• 소음진동
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• 제4권2호
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• pp.221-230
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• 1994

This paper deals with the dynamic stability and the nonlinear behavior of a check valve system. The nonlinear equations of motion of fluid-valve interation model are derived, which are composed of the unsteady Bernoulli's equation included the jet flow mechanism and equation of motion of a check valve formulated by one degree of freedom. Also, the derived equations of motion are nondimensionalized. According to the change of the nondimensional parameters, the stabilities of the system are analyzed, and the nonlinear interaction responses of the check valve and the passing flow rate are obtained. As the results, the stability charts are constructed for the variation of nondimensional parameters. It is shown that self-excited vibrations exist in a check valve system. And also the Hopf bifurcation and the periodic doubling are found. The presented theoretical model of a check valve system can be utilized to the design and operation of a piping system with the check valve.

• 대한전자공학회논문지
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• 제3권4호
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• pp.16-24
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• 1966

레이저 증폭기를 능동영역(Ruby Rod)에서의 Fabry-Perot 공진기의 방법으로 취급했고 5층, 즉 공기일반사판-Ruby-반사판-공기의 구조로 고찰했다. 일차원 스캘라파동방정식으로 Maxwell 전자방정식을 이용하여 입사계가 연속이라는 가정하에 경계치문제로 봤으며 모든 폭사계는 각경계면에 수직으로 입사한다고 생각했다. 모든 방정식은 Laplace 변환으로 과도현상론적으로 취급했으며 증폭기로서의 안정영역과 자려발진기로서의 불안정영역을 고찰했다. 또한 과도항과 관련된 레이저 증폭기 설계상의 문제도 생각했다.

• 한국분무공학회지
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• 제23권1호
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• pp.16-21
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• 2018

The current study has developed an in-house 3D FEM code in order to model thermoacoustic problems in a gas turbine combustion system and compared calculation results of main instability characteristics with measured ones from a lab-scale partially-premixed combustor. From the comparison of calculation results with the measured data, the current model could successfully capture the harmonic longitudinal instability frequencies and their spatial distributions of the acoustic field as well as the growth rate of self-excited modes.

• 대한기계학회논문집B
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• 제31권2호
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• pp.202-207
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• 2007

In order to understand the phenomena of combustion instability, an experimental study was conducted at the moderate pressure and ambient temperature conditions. The flame behavior and the pressure fluctuations were measured in a dump combustor. Various types of combustion modes occurred in accordance with the equivalence ratio and the fuel supplying conditions. The fluctuation of pressure, heat release and equivalence ratio were measured by piezoelectric pressure sensor, high speed Intensified Charge Coupled Device (HICCD) camera and gas chromatography respectively. Two representative modes were self-excited pressure oscillations at the resonance of combustion chamber (200Hz) and instabilities related to the modulated fuel flow rate through the fuel holes (10Hz). It is found that, especially in an unchoked fuel flow condition, the modulation of the fuel flow rate affects the characteristics of flame behavior and pressure fluctuations in a lean premixed flame.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2946-2951
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• 2008

Combustion instability is a major issue in design of gas turbine combustors for efficient operation with low emissions. Combustion instability is induced by the interaction of the unsteady heat release of the combustion process and the change in the acoustic pressure in the combustion chamber. In an effort to develop a technique to predict self-excited combustion instability of gas turbine combustors, a new stability analysis method based on the transfer matrix method is developed. The method views the combustion system as a one-dimensional acoustic system with a side branch and describes the heat source as the input to the system. This approach makes it possible to use the advantages of not only the transfer matrix method but also well-established classic control theories. The approach is applied to a simple gas turbine combustion system to demonstrate the validity and effectiveness of the approach.

• International Journal of Fluid Machinery and Systems
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• 제3권1호
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• pp.91-101
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• 2010

Based on the one-dimensional stability analysis, the self-excited oscillation in hydraulic power generating systems was studied by a simple experiment and numerical simulation. It was shown that a cavity in a conical diffuser can cause surge. With the diffuser, a high amplitude and low frequency oscillation occurs at low cavitation number. This oscillation was not observed with the straight pipe. It was confirmed that the diffuser effect of the draft tube can be the cause of the full load surge in hydraulic power system. Numerical results were also analyzed to check the validity of the one-dimensional stability analysis.

• 한국연소학회지
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• 제10권4호
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• pp.1-9
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• 2005

The usefulness of unsteady combustion was experimentally investigated using confined premixed flames stabilized by a rearward-facing step. For this purpose, apparatus of forced pulsating mixture supply, which could be modulated its amplitude and frequency, was designed. The unsteady combustion used in this experiment plays an important role in controlling self-excited combustion oscillations and furthermore it exhibits desirable performance, from a practical point of view, such as high load combustion and reduction of pollutant emission like nitric oxide.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.295-298
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• 2008

유체내에 잠겨있는 물체의 진동은 공기력을 유발시키며 이러한 공기력에 의해 발생되는 진동을 물체의 거동에 의해 발생되는 가진이라 한다. 또한 물체에 작용하는 외부 공기력이 없이도 물체의 주기적인 움직임에 의해 발생되는 에너지로부터 공기력을 생성시킨다. 이러한 메커니즘에 의해 생성되는 공기력을 공기자발력(self-excited force) 이라 하며 교량의 내풍안정성과 관련이 있다. 본 논문에서는 MIE 메커니즘에 의해 발생되는 플루터 현상을 수학적으로 살펴보고, 단일모드에 대한 플러터계수를 이용한 플러터 발생풍속 산정식을 유도하였다. 또한 준정상 이론을 적용하여 단일모드에 대한 플러터 발생 예측식을 간략화하였다. 제안된 식의 플러터 발생풍속을 구조물의 진동수비가 서로 다른 3개의 $\pi$형 단면에 대해 검토하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1976-1977
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• 2007

This paper introduce the electrical quantities of a three-phase-connected wind induction generator (WIG) under sudden connection of static loads. An intelligent power-system recorder/monitor is employed to measure threephase voltages and currents of the studied system at WIG's terminals and load's terminals for 5 minutes. A laboratory 300 W wound-rotor induction machine driven by a blushless DC motor is utilized as the studied WIG. Since the generated harmonic currents are randomly varied, total harmonic distortion (THD) of current using cumulative probability density function is employed to determine the penetration of harmonic distortion. The results show that the harmonic currents generated by the studied WIG may be severely amplified to a high level by the connected self-excited capacitance at the stator's terminals.

• Journal of the Optical Society of Korea
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• 제8권4호
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• pp.188-191
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• 2004

A new laser Doppler velocimeter employing a $CO_2$ laser has been developed by using its photoacoustic effect. A change in the pressure of a discharge, induced by mixing of a returned wave with an originally existing wave inside the cavity, is employed to detect the Doppler frequency shift. We found that a Doppler frequency shift as small as 50 kHz was detected, and also a good linear relationship between the velocity and the Doppler frequency shift was obtained.