• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.228-233
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• 2004

The spray and acoustic characteristics by the self-oscillation of a swirl coaxial injector were experimentally studied. The self-oscillation of a swirl coaxial injector is defined as pressure and flowrate oscillations by a time-delayed feedback between liquid and gas phase and has strong influences on atomization and mixing processes. Hence the occurrence and effect of the self-oscillation are measured using shadow photography technique, acoustic test and PDPA. The occurrence of self-oscillation largely depends on the injection conditions, such as pressure drop of liquid phase and relative momentum ratio. From the experimental results, self-oscillation occurs when the momentum of gas phase is enough large and the smaller the pressure drop of liquid phase is, the better self-oscillation occurs at the same momentum ratio. The self-oscillation is also affected by injector geometries, increasing the recess length results in the expansion of self-oscillation region and the increase of sound pressure level. The self-oscillation of a swirl coaxial injector accompanies a high intensity scream and this scream may provide harmful disturbances to combustion processes. Self-oscillation leads to strong changes in the drop size distribution and smoothly varies the slope of radial SMD distribution.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.7
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• pp.1111-1122
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• 2004

An idea to suppress the self-excited combustion oscillation was applied to the flames. The characteristics of unsteady combustion were examined and the unsteady combustion was driven by forced pulsating mixture supply that can modulate its amplitude and frequency. The self-excited combustion oscillation having weaker flow velocity fluctuation intensity than that of the forced pulsating supply can be suppressed by this method. The effects of the forced pulsation amplitude and frequency on controlling self-excited combustion oscillations were also investigated comparing with the steady mixture supply. The unsteady combustion used in this experiment plays an important role in controlling self-excited combustion oscillation. Symptoms of self-excited combustion oscillation were also studied in order to predict the onset of combustion oscillation before it proceeded to a catastrophic failure For the purpose, the unique measures to observe the onset of self-excited combustion oscillations based on the careful statistics of fluctuating properties in flames, such as pressure or emission of OH radicals, have been proposed.

• Journal of IKEEE
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• v.6 no.2 s.11
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• pp.128-135
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• 2002

We use the saturation nonlinear feedback element to generate self-oscillation in order to find an ultimate gain and period of linear plant. The use of saturation nonlinear feedback element can improve accuracy of an ultimate gain and period of unknown linear plant. An ultimate gain and period of linear plant can be used to tune a PID controller parameters. It is possible that an asymmetric oscillation can be occurred under the special circumstances such as with static load disturbance. We analyze an asymmetric self-oscillation. As the results of an analysis, we propose a method to find an ultimate gain and period of linear Plant under the asymmetric self-oscillation.

• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1859-1868
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• 2004

Monitoring of OH chemiluminescence through an optical fiber was demonstrated to be a useful method in detecting self-excited combustion oscillations. OH chemiluminescence intensity detected by the optical fiber showed mostly excellent agreement with those obtained by high speed CCD camera measurements when combustion oscillations were strong. Symptoms of self-excited combustion oscillation were also studied in order to predict the onset of combustion oscillation before it proceeded to a catastrophic failure. For the purpose, we have found and proposed unique measures to tell the onset of self-excited combustion oscillations based on the careful statistics of fluctuating properties in flames, such as pressure or emission of OH radicals.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1820-1831
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• 2003

Characteristics of self-excited combustion oscillation are experimentally studied using confined premixed flames stabilized by a rearward-facing step. A new idea to suppress combustion oscillation was applied to the flames. The characteristics of unsteady combustion were examined, which is driven by forced pulsating mixture supply that can modulate its amplitude and frequency. The self-excited combustion oscillation having weaker flow velocity fluctuation intensity than that of the forced pulsating supply can be suppressed by the method. The effects of the forced pulsation amplitude and frequency on controlling self-excited combustion oscillations were also investigated comparing with the steady mixture supply. The unsteady combustion used in this experiment plays an important role in controlling self-excited combustion oscillations, and it also exhibits desirable performances, from a practical point of view, such as high combustion load and reduced pollutant emissions of nitric oxide.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.3
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• pp.90-96
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• 1998

The self-excited oscillation is the phenomenon which can be observed in the systems composed of nonlinear elements. The phenomenon is of fundamental importance in nonlinear systems and, as far as the design of a nonlinear system is concerned, it should be considered along with the stability analysis. In this paper, the oscillation of a system controlled by a static nonlinear fuzzy controller is theoretically addressed. First, the describing functionof a static fuzzy controller is derived and then, based on the derived describing function, self-excited oscillation of the system controlled by a static fuzzy controller is predicted. To obtain the describing function of the static fuzzy controller, a simple struture is assumed for the fuzzy controller. Finally, computer simulation is included to show an example where the describing function given in the paper is used to predict the self-excited oscillation of a fuzzy-control system.

• Korean Journal of Optics and Photonics
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• v.15 no.2
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• pp.104-108
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• 2004

A simple dispersion measurement technique has been demonstrated by using a self-seeding laser oscillation of a Fabry-Perot laser through a closed loop. The optical pulses of different wavelengths emitted from the Fabry-Perot laser travel down an optical fiber and the group velocity difference between the pulses due to the chromatic dispersion of the optical fiber is measured through the self-seeding laser oscillation process. The dispersion parameter of the optical fiber is calculated from the measured group velocity difference. The performance of the proposed technique has been confirmed experimentally and the accuracy of dispersion parameter measurement was comparable to that of commercial instruments with expensive equipment and components. The repeatability of the proposed method was better than 0.5%.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.5
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• pp.1005-1009
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• 2010

This paper presents a digitally-controlled filter calibration technique for biquad RC filter using self oscillation. The biquad RC filter is converted to a fully-differential ring oscillator by changing its resistor connections, where the oscillation frequency reflects the cut-off frequency. The proposed calibration circuit measures the oscillation frequency by counting with a fixed higher-frequency clock and then tunes it to a desired frequency with a digital frequency-locked loop including a PI controller. Because the proposed circuit directly measures the cut-off frequency of the filter itself and calibrates it with the small area digital circuits, the area and the power consumption are much small compared with conventional works. When it is implemented in a 65nm CMOS process, the calibration circuit except the filter consumes the area of 80um X 50um and power consumption is 443uA at 1.2 V supply voltage.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.5
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• pp.41-49
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• 1998

This paper deals with the self-excited oscillation of a system that is controlled by a dynamic nonlinear fuzzy controller. The self-excited oscillation can be observed in the systems composed of nonlinear elements and its analysis is as important as that of stability in the design of nonlinear systems. by using the frequency transfer function analysis known as the describing function method in nonlinear control theory, the oscillation is theoretically predicted. First, the describing function of a dynamic fuzzy controller is derived and then, based on the derived describing fuction, self-excited oscillation of the system controlled by a dynamic fuzzy controller is predicted. To obtain the describing function of the dynamic fuzzy controller, a simple structure is assumed for the fuzzy controller.

• Journal of the Korean Society of Combustion
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• v.13 no.4
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• pp.8-15
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• 2008

When a circular cylinder is placed at the center of a slot burner nozzle, once stable Woflhard-Parker type laminar lean premixed flame is changed to an oscillating flame with self-induced noise. The wrinkled flame surface showed the same pattern and frequency of the Karman vortex street at the downstream of a circular cylinder. The interaction of flame with Karman vortex street is observed to be responsible for flame oscillation. The measured flame oscillation frequency is very similar to the estimated Karman vortex shedding frequency based on the St-Re relationship of the flow past circular cylinder, which could be considered as a strong evidence for the interaction between laminar pre-mixed flame and a Karman vortex street. As Reynolds number increases oscillation frequency decreases and the self-induced noise level increases as well as the flame front is more severly wrinkled. This result suggests that the flame/vortex interaction becomes more active at higher Re.