• 한국연소학회:학술대회논문집
• /
• 2003.12a
• /
• pp.185-193
• /
• 2003

Basic flow fields of two dimensional V flames were examined as a preliminary work to study the instability of premixed flame with vorticity generation. Laminar premixed propane and methane flame were anchored by electrically heated wire to make two dimensional V flames. Flow fields were measured mainly by PIV(Particle Image Velocimetray) and the results were compared with those obtained by LDV(Laser Doppler Velocimetry) to confirm their reliability. Because the curvatures of V flames are so small, V flames were locally assumed to be inclined planar flames in gravitational field. The measured flow fields were locally compared with those of analytical solutions, which showed the qualitatively similar results. In downstream region, the vorticity fields were nearly constant except region near the center line, which support the assumption of locally one dimensional flame. Besides it was tried to find experimentally the similarity of flow fields in downstream region. Finally, stability diagram of propane and methane flames were drawn for the equivalence ratio less than one and the wide range of mean velocity.

• Journal of Korean Port Research
• /
• v.9 no.1
• /
• pp.57-63
• /
• 1995

In this paper we examine the mass transport within the boundary layer near the sea bottom. The fluid domain is seperated into inner and outer region of boundary layers. In outer region, the wave field is assumed to be inviscid and irrotational. When the incident waves enter the arrays of circular cylinders, the scattering of water waves by an array of N bottom mounted vertical circular cylinders is solved using the method proposed by Linton & Evans under the potential theory. In inner region, the Navier-Stokes equation must be satisfied with boundary conditions at the boundary later and bottom is to be represented by the sum of the Eulerian mean drift and the Stokes' drift.

• Journal of Navigation and Port Research
• /
• v.32 no.8
• /
• pp.637-643
• /
• 2008

When planning outfall system, the first target cif design is to maximize initial dilution of discharge effluent. To achieve the target effectively, the characteristics of mixing phenomenon between ambient and discharged water should be analyzed. Especially the analysis at the Near-Field-Region(NFR) as initial dilution zone should be preceded. Usually, the initial behavior of effluent through outfall system is rising toward the surface due to mixing with ambient water for heat discharge and sinking toward the bottom due to the difference of density for brine discharge. After mixed with eddies accompanied by the ambient water, the plumes are showing the same density and internal current pattern by advection and diffusion. Until recently, lots of studies are being carried out for the optimum design of outfall system. but it is difficult to find any studies of heat and brine discharge at the same time. Therefore, this study is hoped to provide some basic data for optimum design of outfall system.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.7
• /
• pp.15-25
• /
• 2003

An experimental. study is carried out to investigate the near-wake characteristics of an airfoil oscillating in pitch. An NACA 4412 airfoil is sinusoidally pitched about the quarter chord point between the angle of attack -6$^{\circ}$ and +6$^{\circ}$. A hot-wire anemometer is used to measure the phase-averaged mean velocities in the near-wake region of an oscillating airfoil. The freestream velocities of present work are 3.4, 12.4, 26.2 m/s, and the corresponding Reynolds numbers are 5.3${\times}10^4$, 1.9${\times}10^5$, 4.l${\times}10^5$, and the reduced frequency is 0.1. Streamwise velocity profiles are presented to show the Reynolds number effects on the near-wake region behind an airfoil oscillating in pitch. All the cases in these measurements show that the velocity defects by the change of the Reynolds number are very large at the lowest Reynolds number $R_N$=5.3${\times}10^4$: and are small at the other Reynolds numbers ($R_N$=1.9${\times}10^5$ and 4.l${\times}10^5$) in the near-wake region. A significant difference of phase-averaged mean velocity between 5.3${\times}10^4$, and 1.9${\times}10^5$ is observed. The present study shows that a critical value of Reynolds number in the near-wake of an oscillating airfoil exists in the range between 5.3${\times}10^4$, and 1.9${\times}10^5$.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.81.3-81.3
• /
• 2017

In this paper, we report a small-scale emerging island and double arc loops, which are associated with a M6.5 flare, in Active Region 12371. We investigate the spatial and temporal changes of both photospheric magnetic fields using SDO/HMI data and coronal magnetic structures obtained from nonliner force-free field (NLFFF) extrapolation. From the vector magnetograms, we find a small-scale emerging island near the main polarityy inversion line about three hours before the flare. The island has a strong shear angle, which is determined by difference between transverse component of observed field and potential field, of around 90 degrees. Furthermore, the NLFFF well reproduces a sigmoidal structure seen in SDO/AIA 94, which is consistent with the double arc loops configuration suggested by Ishiguro and Kusano (2017) who introduced a magnetic configuration showing the double arc instability. The observed emerging island is located among the double arc loops, which is also supproted by their model. Finally, there was an eruption (M6.5 flare) associated with the loops. We discuss a possible role of the double arc instability for the eruption.

• Journal of Welding and Joining
• /
• v.20 no.3
• /
• pp.109-115
• /
• 2002

In this study high power Nd:YAG laser welding of structural steel was investigated. For the test steel blocks of $50{\times}50{\times}200mm$ were cut and machined, and bead-on-plate weld was made on the machined surface. Argon, nitrogen, helium, dry air or mixed gases were used to find the effect of shielding conditions on the bead formation. Results demonstrated that there were Fe I rich region and Fe II rich region in the laser induced plasma column based on the spectral analysis with S-2000 field spectrometer The Fe I region was located at the root of the column near keyhole opening. On the other hand, Fe II region was found at the middle of the plasma column. In the Nd:YAG laser welding, Fe I region emitted continuum which had peak value at wave length of around 710nm, and Fe II region had the peak at 580nm. In the welding of steel by $CO_2$ laser, however, no continuum was observed. There showed two groups of strong spikes in the $CO_2$ laser welding; the first group was displayed at the wave band of 450-560nm. This spike group emitted stronger intensity of light and sharper peaks than those group at 680-800nm.

• Journal of Navigation and Port Research
• /
• v.35 no.1
• /
• pp.45-49
• /
• 2011

The recent trend for numerical experiment requires more higher resolution and accuracy. Generally, in the wave field calculation, it starts with a large region formulation first and follows by a separated detailed region formulation by more denser grids for the main interest area considering the geographical and bathymetrical variation. The wave fields resulted from the large region calculation is being introduced into the detail region calculation as the incident waves. In this process there exists a problem of continuity. In order to get over such problem, method of variable gridding system or spectrum sampling, etc., is being used. However, it seems not enough to examine and analyze the related numerical errors. Therefore, it is investigated in this study the field applicability of the most pervasive use of wave model, the nested SWAN model. For this purpose, we made model experiment for two coastal harbours with different tidal environment, and compared and analyzed the result. From the analysis, it was found that both the extracted values, near the boundaries of the large and detail region and the nested formulation of SWAN model, show almost the same and no different between those with different tidal environment conditions. However it is necessary for reducing the numerical errors to set the boundaries for the detailed region outside of the rapid bathymetric change and deeper region.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.3
• /
• pp.388-397
• /
• 1999

Numerical simulations are carried out for the magnetic Czochralski single crystal growth system. It Is shown that a magnetic field significantly suppresses the convective flow and as the strength of magnetic field becomes to be stronger, the heat transfer in the melt is dominated by conduction rather than convection. By imposing a cusp magnetic field, the growth interface shape becomes convex toward the melt. When the axial magnetic field is imposed, there occurs an inversion of the interface shape with increase of the magnetic field strength. The oxygen concentration near the interface decreases with increasing cusp magnetic field strength while axial field causes an increase of an oxygen concentration at the central region and decrease of that at the edge of the crystal. The results show that the cusp magnetic field has advantages over an axial magnetic field In the radial uniformity of oxygen as well as in the additional degree of control.

• Journal of the Korean Geotechnical Society
• /
• v.27 no.5
• /
• pp.85-92
• /
• 2011

The dynamic behavior of piles becomes very complex due to soil-pile dynamic interaction, soil non-linearity, resonance phenomena of soil-pile system and so on. Therefore, the proper numerical simulation of the pile behavior needs much effort and calculation time. In this research, a new modeling method, which can be applied to the conventional finite difference analysis program FLAC 3D, was developed to reduce the calculation time. The soil domain in this method is divided into a near-field region and a far-field region, which is not influenced by the soil-pile dynamic interaction. Then, the ground motion of the far-field is applied to the boundaries of the near-field instead of modeling the far-field region as finite meshes. In addition, the soil non-linearity behavior is modeled by using the hysteretic damping model, which determines the soil tangent modulus as a function of shear strain and the interface element was applied to simulate the separation and slip between the soil and pile. The proposed method reduced the calculation time by as much as one third compared with a usual modeling method and maintained the accuracy of the calculated results. The calculated results by the proposed method showed a good agreement with the prototype pile behavior, which was obtained by applying a similitude law to the 1-g shaking table test results.

• Publications of The Korean Astronomical Society
• /
• v.15 no.spc2
• /
• pp.21-25
• /
• 2000

The ionosphere, the atmosphere of the earth ionized by solar radiations, has been strongly varied with solar activity. The ionosphere varies with the solar cycle, the seasons, the latitudes and during any given day. Radio wave propagation through or in the ionosphere is affected by ionospheric condition so that one needs to consider its effects on operating communication systems normally. For examples, sporadic E may form at any time. It occurs at altitudes between 90 to 140 km (in the E region), and may be spread over a large area or be confined to a small region. Sometimes the sporadic E layer works as a mirror so that the communication signal does not reach the receiver. And radiation from the Sun during large solar flares causes increased ionization in the D region which results in greater absorption of HF radio waves. This phenomenon is called short wave fade-outs. If the flare is large enough, the whole of the HF spectrum can be rendered unusable for a period of time. Due to events on the Sun, sometimes the Earth's magnetic field becomes disturbed. The geomagnetic field and the ionosphere are linked in complex ways and a disturbance in the geomagnetic field can often cause a disturbance in the F region of the ionosphere. An enhancement will not usually concern the HF communicator, but the depression may cause frequencies normally used for communication to be too high with the result that the wave penetrates the ionosphere. Ionospheric storms can occur throughout the solar cycle and are related to coronal mass ejections (CMEs) and coronal holes on the Sun. Except the above mentioned phenomena, there are a lot of things to affect the radio communication. Nowadays, radio technique for probing the terrestrial ionosphere has a tendency to use satellite system such as GPS. To get more accurate information about the variation of the ionospheric electron density, a TEC measurement system is necessary so RRL will operate the system in the near future.