• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.3
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• pp.31-40
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• 2020

The structure and dynamics of multiple shock waves are studied numerically using a finite volume solver for a model with nozzle exit Mach number of 1.75. At first, the shock variation based on images were analyzed using a Matlab program then later to the wall static pressure variation. The amplitude and frequency variation for multiple shock waves are analyzed. The cross-correlation between the shock location suggests that the first and the second shocks are well correlated while the other shocks show a phase lag in the oscillation characteristics. The rms values of pressure fluctuations are maximum at the shock locations while the other parts in the flow exhibit a lower value os standard deviation.

• International Area Studies Review
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• v.22 no.4
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• pp.3-18
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• 2018

In this study, I examined capital market shock reaction effects of 29 OECD countries with the past 24 years sample period consisting of daily stock market return using T-GARCH model focused on volatility feedback hypothesis. US daily stock market return is used as a unique independent variable in this model in consideration of its characteristics of biggest market share and as an origin country of Global Financial Crisis. As a result, France, Finland, and Mexico in order are shown to be the strongest countries in the aspect of return spillovers from US. Canada, Mexico, and France are shown to be the highest countries in the aspect of explanatory power of model. The degrees of shock reaction are proved to be higher in order in Germany, Chile, Switzerland, and Denmark and those of downside shock reaction are seen higher in order in Greece, Great Britain, Australia, and Japan. Canada and Mexico belonging to NAFTA are shown to be higher in the return spillover from US and in the model explanatory power, but they are shown to be lower in the impact of shock reaction, suggesting that regional distance effect or gravity theory cannot be applied to financial spillovers any longer. In the analysis of subsample period of Global Financial Crisis, north American three countries do not show any consistent results as in the full sample period but shock reaction in the European countries are shown to record stronger, suggesting that shocks from US in the Crisis Times are transferred mainly to European region.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.805-810
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• 2004

The model is verified thorough simulations and experiments. And then the developed model is applied to a half car model and automobile vibrations are analyzed. The effects of tire design parameters on the automobile vibration energy are investigated. The results from laboratory and field tests confirm the validity of the analytical model. The 17-DOF half-car model is built to analyze the automobile vibration. The characteristics of the nonlinear model for a shock absorber are applied to this model. The results from the present 17-DOF half car model incorporating the analytical tire model with tire design parameters, are compared with a 5-DOF half car model where the tire is modeled with linear springs. The results of the 17-DOF model are closed to experimental results. Using the 17-DOF model, the influences of tire design parameter are considered. According to the results of analyses, the vibrations at seat/body/wheel are predicted by simulation and experiment.

• Journal of Astronomy and Space Sciences
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• v.28 no.1
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• pp.17-26
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• 2011

Bow shock, formed by the interaction between the solar wind and a planet, is generated in different patterns depending on the conditions of the planet. In the case of the earth, its own strong magnetic field plays a critical role in determining the position of the bow shock. However, in the case of Mars of which has very a small intrinsic magnetic field, the bow shock is formed by the direct interaction between the solar wind and the Martian ionosphere. It is known that the position of the Martian bow shock is affected by the mass loading-effect by which the supersonic solar wind velocity becomes subsonic as the heavy ions originating from the planet are loaded on the solar wind. We simulated the Martian magnetosphere depending on the changes of the density and velocity of the solar wind by using the three-dimensional magnetohydrodynamic model built by modifying the comet code that includes the mass loading effect. The Martian exosphere model of was employed as the Martian atmosphere model, and only the photoionization by the solar radiation was considered in the ionization process of the neutral atmosphere. In the simulation result under the normal solar wind conditions, the Martian bow shock position in the subsolar point direction was consistent with the result of the previous studies. The three-dimensional simulation results produced by varying the solar wind density and velocity were all included in the range of the Martian bow shock position observed by Mariner 4, Mars 2, 3, 5, and Phobos 2. Additionally, the simulation result also showed that the change of the solar wind density had a greater effect on the Martian bow shock position than the change of the solar wind velocity. Our result may be useful in analyzing the future observation data by Martian probes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.20-28
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• 2004

For the prediction on the onset of oblique shock wave-induced vortex breakdown, computational studies on the Oblique Shock wave/Vortex Interaction (OSVI) are conducted and compared with both experimental results and analytic mode1. A Shock-stable numerical scheme, the Roe scheme with Mach number-based function (RoeM), and a two-equation eddy viscosity-transport approach arc used for three-dimensional turbulent flow computations. The computational configuration is identical to available experiment, and we attempt to ascertain the effect of parameters such as a vortex strength, streamwise velocity deficit, and shock strength at a freestream Mach number of 2.49. Numerical simulations using the k-w SST turbulence model and suitably modeled vortex profiles are able to accurately reproduce many fine features through a direct comparison with experimental observations. The present computational approach to determine the criterion on the onset of oblique shock wave-induced vortex breakdown is found to be in good agreement with both the experimental result and the analytic prediction.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.11
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• pp.939-950
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• 2017

In this work, mathematical models are newly presented for three types of double-acting oleo-pneumatic shock absorbers as the first part of a comparative study on the several types of double-acting oleo-pneumatic shock absorbers. After a typical single-acting shock absorber model is presented for the sake of completeness, mathematical models of three types of double-acting shock absorbers are proposed. To derive the models, Bernoulli equation and orifice discharge coefficient are utilized along with the assumptions of incompressibility and poly-tropic process. The proposed models are expected to be used for investigation of the salient features of several types of double-acting oleo-pneumatic shock absorbers.

• Journal of the Korean Society of Safety
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• v.17 no.3
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• pp.61-65
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• 2002

A study on the characteristics of electric shock in fresh water due to the leakage of submerged electric facility is conducted by using a reduced scale model at a scale of 1:10 in laboratory. Electric potential as a function of distance from leakage source, type of the leakage source, magnitude of the source voltage, submerged depth and diameter of a copper rod electrode is measured. On the basis of safety standard, separation for guarantee of safety is determined by the measured potential. Also supposing that body resistance is 500［$\Omega$］, the human reaction was estimated by calculating body current for some shock duration. Thus, in this paper, the hazard of the electric shock is assessed by introducing representative safety factors, body voltage and body current due to leakage source.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.80-86
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• 2005

In order to control the transonic flow field with a shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock-boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically. The result showed that the flow fields might be effectively controlled by the suitable combination between non-equilibrium condensation and the position of porous wall.

• Journal of Mechanical Science and Technology
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• v.15 no.6
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• pp.788-795
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• 2001

The effects of nonequilibrium condensation on the shock boundary layer interaction over a transonic bump model were investigated experimentally and numerically. An experiment was conducted using a supersonic indraft wind tunnel. A droplet growth equation was incorporated into two-dimensional Navier-Stokes equation systems. Computations were carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. Computation compared with the experimental results. Nonequilibirum condensation suppressed the boundary layer separation and the pressure fluctuations due to the shock boundary layer interaction. Especially the nonequilbrium condensation was helpful to suppress the high frequency components of the pressure fluctuations.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.187-188
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• 2003

In order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock - boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically. The result showed that the flow fields might be effectively controlled by the suitable combination between non-equilibrium condensation and the position of porous wall.