• Metals and materials international
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• v.24 no.6
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• pp.1193-1201
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• 2018

Dilatometry is a useful technique to obtain experimental data concerning transformation. In this paper, a dilation conversional model was established to calculate carbides fraction in AISI H13 hot-work tool steel based on the measured length changes. After carbides precipitation, the alloy contents in the matrix changed. In the usual models, the content of carbon atoms after precipitation is considered as the only element that affects the lattice constant and the content of the alloy elements such as Cr, Mo, Mn, V are often ignored. In the model introduced in this paper, the alloying elements (Cr, Mo, Mn, V) changes caused by carbides precipitation are incorporated. The carbides were identified using scanning electron microscope and transmission electron microscope. The relationship between lattice constant of carbides and temperature are measured by high-temperature X-ray diffraction. The results indicate that the carbides observed in all specimens cooled at different rates are V-rich MC and Cr-rich $M_{23}C_6$, and most of them are V-rich MC, only very few are Cr-rich $M_{23}C_6$. The model including the effects of substitutional alloying elements shows a good improvement on carbides fraction predictions. In addition, lower cooling rate advances the carbides precipitation for AISI H13 specimens. The results between experiments and mathematical model agree well.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.411-418
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• 2018

This paper introduces a new method of ice load generation in the time domain for the station-keeping performance evaluation of Arctic offshore structures. This method is based on the ice load spectrum and mean ice load. Recently, there has been increasing interest in Arctic offshore technology for the exploration and exploitation of the Arctic region because of the better accessibility to the Arctic ocean provided by the global warming effect. It is essential to consider the ice load during the development of an Arctic offshore structure. In particular, when designing a station-keeping system for an Arctic offshore structure, a consideration of the ice load acting on the vessel in the time domain is essential to ensure its safety and security. Several methods have been developed to consider the ice load in the time domain. However, most of the developed methods are computationally heavy because they consider every ice floe in the sea ice field to calculate the ice load acting on the vessel. In this study, a new approach to generate the ice load in the time domain with computational efficiency was suggested, and its feasibility was examined. The ice load spectrum and mean ice load were acquired from a numerical analysis with GPU-event mechanics (GEM) software, and the ice load with the varying heading of a vessel was reconstructed to show the feasibility of the proposed method.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.6
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• pp.799-806
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• 2018

In this paper, we analyzed the communication distances in the flat and spherical earth model using the main specifications of the wireless communication device under development to be installed in the unmanned surface vehicle(USV). We installed the wireless communication device on the test ship and the actual communication test was performed in the South Sea of Korea, it compared the experimental result with the simulated results. If the installation altitude of the transmitting and receiving antennas is low, there is not the big difference between the two models. However, when the altitude of one of the two antennas is high, the spherical earth model has similar results to the experimental data. As the altitude of the antenna installation increases, fading occurs in a certain section. We expect that this fading can be overcome through antenna technologies such as space diversity.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.394-397
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• 2014

Most of Koreans have smartphone. By using smartphone, they have done internet-banking, e-commerce and private scheduling. However, convenience of smart phone has been made side effect such as tool of fraud and crime. Especially, Smishing on smartphone has been increased rapidly since 2013. Smishing have utilized social-engineering technique with social issue such as Korean near-sea cruse ship, 'Sewol-Ho', Sinking and traditional thanks-giving holiday, 'Chu-Seok', etc. This paper proposed the oncoming trend of smishing on smartphone after 2014. This paper also analyzed the process and technique of smishing on internal financial fraud. It also covered smartphone forensic for using legal evidence. By discovering the connectivity of smishing and financial fraud, this paper could be reference for social security on smartphone.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.55 no.2
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• pp.129-137
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• 2019

This study was conducted to investigate the effects of underwater noise caused by pile driving during marine construction on fish. In this study, the three gray rockfish were released about 1 km away from the construction site of wind power generation on July 18, 2018 and traced using two acoustic telemetry techniques. The behavior of the fish was analyzed by calculating the moving distance, swimming speed and direction of the gray rockfish. In the results of the acoustic tracking using the ship, the rockfish moved about 2.11 km for about two hours at a speed of $0.28{\pm}0.14m/s$ (0.94 TL/s). The bottom depth of the trajectory of the rockfish was $1.0{\pm}0.6m$ on average. There was a significant directionality in swimming direction of the gray rockfish, and there was no significant correlation between the swimming direction and tidal current direction. Moving distance during 5 minutes (5MD) during pile driving and finishing operations between rock surface and bedrock were 0.94-0.96 times (76.0-77.0 m) and 1.81-2.73 times (146.0-219.5 m), respectively, compared with no pile driving. This study is expected to be used as a basic data of fish behavior research on underwater noise.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.5
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• pp.296-305
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• 2022

In order to investigate maneuvering characteristics of KCS in waves, captive model test in regular waves was conducted. Purpose of the test is measuring maneuvering hull forces when ship is maneuvering in waves. Model test was carried out using CPMC (Computerized Planar Motion Carriage) of ocean engineering basin in KRISO (Korea Research Institute of Ships and Ocean engineering). Total 6 degrees-of-freedom motion were fixed by two points supporting captive model test device, which is specially designed for this test. This system estimates 6 degrees-of-freedom forces and moments through 12 strain gauge signals. Mapping matrix from strain gauge signals to 6 degrees-of-freedom forces and moments was derived by a well-organized calibration test. Static drift test was conducted in calm sea and in regular waves with various wave conditions. Hydrodynamic coefficients related to drift angle were extracted for each wave conditions, and the effect of waves on course stability was analyzed.

• Journal of the Korea Society for Simulation
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• v.19 no.2
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• pp.99-106
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• 2010

In the anti-submarine warfare, a search using HMS is used as a basic strategy. The importance of HMS operation strategy is increasing, but it is hard to develop effective anti-submarine search strategy due to reciprocal actions among sea environments, search patterns, sonar operational tactics, anti-submarine search strategy, etc. In this research, a simulator was invented so as to analyze anti-submarine search patterns used when an HMS-carrying ship searches for submarine in various anti-submarine search environments. The simulator reflects various factors that influence anti-submarine search, and with consideration of search patterns of anti-submarine ships as well as evasive movement of submarines, it can simulate various anti-submarine search operations such as a collaborative anti-submarine operation by a single or multiple forces. Also, the simulator will contribute to developing and improving systematic and efficient HMS operational tactics in anti-submarine warfare.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.59 no.1
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• pp.1-8
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• 2023

In this study, the stability of fishing boat inducing the change of fishing lamp in accordance with the installation of induction lamp in comparison with metal halide lamp was investigated. Inclining test for 8.55 ton class of hair-tail angling fishing boat was performed in order to find a GM and light weight. A stability calculation of the target fishing boat on the basis of KST-SHIP program was evaluated. The stability of the fishing boat with a metal halide lamp such as induction lamp according to the result obtained by the inclining test is slightly different, and the stability is not so much affected. Due to the induction lamp installation, the wind area increased by about 3.178 m². Before installing the induction fishing lamp, G₀M was found to be 0.209 at full load departure and 0.296 at departure from fishing ground. After installing the induction lamp, the full load departure condition is 0.178 and the fishing ground departure condition is 0.260. The G₀M value before and after installation of the induction fishing lamp shows a difference of about 3% at the full load departure condition. The value of the critical angle of inclination definition showed a difference of about 16%. Despite these differences, it is lower than the regulations; it was confirmed that there will be no significant difference unless it is in an overloaded state.

• Strategy21
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• s.30
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• pp.63-98
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• 2012

Northeast Asia has a multi-layered security structure within which major economic and military powers both confront one another and cooperate at the same time. Major regional powers maintain mutually cooperative activities in the economic sphere while competing one another in order to secure a dominant position in the politico-military arena. The multifarious threats, posed by the North Korea's nuclear development, territorial disputes, and maritime demarcation line issues demonstrate that Northeast Asia suffers more from military conflicts and strifes than any other region in the world. Specifically, major maritime security threats include North Korea's nuclear proliferation and missile launching problems as well as military provocations nearby the Northern Limit Line(NLL) as witnessed in the Cheonan naval ship and Yeonpyong incidents. The ROK Navy has been supplementing its firm military readiness posture in consideration of North Korea's threats on the NLL. It has performed superb roles in defending the nation and establishing the Navy advanced and best picked. It also has been conducive to defend the nation from external military threats and invasion, secure the sea lanes of communications, and establish regional stability and world peace. In order to effectively cope with the strategic environment and future warfares, the ROK Navy needs to shift its military structure to one that is more information and technology intensive. In addition, it should consolidate the ROK-US alliance and extend military cooperative measures with neighboring countries in the Asia-Pacific region. Evolved steadily for the last 60 years, the ROK-US alliance format has contributed to peace and security on the Korean peninsula and in the Northeast Asian region. In conclusion, this manuscript contends that the ROK Navy should strive for the establishment of the following: (1) Construction of Jeju Naval Base; (2) Strategic Navy Equipped with War Deterrence Capabilities; (3) Korean-type of System of Systems; (4) Structure, Budget and Human Resources of the Naval Forces Similar to the Advanced Countries; and (5) Strategic Maritime Alliance and Alignment System as well as Domestic Governance Network for the Naval Families.

• Journal of the Korea Society of Computer and Information
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• v.28 no.4
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• pp.93-104
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• 2023

Recently, the technology of drones is developing remarkably. The role of military drones is so great that they can cause serious damage to the enemy's important strategic assets without any damage to our allies in all battlefield environments (land, sea, air). However, the battleship combat management system currently operated by the Korean Navy is vulnerable to defense because there is no customized defense system against drones. As drones continue to develop, they are bound to pose a major threat to navy in the future. This paper proposes a way for the warfare software of naval combat management system sets a combat mode suitable for anti-drone battle, evaluates the threat priority in order to preemptively respond to drone threats and eliminate drone threats through automatic allocation of self-ship-mounted weapons and sensors, and through a test of the improved warfare software in a simulated environment, it was proved that the time to respond to the drone was improved by 62%.