• Journal of the Korea Institute of Military Science and Technology
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• v.3 no.2
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• pp.213-218
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• 2000

An experimental study was performed to investigate the effect of surface temperature mismatch on measurements of skin friction using a plug-type skin friction gage mounted on the side wall of a supersonic wind tunnel. The freestream Mach number was 2.4 and Reynolds number per meter was $5.25 {\times}10^7$ with total pressure of 50 psi and total temperature of 275K. Temperature mismatch between the gage surface and surrounding wall surface was generated by hot water injection using the active temperature control system. Results of the tests showed that the temperature mismatch made sizable effects on the measurements of skin friction.

• Wind and Structures
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• v.15 no.3
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• pp.247-261
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• 2012

Some numerical investigations are presented concerning the response of a given plate under turbulence driven excitations. Three different input loads are simulated according to the wall pressure distributions derived from the models proposed by Corcos, Efimtsov and Chase, respectively. Modal solutions (finite element based) are used for building the modal stochastic responses in the sub-critical aerodynamic frequency range. The parametric investigations concern two different values of the structural damping and three values of the boundary layer thickness. A final comparison with available experimental data is also discussed. The results demonstrate that the selection of the adequate TBL input model is still the most critical step in order to get a good prediction.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.779-782
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• 2002

We examine the problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick, open-cell foam with fabric covering and a viscoelastic painted plate of 1mm thick over an acoustic board of 4m thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber ($k_{ch}$) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.4
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• pp.327-332
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• 2012

International Towing Tank Conference (ITTC) recommended verifying a ship's ability to move transversely at zero forward speed without altering heading by a crabbing test. In sea trial, all available propellers/rudders/thrusters should be used to find the maximum possible transverse speed. For estimating crabbing ability in the design stage, tests to estimate possible swaying force and yawing moment range using all available propellers/rudders/thrusters are conducted. By butterfly diagram, which compares possible swaying force and yawing moment range with external swaying force and yawing moment by wind, a ship's crabbing ability can be estimated. In this study, model tests of a cruise vessel equipped with bow thrusters and POD system were conducted to find out her crabbing ability in the design stage. To mimic quay condition, a model quay-wall was set in the towing tank.

• Journal of the Korean Society of Visualization
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• v.2 no.1
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• pp.32-38
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• 2004

A new PIV technique was developed for decreasing optical error which was created during simultaneous measurements of velocity fields at a wall-normal plane and wall-parallel plane by a plane PIV and a Stereo-PIV systems. For experimental study, two different Reynolds number based on momentum thickness, Re$_{ =514 and 934 were generated in a blowing type wind tunnel under the condition of zero pressure gradient. The two Nd:Yag laser systems and three CCD cameras were synchronized. to obtain instantaneous velocity fields at the same time. To avoid optical noise at the crossing line by the two laser light sheets, a new optical arrangement using polarization was applied. The obtained velocity fields show the existence of hairpin packet structure vividly and the idealized hairpin vortex signature is confirmed by experiment.

• International Journal of High-Rise Buildings
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• v.11 no.1
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• pp.61-68
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• 2022

The Address Jumeirah Resort is a mixed-use 77-story tower reaching a height of 301 meters with a slenderness ratio of 13.5:1. The development is situated in the Jumeirah Beach District and accommodates 217 key five-star hotel suites, 478 residential apartments, 444 serviced-branded apartments, retail shops, ballrooms and entertainment facilities around the premises. The building has over 242,000 m2 of usable area. The project is an award-winning development that broke multiple Guinness records. The focus of the paper is to present the challenges faced in the structural design and construction of the super tall tower and the highest occupiable skybridge in the world.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.4
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• pp.280-286
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• 2002

It has been long suspected that the transition region may give rise to local pressure fluctuations and radiated sound that are different from those created by the fully-developed turbulent boundary layer at equivalent Reynolds number. Experimental investigation described in this paper concerns the characteristics of pressure fluctuations at the transition. Flush-mounted microphones and hot wires are used to measure the pressure fluctuations and local flow velocities within the boundary layer in the low noise wind tunnel. From this experiment we could observe the spatial and temporal development process of T-S wave using Wigner-Ville method and find the relations between the characteristic frequency of T-S wave and free stream velocity and the boundary layer thickness based on nondimensional pressure spectra scaled on outer variables.

• The Journal of Korea Robotics Society
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• v.5 no.1
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• pp.14-22
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• 2010

Recently researches on the window cleaning robot are being conducted actively. Moving mechanismsof these window cleaning robots are divided into two categories, which are towed type and walking type. Towed type is focused on fast cleaning on the flat surface of building and walking type has priority on cleaning task on relatively complex surface with overcoming obstacles. Currently commercialized towed type window cleaning robot has weakness that it is hard to adhere closely with the wall and easy to be affected by wind. In case of walking type it has the problem that the position errors are continuously accumulated during motion. In this paper, we propose new towed and walking type mechanism which can compensate previous weaknesses. After that we estimate the performance of each proposed mechanism by simulation.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.45.3-46
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• 2015

Space weathering agents such as micrometeoroids and solar wind particles continuously age the uppermost regolith of the lunar surface by comminuting as well as darkening and reddening. Among several maturity indices, we investigate median grain size () and optical maturity (OMAT) of the crater rim walls. Crater rim wall is the most immature place among the impact crater features because the vertical mixing process by mass-movement can enhance the gardening of regolith and the supply of immature materials in the deeper layer to the surface. More than 140 simple and complex craters were considered. Both and OMAT values of the inner rim wall initially increase as the crater size increases until ~10-20 km, then decrease. This transition crater size happens to correspond to the transition diameter from simple to complex craters. For larger craters, i.e., complex craters, it is clear that the inner rim wall of the craters formed in recent eras tend to remain fresh and become mature along with time. For the simple crater case, smaller craters are more mature, which is opposite to the case of complex craters. This is thought to be because smaller craters become flattened more quickly, thus have smaller vertical mixing in the regolith due to mass-movement. We will also discuss on the maturity indices of the crater rim walls at high latitudes as a function of the position angle to see the latitude dependence of the space weathering process.

• Earthquakes and Structures
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• v.26 no.6
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• pp.489-499
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• 2024

Infill masonry walls are vulnerable to lateral loads, including seismic, wind, and concentrated push loads. Various strengthening metal fittings have been proposed to improve lateral load resistance, particularly against seismic loads. This study introduces the use of post-compressed wedges as a novel reinforcement method for infill masonry walls to enhance lateral load resistance. The resistance of the infill masonry wall against lateral-concentrated push loads was assessed using an out-of-plane push-over test on specimens sized 2,300×2,410×190 mm³. The presence or absence of wedges and wedge spacing were set as variables. The push-over test results showed that both the unreinforced specimen and the specimen reinforced with 300 mm spaced wedges toppled, while the specimen reinforced with 100 mm spaced wedges remained upright. Peak loads were measured to be 0.74, 29.77, and 5.88 kN for unreinforced specimens and specimens reinforced with 100 mm and 300 mm spaced wedges, respectively. Notably, a tighter reinforcement spacing yielded a similar strength, as expected, which was attributed to the increased friction force between the masonry wall and steel frame. The W-series specimens exhibited a trend comparable to that of the displacement ductility ratio. Overall, the findings validate that post-compressed wedges improve the out-of-plane strength of infill masonry walls.