• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.4
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• pp.537-549
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• 1999

선형탄성 파괴해석은 균열을 갖는 변형률 경화재료의 파괴거동을 예측하는데 불충분하기 때문에 최근에는 균열 선단 부에서 대규모 소성 역을 갖는 균열 체에 적용할 수 있는 많은 파괴역학개념이 제안되고 있다. 따라서, 본 연구에서는 대규모항복 조건하의 연성파괴를 보이는 평판을 정확하게 해석할 수 있는 새로운 유한요소모델을 제시하고자 한다. 균열 선단 부의 응력 장을 정의하는데 가장 지배적인 파괴매개변수인 J-적분 값과 소성 역의 크기 및 형상을 J-적분법과 등가영역적분법을 통해 파괴거동을 설명할 수 있도록 증분소성이론에 기초를 둔 p-version 유한요소해석이 채택되었다. 제안된 유한요소모델에 의한 수치해석결과는 이론 해와 h-version 유한요소해석과 비교되었다.

• Geotechnical Engineering
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• v.13 no.1
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• pp.101-110
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• 1997

This paper presents a two dimensional p-version static infinite element for analyzing $1/r^n$ displacement decay type problems in unbounded media. The proposed element is developed by using shape functions based on approximate expressions of an analytical solution. Numerical results are presented for an opening in a homogeneous elastic infinite medium and a rigid footing rested on a homogeneous elastic half-space. The numerical results show the effectiveness of the proposed infinite element.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.1
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• pp.3-10
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• 2003

Oil drop formation during the underwater oil discharge is investigated experimentally. The focus is placed on the size of the drops formed with the variation of discharge speed and nozzle diameter. As the Reynolds number based on the nozzle diameter increases, the droplet size decreases first and then increases until an explosive atomization occurs. The length of the jet attached to the nozzle Increases with the Reynolds number and then decreases. The transition occurs when the flow becomes asymmetry.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.11b
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• pp.500-505
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• 1996

고온의 정상상태에서 조사된 후 재조직(restructuring)과 균열(cracking)이 일어난 핵연료 내에서 결정립 외부 공극의 을 결정할 수 있는 퍼콜레이션(Percolation) 모델을 개발하였다. 핵연료 펠렛은 다수의 작은 정육각형 결정립들로 구성된 큰 정육각형으로 모의한다. 핵연료봉은 형상과 열적 특성이 다른 네 개의 영역으로 구분하고 각 경계 위치를 임계온도로부터 계산한다. 공극의 상호연결분율은, 몬테카를로 방법으로써 싸이트(Site)의 채워짐 여부를 점검하고 Hoshen-Kopelman 방법으로써 자유 공간에 연결된 클러스터(Cluster)에 포함된 싸이트들의 수를 계산하여 채워진 싸이트의 총 개수에 대한 연결 싸이트들의 개수의 비로써 구한다. AECL-2230, CBX 핵연료봉 실험의 기체 방출분율 자료에 대하여, FASTGRASS 코드의 상호연결분율 함수를 영역별로 계산한 상호연결분율로 대치하여 계산한 결과와 비교하였다. 균열과 재조직은 핵분열 기체 방출에 상당히 영향을 미치는 것으로 나타났다. 이 모델의 주요 장점은 결정립계에서의 상호연결현상을 단순 상호연결분율보다 좀더 사실적으로 모의하며 결정립의 성장과 균열을 고려할 수 있다는 점이다.

• Annual Conference of KIPS
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• 2010.04a
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• pp.531-533
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• 2010

솔리드 텍스처 합성에서 최종 결과의 품질과 마찬가지로 텍스처 합성에 필요한 계산을 단축하는 것은 중요하다. 최근 연구에서는 데이터 차원 감소나 k-coherence search 같은 매칭 가속화 방법을 사용해서 솔리드 텍스처 합성 시간을 단축하였다. 본 논문에서는 빠르게 2D 이미지로부터 솔리드 텍스처 합성을 할 수 있는 새로운 방법을 제시한다. 제안하는 방법의 기본 아이디어는 주어진 이미지를 다수 영역으로 분할하여 형상 매칭(feature matching) 과정에서 사용되는 후보 수를 줄이는 것으로, 사물을 이루는 복셀과 관련한 픽셀이 포함된 분할 영역내의 후보들과 비교함으로써, 보다 빠르게 최적의 결과값을 제공한다. 실험적으로 본 방법은 k-coherence search 알고리즘에서 k 값을 1 로 사용했을 때보다 빠르거나 비슷한 시간을 갖는다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.8-16
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• 2003

Aerodynamic characteristics over Micro Aerial Vehicle(MAV) in low Reynolds number regime are numerically studied using 3-D unsteady, incompressible Navier-Stokes flow solver with single partitioning method for multi-block grid. For more efficient computation of unsteady flows, this flow solver is parallel-implemented with MPl(Message Passing Interface) programming method. Firstly, MAV wing with not complex geometry is considered and then, we analyze aerodynamic characteristics over full MAV configuration varying the angle of attack. Present computational results show a better agreement with the experimental data by MACDL(Micro Aerodynamic Control and Design Lab.), Seoul National University. We can also find the conceptually designed MAV by MACDL has the static stability.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.2
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• pp.74-80
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• 2005

A new dimension measuring method for the measurement of diameter of an object has been developed using laser triangulation. The 3D data of an object was calculated from the 2 dimensional image information obtained by the laser stripe using the laser triangulation. The system that use existing theory can measure the diameter of hole not only in a normal plane but also ill an incline plane. However, in the existing theory, since the lens with fixed feral length was used, the area of measurement was fixed. The simplest way to solve this problem is to change distance between a CCD camera and object. Other way is to use a zoom lens having variable focal length. In this paper, the zoom lens with variable focal length was used. Therefore, we ran experiment with magnification that is optimized according to size of object using zoom lens with variable focal length.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.2
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• pp.153-158
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• 2017

In this paper, we take into account topology optimization problems considering spatial randomness in the material property of elastic modulus. Based on 88 lines MATLAB Code, Monte Carlo analysis has been performed for MBB(messerschmidt-$b{\ddot{o}}lkow$-blohm) model using 5,000 random sample fields which are generated by using the spectral representation scheme. The random elastic modulus is assumed to be Gaussian in the spatial domain of the structure. The variability of the volume fraction of the material, which affects the optimum topology of the given problem, is given in terms of correlation distance of the random material. When the correlation distance is small, the randomness in the topology is high and vice versa. As the correlation distance increases, the variability of the volume fraction of the material decreases, which comply with the feature of the linear static analysis. As a consequence, it is suggested that the randomness in the material property is need to be considered in the topology optimization.

• Journal of Convergence for Information Technology
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• v.11 no.11
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• pp.166-171
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• 2021

An active mount is devised in same geometric constraints with a conventional rubber mount. The proposed mount features the piezoelectric actuator which can be used to reduce the vibration at marine vessels or automotive vehicles. As a first step, a passive rubber mount is adopted and its dynamic characteristics are experimentally evaluated. Based on the geometry of the rubber mount, a rubber element for the active mount is manufactured and integrated with two piezostacks in series, in which the piezostack is operated as an inertial type of actuator. A conventional PID controller featured by the simple and easy implementation, is then designed to attenuate the non-resonant high frequency vibration transmitted from the base excitation. Finally, the control performances of a proposed active mount are evaluated in the wide frequency range and compared with those of the conventional rubber mount.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.5
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• pp.383-389
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• 2014

POD analysis has been done to investigate the internal flow characteristics using LES calculation results of hybrid rocket combustion chamber. The special emphasis was put on the change in the mode energy distribution caused by the installation of diaphragm compared to the baseline case. Also the comparison was made to investigate the effect of wall blowing on the changes in the mode energy between the regions near and far from the diaphragm. For baseline case, POD results clearly distinguish the primary mode containing most of flow energy from the rest of flow modes (2-9 mode) depicting small scale modes. Also, the increase in the energy of flow modes 2-5 is responsible for the formation of relatively large scale structures due to diaphragm. In addition, the comparison of mode energy distributions of flow fields with diaphragm shows similar patterns in both wall blowing and no blowing case. This implies that the local increase in regression rate just after the diaphragm is directly associated with the increase in energy distributions of 2-5 modes.