• Journal of Korean Society on Water Environment
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• v.29 no.5
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• pp.674-680
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• 2013

Basic studies for the treatment of particulate organic substances contained in wastewater by flotation have been conducted. Four kinds of plastics were chosen as the possibly existing organic particles in wastewater and the Zisman plots for these substances were constructed by measuring the contact angle of liquids on their surfaces. The critical surface tensions for these organic substances were estimated based on the constructed Zisman plot and the floatability of organic substances were regarded to be related with their molecular structure. The existence of dissolved organic substances such as a surfactant was observed to affect the extent of flotation of particulate organics. In addition, the consideration of work of adhesion was thought to be better than adopting the critical surface tension as the analytical basis in the operational design of flotation process of organic particles.

• Progress in Superconductivity and Cryogenics
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• v.14 no.3
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• pp.28-32
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• 2012

The critical current of the HTS(High Temperature Superconductor) tape is governed by cooling temperature, magnetic field and its angle to HTS tape originated from its geometrical structure. At the HTS coil design stage, the critical current of the coil is calculated by considering the Ic-B characteristics of the 2G tape and the operating current is determined based on the critical current. The operating current and the structure of the 5 T coil are suggested through the FEM (Finite Elements Method) analysis and calculation. As a part of our on-going research on a 20 T LTS/HTS magnet, we have designed and constructed a 5 T HTS insert coil and tested it in liquid helium temperature.

• Journal of KSNVE
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• v.4 no.2
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• pp.239-248
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• 1994

Wind tunnel tests and analyses of the response of the concrete pylon for the Seo Han Grand Bridge were conducted using aeroelastic model technique. A 1/250 scale aeroelastic model was used to measure the responses of the pylon at the several critical locations and to find any possible vibrational behavior. In order to confirm the model design and fabrication, natural frequencies and mode shapes measured from the model were compared with those from the calculation. Tests were conducted under the various angles ranging from $0^{\circ}$ to $90^{\circ}$ to find the critical angle of the wind. In order to evaluate the sensitivity of the response to changes in structural damping, a series of tests were conducted with two different values of structural damping such as 0.2% and 1.0% of critical. Additional tests were also conducted considering construction sequence.

• Steel and Composite Structures
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• v.22 no.6
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• pp.1261-1280
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• 2016

We study chaotic motion in a nonlinear laminated composite plate under subsonic fluid flow and a simultaneous external load in this paper. We derive equations of motion of the plate using the von-$K{\acute{a}}rm{\acute{a}}n^{\prime}s$ hypothesis and the Hamilton's principle. Galerkin's approach is adopted as the solution method. We then conduct a divergence analysis to obtain critical velocities of the transient flow. Melnikov's integral approach is used to find the critical parameters in which chaos takes place. Effects of different parameters including the aspect ratio, plate material and the ply angle in laminates on the critical flow speed are investigated. In a parametric study, we show that how the linear and nonlinear stiffness of the plate and the load frequency and amplitude would influence the chaotic behavior of the plate.

• Journal of the Korea Society for Simulation
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• v.28 no.3
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• pp.75-82
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• 2019

A Satellite Communication (SATCOM), which is applied to various systems to communicate with other systems at the limited wired communication situation, is required to head at a stable point of the space, because this system uses a geostationary satellite. It is important to know satellite tracking heading angles such as elevation angle and azimuth angle for the immovable antenna's latitude, longitude, and altitude. Moreover, calculation of heading angle is critical for SATCOM antenna on a moving platform. In this study, a antenna heading angle calculation method is applied to compute elevation and azimuth angle for a SATCOM antenna and the heading angle simulation is executed for the Korea peninsula and surrounding areas. To verify this simulation, satellite tracking test is conducted using a SATCOM antenna which uses monopulse signal tracking method. The simulation is confirmed by comparing this test result with the simulation. And we make a suggestion for calculation of polarization angle of this antenna.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1816-1819
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• 2003

As a result of milling operation, we expect to have burr at the outward edge of workpiece. Also, it causes undesirable problems such as deburring cost, low quality of machined surface, and bottleneck in manufacturing process. Though it is impossible to totally remove burr in machining, it is necessary to plan a machining process that minimizes the occurrence of burr. In this paper, a scheme is proposed which identifies the tool path of the milling operation with minimum burr. In the previous research, a Burr Expert System was developed where the feature identification, the cutting condition identification, and the analysis on exit burr formation are the key steps in the program. The Burr Expert System predicts which portion of workpiece would have the exit burr in advance so that we can calculate the burr length of each milling operation. Here, the critical angle determines whether the burr analyzed is an exit burr or not. So the burr minimization scheme becomes to minimize the burr with critical angle. By iterating all the possible tool paths in certain milling operation, we can identify the tool path with minimum burr.

• Tunnel and Underground Space
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• v.21 no.3
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• pp.174-180
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• 2011

An anisotropic version of Mohr-Coulomb failure criterion is proposed in order to provide a strength criterion for transversely isotropic rock. The concept of fabric tensor introduced by Pietruszczak & Mroz (2001) is employed to define the friction angle and cohesion as scalar functions of the fabric tensors. The anisotroy in these two strength parameters are calculated in association with the consideration of the relative rotation between the principal stress coordinate and the principal material triad. The critical plane on which the anisotropic function maximized is found by an optimization technique based on the Lagrange multiplier method. To demonstrate the performance of the anisotropic failure criterion, conventional triaxial tests on the samples having various inclinations of weakness plane are simulated and the resulting triaxial strength and dip angle of failure plane are discussed.

• Particle and aerosol research
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• v.5 no.4
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• pp.171-178
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• 2009

$PM_{2.5}$ is one of critical air pollutants due to its high absorbability of heavy metallic fumes, PAH and bacillary micro organisms. Such a fine particulate matter is often formed through various nucleation processes including condensation. This study attempts to find the nucleation behaviors of $PM_{2.5}$ arisen from coal power stations using a classical heterogeneous Fletcher's theory. The numerical simulation by C-language could approximate the nucleation process of $PM_{2.5}$ from water vapor, of which approach revealed the required energy for embryo formation and embryo size and nucleation rate. As a result of the calculation, it was found that wetting agents could affect the particle nucleation in vapor condensation. In particular, critical contact angle relates closely with the vapor saturation. Particle condensation could be reduced by lowering the angles. The wetting agents aid to decrease the contact angle and surface tensions, thereby may contribute to save the formation energy.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.10
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• pp.1263-1268
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• 2014

In this study, the variations of swirl center according to evaluating position have been investigated in a steady flow bench of SI engine. For the experiments, two engine heads with different intake valve angles ($11^{\circ}$ and $26^{\circ}$) were tested in the flow bench by varying the evaluating position (1.75~6.0B) and valve lift (2~10 mm). Particle image velocimetry was used to measure the velocity field inside the engine cylinder. The swirl center position is found with a critical point theory and the intensity of turbulence is calculated from PIV velocity data. The results show that the center of swirl is located closer to the center of cylinder and turbulence intensity is lower, when the intake valve angle is the smaller. It is conventional to evaluate the swirl ratio at 1.75B position in the steady flow bench of SI engine. At this position, however, the distance of swirl center from the cylinder center scatters significantly for the variation of valve lift, and the turbulence intensity is much stronger regardless of the valve angle. Thus, to estimate the flow at the end of compression stroke in a real engine from the data in the steady flow experiments, the evaluation position should be moved further downstream more than 4.5B.

• Progress in Superconductivity
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• v.1 no.2
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• pp.146-150
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• 2000

Step edge Josephson junctions in c-axis oriented $YBa_2Cu_3O_7$ films were fabricated on $CeO_2$ buffered sapphire substrates. The step angle was controlled in the wide range of $20^{\circ}\sim75^{\circ}$ by the Ar ion milling technique. I-V curves of junction fabricated on the thickness ratio of $\sim$0.8 and the step angle of $35^{\circ}$ were exhibited RSJ-like behavior with $I_CR_N$ product of $\sim250{\mu}A$ and critical current density of $\sim2\times10^4A/cm^2$ at 77 K. Critical current of step edge junction was increased linearly with decreasing temperature but the normal resistance was almost constant. Total samples of step edge Josephson junction was satisfied a scaling behavior of $I_CR_N{\propto}(J_C)^{0.5}$.