• Journal of KSNVE
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• v.10 no.2
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• pp.319-324
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• 2000

This paper shows hot to model the submerged elastic structures and adequate analysis tools for modal behavior when using finite element and boundary element method. Four different cases are reviewed depending on the location of the water and air. First case is that structures are filled with air and water is located outside. Second case is opposite to case one. These cases are solved by direct approach using collocation procedure. Third case is that water is located both sides of structures. Last case is that air is located both sides. These cases are solved by indirect approach using variational procedure. As analysis tools harmonic frequency sweep analysis and eigenvalue iteration method are selected to obtain the natural frequencies of vibrating submerged structures depending on the cases. Results are compared with closed form solutions of submerged spherical shell.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.7
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• pp.468-473
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• 2010

This paper deals with approximate integral solutions to the one-dimensional model describing the charging process of stratified thermal storage tanks. Temperature is assumed to be the form of Fermi-Dirac distribution function, which can be separated to two sets of cubic polynomials for each hot and cold side of thermal boundary layers. Proposed approximate integral solutions are compared to the previous works of the approximate analytic solutions and show reasonable agreement. The approach, however, has benefits in mathematical difficulties, complicated solution form and unstable convergence of series solution founded in the previous analytic solutions. Solutions for a semi-infinite region, which have simple closed form solutions, give close agreement to those for a finite region. Thermocline thickness is obtained in closed form and shows proportional behavior to the square root of time and inverse proportional behavior to the square root of flow rate.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.5
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• pp.627-634
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• 2011

In the present study, the flow behaviors of square jets surface discharged and submerged discharged into shallow water were each simulated using computational fluid dynamics, and the results were compared. As for the verification of the models, the results of the hydraulic experiment conducted by Sankar, et al. (2009) were used. According to the results of the verification, the present application of computational fluid dynamics to the flow analysis of square jets discharged into shallow water was valid. As for the wall jet, which is one form of submerged discharges, at the bottom wall boundary, the peak velocity of the jet rapidly moved from the center of the jet to the bottom wall boundary due to the restriction of jet entrainment and the no-slip condition of the bottom wall boundary, and, as for the surface discharge, because jet entrainment is limited on the free water surface, the peak velocity of the jet moved from the center of the jet to the free water surface. This is because jet entrainment is restricted at the bottom wall boundary and the surface so that the momentum of the central core of the jet is preserved for considerable time at the bottom wall boundary and the surface. In addition, due to the effect of the bottom wall boundary and the free water surface, the jet discharged into shallow water had a smaller velocity diminution rate near the discharge outlet than did the free jet; at a location where it was so distant from the discharge outlet that the vertical profile of the velocity was nearly equal (b/x =20~30), moreover, it had a far smaller velocity diminution rate than did the free jet due to the effect of the finite depth.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.780-788
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• 1989

An experimental study has been performed to investigate the process from nonequilibrium state to equilibrium state in redeveloping turbulent boundary layer beyond separation-reattachment using pitot tube and hot-wire anemometer. The model sued in the experiment has the form of a backward facing step which is assembled by a two-dimensional 4:1 half elipse and a plate. Measurements are carried out up to a distance of about 50 step height downstream of the step, where the reattachment observed at about x/h=6.5. The profiles of the shape factor H the Clauser parameter G and the coefficient of friction $C^{f}$ exhibited the characteristics similar to those of the equilibrium turbulent boundary layer from x/h=25, and the profiles of the trubulent quantities did from x/h=35. However, the wake region of the boundary layer does not seem to recover the equilibrium turbulent boundary layer even at x/h=50. By considering the distributions of the intermittency factor it has been noted that the turbulence structure changes gradually from a mixing layer to a turbulent boundary layer along downstream direction after reattachment. This becomes clearer as we analyse the one-dimensional energy spectra and the dissipation energy spectra which are measured and caculated at various downstream positions after the backward facing step.p.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.1
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• pp.418-424
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• 2014

In this paper, we propose a boundary input method for video surveillance systems. Since intrusion of a moving object is decided by comparition of its position and the surveillance boundary, the boundary input method is a basic function in video surveillance. Previous methods are difficult to adapt to the change of surveillance environments such as the size of surveillance area, the number of cameras, and the position of cameras because those build up the surveillance boundary using the captured image in the center of each camera. In our approach, the whole surveillance boundary is once defined in the form of polygon based on the satellite map and transformed into each camera environment. Its characteristics is that the boundary input is independent from the surveillance environment. Given the position of a moving object, the time complexity of its intrusion detection shows O(n), where n is the number of polygon vertices. To verify our method, we implemented a 3D simulation and assured that the input boundary can be reused in each camera without any redefinition.

• 한국해양학회지
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• v.29 no.3
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• pp.296-303
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• 1994

Rotating right cylinder of rigid sloping boundaries(top-bottom) is filled with two-layered fluid. External fluid which has the same density as the lower-layer is pumped through the rim boundary at the bottom, and this induces uniform vertical velocity in the interior that produces the Sverdrup type motion such as southward flowing western boundary current with northward interior horizontal motion. The rigid sloping upper boundary meets with lower layer to simulate so called "polar front", and the upper-layer motion influenced by the lower-layer flow has been observed. Barotropic motion in the western part of the basin while baroclinic motion in the eastern half is always present. In particular, both southward flowing eastern boundary flow and western boundary flow meets near the western wall and it induces northward western boundary flow to separate from the boundary With increased ${\beta}$-effect on the upper0layer the width of western boundary decreases and the separated western boundary flow moves into the interior to form an eddy-like motion. Baroclinic Rosebay wave clearly observed in the easter boundary slowly propagates to the west but it seems to be decayed before travelling to the western boundary. A local topograpic effect imposed on the lower-layer causes very sensitive response of upper layer boundary flows. In the east standing0wave0like features are observed in the west whereas the width of the boundary increases without any evidence of the separation of the western boundary flow.This may be due to the gact that even the lower-lauer barotropic motion feels the topography its influence does not propagate into the upper-layer. With large ${\beta}$-effect on the upper-layer,relatively large scale waves whose wavelengths are greater than the internal radius deformation exist in the interior.

• Ocean Systems Engineering
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• v.13 no.2
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• pp.147-172
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• 2023

This study investigates the influence of loading and inflow conditions on tidal turbine performance from a hydrodynamic and hydroacoustic point of view. A boundary element method is utilized for the former to investigate turbine performance at various loading conditions under zero/non-zero yaw inflow. The boundary element method is selected as it has been selected, tested, and validated to be computationally efficient and accurate for marine hydrodynamic problems. Once the hydrodynamic solutions are obtained, such as the time-dependent surface pressures and periodic motion of the turbine blade, they are taken as the known noise sources for the subsequence hydroacoustic analysis based on the Ffowcs Williams-Hawkings formulation given in a form proposed by Farassat. This formulation is coupled with the boundary element method to fully consider the three-dimensional shape of the turbine and the speed of sound in the acoustic analysis. For validations, a model turbine is taken from a reference paper, and the comparison between numerical predictions and experimental data reveals satisfactory agreement in hydrodynamic performance. Importantly, this study shows that the noise patterns and sound pressure levels at both the near- and far-field are affected by different loading conditions and sensitive to the inclination imposed in the incoming flow.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.66-76
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• 2003

The arbitrary V-notched crack problem is considered. The general expressions for the stress components on this problem are obtained as explicit series forms composed of independent unknown coefficients which are denoted by coefficients of eigenvector. For this results eigenvalue equation is performed first through introducing complex stress functions and applying the traction free boundary conditions. Next solving this equation, eigenvalues and corresponding eigenvectors are obtained respectively, and finally inserting these results into stress components, the general equations are obtained. These results are also shown to be applicable to the symmetric V-notched crack or straight crack. It can be shown that this solutions are composed of the linear combination of Mode I and Mode II solutions which are obtained from different characteristic equations, respectively. Through performing asymptotic analysis for stresses, the stress intensity factor is given as a closed form equipped with the unknown coefficients of eigenvector. In order to calculate the unknown coefficients. based on these general explicit equations, numerical programming using the overdetermined boundary collocation method which is algorithmed originally by Carpenter is also worked out. As this programming requires the input data, the commercial FE analysis for stresses is performed. From this study, for some V-notched problems, unknown coefficients can be calculated numerically and also fracture parameters are determined.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.301-307
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• 2012

SiAlON glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in silicon nitride ceramics and these grain boundary phases affect their fracture behaviour. This paper provides an overview of the preparation of M-SiAlON glasses and outlines the effects of composition on properties. As nitrogen substitutes for oxygen in SiAlON glasses, increases are observed in glass transition temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of grain boundary glass chemistry in silicon nitride ceramics. Oxide sintering additives provide conditions for liquid phase sintering, reacting with surface silica on the $Si_3N_4$ particles and some of the nitride to form SiAlON liquid phases which on cooling remain as intergranular glasses. Thermal expansion mismatch between the grain boundary glass and the silicon nitride causes residual stresses in the material which can be determined from bulk SiAlON glass properties. The tensile residual stresses in the glass phase increase with increasing Y:Al ratio and this correlates with increasing fracture toughness as a result of easier debonding at the glass/${\beta}-Si_3N_4$ interface.

• 전기의세계
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• v.19 no.2
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• pp.21-23
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• 1970

Necessary conditions of optimal distributed parameter control systems, Hamiltons coanonical equations, welerstress condition, transversality condition and boundary condition are obtained, when the control function is constrained and the performance index takes on the general form. Also it is concluded that the lumped parameter system is the special case of the distributed parameter system.