• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2004년도 춘계학술발표회
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• pp.49-52
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• 2004

RADARSAT은 선박탐지를 포함하는 해상감시에 있어서 중요한 역할을 할 수 있는 데이터중의 하나이며, 이것은 레이더센서를 가지고 있어 전천후 및 주야불문이라는 두 가지 주요 이점을 가지고 있기 때문에 가능하다. 그러나, 합성개구레이더의 이미징시에 대기의 영향은 무시될 수 없으며, 다양한 형태로 기하 변형이 발생하게 된다. 본 연구에서는, 레벨 1의 georeferenced SGX 데이터를 사용해서 RADARSAT의 합성개구레이더에 대한 기하/대기 보정을 시험하였다. 대기보정을 위한 레이더 산란파 크기 등의 정보는 데이터 헤더자료로부터 추출하였으며, DN을 beat nought와 sigma nought로 변환을 실시하였다. 마지막으로 자동 기하보정결과를 실재 좌표 값과 비교하였다.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2011년도 추계학술논문집 2부
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• pp.529-532
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• 2011

Recently research efforts for ubiquitous technology that includes RFID(Radio Frequency Deification and sensor networks are conducted very actively The architectural framework of the USN sensor network discovery service. The survey of the USN technology is conducted on four technological visions that contain USN system technology USN networking technology and USN middleware along with the service platform, With respect to each technological division domestic and worldwide leading research projects are primarily explored with their technical features and research projects are primarily explored with their technical features and research outputs. Boasted on the result of the survey we establish a USN software model that includes data sensing, sensor data storage sensor data storage sensor data naming and sensor feed name service. This main objective of this model is to provide a reference model for the facilitation of USN application developments.

• 중소기업융합학회논문지
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• 제6권2호
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• pp.31-36
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• 2016

Sniffing은 공격자가 암호화 되지 않은 패킷들을 수집하여 순서대로 재조합 하고난 후 공격 대상의 개인정보, 계좌정보 등 중요 정보를 유출하기 위한 수동적 형태의 공격이다. Sniffing 공격으로 인해 패킷들이 유출되는 것을 방지하기 위해 기존의 방법들을 살펴보고, 효율적인 방어대책을 제시하였다. Sniffing공격은 공격 대상의 근거리 네트워크를 Promiscuous Mode을 이용해 조작한 후 필터링을 해제하고 패킷을 훔치는 방식으로 작동한다. 공격의 형태로 Switch Jamming, Port mirroring, ARP Redirect, ICMP Redirect 공격 등이 있다. 제안하는 공격 대응 방법으로는 SSL을 통한 패킷의 암호화, 스위칭 환경의 네트워크 구성 관리, DNS를 이용하는 방법과 decoy방법을 이용하면 안전한 통신이 가능할 것으로 기대하며, 더 효율적이며 안전한 ICT 연구에 기여한다. 향후 프로토타입 프로토콜을 통하여 효율성을 증명하는 것은 향후 연구로 진행할 예정이다.

• 한국토양비료학회지
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• 제49권6호
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• pp.731-742
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• 2016

Recent technological advance in UAV (Unmanned Aerial Vehicle) technology offers new opportunities for assessing crop situation using UAV imagery. The objective of this study was to assess if reflectance and NDVI derived from consumer-grade cameras mounted on UAVs are useful for crop condition monitoring. This study was conducted using a fixed-wing UAV(Ebee) with Cannon S110 camera from March 2015 to March 2016 in the experiment field of National Institute of Agricultural Sciences. Results were compared with ground-based recordings obtained from consumer-grade cameras and ground multi-spectral sensors. The relationship between raw digital numbers (DNs) of UAV images and measured calibration tarp reflectance was quadratic. Surface (lawn grass, stairs, and soybean cultivation area) reflectance obtained from UAV images was not similar to reflectance measured by ground-based sensors. But NDVI based on UAV imagery was similar to NDVI calculated by ground-based sensors.

• 한국컴퓨터정보학회논문지
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• 제10권5호
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• pp.151-160
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• 2005

웹 기반의 응용 어플리케이션 환경에서 서비스의 가용성과 업무의 연속성 보장은 중요한 고려사항이 되었으며, 이를 위해 서버 및 장비의 이중화, 센터의 이중화, 재난복구 센터의 구축 등의 이중화된 통합센터 구조를 갖는 경우를 볼 수 있다. 이러한 아키택쳐로 구현될 경우 웹 브라우저 사용자는 URL이라는 웹사이트 주소를 통해서 해당 센터의 웹 서버에 접근하게 되는데, 이는 웹 브라우저 사용자들이 임의로 URL을 변경하고 임의의 센터에 접속하여 데이터의 저장위치를 비정상적으로 정의하여 데이터의 무결성을 보장하지 못할 수도 있다. 본 논문에서는 사용자 인증방안, 공인인증기관 연계방안, 장애시 업무의 연속성 보장방안 등의 구현방안을 소개하고, 지능적 서비스 접속관리를 제시한다.

• Journal of Mechanical Science and Technology
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• 제19권9호
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• pp.1801-1810
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• 2005

The effect of longitudinal thin rectangular riblets aligned with the flow direction on turbulent channel flow has been investigated using direct numerical simulation. The thin riblets have been modeled using the immersed boundary method (IBM) where the velocities at only one set of vertical nodes at the riblets positions are enforced to be zeros. Different spacings, ranging between 11 and 43 wall units, have been simulated aiming at getting the optimum spacing corresponding to the maximum drag reduction while keeping the height/spacing ratio at 0.5. Reynolds number based on the friction velocity ${\mu}_\tau$ and the channel half depth $\delta$ is set to 150. The flow is driven by adjusted pressure gradient so that the mass flow rate is kept constant in all the simulations. This study shows similar trend of the drag ratio to that of the experiments at the different spacings. Also, this research provides an optimum spacing of around 17 wall units leading to maximum drag reduction as experimental data. Explanation of drag increasing/decreasing mechanism is highlighted.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1661-1670
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• 1996

Incompressible flow over a backward-facing step is computed by low Reynolds number turbulence models in order to compare with direct simulation results. In this study, selected low Reynolds number 1st and 2nd (Algebraic Stress Model : ASM) moment closure turbulence models are adopted and compared with each other. Each turbulence model predicts different flow characteristics, different re-attachment point, velocity profiles and Reynolds stress distribution etc. Results by .kappa.-.epsilon. turbulence models indicate that predicted re-attachment lengths are shorter than those by standard model. Turbulent intensity and eddy viscosity by low Reynolds number .kappa.-.epsilon. models are still greater than DNS results. The results by algebraic stress model (ASM) are more reasonable than those by .kappa.-.epsilon. models. The convective scheme is QUICK (Quadratic Upstream Interpolation for Convective Kinematics) and SIMPLE algorithm is adopted. Reynolds number based on step height and inlet free stream velocity is 5100.

• 대한기계학회논문집B
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• 제33권12호
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• pp.977-982
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• 2009

Direct numerical simulation (DNS) of a turbulent boundary layer with moderate Reynolds number was performed to scrutinize streamwise-coherence of hairpin packet motions. The Reynolds number based on the momentum thickness (${\theta}_{in}$) and free-stream velocity (U${\infty}$) was varied in the range $Re_{\theta}$=1410${\sim}$2540 which was higher than the previous numerical simulations in the turbulent boundary layer. In order to include the groups of hairpin packets existing in the outer layer, large computational domain was used (more than 50${\delta}_o$, where ${\theta}_o$ is the boundary layer thickness at the inlet in the streamwise domain). Characteristics of packet motions were investigated by using instantaneous flow fields, two-point correlation and conditional average flow fields in xy-plane. The present results showed that a train of hairpin packet motions was propagating coherently along the downstream and these structures induced the very large-scale motions in the turbulent boundary layer.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.815-818
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• 2002

The elliptic relaxation model(ERM) with the inhomogeneous correction intermediate between near wall with and far from the wall. The source of the ERM usually was appled quasi-homogeneous pressure-strain correlation in homogeneous situations. This formulation was easily applied to the linear model or non-linear pressure-strain model. It is observed that the boundary conditions of the relaxation operator dominate the homogeneous pressure-strain model in the near wall region. While looking at high-Reynolds number flows, it was found necessary to modify the effect of the relaxation operator throughout the log region by accounting for gradients of the flatness variable and turbulent length scales. These effects are kinematic blocking of the wall normal velocity fluctuation and pressure reflections from the surface. This model is wall distances and unit vectors which make the model applicable to flows boundary by a complex geometry. Inhomogeneous correction model is computed inertial and non-inertial channel flow These are compared DNS(Kim et at., Kristofffrsen & Andersson) for channel flow. The present model could be predicted well for rotating flows.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1741-1749
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• 2001

Recent studies of the structure of wall turbulence have lead to the development of a conceptual model that validates and integrates many elements of previous models into a relatively simple picture based on self-assembling packets of hairpin vortex eddies. By continual spawning new hairpins the packets grow longer in the streamwise direction, and by mutual induction between adjacent hairpins the hairpins are strained so that they grow taller and wider as they age. The result is a characteristic growth angle in the streamwise-wall normal plane. The spanwise growth of individual packets implies that packets must either merge or pass through each other when they come into contact. Direct numerical simulations of the growth and interaction of spanwise adjacent hairpins shows that they merge by the vortex connection mechanism originally proposed by Wark and Nagib (199). In this mechanism the quasi-streamwise legs of two hairpins annihilate each other, by virtue of having opposite vorticity, leaving a new hairpin of approximately double the width of the individuals. PIV measurements in planes parallel to the wall support this picture. DNS of multiple hairpins shows how the spanwise scale doubles when the hairpins form an array.