• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.6
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• pp.519-529
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• 2010

In the present study, unsteady calculations have been performed to simulate flows around a UH-60A full configuration including main rotor, fuselage, and tail rotor. A flow solver developed for helicopter aerodynamic analysis was used for the simulation of the complete helicopter in high-speed and low-speed forward flight. Unsteady vibratory loads on the main rotor blades were compared with flight test and other calculated data for the assessment of the present flow solver. Aerodynamic interaction of the three components of the helicopter was investigated by comparing with the results of main-rotor-alone, main rotor and fuselage, and tail-rotor-alone configurations. It was found that the existence of the fuselage has an effect on the normal force distribution of the main rotor by varying downwash distribution on the rotor disc, and tip vortices trailed from the main rotor strongly interact with the tail-rotor.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.28 no.4
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• pp.12-20
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• 2020

The purpose of this study was to analyze the face validity of the revised EPTA (English Proficiency Test for Aviation) to see if the tests actually contribute to the enhancement of aviation safety and achieve the purpose of the assessment. In order to reach the above objectives, 103 pilot test takers were surveyed, and nine in-depth interviewees were selected and interviewed. In addition, detailed research results were derived by dividing the participants into the pilot's flight experience (31 captain pilots, 42 first officer pilots, and 30 general commercial pilots). As a result, pilot participants were generally aware that EPTA was more reasonable because the revised EPTA properly implemented the aviation situation and gave participants motivation to learn aviation English. It was also seen that first officer pilots had a higher face validity of EPTA than captain and general commercial pilots. The reason was that first officer pilots considered air traffic control job was more important than other pilots did.

• Smart Structures and Systems
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• v.20 no.3
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• pp.385-396
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• 2017

The recent advancements in sensing technologies allow us to record measurements from target structures at multiple locations and with relatively high spatial resolution. Such measurements can be used to develop data-driven methodologies for condition assessment, control, and health monitoring of target structures. One of the state-of-the-art technologies, Fiber Optic Strain Sensors (FOSS), is developed at NASA Armstrong Flight Research Center, and is based on Fiber Bragg Grating (FBG) sensors. These strain sensors are accurate, lightweight, and can provide almost continuous strain-field measurements along the length of the fiber. The strain measurements can then be used for real-time shape-sensing and operational load-estimation of complex structural systems. While several works have demonstrated the successful implementation of FOSS on large-scale real-life aerospace structures (i.e., airplane wings), there is paucity of studies in the literature that have investigated the potential of extending the application of FOSS into civil structures (e.g., tall buildings, bridges, etc.). This work assesses the feasibility of using FOSS to predict operational loads (e.g., wind loads) on chain-like structures. A thorough investigation is performed using analytical, computational, and experimental models of a 4-story steel building test specimen, developed at the University of Southern California. This study provides guidelines on the implementation of the FOSS technology on building-like structures, addresses the associated technical challenges, and suggests potential modifications to a load-estimation algorithm, to achieve a robust methodology for predicting operational loads using strain-field measurements.

• Korean Journal of Computational Design and Engineering
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• v.18 no.3
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• pp.155-166
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• 2013

We present recent human-vehicle interaction (HVI) research conducted in the area of defense and military application. Research topics discussed in this paper include: training simulation for overland navigation tasks; expertise effects in overland navigation performance and scan patterns; pilot's perception and confidence on an overland navigation task; effects of UAV (Unmanned Aerial Vehicle) supervisory control on F-18 formation flight performance in a simulator environment; autonomy balancing in a manned-unmanned teaming (MUT) swarm attack, enabling visual detection of IED (Improvised Explosive Device) indicators through Perceptual Learning Assessment and Training; usability test on DaViTo (Data Visualization Tool); and modeling peripheral vision for moving target search and detection. Diverse and leading HVI study in the defense domain suggests future research direction in other HVI emerging areas such as automotive industry and aviation domain.

• Physical Therapy Rehabilitation Science
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• v.10 no.2
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• pp.161-166
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• 2021

Objective: The purpose of this study was to quantitatively evaluate the Wii Balance Board (WBB)-based jump performance for the elderly and to confirm the difference in jump performance according to age. Design: Cross-sectional study. Methods: 40 young adults (aged 22.5±2.2 years) and 33 elderly (aged 75.1±5.2 years) without orthopedics disease participated in this study. Standing on the WBB then, with the signal "start," jump vertically to the maximum height at which you can jump, land on the force plate after jump and keep it standing on both feet. All subjects were required to practice the jump sufficiently before starting the measurement, each measuring three times, and the mean values were used. A one-minute break was provided between each trial. Evaluators waited within 1meter for every test to prepare for fall. Results: The vertical ground reaction force of elderly and young adults when jumping using WBB showed a significant difference (p<0.05) and demonstrated discriminant validity. Between two groups, there were significant differences in overall jump time (p<0.05), maximum value (p<0.05), minimum value (p<0.05), center of pressure (COP) pathlength (p<0.05), and flight time p<0.05). Conclusions: This study found that performing the vertical jump, the elderly showed longer jump time, lower vertical ground reaction force, COP pathlength and shorter flight phase than healthy young adults using WBB and demonstrated that as a measurement tool, WBB discriminated vertical jump performance between elderly and young adults.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.439-445
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• 2012

The COMS(Communication, Ocean, and Meteorological Satellite) is subjected to shock loads when the stage or fairing of a launch vehicle is separated and the satellite is separated from the launch vehicle during the launch vehicle flight. And, after the satellite is separated from the launcher, the COMS is subjected to shock loads when the solar array is deployed, Ka-Band communication antenna is deployed, and meteorological imager radiator cover is released. In order to validate the satellite safety against these shock loads on ground, shock tests were performed. In this paper, the shock tests performed in the course of the COMS development are described, and the method to assess the test result is presented with an example of Geostationary Ocean Color Imager(GOCI). In Ariane-5 launch vehicle, the clampband release shock for satellite separation is lower than the fairing or stage separation. In this paper, the extrapolation method to take into account the maximum shock load from the launch vehicle by using the satellite separation shock test result is also introduced.

• Journal of Astronomy and Space Sciences
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• v.28 no.1
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• pp.55-62
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• 2011

The precise orbit determination (POD) of low earth orbiter (LEO) has complied with its required positioning accuracy by the double-differencing of observations between International GNSS Service (IGS) and LEO to eliminate the common clock error of the global positioning system (GPS) satellites and receiver. Using this method, we also have achieved the 1 m positioning accuracy of Korea Multi-Purpose Satellite (KOMPSAT)-2. However double-differencing POD has huge load of processing the global network of lots of ground stations because LEO turns around the Earth with rapid velocity. And both the centimeter accuracy and the near real time (NRT) processing have been needed in the LEO POD applications--atmospheric sounding or urgent image processing--as well as the surveying. An alternative to differential GPS for high accuracy NRT POD is precise point positioning (PPP) to use measurements from one satellite receiver only, to replace the broadcast navigation message with precise post processed values from IGS, and to have phase measurements of dual frequency GPS receiver. PPP can obtain positioning accuracy comparable to that of differential positioning. KOMPSAT-5 has a precise dual frequency GPS flight receiver (integrated GPS and occultation receiver, IGOR) to satisfy the accuracy requirements of 20 cm positioning accuracy for highly precise synthetic aperture radar image processing and to collect GPS radio occultation measurements for atmospheric sounding. In this paper we obtained about 3-5 cm positioning accuracies using the real GPS data of the Gravity Recover and Climate Experiment (GRACE) satellites loaded the Blackjack receiver, a predecessor of IGOR. And it is important to reduce the latency of orbit determination processing in the NRT POD. This latency is determined as the volume of GPS measurements. Thus changing the sampling intervals, we show their latency to able to reduce without the precision degradation as the assessment of their precision.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.784-793
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• 2006

As the number of CFRD constructions increases, the necessity of an accurate assessment on its behavior also has been increasing accordingly. The performance of concrete faced rockfill dam (CFRD) under different water levels is greatly concerned by dam engineers and designers in the world. However, domestic research on CFRD design and construction has yet been insignificant. This study deals with three centrifuge model tests, mainly investigates the deformation of the concrete faced slabs with different face slab stiffness under different water levels. The prototype of a centrifugal model dam is half size of domestic CFRD dam. Detailed material preparation, model design, model set-up, model instrumentation and testing procedures are presented. In order to simulate the prototype concrete faced slab, three kinds of thin fiberglass plates with different thickness was adopted in the three model tests. The water level control facility was specially designed for this experiment to control the water level rise and drawdown during centrifuge flight. Although most of the results from the three model tests are satisfactory, it is also required that the centrifuge test results should be compared with those of numerical analysis and field measurements to analyze the centrifuge test results more in detail.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.8-17
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• 2003

The butt lap joint structures which are usually designed by the concept of slow crack growth damage tolerance, show frequently the behaviors of multiple site fatigue crack growth around the fastener hole edges due to the fretting between the two jointed parts. In this paper, experimental tests of fatigue crack growth have been performed of a bolted butt lap joint structure having an initial corner crack at the fastener hole edge, with different fretting conditions under a flight load spectrum. The obtained test results were reviewed to investigate the effects of fretting fatigue cracks on the damage tolerance crack growth life. Computations of corner crack growth were also carried out using an existed model to compare with test results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.9
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• pp.854-864
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• 2016

The use of small drone platform has become a popular topic in these days but its application for SAR operation has been little known due to the burden of the payload implementation. Drone platforms are distinguished from the conventional UAV system by the increased vulnerability to the turbulences, control-errors and poor motion stability. Consequently, sophisticated motion compensation may be required to guarantee the successful acquisition of high quality SAR imagery. Extremely limited power and mass budgets may prevent the use of additional hardwares for motion compensation and the difficulty of SAR focusing is further aggravated. In this paper, we have carried out a feasibility study of mico-SAR drone operation. We present the image acquisition results from the preliminary flight tests and a quality assessment is followed on the experimental SAR images. The in-flight motion errors derived from the unique drone movements are investigated and attempts have been made to compensate for the geometrical and phase errors caused by motions against the nominal trajectory. Finally, the successful operation of drone SAR system is validated through the focussed SAR images taken over test sites.