• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.12
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• pp.992-998
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• 2014

Acoustic radiation efficiency is one of the important factors in the prediction of underwater radiated noise of ships. A ship has much equipment to operate successful mission in a ship. Most of equipment is running simultaneously as multi-excitation and becomes the source of underwater radiated noise. In many cases of multi-excitation, phase difference between multi-excitation is not considered. Because vibration response under multi-excitation is the vector sum of each single excitation, acoustic radiation efficiency based on surface velocity field can be affected by phase of excitation. In this study, acoustic radiation efficiency of a plate on air and a stiffened cylindrical model in water under multi-excitation with phase difference is investigated.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.1
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• pp.22-30
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• 2021

The ship wake generated by rotation of the propeller yields changes of characteristics of sound wave such as attenuation and scattering. To develope a battle field environment simulator for military purposes, it is very important to understand acoustical properties of ship wake. Existing research results have limitations in direct application because they performed under simple conditions or model ships were applied. In this study, we developed a ship wake generation model based on the ship's geometric wake distribution theory. The model can provide spatial distribution and void fraction with various marine environments as well as ship size. Through the developed model, geometric distribution features of ship wake according to the ship's maneuvering conditions were successfully simulated. In addition, changes of the bubble void fraction with time at any location within the battle field environment were identified. Therefore, the developed model is expected to be used in the development of a simulator to measure the acoustic characteristics of the ship wake.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.3
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• pp.281-292
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• 2021

With the development of deep learning technology, researchers and technicians keep attempting to apply deep learning in various industrial and academic fields, including the defense. Most of these attempts assume that the data are balanced. In reality, since lots of the data are imbalanced, the classifier is not properly built and the model's performance can be low. Therefore, this study proposes cost-sensitive learning as a solution to the imbalance data problem of image classification in the defense field. In the proposed model, cost-sensitive learning is a method of giving a high weight on the cost function of a minority class. The results of cost-sensitive based model shows the test F1-score is higher when cost-sensitive learning is applied than general learning's through 160 experiments using submarine/non-submarine dataset and warship/non-warship dataset. Furthermore, statistical tests are conducted and the results are shown significantly.

• Current Optics and Photonics
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• v.1 no.4
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• pp.344-350
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• 2017

We present a new design approach and an example design for an image-space telecentric two-mirror system that has a fast f-number and a wide-field line image. The initial design of the telecentric mirror system is a conventional axially symmetric system, consisting of a flat primary mirror with fourth-order aspheric deformation and an oblate ellipsoidal secondary mirror to correct spherical aberration, coma, and field curvature. Even though in the optimized design the primary mirror is tilted, to avoid ray obstruction by the secondary mirror, the image-space telecentric two-mirror system shows quite good imaging performance, for a line imager.

• Journal of the military operations research society of Korea
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• v.36 no.1
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• pp.103-121
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• 2010

As a cutting edge technology intensive value-added business, the defense industry is jumping into a new engine of a national growth. Also, the defense industry export is recognized not only as the field to activate the Korean economy but also as an important field to create the national brand value. However, though the consensus on the importance of defense industry export helps achieve the remarkable performance in reality, the rate of increase in the budget for national defence is slowing down gradually, and the investment in R&D is not so big, and there are a lot of drawbacks with the management of core technology and the development of cutting edge weapon system. Accordingly, this thesis tried to find the leverage to make the structure of defense industry export work normally after analyzing the systematical structure of defense industry export to understand its characteristics. Also, through the process to make the leverage a strategy, the thesis tried to present the optimal direction of policy to join the ranks of the advanced countries in defense industry export.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.6
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• pp.810-820
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• 2014

Recently many studies of Radar systems mounted on ground vehicles for autonomous driving, SLAM (Simultaneous localization and mapping) and collision avoidance are reported. In near field, several hits per an object are generated after signal processing of Radar data. Hence, clustering is an essential technique to estimate their shapes and positions precisely. This paper proposes a method of grouping hits in range-doppler domains into clusters which represent each object, according to the pre-defined rules. The rules are based on the perceptual cues to separate hits by object. The morphological connectedness between hits and the characteristics of SNR distribution of hits are adopted as the perceptual cues for clustering. In various simulations for the performance assessment, the proposed method yielded more effective performance than other techniques.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.611-616
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• 2018

With the recent increase in awareness of the diversification of patterns of warfare and security, technological evolution is occurring in the field of autonomous defense robots. As defense science and technology develops with the development of the concept of military utilization focusing on human lives and economic operation, the importance of autonomous robots in the effect-oriented future battlefield is increasing. The major developed countries have developed core technologies, investment strategies, priorities, data securing strategies and infrastructure development related to the field of autonomous defense robots, and research activities such as technology planning and policy strategy for autonomous defense robots in Korea have already begun. In addition, the field of autonomous defense robots encompasses technologies that represent the fourth industrial revolution, such as artificial intelligence, big data, and virtual reality, and so the expectations for this future area of technology are very high. It is difficult to predict the path of technological development due to the increase in the demand for new rather than existing technology. Moreover, the selection and concentration of strategic R&D is required due to resource constraints. It is thought that a preemptive response is needed. This study attempts to derive 6 new technologies that will shape the future of autonomous defense robots and to obtain meaningful results through an empirical study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.117-121
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• 2018

As the paradigm shifts in the era of accelerated technological development and technology convergence, the defense sector is pursuing national defense research and development through selection and concentration, as well as the expansion of investments to develop defense science and technology to the highest possible level. In addition to investing heavily in cutting-edge weapons and core technologies that are consistent with the future, the defense sector is also developing investment strategies within a limited budget. In the private sector, the PD system has been introduced in order to maximize the performance of R&D policy and to improve the professionalism and responsibility of planning & management. In accordance with this trend, in the field of defense, the PD system of defense technology with specialization is being promoted, in order to strengthen the task planning capacity and to promote the utilization of private technology. Considering the need for coherent technical support for the core technology developed by R&D, the improvement of open technology planning systems and expansion of inter-civil & technical linkage, the use of the PD system in the defense field is indispensable. In this study, we review similar cases abroad and at home to examine the introduction and management of the PD system for defense technology. This study is based on the current state of the defense technology PD system that is being pursued.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.248-255
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• 2016

The amount and diversity of information is increasing, as is the information integration connecting data among the related institutions. In the defense field, DTAQ, which is in charge of the quality of military supplies, is attempting to collect and analyze the information which is related with it. In addition, the object of information integration is to expand civil data as well as defense data. There are many ways to integrate data in various environments. In the defense field, which needs enhanced security, it is necessary to establish and apply the information integration methods which are enhanced with more security. In this study, the framework and architecture of information integration was designed by considering task requirements and security conditions. As a result of example application of this framework for information systems to the selected 4 institutions, it was confirmed that the task can be performed through data connections. From the study result, integration architecture which can be applied securely in defense field was suggested. The data accumulated by using this framework with strengthened security are expected to be utilized for the quality improvement of military supplies.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.11
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• pp.1054-1062
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• 2011

This study describes the time domain imaging algorithm which can be well applied to short-range UWB(ultra wideband) bistatic radar. In the imaging method of SAR technology, the frequency domain method is well applied to the areas which satisfy far-field condition. However in the near-field environment, the image quality is not good due to phase error. However back-projection method based on time domain is well applied to short-range imaging radar. Meanwhile because its processing time is very long, real time-processing is very difficult. To resolve this problem FFBP(Fast Factorized Back-Projection) was proposed. Using the raw data gathered on field we implemented back-projection and FFBP method. Then image quality and processing time were analyzed using these methods.