• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2738-2750
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• 1994

The Effects of radiative heat transfer on turbulent flow in a partitioned enclosure is studied numerically. The enclosure is partially divided by a thin, poorly conducting vertical divider projecting from the ceiling of the enclosure. The low Reynolds number $k-{\epsilon}$ model is adopted to calculate the turbulent flow field. The solutions to the radiative transfer equations are obtained by the discrete ordinates method(DOM). This method is based on control volume method and is compatible with the SIMPLER algorithm used to solve the momentum and energy equations. The effects of optical thickness and Planck number on the flow, temperature fields and heat transfer rates are investigated for a moderate Rayleigh number($=10^9$). The changes in buoyant flow fields and temperature distributions due to the variation of baffle length are also analyzed. From the predictions, radiant heat exchange between the baffle and the sidewalls strongly influences the temperature distribution in the baffle and its vicinity and total heat transfer increases as the optical thickness and the baffle length decrease. It is possible to neglect the radiative heat transfer effect when Planck number is over one.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.6
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• pp.682-686
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• 2015

The objective of this study is to validate the performance of the current $k-{\epsilon}$ turbulence model for a single-phase turbulent natural convection, which has been considered an important phenomenon in nuclear safety. As a result, the natural convection problems in the 2D and 3D cavities previously studied are calculated by using the ANSYS Fluent software. The present results show that the current $k-{\epsilon}$ turbulent model accounting for the buoyancy effect is in good agreement with the previous results for the natural convection problems in the 2D and 3D cavities although some improvements should be required to get better prediction.

• Journal of Welding and Joining
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• v.2 no.1
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• pp.41-48
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• 1984

Recrystallization technique was applied to analyze plastic strain at the notch tip of coarse grain HAZ in mild steel (SB 41) and high strength steel (SA 588). The notch tip of specimen was deformed by three point bending. Accumulated displacement (Crack Opening Displacement ${delta}t$) by the monotonic and cyclic loading under room temperature and hot strain embrittlement temperature ($250^{\circ}C$) was 0~1.0mm. Recrystallization heat treatment conditions were $650^{circ}C{ imes}3hr$ for SB 41 and $700^{circ}C{ imes}3hr$ for SA 588. The experimental results obtained were as follows ; 1) Distribution of the effective plastic strain at plastic zone was appeared by the function of crack opening displacement, and plastic zone or the effective plastic strain increased with crack opening displacement. 2) Plastic strain at notch tip of HAZ due to accumulated hot strain calculated as follows. .epsilon. over bar $_{p}$ = .epsilon. over bar $_{cr}$ (x/ $R_{x}$ ) $^{m}$ (m=0.25) 3) Work hardending ratio of notch tip for hot strain was linearly increased with .epsilon. over bar $_{max}$ and dependent upon the material types.s.

• The Journal of the Acoustical Society of Korea
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• v.39 no.4
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• pp.331-341
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• 2020

At liftoff, launch vehicles are subject to harmful acoustic loads due to the intense acoustic waves generated by propulsion systems. Because these waves can cause electronic and mechanical components of launch vehicles and payloads to fail, predicting and mitigating acoustic loads is an important design issue. This article presents the latest information about the generation of acoustic waves and the acoustic design methods applicable to the launch pad. The development of the Japanese Epsilon solid launcher is given as an example of the new methodology for launch pad design. Computational fluid dynamics together with 1/42 scale model testing were performed for this development. Effectiveness of the launch pad design to reduce acoustic loads was confirmed by the post-flight analysis.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.6
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• pp.782-786
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• 2010

Thrust deduction related to the prediction of power performance of a ship is rather resistance increase, and as a preliminary study for it forces upon a circular cylinder in a uniform flow of ideal fluid due to singularities located behind it are investigated. The circle theorem is used to get the complex velocity potential for the flow field under consideration, and the Blasius theorem is applied to obtain forces upon the circular cylinder. As singularities sinks, point vortices and dipoles and their combinations are treated. $\varepsilon$, standing for the strength of a singularity, and $\delta$, representing the distance between the cylinder and the singularity, are important small parameters for the resistance and lateral forces. For sinks or point vortices it is shown that the dimensionless forces upon the cylinder is O($\epsilon$) if $\epsilon$= O($\delta$) is assumed, and the same holds for dipoles if $\epsilon$= O(${\delta}^3$) is supposed. Forces upon the cylinder by a symmetric pair of sinks are greater than a single sink located at the central plane since there is an additional term due to cross effects, and the same is also valid for the case of dipole. Combination of dipole and a point vortex is also considered and a few new aspects are clarified.

• Macromolecular Research
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• v.15 no.5
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• pp.424-429
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• 2007

A procedure for the surface hydrolysis of an electrospun poly(${\epsilon}$-caprolactone) (PCL) fibrous scaffold was developed to enhance the adhesion and proliferation of osteoblasts. The surface hydrolysis of fibrous scaffolds was performed using NaOH treatment for the formation of carboxyl groups on the fiber surfaces. The hydrolysis process did not induce deformation of the fibers, and the fibers retained their diameter. The cell seeding density on the NaOH-treated PCL fibrous scaffolds was more pronounced than on the non-treated PCL fibers used as a control. The alkaline phosphatase activity, osteocalcin and a mineralization assay strongly supported that the surface-hydrolyzed PCL fibrous scaffolds provided more favorable environments for the proliferation and functions of osteoblasts compared to the non-treated PCL fibrous scaffolds use as a control.

• Journal of Korea Water Resources Association
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• v.38 no.10 s.159
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• pp.871-883
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• 2005

This paper investigates the impacts of turbulent anisotropy on the mean flow and turbulence structures in vegetated open-channel flows. The Reynolds stress model, which is an anisotropic turbulence model, is used for the turbulence closure. Plain open-channel flows and vegetated flows with emergent and submerged plants are simulated. Computed profiles of the mean velocity and turbulence structures are compared with measured data available in the literature. Comparisons are also made with the predictions by the k-$\epsilon$ model and by the algebraic stress model. For plain open-channel flows and open-channel flows with emergent vegetation, the mean velocity and Reynolds stress profiles by isotropic and anisotropic turbulence models were hardly distinguished and they agreed well with measured data. This means that the mean flow and Reynolds stress is hardly affected by anisotropy of turbulence. However, anisotropy of turbulence due to the damping effect near the bottom and free surface is successfully simulated only by the Reynolds stress model. In open-channel flows with submerged vegetation, anisotropy of turbulence is strengthenednear the vegetation height. The Reynolds stress model predicts the mean velocity and turbulence intensity better than the algebraic stress model or the k-$\epsilon$ model. However, above the vegetation height, the k-$\epsilon$ model overestimates the mean velocity and underestimates turbulence intensity Sediment transport capacity of vegetated open-channel flows is also investigated by using the computed profiles. It is shown that the isotropic turbulence model underestimates seriously suspended load.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.2
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• pp.78-85
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• 1998

The design method of a temperature stable bandpass filter using dielectric coaxial resonators of with two dielectric ceramics with opposite signs of temperature coefficient of dielectric constant (${\tau}_{\epsilon}$) to compensate for each other in this method. $MgTiO_3$(${\tau}_{\epsilon}$=+99 ppm/${\circ}C$) as a positive ${\tau}_{\epsilon}$ material and Ba($Zn_{1/3}Nb_{2/3}$)$O_3$(${\tau}_{\epsilon}$=-77ppm/${\circ}C$) as a negative material were selected. The length of a SIR for the temperature stability was calculated according to the design method and the susceptance slope parameter of the SIR was obtained. A temperature stable bandpass filter using dielectric SIR's was designed, simulated and fabricated. The center frequency of this filter was 915 MHz and the pass bandwidth was 20 MHz. Temperature properties of this bandpass filter by simulations were compared with the measured results of the bandpass filter fabricated.

• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.61-72
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• 2013

The consolidation tests are conducted to investigate the soil particle crushing stress for understanding the secondary compression characteristics of carbonate sandy sabkha soil caused by particle crushing under a high confining stress. The rate of secondary crushing compression ($C_{{\alpha}{\epsilon}}{^*}$) is introduced instead of the rate of secondary compression to define the characteristic of the particle crushing compression settlement ($S_s{^*}$). Void ratio ($e_p{^*}$) and settlement ($H_p{^*}$) in particle crushing are used as a reference point of secondary behavior, and the ratio of primary compression index ($C_c$) to secondary crushing compression ($C_{{\alpha}{\epsilon}}{^*}$), $C_{{\alpha}{\epsilon}}{^*}/C_c$ value was changed from 0.0105 to 0.0187. When comparing with quartz sands, secondary compression settlement of sabkha is very large due to particle crushing which is not usually observed in quartz sand. It is observed that as the depth of sabkha layer becomes deep, the $S_s{^*}$ and $C_{{\alpha}{\epsilon}}{^*}$ increase under the same stress level.

• Journal of Navigation and Port Research
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• v.47 no.4
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• pp.231-238
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• 2023

The position of a light buoy is always flexible due to the influence of external forces such as tides and wind. The position can be checked through AIS (Automatic Identification System) or RTU (Remote Terminal Unit) for AtoN. As a result of analyzing the position data for the last five years (2017-2021) of a light buoy, the average position error was 15.4%. It is necessary to detect position error data and obtain refined position data to prevent navigation safety accidents and management. This study aimed to detect position error data and obtain refined position data by DBSCAN Clustering position data obtained through AIS or RTU for AtoN. For this purpose, 21 position data of Gunsan Port No. 1 light buoy where RTU was installed among western waters with the most position errors were DBSCAN clustered using Python library. The minPts required for DBSCAN Clustering applied the value commonly used for two-dimensional data. Epsilon was calculated and its value was applied using the k-NN (nearest neighbor) algorithm. As a result of DBSCAN Clustering, position error data that did not satisfy minPts and epsilon were detected and refined position data were acquired. This study can be used as asic data for obtaining reliable position data of a light buoy installed with AIS or RTU for AtoN. It is expected to be of great help in preventing navigation safety accidents.