• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.5
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• pp.479-487
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• 2023

Recently, the destructive power of typhoons is continuously increasing owing to global warming. In a situation where the installation of floating wind turbines is increasing worldwide, concerns about the huge loss and collapse of floating offshore wind turbines owing to strong typhoons are deepening. A new type of disconnectable mooring system must be developed for the safe operation of floating offshore wind turbines. A new submersible mooring pulley considered in this study is devised to more easily attach or detach the floating of shore wind turbine with mooring lines compared with other disconnectable mooring apparatuses. To investigate the structural safety of the initial design of submersible mooring pulley that can be applied to an 8MW-class floating type offshore wind turbine, scale-down structural models were developed using a 3-D printer and structural tests were performed on the models. For the structural tests of the scale-down models, tensile specimens of acrylonitrile butadiene styrene material that was used in the 3-D printing were prepared, and the material properties were evaluated by conducting the tensile tests. The finite element analysis (FEA) of submersible mooring pulley was performed by applying the material properties obtained from the tensile tests and the same load and boundary conditions as in the scale-down model structural tests. Through the FEA, the structural weak parts on the submersible mooring pulley were reviewed. The structural model tests were conducted considering the main load conditions of submersible mooring pulley, and the FEA and test results were compared for the locations that exceeded the maximum tensile stress of the material. The results of the FEA and structural model tests indicated that the connection structure of the body and the wheel was weak in operating conditions and that of the body and the chain stopper was weak in mooring conditions. The results of this study enabled to experimentally verify the structural safety of the initial design of submersible mooring pulley. The study results can be usefully used to improve the structural strength of submersible mooring pulley in a detailed design stage.

• Strategy21
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• s.41
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• pp.232-260
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• 2017

The purpose of this paper is to open a debate about what kind of deterrent strategy the ROK military should pursue in the era of NK's weapons of mass destruction and missile threats. I argue that the ROK military needs a comprehensive deterrent strategy that reflects the international security situations and trends and that builds on clear understanding of the basic concepts and how deterrence operates. The paper starts with surveying the basic knowledge of deterrence from the perspectives of both theory and practice. Then, it provides explanations on why deterrence against NK can be particularly difficult given the security environment in and around the Korean peninsula. For example, South Korea and North Korea hardly share 'common knowledge' that serves as a basic element for the operation of deterrence. Deterrence against North Korea involves complex situations in that both deterrence and compellence strategies may be relevant particularly to North Korea's WMD and missile threats. It also involves both immediate and general deterrence. Based on the discussion, I suggest several ideas that may serve as guidelines for establishing a deterrent strategy against NK. First, our threats for deterrence should be the ones that can be realized, particularly in terms of the international norms. In other words, they must be considered appropriate among other nations in the international community. Second, there should be separate plans for the different kinds of threats: one is conventional, local provocations and the other is WMD/missile related provocations. Third, we should pursue much closer cooperative relations with the U.S. military to enhance the effectiveness of immediate deterrence in the Korean peninsula. Fourth, the ROK military should aim to accomplish 'smart deterrence' maximizing the benefits of technological superiority. Fifth, the ROK military readiness and structure should be able to deny emerging North Korean military threats such as the submarine-launched ballistic missiles and intercontinental ballistic missiles. Lastly, in executing threats, we should consider that the current action influences credibility and reputation of the ROK, which in turn affect the decisions for future provocations. North Korea's WMD/missile threats may soon become critical strategic-level threats to South Korea. In retrospect, the first debate on building a missile defense system in South Korea dates back to the 1980s. Mostly the debate has centered on whether or not South Korea's system should be integrated into the U.S. missile defense system. In the meantime, North Korea has become a small nuclear power that can threaten the United States with the ballistic missiles capability. If North Korea completes the SLBM program and loads the missiles on a submarine with improved underwater operation capability, then, South Korea may have to face the reality of power politics demonstrated by Thucydides through the Athenians: "The strong do what they have the power to do, the weak accept what they have to accept."

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.5
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• pp.602-611
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• 2015

Even though GNSS provides highly accurate navigation information all over the world, it is vulnerable to jamming in the electronic warfare due to its weak signal power. The United States and Korea have plans to use terrestrial navigation systems as back-up systems during outage of GNSS. In order to develop back-up systems of GNSS, an M&S software platform is necessary for performance evaluation of various vehicle trajectories and integrated navigation systems. In this paper a design method of an M&S software is proposed for evaluation of multiple radio positioning integration systems. The proposed M&S software consists of a navigation environment generation part, a navigation algorithm part, a GUI part and a coverage analysis part. Effectiveness of the proposed design method is shown by implementing an M&S software for the GPS, DME and eLoran navigation systems.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.27-32
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• 2008

In the signals-shadowed areas, In order to providing the suitable signals reception level repeaters are used for relay the signals. Repeater receives the weak signals and amplifies it up to required power level, The amplified signals get radiated by the various methods. Both antenna distribution and LCX(Leakage Coaxial Cable) are typical methods in the repeater and BTS signals radiation. Their applications are depended on the environment condition and frequency band. Generally the antenna distribution are used for the mobile telecommunication networks which use the higher frequency band than 500MHz. On the other side, LCX distribution is suitable to the frequency band under 500MHz. The network plan of repeater in FM, T-DMB, Fire Radio and Internal subway communication network are the typical LCX application fields. Cell planning with repeaters are based on the free space loss, LCX connection loss and actual field data. The actual field data can be the most important factor to design the network planning.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.11 no.4
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• pp.1-6
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• 2015

In this study, energy performance of two types of food dryers which are electric heater and heat pump is studied experimentally. With drying chamber temperatures controlled at 45, 50 and $55^{\circ}C$, sliced radish is dried from an initial mass of 90 to final 7 kg. Moisture content, drying time, total power consumption, MER (moisture extraction rate, kg/h) and SMER (specific moisture extraction rate, kg/kWh) are measured and analyzed. As the drying chamber temperature is increased, drying time is shortened but energy efficiency is reduced for both types. For an electric heater dryer, the effect of chamber temperature on drying time is significant but less significant on energy efficiency. For a heat pump dryer, the dependence of chamber temperature on drying time is weak but strong on energy efficiency. Temperature levels have little effect on electric heater dryer performance but strong effect on heat pump dryer which operates on a vapor compression refrigeration cycle. The energy performance of the heat pump dryer is superior with an average SMER of 2.175 kg/kWh which is 2.22 times greater than that of the electric heater dryer with SMER of 1.224 kg/kWh.

• Corrosion Science and Technology
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• v.3 no.5
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• pp.198-208
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• 2004

Although there has been no general agreement on the mechanism of primary water stress corrosion cracking (PWSCC) as one of major degradation modes of Ni-base alloys in pressurized water reactors (PWR's), common postulation derived from previous studies is that the damage to the alloy substrate can be related to mass transport characteristics and/or repair properties of overlaid oxide film. Recently, it was shown that the oxide film structure and PWSCC initiation time as well as crack growth rate were systematically varied as a function of dissolved hydrogen concentration in high temperature water, supporting the postulation. In order to understand how the oxide film composition can vary with water chemistry, this study was conducted to characterize oxide films on Alloy 600 by an in-situ Raman spectroscopy. Based on both experimental and thermodynamic prediction results, Ni/NiO thermodynamic equilibrium condition was defined as a function of electrochemical potential and temperature. The results agree well with Attanasio et al.'s data by contact electrical resistance measurements. The anomalously high PWSCC growth rate consistently observed in the vicinity of Ni/NiO equilibrium is then attributed to weak thermodynamic stability of NiO. Redox-induced phase transition between Ni metal and NiO may undermine the integrity of NiO and enhance presumably the percolation of oxidizing environment through the oxide film, especially along grain boundaries. The redox-induced grain boundary oxide degradation mechanism has been postulated and will be tested by using the in-situ Raman facility.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.824-830
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• 2010

PLC_Zigbee system, implemented in a previous study, uses ZigBee Node based on PLC (Power Line Communication). The weak point of the system is that the long distance powerline communication and PLC is impossible to use in the areas where the powerline is not installed. In this paper, we added CDMA (Code Division Multiple Access) module using a data transfer method of SMS (Short Message Service) and XBee of WSN (Wireless Sensor Network) module to the previous system, and got around the restriction of place and environment of PLC system through the interfacing of each communication media. We, thus, implemented a wide range of real monitoring system.

• Journal of Environmental Science International
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• v.28 no.2
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• pp.169-182
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• 2019

Temporal and spatial variations in surface ozone concentrations in Busan were investigated by using observation data from urban air quality sites during 2001-2016. The annual ozone concentrations showed a significant increasing trend of $+0.40ppb\;yr^{-1}$ in this period, with a more rapid increase of $+0.81ppb\;yr-1$ since 2010. For the monthly analysis, the increase in ozone concentration was the greatest in August ($+0.68ppb\;yr-1$). These ozone trends were due mainly to rising temperature ($+0.05^{\circ}C\;yr^{-1}$) and weak decreasing precipitation ($-6.42mm\;yr^{-1}$). However, the extreme weather events (heat wave, localized heavy rain, etc.) lead to an increase in short-term variability of ozone since 2010. The relatively low ozone concentrations in the downtown area were caused by high NOx emissions from mobile sources. The increases in ozone concentrations were observed at most of the air quality monitoring sites due to the reductions in anthropogenic emissions of NOx during 2001-2015. However, in the southern coastal area, lower rates of increase in ozone concentrations were observed by $-0.10{\sim}0.25ppb\;yr^{-1}$ due to the significant NOx emitted by ships in the Busan port and Busan new port.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.6 no.3
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• pp.36-54
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• 1995

The error performance of digital radio signals (i.e., M-ary PSK signal, DQPSK signal, MSK signal, GMSK signal) interfered by impulsive noise and electromagnetic interference (EMI) is analyzed and discussed. In analysis at first, the error rate equations have been derived in an electromagnetic interference plus impulsive noise environment. And then, the error performance has been evaluated and shown in figures as a function of carrier-to-noise ratio, carrier-to-interference ratio, impu- lsive index, gaussian noise to impulsive noise power ratio, and interference index to measure the amount of error degradation in digital radio signals. From the obtained results we have known that in the presence of m-distributed tone interference plus inpulsive noise, the more significant the electromagnetic interference amplitude varies, the more significant performance degradation is produced. The listing the digital radio signals from the most degraded to the least is that DQPSK, GMSK, QPSK and MSK signal. In the constant amplitude tone interference plus impulsive noise environment, the effect of in- terference nearly disappears over about 20dB in CIR. The effect of constant tone interference on error rate performance is reduced more remarkably in the region from 10dB to 15dB in CIR. In both enviroments of m-distributed tone interference and constant amplitude tone interference, the more electromagnetic interference amplitude varies and CIR increases, the more error perfor- mance is improved. But it is found out that the performance can not be improved significantly even the electromagnetic interference becomes weak. This describes that the impulsive noise affects dominantly to the performance degradation.

• The Journal of Korean Society for School & Community Health Education
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• v.3
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• pp.15-33
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• 2002

Researchers' common findings is that there are positive or negative effect of alcohol expectancy on drinking behavior. Therefore we would effectively prevent troublesome drinking of the youth and university students by inquiring and controlling critical factors affecting alcohol expectancy. The purposes of this thesis are, first, to empirically test factors affecting the alcohol expectancy level of elementary schoolchild(potential drinker).; second, to suggest the necessity for development of pre-alcohol prevention programs. On the basis of previous research, eighteen factors included in four categories(general characters, environmental characters, alcohol knowledge, drinking experience) affecting alcohol expectancy level were found out. 623 subjects used in this study were drawn from 8 elementary schools in Daegu, Korea. The empirical results suggested that the alcohol expectancy level of elementary schoolchildren was negative in general. And it was proved that 9 factors were significantly correlated with alcohol expectancy level. To put it concretely(see Fig.), (1) It was proved that schoolchildren with bad environment(live in oneself, displeased drinking feeling) rather than good environment(live with parents, nice drinking feeling) for drinking had more negative alcohol expectancy. (2) Korean traditional culture that partakes of sacrificial food and drink have an influence on the first drinking of most elementary schoolchildren. And it was proved that schoolchildren with this drinking experience rather than any other motives had less negative alcohol expectancy. (3) It was proved that schoolchildren adapting themselves rather than being difficult in school life had more negative alcohol expectancy. And the more knowledge about alcohol or drinking schoolchildren had, the more they had negative alcohol expectancy (4) It was proved that schoolchildren having drinking experience or drinking at present rather than having no drinking experience or not-drinking at present had less negative alcohol expectancy. (5) It was proved that schoolchildren having strong drinking intention rather than having weak or no drinking intention in the future had more positive alcohol expectancy. Based on previous results, guideline for development of pre-alcohol prevention programs can be represented: discriminated programs development on educatee, drinking education programs development increasing the power of self-control about alcohol and drinking, social education or continuing education programs development on drinking, open preschool education to substantially prevent drinking or alcoholism etc. The findings, however, should be interpreted with caution, because this study has several limitations in measurement and sampling as follows. First, selection bias because of limited selection of sampling. It is because the subjects are drawn from only 8 elementary schools in Daegu. Second, less refined measurement ; Therefore, it is necessary to develop more detailed measures on alcohol knowledge, alcohol expectancy level especially. Further researches should be suggested and encouraged with more refined methodologies.