• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.571-574
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• 2010

Large-eddy simulation has been conducted to simulate turbulent boundary-layer flows over an array of regularly distributed obstacles considering various cases of a wind incident angle. The effect of wind direction was investigated in the square cube array that periodic boundary condition was imposed. Characteristics of the turbulent flow over the obstacle array have been found to be very sensitive to the direction of prevailing wind or of mean wind or of mean pressure gradient but varied with height, specially below the urban canopy. Turbulent statistics are changed sensitively with the direction of mean pressure gradient around 10 degree.

• 한국소음진동공학회논문집
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• 제19권9호
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• pp.922-927
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• 2009

The transducers used in active sonar on surface ships are packed in a specific geometry in the array drum in order to meet the requirements such as the source level, directional beam pattern, etc. This paper describes the acoustic characteristics of the cylindrical array which is based on a 64 vertical staves arrangement, each stave composed 5 independent transducers. Firstly, the single transducer on the rigid baffle in the water is analyzed with the Finite Element Method. From the result of the FE analysis nodal velocities on the radiation surface is calculated and used with the boundary conditions of the transducers mounted on the array drum. Then the acoustic pressure is calculated in the field points using the Boundary Element Method and the other acoustic informations, the source level, beam pattern, near field and far-field distance, were acquired.

• Journal of the Optical Society of Korea
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• 제20권3호
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• pp.363-367
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• 2016

In this paper, we present a resolution-enhanced computational integral imaging reconstruction method by using boundary folding mirrors. In the proposed method, to improve the resolution of the computationally reconstructed 3D images, the direct and reflected light information of the 3D objects through a lenslet array with boundary folding mirrors is recorded as a combined elemental image array. Then, the ray tracing method is employed to synthesize the regular elemental image array by using a combined elemental image array. From the experimental results, we can verify that the proposed method can improve the visual quality of the computationally reconstructed 3D images.

• 한국소음진동공학회논문집
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• 제22권8호
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• pp.756-762
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• 2012

A method of the low-frequency noise reduction in an enclosure by using an array of Helmholtz resonator is presented. An integral form of equation, which represents the acoustical coupling between the internal sound field and the resonator array, is formulated so that the boundary element method can be applied to solve the coupling problem. It is shown that the resonator array on the surface of the enclosure can be regarded as impedance patches on the boundary element. Experiments on a simple enclosure acoustically coupled with an array of resonators are conducted to verify the method. The predicted noise reduction by the boundary element method shows good agreement with the measured one. The effects of the resistance of resonators as well as the number of resonators on the noise reduction are demonstrated. As a practical example, the presented method is applied to the payload fairing of a space launcher with resonator arrays. It is demonstrated that the resistance of resonators affects significantly the required number of resonators to achieve a desired noise reduction.

• 대한기계학회논문집A
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• 제29권9호
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• pp.1161-1168
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• 2005

As a result of vehicle maintenance of rocker arm shaft for 4-cylinder SOHC engine, failure analysis of rocker arm shaft is needed. Because more than $30\%$ of vehicles investigated have been fractured. Failure analysis is classified into an naked eyes, microscope and X-ray fractography etc. It can predict applied load as well as load type. These methods are applicable to components with simple boundary condition but aren't applicable to components with complex boundary condition. The existing fractography don't catch hold of failure boundary condition quantitatively. Especially, in case that the components isn't fractured at same position. We must determine the most dangerous failure boundary condition to evaluate their operation mechanism. The effect of various factors on response should be estimated to solve this statical problem. This study presents the most dangerous failure boundary condition of rocker arm shaft using orthogonal array and ANOVA in order to assure its robustness.

• 한국정보전자통신기술학회논문지
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• 제3권2호
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• pp.31-38
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• 2010

PBG 구조의 메타물질 설계시 패턴 형태와 배열 구조에 따른 금지대역(bandgap)을 정확하게 설계하기 어려운 문제가 있다. 본 논문에서는 2차원 배열구조로 어떤 모양의 패턴에 대해서도 빠르고 정확하게 원하는 금지대역을 설계할 수 있는 방법을 제안한다. 2차원 평면상의 메타물질 구조는 주기배열로 이루어져 있기 때문에 FDTD 수치해석 방법에 주기경계조건을 부여함으로서 계산영역을 줄였다. 또한 각 패턴이 갖는 L, C 값을 2차원적으로 고려하여 계산하였기 때문에 보다 정확한 설계가 가능하였다. 5GHz 대역에서 정사각형 패턴을 갖는 메타물질을 설계하여 기존의 마이크로스트립 선로를 이용한 1차원 메타물질 해석 값과 비교하였을 때 정확도가 평균적으로 14.7% 향상됨을 확인할 수 있었다.

• 한국통신학회논문지
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• 제33권11C호
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• pp.898-904
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• 2008

본 논문에서는 컴퓨터적으로 생성하는 집적영상 시스템에서 요소영상 배열을 생성하기 위한 새로운 fast 알고리즘을 제안한다. 이 알고리즘은 깊이 정보를 사용해서 요소영상 배열을 생성하며, 경계 영역 개념을 도입하여 경계영역 내에 있는 복셀에 대해서만 연산을 수행하여 알고리즘의 계산 속도를 개선하였다. 제안된 알고리즘과 기존 알고리즘의 계산 시간을 이론적 및 실험적으로 비교한 결과 제안된 알고리즘이 더 효율적임을 증명하였다.

• 한국해양공학회지
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• 제25권1호
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• pp.8-13
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• 2011

A compact array system of small buoys is used for wave energy extraction. To evaluate the performance of this system, hydrodynamic analysis is carried out in regular waves using the higher order boundary element method. The motion response of each buoy is calculated considering hydrodynamic interactions caused by other buoys. The effect of energy extraction device is modeled as a linear damping load. The efficiencies of energy conversion are compared using the various sizes and arrangements of the array system and the damping coefficients for energy extraction. The increase in size or the packing ratio of the system gives better efficiency. However, the wave condition and the cost for the system should be considered to optimize performance from the perspective of engineering and economics. The proposed nondimensionalized damping coefficient for energy extraction is 0.1~0.5.

• Korean Journal of Mathematics
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• 제16권2호
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• pp.135-143
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• 2008

We investigate the existence of nontrivial solutions of the nonlinear biharmonic system with Dirichlet boundary condition $$(0.1)\;\begin{array}{lcr}{\Delta}^2{\xi}+c{\Delta}{\xi}={\mu}h({\xi}+{\eta})\;in{\Omega},\\{\Delta}^2{\eta}+c{\Delta}{\eta}={\nu}h({\xi}+{\eta})\;in{\Omega},\end{array}$$ where $c{\in}R$ and ${\Delta}^2$ denote the biharmonic operator.

• Korean Journal of Mathematics
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• 제17권2호
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• pp.197-210
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• 2009

We prove the existence of multiple solutions (${\xi},{\eta}$) for perturbations of the elliptic system with Dirichlet boundary condition $$(0.1)\;\begin{array}{lcr}A{\xi}+g_1({\xi}+ 2{\eta})=s{\phi}_1+h\;in\;{\Omega},\\A{\xi}+g_2({\xi}+ 2{\eta})=s{\phi}_1+h\;in\;{\Omega},\end{array}$$ where $lim_{u{\rightarrow}{\infty}}\frac{gj(u)}{u}={\beta}_j$, $lim_{u{\rightarrow}-{\infty}}\frac{gj(u)}{u}={\alpha}_j$ are finite and the nonlinearity $g_1+2g_2$ crosses eigenvalues of A.