• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.05a
• /
• pp.281-284
• /
• 2009

Acoustic tuning frequency of quarter-wave resonators is investigated numerically to suppress combustion instability in a liquid rocket engine. A quarter-wave resonator is adopted, which was designed from the cold acoustic test for optimal damping condition. First, in a model combustion chamber scaled down from a full-scale chamber, reactive flow filed is analyzed numerically and acoustic-pressure responses are examined. Next, thermodynamic properties in the resonators are predicted. Based on the data, frequency tuning method is studied. The optimum tuning length of each resonator is proposed and thereby, sufficient damping is produced.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.05a
• /
• pp.41-45
• /
• 2009

The small-sized bi-propellant thruster using a high concentrated hydrogen peroxide and kerosene as the oxidizer and fuel was designed and fabricated in this study. The water cold-flow test was performed to verify the performance characteristics of the injector. The mixing head assembly used in this model thruster was designed as a structure to combine igniter, injectors and film cooling, which are capable of regulating each mass flowrate. This maximize the experimental verification and efficiency of the design optimization. Finally, the mass flowrate and spray pattern of injector were evaluated by the hydraulic test. Therefore, the design validity of the mixing head was verified.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2001.02a
• /
• pp.45-47
• /
• 2001

The function of the thermal shield(TS) is to eliminate the thermal radiation from the room temperature side to the coil temperature(4.5K) region so as to reduce the thermal load on the He refrigerator. The TS is composed of multilayer insulation(MLI) which is coated very thin aluminum on the insulating material, cryopanel which is cooled by cold gaseous He, and supports which stand the cryopanel and MLI on the room temperature part. The thermal shield for the TF coils and PF coils has been located between the coils and vacuum vessel. The thermal shielding cryopanel is cooled under 80 K by a forced flow of helium gas using cooling pipes on the cryopanel.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.2
• /
• pp.78.1-78.1
• /
• 2014

An ionization front (IF) surrounding an H II region is a sharp interface through which a cold neutral gas makes transition to a warm ionized phase by absorbing UV photons from central massive stars. We investigate the structure and instability of a plane-parallel D-type IF threaded by magnetic fields parallel to the front. We find that magnetic fields increase the maximum propagation speed of the IFs, while reducing the expansion factor, defined as the density ratio of neutral to ionized phases. IFs become unstable to distortional perturbations due to gas expansion across the fronts, exactly analogous to the Darrieus-Landau instability of ablation fronts in terrestrial flames. The growth rate of the IF instability is proportional linearly to the perturbation wavenumber as well as the upstream flow speed. The IF instability is stabilized by gas compressibility and becomes completely quenched when the front is D-critical. The instability is also stabilized by magnetic pressure when the perturbations propagate in the direction perpendicular to the fields. When the perturbations propagate in the direction parallel to the fields, on the other hand, it is magnetic tension that reduces the growth rate, completely suppressing the instability when ${\beta}$ < 1.5, with ${\beta}$ denoting the square of the ratio of the sound speed to the Alfven speed in the pre-IF region. When the front experiences an acceleration, the IF instability cooperates with the Rayleigh-Taylor instability to make the front more unstable. We discuss potential effects of IF instability on the evolution and dynamics of IFs in the interstellar medium.

• The Korea Journal of Herbology
• /
• v.22 no.1
• /
• pp.81-87
• /
• 2007

Objectives: Angelicae Dahuricae Radix (Baek-Ji in Korean, BJ) is well known to be used as a medicine for cold, headache, supraorbital pain, nasal congestion, and toothache. Little is understood about the roles of BJ in the cytokine and chemokine secretion by immune cells. This study was designed to find out the effects of BJ on the cytokine and chemokine secretion in human mast cells (HMC). Methods : We treated BJ according to consistency on HMC and measured cytokines and chemokines levels using flow cytometry CBA system. Results: In BJ treated group. the expression of interferon-inducible protein 10 (IP-l0), monocyte chemoattractant protein-1 (MCP-1), chemokine (C-X-C motif) ligand 9 (MIG), and interleukin 10 (IL-l0) levels were decreased significantly and chemokine (C-C motif) ligand 5 (RANTES), IL-8, $interferone-{\gamma}$ ($IFN-{\gamma}$), and tumor necrosis factor alpha (TNF-a) were decreased significantly. Conclusion : The results of this experiment supposed that the treatment of BJ will ameliorate the secreting levels of some chemokines or cytokines such as IP-10, MCP-1, MIG, IL-10, RANTES, IL-8, $IFN-{\gamma}$, and TNF-a.

• The Korea Journal of Herbology
• /
• v.27 no.2
• /
• pp.17-24
• /
• 2012

Objective : For the purpose of investigating the herbal resources of Dokdo island, this study was designed. Method : For the first time, we searched the native plants of Dokdo island from research data. And we examined herbological books on the plants of Dokdo island. Result : The native herbaceous plants in Dokdo island were 27 family and 73 species, and the medicinal plants were 49 species among them. The woody plants in Dokdo island were 12 family and 13 species, and the medicinal plants were 10 species among them. The main medicinal parts of medicinal plants were the whole body of herbs, roots, and seeds in order. The herbal medicines with cold or cool nature were 45 species, they took the top nature of the herbal medicines. According to the properties and principal action of native herbal medicines in Dokdo island, the major parts were classified into drugs for clearing away heat, eliminating toxin, activating blood flow and removing blood stasis, urination, removing heat from the blood and stopping of bleeding. The number of native herbal medicines with small toxicity in Dokdo island were 7 species. Conclusion : For the purpose of preserving the native plants of Dokdo island, we should recognize not only medical benefits but also matters that demand special attention.

• Journal of Ecology and Environment
• /
• v.29 no.2
• /
• pp.175-183
• /
• 2006

The discovery of deep-sea hydrothermal vents and their ecosystems is a monumental landmark in the history of Ocean Sciences. Deep-sea hydrothermal vents are scattered along the global mid-ocean ridges and back-arc basins. Under sea volcanic phenomena related to underlying magma activities along mid-ocean ridges generate extreme habitats for highly specialized communities of animals. Multidisciplinary research efforts during past three decades since the first discovery of hydrothermal vents along the Galapagos Rift in 1977 revealed fundamental components of physiology, ecology, and evolution of specialized vent communities of micro and macro fauna. Heterogeneous regional geological settings and tectonic plate history have been considered as important geophysical and evolutionary factors for current patterns of taxonomic composition and distribution of vent faunas among venting sites in the World Ocean basins. It was found that these communities are based on primary production of chemosynthetic bacteria which directly utilize reduced compounds, mostly $H_2S$ and $CH_4$, mixed in vent fluids. Symbioses between these bacteria and their hosts, vent invertebrates, are foundation of the vent ecosystem. Gene flow and population genetic studies in parallel with larval biology began to unveil hidden dispersal barrier under deep sea as well as various dispersal characteristics cross taxa. Comparative molecular phylogenetics of vent animals revealed that vent faunas are closely related to those of cold-water seeps in general. In perspective additional interesting discoveries are anticipated particularly with further refined and expanded studies aided by new instrumental technologies.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.11 s.254
• /
• pp.1093-1100
• /
• 2006

Combustion stability rating of jet injector is conducted numerically using air-injection technique in a model chamber, where air is supplied to oxidizer and fuel manifolds of the model five-element injector head. A sample F(fuel)-O(oxidizer)-O-F impinging-jet injector is adopted. In this technique, we can simulate mixing process of streams flowing through oxidizer and fuel orifices under cold-flow condition without chemical reaction. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions. From numerical data, unstable regions can be identified and they are compared with those from air-injection acoustic and hot-fire tests. The present stability boundaries are in a good agreement with experimental results. The proposed numerical method can be applied cost-effectively to stability rating of jet injectors when mixing of fuel and oxidizer jets is the dominant process in instability triggering.

• Journal of the Korean Society for Precision Engineering
• /
• v.9 no.3
• /
• pp.83-101
• /
• 1992

A systematic method of remeshing is required due to severe mesh distortion after some finite deformation in the finite element analysis of practical forging processes. In order to cope with the problem of mesh degeneracy during deformation, the proper design of meshes plays an improtant role in the analysis. In so-called "Modular Remeshing", the physical characteristics of metal flow and geometric characteristics are incorporated in "Module", which can be applied to the mesh design for a certain mode of deformation in so far as the topology of deforming region remains the same. For the purpose of more effective and systematic use of the modular remeshing scheme, an expert system has been developed in the framework of the proposed remeshing schemel. In oredr to show the effectiveness of the method, the rib-web type forging with axial relief or radial relief and spike forging are simulated. It has been thus shown that the proposed method of automatic remeshing by using modular remeshing and expert system can be futher extended and applied to various forging problems with complicated geometrical configurations.ical configurations.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.6
• /
• pp.860-867
• /
• 2001

In this study, condensation heat transfer experiments were conducted with plate and shell heat exchangers(P&SHE) using R-22. An experimental refrigerant loop has been established to measure the condensation heat transfer coefficient of R-22 in a vertical P&SHE. Two vertical counter flow channels were formed in the P&SHE by three plates of geometry with a corrugated trapezoid shape of a chevron angle of 45°. Downflow of the condensing R-22 in one channel releases heat to the cold upflow of water in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality of R-22 on the measured data were explored in detail. The results indicate that at a higher vapor quality the condensation heat transfer coefficients are significantly higher. A rise in the refrigerant mass flux causes an increase in the h(sub)r. Also, a rise in the average heat flux causes an increase in the h(sub)r. Finally, at a higher system pressure the h(sub)r is found to be slightly lower. Correlation is also provided for the measured heat transfer coefficients in terms of the Nusselt number.