• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2009년도 학술발표회 초록집
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• pp.815-821
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• 2009

하천의 2차원 흐름 및 하상변동, 오염확산 해석을 위한 유체의 수치해석법에는 유한요소법, 유한차분법, 유한차분법의 변형인 유한체적법, 경계적분법 등이 있으며, 국내의 경우 비구조적 요소망(unstructured mesh)을 이용하여 복잡한 형상을 표현하기가 상대적으로 용이한 유한요소법이 널리 사용되고 있다. 하천을 유한 요소화 하는 전처리 과정은 전체 해석 과정을 자동화 하는데 있어 필수적인 요소이며, 주로 삼각 요소망 또는 사각 요소망을 이용하여 해석을 수행하게 된다. 삼각 요소망의 경우 상대적으로 자동화하기 쉬운 반면 사각 요소망의 생성은 절점 생성 자체가 삼각 요소망 보다 더 많은 기하학적 제한 요소를 가지고 있기 때문에 상대적으로 완성도 높은 알고리즘을 구현하기가 어렵다 할 수 있다. 이에 따라 본 연구에서는 2차원 상에서 사각 요소망(quadrilateral elements)을 생성할 수 있는 Paving method를 중심으로 한 요소망 생성 알고리즘에 대해 고찰하고, 국내 최초의 범용 수치해석 모형인 RAMS(River Analysis and Modeling System)에 적용하였다. Paving method는 1990년에 Blacker and Stephenson에 의해 제안되었으며, Sandia National Laboratories에 의해 완성되었다. Paving Method는 advancing front style의 요소망을 생성하게 되고, 바깥쪽에서 안쪽으로 element layer를 생성하면서 채워나간다. 본 연구에서는 기존의 요소망 생성 프로세스에서 element 삽입 전의 검증 기능을 강화한 새로운 버전의 paving method를 적용하엿다.

• Fisheries and Aquatic Sciences
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• 제11권1호
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• pp.61-69
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• 2008

Using empirical data of fish performance and physiological limits as well as physical stimuli and environmental data, a cod-end selectivity model based on a chaotic behavior model using the psycho-hydraulic wheel and neural-network approach was established to predict fish escape or herding responses in trawl and cod-end designs. Fish responses in the cod-end were categorized as escape or herding reactions based on their relative positions and reactions to the net wall. Fish movements were regulated by three factors: escape time, a visual looming effect, and an index of body girth-mesh size. The model was applied to haddock in a North Sea bottom trawl including frequencies of movement components, swimming speed, angular velocity, distance to net wall, and the caught-fish ratio; simulation results were similar to field observations. The ratio of retained fish in the cod-end was limited to 37-95% by optomotor coefficient values of 0.3-1.0 and to 13-67% by looming coefficient values of 0.1-1.0. The selectivity curves generated by this model were sensitive to changes in mesh size, towing speed, mesh type, and mesh shape.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.120-124
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• 2007

Helicopters and rotary-wing vehicles encounter a wide variety of complex aerodynamic phenomena and these phenomena present substantial challenges for computational fluid dynamics(CFD) models. This investigation presents the rotor aerodynamic analysis items for the helicopter development and variety aerodynamic analysis methods to provide the better solution to researchers and helicopter developers between aerodynamic problems and numerical aerodynamic analysis methods. The numerical methods to make an analysis of helicopter rotor are as below - CFD Modelling : actuator disk model, BET model, fully rotor model,... - Grid : sliding mesh, chimera mesh / structure mesh, unstructure mesh,... - etc. : panel method periodic boundary, quasi-steady simulation, incompressible,... The choice of CFD methodology and the numerical resolution for the overall problem have been driven mostly by available computer speed and memory at any point in time. The combination of the knowledge of aerodynamic analysis items, available computing power and choice of CFD methods now allows the solution of a number of important rotorcraft aerodynamics design problems.

• 대한조선학회논문집
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• 제45권4호
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• pp.411-416
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• 2008

A strength problem of propeller blades for large container ships at astern condition has been occasionally reported due to the application of a highly skewed propeller which can reduce the hull surface fluctuation forces. A finite element analysis code for propeller blade was developed and utilized since 1985. Recently, however, further fine mesh modeling for finite element analysis is required to yield higher accuracy in the analysis. The present study shows an application of FE analysis code to the highly skewed propeller for large container ships. Results of FE analysis show that the number of FE mesh affects largely on strength, and also the calculated strength with fine mesh gives good agreements to those of other FEM codes. A method to enlarge strength near the trailing edge was introduced considering the strength criterion on the blade.

• ETRI Journal
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• 제38권1호
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• pp.41-51
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• 2016

Smart metering systems have become widespread around the world. RF mesh communication systems have contributed to the creation of smarter and more reliable power systems. This paper presents an algorithm for positioning GPRS concentrators to attain delay constraints for a ZigBee-based mesh network. The proposed algorithm determines the number and placement of concentrators using integer linear programming and a queueing model for the given mesh network. The solutions given by the proposed algorithm are validated by verifying the communication network performance through simulations.

• 한국정보통신학회논문지
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• 제12권8호
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• pp.1377-1383
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• 2008

3차원 메쉬 매개변수화는 기하학적 모델링과 컴퓨터그래픽스의 여러 응용분야에서 핵심적인 문제이다. 메쉬 매개변수화 방법에는 크게 두 가지의 패러다임, 에너지 최소화 방법과 볼록 조합법이 있다. 일반적으로 볼록 조합법은 간단한 개념과 일대일 대응 때문에 널리 이용되고 있다. 그러나 이 방법은 경계선 근처의 높은 왜곡이 생긴다는 문제와 선형 시스템 구성에 있어 다소 많은 시간이 소요되는 문제를 가지고 있다. 또한 이 방법은 다루는 메쉬 의 기하학 정보에 따라 선형시스템의 안정성이 해손 될 수도 있다. 본 논문에서는 볼록 조합법이 갖고 있는 선형시스템 안정성 문제와 시간 복잡도 문제를 중간값 좌표계를 이용하여 해결한다. 빠른 시간에 안정적으로 처리가 가능하기 때문에 보다 실용적이라 할 수 있다.

• Structural Engineering and Mechanics
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• 제86권6호
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• pp.793-815
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• 2023

The current study looks at the experimental and numerical performance of ferrocement RC channel slabs reinforced with welded steel mesh, expanded steel mesh, and fiber glass mesh individually. Ten RC channel slabs with dimensions of 500 mm×40 mm×2500 mm were subjected to flexural loadings as part of the testing program. The type of reinforcing materials, the number of mesh layers, and the reinforcement volume fraction are the key parameters that can be changed. The main goal is to determine the impact of using new inventive materials to reinforce composite RC channel slabs. Using ANSYS -16.0 Software, nonlinear finite element analysis (NLFEA) was used to simulate the behavior of composite channel slabs. Parametric study is also demonstrated to identify variables that can have a significant impact on the model's mechanical behavior, such as changes in slab dimensions. The obtained experimental and numerical results indicated that FE simulations had acceptable accuracy in estimating experimental values. Also, it's significant to demonstrate that specimens reinforced with fiber glass meshes gained approximately 12% less strength than specimens reinforced with expanded or welded steel meshes. In addition, Welded steel meshes provide 24% increase in strength over expanded steel meshes when reinforcing RC channel slabs. In general, ferrocement specimens tested under flexural loadings outperform conventional reinforced concrete specimens in terms of ultimate loads and energy absorbing capacity.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2020년도 학술발표회
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• pp.122-122
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• 2020

Urban flood simulation plays a vital role in national flood early warning, prevention and mitigation. In recent studies on 2-dimensional flood modeling, the integrated run-off inundation model is gaining grounds due to its ability to perform in greater computational efficiency. The adaptive quadtree shallow water numerical technique used in this model implements the adaptive mesh refinement (AMR) in this simulation, a procedure in which the grid resolution is refined automatically following the flood flow. The method discounts the necessity to create a whole domain mesh over a complex catchment area, which is one of the most time-consuming steps in flood simulation. This research applies the dynamic grid refinement method in simulating the recent extreme flood events in Metro Manila, Philippines. The rainfall events utilized were during Typhoon Ketsana 2009, and Southwest monsoon surges in 2012 and 2013. In order to much more visualize the urban flooding that incorporates the flow within buildings and high-elevation areas, Digital Surface Model (DSM) resolution of 5m was used in representing the ground elevation. Results were calibrated through the flood point validation data and compared to the present flood hazard maps used for policy making by the national government agency. The accuracy and efficiency of the method provides a strong front in making it commendable to use for early warning and flood inundation analysis for future similar flood events.

• 지적과 국토정보
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• 제52권1호
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• pp.69-80
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• 2022

드론사진측량은 일반적으로 상공에서 수직 또는 경사로 영상을 획득하므로 3차원 모델링을 위한 목적으로 촬영할 경우 건물의 지면부분에 대한 영상매칭과 점군데이터의 공간정확도가 불량하여 3D메쉬의 완성도가 떨어진다. 따라서 본 연구에서는 이를 극복하기 위해 드론영상과 지상에서 스마트폰 영상을 획득하여 각각의 공간정확도를 분석함은 물론 드론영상에 스마트폰영상을 조합하지 않았을 경우와 조합해석 했을 경우의 정확도 향상과 3D메쉬의 완성도를 평가하였다. 연구결과 드론사진측량의 수평(x,y)정확도는 1/200,000정도로 전통적인 사진측량 정확도와 유사하였다. 또한, 촬영방법에 따른 정확도는 사진맷수의 증가보다 대상물에 대한 촬영각도에 영향을 더 받는 것으로 분석되었다. 스마트폰영상 조합의 경우 정확도에 별다른 영향을 미치지 않았으나 3D메쉬의 완성도는 디지털트윈시티 기준을 만족하는 LoD3급의 3D메쉬를 얻을 수 있었다. 따라서, 드론영상과 지상에서 촬영한 스마트폰 또는 DSLR영상을 조합처리 함으로써 디지털트윈시티를 위한 3D모델 구축에 충분히 활용할 수 있을 것으로 판단된다.

• 한국정밀공학회지
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• 제29권10호
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• pp.1043-1049
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• 2012

The FEM analysis of machine tools is the general analysis process to evaluate machine performance in the industry for a long time. Despite advances in FEM software, because of difficult simplicity of CAD drawing, little experience of joints stiffness modeling and troublesome manual contact area divide for bindings, the industry designers think the FEM analysis is still an area of FEM analysis expert. In this paper, the automation of modeling process with simplicity of drawing, modeling of joints and contact area divide is aimed at easy FEM analysis to enlarge utilization of a virtual machine tools. In order to verify the effects of modeling automation, a slant bed type model with tilting table is analyzed. The results show FEM modeling automation method only needed 45 minutes to complete the whole modeling process, while manual modeling method requires almost one month with 8200 calculations for coordinate transformations and stiffness data input.