• Wind and Structures
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• 제20권2호
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• pp.169-189
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• 2015

To investigate the effects of "sudden change" of wind fluctuations on vehicle running performance, which is caused by the artificial discrete simulation of wind field, a three-dimensional vehicle model is set up with multi-body dynamics theory and the vehicle dynamic responses in crosswind conditions are obtained in time domain. Based on Hilbert Huang Transform, the effects of simulation separations on time-frequency characteristics of wind field are discussed. In addition, the probability density distribution of "sudden change" of wind fluctuations is displayed, addressing the effects of simulation separation, mean wind speed and vehicle speed on the "sudden change" of wind fluctuations. The "sudden change" of vehicle dynamic responses, which is due to the discontinuity of wind fluctuations on moving vehicle, is also analyzed. With Principal Component Analysis, the comprehensive evaluation of vehicle running performance in crosswind conditions at different simulation separations of wind field is investigated. The results demonstrate that the artificial discrete simulation of wind field often causes "sudden change" in the wind fluctuations and the corresponding vehicle dynamic responses are noticeably affected. It provides a theoretical foundation for the choice of a suitable simulation separation of wind field in engineering application.

• 융합보안논문지
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• 제17권4호
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• pp.47-52
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• 2017

남유럽에서 시작된 민주화라는 물결은 남아메리카와 아시아로 확산되었고, 구소련과 동유럽을 붕괴시켰으며, 북아프리카와 중동지역 국가들에 재스민혁명이라는 모습으로 나타났다. 이로 인하여 다수의 학자들은 재스민혁명이 북한에도 발생할 가능성이 있다는 조심스러운 전망을 하면서, 북한 급변사태와 관련된 연구들을 활발히 하여왔다. 이러한 연구의 주제들은 급변사태의 발생원인과 시기, 그리고 주도세력 등에 초점이 맞추어졌고, 그 전개과정이 어떻게 될 것인가와 체제변화가 있을 것인가에 대한 논의는 부족하였다. 이에 본 연구에서는 재스민혁명 국가들의 체제변화를 분석한 결과에 근거하여, 북한 급변사태 이후에 전개 가능한 시나리오를 I유형 비교적 평화롭게 정권이 교체될 가능성, II유형 분단된 국가에서 통일된 이후에 다시 내전이 발생할 가능성, III유형 정권이 교체된 이후에 김일성가계의 누군가가 재집권할 가능성, IV유형 정권교체는 성공하였지만 내전이 발생할 가능성, V유형 정권교체도 실패하고 내전이 지속적으로 발생할 가능성으로 분류하였다.

• 반도체디스플레이기술학회지
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• 제16권1호
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• pp.11-15
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• 2017

Lithium-ion batteries are widely used, from lightweight to energy-intensive, from small devices to large ESSs. However, it is sensitive to the surrounding environment and there is a change in performance depending on the temperature change. In this study, the temperature dependence of the charge / discharge characteristics of the battery is shown through simulation and the distribution of the salt concentration in the electrolyte is observed when the sudden temperature change is applied.

• Structural Engineering and Mechanics
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• 제26권3호
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• pp.315-341
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• 2007

A sudden change of stiffness in a structure, associated with the events such as weld fracture and brace breakage, will cause a discontinuity in acceleration response time histories recorded in the vicinity of damage location at damage time instant. A new damage index is proposed and implemented in this paper to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. The proposed damage index is suitable for online structural health monitoring applications. It can also be used in conjunction with the empirical mode decomposition (EMD) for damage detection without using the intermittency check. Numerical simulation using a five-story shear building under different types of excitation is executed to assess the effectiveness and reliability of the proposed damage index and damage detection approach for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also examined. The results from this study demonstrate that the damage index and damage detection approach proposed can accurately identify the damage time instant and location in the building due to a sudden loss of stiffness if measurement noise is below a certain level. The relation between the damage severity and the proposed damage index is linear. The wavelet-transform (WT) and the EMD with intermittency check are also applied to the same building for the comparison of detection efficiency between the proposed approach, the WT and the EMD.

• 소음진동
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• 제4권3호
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• pp.353-363
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• 1994

The non-preiodic fluctuation of the engine torque appears to be the major source of the torsional vibration of the automotive driveline. The reduction of this torsional vibration hs become a significant problem along with the requirements of higher performance. The shuffle(tip-in, tip-out) is the transient vibration phenomenon of a vehicle which appears at the sudden change of an accelerator under traveling. By executing of an experiment and a simulation using a model, it has become possible to obtain the design parameter of a driveline for the torsional vibration. This paper presents an experimental and theoretical research on the transient vibration phenomenon of a vehicle which appears at the sudden change of an accelerator under traveling. A dynamic model for the automotive driveline was developed, and all parameters of the mmdel were evaluated with experimental data. The results are as follows: (1) The lower the gea ratio of the transmission is, the more the transient vibration phenomenon of a vehicle appears clearly. (2) The transient vibration phenomenon of a vehicle is affected by the design parmeter of the driveline.

• 융합보안논문지
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• 제17권1호
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• pp.63-68
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• 2017

2011년 1월 튀니지에서 시작된 재스민혁명은 북아프리카와 중동지역 국가들에 많은 변화를 가져왔으며, 우리는 그 원인을 살펴볼 필요가 있다. 우선, 이 지역의 왕정과 독재체제 국가들은 장기집권을 위하여 야당, 언론 등을 탄압하였고, 특권계층에 집중된 권력은 부정부패를 양산하였다. 다음으로, 이 지역 국가들의 국가수입 대부분은 왕실과 독재자에게 귀속되었고, 이를 배분하는 과정에서 문제가 발생하기 시작하였다. 특히, 1990년대 유가하락과 2000년대 생필품 가격 상승은 정부에 대한 불신을 초래하는 계기가 되었다. 마지막으로, 2000년부터 2010년까지 이 지역 국가들의 인터넷 사용자가 평균 4,863% 증가하였고, 페이스북(Facebook), 트위터(Twitter) 등과 같은 소셜 네트워크 서비스(SNS)의 증대도 국가차원의 정보 통제를 어렵게 한 요인이 되었다. 그렇다면, 과연 북한의 급변사태 가능성은 어떠한가에 대한 고민을 해야 한다고 본다. 이를 위해 재스민혁명이 발생 국가들과 북한의 정치, 경제, 사회적 특성 등을 비교 분석할 필요가 있으며, 그 시사점을 도출하고자 한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2785-2790
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• 2007

This study presents an impedance method of in-vitro characterization of the thrombotic potential of whole blood. Whole blood samples of 0.2 cc were put into a micro-cell with embedded three electrodes immediately after venepuncture at $37^{\circ}C$. Anti-coagulated blood samples were also collected for hematocrit and blood viscosity analyses. The rate of change of electron flow was measured, which indicates the inverse of the thrombotic potential. A sudden decrease in the rate of change of electron flow was observed at a time equal to approximately 110 seconds. This sudden decrease was significantly delayed in anti-coagulated samples. After the sudden decrease, the rate continued to decrease, reaching a minimum value in unadulterated samples while the change in the rate in the anti-coagulated ones was found rather moderate. Based on these preliminary findings, the present method may be of used as a new tool for the diagnosis of the thrombotic potential of whole blood.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 학술대회 논문집 정보 및 제어부문
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• pp.268-269
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• 2008

Moving object detection is a fundamental technique in visual surveillance. Robust technique to enhance performance of moving object detection is required for several bad conditions in real external circumtance. In case of sudden illumination change in outdoor condition, many objects are determined as moving object though they are not really moving, but just their illumination changes. This makes the detection result untrustworthy. In this paper, robust moving object detection to sudden illumination change using gaussian mixture background model and new texture information using background from the weighted sum of recent images is proposed.

• 소음진동
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• 제9권2호
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• pp.285-294
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• 1999

Transient analysis for compressible fluid flow has been performed experimentally and analytically to study the dynamic characteristics of the end volume transmission lines following a sudden pressure change a its entrance. The numerical method was developed based on the method of characteristics. The sudden pressure at its entrance was generated by rupture of diaphragm in a shock tube. The sudden pressure was used to obtain the response, as input signal for the numerical analysis. The response to the sudden pressure at the end volume was measured using a pressure transducer. The experimental result shows good agreements with the numerical result. The effects of tube length, its diameter and end volume magnitude are evaluated on the responses of the pressure and on the damping factor. It is found that the viscous damping effects on the response through the transmission pipeline becomes larger with increasing pi;eline length and decreasing diameter of the pipe and the fluid-elastic stiffness decreases with increasing the terminal volume. The numerical approach presented in this paper can be very useful in designing the instrument and control system.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.46-47
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• 2003

Direct numerical simulations are performed for a turbulent flow subjected to a sudden change in pressure gradient. The calculations are started from a fully-developed turbulent channel flow at $Re_{\tau}=180$. The pressure gradient of the channel flow is then changed abruptly. The responses of the turbulence quantities (e.g., turbulence intensities, Reynolds shear stress, and vorticity fluctuations) and the near-wall turbulence structure to the pressure gradient change are investigated. It is found that there are two different relaxations: a fast relaxation at the early stage and a slow one at the later stage. The early response of the velocity fluctuations shows an anisotropic response of the near-wall turbulence.