• Journal of Mechanical Science and Technology
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• v.20 no.9
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• pp.1475-1482
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• 2006

Wet compression means the injection of water droplets into the compressor of gas turbines. This method decreases the compression work and increases the turbine output by decreasing the compressor exit temperature through the evaporation of water droplets inside the compressor. Researches on wet compression, up to now, have been focused on the thermodynamic analysis of wet compression where the decrease in exit flow temperature and compression work is demonstrated. This paper provides thermodynamic and aerodynamic analysis on wet compression in a centrifugal compressor for a microturbine. The meanline dry compression performance analysis of centrifugal compressor is coupled with the thermodynamic equation of wet compression to get the meanline performance of wet compression. The most influencing parameter in the analysis is the evaporative rate of water droplets. It is found that the impeller exit flow temperature and compression work decreases as the evaporative rate increases. And the exit flow angle decreases as the evaporative rate increases.

• Transactions of Materials Processing
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• v.1 no.1
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• pp.42-51
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• 1992

The ring compression test has been widely employed as an experimental means to determine the friction factor. The calibration curves are obtained by the rigid-plastic finite element analysis for various work-hardening exponent and strain-rate hardening exponent. The effects of work-hardening exponent and strain-rate hardening exponent are thoroughly studied and discussed from the finite element computation. The change of friction factor during height reduction in ring compression is also discussed. Then, the method to estimate the change of friction factor during ring compression is proposed.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.18-24
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• 2005

Wet compression means the injection of water droplets into the compressor of gas turbines. This method decreases the compression work and increases the turbine output by decreasing the compressor exit temperature through the evaporation of water droplets inside the compressor. This paper provides thermodynamic and aerodynamic analysis on wet compression in a centrifugal compressor for a microturbine. The meanline performance analysis of centrifugal compressor is coupled with the thermodynamic equation of wet compression to get the meanline performance of wet compression. The most influencing parameter in the analysis is the evaporative rate of water droplets. It is found that the impeller exit flow temperature and compression work decreases as the evaporative rate increases. And the exit flow angle decreases as the evaporative rate increases.

• Transactions of Materials Processing
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• v.14 no.7 s.79
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• pp.635-641
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• 2005

The crystal structure of magnesium was hexagonal close-packed (HCP), so its formability was poor at room temperature. But formability was improved in high temperature with increasing of the slip planes. Purpose of this paper was to know about the mechanical properties of magnesium alloy (AZ31B), before warm and hot forming process. The mechanical properties were defined by the tension and compression tests in various temperature and strain-rate. As the temperature was increased, yield·ultimate strength, K-value, work hardening exponent (n) and anisotropy factor (R) were decreased. But strain rate sensitivity (m) was increased. As strain-rate increased, yield·ultimate strength, K-value, and work hardening exponent (n) were increased. Also, microstructures of grains fined away at high strain-rate. These results would be used in simulations and manufacturing factor fer warm and hot forming process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.69-72
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• 2005

The crystal structure of magnesium is hexagonal close-packed (HCP), so its formability is poor at room temperature. But formability is improved in high temperature with increasing of the slip planes. Purpose of this paper is to know about the mechanical properties of magnesium alloy (AZ31B), before warm and hot forming process. The mechanical properties were defined by the tension and compression tests in various temperature and strain-rate. As the temperature is increased, yield${\cdot}$ultimate strength, K-value, work hardening exponent (n) and anisotropy factor (R) are decreased. But strain rate sensitivity (m) is increased. As strain-rate increased, yield${\cdot}$ultimate strength, K-value, and work hardening exponent (n) are increased. Also, microstructures of grains fine away at high strain-rate. These results will be used in simulations and manufacturing factor for warm and hot forming process.

• 한국연소학회:학술대회논문집
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• 2013.06a
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• pp.33-35
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• 2013

The present work is an experimental investigation on potential operating range using directly injected gasoline fuel in a single-cylinder compression ignition (CI) engine. The objectives of present study were to apply auto-ignited combustion to gasoline fuel and to evaluate potential operating range. In order to auto-ignite gasoline fuel in CI engine, the fuel direct-injection system and the intake air system were modified that a flow rate and temperature of intake air were regulated. The heat-release rate (HRR), net indicated mean effective pressure (IMEP), start of combustion (SOC), and combustion duration were derived from in-cylinder pressure data in a test engine, which has 373.33cc displacement volume and 17.8 compression ratio. The exhaust emission characteristics were obtained emission gas analyzer and smoke meter on the exhaust line system.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.2
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• pp.25-32
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• 1994

The characteristics of the R-22 two-stage compression refrigeration systems were investigated. The apparatus consisted of 0.5HP and 1HP hermetic reciprocating compressors for the high and low stage sides respectively, a condenser, an evaporator, a heat exchanger, four expansion valves, and two intercoolers. The experiments covered a range of refrigerant flow rates from 24 to 84kg/h, and the inlet temperature of cooling water in the condenser and heat source water in the evaporator ranged from 20 to 30$^.\circ}C$The results Showed that the refrigerant flow rate had greater effect on the refrigerating capacities, the compression efficiency and the coefficient of performance of two-stage compression systems than the inlet temperature of heat source water. And all these values were decreased with increasing inlet temperatures of the cooling water. The pressure drops in the evaporator of two-stage compression systems were decreased in proportion to the increase in the inlet temperature of the heat source and cooling water, but it was increased by the refrigerant flow rate.

• Transactions of Materials Processing
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• v.16 no.5 s.95
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• pp.354-359
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• 2007

Effects of forging and mechanical properties of 6061 aluminum alloy wheel for automobiles were investigated in the present study. Microstructural and tensile characteristics of automobile wheel after hot forging process using dynamic screw press were analyzed to evaluate effect of metal flow on mechanical properties. The results showed advanced mechanical properties of 6061 alloy wheel because of $Mg_2Si$ precipitation by T6, elongated grain by forging, and work hardening by dense metal flow, etc. Hot compression tests were conducted in order to characterize high temperature compression deformation behaviors and microstructural variation in the range of $300{\sim}450^{\circ}C$, in the strain rate range of $10^{-3}{\sim}10^1\;sec^{-1}$. As strain rate increased, maximum compression stress increased but it was shown the reverse linear relation between temperature and maximum stress irrelevant to strain rate variation. On the other hand, temperature and yield stress didn't have any linear relation and its relation showed big deviation by a function of strain rate and test temperature.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.12
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• pp.6017-6037
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• 2017

In a multi-resolution image encoding system, the image is encoded into a single file as a layer of bit streams, and then it is transmitted layer by layer progressively to reduce the transmission time across a low bandwidth connection. This encoding scheme is also suitable for multiple decoders, each with different capabilities ranging from a handheld device to a PC. In our previous work, we proposed an edge adaptive hierarchical interpolation algorithm for multi-resolution image coding system. In this paper, we enhanced its compression efficiency by adding three major components. First, its prediction accuracy is improved using context adaptive error modeling as a feedback. Second, the conditional probability of prediction errors is sharpened by removing the sign redundancy among local prediction errors by applying sign flipping. Third, the conditional probability is sharpened further by reducing the number of distinct error symbols using error remapping function. Experimental results on benchmark data sets reveal that the enhanced algorithm achieves a better compression bit rate than our previous algorithm and other algorithms. It is shown that compression bit rate is much better for images that are rich in directional edges and textures. The enhanced algorithm also shows better rate-distortion performance and visual quality at the intermediate stages of progressive image transmission.

• Current Applied Physics
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• v.18 no.11
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• pp.1352-1358
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• 2018

In recent years, one-dimensional (1D) magnetic nanostructures, such as magnetic nanorods and chains of magnetic nanoparticles have received great attentions due to the breadth of applications. Especially, magnetic nanorods has been opened an area of active research and applications in medicine, sensors, optofluidics, magnetic swimming, and microrheology since they possess the unique magnetic and geometric features. This study focuses on the molecular dynamics (MD) simulations of an infinitely long crystal ${\beta}-Fe_2O_3$ nanorod. To elucidate the structural properties and dynamics behavior of ${\beta}-Fe_2O_3$ nanorods, MD simulation is a powerful technique. The structural properties such as equation of state and radial distribution function of bulk ${\beta}-Fe_2O_3$ are performed by lattice dynamics (LD) simulations. In this work, we consider three main mechanisms affecting on deformation characteristics of a ${\beta}-Fe_2O_3$ nanorod: 1) temperature, 2) the rate of mechanical compression, and 3) the rate of mechanical torsion.