• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.6
• /
• pp.966-975
• /
• 1986

유한한 열전도율과 두께를 갖는 수평동심원관 내의 층류자연대류 문제를 유한차분법을 사용하여 수치적으로 연구하였다. 동심원관 내에는 전도-대류가 복합되어, 전체-유체 경계면에서의 온도분포는 미리 알려져 있지 않다. Prandtl수를 0.7, L/D$_{i}$ = 0.8로 고정하고 각각의 Rayleigh수와 열전도계수의 비, 기하학적변수에 대하여 계산을 수행하였으며, 그 결과를 등온 수평동심원관의 경우와 비교하였다. Rayleigh수와 t/D$_{i}$가 클수록, 열전도계수의 비 K가 작을수록 열저도 효과는 강하게 나타났으며, 국소등가전도계수와 온도분포에 비하여 속도분포는 영향을 덜 받는다는 것이 밝혀졌다.

• Journal of the Korean Society of Safety
• /
• v.20 no.1 s.69
• /
• pp.7-12
• /
• 2005

In heavy industrial fields such as power plant and chemical plant, it is often necessary to restore a damaged part of large machinery or structure which is installed in the hazard working place. In this paper, to evaluate the safety of plastic deformed cylindrical beam a finite element technique has been used. The variations of residual stresses on the process of damaging and restoring for surfaces and cross-sections have been examined. The results show that the maximum von Mises stresses occur outer cylinder surfaces of boundary between cylindrical beam support md cylindrical beam when deformation procedure and restoring force is applied. The maximum residual stress remains 158.6MPa in the inner wall and this value correspond to $53\%$ of yield stress then restoration procedure is finished.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2009.03a
• /
• pp.1068-1075
• /
• 2009

The Soil-nailing installed to the slope or the vertical excavation surface shows reinforce effect using frictional resistance between ground and grout. This friction is showed the more the shape of grout is rough, the more efficient.. This study is about the characteristic behavior of Soil-nailing has partial extension grout made artificially control. In this study, we refer to the new boring machine that can make partially extended grout and perform 3D analysis between of the partial extended grout and the general grout of a cylinder shape using the finite element method for comparing.

• Proceedings of the KIEE Conference
• /
• 1994.07a
• /
• pp.119-121
• /
• 1994

In solving axisymmetric field problem by FEM, absorbing boundary condition is introduced to approximate the normal derivatives on artificial boundary to truncate the finite analysis legion. To verify this scheme eddy currents of an conducting sphere in an uniform magnetic field are calculated, and it shows better results than one with Neumann boundary condition. Also eddy currents of conducting cylinder surrounded by coils are calculated, which is typical model in induction heating system.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.20 no.2
• /
• pp.27-36
• /
• 1983

This paper presents numerical results of the added mass and damping coefficients of vertical axisymmetric bodies on or under the free surface. Also computed are the excitation forces on these bodies due to an incident regular wave system. The numerical scheme employs a localized finite-element method, which is based on the theory of the calculus of variations. The excitation forces and moments on a submerged half-spheroid lying on the bottom are computed and compared with the results obtained by others. he agreement is good. Several specific types of floating vertical axisymmetric platforms are considered for ten different wave lengths, in connection with the design of an ocean-thermal-energy converter platform. The added mass and damping coefficient, as well as the excitations, are presented. It is shown that simple strip theory gives a good approximation of the sway(and pitch) added mass for a disc platform having a long circular cylinder.

• Journal of Korean Society for Atmospheric Environment
• /
• v.9 no.E
• /
• pp.347-357
• /
• 1993

The Lagrangian grid-free numerical method, the discrete vortex method, was applied to solve the Navier-Stokes euqations. This method avoids the introduction of numerical viscosity swamping the real physical viscosity at high Reynolds number, unlike Eulerian method, e.g. finite difference and element methods. The boundary integral equation method for the potential flow solution was included to make the discrete vortex method more feasible for complex geometries. The fast adaptive multipole expansion method was incorporated to reduce the computational time from $O(N^2)$ to O(N) for the computations of vortex-vortex interactions. The test problems were air flow around one circular cylinder and two circular cylinders in tandem with various gaps. The numerical results were in excellent gareement with the experimental and other computational results. The applicabilty of the method was discussed with the indoor and the outdoor air pollution problems, especially the contaminant transport in the recirculation regions.

• Journal of Ocean Engineering and Technology
• /
• v.15 no.2
• /
• pp.120-123
• /
• 2001

Despite the increasing necessity of accurate estimation of ring-stiffened cylinders'ultimate strength, the complex structural behavior of cylinders has made their design mainly depend on empirical formulas mostly based on limited test data rather than theoretical background. This paper has developed the imperfection method which enables the ultimate strength analysis of buckling-sensitive structures by combining two separate functions covered by common commercial finite element softwares, which are linear elastic buckling analysis and nonlinear stress analysis. Developed method was applied to two of the world most renowned softwares, MSC/NASTRAN and ABAQUS, for the analysis of ring-stiffened cylinders and unexpectedly big difference in their analysis results was found. This tells that many widely used commercial softwares have their different strong points and weak points and the choice of commercial software should be cautiously made after thorough inspection. This paper ends with some useful information about which of the two aforementioned softwares is more respectively for the linear elastic buckling analysis and the ultimate strength analysis of ring-stiffened cylinders.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.7
• /
• pp.901-910
• /
• 1999

Investigated In this paper is the shock reflection from a blunt body, In particular, a circular cylinder of 20 mm diameter, for the weak shock impinging in the range 1<$M_s$ <2. Pressure and shock speed are measured for various shock strengths. Double-pulse holographic interferograms are taken to study the unsteady flow field at $M_s=1.34$. These experimental results are, in overall, well compared with the unstructured adaptive finite volume computation of the Euler equations performed in this study. Correlation of incident and reflected shocks and shock-shock locus obtained by experiment, computation, and theory are presented in parallel.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.1 no.2
• /
• pp.128-137
• /
• 1989

Numerical solutions for two-dimensional, steady, free convection are presented for a cylinder filled with saturated porous media. An annulus is bounded by inner wall with constant heat flux and two adiabatic horizontal walls with outer wall isothermally cooled. Governing equations are numerically solved for the range of Aspect Ratio 1 to 20, Radius Ratio, 1 to 20, and Rayleigh number, 50 to $10^4$ by Finite Difference method utilizing upwind scheme. Results are presented in terms of stream lines and isotherms, temperature distributions and local Nusselt numbers at the heated wall. Average Nusselt numbers are also presented for the comparisons.

• Journal of the Korean Society for Precision Engineering
• /
• v.20 no.8
• /
• pp.175-184
• /
• 2003

A method of the shape design sensitivity analysis based on the boundary integral equation formulation is presented for two-dimensional inhomogeneous thermal conducting solids with multiple domains. Shape variation of the external and interface boundary is considered. A sensitivity formula of a general performance functional is derived by taking the material derivative to the boundary integral identity and by introducing an adjoint system. In numerical analysis, state variables of the primal and adjoint systems are solved by the boundary element method using quadratic elements. Two numerical examples of a compound cylinder and a thermal diffuser are taken to show implementation of the shape design sensitivity analysis. Accuracy of the present method is verified by comparing analyzed sensitivities with those by the finite difference. As application to the shape optimization, an optimal shape of the thermal diffuser is found by incorporating the sensitivity analysis algorithm in an optimization program.