• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.432-435
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• 2008

Launch vehicle for injecting the satellite into its orbit is composed with propulsion system, guidance and navigation system, telemetry and so on. Among the others, the propulsion system is the most important part, because that is the key factor of failure of launch vehicle. Especially, the most of failures were occurred in time of engine startup. Therefore, the study of the conditions for stable engine startup is needed at the first step of development. The many researches were accomplished for mathematical modeling, stable startup engine and control of liquid propellant rocket engine. But the cavitation problem that can be occurred at an inlet of pump associated with propellant feeding system wasn't considered in these works. In this paper, propulsion system model was integrated with clustered engines and propellant feeding system for the simulations of engine startup. As the results of simulations, the requirements were deduced for the stable engine startup without the cavitation at an inlet of pump.

• The Journal of the Korea Contents Association
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• v.14 no.3
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• pp.414-426
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• 2014

The purpose of this study is to examine the effects of business startup attributes on the overconfidence of business startup and entrepreneur's attitude in foodservice industry. To achieve this, a survey was carried out to 300 entrepreneurs in the foodservice industry through October 1 to October 30, 2012. The results were as follows. First, entrepreneur's characteristics, funds for business startup, locations and products had a statistically significant positive effect on the overconfidence of business startup(p<.05). Second, funds for business startup, locations and products had a statistically significant positive effect on entrepreneurs' attitude(p<.01). Third, the overconfidence of business startup had a statistically significant positive effect on entrepreneurs' attitude(p<.001). The findings stated above mean that knowledge or experience related to specialized management mind as entrepreneur's characteristic factors are just as important, and customers' use and choice of restaurants are also connected to stable management when the floating population of them are located to a suitable place in combination with product characteristics in enough financing and preparation based on this, showing entrepreneur's positive attitude through stable management along with confidence.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.5
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• pp.60-71
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• 2007

The startup characteristic of liquid propellant rocket engine should be focused on the stable ignition of combustion chamber and gas generator. Also, to lessen the propellants consumption during this period which doesn't contribute to the flight thrust, the engine has to be transferred to the nominal mode quickly. Because of the risk of test, it is impossible to develop all the startup cyclogram or the specifications of engine by test, so the precedent numerical approach is quite necessary. In this study we developed a mathematical model for the startup phenomena in a liquid rocket engine driven by gas generator-turbopump system based on the commercial 1-D flow system analysis program, Flowmaster. Using this program we proposed a methodology to obtain the specifications of turbine starter and the opening time of shutoff valves for the stable startup of the engine. To verify this methodology we qualitatively compared the analysis results to the typical startup curve of the published engine, then found it is quite well matched.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10a
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• pp.319-323
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• 1996

A new steel-making process, strip-casting, is introduced. The strip-casting is a new technique making the thin steel strip from the molten steel directly without resorting to repetitive reheating and hot-rolling required in a conventional steel-making method. This paper derives the mathematical model of strip caster, proposes a control strategy for stable startup operation and a fuzzy decision making rule for automatic control mode change in strip-casting process.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.3
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• pp.1-8
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• 2016

It was examined that start-up characteristics of a staged combustion cycle engine powerpack. Among various parameters, valve opening time was considered as a main factor affecting the start-up characteristics. Using monte-carlo method, characteristics variation was analyzed when the valve opening time deviates from the nominal value. As a result, the main fuel valve opening time and the start turbine ending time were significant associated with the startup characteristics. When separating main fuel valve opening time and start turbine stop time, main fuel valve opening time was an important factor. For stable operation, the main fuel valve opening time must be set one second before after driving the start turbine. Likewise, it was confirmed that the startup analysis can suggest an appropriate startup sequence for a stable startup.

• The Journal of the Korea Contents Association
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• v.13 no.6
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• pp.481-495
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• 2013

The purpose of this study is to figure out the effects of business startup attributes on customer orientation and business startup performance in the foodservice industry. To achieve this, a survey was carried on 300 entrepreneurs, who are running 5 or more years of restaurants in Seoul, through February 1 to February 28, 2013. The SPSS v. 17.0 statistical package program was used for data analysis. The results were as follows; First, the effect of business startup attributes on the understanding of customers' desires in the foodservice industry showed that business startup funds, business startup location, business startup facilities and business startup products had a significant positive effect on the understanding of customers' desires. Second, the effect of business startup attributes on customer relationship in the foodservice industry showed that business startup funds, business startup facilities and business startup products had a significant positive effect on the customer relationship. Third, the effect of customer orientation on business startup performance in the foodservice industry showed that the understanding of customers' desires and customer relationship had a significant positive effect on the business startup performance. These results suggest that business startup funds, business startup location, business startup facilities and business startup products in the foodservice industry are important, and the customer-oriented understanding of customers' desires and close adherence to customers lead to ultimate performance, supporting a stable management in the long term.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.5
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• pp.62-70
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• 2015

A liquid rocket engine system can cause rapid pressure and temperature variations during the startup period. Thus the startup analysis is required to reduce time and expense for successful development of liquid rocket engine through the startup prediction. In this study, a startup analysis simulator is developed for a staged combustion cycle engine powerpack. This simulator calculates propellant flow rates using pressure and flow rate balances. In addition, a rotational speed of turbopump is obtained as a function of time by mathematical modeling. A startup analysis result shows that the time to reach a steady-state and a rotational speed at the steady-state are 1.3 sec and 27,500 rpm, respectively. Moreover it can indicate proper startup sequences for stable operation.

• Journal of Korean Society of Rural Planning
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• v.22 no.4
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• pp.147-157
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• 2016

On the purpose to analyze the survival rate of startup companies since their establishment, the companies' survival rate was investigated by surviving period. The average and coefficient of variation(C.V.) of the startup companies' survival rate were examined with the comparison of urban and rural areas, and primary, secondary, and tertiary industries. In this study, the variation of total numbers of new-established companies, from 1998 to 2012, were analyzed with micro-data of the Statistics Korea, 'The Census on Establishments'. The results show that the survival rate of primary industry companies largely fluctuate and don't be stabled during the whole surviving periods, whereas secondary and tertiary industry companies show stabilized survival rate after fifth year from their establishment. Especially, the startup companies of primary industry located at urban areas show the largest fluctuation and the most vulnerable stability of survival rate. It is concluded that the surviving period of primary industry companies don't guarantee their survival, while survival rate of secondary and tertiary industry company became stable after five years from their establishment.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.5
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• pp.395-403
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• 2020

This study presents a stable start-up strategy for v/f scalar-controlled permanent magnet synchronous motors (PMSMs). The v/f-controlled PMSMs easily lose synchronism under low-speed conditions if an insufficient stator voltage is applied to the machine due to errors in measured motor parameters and inverter nonlinearity, such as inverter dead time and on-state voltage drop. The proposed method adopts the I/f control method to ensure a stable start at low speeds and then switches to the v/f control method at medium speeds. A smooth transition method from I/f control to v/f control is proposed to minimize the oscillation of the stator current and rotor speed during transition. Moreover, the stability of the I/f and v/f control methods is analyzed using a small-signal model. Simulation and experimental results are provided to verify the performance of the proposed control strategy.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.324-327
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• 2008

Two stage startup of high thrust liquid rocket engine can reduce the abrupt impulse to the vehicle and engine by changing oxidizer flow rate to the combustion chamber. Also it ensures stable ignition of combustion chamber against hard start and to prevent pump stall by the sudden supply of large mass flow rate. However high discharge pressure of oxidizer pump or temperature rise in gas generator may be a problem in applying the preliminary stage. To solve this problem, we analyzed the effect of the slope of oxidizer pump's head curve and the oxidizer mass flow rate to combustion chamber during preliminary stage using the rocket engine startup analysis code. A moderate slope(${\circleddash}{\sim}$-3) of head curve and 80% mass flow rate during preliminary stage can reduce the oxidizer pump discharge pressure by 15 to 20% comparing with the condition of ${\circleddash}$=-4.37 head curve and 70% mass flow rate. Also it can maintain the turbine inlet temperature rise within 50K from the nominal value.