• 한국시뮬레이션학회논문지
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• 제27권4호
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• pp.69-77
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• 2018

발사관은 탑재물을 보관하고 외부 환경으로부터 부식 및 파손되는 것을 방지하는 역할을 한다. 발사관과 유도탄의 제작, 조립 그리고 장입 상태에 따라 발사할 때 유도탄의 초기 거동을 결정하게 된다. 본 연구의 목적은 유도탄이 발사관에서 사출될 때 유도탄의 초기 거동을 결정하는 요소를 통계적으로 분석하여 발사관의 안전성을 확인하는 것이다. 유도탄이 발사될 때 거동에 영향을 주는 오차 요소들을 선정한 후 Monte-Carlo 시뮬레이션을 수행하여 통계적으로 분석하였다. 시뮬레이션 결과를 바탕으로, 각 오차 요소들을 고려한 다물체 동역학 해석을 상용프로그램인 Recurdyn을 이용하여 동역학 해석을 수행하여 유도탄 발사할 때 발생하는 중력 침하 및 레일과 슈 사이에 발생하는 응력을 구하였다. 해당 결과를 바탕으로 현재 설계된 발사관에 대한 안전성을 검증하였다.

• Advances in aircraft and spacecraft science
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• 제6권2호
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• pp.117-144
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• 2019

High Altitude and Long Endurance (HALE) aircraft are capable of providing intelligence, surveillance and reconnaissance (ISR) capabilities over vast geographic areas when equipped with advanced sensor packages. As their use becomes more widespread, the demand for additional range, endurance and payload capability will increase and designers are exploring non-conventional configurations to meet the increasing demands. One such configuration is the joined-wing concept. A joined-wing aircraft is one that typically connects a front and aft wings in a diamond shaped planform. One such example is the Boeing SensorCraft configuration. While the joined-wing configuration offers potential benefits regarding aerodynamic efficiency, structural weight, and sensing capabilities, structural design requires careful consideration of elastic buckling resulting from the aft wing supporting, in compression, part of the forward wing structural loading. It has been shown already that this is a nonlinear phenomenon, involving geometric nonlinearities and follower forces that tend to flatten the entire configuration, leading to structural overload due to the loss of the aft wing's ability to support the forward wing load. Severe gusts are likely to be the critical design condition, with flight control system interaction in the form of Gust Load Alleviation (GLA) playing a key role in minimizing the structural loads. The University of Victoria Center for Aerospace Research (UVic-CfAR) has built a 3-meter span scaled and flexible wing UAV based on the Boeing SensorCraft design. The goal is to validate the nonlinear structural behavior in flight. The main objective of this research work is to perform Ground Vibration Tests (GVT) to characterize the dynamic properties of the scaled flight vehicle. Results from the experimental tests are used to characterize the modal dynamics of the aircraft, and to validate the numerical models. The GVT results are an important step towards a safe flight test program.

• Ocean Systems Engineering
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• 제8권4호
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• pp.427-439
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• 2018

Floating Production Storage and Offloading (FPSO) units have the advantages of their ability to provide storage and offloading capabilities which are not available in other types of floating production systems. In addition, FPSOs also provide a large deck area and substantial topsides payload capacity. They are in use in a variety of water depths and environments around the world. It is a good solution for offshore oil and gas development in fields where there is lack of an export pipeline system to shore. However due to their inherently high motions in waves, they are limited in the types of risers they can host. The Low Motion FPSO (LM-FPSO) is a novel design that is developed to maintain the advantages of the conventional FPSOs while offering significantly lower motion responses. The LM-FPSO design generally consists of a box-shape hull with large storage capacity, a free-hanging solid ballast tank (SBT) located certain distance below the hull keel, a few groups of tendons arranged to connect the SBT to the hull, a mooring system for station keeping, and a riser system. The addition of SBT to the floater results in a significant increase in heave, roll and pitch natural periods, mainly through the mass and added mass of the SBT, which significantly reduces motions in the wave frequency range. Model tests were performed at the Korea Research Institute of Ships & Ocean Engineering (KRISO) in the fall of 2016. An analytical model of the basin model (MOM) was created in Orcaflex and calibrated against the basin-model. Good agreement is achieved between global performance results from MOM's predictions and basin model measurements. The model test measurements have further verified the superior motion response of LM-FPSO. In this paper, numerical results are presented to demonstrate the comparison and correlation of the MOM results with model test measurements. The verification of the superior motion response through model test measurements is also presented in this paper.

• Journal of Astronomy and Space Sciences
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• 제36권3호
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• pp.159-168
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• 2019

In solstices during the solar minimum, the hemispheric difference of the equatorial ionization anomaly (EIA) intensity (hereafter hemispheric asymmetry) is understood as being opposite in the morning and afternoon. This phenomenon is explained by the temporal variation of the combined effects of the fountain process and interhemispheric wind. However, the mechanism applied to the observations during the solar minimum has not yet been validated with observations made during other periods of the solar cycle. We investigate the variability of the hemispheric asymmetry with local time (LT), altitude, season, and solar cycle using the electron density taken by the CHAllenging Minisatellite Payload satellite and the global total electron content (TEC) maps acquired during 2001-2008. The electron density profiles provided by the Constellation Observing System for Meteorology, Ionosphere, and Climate satellites during 2007-2008 are also used to investigate the variation of the hemispheric asymmetry with altitude during the solar minimum. During the solar minimum, the location of a stronger EIA moves from the winter hemisphere to the summer hemisphere around 1200-1400 LT. The reversal of the hemispheric asymmetry is more clearly visible in the F-peak density than in TEC or in topside plasma density. During the solar maximum, the EIA in the winter hemisphere is stronger than that in the summer hemisphere in both the morning and afternoon. When the location of a stronger EIA in the afternoon is viewed as a function of the year, the transition from the winter hemisphere to the summer hemisphere occurs near 2004 (yearly average F10.7 index = 106). We discuss the mechanisms that cause the variation of the hemispheric asymmetry with LT and solar cycle.

• 스마트미디어저널
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• 제8권1호
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• pp.19-26
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• 2019

2018년 평창 동계 올림픽 개막식에서 출처를 알 수 없는 사이버공격이 발생하였다. 해당 공격에서 사용된 악성코드는 인 메모리 악성코드로 기존 악성코드와 은닉하는 장소가 다르며, 140개 이상의 은행, 통신, 정부 기관에서 발견될 정도로 빠르게 확산되고 있다. 인 메모리 악성코드는 전체 악성코드의 15%이상을 차지하며 매우 심각한 피해를 주고 있다. 비휘발성 저장장치로 알려진 하드디스크에 자신의 정보를 저장하는 것이 아닌 휘발성 저장장치 인 램의 특정 메모리영역인 프로세스에 삽입하여 악성행위를 일으키는 악성코드를 인 메모리 악성코드라고 지칭한다. 결과적으로 자신의 정보를 남기지 않아 메모리 탐지 도구를 우회하여 악성코드 분석가들의 분석을 어렵게 한다. 또한 현대 메모리는 갈수록 크기가 증가해 메모리 탐지 도구를 사용하여 메모리전체를 보기 힘들다. 따라서 본 논문에서는 인 메모리 악성코드인 Dorkbot과 Erger를 대상으로 IDA Pro 디버거를 통해 인젝션을 언 패킹하여 효율적으로 페이로드를 산출하는 방법을 제안한다.

• 대한원격탐사학회지
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• 제35권3호
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• pp.471-482
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• 2019

달 탐사용 고해상도 스테레오 카메라의 임무는 달 궤도선 및 착륙 선에 탑재되어 달 표면의 3차원 지형정보를 제공하는데 있다. 이를 통해, 달 착륙 후보지를 탐색하고 착륙 시에는 달 표면 근접에 따른 근거리 입체영상을 실시간으로 제공하여 정확한 지점에 착륙이 가능하도록 한다. 본 논문에서는 달 탐사선에 탑재되는 달 탐사용 고해상도 카메라 개발을 위한 지상모델인 다기능 스테레오 카메라를 활용하여 고해상도 스테레오 카메라에 요구되는 임무를 검증하고 결과를 분석하기 위해 지상검증 및 분석 시스템을 제안하였다. 지상검증 및 분석 시스템은 임무 검증을 위한 임무검증항목과 시험계획을 제공하며, 시험 수행 후 결과를 분석하게 된다. 이를 위해 본 논문에서는 달 지형과 유사한 지역을 대상으로 지상 임무항목시험 계획을 세우고, 항공촬영을 통해 스테레오 영상을 획득하였다. 분석장치를 통해 스테레오 영상으로부터 영상을 보정 및 매칭 후 수치표고모델(DEM)을 추출하고 3차원 영상을 생성하여 결과를 분석하였다. 달 탐사용 고해상도 카메라에 요구되는 임무수행항목이 검증되었고, 스테레오 영상을 처리할 수 있는 지상처리분석 시스템이 확보 되었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.82-96
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• 2019

A semi-submersible structure has been widely used for offshore drilling and production of oil and gas. The small water plane area makes the structure very sensitive to weight increase in terms of payload and stability. Therefore, it is necessary to lighten the substructure from the early design stage. This study aims at an optimization of hull structure based on a sophisticated yield and buckling strength in accordance with classification rules. An in-house strength assessment system is developed to automate the procedure such as a generation of buckling panels, a collection of required panel information, automatic buckling and yield check and so on. The developed system enables an automatic yield and buckling strength check of all panels composing the hull structure at each iteration of the optimization. Design variables are plate thickness and stiffener section profiles. In order to overcome the difficulty of large number of design variables and the computational burden of FE analysis, various methods are proposed. The steepest descent method is selected as the optimization algorithm for an efficient search. For a reduction of the number of design variables and a direct application to practical design, the stiffener section variable is determined by selecting one from a pre-defined standard library. Plate thickness is also discretized at 0.5t interval. The number of FE analysis is reduced by using equations to analytically estimating the stress changes in gradient calculation and line search steps. As an endeavor to robust optimization, the number of design variables to be simultaneously optimized is divided by grouping the scantling variables by the plane. A sequential optimization is performed group by group. As a verification example, a central column of a semi-submersible structure is optimized and compared with a conventional optimization of all design variables at once.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.1020-1042
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• 2019

Reversible data hiding in encrypted images (RDHEI) provides some real-time cloud applications; i.e. the cloud, acting as a data-hider, automatically embeds timestamp in the encrypted image uploaded by a content owner. Many existing methods of RDHEI only satisfy user privacy in which the data-hider does not know the original image, but leaks owner privacy in which the receiver can obtains the original image by decryption and extraction. In the literature, the method of Zhang et al. is the one providing weak content-owner privacy in which the content-owner and data-hider have to share a data-hiding key. In this paper, we take care of the stronger notion, called strong content-owner privacy, and achieve it by presenting a new reversible data hiding in encrypted images. In the proposed method, image decryption and message extraction are separately controlled by different types of keys, and thus such functionalities are decoupled to solve the privacy problem. At the technique level, the original image is segmented along a Hilbert filling curve. To keep image privacy, segments are transformed into an encrypted image by using random permutation. The encrypted image does not reveal significant information about the original one. Data embedment can be realized by using pixel histogram-style hiding, since this property, can be preserved before or after encryption. The proposed method is a modular method to compile some specific reversible data hiding to those in encrypted image with content owner privacy. Finally, our experimental results show that the image quality is 50.85dB when the averaged payload is 0.12bpp.

• 융합보안논문지
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• 제21권3호
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• pp.57-66
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• 2021

침입탐지 분야에서 딥러닝과 머신러닝을 이용한 탐지성능이 검증되면서 이를 활용한 사례가 나날이 증가하고 있다. 하지만, 학습에 필요한 데이터 수집이 어렵고, 수집된 데이터의 불균형으로 인해 머신러닝 성능이 현실에 적용되는데 어려움이 있다. 본 논문에서는 이에 대한 해결책으로 불균형 데이터 처리를 위해 t-SNE 시각화를 이용한 혼합샘플링 기법을 제안한다. 이를 위해 먼저, 페이로드를 포함한 침입탐지 이벤트에 대해서 특성에 맞게 필드를 분리한다. 분리된 필드에 대해 TF-IDF 기반의 피처를 추출한다. 추출된 피처를 기반으로 혼합샘플링 기법을 적용 후 t-SNE를 이용한 데이터 시각화를 통해 불균형 데이터가 처리된 침입탐지에 최적화된 데이터셋을 얻게 된다. 공개 침입탐지 데이터셋 CSIC2012를 통해 9가지 샘플링 기법을 적용하였으며, 제안한 샘플링 기법이 F-score, G-mean 평가 지표를 통해 탐지성능이 향상됨을 검증하였다.

• 한국기계가공학회지
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• 제19권12호
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• pp.62-69
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• 2020

The demand for industrial robots is proliferating with production automation. Industrial robots are used in various fields, such as logistics, welding, and assembly. Generally, six degrees of freedom are required to move freely in space. However, the palletizing robot used for material management and logistics systems typically has four degrees of freedom. In designing such robots, their main parts, such as motors and reducers, need to be adequately selected while satisfying payload requirements and speed. Hence, this study proposes a practical method for selecting the major parts based on dynamic analysis using ADAMS. First, the acceleration torques for the robot motion were found from the analysis, and then the friction torques were evaluated. This study introduces a constant-speed torque constant instead of friction coefficient. The RMS torque and maximum power of each motor were found considering the above torques. After that, this study recommends the major specifications of all motors and reducers. The proposed method was applied to a palletizing robot to verify the suitability of the pre-selected main parts. The verification result shows that the proposed method can be successfully applied to the early design stage of industrial robots.