• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.167-171
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• 2012

A computational analysis of nozzle flow is conducted to investigate effects of the flight altitude on thrust performance. Reynolds-averaged Navier-Stokes equation with k-${\omega}$ SST(Shear Stress Transport) turbulence model is employed to simulate the nozzle flow in various altitude conditions, where continuum mechanics is to be valid. Thrust performance of the nozzle is exceedingly poor upto 10 km of flight altitude because of the irreversible phenomena such as shock and/or flow separation occurring inside the nozzle, whereas it is restored to the nominal value as the altitude is attained higher than 30 km.

• Tunnel and Underground Space
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• v.33 no.5
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• pp.299-311
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• 2023

Continuous excavation technologies are developed to improve the excavation rate of shield TBM. Continuous excavation is a technology that provides thrust to segments, excluding being installed one, to reduce tunneling downtime. This paper investigated the prior technology related to continuous excavation segments. The main technology was classified into helical segment, honeycomb segment, and conventional segment methods. The helical segment method has not been applied in actual construction yet, and the honeycomb segment method has not succeeded in commercialization. The continuous excavation method using conventional segments has been successfully demonstrated. The thrust force and operation method of the thrust jacks for the semi-continuous technology were analyzed. Continuous excavation TBM research is also progressing in Korea, and through the analysis of successful cases, the need to develop independent continuous excavation methods has been identified.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.3
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• pp.165-172
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• 2022

Pintle injector is the most suitable injector for thrust control because it can control the area of propellant injection. Accordingly, the combustion test of multiple hole pintle injector and continuous type pintle injector was carried out in this paper using liquid oxygen and gas methane. The combustion performance of the two pintles was verified with the characteristic speed efficiency, and the experimental results were compared according to the O/F and combustion chamber pressure and under similar conditions. The efficiency of the multi hole pintle was generally somewhat higher than continuous pintle when pintle opening distance(the area of dispensing oxidizer) was in a 100% thrust condition.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.6
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• pp.27-33
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• 2014

2nd stage of KSLV-I, NaRo-Ho, performs CCAM not to collide with Naro Science Satellite. At that moment, the satellite should pass through the Plume Density area which was generated by KSLV-I KM residual thrust. Therefore, it is necessary to predict Plume Density field of KM residual thrust and guarantee the safety of the trajectory of payload. In this paper, DSMC method was used to simulate Plume Density by KM residual thrust and the simulation showed that the trajectory of Naro Science Satellite was safe.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.942-948
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• 2011

Solid propulsion systems have simple structures compared to other propulsion systems and are suitable for long-term storage. However the systems generally have limits on control of thrust levels. In this paper we introduce controllers for combustion chamber pressure using on-off control techniques which have been known for relatively easy implementation and energy efficiency. For this, we use a simple pressure change model by considering only mass conservation within the combustion chamber and we design a classical controllers and on-off controllers with are Pulse Width Modulation(PWM) and Pulse Width Pulse Frequency Modulation (PWPFM). Then we compare the performance results of the controllers through numerical simulations.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.2
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• pp.9-16
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• 2015

The control law for simultaneous pressure and thrust control of solid DACS(Divert Attitude Control System) is suggested. To regulate the two variables effectively, the control structure of sequential loop closer is applied to the system considering the physical characteristics of each variable and the weighted pseudo-inverse method is suggested to allocate effective command for indeterminate system. Also, the pressure guidance law for safe and high acceleration is applied to the homing stage to verify the effectiveness of the command distribution.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.371-374
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• 2008

The performance of several catalysts to decompose the high test peroxide (HTP) was described in this paper. Manganese oxide, Platinum and Iridium were coated on the gamma alumina. The response time of various catalysts was measured with a 50 Newton class thruster. Ir/$Al_2O_3$ that showed the fastest response time at the thruster, failed the reaction when continuous mode test was carried out with the thruster. Pt/$Al_2O_3$ and MnO_2/Al_2O_3$ can be substitutes to decompose the HTP. In addition, for larger thruster, MnO_2/Al_2O_3$ can be a good catalyst because its cost is below 5 % of Pt/$Al_2O_3$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.7
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• pp.647-654
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• 2007

A Discrete continuation Method/homotopy approaches are studied for energy/fuel optimal low thrust Earth escape trajectory by solving a two point boundary value problem(TPBVP). Recently, maneuvers using low thrust propulsion system have been identified as emerging technologies. The low thruster is considered as the main actuator for orbit maneuvers. The cost function consists of a energy/fuel consumption function, and constraints are position and velocity vectors at the terminal escape point. Solving the minimum energy/fuel problem directly is not an easy task, so we adopt the homotopy analysis. Using a solution of the minimum energy, which is solved by discrete continuation method, we obtain the solution of the minimum fuel problem.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.699-705
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• 2011

High-maneuver missile is a projectile which demands a strong momentum at short time. To produce a necessary thrust for the flight, the gas of high temperature and pressure is generated through explosive combustion of solid propellant, and a great thrust can be obtained by expanding this high temperature and pressure gas. Although the operating time of a rocket motor is less than a few seconds, a failure of part or ablation near the throat of nozzle may take place during the expansion of high temperature and pressure gas for great thrust. In other words, for the precise control of a missile an exact stress analysis considering both, the thermal stress caused by the heat transfer between combustion gas and wall, and the mechanical stress caused by the pressure change in the flow, should be considered first. In this connection, this study investigated the safety, as a point of view of stress and melting point of the material, of the pre-designed thrust generating structure which is subjected to high temperature and pressure as a function of motor operating time.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.4
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• pp.300-309
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• 2017

A spacecraft obtains a reaction momentum required for an orbit correction and an attitude control by exhausting a combustion gas through a small thruster in space. If the exhaust plume collides with spacecraft surfaces, it is very important to predict the exhaust plume behavior of the thruster when designing a satellite, because a generated disturbance force/torque, a heat load and a surface contamination can yield a life shortening and a reduction of the spacecraft function. The purpose of the present study is to ensure the core technology required for the spacecraft design by analyzing numerically the exhaust gas behavior of the 10 N class bipropellant thruster for an attitude control of the spacecraft. To do this, calculation results of chemical equilibrium reaction between a MMH for fuel and a NTO for oxidizer, and continuum region of the nozzle inside are implemented as inlet conditions of the DSMC method for the exhaust plume analysis. From these results, it is possible to predict a nonequilibrium expansion such as a species separation and a backflow in the vicinity of the bipropellant thruster nozzle.