• 대한조선학회논문집
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• 제44권2호
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• pp.101-110
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• 2007

Recently, rudder erosion due to cavitation frequently has occurred at large high speed container carriers. Especially, in the case of a horn-type rudder, the rudder erosion is severe around a gap. The gap-flow characteristics are investigated through a computational method to understand the effects of a gap on the cavitation and rudder efficiency. A viscous flow theory utilizing a cavitation model is applied to calculate the flow around idealized 2-dimensional rudder sections in a full scale. The effects of gap clearance and flow-control projection are also investigated. From the computational results, the mass flow rate through a gap is found to be one of the important parameters to affect the cavitation and rudder efficiency.

• International Journal of Air-Conditioning and Refrigeration
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• 제8권2호
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• pp.11-22
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• 2000

Holographic interferometric tomography can provide reconstruction of instantaneous three-dimensional gross flow fields. The technique however confronts ill-posed reconstruction problems in practical applications. Experimental data are usually limited in projection and angular scanning when a field is captured instantaneously or under the obstruction of test models and test section enclosures. An algorithm, based on a series expansion method, has been developed to improve the reconstruction under the ill-posed conditions. A three-dimensional natural convection flow around two interacting isothermal cubes is experimentally investigated. The flow can provide a challenging reconstruction problem and lend itself to accurate numerical solution for comparison. The refractive index fields at two horizontal sections of the thermal plume with and without an opaque object are reconstructed at a limited view angle of 80$\circ$. The experimental reconstructions are then compared with those from numerical calculation and thermocouple thermometry. It confirms that the technique is applicable to reconstruction of reasonably complex, three-dimensional flow fields.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.835-836
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• 2006

For non-contact structure vibration displacement measurement system, an algorithm for image processing using high speed CCD camera is introduced. The system sets the target to the structure, take picture using camera and image processing is performed to display the vibration data. The algorithm flow is basic preprocessing, projection data generation and curve fitting to find three crossing points for calibration or one center point in limited area.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.155-161
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• 1999

The three-dimensional turbulent cascade flows with and without endwall fences are numerically investigated by solving the incompressible Navier-Stokes equations with a high-Reynolds number $k-{\varepsilon}$ turbulence closure model. A projection method based algorithm is used in the finite-volume formulation, with the second order upwind-differencing scheme for the convective terms. First, assessments on accuracy of the present method are made by comparing the static pressure distributions at the mid-span of the cascade with measured data, and also by confirming the experimental observations on the choice of an optimal fence height for the secondary flow control. In understanding the three-dimensional nature of the secondary flow in turbine cascade, the limiting streamline patterns and the static pressure contours at the suction surface of the blade as well as on the cascade endwall are employed to visualize the effectiveness of the endwall fence for the secondary flow control. Analysis on the streamwise vorticity contour maps along the cascade with the three-dimensional representation of their iso-surfaces reveals the strucuture of the complicated vortical flow in the turbine cascade with endwall fence, and also leads to an understanding on formation of the counter-rotating streamwise vortex over the endwall fence, in explaining the mechanisms of controlling the secondary flow and also for the proper selection of an optimal fence height.

• 한국수자원학회논문집
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• 제53권12호
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• pp.1049-1057
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• 2020

본 연구는 드론을 이용하여 홍수기 하천에서의 유량측정방법 개발을 위해 수행하였다. 홍수기 유량측정은 예산, 인력, 안전 및 하천공사 등의 문제로 매년 모든 지점에서 유량 측정을 실시하지 못하는 어려움이 있다. 특히 태풍 등 큰 호우사상 발생 시 수위-유량관계 변화 검토가 필요하지만 앞에서 언급한 문제 등으로 인하여 측정에 어려움이 있다. 이런 문제점을 개선하기 위해 최소 인력이 단시간 간편하게 측정할 수 있는 방법을 개발하였다. 항공사진측량 개념으로 접근하여 의정부시(신곡교) 지점과 영동군(영동제2교) 지점 하도 주변에 확인 가능한 위치에 지상기준점(GCP, Ground Control Points) 4개점을 선점하고 VRS DGPS 장비를 이용하여 좌표측량을 수행하였다. 드론을 일정높이의 정지상태(Hovering)에서 하도 내 수 표면을 카메라의 인터벌 기능으로 3초 간격 정사영상을 촬영하였다. 정사 촬영된 항공사진의 좌표계를 평면지각좌표계인 GRS80 TM좌표계로 정의한 후 GCP 좌표를 활용하여 보다 정밀하게 정사보정을 실시하였다. 수표면에 유하하는 부유물의 3초 간격 위치를 X, Y좌표 분석을 통해 이동거리를 평균유속으로 산정하고 유하경로에 따른 통수단면적을 적용하여 유량을 산정하였다. 따라서 항공사진측량 기법을 적용하여 홍수기에 드론을 이용한 유량측정방법에 대한 적용성을 확인하였다.

• ETRI Journal
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• 제40권2호
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• pp.246-256
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• 2018

A spatial augmented reality (SAR) system enables a virtual image to be projected onto the surface of a real-world object and the user to intuitively control the image using a tangible interface. However, occlusions frequently occur, such as a sudden change in the lighting environment or the generation of obstacles. We propose a robust object tracker based on a multithreaded system, which can track an object robustly through occlusions. Our multithreaded tracker is divided into two threads: the detection thread detects distinctive features in a frame-to-frame manner, and the tracking thread tracks features periodically using an optical-flow-based tracking method. Consequently, although the speed of the detection thread is considerably slow, we achieve real-time performance owing to the multithreaded configuration. Moreover, the proposed outlier filtering automatically updates a random sample consensus distance threshold for eliminating outliers according to environmental changes. Experimental results show that our approach tracks an object robustly in real-time in an SAR environment where there are frequent occlusions occurring from augmented projection images.

• 지질공학
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• 제22권1호
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• pp.83-94
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• 2012

산악지와 하천지에 위치하는 도로에는 도로 상부와 하부에 모두 비탈면이 조성된 경우가 많다. 북실지구는 도로 하부에 조성된 깎기비탈면으로서 2010년 10월 붕괴가 발생하였다. 정밀 현장조사 결과, 본 비탈면의 붕괴 원인은 도로 상부비탈면 계곡수의 배수 불량과 도로 표면수의 직접적 유입 등인 것으로 판단된다. 이는 층리 발달과 같은 지반 내적 요인과 복합적으로 작용하여 붕괴를 촉진시켰을 가능성이 높다. 평사투영해석 결과 평면파괴, 쐐기파괴, 전도파괴의 가능성이 인지되었다. 한계평형해석을 통한 안전율 산출 결과 우기시 평면파괴 및 쐐기파괴 안전율이 기준치에 미달되었다. 북실지구의 지형요소를 이용한 습윤지수 분석 결과, 9~10.5로 주변지역에 비하여 높은 값을 가지므로 유수의 영향이 집중되었던 것으로 판단된다. 북실지구 비탈면 안정성 확보에는 도로 상부에서 발생하는 유수 제어가 중요한 역할을 할 것으로 사료된다.