• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.9
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• pp.2916-2923
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• 1996

A numerical analysis of the moving bed heat exchanger of solid particles inside the vertical pipe was performed using finite difference method. Also, the theoretical solutions were obtained for comparison when the wall heat flux or the wall temperature was assumed constant. The comparison showed that their results agreed well each other. The moving bed heat exchanger was classified as countercurrent-flow, parallel-flow, and cross-flow types according to the gas flow direction. For each type, the thermal efficiency of heat exchanger was calculated as a function of non-dimensional parameters such as the characteristic length of heat exchanger, Biot number and the ratio of thermal capacities of gas and solid particles.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.75-83
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• 2023

For three-dimensional finite element welding residual stress simulation, several methods are available. Two widely used methods are the moving heat source model using heat flux and the temperature boundary condition model using the temperature profile of the welded beads. However, each model has pros and cons in terms of calculation times and difficulties in determining welding parameters. In this paper, a new method using the moving temperature profile model is proposed to perform efficiently 3-D FE welding residual stress analysis for large structures. Comparison with existing experimental residual stress measurement data of two-pass welding pipe and SNL(Sandia National Laboratories) mock-up canister shows the accuracy and efficiency of the proposed method.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05b
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• pp.643-650
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• 1995

A numerical method for treating transient diffusion Involving change of phase is presented. In other methods of dealing with this class of problems, the mass flux balance at the moving phase boundary requires explicit treatment of two distinct phases. The technique, originating from the apparent heat capacity method in transient heat conduction with the phase change, avoids the difficulty by transferring the concentration discontinuity at the boundary to smoothed physical property variations near the moving front. This technique accomodates the nonlinearities which preclude use of analytical solutions. It was tested against known analytical solutions for simple cases and turned out to be quite accurate.

• Steel and Composite Structures
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• v.24 no.3
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• pp.359-367
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• 2017

In this work, transient heat transfer analysis of functionally graded (FG) carbon nanotube reinforced nanocomposite (CNTRC) cylinders with various essential and natural boundary conditions is investigated by a mesh-free method. The cylinders are subjected to thermal flux, convection environments and constant temperature faces. The material properties of the nanocomposite are estimated by an extended micro mechanical model in volume fraction form. The distribution of carbon nanotube (CNT) has a linear variation along the radial direction of axisymmetric cylinder. In the mesh-free analysis, moving least squares shape functions are used for approximation of temperature field in the weak form of heat transform equation and the transformation method is used for the imposition of essential boundary conditions. Newmark method is applied for solution time depended problem. The effects of CNT distribution pattern and volume fraction, cylinder thickness and boundary conditions are investigated on the transient temperature field of the nanocomposite cylinders.

• Progress in Superconductivity and Cryogenics
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• v.10 no.1
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• pp.15-18
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• 2008

To achieve high transport current without degradation under magnetic field, it is essential to artificially generate the pinning sites at which moving magnetic flux can be pinned. In this work, $ZrO_2$ nanodots were formed on the substrate surface using electro-spray deposition method. On top of the nanodots, the extended and effective pinning centers can be created. The positively charged Zr precursor solution was sprayed out from the needle using the corona discharge phenomena. Then, the sprayed precursor was deposited onto the negatively charged substrate surface followed by the heat treatment under the controlled atmosphere. Using the electrostatic force among the charged particles of precursor, evenly distributed and nano-sized dots were formed on the substrate surface. The size and density of the nanodots were studied by Atomic Force Microscopy. Also discussed are the effect of the deposition time and solution concentration on the size and density of the nanodot and processing variables in electro-spray method for the effective flux pinning centers in the superconducting films.

• Journal of Welding and Joining
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• v.11 no.3
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• pp.34-47
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• 1993

Finite element models were developed for thermal and residual stress analysis for the specific welding problems. They were used to evaluate the effectiveness of the various welding heat input models, such as ramp heat input function and lumped pass models. Through the parametric studies, thermal-mechanical modeling sensitivity to the ramp function and lumping techniques was determined by comparing the predicted results with experimental data. The kinetics for residual stress formation during welding can be developed by iteration of various proposed mechanisms in the parametric study. A ramp heat input function was developed to gradually apply the heat flux with variable amplitude to the model. This model was used to avoid numerical convergence problems due to an instantaneous increase in temperature near the fusion zone. Additionally, it enables the model to include the effect of a moving arc in a two-dimensional plane. The ramp function takes into account the variation in the out of plane energy flow in a 2-D model as the arc approaches, travels across, and departs from each plane under investigation. A lumped pass model was developed to reduce the computation cost in the analysis of multipass welds. Several weld passes were assumed as one lumped pass in this model. Recommendations were provided about ramp lumping techniques and the optimum number of weld passes that can be combined into a single thermal input.

• Journal of Korea Foundry Society
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• v.28 no.2
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• pp.74-78
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• 2008

An integrated riser heating equipment has been developed to control shrinkage defects originated from casting of a marine propeller. The integrated riser heating equipment is composed of up/down moving parts, heating power source parts and an integrated controller. Heat capacity putting into the riser was calculated quantitatively on the base of a heat transfer analysis, which consisted of the establishment of heating model and the theoretical analysis for heat transfer. The riser heating equipment was evaluated through arc heating and electro-slag heating method. With the results, the arc type heating method was selected by considering high thermal efficiency, inexpensive cost, and convenient workship. This equipment improves the quality of a propeller casting and the poor working environment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.43-57
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• 1999

The fluid flow and heat transfer in a thin liquid film are investigated numerically. The flow Is assumed to be two-dimensional laminar and surface tension is considered. The most important characteristics of this flow is the existence of a hydraulic jump through which the flow undergoes very sharp and discontinuous change. Arbitrary Lagrangian-Eulerian(ALE) method is used to describe moving free boundary and a modified SIMPLE algorithm based on streamline upwind Petrov-Galerkin(SUPG) finite element method is used for time marching iterative solution. The numerical results obtained by solving unsteady full Navier-Stokes equations are presented for planar and radial flows subject to constant wall temperature or constant wall heat flux, and compared with available experimental data. It Is discussed systematically how the inlet Reynolds and Froude numbers and surface tension affect the formation of a hydraulic jump. In particular, the effect of temperature dependent fluid properties is also discussed.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.448-450
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• 2010

Free surface liquid jet impingement, which is applicable to cooling of hot plates in a steel-making process, is investigated numerically by solving the conservation equations of mass, momentum and energy in the liquid and gas phases. The free-surface of liquid-gas interface is tracked by an improved level-set method incorporating a sharp-interface technique for accurate imposition of stress and heat flux conditions on the liquid-gas interface. The level-set approach is combined with a non-equilibrium $k-{\omega}$ turbulence model. The computations are made for slit nozzle jets to investigate their flow and cooling characteristics. Also, the effects of jetting angle, velocity and moving velocity of plate on the interfacial motion and the associated flow and temperature fields are quantified.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.2
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• pp.304-311
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• 2001

The present work examines the influence of surface coating on the temperature and the thermo-mechanical stress field produced by friction due to sliding contact. A two-dimensional transient model of a layered medium submitted to a moving heat flux is prsented. A solution technique based on the boundary element method employing the multiregion technique is utilized. Results are presented showing the influence of coating thickness, thermal properties, Peclet number, and mechanical properties. It has been shown that the mechanical properties and thickness of coating have a significant influence on the stress field, even for low temperature increase. The effects of the ratios of shear modulus become more important for low temperature increase than the effects of the ratios of other mechanical properties.