• 한국결정학회지
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• 제7권2호
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• pp.105-112
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• 1996

Tetra-tert-butyl-dipropionyloxy-dihydroxycalis[4]arene (C50H64O6)의 구조를 X-선 회절법으로 연구하였다. 결정의 공간군은 C2/c이다. 단위세포 상수는 a=16.067(2), b=26.391(17), c=10.335(1)Å, β=94.26(1)°, Z=4, V=4370.2(29)Å3, Dc=1.16, Dm=1.2 gcm-3이다. 회절반점들의 세기는 Enraf-Nonius CAD-4 Diffractometer로 얻었으며, Cu-Kα radiation (λ=1.5418Å)을 사용하였다. 분자구조는 직접법으로 풀었으며 최소 자승법으로 정밀화하였다. 최종 신뢰도 R값은 2354개의 회절반점에 대하여 0.07이였다. 이 Calix[4]arene은 1, 3-alternate conformation을 가진 분자로 2개의 propionyloxy groups이 위쪽에 있고, 마주보는 두 개의 hydroxy groups이 아래로 향해 있으며, 분자 한 가운데에 결정학적 symmetry axis와 일치하는 2-fold symmetry axis가 있는 분자이다.

• 천문학논총
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• 제30권2호
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• pp.345-347
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• 2015

We present evolutionary models of rotating self-gravitating systems (e.g. globular clusters, galaxy cores). These models are characterized by the presence of an initial axi-symmetry due to rotation. Central black hole seeds are included in our models, and black hole growth due to the consumption of stellar matter is simulated until the central potential dominates the kinematics of the core. Our goal is to study the long-term evolution (Gyr) of relaxed dense stellar systems which deviate from spherical symmetry, and their morphology and final kinematics. With this purpose in mind, we developed a 2D Fokker-Planck analytical code, and confirmed its results using detailed N-Body simulations, applying a high performance code developed for GPU machines. We conclude that the initial rotation significantly modifies the shape and lifetime of these systems, and cannot be neglected in the study of the evolution of globular clusters, and the galaxy itself. Our models give a constraint for the final intermediate black hole masses expected to be present in globular clusters.

• Design & Manufacturing
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• 제6권1호
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• pp.73-78
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• 2012

The aim of this dissertation is inferring factors controlling the complex strain behavior of the material and the characteristics of the Fine-Blanking in the most narrow area at the shear zone where we are performing the Fine-Blanking. And also this is for inspecting and presenting their uses and the possibilities to make the results data based in order to utilize easily. Therefore, to analyze of shere zone's strain behaviour, the Fine-Blanking process need to be modelled defining the quadratic-nodded and axi-symmetrical elements as the problems of large deformation axi-symmetry and the non-linear contact. For the method of inputting strain-stress values of the material, the piece-wise linear technics were used, the Implicit-Finite Element method also used making balance of forces on each step by the long intervals, calculates and converges many times was done. The materials used for the analysis was the Steel SNCM220 5.5mm respectively. As the result of FEM analysis, we know that shear stress value in the beginning of punch penetration is distributed widely and done high both in the center of the late-thickness and on the both sides centering around shear strain zone as the punch penetration is increasing. Also.

• 대한기계학회논문집B
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• 제28권4호
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• pp.433-440
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• 2004

Since the numerical analysis was adopted in the mold design, lots of computational methods have been proposed for the simulations of casting processes for the various shaped molds. Today, it is possible to simulate the filling and solidification processes of most casts using the VOF technique. Though the three-dimensional numerical model based on the Cartesian coordinate system can be applied to any shape of cast, it becomes very inefficient when the three-dimensional model is applied to the cast of axi-symmetrical shape since the control volume includes at least 11 of the physical model. In addition, the more meshes should be distributed along the circumferential boundaries of curved shape in the Cartesian coordinate system fur the better results, while such curved circumferential boundary does not need to be considered in the two-dimensional cylindrical coordinate system. This motivates the present study i.e. developing a two-dimensional numerical model for the axi-symmetrically shaped casts. The SIMPLER algorithm, the VOF method, and the equivalent specific heat method have been adopted in the combined algorithm for the flow calculation, the free surface tracking, and the phase change heat transfer, respectively. The numerical model has been applied to the casting process of a pulley, and it was proven that the mesh and time effective calculation was accomplished comparing to the calculation using three-dimensional model.

• 해양환경안전학회지
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• 제24권2호
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• pp.246-252
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• 2018

본 논문은 3차원 축대칭 몰수체에 대해 소스 코드가 공개된 OpenFOAM 4.0을 이용하여 첫 번째 격자의 높이와 레이놀즈 수에 따른 마찰저항 변화에 대해 연구하였다. 마찰저항 계산을 위해 경계조건, 수치조건을 정립하였다. 축대칭 물체의 3차원 효과로 인해 거칠기가 매우 작은 $12{\mu}m$에서도 부드러운 표면과 비교해 마찰저항이 다르게 계산되었다. 레이놀즈 수가 커질수록 경계층의 두께 증가가 감소되었으며 이로 인해 마찰저항의 증가량이 감소되었다. 첫 번째 격자의 크기인 y+에 대한 영향에 대해서도 검토하였다. 첫 번째 격자가 log layer에 위치하고 있지 않으면 마찰저항과 표면의 전단력이 과도하게 예측되는 것을 확인하였다. 이는 경계층이 두껍게 예측되어 난류에너지가 과도하게 예측되었기 때문으로 판단된다. 표면의 거칠기가 커질수록 경계층이 두꺼워지고 표면의 난류에너지가 증가되는 것을 확인하였다. 마찰저항을 정확하게 예측하기 위해서는 y+ 값, 거칠기 및 벽함수가 적절한 영역에 위치해야 함을 알 수 있었다.

• Geomechanics and Engineering
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• 제1권3호
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• pp.205-218
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• 2009

The bearing capacity factor $N_{\gamma}$ is computed for a rough conical footing placed over horizontal ground surface. The axisymmetric lower bound limit analysis formulation, in combination with finite elements and linear programming, proposed recently by the authors is used in this study. The variation of $N_{\gamma}$ with cone apex angle (${\beta}$), in a range of $30^{\circ}-180^{\circ}$, is obtained for different values of ${\phi}$; where ${\phi}$ is soil friction angle. For ${\phi}<30^{\circ}$, the magnitude of $N_{\gamma}$ is found to decrease continuously with an increase in ${\beta}$ from $30^{\circ}$ to $180^{\circ}$. On the other hand, for ${\phi}>30^{\circ}$, the minimum magnitude of $N_{\gamma}$ is found to occur generally between ${\beta}=120^{\circ}$ and ${\beta}=150^{\circ}$. In all the cases, it is noticed that the magnitude of $N_{\gamma}$ becomes maximum for ${\beta}=30^{\circ}$. For a given diameter of the cone, the area of the plastic zone reduces generally with an increase in ${\beta}$. The obtained values of $N_{\gamma}$ are found to compare quite well with those available in literature.

• Smart Structures and Systems
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• 제9권5호
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• pp.461-472
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• 2012

This study proposes an optics-based active sensing system for continuous monitoring of underground pipelines in nuclear power plants (NPPs). The proposed system generates and measures guided waves using a single laser source and optical cables. First, a tunable laser is used as a common power source for guided wave generation and sensing. This source laser beam is transmitted through an optical fiber, and the fiber is split into two. One of them is used to actuate macro fiber composite (MFC) transducers for guided wave generation, and the other optical fiber is used with fiber Bragg grating (FBG) sensors to measure guided wave responses. The MFC transducers placed along a circumferential direction of a pipe at one end generate longitudinal and flexural modes, and the corresponding responses are measured using FBG sensors instrumented in the same configuration at the other end. The generated guided waves interact with a defect, and this interaction causes changes in response signals. Then, a damage-sensitive feature is extracted from the response signals using the axi-symmetry nature of the measured pitch-catch signals. The feasibility of the proposed system has been examined through a laboratory experiment.

• 터널과지하공간
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• 제23권3호
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• pp.192-202
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• 2013

최근 유가 상승 및 지구 온난화에 대한 온실가스의 규제 강화로 인해 국내 천연가스 수요가 지속적으로 증가하고 있다. 이에 국내 천연가스 시장의 공급 안전성을 높이기 위하여, 2008년 한국가스공사와 Gazprom 간에 러시아 파이프라인 천연가스 공급에 관한 협약서를 체결하기도 했다. 러시아 PNG 도입계획이 본격화되어 천연가스가 도입되면 겨울철에 가스 수요가 집중되는 국내의 경우엔 천연가스 수급 균형을 위하여 지하저장시설이 필수적으로 요구될 것이다. 본 연구는 암반등급, 토피고, 저장압력, 현지측압계수(Ko)를 변수로 하여 천연가스 저장 공동의 안정성을 정량적으로 평가하였다. 제안된 설계변수에 따른 저장 공동의 거동을 파악하기 위해 축대칭 조건을 사용하여 2차원 응력해석을 수행하였다. 해석 결과 전단강도/전단응력으로 정의된 공동의 안전율은 심도, 암반등급 및 저장압력에 크게 영향을 받았으나 측압계수의 영향은 거의 없었다.