• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.1
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• pp.59-63
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• 2011

In small-power applications, variable-speed motors having high efficiency and controllability become more dominant than brushed DC motors. BLDC motors with permanent magnets in the rotor and SRMs directed by reluctance torque due to no permanent magnets have been strongly studied as a candidate. Compared to the BLDC motors, SRMs are more suitable for low-cost applications since the magnetic structure is simple, mechanically robust, and cheap due to no additional excitation in the rotor such as copper wire, aluminum, and permanent magnets. In addition, relatively small number of phases in single and two-phase SRMs allows more cost savings with regards to material in the motor and switching devices in the converter. In this paper, several 2 phase SRMs are compared to a 3 phase 6/4 SRM in terms of flux distribution in key parts of the motors.

• The KSFM Journal of Fluid Machinery
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• v.13 no.3
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• pp.18-23
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• 2010

This paper predicts the unbalance and transient (start-up) response of a 5MW industrial gas turbine by using commercial rotordynamic tool, DYNAMICS 4.3. The gas turbine is operated at 12,975rpm on squeeze film dampers or tilting pad bearings. The stiffness and damping coefficients of the squeeze film dampers and tilting pad bearings are estimated. It is seen that the vibration amplitude of the gas turbine rotor is sufficiently small around the critical speeds and at the rated speed.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.27-36
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• 2006

This paper describes the performance test procedures and results of NRSB-1M and NRSB-2M Not only aerodynamic performance test but also sound measurement test were performed for the small-scaled blades in the ground Total thrusts and torques of the rotor were measured using rotating balance for aerodynamic performance test. Sound pressure levels were measured using microphone in 1.64D distance for sound measurement test. Non-dimensionalized test data are compared and analyzed. Consequently, It was confirmed that NRSB-2 was better than NRSB-1.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.5
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• pp.522-530
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• 2007

In order to extract small hydropower in the very low specific speed range of $n_s<10$, a Positive Displacement Turbine (PDT) has been proposed and steady performances have been determined experimentally. However, the suppression of large pressure fluctuation is inevitable for practical application of PDT. Therefore, present study adopted 4-lobe helical type robe to reduce the pressure fluctuation. The results show that 4-lobe helical type robe can be adopted to suppress the pressure fluctuation drastically. Moreover, efficiency and unit power of the turbine with newly proposed 4-lobe helical type lobe are higher than those of the turbine with 3-lobe straight type robe.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.330-335
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• 2012

Brushless doubly-fed machine (BDFM) doesn't use brush and slip ring, and has advantages such as high system reliability, small capacity of its frequency converter, low system cost, adjustable power factor and speed, etc. At the same time, it has good applicable potentials on the variable frequency motors and the variable speed constant frequency generators. However, due to the complicacy and particularity of BDFM in the structure and operating mechanism, the effect of magnetic field modulation directly influences the operating efficiency of BDFM. To study the effect of different cage rotor structures on the magnetic field modulation of BDFM, the rotor magnetomotive force (MMF) of BDFM with cage rotor is studied by the analytical method. The components and features of rotor harmonic MMFs are discussed. At the same time, the method to weaken the higher harmonics is analyzed by the theoretic formulae. Furthermore, the magnetic field modulation mechanism is expounded on in detail and the relationship between the magnetic field modulation effect and the operating efficiency of BDFM is established. And then, a new method for estimating the magnetic field modulation effect is proposed. At last, the magnetic field modulation effects of four BDFM prototypes with different cage rotor structures are compared by the MMF analysis and the efficiency data of electromagnetic design. The results verify the effectiveness of the new method for estimating the magnetic field modulation effect of BDFM with cage rotor.

• The KSFM Journal of Fluid Machinery
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• v.12 no.3
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• pp.44-52
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• 2009

Small scale steam turbines are used as mechanical drivers in chemical process plant or power generators. In this study, a design technology was developed for a 100kW class steam turbine which will be used for removing $CO_2$ from the emission gas on a reheated cycle system. This turbine is operated at a low inlet total pressure of $5\;kgf/cm^2$. It consists of two stages and operates at the partial admission. For the meanline analysis, a performance prediction method was developed and it was validated through the performances on the operating small steam turbines which are using at plants. Their results showed that the output power was predicted within 10% deviation although the steam turbines adopted in this analysis were operated at different flow conditions and rotor size. The turbine blades was initially designed based on the computed results obtained from the meanline analysis. A supersonic nozzle was designed on the basis of the operating conditions of the turbine, and the first stage rotor was designed using a supersonic blade design method. The stator and second stage rotor was designed using design parameters for the blade profile. Finally, Those blades were iteratively modified from the flow structures obtained from the three-dimensional flow analysis to increase the turbine performance. The turbine rotor system was designed so that it could stably operate by 76% separation margin with tilting pad bearings.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.12
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• pp.997-1004
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• 2020

A synchropter is a type of rotorcraft in which a pair of blades inclined with each other rotates in synchronization. Removing the tail rotor enables an efficient and compact configuration similar to a coaxial-rotor helicopter. This paper describes the design and flight test results of a small synchropter to examine the suitability of a drone system for the army. The synchropter in this paper is a small vehicle with a rotor diameter of 1.4m and a weight of 7kg and was assembled based on commercial parts to examine flight characteristics effectively. The flight control system adopted Pixhawk, which is designed based on an open-architecture. The model-based design technique is applied to develop the control law of the synchropter and a new firmware embedded on the Pixhawk. Through qualitative flight tests, we analyzed the flight characteristics. As a result of the analysis, we confirmed the possibility of application as a drone system of the synchropter.

• Journal of Mechanical Science and Technology
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• v.20 no.4
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• pp.561-568
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• 2006

CFD simulation for one of tilt-rotor UAV configurations, TR-E2S1, was performed to investigate its aerodynamic characteristics. Control surfaces such as elevator and rudder were deflected and wing incidence angle was changed. Also aerodynamic stabilities were analyzed with the variation of pitch and yaw angles. The comparison of CFD with wind tunnel test results reveals the same trends in the aerodynamic characteristics and stabilities. However 12% scale wind tunnel test model is too small for accurate data collection and should build a high fidelity model for quantitative data comparison.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.1
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• pp.56-63
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• 2014

This paper provides a comprehensive study on the Sommerfeld phenomena in an asymmetric rotor with a nonideal power supply. An analytical approach is employed by deriving the equations of motion in a nondimensional form. The system parameters, including the asymmetry, external and internal damping, and motor power, are chosen to find their effects on the characteristics of the Sommerfeld phenomena and critical behavior around resonance. Results show that the rotor asymmetry suppresses the Sommerfeld phenomena and helps pass through resonance if the asymmetry is small. However, it is observed that the opposite effects exist in case of a large asymmetry. It is also found that the effects of external damping on the Sommerfeld phenomena are similar to those of the asymmetry, whereas internal damping has less effects than external damping and the asymmetry. By performing numerical simulations, four types of critical behavior are identified from the viewpoints of the stability and the passage through resonance.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.322-325
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• 1991

An induction type small size electrostatic actor has been fabricated and tested using different rotor dielectric sheet type materials and 3 phase ac various frequencies ans volatages. It's maximum no-load speed was about 2800rpm at the applied voltage of 3030V and frequency of 47Hz for the rotor material of polypropylene sheet. The motor speed was increased linearly by increasing with an applied volatage and frequency, and it also influenced greatly by the electrical properties of rotor dielectric material of relative dielectric constant, resistivity and relaxtion time