• Journal of ILASS-Korea
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• v.25 no.3
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• pp.126-131
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• 2020

Throttleable rocket engines are in high demand due to the diversification of space missions. Pintle injector is known to be suitable for throttleable rocket engines, because of its high efficiency in overall thrust zone. In this study, the relationship between spray angle of a throttleable pintle injector and total momentum ratio based on hot fire test conditions was investigated. As a result, the spray angle in 100% and 60% throttling level is higher than the spray angle obtained by the case which considers only propellant mass flow rate, owing to higher total momentum ratio (TMR). The results of this study may be useful for predicting spray angle in hot fire test.

• Journal of the Korean Applied Science and Technology
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• v.38 no.1
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• pp.271-279
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• 2021

The purpose of this study was to investigate the effects of maximum and endurance resistance exercises on total work, blood viscosity, and erythrocyte volume ratio. The study subjects were selected as 15 men in their twenties with 12 months or more of resistance exercise experience, and the bench press 1RM was measured before the experiment, and the experiment for each condition was cross-allocated at intervals of one week, and the maximum repetition was performed in 6 sets. As a result, the total amount of exercise showed that the muscular endurance strength was higher than that of the maximum muscular strength (p<.001), and the blood viscosity and erythrocyte volume ratio were higher after exercise than before (p<.01) regardless of the total exercise amount. In summary, it was found that blood viscosity was not affected by exercise intensity and amount of exercise, and increased with one-time resistance exercise. This is clinically significant in constructing a resistance exercise program, and it is considered to be a reference material in creating an exercise program for clinical patients related to vascular disease.

• 한국체육학회지인문사회과학편
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• v.51 no.5
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• pp.639-647
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• 2012

The purpose of this study was to examine the effects of varied resistance training intensities and rest intervals between training sets on integral electromyography (iEMG), repetition rate, and total work. All subjects, 14 college students, were tested one repetition maximum (1RM). Then, all subjects were weekly tested with 9 practice procedures, composed of diverse intensities (60, 75, 90% of 1RM) and rest intervals (1, 3, 5 min). As results show, to maintain the same load and target repetition maximum for an untrained person, muscular power training (90% of 1RM), muscular hypertrophy training (75% of 1RM), and muscular endurance training (60% of 1RM) should be applied with 5 min or longer rest interval periods for 3 training sets. In addition, 2 training sets with 3 min rest intervals and a set with an 1 min rest interval were capable by the subjects. Thus, at least 3 min or longer rest intervals should be applied to maintain multiple training sets. In case for muscular endurance training, which requires shorter rest intervals, the intensity of exercise should be adjusted to 60% of 1RM or less. In conclusion, depending on diverse purposes of resistance training such as improving muscular power, muscular hypertrophy, or muscular endurance, appropriate exercise intensity and rest intervals should be applied.

• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.2
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• pp.60-71
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• 2022

The reusable, low-cost launch vehicle development trend in the recent launch vehicle market is being subdivided into several ways, and the throttleable engine is one of them. Plus, several nations have selected methane as a next-generation propellant due to its cleanness. In this research, a throttleable pintle injector using gas methane and liquid oxygen as propellants was developed, followed by its spray and combustion characteristics analysis, including high pressure cold and hot tests. The designed throttleable pintle injector has a double sleeve structure, and its tightness and functionality are confirmed through repetitive atmospheric, high-pressure cold tests, and hot tests. Though some design errors were discovered and a low throttling level was unable to be achieved in the combustion test.