• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.10
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• pp.1708-1712
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• 2008

This paper describes a linear matrix inequality (LMI) approach to the design of robust low-order power system stabilizers (PSSs), which are used to damp out local-mode oscillations of synchronous generators. The performance of a PSS is expressed as the location of the closed-loop poles, and a single fixed-gain pole-placement controller is synthesized for a wide range of operating conditions. The synthesis results in simultaneous regional pole-placement stabilization. and is formulated as an LMI feasibility problem with a rank condition. A penalty method is applied to solve the rank-constrained LMI problem. Numerical experiments with a single-machine connected to an infinite bus system were performed to demonstrate the proposed method.

• Wind and Structures
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• v.10 no.1
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• pp.83-97
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• 2007

In the last decades there have been frequent reports of oscillations of slender tension members under simultaneous action of rain and wind - characterized by large amplitudes and low frequencies. The members, e.g. cables of cable-stayed bridges, slightly inclined hangers of arch bridges or cables of guyed-masts, show a circular cross section and low damping. These rain-wind induced vibrations negatively affect the serviceability and the lifespan of the structures. The present article gives a short literature review, describes a mathematical approach for the simulation of rain-wind induced vibrations, sums up some examples to verify the calculated results and discusses measures to suppress the vibrations.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.228-236
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• 2011

The analysis of the performance and the internal flow according to various numerical models used for the interior ballistics has been conducted. The internal flow has been mainly affected by the drag model. As results, oscillations of the pressure differences between the breech and the shot base has been reduced with a deceased drag of the propellant. The major performance of the interior ballistics has no relation to the models using Nusselt number for heat transfer coefficient. The negative pressure difference without the heat transfer of the propellant has not been shown.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.41 no.6
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• pp.518-524
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• 2008

A three-dimensional primitive equation model (POM) and the buoy data (2900 N, 13500 E) from the Japan Meteorological Agency (JMA) for 27 typhoons between 1982 and 2000 are used to investigate the sea surface cooling (SSC) that accompanies typhoons in the northwestern Pacific. Observed sea surface temperatures (SSTs) rapidly drop 0.6 to 4.3 C, and SSC continues for several weeks after the passage of a typhoon. The model, which covers most of the northwestern Pacific ($24^{\circ}N$ to $52^{\circ}N$), simulated Typhoon Abby over the tropical Pacific, and successfully reproduces many observed features, including the pattern of SST decrease, inertial oscillations, etc. The model accurately simulated the SSC process, suggesting that the cyclonic eddy with a radius of a few hundred kilometers that trailed Typhoon Abby plays an important role in SSC.

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

• Bulletin of the Korean Chemical Society
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• v.26 no.4
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• pp.543-547
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• 2005

The Belousov-Zhabotinskii system measured by a Pt electrode is investigated under external electrode current constraint. A dynamical analysis of the electrode reaction phase has been made by means of a linearized stability criterion valid for three-variable system. It turns out that limit cycle oscillatory regime and dynamical behaviors of the electrode reaction phase have been degenerated under periodical electrode current.

• Journal of Ocean Engineering and Technology
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• v.5 no.1
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• pp.25-34
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• 1991

An accurate estimation of water level variation when thewaves propagate to the coastal regionis very important for the port and harbor development plan. This study describes the application of a hybrid element model to harbor oscillation problem due to the construction of shore structure and implementation of shore boundary. The site selected is Pusan Harbor area with the third development and the Artificial Island plan. The observed water level changes at the site are compared with the result of the numerical experiment. The model gives a very important prediction of water level changes for navigation and harbor design.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.110-112
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• 2003

A numerical simulation of an incompressible cavity flow is conducted using turbulence models. Cavity geometry and flow conditions are based on Cattafesta's experiment. Baldwin-Lomax model and ${\kappa}-{\varpi}$ model are employed. While simulation with Baldwin-Lomax model predicts the oscillatory features of the flow, the use of ${\kappa}-{\varpi}$ model in its original form makes the simulation converge to steady flow. To acquire oscillatory flow solution, Kato-Launder form and Time scale bound are adopted in production term of ${\kappa}-{\varpi}$ model. The strouhal number of the flow oscillations from the simulation results corresponds to 1 st mode in simulation but 2 nd mode in experiments. However mean velocity profile is in good agreement with the experimental data and the fluctuation profile follows the tendency of Cattafesta's results.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.378-385
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• 2008

The present paper deals with the accurate and robust limiting procedure for the multi-dimensional flow analysis on unstructured meshes. The multi-dimensional limiting process (MLP) which was successfully proposed on structured grid system is extended to unstructured meshes. Based on MUSCL-type framework on unstructured meshes, the new slope limiter is devised to satisfy the MLP condition, which is quite effective to regulate the unwanted oscillations, especially on multiple dimensions. Considering the neighborhood based on the vertex of the cell, as well as the edge, this limiting strategy captures the multi-dimensional flow features very accurately with the proper stencils. From the various numerical results, these desirable characteristics of the proposed limiting strategy are clearly shown.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.378-385
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• 2008

The present paper deals with the accurate and robust limiting procedure for the multi-dimensional flow analysis on unstructured meshes. The multi-dimensional limiting process (MLP) which was successfully proposed on structured grid system is extended to unstructured meshes. Based on MUSCL-type framework on unstructured meshes, the new slope limiter is devised to satisfy the MLP condition, which is quite effective to regulate the unwanted oscillations, especially on multiple dimensions. Considering the neighborhood based on the vertex of the cell, as well as the edge, this limiting strategy captures the multi-dimensional flow features very accurately with the proper stencils. From the various numerical results, these desirable characteristics of the proposed limiting strategy are clearly shown.