• Aerospace Engineering and Technology
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• v.8 no.2
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• pp.133-139
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• 2009

An analysis has been performed on the specific impulse for a liquid rocket engine of gas generator cycle. The present analysis method has been validated through the comparison of the optimal specific impulse for the 300t thrust conceptual engine against the published data. The engine specific impulse can be increased by applying film coolant decreasing the fuel pump head for regenerative cooling despite the decrease of specific impulse of the combustion chamber when the film coolant participates combustion more than the critical amount. The improved condition shows that higher combustion chamber pressure is achieved with less fuel pump head rise by additional film cooling.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.4
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• pp.1-11
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• 2004

Combustion and fuel distribution characteristics of heavy duty engine with the liquid phase LPG injection(LPLI) were studied in a single cylinder engine, Swirl ratio were varied between 1.2, 2.3, and 3.4 following Ricardo swirl number(Rs) definition, Rs=2.3 showed the best results with lower cycle-by-cycle variation and shorter burning duration in the lean region while strong swirl(Rs=3.4) made these worse for combustion enhancement. Excessive swirl resulted in reverse effects due to high heat transfer and initial flame kernel quenching. Fuel injection timings were categorized with open valve injection(OVI) and closed valve injection(CVI). Open valve injection showed shorter combustion duration and extended lean limit. The formation of rich mixture in the spark plug vicinity was achieved by open valve injection. With higher swirl strength(Rs=3.4) and open valve injection, the cloud of fuel followed the flow direction and the radial air/fuel mixing was limited by strong swirl flow. It was expected that axial stratification was maintained with open-valve injection if the radial component of the swirling motion was stronger than the axial components. The axial fuel stratification and concentration were sensitive to fuel injection timing in case of Rs=3.4 while those were relatively independent of the injection timing in case of Rs=2.3.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2625-2632
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• 2024

In this study, we investigated the possibility of employing accident tolerant fuel (ATF) in VVER-1200/V491 assembly without gadolinium-containing fuel rods using the Monte Carlo code Serpent 1.1.7 with ENDF/B-VII cross-section library. The analysis involves assembly design with reflective boundary conditions. To compare the neutronic performances, U-5Mo, U-7.5Mo, U-10Mo, and U-15Mo fuels were chosen in addition to ordinary UO₂ fuel. The concentration of ¹³⁵Xe, ¹⁴⁹Sm, fissile and fertile isotopes with burnup, reactivity feedback with fuel temperature variation, and β eff values were calculated. The results indicate that the fuel cycle length increases by 54.27% for U-5Mo, 32.6% for U-7.5Mo, and 13.8% for U-10Mo, while it decreases by 16.4% for U-15Mo fuel. Additionally, the effect of ⁹⁵Mo content in natural Mo was investigated by reducing the ⁹⁵Mo concentration. According to the results, each proposed fuel's fuel cycle length extended when the depletion ratio of ⁹⁵Mo increased. Additionally, the calculations for reactivity feedback guarantee safe operating conditions for all U-xMo fuels.

• Journal of Korean Society for Quality Management
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• v.28 no.3
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• pp.91-103
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• 2000

It is very important to rationally allocate manufacturing processes because customer's needs are being various, and product life cycle in the market Is being shortened. The process allocation is needed before making process control plan and is mostly being done by the field experience or intuition of machine operator, process engineer and/or maintenance technician. Therefore, a modified allocation method using the process variation is proposed. This paper presents the result of comparative studies between current method and the proposed one.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.700-705
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• 2005

This study presents a fatigue line with a plastic rotational angle to a great extent of plastic strain of Low-Cycle-fatigue period, such as earthquake, etc. This fatigue line with a plastic rotational angle is measured and analysed more simply in practice rather than Woehler's fatigue line which is developed in stress variation of the structure. It shows that the slope of fatigue line with a plastic rotational angle is equal to that with plastic strain through the experiments by proving the correlation that the plastic strain ratio is directly proportional to the plastic rotational angle in plastic hinge.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.4
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• pp.317-324
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• 2015

In this study, a solar thermal system is designed to provide hot water and electricity for improvement of solar thermal energy availability in an apartment complex. The electricity is generated with Organic Rankine Cycle (ORC) by the solar thermal energy. R134a, R141b and R245fa are selected for operating fluid of the solar thermal ORC system. ORC with R245fa shows the best performance based on the variation of pressure. The irreversibility of component showed that the technology advance of the evaporator ensures a performance improvement. The sensitivity study results indicate that the turbine performance is most effective way to improve the performance of ORC system. An economic analysis showed that approximately 50% more income could be achieved by a solar thermal ORC system with a hot water supply.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.367-373
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. Activation energy is used as parameter as 10, 20, 27 and 35, and the specific heat ratio and the heat release are fixed as 1.2 and 50. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable pitch at Ea=10, periodical unstable pitch at Ea=20 and 27 and unstable pitch consisting of stable, periodical unstable and weak modes at Ea=35, respectively. In the weak mode, there is no Mach leg on the shock front, where the pressure level is much lower than the other modes. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of these stable and unstable modes. In the stable pitch at Ea=10, the maximum pressure history on the tube wall remained nearly constant, and the steady single Mach leg on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the periodical unstable pitch at Ea=20 and 27 of the maximum pressure history. The high frequency was one cycle of a self-induced oscillation by generation and decay in complex Mach interaction due to the variation in intensity of the transverse wave behind the shock front. Eventually, sequential high frequency oscillations formed the low frequency behavior because the frequency behavior was not always the same for each cycle. In unstable pitch at Ea=35, there are stable, periodical unstable and weak modes in one cycle of the low frequency oscillation in the maximum pressure history, and the pressure amplitude of low frequency was much larger than the others. The pressure peak appeared after weak mode, and the stable, periodical unstable and weak modes were sequentially observed with pressure decay. A series of simulations of spinning detonations clarified that the unsteady mechanism behind the shock front depending on the activation energy.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.367-373
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. Activation energy is used as parameter as 10, 20, 27 and 35, and the specific heat ratio and the heat release are fixed as 1.2 and 50. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable pitch at Ea=10, periodical unstable pitch at Ea=20 and 27 and unstable pitch consisting of stable, periodical unstable and weak modes at Ea=35, respectively. In the weak mode, there is no Mach leg on the shock front, where the pressure level is much lower than the other modes. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of these stable and unstable modes. In the stable pitch at Ea=10, the maximum pressure history on the tube wall remained nearly constant, and the steady single Mach leg on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the periodical unstable pitch at Ea=20 and 27 of the maximum pressure history. The high frequency was one cycle of a self-induced oscillation by generation and decay in complex Mach interaction due to the variation in intensity of the transverse wave behind the shock front. Eventually, sequential high frequency oscillations formed the low frequency behavior because the frequency behavior was not always the same for each cycle. In unstable pitch at Ea=35, there are stable, periodical unstable and weak modes in one cycle of the low frequency oscillation in the maximum pressure history, and the pressure amplitude of low frequency was much larger than the others. The pressure peak appeared after weak mode, and the stable, periodical unstable and weak modes were sequentially observed with pressure decay. A series of simulations of spinning detonations clarified that the unsteady mechanism behind the shock front depending on the activation energy.

• Science of Emotion and Sensibility
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• v.17 no.2
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• pp.85-90
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• 2014

The purpose of the study is to develop self-management system that people can enhance physical and psychological health through repeating by themselves to relieve work-related stress. The regular respiration can help homeostasis of heart to maintain. Also the effect can be stabilized from irregular heart rhythm by work-related stress. People have optimal respiration cycle to stabilize heart rhythm and repeat training using their RSP(respiration) time including expiration and inhalation. This system is not only offering optimal respiration training service but also finding optimal respiration cycle. The adults who have stress from work participated in verification experiment. This study expects to help those people who are workers related to call center jobs in emotional labor can relieve their stress. It can also help to enhance their own health and increase their work efficiency.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.8
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• pp.405-411
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• 2000

When faults occur in transmission lines, the classification of faults is very important. If the fault is HIF(High Impedance Fault), it cannot be detected or removed by conventional overcurrent relays (OCRs), and results in fire hazards and causes damages in electrical equipment or personal threat. The fast discrimination of fault needs to effective protection and treatment and is important problem for power system protection. This paper propolsed the fault detection and discrimination algorithm for LIFs(Low Impedance Faults) and HIFs(High Impedance Faults). This algorithm uses artificial neural networks and variation of 3-phase maximum currents per period while faults. A double lines-to-ground and line-to-line faults can be detected using Neural Network. Also, the other faults can be detected using the value of variation of maximum current. Test results show that the proposed algorithms discriminate LIFs and HIFs accurately within a half cycle.