• Journal of Positioning, Navigation, and Timing
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• v.7 no.4
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• pp.217-226
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• 2018

According to the Korea Coast Guard's maritime disaster statistics (Korea Coast Guard 2017, Korean Statistical information Service 2018), an average of 2,140 marine accidents occurred every year for the past 6 years and the number of accidents is increasing every year. Among them, maritime accidents of fishing vessels are the most frequent, and recently accidents involving fishing boat and leisure vessels are rapidly increasing as well. In particular, the number of accidents involving leisure vessels increased to about one-third of the accidents of fishing vessels, and emergency rescue requests are increasing every year accordingly. However, the number of crash accidents involving users of small vessels and marine leisure activities are increasing because of the difficulties of installing navigation equipment and electronic navigation charts. Recently, the demand for precise positioning using mobile devices is increasing in the fields of maritime safety, piloting support, and coastal survey. Although various applications of smart devices provide location-based services for users, the measurement results are discontinuous when using the position coordinates of the National Marine Electronics Association (NMEA) calculated by smartphone. Recently, Google announced that they will provide GPS raw data to developers from Android 7.0 Nougat. As a result, developers have an opportunity to receive precise carrier phase and code measurements to make more accurate positioning according to the performance of Android devices. This study analyzed GPS positioning performance using Android devices, and compared and analyzed the positioning performance at sea with high-performance GPS receivers.

• Journal of Wetlands Research
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• v.21 no.2
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• pp.157-162
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• 2019

Recently, the occurrence of unusual heavy snow and cold are increasing due to the unusual global climate change. In particular, the temperature dropped to minus 69 degrees Celsius in the United States on January 8, 2018. In Korea, on February 17, 2014, the auditorium building in Gyeongju Mauna Resort was collapsed due to the heavy snowfall. Because of the tragic accident many studies on the reduction of snow damage is being conducted, but it is difficult to predict the exact damage due to the lack of historical damage data, and uncertainty of meteorological data due to the long distance between the damaged area and the observatory. Therefore, in this study, available data were collected from factors that are thought to be corresponding to snow damage, and the amount of snow damage was estimated categorically using a random forest. At present, the prediction accuracy was not sufficient due to lack of historical damage data and changes of the design code for green houses. However, if accurate weather data are obtained in the affected areas. the accuracy of estimates would increase enough for being used for be the degree preparedness of disaster management.

• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.5
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• pp.131-138
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• 2023

In this paper, a free space optical communication device that can be used in a mobile base station of several km or less was fabricated and its characteristics were investigated. To overcome the loss due to atmospheric transmission, an optical fiber amplifier (EDFA) with an output of 23 dBm or more was used. In order to increase the focusing speed and miniaturization of the laser beam, an optical lens was manufactured, and a transmission lens was designed to have beam divergence within the range of 1.5 to 1.8 [mrad]. A PT module that controls PAN/TILT was fabricated in order to reduce pointing errors and effective automatic alignment between transceiver devices. In this study, Reed-Solomon (RS) code was used to maintain the transmission quality above a certain level. It was manufactured to be able to communicate at a wireless distance of 300m in a weather situation with visibility of 300m. For performance measurement, it was measured using BERT and eye pattern analyzer, and it was confirmed that BER can be maintained at 2.5Gbps.

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.521-530
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• 2015

Design of fiber reinforced ultra-high strength concrete members should be verified with analytical or experimental methods for safety. Members with compressive strength larger than limitation of current design code usually be designed with analytical verification using stress-strain relation of concrete and reinforcements. For this purpose, mechanical characteristics of steel fiber reinforced ultra-high strength concrete were defined under uniaxial compression. Mix proportions of test specimens were based on reactive powder concrete and straight steel fibers were mixed with different volume fraction. Compressive strength of matrix were distributed from 80 MPa to 200 MPa. Effect of fiber inclusion were investigated : increase of compressive strength of concrete, elastic modulus and strain corresponding to peak stress. For the wide range application of investigation, previously tested test specimens were collected and used for investigation and estimation equation. Based on the investigation and evaluation of previous research results and estimation equation of mechanical characteristics of concrete, regression equations were suggested.

• Journal of Korean Society of Forest Science
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• v.109 no.2
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• pp.211-222
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• 2020

This study tried to find out whether there is a change over time in the functional classification of forests in relation to human demand for forests. The level in which the concept of ecosystem services has been considered in national forest management plans was also examined. A total of 98 current and previous national forest management plans were available for this study. The composition ratios of the six functions of forests in both the current and previous national forest management plans were surveyed. We used a parametric t-test when the mean values of two (current and previous) groups were normally distributed and used nonparametric Wilcoxon code rank test when the assumption of normality was not met. Timber production forests were shown to follow a normal distribution, while five others, including water regeneration forests, disaster prevention forests, natural environment conservation forests, recreation forests, and living environment conservation forests were not shown to follow a normal distribution. Timber production forests and natural environment forests showed significant changes in the proportion of forest area between previous and current forest management plans. The concept of 'ecosystem services' began to actively appear in the 6th Basic Forest Plan, which started in 2018. However, the level of frequency of the ecosystem services mentioned varied by Regional Forest Services.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.4
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• pp.269-282
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• 2006

We numerically studied tsunami propagation characteristics through Korean Straits based on nonlinear shallow water equation, a robust wave driver of the near field tsunamis. Tsunamis are presumed to be generated by the earthquake in Tsuhima-Koto fault line. The magnitude of earthquake is chosen to be 7.5 on Richter scale, which corresponds to most plausible one around Korean peninsula. It turns out that it takes only 60 minutes for leading waves to cross Korean straits, which supports recently raised concerns at warning system might be malfunctioned due to the lack of evacuation time. We also numerically obtained the probability of tsunami inundation of various levels, usually referred as tsunami hazard, along southern coastal area of Korean Peninsula based on simple seismological and Kajiura (1963)'s hydrodynamic model due to tsunami-generative earthquake in Tsuhima-Koto fault line. Using observed data at Akita and Fukaura during Okushiri tsunami in 1993, we verified probabilistic model of tsunami height proposed in this study. We believe this inundation probability of various levels to give valuable information for the amendment of current building code of coastal disaster prevention system to tame tsunami attack.

• Fire Science and Engineering
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• v.27 no.3
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• pp.38-46
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• 2013

Permanent water supply and water sprinkling systems are essential to protect major forests and facilities from forest fire. Back in 2005, Naksan Temple, a valuable cultural asset of Korea, was burned down in a forest fire that took place in Yangyang. This started a series of movements including installing water supply facilities and managing forests near important cultural assets. As for the existing facilities, however, they were installed without any standard guidelines for management and installation according to each constructor's specifications, which were based on the National Fire Safety Code 109. Unfortunately, this is not effective in protecting facilities from forest fires such as they have a small protection area, limited simultaneous sprinkling, and a difficult the movement of fire hose. Against this background, the study examines the condition of water supply facilities currently in use, identifies their deficiencies, and suggests how to improve the criteria for water supply service to effectively prevent forest fire. Specifically, three systems were proposed: Water Sprinkler Tower System for preventing spread of crown fires, and Forest Fire Hydrant System and Portable Water Spray System to be effective for suppressing surface fires. In addition, the standards on the performance and components of water pumps are also suggested.

• Fire Science and Engineering
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• v.31 no.6
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• pp.47-52
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• 2017

The recent tragic outbreak of fire at the Grenfell Tower in the United Kingdom compels all branches of government to reexamine and reassess the safety measures against fires in high-rise buildings from a broad perspective. Accordingly, this study examined what problems stem from the current evacuation codes by comparative analysis of the high-rise apartment evacuation codes that range over various individual laws before introducing a new evacuation code. The outcome of this study can be utilized as basic data for amending the existing evacuation codes for high-rise buildings. The codes related to high-rise building evacuation include the Building Act, the Housing Act, the Skyscraper Disaster Management Act, and the Fire-Fighting System Act. Some local governments have also drawn up their own codes and put them into practice. Comparative analysis of the major evacuation codes has helped identify a variety of problems, such as different codes being applied to each individual law and ordinance, the use of additional codes other than the provisions of laws and ordinances, and the in effectiveness of evacuation codes. Most of these problems occur when diverse codes are applied to a single building, which means that cooperation among the relevant ministries is urgently needed to improve the related codes in the future.

• Journal of Broadcast Engineering
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• v.12 no.6
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• pp.630-640
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• 2007

This paper presents the design of service model, transport channel, and service signaling for the Terrestrial DMB Automatic Emergency Alert Service (AEAS) Standard. The paper begins with the analysis of technical backgrounds related to the design topics. Next, the raper presents the design of service model for the AEAS. Since, unlike the regular T-DMB services, the AEAS is event-driven and common to all services, some problems have been identified to design a service model conforming to the T-DMB standard. So, the paper proposes a new concept, called the common service, and the AEAS is modeled using the common service. Next, in order to decide the transport channel for the alert information, the paper proposes to divide the alert information into the message which contains code/text-based essential information, and the supplemental multimedia information. Then, the paper tries to find the most efficient transport channels. Emergency Warning Service (EWS) which uses FIG 5/2 is selected for the delivery of the message. The paper proposes no constraints on delivery of supplemental information except that it shall use the MSC. Finally, it proposes the service signaling for the common service and transport channel. Due to the problems of conventional signaling using the MCI, it proposes a new signaling method. The paper will contribute as a guideline to the development for emergency alert service standards fur other broadcasting media.