• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.519-521
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• 2022

As appearance of diverse electric power supplies and fuel cells have been emerging, UAVs have capacity to prolong their flight missions. Nowadays, the rotary based UAVs that are commonly distributed on the open market, adapt rechargeable batteries and have around 50 centimeters in width and generally within 30 minutes in hovering flight capacities. UAV's flight time highly depends on the capacity and the weight of its batteries. To cope with the flight time, recharging methods are also being researched. their researches are mainly divided into coupled and decoupled in manner. In this article, we propose the method to refine the position more effectivly and precisely adapting QR Code and 3-D position estimation so that UAVs enable to land on the recharging system successfully.

• Journal of Advanced Navigation Technology
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• v.28 no.1
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• pp.123-128
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• 2024

When mid-span spectral inversion (MSSI), which inverts the propagated wave into phase-conjugated wave in the middle of the entire transmission distance, is combined with dispersion-managed link, it is very effective in compensating for the wavelength division multiplexed (WDM) signal distortion due to chromatic dispersion and nonlinear effects. In this MSSI combined dispersion-managed link, the shape of the dispersion map, channel data rate, channel wavelength and wavelength spacing, etc. affect the compensation and, consequently, determine the transmission distance and capacity of the WDM signal. In this paper, the compensation according to the extinction ratio of the return-to-zero (RZ) pulse that constitutes the WDM signal in the MSSI combined distributed control link was numerically analyzed. As a result of the simulation, it was conformed that the extinction ratio to obtain the best compensation should be determined depending on the shape of the dispersion map and the size of the residual dispersion per span, which determines the specific shape of the dispersion map. These results show a significant difference from the results in a general optical transmission system, where as the extinction ratio increases, the power difference between the '1' and '0' signals increases, thereby improving reception performance.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1209-1215
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• 2022

The selective catalytic reduction (SCR) is known as a very efficient method to reduce nitrogen oxides (NOx) and the catalyst performs reduction from nitrogen oxides (NOx) to nitrogen (N₂) and water vapor (H2O). The catalyst, which is one of the factors determining the performance of the nitrogen oxide (NOx) ruduction method, is known to increase catalyst efficiency as cell density increases. In this study, the reduction characteristics of nitrogen oxides (NOx) under various engine loads investigated. A 100CPSI(60Cell) catalysts was studied through a laboratory-sized simulating device that can simulate the exhaust gas conditions from the power generation engine installed in the training ship SEGERO. The effect of 100CPSI(60Cell) cell density was compared with that of 25.8CPSI(30Cell) cell density that already had NOx reduction data from the SCR manufacturing. The experimental catalysts were honeycomb type and its compositions and materials of V₂O₅-WO₃-TiO₂ were retained, with only change on cell density. As a result, the NOx concentration reduction rate from 100CPSI(60Cell) catalyst was 88.5%, and IMO specific NOx emission was 0.99g/kwh satisfying the IMO Tier III NOx emission requirement. The NOx concentration reduction rate from 25.8CPSI(30Cell) was 78%, and IMO specific NOx emission was 2.00g/kwh. Comparing the NOx concentration reduction rate and emission of 100CPSI(60Cell) and 25.8CPSI(30Cell) catalysts, notably, the NOx concentration reduction rate of 100CPSI(60Cell) catalyst was 10.5% higher and its IMO specific NOx emission was about twice less than that of the 25.8CPSI(30Cell) catalysts. Therefore, an efficient NOx reduction effect can be expected by increasing the cell density of catalysts. In other words, effects to production cost reduction, efficient arrangement of engine room and cargo space can be estimated from the reduced catalyst volume.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.1-8
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• 2015

Wind power systems have gained much attention due to the relatively high reliability, good infrastructures and cost competitiveness to the fossil fuels. Advances have been made to increase the power efficiency of wind turbines while less attention has been focused on structural integrity assessment of structural sub-systems such as towers and foundations. Among many parameters for integrity assessment, the most perceptive parameter may be the induced horizontal displacement at the hub height although it is very difficult to measure particularly in large-scale and high-rise wind turbine structures. This study proposes an indirect displacement estimation scheme based on the combined use of inclinometers and accelerometers for more convenient and cost-effective measurements. To this end, (1) the formulation for data fusion of inclination and acceleration responses was presented and (2) the proposed method was numerically validated on an NREL 5 MW wind turbine model. The numerical analysis was carried out to investigate the performance of the propose method according to the number of sensors, the resolution and the available sampling rate of the inclinometers to be used.

• Strategy21
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• s.31
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• pp.57-84
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• 2013

North Korea's continuous threats and provocative behaviors have aggravated tension on the Korean peninsula particularly with the recent nuclear weapons test. South Korea's best way to cope with this situation is to maintain the balance among three policy directions: dialogue, sanctions, and deterrence. Among the three, I argue that deterrence should be prioritized. There are different sources of deterrence such as military power, economic power, and diplomatic clouts. States can build deterrence capability independently. Alternatively, they may do so through relations with other states including alliances, bilateral relations, or multilateral relations in the international community. What South Korea needs most urgently is to maintain deterrence against North Korea's local provocations through the enhancement of independent military capability particularly by addressing the asymmetric vulnerability between militaries of the South and the North. Most of all, the South Korean government should recognize the seriousness of the negative consequences that North Korea's 'Nuclear shadow strategy' would bring about for the inter-Korea relations and security situations in Northeast Asia. Based on this understanding, it should develop an 'assertive deterrence strategy' that emphasizes 'multi-purpose, multi-stage, and tailored deterrence whose main idea lies in punitive retaliation.' This deterrence strategy requires a flexible targeting policy and a variety of retaliatory measures capable of taking out all targets in North Korea. At the same time, the force structures of the army, the air force, and the navy should be improved in a way that maximizes their deterrence capability. For example, the army should work on expanding the guided missile command and the special forces command and reforming the reserve forces. The navy and the air force should increase striking capabilities including air-to-ground, ship-to-ground, and submarine-to-ground strikes to a great extent. The marine corps can enhance its deterrence capability by changing the force structure from the stationary defense-oriented one that would have to suffer some degree of troop attrition at the early stage of hostilities to the one that focuses on 'counteroffensive landing operations.' The government should continue efforts for defense reform in order to obtain these capabilities while building the 'Korean-style triad system' that consists of advanced air, ground, and surface/ subsurface weapon systems. Besides these measures, South Korea should start to acquire a minimum level of nuclear potential within the legal boundary that the international law defines. For this, South Korea should withdraw from the Nuclear Non-proliferation Treaty. Moreover, it should obtain the right to process and enrich uranium through changing the U.S.-South Korea nuclear cooperation treaty. Whether or not we should be armed with nuclear weapons should not be understood in terms of "all or nothing." We should consider an 'in-between' option as the Japanese case proves. With regard to the wartime OPCON transition, we need to re-consider the timing of the transition as an effort to demonstrate the costliness of North Korea's provocative behaviors. If impossible, South Korea should take measures to make the Strategic Alliance 2015 serve as a persisting deterrence system against North Korea. As the last point, all the following governments of South Korea should keep in mind that continuing reconciliatory efforts should always be pursued along with other security policies toward North Korea.

• Strategy21
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• s.39
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• pp.5-46
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• 2016

North Korea's 4th nuclear test on Jan. 6 and following developments once again awakened the world into seriousness of the nuclear matters on the Korean peninsula. On March 2, UNSC adopted Resolution 2270 which is complemented by Seoul government's measures such as withdrawal from the Gaesung Industrial Complex (Feb. 9) and announcement of unilateral sanction (March 8). Seoul government also strongly urged the international community to strangle North Korea's 'financial resources.' The U.S., Japan, China, and other countries have issued unilateral sanctions to complement the UNSC measure. South Korea and the U.S. conducted their annual joint military drill (Resolve-Foal Eagle) in the largest-ever scale. North Korea, however, responded with demonstration of its nuclear capabilities and announcement of de facto 'nuclear-first' politics. North Korea test-fired a variety of delivery vehicles, threatened nuclear strikes against South Korea and the U.S., and declared itself as an 'invincible nuclear power armed with hydrogen bombs' at the 7th Workers 'Party Congress held in May, 2016. Considering the circumstantial evidences, the North's 4th nuclear test may have been a successful boosted fission bomb test. North Korea, and, if allowed to go on with its nuclear programs, will become a nuclear power armed with more than 50 nuclear weapons including hydrogen bombs. The North is already conducting nuclear blackmail strategy towards South Korea, and must be developing 'nuclear use' strategies. Accordingly, the most pressing challenge for the international community is to bring the North to 'real dialogue for denuclearization through powerful and consistent sanctions. Of course, China's cooperation is the key to success. In this situation, South Korea has urgent challenges on diplomacy and security fronts. A diplomatic challenge is how to lead China, which had shown dual attitudes between 'pressure and connivance' towards the North's nuclear matters pursuant to its military relations with the U.S, to participate in the sanctions consistently. A military one is how to offset the 'nuclear shadow effects' engendered by the North's nuclear blackmail and prevent its purposeful and non-purposeful use of nuclear weapons. Though South Korea's Ministry of Defense is currently spending a large portion of defense finance on preemption (kill-chain) and missile defense, they pose 'high cost and low efficiency' problems. For a 'low cost and high efficiency' of deterrence, South Korea needs to switch to a 'retaliation-centered' deterrence strategy. Though South Korea's response to the North's nuclear threat can theoretically be boiled down into dialogue, sanction and deterrence, now is the time to concentrate on strong sanction and determined deterrence since they are an inevitable mandatory course to destroy the North' nuclear-first delusion and bring it to a 'real denuclearization dialogue.'

• Strategy21
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• s.39
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• pp.82-113
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• 2016

This paper analyzes the contents and the effects of the UNSC 2270, and its implications to South Korea's defense strategy and navy. The UN Security Council passed strong sanctions against North Korea which punish North Korea's 4^th nuclear test. The sanctions compared to the previous ones require international society to take practical actions such as comprehensive trade bans as well as diplomatic isolation which will put significant pains on North Korea. Especially, these measures would greatly hamper economic development policy of Kim Joung-un regime. Because Kim Jung-un regime has inherent legitimacy problems which stems from the third family succession of the power, economic difficulties may play an important cause on the regime instability in the long term. In fact, the United States sees this possibility as an option to coerce North Korea in which North Korea choose denuclearization for its regime survival. Nevertheless, the prospects of the UN sanctions are not so optimistic. Considering North Korea's willingness for nuclear development and its level of nuclear technology, North Korea will try to play a gambit with the US and South Korea by exploiting its strategic advantages. North Korea's response will have three following strategies. First, it would actively pursue political and economic survival strategy by using China's support for the regime, strengthening its power grip in the name of countering US hostile policy, and enhancing peace propaganda. Second, North Korea will accelerate efforts to position its status as a nuclear de facto state. For this purpose, it could create nuclear crisis on the peninsula. Third, it would exploit local provocations as an exit strategy to get over the current situation. In order to counter North Korea's actions and punish North Korea's behavior strongly, South Korea needs following strategies and efforts. It should first make all the efforts to implement the UN sanctions. Strong and practical nuclear deterrence strategy and capability with the U.S. should be developed. Effective strategy and capabilities for the prevention and deterrence of North Korea's provocation should be prepared. For this purpose, North Korea's provocation strategy should be thoroughly reviewed. Active international cooperation is needed to punish and coerce North Korea's behavior. Finally, South Korea should prepare for the possible occurrence of North Korea's contingency and make use of the situation as an opportunity to achieve unification. All these strategies and efforts demand the more active roles and missions of South Korea's navy and thus, nullify North Korea's intention militarily.

• Strategy21
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• s.41
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• pp.261-293
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• 2017

Nuclear power is a way of attaining an enormous amount of energy with relatively small amount of resources and after it has been introduced to the submarine since 1954, there are approximately 150 of nuclear powered submarine currently on a mission around the world. This is due to the maneuverability, mountability and covertness of nuclear submarines. However, there are other tasks, not only the high level of nuclear technology that are needed to be dealt with in order to construct nuclear powered submarine. The biggest task of all is to secure the enriched uranium. Accordingly, this research is about the way of enriching and securing the nuclear fuel that are used in the nuclear submarine with the characteristics, merits and demerits of the nuclear submarine. Due to the fact that the pressurized water reactor in South Korea is the reactor that was originally built for the development of nuclear powered submarine, many parts is designed to be suitable for the submarine propulsion. However, in order to apply this to submarine it is needed to consider additional requests such as the position of reactor, accident-coping system, radioactive covering, reactor output adjustment and ship's pitch and roll in order to apply this to submarine. Nuclear submarines have much higher speed based on the powerful propulsion in comparison with diesel-electric submarine and also have bigger loading area. Besides, there is no need to snorkel and they also have advantages in covertness with the multi-noise proof system. The nuclear technology in South Korea has seen the dramatic development since 1962 and in 1998 reached to the level that we have succeeded in the localization of nuclear plant and exported the world-class one-piece small-sized reactor (SMART) to UAE. To operate these reactors, we import the whole quantity of low-enriched uranium and having our own uranium enrich facility is not probable because of the budget and international regulations. With the ROK/US nuclear agreement revised on 2015 November, the enrichment of uranium that are available without special permission has changed up to 20%. According to the assumption that we use the 20% enrichment of Uranium on U.S. virginia class submarine, it is necessary to change the fuel after 11 years and it will cause additional cost of 1 billion dollars. But the replace period by the uranium's enrichment rate is not fixed so that it is possible to change according to the design of reactor. Therefore, I would like to make a suggestion on two types of design concepts of nuclear submarine that can be operated for 30 years without nuclear fuel change by using the 20% enriched uranium from ONNp.First of all, it is possible by increasing the size of reactor by 3 times and it results in the 1,000t increase of the weight. And secondly, it is by designing the one piece reactor to insert devices such as steam turbine, condenser into the inside of nuclear core like the Rubis class submarines of France.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.9
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• pp.1045-1050
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• 2014

$N_2O$(Nitrous Oxide) is known as the third major GHG(Green House Gas) following $CO_2$(Carbon Oxide) and $CH_4$(Methane). The GWP(Global Warming Potential) factor of $N_2O$ is 310 times as large as that of $CO_2$ because $N_2O$ in the atmosphere is very stable, and it becomes a source of secondary contamination after photo-degradation in the stratosphere. Investigation on the cause of the $N_2O$ formation have been continuously reported by several researchers on power sources with continuous combustion form, such as a boiler. However, in the diesel engine, research on $N_2O$ generation which has effected from fuel components has not been conducted. Therefore, in this research, author has investigated about $N_2O$ emission rates which was changed by nitrogen and sulfur concentration in fuel on the diesel engine. The test engine was a 4-stroke direct injection diesel engine with maximum output of 12 kW at 2600rpm, and operating condition of that was set up at a 75% load. Nitrogen and sulfur concentrations in fuel were raised by using six additives : nitrogen additives were Pyridine, Indole, Quinoline, Pyrrol and Propionitrile and sulfur additive was Di-tert-butyl-disulfide. In conclusion, diesel fuels containing nitrogen elements less than 0.5% did not affect $N_2O$ emissions in the all concentrations and kinds of the additive agent in the fuel. However, increasing of the sulfur additive in fuel increased $N_2O$ emission in exhaust gas.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.216-221
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• 2017

Diesel engines have the highest brake thermal efficiency among internal combustion engines. Therefore, they are utilized in medium and large transportation vehicles requiring large amounts of power such as heavy trucks, ships, power generation systems, etc. However, diesel engines have a disadvantage of generating large quantities of nitrogen oxides during the combustion process. Therefore, the authors tried to reduce the amount of nitrogen oxides in marine diesel engines using a wet-type exhaust gas cleaning system utilizing the undivided electrolyzed seawater method. In this method, electrolyzed seawater in injected into the harmful gas discharge from the diesel engine using real seawater. The authors investigated the reduction of NO and NOx from the pH value, available chlorine concentration, and the temperature of electrolyzed seawater. The results of this experiment indicated that when the electrolyzed seawater is acidic, the NO oxidation rate in the oxidation tower is higher than that when the electrolyzed seawater has a neutral pH. Likewise, the NO oxidation rate increased with the increase in concentration of chlorine. Further, it was confirmed that the electrolyzed seawater temperature had no effect on the NO oxidation rate. Thus, the NOx exhaust emission value produced by the diesel engine was reduced by means of electrolyzed seawater treatment.