• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.64-73
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• 2007

Turbulent flows around yacht sails were calculated to access the applicability of CFD for yacht design. Multi-block grid system was generated by using Gridgen package and Fluent was used to calculate flows around two sail system. A 30ft class sailing yacht designed and tested by KRISO was chosen. The interference effect between main and jib sails was analyzed. Pressure distribution on the sails was obtained and the center of effort was estimated. It was found that the jib angle affects the flow phenomena around a main sail due to the change of inflow angle. The location of center of effort is much different from the empirical formula based on a simple geometrical consideration. The calculated results are compared with the previous numerical and experimental results. Both CFD results are similar, but there are some discrepancies with experimental data. However, it is certain that CFD can be a very useful tool for yacht design.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.3 s.153
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• pp.248-257
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• 2007

Turbulent flows around a sailing yacht hull were calculated using CFD technique. Grid system was generated by using Gridgen package and Fluent package was used to calculate flows around a 30ft-class yacht hull designed by MOERI. The drafts at starboard and port sides of a yacht. when the hull was heeled, were determined by adjusting the same displacement in the generated grid system. Pressure distribution on the sailing yacht hull was obtained and the changes of drag and side force by heel and leeway variation were shown. The flow calculations have been carried out both with and without free surface, and keel and rudder were included for both cases. It was found that the calculated results with free surface gives better agreement with experiments than those without free surface, although there are still a room for the improvement in correct prediction of forces.

• Journal of Energy Engineering
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• v.8 no.2
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• pp.224-232
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• 1999

Latent heat storage system using micro-encapsuled phase change material is effective method for floor heating of house and building. The temperature profile in capsule block and flow rate of hot water are important parameters for the development of heat storage system. In the present study, a mathematical model based on 3-D, non-steady state, Navier-Stokes equations, scalar conservation equations and turbulence model ($\kappa$-$\varepsilon$), is used to predict the temperature profiles in capsule and the velocity vectors in hot water pipe. The multi-block grids and fine grids embedding are used to join the circle in hot water pipe and square in capsule block. The phase change process of the capsule is quite complex not only because the size of phase change material is very small, but also because phase change material is mixed with the cement to form thermal storage block. In calculation, it's assumed that the phenomena of phase change is limited only the thermal properties of phase change material and the change of boundary is not happened in capsule. The purpose of this study is to calculate the temperature profiles in capsule block and velocity vectors in hot water pipe using the numerical calculation. Two kinds of thermal boundary condition were considered, the first (case 1) is the adiabatic condition for the both outside surfaces of the wall, the second (case 2) is the case in which one surface is natural convection with atmosphere and another surface is adaibatic. Calculation results are shown that the temperature profile in capsule block for case 1 is higher than that for case 2 due to less heat loss in adaibatic surface. Specially, in the domain of near Y=0, the difference of temperature is greater in case 1 than in case 2. The detailed experimental data of capsule block on the temperature profile and the thermal properties such as specific heat and coefficient of heat transfer with the various temperature are required to predict more exact phenomena of heat transfer.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.1
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• pp.43-48
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• 2009

We constructed a simple wavelength readout system for a tunable fiber laser which was used for a fiber Bragg grating sensor array system. A quadrature sampling method was used to demodulate wavelength variations of the tunable laser which consisted of a SOA(semi-conductor optical amplifier) and a fiber-optic Fabry-Perot filter. Internal triggers, which have a 90 degree phase period, have been generated by using a double-pass Mach-Zehnder interferometer. From Lissajous plots with quadrature sampled data, a mean phase error of ${\sim}2.51$ mrad was obtained. From the wavelength readout experiments, an accurate and fast linear wavelength demodulation has been confirmed.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.11-23
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• 1997

This paper contains a new approach to blade section design method for marine propellers. The hydrodynamic characteristics of 2-D section are highly influenced by its geometrical parameters i.e., thickness and camber distributions and leading edge radius etc. To consider fully turbulent flow field near 2-D section. the finite volume method with k-${\varepsilon}$ turbulent model which solve Reynolds time averaged Navier-Stokes(RANS) equation is applied. In this study, O-type grid system that can provide many calculation points on blade surface is used. The results were compared with those of the experiment of NACA0012 to confirm the accuracy of the developed codes. The goal of this study is the development of a blade section with high efficiency and low drag. To achieve this, we carried out the tests of lift, drag and cavitation characteristics in cavitation tunnel. The results of experiment were compared with numerical results in order to validate the proposed blades design method. By comparing the numerical results with the experiments, we found that the new blade section, KH28 allows superior performance in efficiency and cavitation avoidance characteristics. We further investigated the blade section design method and an application study of this section, KH28 to apply to the marine propeller. In order to improve the accuracy of numerical results on prediction of lift and drag, we conclude here that the 2-layer boundary model must be used.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.129-136
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• 2010

Axial piston pumps have been widely used as power sources for hydraulic systems, but studies on the fluid flow within the pump have been usually performed using 1-D analysis because of the difficulties in considering the fluid compressibility, high-speed revolution, variation of the flow rate, and complicated geometry. The goal of this study was to understand the hydraulic fluid flow within axial piston pumps by using the 3-D numerical method and the process of generating discharge pressure ripples. To improve the convergence and robustness of the simulation model, a grid system was constructed with hexahedron-type grids around the valve plate. Furthermore, we employed an empirical formula to describe the relationship between the oil density and pressure. The CFD (computational fluid dynamics) results compared well with the experimental data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.6
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• pp.520-529
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• 2016

The main purpose of this study was to analyze the performance of a medium-altitude long endurance unmanned aerial vehicle through reverse-engineering method. The external configuration data of the RQ-1 Predator was reverse-engineered from related photos and specification data available on public domains, which also were used to generate the CATIA modeling and weigh distribution data of the UAV. The aerodynamic characteristics of RQ-1 Predator were mainly predicted the vortex lattice method and an empirical method, which the propeller performance was analyzed by the empirical method proposed by Howe. The rate of climb, service ceiling, range, and the loiter endurance of the UAV was analyzed, which showed good agreement with the reference data.

• Journal of Broadcast Engineering
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• v.16 no.4
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• pp.669-679
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• 2011

In this paper, we propose a POCS based irregularly sampled image interpolation method exploiting non-local block-based wavelet shrinkage denoising algorithm. The method provides convex sets to improve the performance. The Delaunay triangulation interpolation is first applied to interpolate the missing pixels of the irregularly sampled image into the regular grids. Then, the non-local block-based wavelet shrinkage denoising algorithm is applied, and the originally observed pixels are enforced. After iteration is performed, the denoising algorithm for non-edge areas is applied to acquire the final result. The experimental results show that the proposed method outperforms the conventional methods.

• Journal of Korean Society of Forest Science
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• v.102 no.1
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• pp.113-121
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• 2013

It has been known that edges of forest fire areas play significant roles in post-fire change of forest ecosystem and recovery process. The purpose of this study was to analyze the relationships between edge formation of burned forests and landscape characteristics with consideration on spatial autocorrelation. Samcheok fire site burned in 2000 was selected as the study area. Seven hundred fifty three of 500 $m^2$ grid cells were generated for measuring landscape characteristics. This study used the topographic variables including slop, elevation, topographic wetness index, solar radiation index and proportions of fuel and land use types. In delineating landscape characteristics correlation analysis with modified t-test were performed for exploring the relationships between edge formation and landscape characteristics. The results indicated that edge formation of burned forests was positively correlated with most variables including TWI, SRI, water, paddy, developed, farm, grass, bare soil, and negatively related with elevation, slope and all fuel types. Especially TWI (r=0.437) showed a strong positive correlation with edge formation. According to the results, edge of burned forests were likely formed when proportions of heterogeneous land use types were high with mild slope and low elevation.

• Korean Journal of Crystallography
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• v.4 no.1
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• pp.18-24
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• 1993

The phase diagram of the Pt-Sb system was reinvestigated, using the conventional sealedcapsule technique. The identification of phases present in the reaction products was made by reflected light microscopy, X-ray diffraction and electron microprobe analysis. The existence of compounds, Pt5Sb, Pt3Sb, Pt3Sb2, PtSb and PtSb5 was confirmed. A new phase, Pt5Sb with a composition of 83at% Pt and tetragonal structure of the lattice parameters a=3.948(3), c=16.85(1)A, was found. The X-ray powder data of Ptsb may be indexable on a tetragonal cell with a=3.9455(7), c=16.959(5)A. PtSb is stoichiometric up to 800t and becomes Pt-deficient as much as lat% at 1000t. Solid solubility limits of Sb in Pt were determined to be 7.5,10.0 and 6.1at% at 1000˚,800˚ and 600˚ , respectively. The earlier reported Pts Sbf was not found in this study. The liquidus curve between the Ptsb2 and Sb phases was revised.