• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.123-128
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• 1998

This study presents the measurement techniques on the periodic fluctuating flow such as the discharge flow of a centrifugal impeller in unstable operating region. During rotating stall, the flow at the exit of a centrifugal compressor impeller fluctuates periodically with lower frequency than that of the blade passing. To observe the blade-to-blade flow characteristics during rotating stall, the phases of all the sampled data sets should be adjusted to those of the reference signals with two processes, in these processes, DPLEAT (Double Phase-Locked Ensemble Averaging Technique) can be used. From these measurement and data processing techniques, the characteristics not only on the blade-to-blade flow with high frequency, but also on the periodic rotating stall flow with low frequency at the centrifugal impeller exit can be clearly observed.

• The KSFM Journal of Fluid Machinery
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• v.2 no.1 s.2
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• pp.81-87
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• 1999

This study presents the measurement techniques on the periodic fluctuating flow such as the discharge flow of a centrifugal impeller in an unstable operating region. During rotating stall, the flow at the exit of a centrifugal compressor impeller fluctuates periodically with a lower frequency than that of the blade passing. To observe the blade-to-blade flow characteristics during the rotating stall, the phases of all the sampled data sets should be adjusted to those of the reference signals with two processes, in these processes, DPLEAT (Double Phase-Locked Ensemble Averaging Technique) can be used. From these measurements and data processing techniques, the characteristics illustrated a blade-to-blade flow with high frequency, but also a periodic rotating stall flow with a low frequency at the centrifugal impeller exit which was clearly observed.

• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.709-711
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• 1999

In this paper, Fuzzy Logic Controller was Designed for the Degree control of Arago's disk system. Arago's disk system is an application of Arago's disk phenomenon which is the operating principle of induction motor. Since the Arago's disk system varies to stable region. maginally stable region, unstable region according to the degree of bar respectively, it is a sutable system which can be evaluate an efficiency of the system. While an existing controller which was designed using linearized system modeling could control the system on only one operating point, fuzzy logic controller has the advantage in showing good response for multi-operating points because it does not need system modeling.

• The KSFM Journal of Fluid Machinery
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• v.15 no.2
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• pp.12-19
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• 2012

This study presents unsteady and unstable characteristics of three stage transonic axial compressor, developed by Korea Aerospace Research Institute. As approaching to the unstable operating region at the 103% design speed of the compressor, a modal type stall precursor appears in front of highly loaded 3rd rotor row at first, and it propagates to the upstream. On the contrary, actual stall cell initiates from the stall precursor in front of the 1st rotor row, and it propagates to the downstream of the compressor. After the stall region reached the 3rd stage and stall cell rotates circumferentially about 360 deg, it develops to one dimensional compressor surge mode. It shows a mild surge behaviour with 3~4 Hz frequency. From the test data, it can be suggested that there is a priority to give an optimum blade loading distributions to construct a multi stage transonic axial compressor stages either to secure more stable compressor operating ranges, or to maximize the compressor efficiency.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.91-98
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• 2007

This paper presents the induced mathematical modeling equations for evaluating the operation stability with automatic transmission of heavy duty vehicle. This theoretical approach indicates that linearized governing equations of system can be converted into eigen-value problems. if the eigen-value has positive number, we can predict the engine operating point locates an unstable operating region. To be a stable state, the unstable operating point diverges toward a stable point which is able to maintain uniform velocity. Based on the previous theoretical analysis, we carry out dynamic simulation to show the behavior of engine operating point and torque converter in transient state. As a result of the dynamic simulation, the suggested theoretical method is found to be reasonable for evaluating the operation stability of a torque converter. In addition, the numerical results explain the engine stops and fluctuating phenomenon in reality.

• Proceedings of the KIEE Conference
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• 2003.07d
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• pp.2325-2327
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• 2003

This thesis is concerned with the control of Arago's disk system using CAN(Controller Area Network). CAN protocol is used widely for the real time control in networked control systems(NCS). A networked control system using CAN is constructed to perform position control of Arago's disk. The mathematical model, of overall system is derived to design an appropriate controller analytical1y. Various operating points of the Arago's disk system in the real time control are chosen as stable region ($45^{\circ}$), marginal1y stable region($90^{\circ}$) and unstable region($120^{\circ}$), and the experiment for the position control of arago's disk system is done for each operating point. The performance of the suggested NCS is verified by experiments. It is shown that the NCS using CAN has stability and excel1ency in real time control.

• The KSFM Journal of Fluid Machinery
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• v.14 no.4
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• pp.5-11
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• 2011

This study investigated on details of flow characteristics in a vaneless diffuser of a compressor with 2-dimensional impeller at various flow rates. Experiment for a low speed compressor model in a water reservoir was performed to analyze the flow field in the vaneless diffuser and volute casing, which was done by PIV measurement. It was also focused on the periodic flow patterns occurring at low flow rate near unstable operating region of the compressor. At low flow rate condition, the flow visualization clearly shows that the flow energy from impeller is highly accumulated at the compressor exit by the blockage effect of a flow damper and consequently the reverse flow occurs in the diffuser.

• Journal of Power Electronics
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• v.14 no.2
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• pp.226-236
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• 2014

A new active LED driver with high power factor (PF) and low total harmonic distortion (THD) compatible with a rapid-start ballast is proposed. An LC input filter is attached to the ballast to increase PF and reduce THD. A boost converter is then installed to regulate the LED current, where an unstable operating region has been newly identified. The unstable region is successfully stabilized by feedback control with two zeroes. The extremely high overall system of the 10th order is completely analyzed by the newly introduced phasor transformed circuits in static and dynamic analyses. Although a small DC capacitor is utilized, the flicker percentage of the LED is drastically mitigated to 1% by the fast controller. The proposed LED driver that employs a simple controller with a start-up circuit is verified by extensive experiments whose results are in good agreement with the design.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.50 no.7
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• pp.340-347
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• 2001

In this Paper, we proposed a new voltage stability analysis algorithm. Using $ $ calculated by the optimal load How method(OLF), it rapidly and correctly calculates a PV curve with voltage collapse point in the stable region. OLF can calculates voltage collapse point as well as the operating point in the stable region. Specially, $ $ indicates the relative distance between voltage collapse point and the solution in the unstable region. In the study of a sample system, we verified the superiority of proposed algorithm.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.287-293
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• 2005

Most of all combustion system has combustion instability. It is a serious problem in combustion system. Unstable injection is one of the source of combustion instability. The experimental investigation of spray characteristics for simplex swirl injector were conducted experimentally. Two kerosene based fuels were chosen as the atomizing fluid. As the major operating parameters, fuel temperature and injection pressure were chosen, and varied in the range from 253 K to 293 K and from 0.2 MPa to 1.0 MPa, respectively. Direct spray images and mean diameter were measured for the various combination of operating parameters in the flow field. The results of present study show that the injection pressure and spray cone angle are fluctuated at specific conditions while it is continuous steady injection. As the fuel temperature changes continuously, spray cone angle varies discontinuously through the region of injection instability.