• 제목/요약/키워드: Oscillation frequency

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Large Eddy Simulation of Heat Transfer Performance Enhancement due to Unsteady Flow in Compound Channels (복합 부수로의 비정상 유동이 유발하는 난류열전달 증진에 대한 LES 해석)

  • Hong, Seong-Ho;Shin, Jong-Keun;Choi, Young-Don
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.23 no.2
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    • pp.132-138
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    • 2011
  • In the present article, we investigate numerically turbulent flow of air through compound rectangular channels. Large eddy simulation(LES) is employed for unsteady turbulence modeling. LES gives better predictions for the axial mean velocity distribution than those of other turbulent models. Strong large-scale quasi-periodic flow oscillations are observed in most of the geometries investigated. Such large-scale flow oscillations in compound rectangular channels are similar to the quasi-periodic flow pulsation through the gaps between fuel rod bundle in nuclear reactor. It exists in any longitudinal connecting gap between two flow channels. The frequency of this flow oscillation is determined by the geometry of the gap. The large scale cross motions through the rectangular compound channels induce significant heat transfer enhancement of the compound channel flow.

A Study on New Harmonic Elimination Method Using Walsh Series (왈쉬급수를 사용한 새로운 고조파 제거 방법에 관한 연구)

  • 박민호;안두수;원충연;이해기;이명규;김태훈
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.39 no.3
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    • pp.263-272
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    • 1990
  • In the variable speed driving system of a three phase induction motor controlled by a PWM inverter, the output terminal contains considerable amount of harmonic components of the voltage waveform due to the switching action of semiconductor devices, causing torque ripples, acoustic noise and oscillation of the motor. This paper describes a new algorithm which eliminates the harmonics and controls the fundamental voltage in three phase PWM inverter output waveform. The new algorithm utilizes the technique of particular harmonics elimination (PHE) by walsh series in three phase PWM inverter output waveform. A microprocessor (8086 CPU)-controlled three phase induction motor system is described to realize this algorithm. The system is designed for 3 phase output voltage in the 1-60Hz interval where 5th and 7th harmonics, and 5th, 7th, 11th, and 13th harmonics are eliminated. Also, the fundamental wave amplitude is designed to be proportional to the output frequency. The performance of the proposed method shows sufficient elimination of the harmonics and also reduction of computation time which determines switching pattern. The proposed PWM pattern by Walsh series, is effective not only to induction motors but also to other electromagetic equipments such as voltage regulators and UPS.

A Study on the Optimal Design Fuzzy Type Stabilizing Controller using Genetic Algorithm (유전 알고리즘을 이용한 퍼지형 안전화 제어기의 최적 설계에 관한 연구)

  • Lee, Heung-Jae;Lim, Chan-Ho;Yoon, Byong-Gyu;Lim, Hwa-Young;Song, Ja-Youn
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.48 no.11
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    • pp.1382-1387
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    • 1999
  • This paper presents an optimal fuzzy power system stabilizer to damp out low frequency oscillation. So far fuzzy controllers have been applied to power system stabilizing controllers due to its excellent properties on the nonlinear systems. But the design process of fuzzy logic power system stabilizer requires empirical and heuristic knowledge of human experts as well as many trial-and-errors in general. This paper presents and optimal design method of the fuzzy logic stabilizer using the genetic algorithm. Non-symmetric membership functions are optimally tuned over an evaluation function. The present inputs of fuzzy stabilizer are torque angle error and the change of torque angle error without loss of generality. The coding method used in this paper is concatenated binary mapping. Each linguistic fuzzy variable, defined as the peak of a membership function, is assigned by the mapping from a minimum value to a maximum value using eight bits. The tournament selection and the elitism are used to keep the worthy individuals in the next generation. The proposed system is applied to the one-machine infinite-bus model of a power system, and the results showed a promising possibility.

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An Adaptive UPFC Based S tabilizer forDamping of Low Frequency Oscillation

  • Banaei, M.R.;Hashemi, A.
    • Journal of Electrical Engineering and Technology
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    • v.5 no.2
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    • pp.197-208
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    • 2010
  • Unified power flow controller (UPFC) is the most reliable device in the FACTS concept. It has the ability to adjust all three control parameters effective in power flow and voltage stability. In this paper, a linearized model of a power system installed with a UPFC has been presented. UPFC has four control loops that by adding an extra signal to one of them, increases dynamic stability and load angle oscillations are damped. In this paper, after open loop eigenvalue (electro mechanical mode) calculations, state-space equations have been used to design damping controller and it has been considered to influence active and reactive power flow durations as the input of damping controller, in addition to the common speed duration of synchronous generators as input damper signal. To increase stability, further Lead-Lag and LQR controllers, a novel on-line adaptive controller has been used analytically to identify power system parameters. Closed-loop calculations of the electro mechanical mode verify the improvement of system pole placement after controller designing. Suitable operation of adaptive controller to decrease rotor speed oscillations against input mechanical torque disturbances is confirmed by the simulation results.

Fast Voltage-Balancing Scheme for a Carrier-Based Modulation in Three-Phase and Single-Phase NPC Three-Level Inverters

  • Chen, Xi;Huang, Shenghua;Jiang, Dong;Li, Bingzhang
    • Journal of Electrical Engineering and Technology
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    • v.13 no.5
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    • pp.1986-1995
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    • 2018
  • In this paper, a novel neutral-point voltage balancing scheme for NPC three-level inverters using carrier-based sinusoidal pulse width modulation (SPWM) method is developed. The new modulation approach, based on the obtained expressions of zero sequence voltage in all six sectors, can significantly suppress the low-frequency voltage oscillation in the neutral point at high modulation index and achieve a fast voltage-balancing dynamic performance. The implementation of the proposed method is very simple. Another attractive feature is that the scheme can stably control any voltage difference between the two dc-link capacitors within a certain range without using any extra hardware. Furthermore, the presented scheme is also applicable to the single-phase NPC three-level inverter. It can maintain the neutral-point voltage balance at full modulation index and improve the voltage-balancing dynamic performance of the single-phase NPC three-level inverter. The performance of the proposed strategy and its benefits over other previous techniques are verified experimentally.

Development of the High Performance 94 GHz Waveguide VCO (우수한 성능의 94 GHz 도파관 전압조정발진기의 개발)

  • Ryu, Keun-Kwan;Kim, Sung-Chan
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.16 no.5
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    • pp.1035-1039
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    • 2012
  • In this paper, we developed a 94 GHz waveguide VCO(voltage controlled oscillator) using a GaAs-based Gunn diode and a varactor diode. The cavity is designed for fundamental mode at 47 GHz and operated at second harmonic of 94 GHz. Bias posts for diodes operate as LPF(low pass filter) and resonator. The fabricated waveguide VCO achieves an oscillation bandwidth of 760 MHz. Output power is from 12.61 to 15.26 dBm and phase noise is -101.13 dBc/Hz at 1 MHz offset frequency from the carrier.

The Response of the Burke-Schumann Flame to External Excitation with Flame Shape and Heat Release (외부 교란에 대한 Burke-Schumann 화염에서 형상과 열방출량을 통한 응답 특성 파악)

  • Kim, Taesung;Ahn, Myunggeun;Hwang, Jeongjae;Jeong, Chanyeong;Kwon, Oh Chae;Yoon, Youngbin
    • Journal of the Korean Society of Combustion
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    • v.22 no.1
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    • pp.32-38
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    • 2017
  • This paper shows the dynamics of the Burke-Schumann flame. To show flame dynamics, this paper measures the flame surface and heat release rate. The flame shape is divided into three types with forcing frequencies. When the forcing frequency is lower than 120 Hz, the upper region of flame is cut. The flame is stagnant with 220 to 280 Hz forcing frequencies. The rest conditions of forcing frequencies make the connected wave shape of flame. The heat release rate is expressed by the flame transfer function. The gain of the flame transfer function is similar with the oscillation magnitude of the flame area except for flame cutting conditions. The flame is cut because the fuel is not supplied to upper flame region.

Development of Interference Cancellation DSP Module and Software for DTV-OCR (DTV- OCR의 궤환 간섭신호 제거용 DSP 모듈 및 SW 개발)

  • 이종현;차재상
    • Journal of Broadcast Engineering
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    • v.8 no.2
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    • pp.116-125
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    • 2003
  • In this paper, we introduce a newly developed DSP module and Software which Is applicable to DTV-OCR and is designed to cancel the interference signal. In general, RF repeater has problems of system oscillation and signal Quality degradation due to feedback interference signal coming from transmit antenna. In this paper, we demonstrate newly developed DSP HW and SW module for cancelling the interference signal by investigating the field data measured through a RF repeater. Also, the structure and signal processing method for non-regenerative repeater system based on the newly developed DSP HW and SW module is illustrated as well.

Velocity Controller Design for Fish Sorting Belt Conveyor System using M-MRAC and Projection Operator

  • Nguyen, Huy Hung;Tran, Minh Thien;Kim, Dae Hwan;Kim, Hak Kyeong;Kim, Sang Bong
    • Journal of Power System Engineering
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    • v.21 no.4
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    • pp.42-50
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    • 2017
  • A velocity controller using a modified model reference adaptive controller (M-MRAC) and a projection operator for a fish sorting belt conveyor system with uncertainty parameters, input saturation and bounded disturbances is proposed in this paper. To improve the tracking performance and robustness of the proposed controller in the presence of bounded disturbances, the followings are done. Firstly, the reference model for the conventional model reference adaptive controller (CMRAC) is replaced by a modified reference model for a M-MRAC to reduce unexpected high frequency oscillation in control input signal when the adaptation rate is increased. Secondly, estimated parameters in an adaptive law are varied smoothly under bounded external disturbances and a projection operator is utilized in an adaptive law for the proposed M-MRAC controller to be robust. Thirdly, an auxiliary error vector is introduced for compensating the error dynamics of the system when the saturation input occurs. Finally, the experimental results are shown to verify the better effectiveness and performance of the proposed controller under the bounded disturbance and saturated input than that of a CMRAC.

The Effects of Damping on the Limit Cycle of a 2-dof Friction Induced Self-oscillation System (마찰 기인 2자유도계 시스템의 자려진동에 대한 댐핑의 영향)

  • 조용구;신기홍;이유엽;오재응
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.12 no.7
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    • pp.502-509
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    • 2002
  • A two-degree of freedom model Is suggested to understand the basic dynamical behaviors of the interaction between two masses of the friction induced vibration system. The two masses may be considered as the pad and the dusk of the brake. The phase space analysis is performed to understand complicated dynamics of the non-linear model. Attractors in the phase space are examined for various conditions of the parameters of the model especially by emphasizing on the damping parameters. In certain conditions, the attractor becomes a limit cycle showing the stick-slip phenomena. In this Paper, not only titre existence of the limit cycle but also the sloe of the limit cycle is examined to demonstrate the non-linear dynamics that leads the unstable state. For the two different cases of the system frequency[(1) Two masses with same natural frequencies, (2) with different natural frequencies] . the propensity of limit cycle Is discussed In detail. The results show an important fact that it may make the system worse when too much damping Is present in the only one part of the masses.