• Journal of the Korean Society of Safety
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• v.11 no.4
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• pp.64-71
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• 1996

Detonation phenomena of $C_2H_2$were invesgated using the various shock tube. To study the detonation characteristics according to the composition of $C_2H_2-0_2$$_2$ and $C_2H_2$-air mixtures, the composition were varied from 5 to 90% and 5 to 50% of acetylene each other. A spiral ring was installed in the shock tube to study the effect of obstacles in DDT phenomena. Detonation velocities were measured using the photodiode, and the DDT phenomena was visualized using the high speed schlieren photograph. From the experimental result, it was found that the detonation velocity was most high near the 1. 8times the stoichiometric ratio of acetylene. And from the visualization of DDT phenomena, it was found that the detonation wave was strengthened throuth the pile up of small compression wave of burned gas. And the obstacles in shock tube accelerate the detonation reaction by turblent effect of flammable gas mixture.

• Journal of computational fluids engineering
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• v.9 no.2
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• pp.18-22
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• 2004

Numerical investigation has been conducted to figure out flow behavior and pressure drop characteristics of spirally corrugated steel pipe which is widely used in civil, industrial and agricultural field owing to many advantages such as good corrosion resistance and durability, strength, easy and quick installation. Also the poly-ethylene coating spirally corrugated steel pipe has the long life under condition of sea water immerged. In the present study, flow behavior in the spirally corrugated pipe and influence of P/d/sub h/(ratio of wave pitch to hydraulic diameter) to pressure drop are investigated by CFD with various Reynolds number. And also friction factor is estimated by pressure drop obtained by flow analysis. According to computation results, the flow runs spirally up and down along the spiral corrugation in the vicinity of wall, but the effect of spiral corrugation disappears in core region of pipe. As P/d/sub h/ becomes small, more pressure drop occurs in spirally corrugated Pipe. Besides, friction factor augmentation becomes much larger as Re increases. In case of p/d/sub h/=0.38, Pressure drop and friction factor of spirally corrugated pipe are about four times larger than smooth pipe at Re: 1.46×10/sup 6/.

• Smart Structures and Systems
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• v.18 no.3
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• pp.471-484
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• 2016

Optical fiber sensors have been proven that they have the potential to detect high-frequency ultrasonic signals, in structural health monitoring field which generally refers to acoustic emission signals from active structural damages and guided waves excited by ultrasonic actuators and propagating in waveguide. In this work, the sensing properties of optical fiber sensors based on Mach-Zehnder interferometer were investigated in the metal plate. Analytical formulas were conducted first to explore the parameters affecting its sensing performances. Due to the simple and definable frequency component, the Lamb wave excited by the piezoelectric wafer was employed to study the sensitivity of the proposed optical fiber sensors with respect to the frequency, rather than the acoustic emission signals. In the experiments, according to above investigations, spiral shape optical fiber sensors with different size were selected to increase their sensitivity. Lamb waves were excited by a circular piezoelectric wafer, while another piezoelectric wafer was used to compare their voltage responses. Furthermore, by changing the excitation frequency, the tuning frequency characteristic of the proposed optical fiber sensor was also investigated experimentally.

• Journal of the Korean Society of Visualization
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• v.22 no.1
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• pp.49-60
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• 2024

The purpose of this study establishes the deep neural network (DNN) and Decoder models to predict the flow and thermal fields of three-dimensional wavy wings as a passive flow control. The wide ranges of the wavy geometric parameters of wave amplitude and wave number are considered for the various the angles of attack and the aspect ratios of a wing. The huge dataset for training and test of the deep learning models are generated using computational fluid dynamics (CFD). The DNN and Decoder models exhibit quantitatively accurate predictions for aerodynamic coefficients and Nusselt numbers, also qualitative pressure, limiting streamlines, and Nusselt number distributions on the surface. Particularly, Decoder model regenerates the important flow features of tiny vortices in the valleys, which makes a delay of the stall. Also, the spiral vortical formation is realized by the Decoder model, which enhances the lift.

• Journal of Wind Energy
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• v.14 no.1
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• pp.29-36
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• 2023

The analysis of the floating offshore wind turbine platform is based on the procedures provided by the IEC including the International Classification Society, which recommends the analysis in the time domain. But time-domain simulation requires a lot of time and resources to solve tens of thousands of DLCs. This acts as a barrier in terms of floating structure development. For final verification, it requires very precise analysis in the time domain, but from an initial design point of view, a simplified verification procedure to predict the quantity of materials quickly and achieve relatively accurate results is crucial. In this study, a structural design procedure using a design wave applied in the oil and gas industries is presented combined with a conservative turbine load. With this method, a quick design spiral can be rotated, and it is possible to review FOWTs of various shapes and sizes. Consequently, a KRISO Semi-Submersible FOWT platform was developed using a simplified design procedure in frequency-domain analysis.

• Korea-Australia Rheology Journal
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• v.21 no.2
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• pp.119-126
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• 2009

A numerical analysis is performed to investigate the effect of rotation on the blood flow characteristics with four different angular velocities. The artery has a cylindrical shape with 50% stenosis rate symmetrically distributed at the middle. Blood flow is considered a non-Newtonian fluid. Using the Carreau model, we apply the pulsatile velocity profile at the inlet boundary. The period of the heart beat is one second. In comparison with no-rotation case, the flow recirculation zone (FRZ) contracts and its duration is reduced in axially rotating artery. Also wall shear stress is larger after the FRZ disappears. Although the geometry of artery is axisymmetry, the spiral wave and asymmetric flow occur clearly at the small rotation rate. It is caused that the flow is influenced by the effects of the rotation and the stenosis at same time.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.155-158
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• 1996

Magnetic fields correlated on several kiloparsec scales are seen in spiral galaxies. Their origin could be due to the winding up of a primordial cosmological field or due to amplification of a small seed field by a turbulent galactic dynamo. Both options have difficulties: There is no known battery mechanism for producing the required primordial field. Equally the turbulent dynamo may self destruct before being able to produce the large scale field, due to excess generation of small scale power. The current status of these difficulties is discussed. The resolution could depend on the nature of the saturated field produced by the small scale dynamo. We argue that the small scale fields do not fill most of the volume of the fluid and instead concentrate into intermittent ropes, with their peak value of order equipartition fields, and radii much smaller than their lengths. In this case these fields neither drain significant energy from the turbulence nor convert eddy motion of the turbulence on the outer scale to wave like motion. This preserves the diffusive effects needed for the large scale dynamo operation.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.7
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• pp.17-24
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• 1998

We proposed a novel bondwire inductor buried in plastic package for low cost MMIC and characaterized the electrical perofmrance in a wide frequency range using the full-wave analysis of finite element method(FEM), and then we fabricated and measured the scale-up model in order to prove the characteristics. Th ebondwire inductor has higher quality factor and higher cutoff frequency than the conventional spiral inductor designed n the same area as the bondwire inductor. Since the air-bridge process is not requried for the bondwire inductor, it is very suitable for low cost plastic-packaged MMIC production. The bondwire inductor has the field distribution localized around the bondwire inductor and hence is more compatible to the crosstalk problems.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.124-125
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• 2000

Since Nye and Berry$^{(1)}$ showed that in free space the electromagnetic field could contain stable, propagating phase singularities termed "dislocations", optical dislocations have been extensively investigated in nonlinear optics and laser physics. As the wave propagates, the lines of constant phase surrounding a dislocation trace out a spiral in space or in time. So these phase singularities are now usually referred to as optical vortices. Baranova and her co-workers$^{(2)}$ have shown that in fully developed speckle patterns, there is, one optical vortex accompanying each speckle spot on average. Among these vortices there are networks in phasemap because only one phase is to be assigned in one point except optical dislocations having zero amplitude. Freund et al.$^{(3)}$ have been studied optical dislocation networks and simulations are compared with experimental results. (omitted)

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.11
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• pp.2242-2246
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• 2009

In this paper, a homogeneous dual composite right/left-handed (D-CRLH) transmission line (TL) is proposed by using a defected ground structure (DGS) on the ground plane. In order to satisfy a homogeneity condition of metamaterial, a subwavelength unit cell is designed by way of a spiral DGS and a meander stub. From a dispersion diagram, it is expected that the frequency bands for the left-handed (LH) property is 3.5 - 4.4 GHz. At 3.8 GHz in the LH band, backward propagating phenomenon is observed from full-wave analysis. The experimental results show that the proposed TL has a stop-band in 1.75 - 3.6 GHz.