• Journal of the Korea Convergence Society
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• v.11 no.12
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• pp.131-135
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• 2020

In this study, the models with three, five and ten wings of the propeller which made a light aircraft fly were performed by air flow analyses. As for the flow model A with the shape with five wings, Model A can be seen to be the most ideal flow of air. The flow of air through the number of wings, which is not too many or too few, shows the most smooth flowing form. The smaller the number of propeller blades, the smaller the flow of air. Model A is applied under pressure of up to 0.5631 MPa at the front of air flow. Also, models B and C are applied under pressures of 0.5758 MPa and 0.5589 MPa, respectively. Comparing the pressure contours for each model of flux, model B can be shown to have the highest pressure distribution. The result of this study can be used to investigate the air flow without actual testing. It also seems to be helpful in the aesthetic convergent design of light aircraft propeller.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.10
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• pp.1247-1255
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• 2016

The safety and autonomous flight function of micro UAV or drones is crucial to its commercial application. The requirement of own building stable drones is still a non-trivial obstacle for researchers that want to focus on the intelligence function, such vision and navigation algorithm. The paper present a GCS using commercial drone and hardware platforms, and open source software. The system follows modular architecture and now composed of the communication, UI, image processing. Especially, lane-keeping algorithm. are designed and verified through testing at a sports stadium. The designed lane-keeping algorithm estimates drone position and heading in the lane using Hough transform for line detection, RANSAC-vanishing point algorithm for selecting the desired lines, and tracking algorithm for stability of lines. The flight of drone is controlled by 'forward', 'stop', 'clock-rotate', and 'counter-clock rotate' commands. The present implemented system can fly straight and mild curve lane at 2-3 m/s.

• Applied Chemistry for Engineering
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• v.21 no.1
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• pp.111-114
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• 2010

In the attrition reactor for the American Society for Testing and Materials (ASTM) D5757-95, the attrition characteristics of catalysts for water gas shift reaction were investigated. The effects of attrition characteristics of low temperature shift catalysts (LTS) and high temperature shift catalysts (HTS) on fluidization phenomena and average particle size were investigated and compared with the attrition characteristics of sand particles. The particle size of catalysts was decreased and particle size distribution in attrition tube was changed due to the effect of gas injection. About 40~50 wt% samples of original catalyst particles were entrained and lost. The amount of fly ash of LTS catalyst was less than that of HTS. Also, the weight of entrained particles which had original particle size of $212{\sim}300{\mu}m$ was lower than any other cases.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.2
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• pp.98-106
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• 2003

Nondestructive test (NDT) provides much information on concrete without damage of structural functions. Of NDT methods, elastic wave propagation methods, such as ultrasonic pulse velocity (UPV) method and impact-echo (IE) method, have been successfully used to estimate the strength, elastic modulus, and Poisson's ratio of concrete as well as to detect the internal microstructural change and defects. In this study, the concretes with water-binder ratio ranging from 0.27 to 0.50 and fly ash content of 20% were made and then their longitudinal wave velocities were measured by UPV and IE method, respectively. Test results showed that the UPV is greater than the longitudinal wave velocity measured by the If method, i.e., rod-wave velocity obtained from the same concrete cylinder. It was found that the difference between the two types of velocities decreased with increasing the ages of concrete and strength level. Moreover, for the empirical formula, the dynamic Poisson's ratio, static and dynamic moduli of elasticity, and velocity-strength relationship were determined. It was observed that the Poisson's ratio and the modulus of elasticity determined by the dynamic method are greater than those determined by the static test. Consequently, for the more accurate estimation of concrete properties using the elastic wave velocities, the characteristics of these velocities should be understood.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.3
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• pp.37-46
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• 2024

This study investigates the evolution of concrete damage due to chloride-induced steel corrosion through Impact-echo (IE) testing. Three reinforced concrete specimens, each measuring 1500 mm in length, 400 mm in width, and 200 mm in thickness, were fabricated using three concrete mixture proportions of blended cement types: ordinary Portland cement, ground granulated blast-furnace slag and fly ash. Steel corrosion in the concrete was accelerated by impressing a 0.5 A current following a 35-day cycle of wet-and-dry saturation in a 3% NaCl solution. Initial IE data collected during the saturation phase showed no significant changes, indicating that moisture had a minimal impact on IE signals and highlighting the slow progress of corrosion under natural conditions. Post-application of current, however, there was a noticeable decline in both IE peak frequency and the P-wave velocity in the concrete as the duration of the impressed current increased. Remarkably, progressive monitoring of IE proves highly effective in capturing the critical features of steel-corrosion induced concrete deterioration, such as the onset of internal damages and the rate of damage propagation. These results demonstrate the potential of progressive IE data monitoring to enhance the reliability of diagnosing and prognosticating the evolution of concrete damage in marine environment.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.319-326
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• 2004

This paper investigates the effect of the concrete containing mineral admixtures(pozzolanic materials such as fly-ash, ground granulated blast-furnace slag, silica fume and meta kaolin) on the resistance properties to chloride ion invasion. The purposed testing procedure was applied to the concrete replaced mineral admixtures for 3${\~}$4 replacement ratios under water-binder ratios ranged from 0.40 to 0.55. For the electro-migration test, Tang and Nilsson's method was used to estimate the diffusion coefficient of chloride ion. As a results, the water-binder ratios, kinds of mineral admixtures and replacement ratios, water curing periods had a great effect on the diffusion coefficient of chloride ion, and the optimal replacement ratios had a limitation for each mineral admixtures. Also, the use of mineral admixtures by mass(replacement of OPC) enhance the resistance ability against chloride penetration compared with the plain concrete. The compressive strength was shown related to the diffusion coefficient of chloride ion, the compressive strength increases with the diffusion coefficient of chloride ion decreasing. Below the 50 MPa, the variation of diffusion coefficient of concrete replaced mineral admixtures was bigger than that of plain concrete.

• Journal of Advanced Navigation Technology
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• v.25 no.6
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• pp.510-516
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• 2021

Recently, the range of utilization and demand for unmanned aerial vehicle (UAV) has been continuously increasing, and research on the construction of a separate operating system for low-altitude UAV is underway through the development of a management system separate from manned aircraft. Since low-altitude UAVs also fly in the airspace, it is essential to establish technical standards and certification systems necessary for the operation of the aircraft, and research on this is also in progress. If the operating standards and certification requirements of the aircraft are presented, a test method to confirm this should also be presented. In particular, the accuracy of small UAV's navigation required during flight is required to be more precise than that of a manned aircraft or a large UAV. It was necessary to calculate a separate navigation error. In this study, we presented a test method for deriving navigation errors that can be applied to UAVs that have difficulty in acquiring long-term operational data, which is different from existing manned aircraft, and conducted verification tests.