• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.63-67
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• 2009

The previous work (Cheong et al., 2006) where the characteristics of acoustic emissions of wind turbines has been investigated according to the methods of power regulation, has showed that the acoustic power of wind turbine using the stall control for power regulation is more correlated with the wind speed than that using the pitch control. In this paper, basically extending this work, the noise generation characteristics of large modern upwind wind turbines are experimentally indentified according to the power regulation methods. To investigate the noise generation mechanisms, the distribution of noise sources in the rotor plane is measured by using the Beam-forming measurement system (B&K 7768, 7752, WA0890) consisting of 48 microphones. The array results for the 660 kW wind turbine show that all noise is produced during the downward movement of the blades. This result show good agreement with the theoretical result using the empirical formula with the parameters: the convective amplification; trailing edge noise directivity; flow-speed dependence. This agreement implies that the trailing edge noise is dominant over the whole frequency range of the noise from the 660 kW wind turbine using the pitch control for power regulation.

• Advances in aircraft and spacecraft science
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• v.4 no.4
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• pp.487-501
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• 2017

The main purpose of the paper is to analyze effect of geometrical parameters of the reentry capsules such as radius of the spherical cap, shoulder radius, back shell inclination angle and overall length on the flow field characteristics. The numerical simulation with viscous flow past ARD (Atmospheric Reentry Demonstrator), Soyuz (Russian) and OREX (Orbital Reentry EXperimental) reentry capsules for freestream Mach numbers range of 2.0-5.0 is carried out by solving time-dependent, axisymmetric, compressible laminar Navier-Stokes equations. These reentry capsules appear as bell, head light and saucer in shape. The flow field features around the reentry capsules such as bow shock wave, sonic line, expansion fan and recirculating flow region are well captured by the present numerical simulations. A low pressure is observed immediately downstream of the base region of the capsule which can be attributed to fill-up in the growing space between the shock wave and the reentry module. The back shell angle and the radius of the shoulder over the capsule are having a significant effect on the wall pressure distribution. The effects of geometrical parameters of the reentry capsules will useful input for the calculation of ballistic coefficient of the reentry module.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.4
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• pp.643-650
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• 2017

This pap4er analyzes resonance characteristics of a slave motor that is not controlled by load and parameter differences between Dual motors during parallel operation in middle-low speed. Dual SPMSMs(Surface mounted Permanent Magnet Synchronous Motor) connected in parallel to a single inverter controlled by the master and slave control in this paper. Based on the stability analysis of the SPMSM for a variation of torque angle, the 6th nonlinear state equation of the torque angle variation in the SIMM(Single Inverter Multi Motor) structure is derived according to a mathematical model for the dual motors. In general, an analysis of the 6th order nonlinear state equation is complex. Therefore, a resonance frequency generated from the slave motor is found from the characteristic equation of the 2nd order system obtained by linearization and model reduction near steady state operation point. Through simulations and experiments, it is confirmed that the stability analysis of the SPMSMs and state equation models are useful for the variation of the torque angle analyzed in this paper.

• Journal of Power Electronics
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• v.5 no.2
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• pp.120-128
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• 2005

This paper deals with the analysis of switched reluctance motor drives for different drive circuit topologies used in automobile. So we attempt to improve the weaknesses associated with the asymmetric bridge converter in the limited internal environment of automotive application. Two kinds of c-dump converters are tested in terms of dump capacitor voltage, speed response according to the variation of advance angle and efficiency for the radiator cooling-fan drive of an automobile. They enable more economical and efficient converter topology for automobile industries. This paper describes the performance characteristics of 12V-250W-3000rpm SRM drives for automotive application. Computer simulation and experiment results are then presented to verify the performance of the two kinds of c-dump converters.

• Tribology and Lubricants
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• v.29 no.5
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• pp.318-323
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• 2013

Overheating in electrical motors results in detrimental effects such as degradation of the insulation materials, demagnetization of magnets, increases in Joule losses, and decreases in motor efficiency and lifetime. Thus, it is important to find ways to dissipate heat from the motor and to keep the motor operating at its most efficient temperature. In this study, a new design to guide air flow through a given brushless direct current (BLDC) motor is developed and the design is analyzed, specifically by using computational fluid dynamics (CFD) simulations. The results showed that the temperature distribution in the three proposed models is lower than that in the original model, although the speed of the cooling fan in the original model reaches a very high value of $15{\times}10^3$ rpm. The results also showed that CFD can be effectively used to simulate the heat transfer of BLDC motors.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1334-1337
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• 2004

This paper presents a novel method to speed up neural network (NN) based face detection systems. NN-based face detection can be viewed as a classification and search problem. The proposed method formulates the search problem as an integer nonlinear optimization problem (INLP) and expands the basic particle swarm optimization (PSO) to solve it. PSO works with a population of particles, each representing a subwindow in an input image. The subwindows are evaluated by how well they match a NN-based face filter. A face is indicated when the filter response of the best particle is above a given threshold. To achieve better performance, the influence of PSO parameter settings on the search performance was investigated. Experiments show that with fine-adjusted parameters, the proposed method leads to a speedup of 94 on 320${\times}$240 images compared to the traditional exhaustive search method.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1031-1036
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• 2007

Torsional vibration analysis is necessary at design stage to ensure the reliability of a system particularly when the driven machine is a reciprocating compressor. This paper contains the results of torsional vibration analysis and fatigue strength evaluation for 540 kW compressor driving motor. Torsional vibration analysis showed that the $2^{nd}$ torsional mode of the entire shaft system has the possibility of resonance with the $14^{th}$ order excitation of compressor and twin line frequency of motor at operating speed. Therefore, the analyses were required to ensure the structural reliability of the motor. The fatigue strength was evaluated for the shaft and inner fans using the results of forced vibration analysis. It is concluded that the motor has sufficient fatigue strength under normal operating condition.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.7
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• pp.693-698
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• 2009

Various acoustic tests were carried out to investigate the acoustic performance of diesel engine exhaust silencers. In order to consider flow effects, the test facility was set up composed of fan, duct and silencer. Using the test facility, insertion loss tests were carried out to improve the acoustic performance in the low-frequency ranges. Through a series of tests, it was found out that the array resonators having multi-perforated holes inside the exhaust silencer, might be very effective in the low frequency range. Consequently, the hybrid-type silencer which is the combination of reflective silencer with array resonators and conventional absorptive silencer, was proposed and its high performance in the low-frequency range was also verified.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.26 no.2
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• pp.83-90
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• 2018

This paper describes a case study on the design factor analysis of vertical wind tunnel for skydiver's training or experiencing of paradropping exercise in the air. The case study of vertical wind tunnel design is to provide the knowledges on effects of parameter's variation when it is applied to overall or partial duct of tunnel circuit. The analysis of design parameters based on pressure loss are produced one by one through the tunnel components from the flight chamber because the wind tunnel must satisfy the requirement of flight chamber such as flow speed, quality and quantity. Results shows the various effects of parameter variation with pressure loss in the wind tunnel circuit. Pressure loss should be based on the determination of fan and power system which can be selected from market or new design.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1034-1038
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• 2005

This paper presents a novel method to speed up neural network (NN) based face detection systems. NN-based face detection can be viewed as a classification and search problem. The proposed method formulates the search problem as an integer nonlinear optimization problem (INLP) and develops an improved genetic algorithm (IGA) to solve it. Each individual in the IGA represents a subwindow in an input image. The subwindows are evaluated by how well they match a NN-based face filter. A face is indicated when the filter response of the best particle is above a given threshold. Experimental results show that the proposed method leads to a speedup of 83 on $320{\times}240$ images compared to the traditional exhaustive search method.