• 한국군사과학기술학회지
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• 제21권2호
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• pp.180-187
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• 2018

In this study, we develop a prediction method of cavity shape taking gravity effect and angle of attack of cavitator into consideration simultaneously. Logvinovich's theoretical formulas are superimposed to predict the change of cavity centerline due to both gravity effect and angle of attack of cavitator. It is found that as the angle of attack of cavitator increases, the gravity effect is weakened due to decrease in cavity volume, and even in case of the same angle of attack, cavity shape changes in different ways depending on whether the angle of attack of cavitator is positive or negative. We conclude that cavity shapes are largely affected by the angle of attack of cavitator, and the gravity effect and angle of attack of cavitator should be considered at the same time for the prediction of cavity shape.

• 한국가시화정보학회지
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• 제20권1호
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• pp.18-28
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• 2022

In this study, a cavity shape measurement experiment was conducted by changing the diameter and the angle of attack of a disk cavitator. Since the gravity effect is proportional to the cavity volume, the larger the cavity, the greater the effect. It is concluded that the gravity effect becomes smaller as the cavitation number decreases because of a short cavity maintaining time. The cavity centerline rises in case of the positive angle of attack and descends in case of the negative angle of attack. Since the effect of the angle of attack is inversely proportional to the square of the cavity radius, the effect of the angle of attack becomes dominant in the vicinity of the cavitator. It is judged that the horizontal section of the cavity centerline cannot be extended because the factors affecting the gravity effect and the angle of attack effect are different.

• 한국가시화정보학회지
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• 제19권3호
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• pp.22-30
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• 2021

Ventilated cavity shapes by varying angle of attack of a circular cavitator were predicted based on Logvinovich's Independence Principle in order to verify the cavity shape prediction method. The prediction results were compared with model experiments conducted in the high-speed cavitation tunnel. In the prediction of the cavity centerline, the movement of the cavity centerline due to the effect of gravity and cavitator's angle of attack were well predicted. In the prediction of the cavity contour, it was found that the cavity edge prediction error increased as the angle of attack increased. The error of the upper cavity contour was small at the positive angle of attack, and the error of the lower cavity contour was small at the negative angle of attack.

• 한국전산유체공학회지
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• 제18권1호
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• pp.28-35
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• 2013

Behavior of the side force generated at high angles of attack by two ogive-cylinder bodies of revolution with nose fineness ratio of 2.3 (B1) and 3.5 (B2) and the effect of a strip placed close the nose tip of each body (B1S and B2S) are analyzed through the wind tunnel test at ReD=200,000 and a=42~60 deg. The side force generated by B1 is increased by placing a strip. The side force generated by B2 is in the starboard direction and its magnitude is higher than that of the B1S. The effect of the strips with various dimensions placed on B2 is investigated. It is found that the 4-layer strip placed on the starboard reversed the direction of the side force into port direction. It is confirmed by numerical simulations that the strip promotes the flow separation and increases the average pressure on the side where it is placed and consequently produces the side force in the corresponding direction.

• 한국정보전자통신기술학회논문지
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• 제15권1호
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• pp.27-35
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• 2022

본 논문에서는 영상 데이터에 대한 적대적 공격으로부터 생성된 적대적 예제로 인하여 발생할 수 있는 딥러닝 시스템의 오분류를 방어하기 위한 방법으로 분류기의 입력 영상에 백색 잡음을 가산하는 방법을 제안하였다. 제안된 방법은 적대적이든 적대적이지 않던 구분하지 않고 분류기의 입력 영상에 백색 잡음을 더하여 적대적 예제가 분류기에서 올바른 출력을 발생할 수 있도록 유도하는 것이다. 제안한 방법은 FGSM 공격, BIM 공격 및 CW 공격으로 생성된 적대적 예제에 대하여 서로 다른 레이어 수를 갖는 Resnet 모델에 적용하고 결과를 고찰하였다. 백색 잡음의 가산된 데이터의 경우 모든 Resnet 모델에서 인식률이 향상되었음을 관찰할 수 있다. 제안된 방법은 단순히 백색 잡음을 경험적인 방법으로 가산하고 결과를 관찰하였으나 에 대한 엄밀한 분석이 추가되는 경우 기존의 적대적 훈련 방법과 같이 비용과 시간이 많이 소요되는 적대적 공격에 대한 방어 기술을 제공할 수 있을 것으로 사료된다.

• 한국컴퓨터정보학회논문지
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• 제23권11호
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• pp.75-84
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• 2018

Social engineering attack means to get information of Social engineering attack means to get information of opponent without technical attack or to induce opponent to provide information directly. In particular, social engineering does not approach opponents through technical attacks, so it is difficult to prevent all attacks with high-tech security equipment. Each company plans employee education and social training as a countermeasure to prevent social engineering. However, it is difficult for a security officer to obtain a practical education(training) effect, and it is also difficult to measure it visually. Therefore, to measure the social engineering threat, we use the results of social engineering training result to calculate the risk by system asset and propose a attack graph based probability. The security officer uses the results of social engineering training to analyze the security threats by asset and suggests a framework for quick security response. Through the framework presented in this paper, we measure the qualitative social engineering threats, collect system asset information, and calculate the asset risk to generate probability based attack graphs. As a result, the security officer can graphically monitor the degree of vulnerability of the asset's authority system, asset information and preferences along with social engineering training results. It aims to make it practical for companies to utilize as a key indicator for establishing a systematic security strategy in the enterprise.

• Communications for Statistical Applications and Methods
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• 제23권4호
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• pp.297-319
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• 2016

Football match predictions are of great interest to fans and sports press. In the last few years it has been the focus of several studies. In this paper, we propose the Poisson regression model in order to football match outcomes. We applied the proposed methodology to two national competitions: the 2012-2013 English Premier League and the 2015 Brazilian Football League. The number of goals scored by each team in a match is assumed to follow Poisson distribution, whose average reflects the strength of the attack, defense and the home team advantage. Inferences about all unknown quantities involved are made using a Bayesian approach. We calculate the probabilities of win, draw and loss for each match using a simulation procedure. Besides, also using simulation, the probability of a team qualifying for continental tournaments, being crowned champion or relegated to the second division is obtained.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권9호
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• pp.4529-4548
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• 2016

DDoS attacks have had a devastating effect on the Internet, which can cause millions of dollars of damage within hours or even minutes. In this paper we propose a practical dynamic defense approach that overcomes the shortage of static defense mechanisms. Our approach employs a group of SDN-based proxy switches to relay data flow between users and servers. By substituting backup proxy switches for attacked ones and reassigning suspect users onto the new proxy switches, innocent users are isolated and saved from malicious attackers through a sequence of remapping process. In order to improve the speed of attacker segregation, we have designed and implemented an efficient greedy algorithm which has been demonstrated to have little influence on legitimate traffic. Simulations, which were then performed with the open source controller Ryu, show that our approach is effective in alleviating DDoS attacks and quarantining the attackers by numerable remapping process. The simulations also demonstrate that our dynamic defense imposes little effect on legitimate users, and the overhead introduced by remapping procedure is acceptable.

• 한국항공우주학회지
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• 제43권3호
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• pp.224-231
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• 2015

람다 날개 형상의 공력 계수에 대한 실험적 연구를 국방과학연구소의 중형아음속 풍동에서 수행하였다. 본 연구의 주목적은 옆미끄럼각의 변화에 따라 다양한 공력 계수가 어떻게 변화하는지를 조사하는 것이다. 옆미끄럼각이 $0^{\circ}C$인 경우, 피칭 모멘트가 급격히 불안정해지는 현상을 확인하였으며, 옆미끄럼각이 증가함에 따라 pitch break 현상이 더 높은 받음각에서 발생하는 것을 확인하였다. 롤링 모멘트는 옆미끄럼각이 있는 경우 pitch break와 유사한 특성을 보여준다. 이런 경향은 옆미끄럼각이 증가할수록 더 심하게 나타났다. 요잉 모멘트는 높은 받음각에서 옆미끄럼각에 따라 기울기가 크게 변화하였고 불안정한 방향 안정성이 뚜렷이 나타났다. 모멘트의 이런 특성들은 비행 제어를 위해서는 보다 효과적인 조종성 증가 장치가 필수적이란 것을 의미하고 있다.

• 한국군사과학기술학회지
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• 제13권6호
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• pp.1106-1112
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• 2010

One of the considerations in weapon systems procurement is the objective of maximizing the current force. Also, offensive effects, rather than defense are valued in weapons system development and procurement. Especially, the survivability of a naval ship is equally important as the offensive effect of onboard weapons. In case of naval ships, development of attack tactics and research regarding damage minimization must be conducted through live fire exercise against actual targets in order to minimize damage from the enemy. However, it is difficult to conduct such adequate measures due to realistic limitations such as time and budget in order to verify and calculate a weapon system's attack and damage effects along with the lack of practical studies in this subject despite numerous interests. Research are being conducted utilizing M&S to estimate attack effects and study damages due to such reason, but the lack of authoritative data and development ability are limiting calculation of reliable results. Therefore, this study will propose a measure to increase survivability of a weapon system(ship/vessel) utilizing research of vulnerability from enemy attacks analysis method against a naval ship(Craft Air Cushion).