• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.1218-1220
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• 2000

A new control technique is proposed to reduce the distortion of UPS output voltage. The Load of UPS is rectifier which has many harmonics on its output current in many cases. The distortion of output voltage by the harmonics is repeated at the same position in one cycle. Therefore we can assume that the next cycle wave form would be similar to the previous one. The repeated error can be estimated and be compensated by the Multi controller at every sampling times.

• Journal of Power Electronics
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• v.11 no.3
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• pp.342-349
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• 2011

We propose a torque and pitch control scheme for variable speed wind turbines with permanent magnet synchronous generator (PMSG). A torque controller is designed to maximize the power below the rated wind speed and a pitch controller is designed to regulate the output power above the rated wind speed. The controllers exploit the sliding mode control scheme considering the variation of wind speed. Since the aerodynamic torque and rotor acceleration are difficult to measure in practice, a finite time convergent observer is designed which estimates them. In order to verify the proposed control strategy, we present stability analysis as well as simulation results.

• Journal of Contemporary Eastern Asia
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• v.20 no.2
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• pp.138-156
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• 2021

The aim of this article is to describe direction of Sino-Russian relations toward a new epoch - as the decision-making centers of both countries define them - indicating the commitment to building the future international order. It includes the synthesis of evolution of relations, descriptions of cooperation building of mutual confidence by both sides in variety of institutions; analyses of geo-economic relations emphasizing their geostrategic dimension and finally dynamics showing how two great powers want to achieve new areas of cooperation focused on building multipolar world order which is the essence of "new epoch". The argument goes towards recognizing the relationship as a "hhybrid alliance". This hybridity is a structural factor that can constrain the use of new dimensions of asymmetric interdependence as political leverage especially by United States against the two non-western powers but also facilitate to use it against West.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.692-698
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• 2020

This paper examines the effects of a multi-stage pilot split injection strategy on combustion and exhaust emission factors in a single-cylinder diesel engine. One analysis noted that in the single-injection condition, the maximum in-cylinder pressure and rate of heat release were highest. The pilot injection quantity was evenly divided, showing a tendency to decrease as the number of injections increased. In another injection condition, when the multi-stage pilot split injection strategy was applied, IMEP, engine torque, and combustion increased. The COV_IMEP was greatest with the lowest combustion efficiency. The combustion ability was poor. In a single injection condition, the O₂ concentration in the exhaust gas was the lowest and the CO₂ was the highest. When the multi-stage split injection strategy was applied, the low temperature combustion process proceeded, and the oxidation rate of CO₂ decreased while the emission level increased. In a single injection condition in which a locally rich mixture was formed, the HC emission level showed the highest results. A 55.6% reduction of NOx emission occurred under a three-stage pilot injection condition while conducting a multi-stage pilot split injection strategy.

• Maritime Security
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• v.6 no.1
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• pp.83-107
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• 2023

To Republic of Korea in the Indo-Pacific region, the stability and prosperity of the area are directly coupled with national survival, interest. Currently, on account of strategic competition between U.S.A, and China in this area as well as supranational·non-conventional threats, the security environment is unstable, required joint/allied responses. So, lots of states inside(U.S.A., Japan, ASEAN, etc.), also, out of this Indo-Pacific area like EU-NATO, open their own strategy related in Indo-Pacific issues to be involved. R.O.K. government took its own line with publishing self strategy following this international trend, it can be shown korean government's strong intend to join in the pending security issues in this region with 'strategic clarity'. Now, R.O.K. Navy has to back up governments, policy. First, R.O.K. Navy should strengthen the relationship inside and take part in the multilateral cooperation of security. Second, to convey this deterrence message to potential threats, Navy is required to show of forces and have combined exercises. Also, as naval forces of advanced countries, Korea, Navy should be taken action in non-traditional threats, and help developing states improve their sea power. To fulfill this tasks in the wide ocean area, Navy need five inherent characteristics(mobility, flexibility, sustainability, capability of presence and projection). In the end, this paper propose the development plan following operational environment (SWOT) analysis as well.

• Maritime Security
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• v.6 no.1
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• pp.109-135
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• 2023

The North Korean military's maneuver toward Honam was the fastest maneuver the North Korean army had demonstrated during the Korean War, and it was a threatening attack that forced the Korean and Allied forces to fully adjust the defenses of the Nakdong River. However, when this study analyzed the North Korean military's maneuver toward Honam in terms of indirect approach strategy, there were a number of factors that inevitably led to its failure. In terms of implementing the indirect approach strategy, the North Korean military cited a number of failure factors, including the dispersion of combat forces, the inflexibility of changing the line of operation, the maneuvering of ground forces, and the lack of psychological distaction. However, the North Koreans were preparing for a final "surprise attack," in which the 7th Division, which was following the North Korean 6th Division, took another diversion and attempted to attack in the direction of Tongyeong. With this, the North Koreans intended to break through the Nakdong River defenses and head for Pusan. However, the North Korean attack was ultimately thwarted by the Korean Navy and Marine Corps' Tongyeong Amphibious Operation. With a swift maneuver using the sea as a maneuvering space, the Navy and Marine Corps occupied key points first, creating an advantageous situation and fending off an attack by the North Korean 7th Division. The Navy and Marine Corps' Tongyeong Amphibious Operation finally thwarted the North Korean military's maneuver toward Honam, thus maintaining the Nakdong River defenses.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.9-16
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• 1995

The erection process planning is to decide erection strategy and sequence that satisfies dock duration. The erection scheduling is to decide erection date of each block. The load profile varies according to scheduling and it is related to building cost. It must be possible to simulate the various combinations of process plan and schedule for optimal planning. To develop the process planning system for optimal planning, the system that generate the sequence of erection automatically and the load leveling system are required. This paper suggests the method that generates the erection sequence. The load leveling should be done to all the ships in the same dock batch to get reliable results. In this case since the search space is very large, efficient optimization method is needed Our research achieved the load leveling system using Genetic Algorithm. This system made it possible to simulate various process plans to which schedule is considered.

• Journal of Ocean Engineering and Technology
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• v.32 no.2
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• pp.95-105
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• 2018

An FLNG (floating liquefied natural gas) or LNG FPSO (floating production, storage and offloading) unit is a notable offshore unit with the increasing demand for LNG. The liquefaction process on an FLNG unit is the most important process because it determines the economic feasibility, but would be a hazard source because of the large quantity of hydrocarbons. While a high efficiency process such as C3MR has been preferred for onshore liquefaction processes, a relatively simple process such as the SMR (single mixed refrigerant) or DMR (dual mixed refrigerant) liquefaction process has been selected for offshore units because they require a more compact size, lighter weight, and higher safety due to their space limitation for facilities and long distance from shore. It is known that an SMR has the advantages of a simple configuration, small footprint, and lower risk. However, with an increased production rate, the inherent safety of SMR needs to be evaluated because of its small train capacity. In this study, the potential explosion risks of the SMR and DMR liquefaction processes were evaluated at the conceptual design stage. The results showed that an SMR has a lower overpressure than a DMR at the same frequency, only with a small production capacity of 0.9 MTPA. With increased capacity, the overpressure of the SMR was higher than that of the DMR. The increased number of trains increased the frequency in spite of the small amount of equipment per train. This showed that the inherent risk of an SMR is not always lower than that of a DMR, and an additional risk management strategy is recommended when an SMR is selected as the concept for an FLNG liquefaction process compared to the DMR liquefaction process.

• International Journal of Naval Architecture and Ocean Engineering
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• v.2 no.3
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• pp.132-138
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• 2010

In the present study, the real-time monitoring system is developed based on the wireless sensor network (WSN) and power line communication (PLC) employed in the 3,000-ton-class training ship. The WSN consists of sensor nodes, router, gateway and middleware. The PLC is composed of power lines, modems, Ethernet gateway and phase-coupler. The basic tests show that the ship has rather good environments for the wired and wireless communications. The developed real-time monitoring system is applied to recognize the thermal environments of main-engine room and one cabin in the ship. The main-engine room has lots of heat sources and needs careful monitoring to satisfy safe operation condition or detect any human errors beforehand. The monitoring is performed in two regions near the turbocharger and cascade tank, considered as heat sources. The cabin on the second deck is selected to monitor the thermal environments because it is close to the heat source of main engine. The monitoring results of the cabin show the thermal environment is varied by the human activity. The real-time monitoring for the thermal environment would be useful for the planning of the ventilation strategy based on the traces of the human activity against inconvenient thermal environments as well as the recognizing the temperature itself in each cabin.

• Journal of Aerospace System Engineering
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• v.10 no.4
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• pp.98-104
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• 2016

This research describes the functional requirements of anti-ship ballistic missile (ASBM) defense systems, which depend on the threat characteristics of the ASBM. Recently, China has carried out a training launch of the DF-21D strategic countermeasures for the placement of Korean terminal high-altitude air defense (THAAD). The ASBM is being used as a primary means of attacking aircraft carriers, using an anti-access/area denial (A2/AD) strategy. Considering the missile technology connection between China and North Korea, there is a very high probability that North Korea already owns an ASBM. From this point of view, work with Aegis operational concepts provided implications for an ASBM threat. Utilizing quality function deployment (QFD) based on the operational concepts, the functional requirement were calculated.