• 한국가시화정보학회:학술대회논문집
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• 2001.12a
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• pp.36-43
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• 2001

The flow field structures of two interacting parallel supersonic free jets are studied by flow visualization using planar laser-induced fluorescence of NO seeded in nitrogen gas. The experiments are carried out for several distances between two orifice centers and for various ratios of the pressure in the reservoir to that in the expansion chamber. The flow fields are visualized mainly on the plane including two jet centerlines and its characteristic shock system, especially a cell structure formed secondly by interaction of two jets, are analyzed. The positions of the normal shock depending on the pressure ratios are also compared.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.610-615
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• 2002

This study is to evaluate the risk perception of noise of the ground-crews in the Korean airbases who exposed to noise of jet plane. 1148 ground-crews and 231 pilots of 2 airbases participated in this study. The questionnaires of risk perception with visual analogue scale were completed by the participants. For comparison, the perception of other risks such as beef contaminated with dioxin, AIDS, lung cancer, otitis media, shigellosis, driving, drinking, and smoking were also included in the questionnaire of risk perception. The results of this study suggested the necessity of risk communication about noise and activation of effective hearing conservation program in the Korean air-force.

• Bulletin of the Korean Chemical Society
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• v.17 no.5
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• pp.461-463
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• 1996

The laser-induced fluorescence excitation spectrum of 7-amino-4-(trifluoromethyl)coumarin in a supersonic jet has been recorded in the 340-352 nm region. The electronic band origin was observed at 28622.8 cm-1. Vibrational assignments for the three fundamental low-frequency modes and eight combination bands have been made for the S1 electronic excited state. The out-of-plane vibrations of this molecule have been characterized from the low-frequency assignments of the spectrum. The periodic potential energy function for the CF3 torsion, which satisfactorily fits the observed data, were also determined to be V(Φ)=95X(1-cos3Φ)-32X(1-cos6Φ) where Φ is the torsional angle. The relatively low torsional barrier of 99 cm-1 in S1 state could be explained by the small steric interactions between the functional groups attached to a bicyclic ring.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.325-333
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• 2012

An experimental study was carried out to determine the correlation between the internal flow in a circular nozzle and elliptical nozzles with the external flow. The flow rate, spray angle and drop size were measured under various conditions of the injection pressure. Numerical simulations were attempted to investigate the internal flow structure in the elliptical nozzles, because the experimental study was limited in its measurements of flow velocity and pressure distributions in the relatively small orifice. In the case of the elliptical nozzles, the disintegration characteristics of the liquid jet were significantly different from those of the circular nozzle. Surface breakup was observed at the jet issued from the elliptical nozzles with injection pressure. This is due to the internal flow structure, which is reattached to the orifice wall at the minor axis plane of the elliptical nozzle, unlike that observed with the circular nozzle.

• Journal of Astronomy and Space Sciences
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• v.39 no.3
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• pp.117-126
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• 2022

The Ionospheric Anomaly Monitoring by Magnetometer And Plasma-probe (IAMMAP) is one of the scientific instruments for the Compact Advanced Satellite 500-3 (CAS 500-3) which is planned to be launched by Korean Space Launch Vehicle in 2024. The main scientific objective of IAMMAP is to understand the complicated correlation between the equatorial electro-jet (EEJ) and the equatorial ionization anomaly (EIA) which play important roles in the dynamics of the ionospheric plasma in the dayside equator region. IAMMAP consists of an impedance probe (IP) for precise plasma measurement and magnetometers for EEJ current estimation. The designated sun-synchronous orbit along the quasi-meridional plane makes the instrument suitable for studying the EIA and EEJ. The newly-devised IP is expected to obtain the electron density of the ionosphere with unprecedented precision by measuring the upper-hybrid frequency (f_UHR) of the ionospheric plasma, which is not affected by the satellite geometry, the spacecraft potential, or contamination unlike conventional Langmuir probes. A set of temperature-tolerant precision fluxgate magnetometers, called Adaptive In-phase MAGnetometer, is employed also for studying the complicated current system in the ionosphere and magnetosphere, which is particularly related with the EEJ caused by the potential difference along the zonal direction.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.475-485
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• 2004

This paper was studied to investigate and compare the effects of inclined baffle plate on the turbulent flow characteristics of a gun-type gas burner through X-Y plane and Y-Z plane respectively by using X-probe from hot-wire anemometer system. For this purpose, two burner models with a cone-type baffle plate and a flat-type one respectively were used. The fast jet flow spurted from slits plays a role such as an air-curtain because it encircles rotational flow by swirl vanes and drives mixed main flow to axial direction regardless of the inclination of baffle plate. The inclined baffle plate causes axial mean velocity component and turbulent intensities etc. to be greatly concentrated towards the central part of a burner, and its effect especially appears in the range of about X/R=1.0-2.0. Also, it gives much larger size to axial mean velocity component and turbulent intensities etc formed near the slits in the range of X/R=1.4103. Especially the inclined baffle plate shifts more the Reynolds shear stress uw to the central region of a burner(Y/R=${\pm}$0.75) than the flat-type one, moreover it develops more strongly than uv.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.19-28
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• 2017

Effects of cavitation and hydraulic flip in circular and elliptical nozzles on the flow characteristics have been studied. Spray tests were conducted using injectors with different ratios of an orifice length(L) to a diameter(d) and of a major axis diameter(a) to a minor axis diameter(b). With the increment of an injection pressure drop, discharge coefficients slightly decreased in cavitation flows, and those suddenly dropped and were almost constant in hydraulic flip flows. For elliptical nozzles with L/b > 8 and L/a < 8, discharge coefficients and flow patterns showed different results from those in previous circular nozzles. When a flow in the elliptical nozzle was under steady condition, as the liquid column went downstream from the nozzle, its spray angle a little decreased in the plane of a major axis and increased in the plane of a minor axis.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.236.1-236.1
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• 2012

We conducted simultaneous 22GHz water maser and 44GHz class I methanol maser surveys of newly-identified 282 H2 emission features from the $2.122{\mu}m$ H2 narrowband image survey in the Galactic plane (UWISH2 project) using Korea VLBI Network (KVN) 21-m radio telescopes. We detected 16 and 13 new water and methanol maser sources, respectively. This result indicates that at least ~5% of the H2 emission features originate from young stellar objects (YSOs) that are in the right physical condition to produce the water and methanol masers. The masers are closely related to the current outflow activities in the Galactic plane. The power sources of these 23 diffused/collimated H2 emission features (six sources are detected for both masers) are likely to be intermediate-to high-mass YSOs, based on a comparison with the maser luminosities of other well-studied YSOs. Both maser velocities are mostly close to their own systemic velocities within 5 km/s, even though water masers generally show larger variabilities in the line intensities, velocities, and shapes than methanol masers. We also discovered three new water maser sources with high-velocity components: ~25 km/s red-shifted CMHO019, ~50 km/s blue-shifted CMHO132, and ~120 km/s blue-shifted CMHO182. In particular, we propose that the dominant blue-shifted water maser of CHMO182 could become a unique laboratory for the study of high-mass stellar jet and their accelerations.

• Geomechanics and Engineering
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• v.30 no.6
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• pp.565-577
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• 2022

In this study, a series of three-dimensional numerical parametric study was conducted to investigate deformation mechanisms of an existing box culvert due to an adjacent multi-propped basement excavation in clays. Field measurements from an excavation case history are first used to calibrate a baseline Hardening Soil Small Strain (HS-small) model, which is subsequently adopted for parametric study. Results indicate that the basement-box culvert interaction along the basement centerline can be considered as a plane strain condition when the length of excavation (L) reaches 14 H_e (i.e., final excavation depth). If a plane strain condition (i.e., L/H_e=12.0) is assumed for analyzing the basement-box culvert interaction of a short excavation (i.e., L/H_e=2.0), the maximum settlement and horizontal movement of the box culvert are overestimated significantly by up to 15.7 and 5.1 times, respectively. It is also found that the deformation of box culvert can be greatly affected by the basement excavation if the distance between the box culvert and retaining wall is less than 1.5 H_e. The induced deformation in the box culvert can be dramatically reduced by improving the ground inside the excavation or implementing other precautionary measures. For example, by adding jet grouting columns within the basement and installing an isolation wall behind the retaining structures, the maximum settlements of box culvert are shown to reduce by 37.2% and 13.4%, respectively.

• Advances in aircraft and spacecraft science
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• v.3 no.4
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• pp.367-378
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• 2016

Thrust Vectoring is a dynamic feature that offers many benefits in terms of maneuverability and control effectiveness. Thrust vectoring capabilities make the satisfaction of take-off and landing requirements easier. Moreover, it can be a valuable control effector at low dynamic pressures, where traditional aerodynamic controls are less effective. A numerical investigation of Fluidic Thrust Vectoring (FTV) is completed to evaluate the use of fluidic injection to manipulate flow separation and cause thrust vectoring of the primary jet thrust. The methodology presented is general and can be used to study different techniques of fluidic thrust vectoring like shock-vector control, sonic-plane skewing and counterflow methods. For validation purposes the method will focus on the dual-throat nozzle concept. Internal nozzle performances and thrust vector angles were computed for several range of nozzle pressure ratios and fluidic injection flow rate. The numerical results obtained are compared with the analogues experimental data reported in the scientific literature. The model is integrated using a finite volume discretization of the compressible URANS equations coupled with a Spalart-Allmaras turbulence model. Second order accuracy in space and time is achieved using an ENO scheme.