• Communications of the Korean Mathematical Society
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• v.13 no.1
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• pp.123-129
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• 1998

In this paper, we study some dynamical properties of a weakly almost periodic flow. In particular we get, in a weakly almost periodic flow (X,T), the groups I and A(I) of all automorphisms of I are isomorphic, where E(X) is the enveloping semigroup of (X,T) and I is the minimal right ideal in E(X).

• Korean Journal of Mathematics
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• v.12 no.2
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• pp.171-175
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• 2004

The purpose of this paper is to investigate some lifting properties of homomorphisms of flows. It is shown that an almost one to one extension of a minimal proximal flow is proximal. It is also shown that a distal extension of a pointwise almost periodic flow is pointwise almost periodic.

• Korean Journal of Mathematics
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• v.11 no.2
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• pp.161-167
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• 2003

The purpose of this paper is to study and characterize the notions of characteristic 0 and weakly almost periodicity in flows. In particular, we give sufficient conditions for the weakly almost periodic flow to be almost periodic.

• Korean Journal of Mathematics
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• v.13 no.2
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• pp.235-239
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• 2005

In this paper we study some characterizations of proximal, distal and almost one to one homomorphisms of flows. In particular we show that if the almost one to one proximal extension of a minimal flow is weakly almost periodic, then it is minimal.

• Korean Journal of Mathematics
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• v.10 no.2
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• pp.173-177
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• 2002

The purpose of this paper is to study and characterize the flows of characteristic 0. It is shown that the homomorphic image of distal flow of characteristic 0 is a distal flow of characteristic 0. It is also shown that the closure of every orbit in a 0-graphic flow is regular minimal.

• Journal of the Korean Institute of Gas
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• v.23 no.3
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• pp.27-32
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• 2019

In this study, the vorticity distribution and the temperature distribution change around a circular cylinder were compared and analyzed with time for constant inlet velocity and periodic inlet velocity. Also, the frequency characteristics of the flow were analyzed by analyzing the time variation of lift and drag and their PSD(power spectral density). In the case of constant inlet velocity, the well known Karman vorticity distribution was shown, and vortices were alternately generated at the upper and lower sides of the circular cylinder. In case of periodic inlet velocity, it was observed that vortex occurred simultaneously in the upper and lower sides of the circular cylinder. In both cases, it was confirmed that the time dependent temperature distribution changes almost the same behavior as the vorticity distribution. For the constant inlet velocity, the vortex flow frequency is 31.15 Hz, and for the periodic inlet velocity, the vortex flow frequency is equal to the preriodic inlet velocity at 15.57 Hz. The mean surface Nusselt number was 99.6 for the constant inlet velocity and 110.7 for the periodic inlet velocity, which showed 11.1% increase in surface heat transfer.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.2
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• pp.216-222
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• 2013

A solar power generator is usually installed outdoors and it is exposed to extreme environments such as heavy fall of snow and high speed wind. Therefore, the solar tracker structure should be designed to have sufficient static and dynamic stiffness against such environmental conditions. In this paper, eigenvalue analysis of the solar tracker is carried out by varying the pose of the solar panel and unsteady flow analysis around a single tracker or multi-trackers arranged in a line is performed by varying the parameters such as wind directions, wind speeds and the pose of the solar panel to evaluate whether there exists an instability of resonance due to vortex shedding. Finite element eigenvalue analysis shows that natural frequencies and modes are almost not influenced by the pose of the solar panel and the finite element flow analysis shows that there does not exist periodic vortex shedding due to the flow around single tracker or multiple solar trackers in a line.

• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.505-512
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• 2006

Characteristics of particle holdup and heat transfer were investigated in a liquid-particle swirling fluidized bed whose diameter was 0.102 m and 2.5 m in height. Effects of liquid velocity, particle size and swirling liquid ratio($R_s$) on the particle holdup and immersed heater-to-bed overall heat transfer coefficient were examined. The particle holdup increased with increasing particle size and swirling liquid ratio but decreased with increasing liquid velocity.The local particle holdup was relatively high in the region near the heater when the $R_s$ value was 0.1~0.3, but the radial particle holdup was almost uniform when the $R_s$ value was 0.5, whereas, when the $R_s$ value was 0.7, the local particle holdup was relatively low in the region near the heater. The heat transfer characteristics between the immersed heater and the bed was well analyzed by means of phase space portraits and Kolmogorov entropy(K) of the time series of temperature difference fluctuations. The phase space portraits of temperature difference fluctuations became stable and periodic and the value of Kolmogorov entropy tended to decrease with increasing the value of $R_s$ from 0.1 to 0.5. The Kolmogorov entropy exhibited its maximum value with increasing liquid velocity. The value of overall heat transfer coefficient(h) showed its maximum value with the variation of liquid velocity, bed porosity or swirling liquid ratio, but it increased with increasing particle size. The value of K exhibited its maximum at the liquid velocity at which the h value attained its maximum. The particle holdup and overall heat transfer coefficient were well correlated in terms of dimensionless groups of operating variables.