• Title/Summary/Keyword: Oscillation methods

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Contingency Analysis for Small Signal Stability of Power Systems (전력계통의 미소신호안정도 상정사고 해석)

  • 심관식;김용구;문채주
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.17 no.3
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    • pp.127-137
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    • 2003
  • Contingency analysis is one of the most important tasks encountered by planning and operation of lafe scale power systems. This paper describes a new contingency analysis methods for small signal security assessment based on the eigen-sensitivity/perturbation of the electromechanical oscillation modes. The eigen-sensitivity/perturbation with respect to line suceptances and controller parameters can he used to find possible sources of the system instability, and to select contingency for small signal stability. Also, the contingency selection to identify critical generators for MW changes can be obtained by computing the relative movement of the system oscillation modes. The proposed algorithm has been successfully tested on the KEPCO systems which is comprised of 791-bus, 1575-branch and program PSS/E

Oscillation Motion Control of Gantry Crane System with Arm for Anti-Sway (Anti-sway용 암을 가진 겐트리 크레인의 흔들림저감 제어)

  • Kim, H.S.;Park, H.S.;Lee, D.H.;Park, J.H.;Kim, S.B.
    • Journal of Power System Engineering
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    • v.2 no.1
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    • pp.73-79
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    • 1998
  • In practical fields, the sway of crane systems leads to extra stress to the crane structure during the transporting operation and it is in close connection with its life. Usually, when we operate the cranes with high speed and manual control, the sway motion is irreducible. In this paper, a new type of crane system is proposed to avoid the irreducible sway of the crane systems. The proposed system is composed of mechanical arm with function of anti-sway based on conventional line system. By the anti-sway arm, we can realize to prevent the sway of the container box but cannot avoid the oscillation for the overall body of the crane. So, a controller design method to solve the above stated problem must be considered. The problem is solved by adopting the velocity pattern control methods of trapezoidal and curve types and its effectiveness is proved through experimental results.

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A Study on Resonance Tracking Method of Ultrasonic Welding Machine Inverter (초음파 용접기 인버터의 공진 추종 방법에 관한 연구)

  • Moon, Jeong-Hoon;Park, Sung-Jun;Lim, Sang-Kil;Kim, Dong-Ok
    • Journal of the Korean Society of Industry Convergence
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    • v.24 no.4_2
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    • pp.481-490
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    • 2021
  • In the ultrasonic welding machine, when the load fluctuates, the L and C of the piezo element in the oscillation part change. As a result, the resonant frequency is changed, so it is necessary to match the operating frequency of the ultrasonic welding machine to the new resonant frequency. That is, in order to maximize the output of the oscillation unit of the ultrasonic welding machine, it is inevitable to follow the resonance frequency. Accordingly, many methods for following the resonant frequency are being actively studied. In addition, in order to check the effect of external inductance on the operation of the ultrasonic welding machine, The equivalent circuit of the piezo element was analyzed by including the external inductance for resonance in the equivalent circuit of the piezo element, and the method of selecting an appropriate inductance was described. In this paper, we propose a new system that allows the switching frequency of the inverter to tracking the resonance frequency even if the resonance frequency is changed due to the load of the ultrasonic welding machine.

Compensation for temperature-level control of tanked water system with time delay

  • Nakamura, Masatoshi;Watanabe, Kiyoto
    • 제어로봇시스템학회:학술대회논문집
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    • 1993.10b
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    • pp.42-47
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    • 1993
  • Importance of separation of a nonlinear dynamical system into nonlinear static part and linear dynamical part was insisted in designing a controller for the nonlinear system. We further proposed compensation techniques for oscillation of controlled variables caused by system time delay and compensation of steady state errors caused by modelling errors of the systems. The proposed principle of designing procedure and the compensation methods were discussed by applying them for temperature and level control of an actual tanked water system.

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AERODYNAMIC ANALYSIS OF A PITCH OSCILLATING MID-SIZED AIRCRAFT (피치 진동하는 중형항공기의 공력 특성 해석)

  • Lee, Yung-Gyo;Kim, Cheol-Wan;Ahn, Seok-Min
    • Journal of computational fluids engineering
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    • v.16 no.1
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    • pp.48-52
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    • 2011
  • Aerodynamic analysis was done for a fuselage and wing configuration of a mid-sized aircraft using unsteady 3-dimensional Navier-Stokes solver. Various turbulent models including a transitional SST were used to observe a dynamic stall as well as cruise characteristics. Also, different mesh moving methods were evaluated. Flow hysteresis which causes dynamic stall was investigated through flow field investigations.

Combustion Instability Modeling for a Lean Premixed Gas Turbine Combustor using Flame Transfer Function Approach

  • Kim, Daesik;Cha, Dong-Jin
    • 한국연소학회:학술대회논문집
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    • 2012.11a
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    • pp.53-54
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    • 2012
  • In an IGCC plant, one of the most important issues on fuel flexibility in the lean premixed combustor is combustion instabilities. They are characterized by large amplitude pressure oscillations which are caused by unsteady heat release from the flames. The relationship between the unsteady heat release and flow oscillation can be qualitatively and quantitatively explained by flame transfer function. This paper introduces combustion instability modeling methods based on the flame transfer function approach.

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DYNAMIC STALL ANALYSYS OF A MID-SIZED AIRCRAFT (중형항공기 동적 실속 특성 해석)

  • Lee, Yung-Gyo;Kim, Cheol-Wan;Ahn, Seok-Min
    • 한국전산유체공학회:학술대회논문집
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    • 2010.05a
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    • pp.37-39
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    • 2010
  • Aerodynamic analysis was done for a fuselage and wing configuration of a mid-sized aircraft using 3-dimensional Navier-Stokes solver. Various turbulent models including a transitional SST were implemented to observe a dynamic stall as well as cruise characteristics. Also, different mesh moving methods were evaluated. Flow hysteresis which causes dynamic stall was investigated through flow field investigations.

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Optical Parametric Oscillation in Periodically Poled Lithium Niobate Crystal (주기적으로 분극반전된 $LiNbO_3$ 결정에서 광매개증폭)

  • Kim Hong-Gi;Cha Myeong-Sik;Lee Beom-Gu
    • Proceedings of the Optical Society of Korea Conference
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    • 2001.02a
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    • pp.222-223
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    • 2001
  • Optical parametric oscillator(OPO) has been used to generate coherent and tunable laser source with birefringent phase-matching technique in various nonlinear materials. In birefringent phase-matching, the output wavelength is controlled with angle or temperature tuning of the refractive index. However these tuning methods have several limitations such as restriction of tuning wavelength due to reasonable angular and temperature tuning ranges, Poynting vector walk-off which limits the interaction length, and thermal stabilization time. (omitted)

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A development of move limit strategy based on the accuracy of approximation for structural optimization (구조최적설계시 근사법의 정확도를 이용한 이동한계 전략의 개발)

  • Park, Young-Sun;Park, Gyung-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.8
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    • pp.1218-1228
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    • 1997
  • The move limit strategy is used to avoid the excessive approximation in the structural optimization. The size of move limit has been obtained by engineering experience. Recently, efforts based on analytic methods are performed by some researchers. These methods still have problems, such as prematurity or oscillation of the move limit size. The existing methods usually control the bound of design variables based on the magnitude. Thus, they can not properly handle the configuration variables based on the geometry in the configuration optimization. In this research, the size of move limit is calculated based on the accuracy of approximation. The method is coded and applied to the two-point reciprocal quadratic approximation method. The efficiency is evaluated through examples.

Non-stationary Frequency Analysis with Climate Variability using Conditional Generalized Extreme Value Distribution (기후변동을 고려한 조건부 GEV 분포를 이용한 비정상성 빈도분석)

  • Kim, Byung-Sik;Lee, Jung-Ki;Kim, Hung-Soo;Lee, Jin-Won
    • Journal of Wetlands Research
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    • v.13 no.3
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    • pp.499-514
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    • 2011
  • An underlying assumption of traditional hydrologic frequency analysis is that climate, and hence the frequency of hydrologic events, is stationary, or unchanging over time. Under stationary conditions, the distribution of the variable of interest is invariant to temporal translation. Water resources infrastructure planning and design, such as dams, levees, canals, bridges, and culverts, relies on an understanding of past conditions and projection of future conditions. But, Water managers have always known our world is inherently non-stationary, and they routinely deal with this in management and planning. The aim of this paper is to give a brief introduction to non-stationary extreme value analysis methods. In this paper, a non-stationary hydrologic frequency analysis approach is introduced in order to determine probability rainfall consider changing climate. The non-stationary statistical approach is based on the conditional Generalized Extreme Value(GEV) distribution and Maximum Likelihood parameter estimation. This method are applied to the annual maximum 24 hours-rainfall. The results show that the non-stationary GEV approach is suitable for determining probability rainfall for changing climate, sucha sa trend, Moreover, Non-stationary frequency analyzed using SOI(Southern Oscillation Index) of ENSO(El Nino Southern Oscillation).