• Journal of the Korean Society of Combustion
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• v.10 no.3
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• pp.25-33
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• 2005

Fast-time instability is investigated for diffusion flames with Lewis numbers greater than unity by employing the numerical technique called the Evans function method. Since the time and length scales are those of the inner reactive-diffusive layer, the problem is equivalent to the instability problem for the $Li\tilde{n}\acute{a}n#s$ diffusion flame regime. The instability is primarily oscillatory, as seen from complex solution branches and can emerge prior to reaching the upper turning point of the S-curve, known as the $Li\tilde{n}\acute{a}n#s$ extinction condition. Depending on the Lewis number, the instability characteristics is found to be somewhat different. Below the critical Lewis number, $L_C$, the instability possesses primarily a pulsating nature in that the two real solution branches, existing for small wave numbers, merges at a finite wave number, at which a pair of complex conjugate solution branches bifurcate. For Lewis numbers greater than $L_C$, the solution branch for small reactant leakage is found to be purely complex with the maximum growth rate found at a finite wave number, thereby exhibiting a traveling nature. As the reactant leakage parameter is further increased, the instability characteristics turns into a pulsating type, similar to that for L < $L_C$.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.167.2-167.2
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• 2011

Motions in nature, for example ocean wave, has been playing a significant role for generating electricity production in our modern life. This paper presents an innovative approach for electric power conversion of the vast ocean wave energy. Here, a floating-buoy wave energy converter (WEC) using hydrostatic transmission (HST), which is shortened as HSTWEC, is proposed and designed to enhance the wave energy harvesting task during all wave fluctuations. In this HSTWEC structure, the power take-off system (PTO) is a combination of the designed HST circuit and an electric generator to convert mechanical energy generated by ocean wave into electrical energy. Several design concepts of the HSTWEC have been considered in this study for an adequate investigation. Modeling and simulations using MATLAB/Simulink and AMESim are then carried out to evaluate these design concepts to find out the best solution. In addition, an adaptive controller is designed for improving the HSTWEC performance. The effectiveness of the proposed HSTWEC control system is finally proved by numerical simulations.

• Journal of Astronomy and Space Sciences
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• v.33 no.3
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• pp.197-205
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• 2016

We investigated two flares in the solar atmosphere that occurred on June 3, 2012 and July 6, 2012 and caused propagation of Moreton and EIT waves. In the June 3 event, we noticed a filament winking which presumably was caused by the wave propagation from the flare. An interesting feature of this event is that there was a reflection of this wave by a coronal hole located alongside the wave propagation, but not all of this wave was transmitted by the coronal hole. Using the running difference method, we calculated the speed of Moreton and EIT waves and we found values of 926 km/s before the reflection and 276 km/s after the reflection (Moreton wave) and 1,127 km/s before the reflection and 46 km/s after the reflection (EIT wave). In the July 6 event, this phenomenon was accompanied by type II and type III solar radio bursts, and we also performed a running difference analysis to find the speed of the Moreton wave, obtaining a value of 988 km/s. The speed derived from the analysis of the solar radio burst was 1,200 km/s, and we assume that this difference was caused by the different nature of the motions in these phenomena, where the solar radio burst was caused by the propagating particles, not waves.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.4
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• pp.627-636
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• 2019

The Radio Law was revised twelve times since the full revision in 2000, and now it is equipped with the current status of securing radio resources, distribution and allocation of radio resources, utilization of radio resources, protection of radio resources and promotion of radio waves, which can be evaluated to include the legal nature of securing radio resources and propagation beyond the simple administrative legal nature of radio resources. The legal system in the telecommunication sector is also being improved, and the Radio Law is also supplementing the weak points through two revisions. The domestic radio law, and it is considered to form a legal system for promoting the effective allocation and utilization of resources in accordance with the changes in radio wave usage environment. It can be evaluated that it has become a law related to radio promotion and competition in the existing simple administrative law. It is considered necessary to adjust the detailed regulations for each type of use.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.105-112
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• 2006

Freak waves in the ocean are recently drawing much attention as a natural disaster to ocean structures and navigating ships as well. Several observation data, among them the Draupner New Year Wave, show the very impressive feature of Freak waves whose wave height is up to three times as high as the significant wave height of surrounding waves, In addition, Freak wave appears as an isolated very high crest in somewhat stationary random waves of same order in their wavelengths. Bearing such characteristics in mind, one notices its extraordinary steepness. This strongly suggests that Freak wave is not long lived but transient nature on the whole. A great number of studies to explain these natures were published from both theoretical and numerical point of view. However it is not sure if they are applicable to actual ocean environment. In this paper, we deal with the results concerning abnormal and/or Freak waves from in-situ ocean wave data and point out several remarks to the problems lain behind the contributions in this context. A physical experiment is described to reinforce the subject discussed from the observation data.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.57-58
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• 2015

In this study, we present geometrical and kinematical analysis of Moreton wave observed in 2012 June 3rd and July 6th, recorded in H-${\alpha}$ images of Global Oscillation Network Group (GONG) archive. These large-scale waves exhibit different features compared to each other. The observed wave of June 3rd has angular span of about $70^{\circ}$ with a diffuse wave front associated to NOAA active region 11496. It was found that the propagating speed of the wave at 17:53 UT is about $931{\pm}80km/s$. The broadness nature of this Moreton wave can be interpreted as the vertical extension of the wave over the chromosphere. On the other hand, the wave of July 6th associated with X1.1 class are that occurred at 23:01 UT in AR NOAA11515. From the kinematical analysis, the wave propagated with the initial velocity of about $994{\pm}70km/s$ which is in agreement with the speed of coronal shock derived from type II radio burst, v ~ 1100 km/s. These two identified waves add the inventory of the large-scale waves observed in 24th Solar Cycle.

• Bulletin of the Korean Mathematical Society
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• v.50 no.1
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• pp.201-216
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• 2013

In this note, we consider the Riemann problem for a two-dimensional nonstrictly hyperbolic system of conservation laws. Without the restriction that each jump of the initial data projects one planar elementary wave, six topologically distinct solutions are constructed by applying the generalized characteristic analysis method, in which the delta shock waves and the vacuum states appear. Moreover we demonstrate that the nature of our solutions is identical with that of solutions to the corresponding one-dimensional Cauchy problem, which provides a verification that our construction produces the correct global solutions.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1995.10a
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• pp.66-70
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• 1995

The oscillatory boundary layer that develops when surface waves propagate over the sea bottom affects many flow-pendent phenomena in the coastal zone. Examples of such phenomena are wave energy dissipation due to bottom friction and the initiation and transport of sediment (Grant and Madsen 1986). In nature the boundary layer under waves will almost always be turbulent (Nielsen 1992). (omitted)

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.742-748
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• 1993

The dynamics and control of two complex column configurations (sidestream column with stripper; prcfractionater/sidestream column configuration), which are multivariable interacting and nonlinear, have been studied. A new control scheme developed by Hanand Park(1993) to deal with the nonlinear and multivariable nature of distillation processes has been applied to these complex distillation configurations. The control scheme incorporates a nonlinear wave model into a generic model control framework. An observer based on the nonlinear wave model is used to determine the profile positions of distillation column sections. The control scheme enables tight control of the profile position of each column section that leads to fast stabilization of product compositions.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.79.2-79.2
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• 2014

A few years from now, gravitational wave (GW) detectors of LIGO and VIRGO consortiums are expected to reach the sensitivity necessary to detect GW signals from astronomical sources. Identification of the counterparts to the GW sources in electromagnetic wave is very important, since the localization of the GW signals is going to be very poor (~1000 $deg^2$) for the first detections and the nature of the GW-emitting sources will be uncertain with the GW detection only. In this talk, we will discuss possible astronomical sources that could be responsible for the first GW signals, and outline our current efforts to do follow-up observation of GW sources in collaboration with LIGO/VIRGO groups.