• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.305-307
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• 2010

In this study, we develop a method to achieve heat transfer enhancement inside a square duct with high aspect ratio without changing any inner structures. Especially, a method to lower the possible maximum temperature is suggested if constant heat flux is provided to single surface of square duct. Knowing the fact that heat transfer rate is inversely proportional to flow area, we proposed tapered channel concept which uses narrower gap toward the flow exit where the maximum temperature is expected. To maintain equivalent power consumption, inlet section has been enlarged. To verify the proposed concept, experimental tests have been performed.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.5
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• pp.643-651
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• 1998

Turbulent unsteady flows in the entrance region of a square duct are investigated with a hot-wire anemometer system. The velocity waveforms the mean and turbulence components of the axial velocity and the entrance length are obtained as a major characteristics of the developing turbulent unsteady flows. An inviscid flow theory is presented to describe the developing axial mean velocity profiles. A good agreement is seen between the measured and theoretically predicted values. The propagation of turbulence generated near the entrance of the square duct is satisfactorily approximated by an empirical correlation of the propagation of turbulence proposed so far. The local turbulence intensi-ty is found to be a little smaller in the accelerating phase than in the decelerating phase. The entrance length is about 60 times as large the hydraulic diameter.

• Journal of applied mathematics & informatics
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• v.16 no.1_2
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• pp.483-488
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• 2004

Results on the analytic behavior of the limiting spectral distribution of large dimensional random matrices, studied in Marcenko and Pastur [2], are derived. Using the Stieltjes transform, it is shown that the limiting distribution has a continuous derivative away from zero, the derivative being analytic whenever it is positive [3]. In the present paper, it is derived that the behavior of it resembles the behavior of a square root function near the boundary of its support.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.825-830
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• 2001

A numerical study on a quantitative analogy of the fully developed flow between in a straight square duct rotating about an axis perpendicular to that of the duct and a stationary curved duct of square cross-section is carried out. In order to clarify the similarity of two turbulent flows, the dimensionless parameters $K_{TR} = Re^{1/4}/\sqrt{Ro}$ and the Rossby number, Ro, in a rotating straight duct flow were used as a set corresponding to $K_{TC} = Re^{1/4}/\sqrt{{\lambda}}$ and curvature ratio, ${\lambda}$, in a stationary curved duct flow so that they have the same dynamical meaning as $K_{LR} = Re/\sqrt{Ro}$ and $K_{LC} = Re/\sqrt{{\lambda}}$ of the fully developed laminar flows. For the large values of Ro or A, it is shown that the flow field satisfies the asymptotic invariance property: there are strong quantitative similarities between the two flows such as flow patterns and friction factors for the same values of $K_L$ and $K_T$.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.2
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• pp.114-123
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• 2020

A high-order potential-based panel method based on Green's theorem, with piecewise-linear dipole strength on triangular panels, is formulated for the analysis of potential flow around a three-dimensional wing. Previous low-order panel methods adopt square panels with piecewise-constant dipole strength, which results in inherent errors. Square panels can not represent a high curvature lifting body, such as propellers, since the four vertices of the square panel do not locate at the same flat plane. Moreover the piecewise-constant dipole strength induces inevitable errors due to the steps in dipole strength between adjacent panels. In this paper a high-order panel method is formulated to improve accuracy by adopting a piecewise linear dipole strength on triangular panels. Firstly, the square panels are replaced by triangular panels in order to increase the geometric accuracy in representing the shape of the object with large curvature. Next, the step difference of the dipole strength between adjacent panels is removed by adopting piecewise-linear dipole strength on the triangular panels. The calculated results by the present method is compared with analytical ones for simple non-lifting geometries, such as ellipsoid. The results for an elliptic wing with zero thickness at finite angle of attack are compared with Jordan's results. The comparison shows reasonable agrements for the both lifting and non-lifting bodies.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.409-412
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• 2006

EEFL can be driven by square wave driving method. A square wave is applied directly to both ends of EEFL by cascaded multi-stage full-bridge inverter. The various current shapes of lamp are achieved by various inductors between lamp and inverter. In this paper, it is newly investigated that the area of current directly influences the luminance. Furthermore, the 3-level square wave is considered to drive EEFL with self-discharge characteristics. The highest luminance efficiency is achieved by properly controlling the rate of self-discharge usage.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.5
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• pp.731-740
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• 2001

A numerical study on the quantitative analogy between the fully developed turbulent flow in a straight square duct rotating about an axis perpendicular to that of the duct and that in a stationary curved duct of square cross-section is carried out. In order to clarify the similarity of the two flows, dimensionless parameters K(sub)TR=Re(sup)1/4/√Ro and Rossby number, Ro, in a rotating straight duct flow were used as a set corresponding to K(sub)TC=Re(sup)1/4/√λ and curvature ratio, λ, in a stationary curved duct flow so that they have the same dynamical meaning as those of the fully developed laminar flows. For the large values of Ro or λ, it is shown that the flow field satisfies the asymptotic invariance property, that is, there are strong quantitative similarities between the two flows such as flow patterns and friction factors for the same values of K(sub)TR and K(sub)TC.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.1
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• pp.8-15
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• 2021

Micro-LEDs can be applied to various parts of a product. However, it has disadvantages compared to general LEDs in large displays such as low efficiency, intensity, and contrast ratio, among others, owing to their short history of study. The simulations were carried out using ray-tracing software to investigate the change in light intensity and light distribution according to pattern shapes on the sapphire substrate of the flip-chip micro-LED (FC μ-LED) array. Three patterns-concave square patterns, convex square patterns, and Ag coated convex patterns-which existed on the opposite side of FC μ-LEDs (115 ㎛ × 115 ㎛) array, were applied. The intensity of FC μ-LEDs on the center of the receivers depends on the pattern depth with shape. The concave square patterns having FC μ-LEDs arrays show that decreasing intensity as the patterns depth. On the contrary, the convex square patterns having FC μ-LEDs arrays shows that increasing intensity as the patterns depth. In addition, the highest intensity shows that FC μ-LEDs having Ag-coated convex patterns on the opposite side of sapphire lead to a reduction in light crosstalk owing to the Ag film.

• Structural Engineering and Mechanics
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• v.77 no.6
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• pp.745-751
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• 2021

Concrete filled double skin tubular members (CFDST) consist of double concentric circular or square steel tubes with concrete filled between the two steel tubes. The CFDST members, having a hollow section inside the internal tube, are generally lighter than ordinary concrete filled steel tubular members (CFT) which have a solid cross-section. Therefore, when the CFDST members are applied to bridge piers, reduction of seismic action can be expected. The present study aims to investigate, experimentally, the behavior of CFDST stub columns with double concentric square steel tubes filled with concrete (SS-CFDST) when working under centric compression. Two test parameters, namely, inner-to-outer width ratio and outer square steel tube's width-to-thickness were selected and outer steel tube's width-to-thickness ratio ranging from 70 to 160 were considered. In the results, shear failure of the concrete fill and local buckling of the double skin tubes having largest inner-to-outer width ratio were observed. A method to predict axial loading capacity of SS-CFDST is also proposed. In addition, the load capacity in the axial direction of stub column test on SS-CFDST is compared with that of double circular CFDST. Finally, the biaxial stress behavior of both steel tubes under plane stress is discussed.

• The Journal of the Convergence on Culture Technology
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• v.10 no.1
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• pp.345-352
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• 2024

K-Pop Square Media, located at COEX in Samseong-dong, has gained public attention and mass media focus by showcasing various three-dimensional videos on a large LED display. The video content on the distinctive large curved LED display utilizes a form of media façade technique, establishing itself as a new landmark and attraction within the spatial characteristics of the COEX Plaza. This study aims to examine the characteristics of media facades used in outdoor advertising in urban spaces, focusing on K-Pop Square Media. The approach for this research involves three aspects: Firstly, examining the 'spatial characteristics' of urban public spaces by referencing Kevin Lynch's five elements constituting urban space and William J. Mitchell's exploration of smart spaces and changes in spatial paradigms. Secondly, analyzing the 'digital nature' of outdoor advertising through an examination of three types of Digital Out-Of-Home (DOOH) Media. Thirdly, exploring the 'technological advancements and content composition of media facades' by investigating types of display media (projection, LED screens), the inception of media facades, and the latest display technology like Anamorphic displays. Through this research, it becomes evident that K-Pop Square Media exhibits characteristics of publicness, communicativeness, artistry, and placemaking through the spatial characteristics of smart spaces, the media-specific aspects of Digital Out-Of-Home advertising, and the content composition of media facades.