• Design & Manufacturing
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• v.2 no.2
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• pp.43-47
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• 2008

This paper is concerned with the analysis of material flow characteristics of stepped rod forming. The analysis in this paper concentrated on the evaluation of the design parameters for deformation patterns of tube forming, load characteristics, extruded length, and die pressure. The design factors such as punch nose radius, die corner radius, friction factor, and punch face angle are involved in the simulation. The stepped rod forming is analyzed by using a commercial finite element code. This simulation makes use of stepped rod material and punch geometry on the basis of punch geometry recommended by International Cold Forging Group. As radius ratio is large, forming load was reduced but extruded length ratio was increased.

• 한국연소학회:학술대회논문집
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• 1998.10a
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• pp.91-101
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• 1998

The effect of secondary flow on both methane/air and propane/air premixed flame was investigated experimentally. By changing the radius of curvature, various flame behavior was observed. In the V-bend nozzles, flame surface is deformed from axisymmetry. As the exit velocity increased, flame lifted off partially. When the radius of curvature of the V-bend increased, the region where premixed flame is entirely on the rim increased. Since the axial velocity field is changed due to the secondary flow effect, comparison of V-bend and straight tube with the same diameter shows larger V-bend nozzle exit velocity for both flash back and flame blowout. The flame characteristics are mapped with a equivalence ratio, a velocity, and a nozzle radius of curvature. To identify physical reasoning on the flame surface deformation, numerical calculations are conducted. OH radical distributions in flames are visualized by PLIF technique.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.531-535
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• 2008

Present study examines the detonation wave propagation characteristics in annular channel. A normalized value of channel width to the annular radius was considered as a geometric parameter. Numerical approaches used in the previous studies of detonation wave propagation were extended to the present study with OpenMP parallelization for multicore SMP machines. The major effect of the curved geometry on the detonation wave propagation seems to be a flow compression effect, regardless of the detonation regimes. The flow compression behind the detonation wave by the curved geometry of the circular channel pushes the detonation wave front and results in the overdriven detonation waves with increased detonation speed beyond the Chapmann-Jouguet speed. This effect gets stronger as the normalized radius smaller, as expected. The effect seems to be negligible beyond the normalized radius of 10.

• Journal of computational fluids engineering
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• v.21 no.3
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• pp.1-7
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• 2016

In the present study, the homogeneous model is used to simulate the natural convection heat transfer of the CuO-water nanofluid in a concentric annular enclosure. Simulations have been carried while the Rayleigh number ranges from $10^3$ to $10^6$, solid volume fraction ranges from 0.01 to 0.04 and the radius ratio varies between 0.1 and 0.7. Results are presented in the form of streamlines, isotherm patterns and averaged Nusselt numbers for different values of solid volume fraction, radius ratio of the annulus and Rayleigh numbers. The results show that by decreasing the radius ratio and/or increasing the Rayleigh number, the averaged Nusselt number increases. Also the heat transfer rate increases as increased solid volume fractions.

• International Journal of CAD/CAM
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• v.7 no.1
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• pp.51-60
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• 2007

This paper presents an algorithm of optimal cutting tool selection for machining of the point-based surface that is defined by a set of surface points rather than parametric polynomial surface equations. As the ball-end and fillet-end mills are generally used for finish machining in a 3-axis computer numerical control machine, the algorithm is applicable for both cutters. The optimum tool would be as large as possible in terms of the cutter radius and/or corner radius which maximise (s) the material removal rate (i.e., minimise (s) the machining time), while still being able to machine the entire point-based surface without gouging any surface point. The gouging are two types: local and global. In this paper, the distance between the cutter bottom and surface points is used to check the local gouging whereas the shortest distance between the surface points and cutter axis is effectively used to check the global gouging. The selection procedure begins with a cutter from the tool library, which has the largest cutter radius and/or corner radius, and then adequacy of the point-density is checked to limit the accuracy of the cutter selection for the point-based surface within tolerance prior to the gouge checking. When the entire surface is gouge-free with a chosen cutting tool then the tool becomes the optimum cutting tool for a list of cutters available in the tool library. The effectiveness of the algorithm is demonstrated considering two examples.

• Journal of the Korean Society of Safety
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• v.19 no.3 s.67
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• pp.124-129
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• 2004

To evaluate the numerical method in simulation of diffusion flames and to see the effects of strain rate and fuel concentration on the flame radius and thickness, the nonpremixed methane-air counterflow flames in microgravity were simulated axisymmetrically by using the MST Fire Dynamics Simulator (FDS). The $1000^{\circ}C$ based flame radius and thickness were investigated for the mole fraction of methane in the fuel stream, $X_m=20,\;50,\;and\;80\%$ and the global strain rates $a_g=20,\;60,\;and\;90s^{-1}$ for each mole fraction. The flame radius increased with the global strain rate while the flame thickness decreased linearly as the global strain rate increased. The flame radius decreased as the mole fraction increased, but it was not so sensitive to the mole fraction compared with the global strain rate. Since there was good agreement in the nondimensional flame thickness obtained with OPPDIF and FDS respectively, it was confirmed that FDS is capable of predicting well the counterflow flames in a wide range of strain rate and fuel concentration.

• Journal of electromagnetic engineering and science
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• v.12 no.1
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• pp.128-134
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• 2012

In this manuscript, we consider electromagnetic imaging of perfectly conducting cracks completely hidden in a homogeneous material via boundary measurements. For this purpose, we carefully derive a topological derivative formula based on the asymptotic expansion formula for the existence of a perfectly conducting inclusion with a small radius. With this, we introduce a topological derivative based imaging algorithm and discuss its properties. Various numerical examples with noisy data show the effectiveness and limitations of the imaging algorithm.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.959-964
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• 2007

In this study, it is offering a numerical method which assesses running safety of the freight car loaded CWR when passing through on the conventional railway by additional lateral load. It is suggested based on the numerical reviews of the safety against derailment after seeking the derailment coefficient estimated by wheel load-lateral force equation in the section that curve radius is small

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.301-304
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• 2015

With the experiment observation of single particle combustion, this model is built for the numerical analysis of the process. It's about the single coal particle combustion process under different conditions with reasonable assumptions. The model can express the mass, radius, density, temperature changing with different particle sizes, oxygen concentration and gas temperature. It also includes the flame sizes change in different condition and the diffusion of each species. The result shows the characters of the combustion.

• International Journal of Precision Engineering and Manufacturing
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• v.3 no.3
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• pp.44-49
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• 2002

A study of free vibration of axisymmetric circular plates based on Mindlin theory using a pseudospectral method is presented. The analysis is based on Chebyshev polynomials that are widely used in the fluid mechanics research community. Clamped, simply supported and flee boundary conditions are considered, and numerical results are presented for various thickness-to-radius ratios.