• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.6
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• pp.452-459
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• 2003

The characteristics of fluid-elastic instability and effects of turbulent excitations for the KSNP steam generator tubes were investigated numerically. The information for the thermal-hydraulic data of the steam generator has been obtained by using the ATHOS3-MOD1 code and the flow-induced vibration(FIV) analysis has been conducted by using the PIAT(program for Integrity assessment of SG tube) code. The KSNP steam generator has the concentrated plugging zone at the vicinity of the stay cylinder inside the SG. To investigate the cause of the concentrated tube plugging zone, the FIV analysis has been performed for various column and row number of the steam generator tubes. From the results of FIV analysis the stability ratio due to the fluid-elastic instability and vibrational amplitude due to the turbulent excitation in the concentrated plugged zone have a trend of larger values than those of the outer concentrated tube Plugging zone.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.3
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• pp.161-167
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• 2004

Zone 3 of the distance relay is used to provide the remote back-up protection in case of the failure of the primary protection. However, the risk lot mal-operations under stressed conditions such as heavy loading, voltage and transient instability is usually high. Zone 3 is used in combination with the derivatives of the voltage, and current, etc to prevent mal-operations. Sometimes, the impedance characteristics that restrict the tripping area of relay are used to avoid the mal-operations due to load encroachment. This paper presents a novel Zone 3 scheme based on combining the steady-state components (i.e. 60Hz) and the transient components (TCs) using a state diagram that visualizes the sequence of studies that emanate from the sequence of events. The simulation results show that the novel zone 3 distance relay elements using the proposed method operates correctly for the various events.

• Nuclear Engineering and Technology
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• v.40 no.7
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• pp.561-570
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• 2008

When reactivity insertion such as refueling occurs in CANDU reactors, the power and the water levels are tilted in the upper outer zone of the LZCS (Liquid Zone Control System) and fluctuate unstably for a certain period of time (1-5 days). The instability described above is observed in most CANDU reactors in service around the world, but its root cause is unidentified and no solutions to this problem have been established. Therefore, this study attempted to prove experimentally and analytically that the root cause lies in the hold-up of light water on the top of the TSP (Tube Support Plate) due to the mismatch between net volumetric flow rate of light water and helium crossing the narrowed porous TSP installed within the LZCS compartment. Our method was to perform a hydrodynamic simulation of in/outflow of light water and helium. Two solutions for the aforementioned instability of LZCS are suggested. One is to regulate the compartment for both inflowing helium gas and outflowing light water; the other is to enlarge the flow paths of helium and light water within TSP. The former may be applicable to nuclear reactors in service and the latter to those planned for construction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.670-676
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• 2003

To investigate the group plugging effect the fluid-elastic instability analysis has been performed on various column and row number of the KSNP steam generator lutes. This study compares the stability ratio of the plugged tube with that of the intact one. The information on the thermal-hydraulic data of the steam generator have been obtained by using the ATHOS3-MOD1 code with and without the thermal energy transfer at the plugged region. Both of the boundary conditions of hot-leg temperature and feedwater mass flow rate are fixed for this investigation. From the results of this study the stability ratios inside the group plugging zone are decreased slightly. At the outside of group plugging zone, however, most of the stability ratios tend to be increased.

• Journal of Astronomy and Space Sciences
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• v.3 no.2
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• pp.71-79
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• 1986

According to recent satellite observations, strong ion transverse acceleration to the magnetic field(ion conics) has been known. The ion conics may be a result of electrostatic waves frequently observed on the auroral zone. Both linear and nonlinear theory of electrostatic instability driven by an electron current based on 1-dimensional particle simulation experiment have been considered. From the results of simulation strong ion transverse acceleration has been shown.

• Proceedings of the Korean Nuclear Society Conference
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• 2005.10a
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• pp.472-473
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• 2005

• KIEE International Transactions on Power Engineering
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• v.5A no.2
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• pp.144-151
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• 2005

This paper presents a framework for determining control strategies against unwanted tripping actions during relay operation that plays a very important role in cascading events leading to voltage collapse. The framework includes an algorithm for quick identification of possible zone 3 relay operation during voltage instability. Furthermore, it comes up with the control strategy of load shedding at the selected location with active power and relay margin criteria. In addition, Quasi Steady-State (QSS) simulation is employed to obtain time-related information that is valuable in the determination of control strategy. As a case study, an example applying the framework is shown with the modified New England 39-bus system.

• Journal of the Korean Society of Combustion
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• v.22 no.3
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• pp.41-46
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• 2017

This study has numerically investigated the flame-acoustics interactions in the turbulent partially premixed flame field. In the present approach, in order to analyze the combustion instability, the present approach has employed the LES-based combustion model as well as the Helmholtz solver. Computations are made for the validation case of the partially premixed LIMOUSINE burner. In terms of the FFT data, numerical results are compared with experimental data. Moreover, Helmholtz equation in frequency domain is solved by combining CFD field data including the flight time from a nozzle to the flame zone. Based on numerical results, the detailed discussions are made for the essential features of the combustion instability encountered in the partially premixed burner.

• Structural Engineering and Mechanics
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• v.19 no.5
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• pp.503-517
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• 2005

The parametric dynamic stability of an asymmetric sandwich beam with viscoelastic core on viscoelastic supports at the ends and subjected to an axial pulsating load is investigated. A set of Hill's equations are obtained from the non-dimensional equations of motion by the application of the general Galerkin method. The zones of parametric instability are obtained using Saito-Otomi conditions. The effects of shear parameter, support characteristics, various geometric parameters and excitation force on the zones of instability are investigated.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.245-247
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• 2003

Zone 3 of the distance relay is used to provide the remote back-up protection in case of the failure of the primary protection. However, the risk for mal-operations under stressed conditions such as heavy loading, voltage and transient instability is usually high. Zone 3 is used in combination with the derivatives of the voltage, and current, etc to prevent mal-operations. Sometimes, the impedance characteristics that restrict the tripping area of relay are used to avoid the mal-operations due to load encroachment. This paper presents a novel zone 3 scheme based on combining the steady-state components(i.e. 60Hz) and the transient components(TCs) using a state diagram that visualizes the sequence of studies that emanate from the sequence of events. The simulation results show that the novel zone 3 distance relay elements using the proposed method operates correctly for the various events.