• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.61.1-61.1
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• 2014

GSH 006-15+7 is a Milky Way supershell discovered by Moss et al. (2012). This supershell shows large shell-like structures in H I velocity maps. We have analyzed FUV emission for the supershell regions based on the FIMS and GALEX observations. Bright FUV flux at the boundaries of the supershell is mostly originated from dust scattering of FUV photons by dust clouds which was also observed at the boundaries of the supershell. We could find the distance to the supershell can be closer more than 30% compared with the distance of 1500 pc suggested by Moss et al. (2012) from the dust scattering simulation. And we also found the albedo and the phase function asymmetry factor of interstellar grains were 0.30 and 0.40, respectively. The confidence range for the albedo covers the theoretical value of 0.40, but g-factor is rather smaller than the theoretical value of 0.65. The small g-factor might mean the environment of turbulent ISM of the supershell. Meanwhile, the excess of C IV and X-ray emissions in the inside of the supershell can support the existence of hot gas and cooling in the supershell. And the C IV and X-ray emissions are monotonically decrease as away from the center of the SNR. This indicates the size of the hot bubble has considerably shrunk. We applied a simple simulation model to the PDR candidate region of the lower part of the supershell and obtained a H2 column density N(H2) = 1017.0-18.0 cm-2 and total hydrogen density nH ${\geq}$ 10 cm-3. This result shows the PDR candidate region represents a transition region from the warm phase to the cool phase in the PDR.

• Wind and Structures
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• v.13 no.6
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• pp.557-580
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• 2010

A new inflow turbulence generation method and a combined dynamic SGS model recently developed by the authors were applied to evaluate the wind effects on 508 m high Taipei 101 Tower. Unlike the majority of the past studies on large eddy simulation (LES) of wind effects on tall buildings, the present numerical simulations were conducted for the full-scale tall building with Reynolds number greater than $10^8$. The inflow turbulent flow field was generated based on the new method called discretizing and synthesizing of random flow generation technique (DSRFG) with a prominent feature that the generated wind velocity fluctuations satisfy any target spectrum and target profiles of turbulence intensity and turbulence integral length scale. The new dynamic SGS model takes both advantages of one-equation SGS model and a dynamic production term without test-filtering operation, which is particular suitable to relative coarse grid situations and high Reynolds number flows. The results of comparative investigations with and without generation of inflow turbulence show that: (1) proper simulation of an inflow turbulent field is essential in accurate evaluation of dynamic wind loads on a tall building and the prescribed inflow turbulence characteristics can be adequately imposed on the inflow boundary by the DSRFG method; (2) the DSRFG can generate a large number of random vortex-like patterns in oncoming flow, leading to good agreements of both mean and dynamic forces with wind tunnel test results; (3) The dynamic mechanism of the adopted SGS model behaves adequately in the present LES and its integration with the DSRFG technique can provide satisfactory predictions of the wind effects on the super-tall building.

• Wind and Structures
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• v.30 no.4
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• pp.367-378
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• 2020

Two-dimensional Delayed Detached Eddy Simulation (DDES) was carried out to investigate the uniform flow over a twin-box bridge deck (TBBD) with various gap ratios of L/C=5.1%, 12.8%, 25.6%, 38.5%, 73.3% and 108.2% (L: the gap-width between two girders, C: the chord length of a single girder) at Reynolds number, Re=4×104. The aerodynamic coefficients of the prototype deck with gap ratio of 73.3% obtained from the present simulation were compared with the previous experimental and numerical data for different attack angles to validate the present numerical method. Particular attention is devoted to the fluctuating pressure distribution and forces, shear layer reattachment position, wake velocity and flow pattern in order to understand the effects of gap ratio on dynamic flow interaction with the twin-box bridge deck. The flow structure is sensitive to the gap, thus a change in L/C thus leads to single-side shedding regime at L/C≤25.6%, and co-shedding regime at L/C≥35.8% distinguished by drastic changes in flow structure and vortex shedding. The gap-ratio-dependent Strouhal number gradually increases from 0.12 to 0.27, though the domain frequencies of vortices shedding from two girders are identical. The mean and fluctuating pressure distributions is significantly influenced by the flow pattern, and thus the fluctuating lift force on two girders increases or decreases with increasing of L/C in the single-side shedding and co-shedding regime, respectively. In addition, the flow mechanisms for the variation in aerodynamic performance with respect to gap ratios are discussed in detail.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.5
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• pp.510-519
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• 2013

In this study, the spray characteristics of a pressure swirl atomizer classified into a liquid sheet-type swirl nozzle for Urea-SCR system were investigated experimentally with the variation of injection pressure. The length to diameter ratio ($l_o/d$) of the nozzle was 3.1, and the swirler was set inside the nozzle tip to give injecting fluid angular momentum. The injection duration of the nozzle was controlled by PWM (pulse width modulation) modes. The development processes of the spray were imaged by a 2-D PIV system, and the change of spray angle was measured. The atomization characteristics, including axial velocity and SMD, were measured using a 2-D PDA system with the injection pressures at room temperature and ambient pressure conditions. As the experimental results, the injection pressure had a significant impact on the spray structure showing a different shape around the spray leading edge, and the smaller SMD was observed with increasing injection pressures, which was similar to that of the previous work.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1687-1692
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• 2004

Airflow in the nasal cavity of a normal Korean adult is investigated experimentally by tomographic PIV measurement. Knowledge of airflow characteristics in nasal cavities is essential to understand the physiology and pathology aspects of nasal breathing. Several studies have utilized physical models of the healthy nasal cavity to investigate the relationship between nasal anatomy and airflow. All of these researches on nasal airflow are under the condition of constant flow-rate. In this study, nasal cavity flow with the physiological period is investigated by tomographic PIV, for the first time. A pumping system that can produce the periodic flow is created. Thanks to a new method for the model casting by a combination of the rapid prototyping and curing of clear silicone, a transparent rectangular box containing the complex nasal cavity can be made for PIV. The CBC PIV algorithm is used for analysis. Phase-averaged mean and RMS velocity distributions are obtained for inspirational and expiration nasal airflows. The comparison with the constant flow case is appreciated. There exist many flow patterns depending on each phase.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.7
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• pp.435-440
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• 2016

Effects of the increase rate of Reynold number on near-wall turbulent structures are investigated by performing direct numerical simulations of transient turbulent channel flows. The simulations were started with the fully-developed turbulent channel flow at $Re_{\tau}=180$, then temporal accelerations were applied. During the acceleration, the Reynolds number, based on the channel width and the bulk mean velocity, increased almost linearly from 5600 to 13600. To elucidate the effects of flow acceleration rates on near-wall turbulence, a wide range of durations for acceleration were selected. Various turbulent statistics and instantaneous flow fields revealed that the rapid increase of flow rate invoked bypass-transition like phenomena in the transient flow. By contrast, the flow evolved progressively and the bypass transition did not clearly occur during mild flow acceleration. The present study suggests that the transition to the new turbulent regime in transient channel flow is mainly affected by the flow acceleration rate, not by the ratio of the final and initial Reynolds numbers.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2465-2470
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• 2008

A new surface shape of an internal cooling passage which largely reduces the pressure drop and enhances the surface heat transfer is proposed in the present study. The surface shape of the cooling passage is consisted of the concave dimple and the riblet inside the dimple which is protruded along the stream-wise direction. Direct Numerical Simulation (DNS) for the fully developed turbulent flow and thermal fields in the cooling passage is conducted. The Numerical simulations for the 5 different surface shapes are conducted at the Reynolds number of 2800 based on the mean bulk velocity and channel height and Prandtl number of 0.71. The driving pressure gradient is adjusted to keep a constant mass flow rate in the x direction. The thermo-aerodynamic performance for the 5 different cases used in the present study was assessed in terms of the drag, Nusselt number, Fanning friction factor, Volume and Area goodness factor in the cooling passage. The value of maximum ratio of drag reduction is -22.86 [%], and the value of maximum ratio of Nusselt number augmentation is 7.05 [%] when the riblet angle is $60^{\circ}$ (Case5). The remarkable point is that the ratio of Nusselt number augmentation has the positive value for the surface shapes which have over $45^{\circ}$ of the riblet angle. The maximum Volume and Area goodness factor are obtained when the riblet angle is $60^{\circ}$ (Case5).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.5
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• pp.342-350
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• 2008

The effects of combustion instability on flow structure and flame dynamics with the inlet configurations in a model gas turbine combustor were investigated using large eddy simulation (LES). A G-equation flamelet model was employed to simulate the unsteady flame behaviors. As a result of mean flow field, the change of divergent half angle($\alpha$) at combustor inlet results in variations in the size and shape of the central toroidal recirculation (CTRZ) as well as the flame length by changing corner recirculation zone (CRZ). The case of ${\alpha}=45^{\circ}$ show smaller size and upstream location of CTRZ than those of $90^{\circ}$ and $30^{\circ}$ by the development of higher swirl velocity. The flame length in the case of ${\alpha}=45^{\circ}$ is shorter than other cases, while the case of ${\alpha}=30^{\circ}$ yields the longest flame length due to the decrease of effective reactive area with the absence of CRZ. Through the analysis of pressure fluctuation, it was identified that the case of ${\alpha}=45^{\circ}$ shows the largest damping effect of pressure oscillation in all configurations and brings in the noise reduction of 2.97dB, compared to that of ${\alpha}=30^{\circ}$ having the largest pressure oscillation. These reasons were discussed in detail through the analysis of unsteady phenomena related to recirculation zone and flame surface. Finally the effects of flame-acoustic interaction were evaluated using local Rayleigh parameter.

• Annals of Clinical Neurophysiology
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• v.5 no.2
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• pp.192-196
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• 2003

The Lateral dorsal cutaneous branch of sural nerve (LDCB) is a terminal sensory branch of lower extremities. It can be injured frequently in peripheral nerves. However, the normal data of each component of nerve conduction study (NCS) of were not studied at this time. The Nerve Conduction Study of LDCB adults were assessed for amplitude, area, duration and nerve conduction velocity (NCV) in normal fifty. We also evaluated how age, sex and dexterity affect the various components of NCS. The Mean amplitude of LDCB was $9.45{\pm}1.93{\mu}V$, area was $4.05{\pm}0.55{\mu}V/s$, duration was $1.50{\pm}0.13s$, and NCV was $37.9{\pm}3.09m/s$, respectively. The amplitude of right was $10.1{\mu}V$ in men, $8.65{\mu}V$ in women. The area of right was $3.83{\mu}V/s$ in less than 40 years and $4.24{\mu}V/s$ in older than 40 years. The areas of left was $3.86{\mu}V/s$ in less than 40 years and $4.30{\mu}V/s$ in older than 40 years. The NCV was 39.0 m/s in less than 40 years and 36.7 m/s in older than 40 years. All of above differences were statistically significant. There were no statistically significant differences between right and left NCS. Normal data of LDCB could be applicable in peripheral neuropathy or nerve injury.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.101.2-101.2
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• 2012

Shocks are ubiquitous in astrophysical plasmas: bow shocks are formed by the interaction of solar wind with planetary magnetic fields, and supernova explosions and jets produce shocks in interstellar and intergalactic spaces. The global morphologies of these shocks are usually described by a set of magnetohydrodynamic (MHD) equations which tacitly assumes local thermal equilibrium, and the resulting Rankine-Hugoniot shock jump conditions are applied to obtain the relationship between the upstream and downstream physical quantities. While thermal equilibrium can be achieved easily in collisional fluids, it is generally believed that collisions are infrequent in astrophysical settings. In fact, shock widths are much smaller than collisional mean free paths and a variety of kinetic phenomena are seen at the shock fronts according to in situ observations of planetary shocks. Hence, both the MHD and kinetic equations have been adopted in theoretical and numerical studies to describe different aspects of the physical phenomena associated with astrophysical shocks. In this paper, we present the results of 3D relativistic particle-in-cell (PIC) simulations for ion-electron plasmas, with focus on the shock structures: when a jet propagates into an unmagnetized ambient plasma, a shock forms in the nonlinear stage of the Weibel instability. As the shock shows the structures that resemble those predicted in MHD systems, we compare the results with those predicted in the MHD shocks. We also discuss the thermalization processes of the upstream flows based on the time evolutions of the phase space and the velocity distribution, as well as the wave spectra analyses.