• Proceedings of the Korean Nuclear Society Conference
• /
• 1997.05a
• /
• pp.90-95
• /
• 1997

In this work, linear dynamics of a circulating fluid-fueled subcritical reactor system with temperature feedback and external neutron source was modeled and examined. In a circulating fluid-fuel system, the stable region is slightly moved by a circulation fluid effect. The effects of subcriticality and temperature feedback coefficient on the reactor stability were tested by calculating frequency response of neutron density originated from reactivity perturbation or external source oscillation of system. The amplitude transfer function has a different shape near subcritical region due to the exponential term in the transfer function. The results of the study show that at a slightly subcritical region, low frequency oscillation in accelerator current or reactivity can be amplified depending on the temperature feedback. However, as the subcriticality increases, the oscillation becomes negligible regardless of the magnitude of the temperature feedback coefficient.

• Journal of Korean Vacuum Science & Technology
• /
• v.6 no.1
• /
• pp.43-45
• /
• 2002

We have theoretically investigated steady-state carrier transport and current self-oscillation in negative-effective-mass (NEM) p$\^$+/pp$\^$+/diodes. The current self-oscillation here is a result of the formation and traveling of electric field domains in the p base having a NEM. The dependence of self-oscillating frequency on the applied dc voltage is obtained by detailed numerical simulations. In the calculations, we have considered the scatterings by carrier-impurity, carrier-acoustic phonon, carrier-polar-phonon, and carrier-nonpolar-phonon-hole interactions . This kind of NEM oscillator allows us to reach a current oscillation with terahertz frequency, thus it may be used as a broadband source of terahertz radiation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.3
• /
• pp.253-262
• /
• 2003

In this paper, the interference cancellation system, which is used to cancel the feedback signal in the wireless communication system with the same frequency, is studied. The time varying feedback signal generated from transmitter antenna to receiver antenna reduces the performance of the receiver system. the interference cancellation system using adaptive feedback method(AF-ICS) is suggested to prevent the oscillation of the receiver system and maintain the maximum output power of the power amplifier by the reduction of time-varying feedback signal and also this paper conforms that the oscillation disappears from the output signal by cancellation of the feedback signal and the total output power is satisfied the system specification.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 1999.11a
• /
• pp.149-154
• /
• 1999

This paper describes a passive safety injection system with free piston Stirling pump working withabundant decay heat in the nuclear reactor during the hypothetical accident. The water column in the tube assembly connected from the hot chamber to the cold chamber in the pump oscillates periodically due to thermal volume changes of non-condensable gas in each chamber. The oscillating pressure in the water column is converted into the pumping power with a suction-and-bleed type valve assembly. In this paper a dynamic model describing the frequency of oscillation and pumping pressure is developed. It was found that the pumping pressure is a function of the temperature difference between the chambers. Also, the frequency oscillation depends on the length of the tube with water column.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.03a
• /
• pp.606-611
• /
• 2008

The objective of the present study is to actively control the flame oscillation in the experimental lean premixed methane burner by the phase-controlled sound waves. The authors propose the methodology of generating the phase-controlled sound waves by directly sensing the preferential frequency and generating the sensor-triggered sound waves with fixed optimum phase difference with the flame oscillation. The real-time controller is implemented in the present study, and the combustion noise reduction is achieved. The reduction is 20dB at peak frequency and 13dB in the OASPL.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.11a
• /
• pp.359-362
• /
• 2009

Damping characteristics of pressure oscillation induced by an orifice in fluid feeding line for are investigated numerically and experimentally. Assuming small pressure oscillation, acoustic damping effect of orifice is confirmed experimentally, and with the mean flow, damping characteristics of an orifice are investigated numerically. When an orifice is installed at the node of pressure oscillation corresponding to the anti-node of velocity oscillation, suppression of pressure oscillation is maximized and with the mean flow, the resonant frequency is decreased. And, it is found that the optimal position of an orifice for damping shouled be changed.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.49 no.5
• /
• pp.226-232
• /
• 2000

This paper presents application results of the augmented matrix eigen-sensitivity theories to TCSC siting problem for damping the inter-area low frequency oscillation in the large KEPCO system. First and second-order eigen-sensitivities of the inter-area low frequency oscillation in the large KEPCO system. First and second-order eigen-sensitivities of the inter-area mode are computed fro changes in susceptance of the transmission lines. The lines having high sensitivity are chosen as the initial candidates for installing TCSC. Then for each of the chosen candidates, Bodeplot of the transfer function with line susceptance as the input and the bus voltage at one side of the line as the output is computed. Using the Bode plots, the lines having any zeros near the inter-area mode are screened out since design of TCSC controller is very difficult in such a case. The $H_{\infty}$ TCSC controller installed at any finally chosen candidate is found to be effective in damping the inter-area oscillation, and the proposed TCSC siting algorithm is proved to be valid. Design of $H_{\infty}$ controller is described in Part IIof this paper.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.2 no.2
• /
• pp.112-118
• /
• 2010

The numerical study about the vortex-induced vibration and vortex shedding in the wake has been presented. Prior to the numerical simulation of flexible riser systems concerning engineering conditions, efficiency validating of the proposed FSI solution method have been performed. The comparison between numerical simulation and published experimental data shows that the CFD method designed for FSI solution could give acceptable result for the VIV prediction of flexible riser/pipe system. As meaningful study on VIV and vortex shedding mode with the focus on flexible riser model systems, two kinds of typical simulation cases have been carried out. One was related to the simulation of vortex visualization in the wake for a riser model subject to forced oscillation, and another was related to the simulation of fluid-structure interaction between the pipes of coupled multi-assembled riser system. The result from forced oscillation simulation shows that the vortex-induced vibration with high response frequency but small instantaneous vibration amplitude contributes to vortex conformation as much as the forced oscillation with large normalized amplitude does, when the frequency of forced oscillation was relatively high. In the multi-assembled riser systems, it has been found that the external current velocity and the distance between two pipes are the critical factors to determine the vibration state and the steady vibration state emerging in quad-pipe system may be destroyed more easily than dual-pipe system.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.2
• /
• pp.390-396
• /
• 2010

An 80MHz surface acoustic wave (SAW)-based gyroscope utilizing a progressive wave was developed on a piezoelectric substrate. The developed sensor consists of two SAW oscillators in which one is used for sensing element and has metallic dots in the cavity between input and output IDTs. The other is used for a reference element. Coupling of mode (COM) modeling was conducted to determine the optimal device parameters prior to fabrication. According to the simulation results, the device was fabricated and then measured on a rate table. When the device was subjected to an angular rotation, oscillation frequency differences between the two oscillators were observed because of the Coriolis force acting on the metallic dots. Depending on the angular rate, the difference of the oscillation frequency was modulated. The obtained sensitivity was approximately 52.35 Hz/deg.s within the angular rate range of 0~1000 deg/s. The performances of devices with three IDT structures for two kinds of piezoelectric substrates were characterized. Good thermal stability was also observed during the evaluation process.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.394-394
• /
• 2013

The spin-orbit interaction has received great attention in the field of spintronics, because of its property and applicability. For instance, the spin-orbit interaction induces spin precession which is the key element of spin transistor proposed by Datta and Das, since frequency of precession can be controlled by electric field. The spin-orbit interaction is classified according to its origin, Dresselhaus and Rashba spin-orbit interaction. In particular, the Rashba spin-orbit interaction is induced by inversion asymmetry of quantum well structure and the slope of conduction band represents the strength of Rashba spin-orbit interaction. The strength of spin-orbit interaction is experimentally obtained from the Shubnikov de Hass (SdH) oscillation. The SdH oscillation is resistance change of channel for perpendicular magnetic field as a result of Zeeman spin splitting of Landau level, quantization of cyclotron motion by applied magnetic field. The frequency of oscillation is different for spin up and down due to the Rashba spin-orbit interaction. Consequently, the SdH oscillation shows the beat patterns. In many research studies, the spin-orbit interaction was treated as a tool for electrical manipulation of spin. On the other hands, it can be considered that the Rashba field, effective magnetic field induced by Rashba effect, may interact with external magnetic field. In order to investigate this issue, we utilized InAs quantum well layer, sandwiched by InGaAs/InAlAs as cladding layer. Then, the SdH oscillation was observed with tilted magnetic field in y-z plane. The y-component (longitudinal term) of applied magnetic field will interact with the Rashba field and the z-component (perpendicular term) will induce the Zeeman effect. As a result, the strength of spin-orbit interaction was increased (decreased), when applied magnetic field is parallel (anti-parallel) to the Rashba field. We found a possibility to control the spin precession with magnetic field.