• Journal of environmental and Sanitary engineering
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• v.20 no.1 s.55
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• pp.40-54
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• 2005

This dissertation aims to develop adsorption tubes for measuring organic solvents in the working environment, by comparing and analyzing breakthrough condition and adsorption capacity with ACF. 1. In breakthrough characteristics, the raising velocity of breakthrough curve is increasing according to assault concentration, but $50\%$ breakthrough time is decreasing. As breakthrough curve of calculated data using this agrees with the one of experimental data both of them can be used on determining sampling time of adsorption tubes. It is predicted by theoretical that $10\%$ breakthrough time is increasing in the case of increasing filled adsorbent amount. 2. $10\%$ breakthrough time is regularly decreasing as much as assault concentration is increasing. As a result, we can predict the life of adsorbent within the range of the low concentration, and adsorption amount that ACF can sample during $10\%$ breakthrough time is increasing as much as assault concentration is increasing.

• Tribology and Lubricants
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• v.16 no.6
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• pp.409-414
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• 2000

The friction and wear behaviors of MoS$_2$ coatings were investigated by using a pin and disk type tester. The experiment was conducted by using silicon nitride as pin material and MoS$_2$-on-bearing steel as disk material under different operating conditions that include linear sliding velocities in the range of 22-66 ㎜/sec, normal loads varying from 9.8 N to 29.4 N, corresponding to maximum contact pressures of 1.18-2.83 GPa and atmospheric conditions of high vacuum, medium vacuum, ambient air. The results showed that low friction coefficient of the coating has been identified in high vacuum and that friction coefficient and wear volume increased with increasing normal load. Also at high load conditions, the friction coefficient and wear volume increased with increasing sliding velocity.

• Journal of Welding and Joining
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• v.14 no.6
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• pp.101-108
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• 1996

In this study, WC-l7wt% Co composite powder for thermal spray was fabricated by spray drying method. The agglomerated composite powder had spheroidal morphology and the particle size distribution was 20~60${\mu}{\textrm}{m}$. WC and Co were distributed homogeneously. However, the strength of the spray-dried agglomerate was low due to the pores within the agglomerate. Therefore, the spray-dried agglomerate was broken down during HVOF thermal spray and the microstructure was inhomogeneous with many pores within the coating layer. And the decomposition of WC to W and $W_{6}$ $C_{2.54}$ was accelerated. The strength and flowability of the agglomerate were greatly improved by sintering heat treatment(110$0^{\circ}C$, 1 hour, hi atmosphere), and then the coating layer showed dense and homogeneous microstructure with well-developed splats. The hardness of the coating layer was H $v_{300}$ = 1072.2.2.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.223-228
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• 2006

Brake judder of an automotive vehicle is defined as an abnormal vibration of low frequency during braking. Under the assumption that judder occurs due to disc run-out and is a resonance phenomenon with a specific parts of the automobile, computational simulations using SAMCEF software were performed in this paper. The results show that the stabilizer of the car is a possible part which makes the judder vibration due to resonance. And initial braking velocity, the magnitude of run-out, and the friction coefficient between disk and pad are the influential factors to the brake judder.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.1
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• pp.33-43
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• 2007

Using the more common conventional chordwise aerodynamic approach, flapping a flat plate wing with zero degree chordwise pitch angle of attack and no relative wind should not produce lift. However, in hover, with no forward relative velocity and zero degree chordwise pitch angle of attack, flapping flat plate wings does in fact produce lift. In the experiments peformed for this paper, the flapping motion is considered pure(downstroke and upstroke) with no flapping stroke plane inclination angle. No changes in chordwise pitch angle are made. The total force is measured using a force transducer and the net aerodynamic force is determined from this measured total force by subtracting the experimentally determined inertial contribution. These experiments were repeated at various flapping frequencies and for various wing planform sizes for flat plate wings. The trends in the aerodynamic lift variation found using a force transducer have nearly identical shape for various flapping frequencies and wing planform sizes.

• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.1
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• pp.207-215
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• 2001

Plastic bonded explosive(PBX) is mainly composed of the nitramine-ploymer compositions. PBX is characterized by high velocity and pressure of detonation, low vulnerability and good thermal stability. Many important applications of PBX require the good adhesion between nitramine crystals and the binder. For PBXs as well as propellants, where good mechanical properties are of great importance, dewetting therefore must be prevented by strong adhesion between filler-binder. Adhesion depends on surface characteristics of filler and binder. In order to design for better adhesion, an understanding of the surface properties of explosive and binder is required. The surface free energies are calculated from contact angle values by the method of Kaelble. Critical surface tension of solids are calculated by Zisman plot. Critical surface tension is a useful parameter for characterizing the wettability of solid surface. In this study, HMX and 3 kinds of copolymers are selected, since they are widely used in many plastic bonded explosives. The technical objective of this investigation is to predict the interaction between filler and binder from their surface free energies.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.7
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• pp.590-596
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• 2008

The ultrasonic velocities of sintered aluminum with varying density were measured in order to deduce the mechanical properties for optimum design of the sintered aluminum. Specimens with different densities were prepared by the plasma activated sintering machine. The density distribution of sintered aluminum becomes partially inhomogeneous because of the friction between the powder and the die during compaction. The elastic moduli are increased as the ultrasonic velocity is increased. Furthermore, Poisoon's ratio is depending on not only the density but also the size and distribution of voids. As the specimen's thickness increases, the center frequency in the frequency spectrum of the reflection wave is shifted to the low frequency. The attenuation coefficient of ultrasonic wave is decreased inversely as the density increased.

• Journal of Ocean Engineering and Technology
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• v.17 no.6
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• pp.1-6
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• 2003

Wave energy dissipation and energy transfer between wave components, during the directional wave breakings, are investigated. Directional incipient and plunging breakers were generated by focusing the multi-frequency and multi-directional wave components at a designed location, based on a constant wave amplitude and a constant wave steepness frequency spectrum. The time series of surface wave elevation was measured at 9 different locations around the wave focusing point, using a wave gauge array. In order to examine the variation of the directional spreading function, the horizontal velocity of fluid motion was also measured. By comparing energy spectrums, before and after the breaking, the characteristics of energy dissipation and energy transfer, caused by wave breaking, are investigated. Their dependencies on directionality, as well as frequency, are analyzed. The breakings significantly dissipate wave energy, through energy transfer, in the upper region of the peak-frequency band, while enhancing wave energy in the low-frequency band.

• International Journal of Safety
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• v.1 no.1
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• pp.7-12
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• 2002

This paper demonstrates the impact stresses and wave propagation characteristics of glass/epoxy laminates subjected to the low-velocity impact by a steel ball theoretically and experimentally. A plate finite element model in conjunction with experimental contact laws is used for the theoretical investigation. The specimens for statical indentation and impact test are composed of $[0/45/0/-45/0]_28 and [90/45/90/-45/90]_28$ stacking sequences and have clamped-simply supported boundary conditions. Finally, these two results are compared and then the impulsive stress and wave propagation characteristics of this laminated composite are studied.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.4
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• pp.579-592
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• 2016

CNUSAIL-1, to be launched into low-earth orbit, is a cubesat-class satellite equipped with a $2m{\times}2m$ solar sail. One of CNUSAIL's missions is to deploy its solar sail system, thereby deorbiting the satellite, at the end of the satellite's life. This paper presents the design results of the attitude control system for CNUSAIL-1, which maintains the normal vector of the sail by a 3-axis active attitude stabilization approach. The normal vector can be aligned in two orientations: i) along the anti-nadir direction, which minimizes the aerodynamic drag during the nadir-pointing mode, or ii) along the satellite velocity vector, which maximizes the drag during the deorbiting mode. The attitude control system also includes a B-dot controller for detumbling and an eigen-axis maneuver algorithm. The actuators for the attitude control are magnetic torquers and reaction wheels. The feasibility and performance of the design are verified in high-fidelity nonlinear simulations.