• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.5
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• pp.422-429
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• 2011

The critical fluid velocity of cantilevered cylindrical shells subjected to internal fluid flow is investigated in this study. The fluid-structure interaction is considered in the analysis. The cantilevered cylindrical shell is supported intermediately at an arbitrary axial position. The intermediate support is simulated by two types of artificial springs: translational and rotational spring. It is assumed that the artificial springs are placed continuously and uniformly on the middle surface of an intermediate support along the circumferential direction. The steady flow of fluid is described by the classical potential flow theory. The motion of shell is represented by the first order shear deformation theory (FSDT) to account for rotary inertia and transverse shear strains. The effect of internal fluid can be considered by imposing a relation between the fluid pressure and the radial displacement of the structure at the interface. Numerical examples are presented and compared with existing results.

• Journal of Korea Game Society
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• v.1 no.1
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• pp.49-54
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• 2001

본 논문에서는 복잡한 랜덤 배경 하에서 위치하고 있는 게임 플레이어의 얼굴 영상을 스테레오 매칭을 이용하여 배경과 분리하여 추출할 수 있는 방법에 대하여 기술한다. 사람과의 상호 작용이 필요한 게임일수록 사람의 동작이나 각 부위에 대한 인식이 필요하다. 이 방법은 게임 이외에도 보안 시스템, 의류 시뮬레이션, 3D 모델링 그리고 로보틱스와 같은 분야에 적용될 수 있다. 스테레오 매칭에 관해서는 많은 연구가 있어왔으며, 기본적으로 영역기반 방법과 특징기반 방법으로 분류될 수 있다. 본 논문의 제안 방법 에서는 영역기반 방법으로 처리를 시작하고, 다단계 크기의 윈도우를 적용하여 물체의 경계선을 찾는 작업을 진행한다. 각 윈도우 크기에 대하여 유사성 커브가 생성되며, 이 값은 물체의 경계선을 판별하는 특징으로 사용된다. 전단계에서 생성된 코어스(coarse) 영역은 유사성 커브 방식에 의하여 머지 작업을 거치며, 최종적으로 대상 물체의 영상을 추출하게 된다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.639-642
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• 2011

이 연구에서는 완전 조립식 교량 하부구조의 비선형해석을 위한 전산플랫폼을 개발하였다. 완전 조립식 교량 하부구조의 비선형거동을 정확하게 파악하고 합리적이면서 경제적인 설계기준의 개발을 위한 자료를 제공하는데 그 목적이 있다. 재료적 비선형성에 대해서는 균열콘크리트에 대한 인장, 압축, 전단모델과 콘크리트 속에 있는 철근모델을 조합하여 고려하였다. 사용된 부착 또는 비부착 텐던요소는 유한요소법에 근거하며 프리스트레스트 콘크리트 부재의 콘크리트와 텐던의 상호작용을 구현할 수 있다. 그리고 접합면요소는 세그먼트 접합부의 비탄성거동을 예측할 수 있다. 제안된 해석기법은 수치예제에 대하여 비선형거동을 비교적 정확하게 예측하였다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.6
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• pp.637-652
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• 2013

After studying the characteristics of three different evaluation methods of rock load; namely theoretical method, empirical method and numerical method, there were too many limitations for them to be applied on tunnels. Therefore, in this research paper, the method based on numerical analysis is selected to use as this method is the most reasonable one since it considers all parameters that are necessary for rock load estimations, and it also considers the interaction between ground and tunnel support. The critical shear strain concept formulated by Sakurai (1981) was used in order to measure exact rock load values based on numerical analysis. Evaluation on a Level 1 rock load height, which is depicted by the stable region in the graph shows that rock load is not affecting between ground grade 1~3, and it was evaluated that the fourth and fifth grades show less values of rock load height which led to the conclusion of a more economical design of concrete lining.

• Polymer(Korea)
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• v.38 no.2
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• pp.225-231
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• 2014

The rheological properties of highly concentrated polymer bonded explosive simulant were studied by using poly(ethylene-co-vinyl acetate) with 30 and 60% vinyl acetate (VA) content as a binder, respectively. Calcium carbonate and Dechlorane, whose physical properties are similar to resarch department explosive (RDX)'s, were used as fillers. The suspensions were mixed in a batch melt mixer and it was possible to fill 75 v% at maximum. From dynamic mechanical analysis, Dechlorane showed higher interaction with binder resins than that with calcium carbonate fillers. The effects of microstructural change on the rheological properties of the suspensions were investigated by a plate-plate rheometer with constant shear rate and constant shear stress modes, respectively. The theoretical maximum packing fraction of EVA31/Dechlorane suspension obtained from Krieger-Dougherty equation was 70 v% and it was thought that 2000 Pa was proper shear stress condition for this melt processing.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.395-395
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• 2015

하천 내 식생은 수리학, 지형학 및 생태학적으로 매우 중요하다. 식생은 하천 수생물들의 서식처를 제공할 뿐만 아니라 필터와 같은 역할을 함으로써 부유사에 의한 하천오염물의 퇴적을 유발하여 하천의 수질을 개선시킨다. 더욱이, 하천 내 흐름 및 난류구조를 변경시킴으로써 식생주변의 유사 퇴적량 및 분포에 크게 영향을 미치고, 결국 하천의 지형을 변화시킨다. 개수로의 식생에 대한 영향은 주로 실험 및 수치모델을 이용하여 연구되었고 전단면이 식재된 조건에서 식생의 항력계수, 식생역내의 부유사 및 확산에 관한 연구가 진행되어왔다. 이러한 연구를 통해 식생역 내의 전단력이 감소하여 부유사퇴적이 증가하고 식생역과 비식생역 사이의 운동량 교환에 의해 부유사 퇴적이 증가함을 보였다. 그러나 개수로에서 존재하는 유한한 크기의 식생에 의한 흐름 및 유사분포에 관한 연구는 아직 미흡하다. 이에 본 연구에서는 침수하지 않은 원형 식생 주변에서 발생하는 흐름특성을 수치모의 하였다. 침수하지 않은 원형식생 하류에서 발생하는 흐름을 계산하기 위해 2차원 수치모형을 적용하였다. 식생에 의한 저항을 고려하기 위해 운동량 방정식에 식생항을 추가하였고 $k-{\varepsilon}$ 난류모형을 적용하였다. 수치모의 조건은 Zong and Nepf (2012)의 수리실험을 참고하여 수로의 길이는 12 m, 폭은 1.2 m로 설정하였다. 0.13 m 수심을 갖는 개수로에 0.22 m 지름을 갖는 원형식생을 상류경계로부터 1.0 m 떨어진 곳에 설정하였다. 식생의 밀도($6{\sim}77m^{-1}$)를 변화시키면서 원형식생 하류의 흐름거동을 분석하였다. 식생밀도가 높은 경우에는 원형식생 양 측면에서 유발된 전단층들의 상호작용에 의해 하류에서 와류가 발생하였다. 와류가 발생하는 위치에서 난류강도가 가장 크게 나타났다. 그러나 식생밀도가 일정 값보다 낮아지면 와류가 발생하지 않는 것으로 나타났다.

• Journal of Navigation and Port Research
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• v.29 no.6 s.102
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• pp.515-522
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• 2005

The ship plating is generally subjected to. combined in-plane load and lateral pressure loads, In-plane loads include axial load and edge shear, which are mainly induced by overall hull girder bending and torsion of the vessel. Lateral pressure is due to. water pressure and cargo. These load components are nat always applied simultaneously, but mare than one can normally exist and interact. Hence, far mare rational and safe design of ship structures, it is af crucial importance to. better understand the interaction relationship af the buckling and ultimate strength far ship plating under combined loads. Actual ship plates are subjected to relatively small water pressure except far the impact load due to. slamming and panting etc. The present paper describes an accurate and fast procedure for analyzing the elastic-plastic large deflection behavior up to. the ultimate limit state of ship plates under combined loads. In this paper, the ultimate strength characteristics of plates under axial compressive loads and lateral pressure loads are investigated through ANSYS elastic-plastic large deflection finite element analysis with varying lateral pressure load level.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.2
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• pp.1-12
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• 1990

Interactions between a propeller and vortex system contained in a ship stern flow is treated theoretically. A new formulation to determine the effective velocity distributions is developed, which may be immediately applicable to the design and analysis of compound propulsors under the influence of severe vortical cross-flows around ship stern. An axisymmetric shear flow is represented by a system of ring vortices and the axial variation of the stream lines due to the action of propeller is represented by a cubic function. The strengths of ring vortices, which are varying along the stream lines, are determined by the conservation of angular momentum. Two simplified effective velocity models are proposed to confirm the theory. Sample calculations using the simplified models are made to compare with the results by other investigators.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.4
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• pp.238-245
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• 2015

Recently, Choi et al.(2015) showed that a numerical simulation of the SandyDuck experiment under a directional random wave environment agreed well with the experimental data including the wave height distribution of the random waves, the well-developed longshore current and its energetic fluctuation. Based on the Boussinesq modeling, this study investigates the effect of the alongshore variations, which are induced by not only the field topography but also the phase interaction of multidirectional random waves in the surf zone wave field, on the rip currents. As a result, transient rip currents as well as topographical rip currents cause the complicated surfzone circulation and mixing process due to their interactions in a multi-directional random wave condition while the topographical rip currents are dominant in a monochromatic wave condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.1
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• pp.62-68
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• 2009

The interaction between wall blowing and oxidizer flow can generate a very complicated flow characteristics in combustion chamber of hybrid rockets. LES analysis was conducted with an in-house CFD code to investigate the features of turbulent flow without chemical reactions. The numerical results reveal that the flow oscillations at a certain frequency exists on the fuel surface, which is analogous to those observed in the solid propellant combustion. However, the observation of oscillating flow at a certain frequency is only limited to a very thin layer adjacent to wall surface and the strength of the oscillation is not strong enough to induce the drastic change in temperature gradient on the surface. The visualization of fluctuating pressure components shows the periodic appearance of relatively high and low pressure regions along the axial direction. This subsequently results in the oscillation of flow at a certain fixed frequency. This implies that the resonance phenomenon would be possible if the external disturbances such as acoustic excitation could be imposed to the oscillating flow in the combustion chamber.