• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.2
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• pp.172-180
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• 2016

A cubesat classified as a pico-satellite typically uses commercial-grade components that satisfy the vibration and thermal environmental specifications and goes into mission orbit even after undergoing minimum environment tests due to their lower cost and short development period. However, its reliability exposed to the physical environment such as on-orbit thermal vacuum for long periods cannot be assured under minimum tests criterion. In this paper, we have analysed the reliability and life prediction of the failure mechanisms of the cubesat mission board during its service life under the launch and on-orbit environment by using the sherlock software which has been widely used in automobile fields to predict the reliability of electronic devices.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.6
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• pp.523-530
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• 2017

Laser-Induced Breakdown Spectroscopy (LIBS) which a plasma is irradiated at a specific wavelength depending on the material when a high-energy laser is irradiated, and a Raman spectroscopy which measures rotation and vibration in molecules as light-scattering phenomenon occurs, are attracting attention as a space exploration technology because of the advantages of high accuracy and real-time analysis, and the ability to perform long-range detection. In this study, the tendency of the laser spectrum according to the change of the soil component was analyzed by laser spectroscopy and the two - dimensional chemical distribution was conducted based on the trend of laser spectrum. We have also established the environment of Mars (4-7 torr) and lunar atmosphere (<1 torr) in experimental setup, to prove that it is possible to measure by difference of soil chemical composition using LIBS and Raman spectroscopy even in artificial space environment.

• Structural Engineering and Mechanics
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• v.54 no.1
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• pp.105-119
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• 2015

Structural damage detection using modal strain energy (MSE) is one of the most efficient and reliable structural health monitoring techniques. However, some of the existing MSE methods have been validated for special types of structures such as beams or steel truss bridges which demands improving the available methods. The purpose of this study is to improve an efficient modal strain energy method to detect and quantify the damage in complex structures at early stage of formation. In this paper, a modal strain energy method was mathematically developed and then numerically applied to a fixed-end beam and a three-story frame including single and multiple damage scenarios in absence and presence of up to five per cent noise. For each damage scenario, all mode shapes and natural frequencies of intact structures and the first five mode shapes of assumed damaged structures were obtained using STRAND7. The derived mode shapes of each intact and damaged structure at any damage scenario were then separately used in the improved formulation using MATLAB to detect the location and quantify the severity of damage as compared to those obtained from previous method. It was found that the improved method is more accurate, efficient and convergent than its predecessors. The outcomes of this study can be safely and inexpensively used for structural health monitoring to minimize the loss of lives and property by identifying the unforeseen structural damages.

• Journal of the Korean housing association
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• v.25 no.2
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• pp.1-9
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• 2014

This study investigates supply patterns and residential characteristics of the Urban-type Housing in Seoul. There have been 3,336 buildings and 71,790 housing units approved until the end of 2012. One-room apartments and small units less than 30 $m^2$ of residential area amount to 81% and 82% of total units, respectively. Major findings are as follows. First, single- and two-person households less than 30 years of age are mostly lived in the housing. Respondents are mainly professional and white-collar (43%) and service and sales workers (27%). Most of them are mid-income classes (67%), which is twice more than that of single- and two-person households in Seoul. They pay 672 thousand won in rent more than average rent of mid-income class. The rent to income ratios are 29.9% for single households and 24.5% for two-person households, which are higher than that of mid-income bracket. Third, their satisfaction level is relatively high in internal environment and access to public service facilities, but not in external environment and community service facilities. They are satisfied with security and daylight, walking and safety, access to public transport and parking space, but not with noise and vibration, natural environment, access to park and cultural and sports facilities, and most community service facilities. It is necessary to reexamine the articles of deregulation and prepare design standards while considering different housing and locational types.

• Wind and Structures
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• v.17 no.1
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• pp.43-68
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• 2013

The fluctuating wind induced vibration is one of the most important factors which has been taken into account in the design of long-span bridge due to the low stiffness and low natural frequency. Field measurement characteristics of sustained wind on structure site can provide accurate wind load parameters for wind field simulation and structural wind resistance design. As a suspension bridge with 1490 m main span, the Runyang Suspension Bridge (RSB) has high sensitivity to fluctuating wind. The simultaneous and continuously wind environment field measurement both in mid-span and on tower top is executed from 2005 up to now by the structural health monitoring system installed on this bridge. Based on the recorded data, the wind characteristic parameters, including mean wind speed, wind direction, the turbulence intensity, the gust factors, the turbulence integral length, power spectrum and spatial correlation, are analyzed in detail and the coherence functions of those parameters are evaluated using statistical method in this paper. The results indicate that, the turbulence component of sustain wind is larger than extremely strong winds although its mean wind speed is smaller; the correlation between turbulence parameters is obvious; the power spectrum is special and not accord with the Simiu spectrum and von Karman spectrum. Results obtained in this study can be used to evaluate the long term reliability of the Runyang Suspension Bridge and provide reference values for wind resistant design of other structures in this region.

• Journal of Environmental Impact Assessment
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• v.20 no.3
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• pp.397-409
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• 2011

This study was carried out for improving the effectiveness of water resources development project through local resident opinions in the environmental impact assessment(EIA). The EIA reports of seven dams were examined. Four dams -Youngju Dam, Seongduck Dam, Buhang Dam and Hantangang Dam- which included many local opinions including 470 opinions of 341 local residents were selected to be analyzed. Local residents submitted their opinions in the six fields which are meteorological phenomena, water quality, land use, fauna and flora, noise and vibration, and residence, and the major opinions of those opinions came from the atmosphere environment field which is 32% of total opinions and social and economic field which is 38% of total opinions, respectively. In submerged area, opinions of the measure for migration and compensation were 91% and in non-submerged area, opinions of the measure for meteorological phenomena was 86%. Those percentages were maximum in each area. Opinions concerned meteorological phenomena were 86% and 53% in Youngju Dam and Seongduck Dam where area is surrounded by existing dam, but there was only 9% and 0% of opinions in Buhang Dam and Hantangang Dam where area is without existing dam nearby. The reformation methods which reflected the resident's opinions were suggested on EIA in dam development projects. First of all, reliability and objectivity of the field of meteorological phenoma should be enhanced by scientific prediction of the phenomenon days. Secondly, techniques reducing uncertainty of various water quality prediction models ought to be developed and effectiveness of the reduction strategies in environmental impact should be quantified. Finally, the draft of EIA report should involve the detailed plans of migration and compensation's procedures, criteria and measures to support.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.6
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• pp.536-541
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• 2012

An instrumented pod has been developed to measure the aeroacoustic environment as well as the conventional data such as load, vibration, and aerodynamic heating of fighters during flight tests, confirming to the recently developed external pod design for fighters. This study presents the development of the measurement system in detail, being the first indigenous effort in its kind. The pod was designed to meet the requirements of the MIL-HDBK-1763 and MIL-STD-810 Method 515, which are the base to determine the locations and range of sensors. The Endevco 8510B-2 was selected as the sensor to withstand the harsh environment during the flight tests. In order to assess the integrity of the fabricated pod design, a ground run-up test of a KF-16 has been conducted with the pod installed at Station 5. The test results show that the system works well but the sound level exceeds the predetermined sensor range. The sensor range has been readjusted for flight test performed later.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.29 no.3
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• pp.383-393
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• 2019

Objectives: The proportion of those working beyond 53 hours a week in 2018 has reached 16.8% of the total number of workers in the Republic of Korea (Statistics Korea, 2018). Although there are many studies that have dealt with the correlation of long working hours and increasing risk of work-related health problems, studies dealing with the factors impacting work-related health problems of workers according to their working hours are few. This study aims to ascertain factors impacting work-related health problems of workers based on their working hours through thorough research on their work environment. Methods: Necessary factors for this study were extracted from 'the 4th Korean Working Conditions Survey to analyze details on normal characteristics and work environments used for the study analysis, work hours, and health problems related to work. Results: The results are as follows: First, men showed a greater probability of exposure to work-related health problems than did women, especially in the 50s age group, which showed the highest potential for health problems from work among age groups. Second, service providers and sales professionals showed a higher probability of work-related health problems. Third, for the work environment, health problems at work related to vibration, noise, chemical and poison exposure, exhaustion, pain, standing position, and repeated motion showed a higher probability if the work hours are long. Conclusions: This study suggests that the minimization of overtime labor would prevent work-related health problems and diseases, improve the well-being of workers, and decrease the negative impact on workers in the subject area.

• Journal of the Korea Society of Computer and Information
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• v.28 no.8
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• pp.111-118
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• 2023

In this paper, we propose a WiFi-based joystick with an acceleration sensor and a vibration sensor that can be used in flight simulators and VR fields. The flight simulator is a technology belonging to the ICT and SW application field and provides a simulation environment that reproduces the aircraft environment. Existing flight simulator control devices are fixed to a specific device and the user's activity area is limited. In this paper, a 3D space manipulation device was implemented for the user's free use of space. In addition, the proposed control device is designed as a WiFi communication board and display that displays information and performs 3-axis sensing for accurate and sophisticated control compared to existing VR equipment controllers. And the applicability was confirmed by implementing a Unity-based virtual environment. As a result of the implementation device verification, it was confirmed that the control device operates normally through the communication interface, It was confirmed that the sensing values in the game and the sensing values measured on the implemented board matched each other. The results of this study can be used for VR and various metaverse related contents in addition to flight simulators.

• Smart Structures and Systems
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• v.25 no.2
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• pp.241-254
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• 2020

Using confined shape memory alloy (SMA) bar or plate, this study proposes an innovative self-centering damper. The damper is essentially properly machined SMA core, i.e., bar or plate, that encased in buckling-restrained device. To prove the design concept, cyclic loading tests were carried out. According to the test results, the damper exhibited desired flag-shape hysteretic behaviors upon both tension and compression actions, although asymmetric behavior is noted. Based on the experimental data, the hysteretic parameters that interested by seismic applications, such as the strength, stiffness, equivalent damping ratio and recentering capacity, are quantified. Processed in the Matlab/Simulink environment, a preliminary evaluation of the seismic control effect for this damper was conducted. The proposed damper was placed at the first story of a multi-story frame and then the original and controlled structures were subjected to earthquake excitations. The numerical outcome indicated the damper is effective in controlling seismic deformation demands. Besides, a companion SMA damper which represents a popular type in previous studies is also introduced in the analysis to further reveal the seismic control characteristics of the newly proposed damper. In current case, it was found that although the current SMA damper shows asymmetric tension-compression behavior, it successfully contributes comparable seismic control effect as those having symmetrical cyclic behavior. Additionally, the proposed damper even shows better global performance in controlling acceleration demands. Thus, this paper reduces the concern of using SMA dampers with asymmetric cyclic behavior to a certain degree.