• Geomechanics and Engineering
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• v.29 no.5
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• pp.567-582
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• 2022

In the present study, a series of physical experiments and numerical simulations were conducted to investigate the effects of mode I and mixed-mode I/II cracks on the fracture modes and stability of roadway tunnel models. The experiments and simulations incorporated different inclination angle flaws under both static and dynamic loads. The quasi-static and dynamic testing were conducted by using an electro-hydraulic servo control device and drop weight impact system (DWIS), and the failure process was simulated by using rock failure process analysis (RFPA) and AUTODYN software. The stress intensity factor was also calculated to evaluate the stability of the flawed roadway tunnel models by using ABAQUS software. According to comparisons between the test and numerical results, it is observed that for flawed roadways with a single radical crack and inclination angle of 45°, the static and dynamic stability are the lowest relative to other angles of fractured rock masses. For mixed-mode I/II cracks in flawed roadway tunnel models under dynamic loading, a wing crack is produced and the pre-existing cracks increase the stress concentration factor in the right part of the specimen, but this factor will not be larger than the maximum principal stress region in the roadway tunnel models. Additionally, damage to the sidewalls will be involved in the flawed roadway tunnel models under static loads.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.6
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• pp.41-46
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• 2023

Design of W-band TE10 to TEM mode converter for radial power combiner is proposed in this paper. The proposed structure is used with generally available pin to realize TEM mode and is designed to convert TE10 to TEM mode gradually using 2-step impedance transformer and back short. The pin of proposed mode converter is well bonded to the housing so that environment conditions such as vibration or shock are not affected. The proposed mode converter, in a back-to-back configuration, has less than 1.55 dB insertion loss and more than 10 dB return loss from 92.5 GHz to 97.7 GHz. Proposed converter is expected compact radar and various applications requiring for high power and stable environment conditions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.2
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• pp.175-181
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• 2024

In electrical power substations, bulky iron-core potential transformers (PTs) are installed in a tank of gas-insulated switchgear (GIS) to measure system voltages. This paper proposed a low-power voltage transformer (LPVT) that can replace the conventional iron-core PTs in response to the demand for the digitalization of substations. The prototype LPVT consists of a capacitive voltage divider (CVD) which is embedded in a spacer and an impedance matching circuit using passive components. The CVD was fabricated with a flexible PCB to acquire enough insulation performance and withstand vibration and shock during operation. The performance of the LPVT was evaluated at 80%, 100%, and 120% of the rated voltage (38.1 kV) according to IEC 61869-11. An accuracy correction algorithm based on LabVIEW was applied to correct the voltage ratio and phase error. The corrected voltage ratio and phase error were +0.134% and +0.079 min., respectively, which satisfies the accuracy CL 0.2. In addition, the voltage ratio of LPVT was analyzed in ranges of -40~+40℃, and a temperature correction coefficient was applied to maintain the accuracy CL 0.2. By applying the LPVT proposed in this paper to the same rating GIS, it can be reduced the length per GIS bay by 11%, and the amount of SF6 by 5~7%.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.24 no.3
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• pp.21-26
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• 2024

Design and fabrication method of W-band 12-way radial power combiner is proposed in this paper. The proposed structure is used with TE₁₀ to TEM mode converter, which is realized using 2-step impedance transformer. The pin structure for mode converter is well bonded to the housing so that environment conditions such as vibration or shock are not affected. Proposed W-band power combiner has less than 0.7 dB insertion loss and more than 13 dB return loss from 88 GHz to 98 GHz. The measured output isolations between each other are greater than 7.5 dB from 82 to 100 GHz and phase differences are less than 10 degree from 88 to 96 GHz. Proposed power combiner is expected compact radar and various applications requiring for high power and stable environment conditions.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.21 no.2
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• pp.55-60
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• 2015

Packaging of export cut lilies reduces physical damage during distribution like dropping, shock, vibration, compression and serves to protect from necrosis, microbial contamination and decomposition. Study on which packaging materials must be selected is necessary because it serves to direct effect maintaining quality and the degree of freshness. newspaper, perforated OPP film, Oriented Nylon film (ON), punched OPP film, OPP films are used in this study. Plant senescence of lilies was happened rapidly during storage at $25^{\circ}C$ rather than at $5^{\circ}C$. Also, water absorption, fresh weight at during storage $25^{\circ}C$ rather than at $5^{\circ}C$ In addition, fresh weight of lilies storage at $25^{\circ}C$ appears higher than at $5^{\circ}C$ all of the packaging materials except OPP because water absorption of lily storage at $5^{\circ}C$ appears higher than at $25^{\circ}C$, thereby suppressing the fresh weight reducing Also, effect on biological activity of lilies from shape of packaging material appears higher during storage at $5^{\circ}C$ than at $25^{\circ}C$. Compared with each packaging materials, newspaper packaging is the smallest effect on changes in biological activity of cut lilies during storage. Thus, the results demonstrate that flowering date are affected mainly by the storage temperature rather than packaging materials.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.39.3-40
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• 2015

The NISS (Near-infrared Imaging Spectrometer for Star formation history) onboard NEXTSat-1 is the near-infrared instrument optimized to the first small satellite of NEXTSat series. The capability of both imaging and low spectral resolution spectroscopy in the near-infrared range is a unique function of the NISS. The major scientific mission is to study the cosmic star formation history in local and distant universe. For those purposes, the main targets are nearby galaxies, galaxy clusters, star-forming regions and low background regions. The off-axis optical design of the NISS with two linear variable filters is optimized to have a wide field of view ($2deg.{\times}2deg.$) as well as the wide wavelength range from 0.95 to $3.8{\mu}m$. The mechanical structure is considered to endure the launching condition as well as the space environment. The dewar inside the telescope is designed to operate the infrared detector at 80K stage. From the thermal analysis, we confirmed that the telescope and the dewar can be cooled down to around 200K and 80K, respectively in order to reduce the large amount of thermal noise. The stray light analysis is shown that a light outside a field of view can be reduced below 1%. After the fabrications of the parts of engineering qualification model (EQM), the NSS EQM was successfully assembled and integrated into the satellite. To verify operations of the satellite in space, the space environment tests such as the vibration, shock and thermal-vacuum test were performed. Here, we report the results of the critical design review for the NISS.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.101-112
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• 2002

In this study, a new methodology fur the assessment of liquefaction potential is proposed and characteristics of the proposed methodology are verified. The experimental parameter of this methodology, that is, the plastic shear strain trajectory, is compared with the dissipated energy. It is shown that this parameter can express the liquefaction behavior which is generated by excess pore water pressure. This methodology takes advantage of the shear strain time history determined from the site response analysis based on the real time history of earthquake. In this site response analysis, shock type and vibration type records of similar predominant frequency are inputted. The liquefaction safely factors based on the proposed methodology and Korean detailed assessment related to the classical method are calculated from the results of the site response analysis and laboratory dynamic tests. Through this study, it is found that the proposed methodology can not only simulate the liquefaction behavior of saturated soils hut also express the seismic characteristics reasonably : leading type, predominant frequency, maximum acceleration, duration time.

• Journal of Conservation Science
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• v.17 s.17
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• pp.39-56
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• 2005

The Gwangtonggyo(bridge) on the Cheonggyecheon(river) is mainly composed of biotite granite with coarse grain. The rock consists mainly of quartz, plagioclase, microcline, orthoclase and biotite with lesser amount of muscovite, sericite and chlorite. Muscovite and sericite may be formed from feldspars and chlorite from biotite by alteration(including weathering). These rocks are relatively deteriorated by weathering, polluted water running the river and heavy traffic. The main phenomena of damages are surface exfoliation, grain separation, deceleration, pollution of organic and heavy chemical elements, cracks and breakage. These phenomena have been analyzed by polarized microscope, XRD and SEM/EDX. The analyzed results show organic pollution and secondarily formed gypsum and apatite on the rock surface and micro-pores. NaCl and $CaCO_3$ as rock salt and calcite probably may be formed secondarily in some points. Also heavy chemical elements such as Cr, Pb, Pd, W, La, Zn and Nd are polluted in some samples. The contacts between rocks are generally breakdown in small scale or cracks are developed due to mainly load and vibration shock of heavy traffic.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.331-346
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• 2018

In the tunnel of domestic high - speed railway, the main fire - fighting facility, fire - extinguishing passageway, is installed. However, due to the high pressure of the high - speed train, frequent breakage and maintenance are caused by strong shock and long - term vibration. In order to solve these problems, it is necessary to improve the fire door, but in Korea, it is installed by submitting a certificate by simple KS F 2296 performance test. At present, it is developed as a simple test certification by producing a real scale fireproof door without the theoretical examination in advance, so that a high cost for improvement is occurring in Korea. Therefore, through this study, structural analysis study which can preliminary structure review was carried out in order to design the refuge connection passage fire door and to improve the performance improvement. In order to secure the reliability of the result value, the official authentication test (KS F 2296) were compared.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.64.3-65
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• 2016

The NISS (Near-infrared Imaging Spectrometer for Star formation history) is the near-infrared instrument optimized to the Next Generation of small satellite series (NEXTSat). The capability of both imaging and low spectral resolution spectroscopy in the near-infrared range is a unique function of the NISS. The major scientific mission is to study the cosmic star formation history in local and distant universe. For those purposes, the main observational targets are nearby galaxies, galaxy clusters, star-forming regions and low background regions. The off-axis optical design is optimized to have a wide field of view ($2deg.{\times}2deg.$) as well as the wide wavelength range from 0.95 to $3.8{\mu}m$. Two linear variable filters are used to realize the imaging spectroscopy with the spectral resolution of ~20. The mechanical structure is considered to endure the launching condition as well as the space environment. The compact dewar is confirmed to operate the infrared detector as well as filters at 80K stage. The electronics is tested to obtain and process the signal from infrared sensor and to communicate with the satellite. After the test and calibration of the engineering qualification model (EQM), the flight model of the NSS is assembled and integrated into the satellite. To verify operations of the satellite in space, the space environment tests such as the vibration, shock and thermal-vacuum test were performed. Here, we report the test results of the flight model of the NISS.