• Publications of The Korean Astronomical Society
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• v.13 no.1 s.14
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• pp.135-147
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• 1998

We have simulated the interaction of supernova remnants with constant ambient medium to explore the dynamics of Type Ia supernova remnant. We assumed the supernova ejecta density distribution of the central constant and the outer power-law density distribution$({\rho}{\propto}{\gamma}^{-n})$. We have calculated four different cases with different n. By scaling the length and time scales from the initial parameters-ejecta mass, ejecta energy, the ambient density, we could compare effects of the different density distribution of the ejecta on the dynamics of the SNRs. The radius of the outer forward shock converges the Sedov-Talyor solution at t' = 2.3 when the swept-up mass is 8 times of the ejecta mass. On the other hand, the motion of the reverse shock are largely affected by n. The ejecta with smaller n takes comparably long time to thermalize the whole ejecta at $t'{\simeq}5.3,\;M_{sw}{\simeq}18M_{ej}$. We have applied our calculated results to obtain the ejecta density distributions of Tycho and SN1006 with $n{\simeq}6$.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.220-223
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• 2008

A test facility to measure the performance of a KM(Kick Motor) is constructed, and prediction of blast wave propagation over the facility is performed to check if the safety of test personnel in MCC(Main Control Center) can be guaranteed even for the most severe explosion. Assuming that the initial explosion energy is contained in a sphere under the pressure of 500, 1000, 1500 psi, respectively, the radius of the sphere is determined for each pressure to set the mass of contained explosion gas to 35 kg. The material properties of explosion gas are set to be the ones of KM propellant combustion gas under normal condition. To reduce the effort and time required for a complex three-dimensional modeling, the flowfield is approximated to axismmetry. Calculations are performed for all three initial pressure conditions, and the analysis of the result is given for 1500 psi which is expected to be the worst case. The maximum pressure is 3.5 psig while the minimum pressure is -1.2 psig on the outer wall of MCC, and the maximum pressure difference between the inner and outer walls of protection wall amounts to 3.0 psi.

• Transactions of Materials Processing
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• v.20 no.6
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• pp.450-455
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• 2011

This paper presents an inverse design methodology for the cross section geometry of mold spring with a rectangular cross section as the starting material for a coiling process. The cross-sections of mold springs are universally rectangular, as the parallel sides minimize the possibility of failure under high service loads. Pre-coiled wires are initially designed to have a trapezoidal cross section, which becomes a rectangle by the coiling process. This study demonstrates a numerical exercise to predict changes in the sectional geometry in spring manufacture and to obtain the initial cross section which becomes the exact rectangle desired from the manufacturing process. Finite element analysis was carried out to calculate the sectional changes for various mold springs. Geometrical parameters were the widths at inner and outer radii, the inner and the outer corner radii, and the height. A partial least square regression analysis was carried out to find the main contributing factors for deciding initial design values. The height and the width mainly affected various initial parameters. The initial width at the inner radius was mostly affected by various specification parameters.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.185-191
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• 2002

In this study a 3-dimensional analytical model is developed, which can analyses dynamic responses of curved bridges subject to moving vehicles. A 5-axle semi-trailer is modeled to simulate the actual tire forces that are redistributed by vehicle rolling effect due to the centrifugal force. The 1-span curved bridge with two steel box girders is modeled using the frame elements. The dynamic response characteristics of curved box girder bridges are examined and compared for two different support conditions. One is the case that two shoes are arranged at the outer sides of box girders with larger space between the two shoes and the other is that two shoes at the center of each box girder. In the curved bridges, the dynamic effect of moving vehicles influences the reaction force much more than other responses, such as displacement or stress, especially the upward reaction of inner-radius shoes. It is more advantageous for the reaction considering dynamic effect when shoes are arranged further at the outer sides of box girders than when shoes at the center of each box. The shoes for curved bridges with two-box girder system should be arranged to have larger distance.

• Steel and Composite Structures
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• v.10 no.4
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• pp.361-371
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• 2010

Enhancement in the seismic buckling capacity of steel tanks caused by the addition of fiber reinforced polymers (FRP) retrofit layers attached to the outer walls of the steel tank is investigated. Three-dimensional non-linear finite element modeling is utilized to perform such analysis considering non linear material properties and non-linear large deformation large strain analysis. FRP composites which possess high stiffness and high failure strength are used to reduce the steel hoop stress and consequently improve the tank capacity. A number of tanks with varying dimensions and shell thicknesses are examined using FRP composites added in symmetric layers attached to the outer surface of the steel shell. The FRP shows its effectiveness in carrying part of the hoop stresses along with the steel before steel yielding. Following steel yielding, the FRP restrains the outward bulging of the tank and continues to resist higher hoop stresses. The percentage improvement in the ultimate base moment capacity of the tank due to the addition of more FRP layers is shown to be as high as 60% for some tanks. The percentage of increase in the tank moment capacity is shown to be dependent on the ratio of the shell thickness to the tank radius (t/R). Finally a new methodology has been explained to calculate the location of Elephant foot buckling and consequently the best location of FRP application.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.2
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• pp.114-123
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• 2018

Wind power tower (WPT) has been used to augment the performance of vertical axis wind turbine (VAWT). However, the performance of the WPT depends on several design parameters, such as inner and outer radius, or number of guide walls. Therefore, an experimental study was conducted to investigate efficient design parameters on the WPT. A wind tunnel was utilized and its test section dimension was 2m height and 2.2m width. One story model of the WPT was manufactured with seven guide walls and a VAWT was installed within the WPT. Three different sizes of guide walls were applied to test with various design parameters. The power coefficients were measured along the azimuthal direction in a state of equal inlet velocity in order to compare its performance relatively. The experimental results showed that the gap between the inner radius of the WPT and the rotating radius of the VAWT was a major parameter to improve the performance of VAWT within the WPT.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.3
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• pp.177-186
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• 2019

Wind power tower has been used to augment the performance of VAWT (Vertical Axis Wind Turbine). However, inappropriately designed wind power tower could reduce the performance of VAWT. Hence, an optimization study was conducted on a wind power tower. Six design variables were selected, such as the outer radius and the inner radius of the guide wall, the adoption of the splitter, the inner radius of the splitter, the number of the guide wall and the circumferential angle. For the objective function, the periodic averaged torque obtained at the VAWT was selected. In the optimization, Design of Experiment (DOE), Genetic Algorithm (GA), and Artificial Neural Network (ANN) have been applied in order to avoid a localized optimized result. The ANN has been continuously improved after finishing the optimization process at each generation. The performance of the VAWT was improved more than twice when it operated within the optimized wind power tower compared to that obtained at a standalone.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.7
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• pp.33-40
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• 2021

Current industrial flow is directed toward reducing the usage of raw materials by reusing parts, which is referred to as a circular economy (CE). Repair is one of the most value-added approaches in CE, which can be efficiently accomplished via additive manufacturing. The repair technology of metallic parts via the directed energy deposition process, which includes the selective removal and redeposition of damaged regions of metallic parts. Residual stress characteristics depend on the shape of the part and the shape of the redeposition region. The objective of this study is to investigate the effects of the radius and corner position of the substrate on the residual stresses for repair by using finite element analysis (FEA). The residual stress distribution of the 45° angle groove at the edge of the circular shape models on the outer and inner radii was analytically investigated. The analysis was accomplished using SYSWELD software by applying a moving heat source with defined material properties and cooling conditions integrated into the FEA model. The results showed a similar pattern of concentrated stress distribution for all models except the 40-mm and 60-mm radii, for which the maximum stress locations were different. The maximum residual stresses are high but lower than the yield strength, suggesting the absence of cracks and fractures due to residual stresses.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1434-1439
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• 2004

CFRP composite materials have wide application in structure materials of airplane, ships, and aero space vehicles because of their high strength and stiffness. This paper is to study the effects of curvature and orientation angle on the penetration characteristics of CFRP laminate shell. They are staked with 8 Ply specimens [0$_2$/90$_2$]$_{s}$, [0/90$_2$/0]$_{s}$ and the stacked of outer plates degree with 12 Ply specimens [0$_3$/90$_3$]$_{s}$, [0$_2$/90$_2$/0]$_{s}$ and [90$_3$/0$_3$], [90$_2$/0$_2$/90]S. They are manufactured to varied curvature radius (R=100,150,200mm and $\infty$). They are cured by heating to the appropriate harding temperature(13$0^{\circ}C$) by mean of a heater at the vaccum bag of the autoclave. Test specimens were prepared with dimensions 100mm$\times$140mm. When the specimen is subjected to transverse impact by a steel ball, the velocity of the steel ball was measured both before and after impact by determining the time for it to pass two ballistic-screen sensor located a known distance apart. In general, kinetic energy after impact-kinetic energy before impact rised in all specimens. This study observed a fracture mode inside the specimen after a penetration test using a digital camera and it examined a fracture mode and a penetration mode to stack of outer orientation angle and curvature.rvature.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.11
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• pp.32-36
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• 2008

In this paper, we investigate the capacity of CDMA/TDD in the inner zone of multimode scenario with dual-band operation where high frequency band is used for TDD in the inner zone and lower frequency band is utilized for FDD in the outer zone. The effects of various system parameters such as cell radius, date rate, and time slot allocation are analyzed.