brake dynamometer during 15 braking operations. Also the temperature distribution was analyzed by the finite element analysis(FEA). In this experiment, both lower temperature rise near the drum surface and less variation of friction coefficient, compared to those of cast iron, were observed with Al-MMC drums during braking operations.

• Journal of Electrical Engineering and information Science
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• v.2 no.6
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• pp.36-42
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• 1997

This paper presents a new design technique for performing high quality low bit rate image compression. A hybrid coder(HC) which combines Mean Removed Important Coefficient Selection based JPEG(MR-ICS-JPEG) and Adaptive Vector Quantization (AVQ) is proposed. A new quantization table is developed using the Important Coefficient Selection(ICS) method; the importance of each coefficient is determined using the orthonormal property of the DCT. This quantization table is applied to standard JPEG with mean removal(MR) strategy before processing. This scheme, called MR-ICS-JPEG, produces more than 2 dB enhanced performance in terms of PSNR over standard JPEG. A set of homogeneous codebooks is generated by homogeneous training vectors. Before compression, an image is uniformly divided into 8${\times}$8 blocks. Low detail regions such as backgrounds are roughly coded by AVQ while high detail regions such as edges or curves are finely coded by the proposed MR-ICS-JPEG. This hybrid coder procuces consistently about 3 dB improved performance in terms of PSNR over standard JPEG.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.3
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• pp.977-985
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• 2012

Performance optimization of a small engine intake port has been studied through computational and experimental approach. Port angle, flange area and port shape are very important design parameters affecting performance of an intake port. Especially, radius of curvature of intake port inner surface has major effect on the flow coefficient of an intake port. As increasing port angle and flange area, flow coefficient is increased because pressure distribution and pressure gradient in the intake port are improved. Even though computational results over-predict maximum 8% compared with experimental result, they describe the tendency of flow coefficient according to the design parameters. Optimized intake port shows about 4.5% improved flow performance.