• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.7
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• pp.539-549
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• 2017

In this paper, experimental studies on the shroud separation were performed to investigate characteristics of the shroud separation at mach 3. Shroud separation tests were carried out in the vertical free-jet wind tunnel that is capable of testing separable structures. A shroud model was miniaturized to meet test objectives and test section dimensions of the wind tunnel. Pneumatic Locking and separation mechanisms were designed considering external force due to free stream. High speed cameras were used to record the shroud motion and unsteady shock patterns over the deploying shrouds during the shroud separation process. Also, unsteady pressures on the nose surface were measured by using the pressure sensors. Through the tests, the measurement data necessary for researches on the shroud separation technology were obtained. Shroud separation behaviors and characteristics of unsteady pressure on the nose surface for each external flow conditions were analyzed.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.6
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• pp.673-677
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• 2010

Recently, NAND flash memory has been widely used in embedded systems, personal computers, and server systems because of its attractive features, such as non-volatility, fast access speed, shock resistance, and low power consumption. Due to its hardware characteristics, specifically its 'erase-before-write' feature, Flash Translation Layer is required for using flash memory like hard disk drive. Many FTL schemes have been proposed, but conventional FTL schemes have problems such as block thrashing and block associativity problem. The KAST scheme tried to solve these problems by limiting the number of associations between data block and log block to K. But it has also block thrashing problem in random access I/O pattern. In this paper, we proposed a new FTL scheme, UDA-LBAST. Like KAST, the proposed scheme also limits the log block association, but does not limit data block association. So we could minimize the cost of merge operations, and reduce merge costs by using a new block reclaim scheme, log block garbage collection.

• Journal of Biosystems Engineering
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• v.30 no.3 s.110
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• pp.147-154
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• 2005

The improved hitch device, which connecting the trailer to power tiller, was developed. This device, composed with spring and rubber, could reduce the vibration and shock levels during driven on off-road. The vertical vibration accelerations for the improved hitch device were measured at 6 positions, i.e. engine, hitch, seat, and three points in trailer (front, middle, and rear) for not driving but at low engine speed of 500 rpm, and compared with the existing hitch device. The results of this study could be summarized as follows; The average vibration acceleration up to 120 Hz was $0.4m/s^2$ at engine part, but it was 0.08 and $0.05m/s^2$ at trailer for existing and improved hitch device, respectively. About $38\%$ of average acceleration level could be absorbed for the improved hitch device compared with existing hitch device. The average vibration acceleration up to 40 Hz was reduced to 0.12 and $0.06m/s^2$ at trailer for existing and improved hitch device respectively, showing the reduction effect of $50\%$. The maximum acceleration occurred at up to 20 Hz of low frequency was much higher than total acceleration occurred at up to 120 Hz, which means that much loss or damage could be occurred during transporting of agricultural products on off-road. The portions of average acceleration occurred at up to 20 Hz of low frequency were $27\%\;and\;21\%$ for the existing and improved hitch device, respectively.

• Journal of the Korea Institute of Building Construction
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• v.2 no.3
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• pp.163-170
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• 2002

Recently, polishing tile(porcelain homogeneous polished tile) was used in the construction field as a finishing material. But, there happened some problems such as tile exfoliation by construction condition in early ages. Also, for use of polishing tile in the dry wall system which used to lightweight wall, the examination of adhesive stability of polishing tile is needed. In this study, adhesive strength of Polishing tile was investigated by tile bond types on gypsum board and non asbestos board coated by tar-urethane and Polymer modified cementitious waterproofing membrane(Series I). Then, the effect of heat stress and vibration was estimated on gypsum and non asbestos board(Series II). As the result of study are the follows; (1) Polishing tile(600$\times$400mm) construction on waterproofing layer : Both laboratory estimation and spot examination sieve were happened that fall of tile because their hardening speed is late. (2) To using powder style adhesives in the dry wail with waterproofing layer : Adhesive strength of tile is Influenced by interface bond area and base side condition. (3) Shock and heat stresses : obvious decline of adhesive strength is not happened

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.91-91
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• 2011

The passage of the interplanetary discontinuity (i.e., sudden increases in the solar wind speed, density, and IMF strength) was detected by ACE near GSE (x, y, z) ~ (222, -36, 3) Re upstream of Earth around 22:48 UT on November 24, 2008. About 55 min later, this solar wind discontinuity was observed by Geotail near GSE (x, y, z) ~ (23, 18, -7) Re in front of Earth's bow shock. From the propagation time of the solar wind discontinuity between ACE and Geotail, it is expected that the discontinuity front is aligned with the Parker spiral and strikes the postnoon dayside magnetopause first. Using coordinated multi-point measurements (THEMIS and GOES) at or in geosynchronous orbit, we observed a tailward propagating sudden impulse (SI), excited by the interplanetary discontinuity, around 23:50 UT with its front retaining alignment similar to that of solar wind discontinuity. The SI event appears a negative-then-positive variation in the H component at high latitude Chokurdakh (CHD: MLAT ~ 64.7 deg) in the prenoon sector, which is opposite sense of normal SI event. During the positive deflection at CHD, the SuperDARN Hokkaido radar detected the downward motion of the ionosphere, implying westward electric field enhancement, at subauroral latitudes near CHD meridian. In our study we will discuss magnetospheric and ionospheric responses to the passage of the solar wind discontinuity using multi-point observations in space and on the ground.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.177-180
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• 2010

Two-stage light gas gun, sorted with Ballistic Range System, is used to research spray characteristics of supersonic liquid jets. When high pressure tube was pressurized to the 135 bar, diaphragm films which composed with OHP film are ruptured. Expansion gases accelerate a projectile approximately 250 m/s at the exit of pump tube. And accelerated projectile collides with liquid storage part and liquid jets were injected into supersonic conditions. Supersonic liquid jets show the multiple jets and generate shockwave at the forward region of jets. Supersonic liquid jets of speed and shockwave angle have different value at each case. Supersonic liquid jets with minimum velocities are injected with M=1.53 at the geometry condition of L/d=23.8.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.634-643
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• 2004

In this paper are presented a concept of a new supersonic air inlet, which is designated a Multi-Row Disk (MRD) inlet, aiming at performance improvement under off-design conditions, and results of wind tunnel tests examined performance characteristics of the MRD inlet. The MRD inlet is frequently called ‘a skeleton inlet’ because of its appearance. The performance of a conventional axisymmetric inlet with a solid center body (spike) deteriorates under off-design Mach number conditions. It is due to the fact that total pressure recovery (TPR) governed by the throat area of inlet and mass capture ratio (MCR) governed by an incidence position of an oblique shock from the spike tip into the cowl can not be controlled independently in such air inlet. The MRD inlet has the spike that is composed of a tip cone and several disks arranged downstream of it, based on the experimental fact that several deep cavities on a conical surface have little negative effect on the boundary layer growth. The overall spike length of the MRD inlet is adjustable to the given flight speed by changing space between disks so that a spillage flow can be controlled independently from controlling the throat area. It could be made clear from the result of wind tunnel tests that the MRD inlet improves TPR by 10% compared with a conventional inlet with a solid spike under off-design conditions.

• International Journal of Automotive Technology
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• v.6 no.2
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• pp.149-159
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• 2005

A full nonlinear finite element P185/70Rl4 passenger car radial-ply tire model was developed and run on a 1.7-meter-diameter spinning test drum/cleat model at a constant speed of 50 km/h in order to investigate the tire transient response characteristics, i.e. the tire in-plane free vibration modes transmissibility. The virtual tire/drum finite element model was constructed and tested using the nonlinear finite element analysis software, PAM-SHOCK, a nonlinear finite element analysis code. The tire model was constructed in extreme detail with three-dimensional solid, layered membrane, and beam finite elements, incorporating over 18,000 nodes and 24 different types of materials. The reaction forces of the tire axle in vertical (Z axis) and longitudinal (X axis) directions were recorded when the tire rolled over a cleat on the drum, and then the FFT algorithm was applied to examine the transient response information in the frequency domain. The result showed that this PI 85/70Rl4 tire has clear peaks of 84 and 45 Hz transmissibility in the vertical and longitudinal directions. This result was validated against more than 10 previous studies by either theoretical or experimental approaches and showed excellent agreement. The tire's post-impact response was also investigated to verify the numerical convergence and computational stability of this FEA tire model and simulation strategy, the extraordinarily stable scenario was confirmed. The tire in-plane free vibration modes transmissibility was successfully detected. This approach was never before attempted in investigations of tire in-plane free vibration modes transmission phenomena; this work is believed to be the first of its kind.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.5
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• pp.333-339
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• 2016

In this paper, a fundamental experiment regarding the formation of porous 3D structures for personal safety products using 3D PPP (Porous Polymer Printing) was introduced for the first time. The filament was manufactured by mixing PP (Polypropylene) and CBA (Chemical Blowing Agent) with polymer extruder, and the diameter of the filament was approximately 1.75mm. The proposed 3D PPP method, combined with the conventional FDM (Fused Deposition Modeling) procedure, was influenced by process parameters, such as the nozzle temperature, printing speed and CBA density. In order to verify the best processing conditions, the depositing parameters were experimentally investigated for the porous polymer structure. These results provide parameters under which to form a multiple of 3D porous polymer structures, as well as various other 3D structures, and help to improve the mechanical shock absorption for personal safety products.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.3
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• pp.169-176
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• 2019

In the present study, a CFD/DSMC hybrid method performed by a coupled analysis between the CFD method and the DSMC method was developed to obtain the flow information on the rarefied gas flows effectively. Flow simulations around the high speed vehicles on the transition flow regimes were conducted by using the developed method. The FRESH-FX vehicle made of cone and cylinder shapes was considered for the simulations. The results of the hybrid method were compared with the results of the pure CFD and the pure DSMC method to confirm the reliability and efficiency of the hybrid method. It was found that the gradient and the intensity of the shock waves were weakened due to the relatively low density on the transition flow regime. It was confirmed that the results of the hybrid analysis were different to those of the pure CFD analysis and almost identical to those of the pure DSMC analysis. In addition, the computational time of the hybrid method was reduced than that of the pure DSMC method. As a result, it was obtained that the validity and the efficiency of the CFD/DSMC hybrid method.