• Journal of Broadcast Engineering
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• v.21 no.5
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• pp.792-802
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• 2016

Real time verification is necessary, since there are several features that cannot be verified through design simulation in the design of multiband soundbar system. And then this paper describes an implementation of an FPGA-based real-time verification system for a soundbar SoC with an embedded processor. It is verified a real-time performance test and a listening test which are several features in the design stage that cannot be verified through a design simulation. The measurement of quantitative specifications such as SNR, THD+N, frequency response, etc. as well as the listening test were performed through the implemented FPGA system, and it was verified that test results satisfied the target specifications.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.9
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• pp.2744-2751
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• 1996

In case of limited power supply, a rotating shaft system may not reach its operating speed that is greater than its critical speed, but the speed oscillates with small ampllitude near critical speed. As a result, it is considered that the operating mode plays an important role in the smooth start of machines. In order to investigate the dynamic behaviors of the rotating shaft system at the beginning stage, one has derived the equations of motion whose degrees of freedom is three, two translations and one rotation. The simultaneous differential equations are numerically solved by using runge-Kutta method, and thus the small time step length could be required corresponding to the stability of solution. Three types of operating modes dependent upon the driving torque rate have been numerically investigated according to the maximum displacement of shaft center. The first type of relation is linear, the second type is composed of two linear curves recommended by machine manufacturer, and the last one is the proposed torque curve reflecting the frequency response curve of one degree of freedom system. For the second type of modes, it is found that the optimal range of intermediate speed to the critical speed lies between 0.8 and 0.9. In addition to that, the maximum displacement can be reduced more if the third type of mode is utilized.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1681-1688
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• 2000

A dynamic model for the prediction of surface topography in high speed end milling process is developed. In this model the effect of tool runout, tool deflection and spindle vibration were taken in to account. An equivalent diameter of end mill is obtained by finite element method and tool deflection experiment. A modal parameter of machine tool is extracted by using frequency response function. The tool deflection, spindle vibration chip thickness and cutting force were calculated in dynamic cutting condition. The tooth pass is calculated at the current angular position for each point of contact between the tool and the workpiece. The new dynamic model for surface predition are compared with several investigated model. It is shown that new dynamic model is more effective to predict surface topography than other suggested models. In high speed end milling, the tool vibration has more effect on surface topography than the tool deflection.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1342-1350
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• 2003

A direct numerical simulation of a spatially-developing turbulent boundary layer is performed to examine the characteristics of wall pressure fluctuations after the sudden application of wall blowing or suction. The uniform blowing or suction is given by the wall-normal velocity through a spanwise slot at the wall. The response of wall pressure fluctuations to uniform blowing or suction is analyzed by computing the turbulence statistics and frequency spectra. It is found that wall pressure fluctuations are more affected by blowing than by suction. The large elongated structure of wall pressure fluctuations is observed near the maximum location of $(p_w)_{rms}$ for blowing. The convection velocities for blowing increase with increasing the streamwise location after the slot. For both blowing and suction, the small scale of wall pressure fluctuations reacts in a short downstream distance to the spanwise slot, whereas the large scale recovers slowly in a farther downstream.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1458-1463
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• 2003

This paper presents an improved identification algorithm of active magnetic bearing rotor systems considering sensor and actuator dynamics. An AMB rotor system has both real and complex poles so that it is very hard to identify them together. In previous research, a linear transformation through a fictitious proportional feedback was used in order to shift the real poles close to the imaginary axis. However, the identification result highly depends on the fictitious feedback gain, and it is not easy to identify the additional dynamics including sensor and actuators at the same time. First, this paper discusses the necessity and a selection criterion of the fictitious feedback gain. An appropriate feedback gain minimizes dominant SVD(Singular Value Decomposition) error through maximizing rank deficiency. Second, more improvement in the identification is achieved through separating the common additional dynamics in all elements of frequency response matrix. The feasibility of the proposed identification algorithm is proved with two theoretical AMB rotor models. Finally, the proposed scheme is compared with previous identification methods using experimental data, and a great improvement in model quality and large amount of time saving can be achieved with the proposed method.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.2
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• pp.144-151
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• 2012

Polishing is not only one of the most frequently adopted processes in modern industries, but also the most critical one to the surface quality of the products such as semi conductor wafers and LED sapphire wafers. With the required specifications for the wafer surface quality getting more and more strengthened, the manufacturers are spending huge amount of cost to renew the machine to meet the enhanced surface specifications. Surface qualities of the wafers are mostly damaged by the structural vibrations of the polishing machines. In this paper, the dynamic characteristics of a wafer polishing machine have been analyzed through the frequency response test and the computer simulation. And the supporting structure of a polishing machine has been investigated to minimize the vibration transmissions, to improve the stability of the machine and further to reduce the defects of the polished products. The result of the study shows that simple design modifications of the supporting structure without altering the main structure of the machine can substantially suppress the vibrations of the machine with negligible expenses.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.220-220
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• 2011

관개배수를 수행하는 농업용 수리시설물은 소규모이고 개소수가 많아 효율적으로 관리하기가 어려우며, 넓은 지역에 분포하고 있어 시설 현황의 파악조차 쉽지 않다. 농업용 수리시설물은 점검자가 관리항목을 종이 조사표에 수기로 작성하여 시설상태를 점검하고 있기 때문에 자료의 누락 및 오류, 전산화를 위한 재입력 과정 등에 있어서 어려움이 발생할 수 있다. 이러한 시설물을 효과적으로 관리하기 위해서는 정보망을 구성하여 원격으로 관리하거나, 직접 시설물을 돌아보며 관리해야 한다. 전자의 경우에는 비용이 많이 들기 때문에 적은 수의 관리지점을 제어하는 데는 유리하나, 농업용 수리시설물과 같이 개체수가 많을 경우에는 적용이 어렵다는 단점이 있다. 본 연구에서는 농업용 수리시설 점검 및 관리의 편의성, 효율성을 제고하기 위하여 농업용 수리시설물에 대하여 점검표준코드를 설계하였으며, WSN (Wireless Sensor Network) 기반의 점검기술 (RFID 및 QR코드)을 개발, 현장 적용을 통하여 활용성을 평가하였다. WSN 기술을 바탕으로 빠르고 정확하게 시설물을 인식할 수 있으며, 식별한 시설물의 정보를 바탕으로 현장에서 시설물에 대한 적절한 대응이 가능하도록 설계하였다. 개발한 기술은 대한민국 이동 지구의 시설물을 관리하는 데 직접 이용함으로써 평가하였다. 본 연구는 기존 농업용 수리시설물 점검의 비효율성을 개선하고 시설물 안전 평가 및 현장 이력 관리 등 현장 업무 효율 향상을 통해 농업용 수리시설 관리 및 농업용수 관리에 기여하는 바가 클 것으로 기대된다.

• Journal of Power Electronics
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• v.16 no.2
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• pp.572-583
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• 2016

In view of the speed control characteristics of induction traction motors and the problems of direct torque control (DTC) algorithms in current applications, this paper presents a DTC algorithm characterized by a symmetrical polygon flux control and a closed loop power control in the constant-torque base speed region and constant-power field-weakening region of induction traction motors. This algorithm only needs to add a stator flux control algorithm to the traditional DTC structures. This has the benefit of simplicity, while maintaining the features of traditional algorithms such as a rapid dynamic response, uncomplicated control circuit, reduced dependence on motor parameters, etc. In addition, it obtains a smoother flux trajectory that is conducive to improvement of the harmonic elimination capability, the switching frequency utilization as well as the torque and power performance in the field-weakening region. The effectiveness and feasibility of this DTC algorithm are demonstrated by both theoretical analysis and experimental results.

• Journal of Power Electronics
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• v.16 no.2
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• pp.542-552
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• 2016

Central 60° synchronous modulation is an easy pulse-width modulation (PWM) method to implement for the traction inverters of urban rail trains at a very low switching frequency. Unfortunately, its switching patterns are determined by a Fourier analysis of assumed steady-state voltages. As a result, its transient responses are not very good with over-currents and high instantaneous torque pulses. In the proposed solution, the switching patterns of the conventional central 60° modulation are modified according to the dynamic error between the target and actual stator flux. Then, the specific trajectory of the stator flux and current vector can be guaranteed, which leads to better system transients. In addition, stator flux control is introduced to get smooth mode switching between the central 60° modulation and the other PWMs in this paper. A detailed flow chart of the control signal transmission is given. The target flux is obtained by an integral of the target voltage. The actual PMSM flux is estimated by a minimum order flux state observer based on the extended flux model. Based on a two-level inverter model, improved rules in the α-β stationary coordinate system and equations of the switching patterns amendment are proposed. The proposed method is verified by simulation and experimental results.

• Journal of Electrical Engineering and Technology
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• v.5 no.3
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• pp.503-510
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• 2010

This paper proposes the use of fuzzy applications to a 4-machine and 10-bus system to check stability in open conditions. Fuzzy controllers and the excitation of a synchronous generator are added. Power system stabilizers (PSSs) are added to the excitation system to enhance damping during low frequency oscillations. A fuzzy logic power system stabilizer (PSS) for stability enhancement of a multi-machine power system is also presented. To attain stability enhancement, speed deviation ($\Delta\omega$) and acceleration ($\Delta\varpi$) of the Kota Thermal synchronous generator rotor are taken as inputs to the fuzzy logic controller. These variables have significant effects on the damping of generator shaft mechanical oscillations. The stabilizing signals are computed using fuzzy membership functions that are dependent on these variables. The performance of the fuzzy logic PSS is compared with the open power system, after which the simulations are tested under different operating conditions and changes in reference voltage. The simulation results are quite encouraging and satisfactory. Similarly, the system is tested for the different defuzzification methods, and based on the results, the centroid method elicits the best possible system response.