• Bulletin of the Korean Space Science Society
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• 2003.10a
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• pp.47-47
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• 2003

Analytical formulae are presented to approximate the evolution of the semi major axis, the maneuver time, and the final mass fraction for low thrust orbital transfers with circular initial orbit, circular target orbit, and constant thrust directed either always along or always opposite the velocity vector. For comparison, the associated results for high-thrust transfers, i.e. the two-impulse Hohmann transfer, are summarized. All results are implemented in a computer code designed to analyze planar planetary and interplanetary space missions. This implementation yields fast and reasonably accurate approximations to trajectory performance boundaries. Consequently, the approach can provide trajectory analysis for each spacecraft configuration during the conceptual space mission design phase. As an example, a mission from Low-Earth Orbit (LEO) to Jupiter's moon Europa is analyzed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.14-17
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• 2011

Numerical simulation was carried out for the SNECMA modulatable thrust devices, with four different nozzle contraction angle $45^{\circ}$, $60^{\circ}$, $83^{\circ}$, and $90^{\circ}$, respectively. Results show that $83^{\circ}$ nozzle contraction is better in that it comes up with good thrust level with small aerodynamic load.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1599-1604
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• 2007

LIMs propelling the MAGLEV which has been developed in Korea have 3-series and 2-parallel connection, so that 6 LIMs per one vehicle are fed by one inverter. Thrust performance of the parallel-operated LIMs can be different from each other because of variant magnetic air gaps and electrical impedance. The thrust difference between the parallel LIMs cause a twist force on the vehicle. This paper proposes an algorithm to measure thrust of the parallel-operated LIMs. The method uses a digital signal processor(TMS320F2812), voltage and current sensors. As a result, thrust, flux and currents of the parallel-operated small LIMs which are manufactured in our laboratory are monitored by the developed measurement system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.569-572
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• 2010

In order to study the performance characteristics of the thrust vector nozzle, the test facility and instrumentation system were designed. In this system, axial thrust, moment, exhaust gas velocity and pressure will be measured by using the scale down experimental model devices. The test facility are composed of high pressure air storage system, flow measuring and control system, test nozzle and thrust measurement system.

• Proceedings of the KIPE Conference
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• 2002.11a
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• pp.40-44
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• 2002

In this paper, robust control method using fuzzy PI parameter tuning is proposed to control constant thrust force on load variation. First, a structure and thrust force equations of the LPM are described. Second, an controller with PI parameter-tuning using a fuzzy theory is proposed to achieve high-precision position with constant thrust force of the LPM. Finally, the effectiveness of an fuzzy PI controller is demonstrated by some simulated and experimental results. Accurate tracking response and superior dynamic performance can be obtained due to the powerful on-line Fuzzy PI gain tuning method with regard parametric variations and load thrust force variations.

• Tribology and Lubricants
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• v.27 no.6
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• pp.302-307
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• 2011

Laser surface texturing (LST) methods are widely applied recently to reduce friction and improve reliability of machine components such as thrust bearings, mechanical face seals and piston rings, etc. In this paper, numerical analysis is carried out to investigate the effect of number of dimples on the lubrication characteristics of parallel thrust bearing using a commercial computational fluid dynamics (CFD) code, FLUENT. Pressure distributions of present analysis are physically consistent than those obtained from numerical analysis of Reynolds equation. The overall lubrication characteristics are highly affected by number of dimples and their locations. The results can be use in design of optimum dimple characteristics to improve thrust bearing performance and further researches are required.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.4
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• pp.73-77
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• 2005

Linear motor has been considered to be the most suitable electric machine for linear control with high speed and high precision. Thrust of linear motor is one of the important factors to specify motor performance. Maximum thrust can be obtained by increasing the magnitude of current in conductor and is relative to the sizes of conductor and magnet. However, the magnitude of current and the size of conductor have an effect on temperature of linear motor. Therefore, it is practically important to find optimum design that can effectively maximize thrust of linear motor within limited range of temperature. Finite element analysis was applied to calculate thrust and numerical solutions were compared with experiments. The temperature of the conductor was calculated from the experimentally determined thermal resistance. The ADPL of ANSYS was used for the optimum design process, which is commercial finite element analysis software. Design variables and constraints were chosen based on manufacturing feasibility and existing products. As a result, it is shown that temperature of linear motor plays an important role in determining optimum design.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.3
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• pp.13-19
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• 2007

This paper described design method to minimize the crosstalk effect of multiaxis thrust measurement stand which can measure the thrust vector control performance of Solid Rocket Motor. This paper presents a theoretical solution for predicting the magnitude of crosstalk and calculates design sensitivity. The results indicate that the most important parameter of crosstalk is the displacement of flexure-loadcell-flexure assembly. And shape, dimension and mechanical properties of flexure and loadcell can also influence the magnitude of crosstalk.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.2
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• pp.63-70
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• 2013

To analyze flow characteristics of the side jet thruster with 4 shutters and rectangular nozzles, a 3-D simulation has been implemented. Numerical calculations for two rotation angles of the shutter, have been conducted. Internal recirculation in a chamber and asymmetric flow structure in a nozzle were observed. In addition, the more shutter rotated, the more asymmetries of flow increased, and this phenomena resulted in thrust bias. The degrees of thrust bias and thrust performance with the rotation angles of the shutter were predicted and compared with theoretical thrust.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.590-595
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• 2006

This paper presents the friction and anti-wear characteristics of nano-oil with a mixture of a refrigerant oil and carbon nano-particles in the thrust slide-bearing of scroll compressors. Frictional loss in the thrust slide-bearing occupies a large part of total mechanical loss in scroll compressors. The characteristics of friction and anti-wear using nano-oil are evaluated using the thrust bearing tester for measuring friction surface temperature and the coefficient of friction at the thrust slide-bearing as a function of normal loads up to 4,000 N and orbiting speed up to 3,200 rpm. It is found that the coefficient of friction increases with decreasing orbiting speed and normal force. The friction coefficient of carbon nano-oil is 0.015, while that of pure oil is 0.023 under the conditions of refrigerant gas R-22 at the pressure of 5 bars. It is believed that carbon nano-particles can be coated on the friction surfaces and the interaction of nano-particles between surfaces can be improved the lubrication in the friction surfaces. Carbon nano-oil enhances the characteristics of the anti-wear and friction at the thrust slide-bearing of scroll compressors.