• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.12-19
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• 2004

Low-speed gas flows around a micro-scale flat plate are investigated using a kinetic theory analysis. The Boltzmann equation simplified by a collision model is solved by means of a finite difference approximation with the Discrete Ordinate method. Calculations are made for flows around a 5% flat plate with a finite length of 20 microns. The results are compared with those from the Information Preservation method and a continuum approach with slip boundary conditions. It is shown that three different approaches predict a similar basic flow patterns, while the results from the present method are more accurate than those from the other two methods in details.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.607-618
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• 1994

Effects of wave grouping on the harbor oscillation are studied in order to clarify the energy source of harbor resonance. The resonant periods of Donghae harbor and Imwon harbor are calculated using the boundary integral equation method. Also, the periods of the group-bounded long waves due to the irregular wave group are calculated using the theory developed in this study. Analyzing from the view point of period, it is concluded that the group-bounded long waves due to the irregular wave group can cause resonance in small harbors such as fishery harbors, and heavy ship motion in large harbors such as industrial ones.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.4
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• pp.368-378
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• 1995

Using two-dimensional depth-integrated tidal computation model. tidal charts of eight major tidal constituents (M$_2$, S$_2$, $K_2$, $N_2$, $K_1$, $O_1$, P$_1$, Q$_1$) are presented for Namhaedo area. Computed distributions of tides were compared with observations. Subsequently, the model was run for one month to derive harmonic constants of tides and tidal currents, thus for formulating predictive data tables. Data tables are then used as PC-based rapid estimation of tides in this area.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.9
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• pp.950-954
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• 2003

This paper presents the delivered power and reflection coefficient in metallic shielding enclosure excited by the interior source, which are evaluated with the method of moments, and describes a method for reducing the radiation of electromagnetic fields in the cavity by putting lossy dielectric material in one inside wall. In this paper we introduce carbon polystyrene-foam as lossy dielectric material and observe it's effects of reduction when the thickness and permittivity of lossy dielectric material are changed. The results show that the reduction of the electromagnetic radiation can be achieved by controlling the amount of carbon in lossy dielectric material. The theoretical analysis is verified by the measured delivered power.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.3
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• pp.71-79
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• 1992

In order to obtain the wave-making resistance of a ship, so-called the Neumann-Kelvin problem is solved numerically. For computing the Havelock source, which is the Green's function of the problem, we adopted the methods given by Newman(1987) for the term representing the local disturbance, and Baar and Price(1988) for the wave disturbance, respectively. In the numerical code we developed, the source strength is assumed as bilinear on each panel and continuous throughout the hull surface. The wave-making resistance is calculated using the algorithm of de Sendagorta and erases(1988), which makes use of the wave amplitude far downstream. The Wigley hull was chosen for the sample calculation, and our results showed a good agreement with other existing experimental and numerical results.

• Journal of Korean Society of Steel Construction
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• v.11 no.1 s.38
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• pp.13-22
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• 1999

The objective of this paper is to develop a program for distortional analysis of steel box girder bridges. This program is formulated by using MSDM(modified slope deflection method). Two examples are carried out to verify the validity of the developed technique and its computation procedures. The analyzed results are compared with the previously proposed methods, BEF(beam on elastic foundation) and EBEF(equivalent beam on elastic foundation). The BEF method is limited only to prismatic straight box girders. In the EBEF method, stiffness of the intermediate diaphragms is infinitely considered. On the other hand, stiffness of the intermediate diaphragms is idealized as spring contant in this study. And then, nonprismatic straight box girders can be analyzed using the same procedure. Therefore, the comparison shows that the MSDM algorithm proposed in this paper is more efficient and reliable. Also parametric studies are perfomed using the proposed algorithm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1555-1561
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• 2003

Finite element analysis using modern constitutive equation is one of the most general tools to simulate the deformation behavior and to predict the life of the structure. Constitutive equation becomes complicated so as to predict the material behavior more accurately than the classical models. Because of the complexity of constitutive model, numerical treatment becomes so difficult that the calculation should be verified carefully. One-element tests, simple tension or simple shear, are usually used to verify the accuracy of finite element analysis using complicated constitutive model. Since this test is mainly focused on the time integration scheme, it is also necessary to verify the equilibrium iteration using material stiffness matrix and to compare FE results with solution of structures. In this investigation, viscoplastic solution of thick walled cylinder was derived considering axial constraints and was compared with the finite element analysis. All the numerical solutions showed a good coincidence with FE results. This numerical solution can be used as a verification tool for newly developed FE code with complicated constitutive model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.2
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• pp.240-252
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• 1998

The purpose of this study is to develop a method for predicting the aerodynamic performance of the low speed airfoils in the 2-dimensional, steady and viscous flow. For this study, the airfoil geometry is specified by adopting the longest chord line system and by considering local surface curvature. In case of the inviscid incompressible flow, the analysis is accomplished by the linearly varying strength vortex panel method and the Karman-Tsien correction law is applied for the inviscid compressible flow analysis. The Goradia integral method is adopted for the boundary layer analysis of the laminar and turbulent flows. Viscous and inviscid solutions are converged by the Lockheed iterative calculating method using the equivalent airfoil geometry. The analysis of the separated flow is performed using the Dvorak and Maskew's method as the basic method. The wake effect is also considered by expressing its geometry using the formula of Summey and Smith when no separation occurs. The computational efficiency is verified by comparing the computational results with experimental data and by the shorter execution time.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.3
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• pp.126-136
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• 1991

This study is concerned with the nonlinear dynamic behaviors of guyed towers for wave loadings. In order to analyze the nonlinear responses of guyed towers efficiently, the main tower is modeled as an equivalent stick, the guyline system is idealized as a spring with nonlinear stiffness in the horizontal direction. and the pile foundation system is represented as a linear spring in the rotational direction. The wave forces on the main tower are evaluated by using Morison's equation. In order to consider adequately the nonlinearities of the guying system and drag forces due to fluid viscosity. the analyses are performed in the time domain. The mode superposition method is adopted for solving the nonlinear equation of motion efficiently. which is based on the Newmark integration scheme. Numerical analyses are carried out to investigate the sensitivity of two major design parameters for guyed towers. i.e., the clump weight conditions and the base renditions of the tower.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.841-850
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• 2004

The modeling of uplift pressure within dam, on the foundation on which it was constructed, and on the interface between the dam and foundation is a critical aspect in the analysis of concrete gravity dams, i.e. crack stability in concrete dam can correctly be predicted when uplift pressures are accurately modelled. Current models consider a uniform uplift distribution, but recent experimental results show that it varies along the crack faces and the procedures for modeling uplift pressures are well established for the traditional hand-calculation methods, but this is not the case for finite element (FE) analysis. In large structures, such as dams, because of smaller size of the fracture process zone with respect to the structure size, limited errors should occur under the assumptions of linear elastic fracture mechanics (LEFM). In this paper, the fracture behaviour of concrete gravity dams mainly subjected to uplift Pressure at the crack face was studied. Triangular type, trapezoidal type and parabolic type distribution of the uplift pressure including uniform type were considered in case of evaluating stress intensity factor by surface integral method. The effects of body forces, overtopping pressures are also considered and a parametric study of gravity dams under the assumption of LEFM is performed.