• 한국의학물리학회:학술대회논문집
• /
• 한국의학물리학회 2002년도 Proceedings
• /
• pp.365-366
• /
• 2002

A novel TEM resonator coil was developed for the imaging of small animals. The functional elements of the TEM resonator were 8 inner conductors, distributed in a cylindrical pattern and connected at the ends with capacitors to the cylindrical outer shield. The TEM resonator coil with cavity elements was robust to the surrounding influences due to the self-shielding structure. The TEM resonator coil with high Q factor could provide high quality MR images at 3.0T MRI system. Also, the TEM resonator coil has an advantage for a fine tune with length adjustment of each cavity elements. Thus, The TEM resonator coil at 3.0T, even higher field could be used in the research studies.

• 한국터널지하공간학회 논문집
• /
• 제19권6호
• /
• pp.1013-1028
• /
• 2017

본 논문은 원형 자유면을 이용한 암반 파쇄에 대한 수치해석적 연구이다. 암반 파쇄시 균열 발생에 대한 메커니즘을 알아보기 위하여 수치해석을 통해 응력 및 변형율 경로를 분석하였다. 수치해석 결과로부터 균열선의 주응력 분석으로 최대 주응력을 산출하여 취성 재료의 파괴와 균열 진전에 대하여 분석 규명하였다. 또한 본 연구결과를 통하여 암반파쇄시 균열 진전 방향이 전환되는 거동 메커니즘을 제시하였다.

• Structural Engineering and Mechanics
• /
• 제49권4호
• /
• pp.427-448
• /
• 2014

At present, the time of easy oil and gas is over. Now, the largest part of fossil fuels is concentrated in the deepest levels of tectonic structures and in the sea shelves. One of the most cumbersome operations of their extraction is the bore-hole drilling. In connection with austere tectonic and climate conditions, their drivage every so often is associated with great and diversified technological difficulties causing emergencies on frequent occasions. As a rule, they are linked with drill string accidents. A key role in prediction of these situations should play methods of theoretical modelling. For this reason, there is a growing need for development and implementation of new numerical methods for computer simulation of critical and post-critical behavior of drill strings (DSs). In this paper, the processes of non-linear deforming of a DS in cylindrical cavity of a deep bore-hole are considered. On the basis of the theory of curvilinear flexible rods, non-linear constitutive differential equations are deduced. The effects of the longitudinal non-uniform preloading, action of torque and interaction between the DS and the bore-hole surface are taken into account. Owing to the use of curvilinear coordinates in the constraining cylindrical surface and a specially chosen concomitant reference frame, it became possible to separate the desired variables and to reduce the total order of the equation system. To solve it, the method of continuation the solution by parameter and the transfer matrix technique are applied. As a result of the completed numerical analysis, the critical states of the DS loading in the cylindrical channels of inclined bore-holes are found. It is shown that the modes of the post-critical deforming of the DS are associated with its irregular spiral curving prevailing in the zone of bottom-hole-assembly. The possibility of invariant state generation during post-critical deforming is established, condition of its bifurcation is formulated. It is shown that infinite variety of loads can correspond to one geometrical configuration of the DS. They differ each from other by contact force functions.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2001년도 춘계학술대회 논문집
• /
• pp.1080-1084
• /
• 2001

In manufacturing a micro die with half spherical cavity by MEDM, it is necessary to prepare an electrode with the same shape. This paper suggests a simple method to manufacture a half spherical electrode based on tool wear. The tool wears more rapidly at the edge of a cylindrical electrode. In order to make a half spherical micro electrode, cylindrical electrode was fed into the workpiece by the distance of its radius. The d/R(depth/Radius) value varied with respect to capacitance and electrode diameter. The smaller the size of electrode was, the closer the electrode tip geometry approached to a half sphere.

• 전기학회논문지
• /
• 제57권4호
• /
• pp.641-647
• /
• 2008

In this paper, we have studied the basic discharge characteristics of ac-type cylindrical microcavity structure. The structure has a two electrodes, which are positioned in the bottom of the cavity and in the side wall of the cylinder, respectively. The discharge showed asymmetric phenomena depending on the position of a cathode electrode. When the bottom electrode was a cathode, the discharge was stronger even though the area of the cathode was smaller than that of the anode. Simulation results revealed that the focused electric field toward the bottom electrode increased ion density in the space which in turn strengthened the cathode sheath and ionization process.

• ETRI Journal
• /
• 제21권2호
• /
• pp.1-8
• /
• 1999

We analyze the characteristics of a coaxial-to-waveguide transition based on the finite difference time domain (FDTD) method with the cylindrical to rectangular cell interpolation scheme. The scheme presented in this paper is well suited for the analysis of a microwave device with a probe near waveguide discontinuity because perfect TEM mode can be generated inside the coaxial cable by using the cylindrical cell. The scattering parameters of a designed Ka-band transition are evaluated and compared with those of commercially available software, High Frequency Structure analysis Simulator (HFSS) and measured data. There exists good agreement between the measured and calculated data. In order to prove an accuracy of the interpolation scheme, a coaxial to waveguide transition with a disk-loaded probe is analyzed by the present approach and the results of this analysis are compared with measured data. Comparison shows that our results match very closely to those of measurement and other approaches. The method presented in this paper can be applied to analyze the characteristics of a probe excited cavity, coaxial waveguide T-Junctions, and so on.

• 한국음향학회지
• /
• 제20권4호
• /
• pp.62-70
• /
• 2001

최근 개발된 탄성파 공명산란이론에 기초하여, 원통형 유체산란체, 원통형 구멍 및 공명산란체의 문제에서 초음파탐촉자로 측정할 수 있는 응력 성분간 관계식을 유도하였다. 계산된 공명산란 응력부분파는 산란계수와 유사한 주파수 거동을 보이는데, 특히 공명주파수 근처에서 180°의 급격한 위상변화를 보인다. 유체 매질내 압력의 주파수 거동도 고찰함으로써, 탄성파 공명산란이론에 대한 이해를 증진하였다. 본 논문에서 연구되고 개발된 방법을 사용하면, 탄성매질 내의 유체개재물에 대한 비파괴평가의 신뢰성이 더욱 향상될 것이다.

• 소음진동
• /
• 제7권4호
• /
• pp.631-636
• /
• 1997

A method to estimate the radiatio power to the surrounding formation due to axial vibration of the pipe in a fluid-filled borehole has been developed, by using the propagation modes of stress wave in an infinitely-long and uniform drilling borehole surrounded by a radially-infinite homogeneous formation. Also, the equivalent damping coefficient for the axial vibration of the pipe has been derived. As an example, results for a real drilling borehole has been presented. The analysis of the elastic motion of the infinite formation which has cylidrical cavity is simplified with the geometric axisymmetry and the low-frequency assumption so that the analytic solution is obtained.

• 대한기계학회논문집
• /
• 제16권11호
• /
• pp.2181-2188
• /
• 1992

본 연구에서는 크기가 45˚인 부채형 공간내의 자연대류 열전달 특성을 고찰 하기 위하여 간격비, 경사각 그리고 Rayleigh 수를 변수로 하여 유한 차분법으로 수치 해석 하고, 대료적인 간격비 L/r$_{i}$=1.6에서 Ra=2.51*$10^{4}$ 및 Pr=0.71일때, Machzehnder 간섭계를 사용하여 실험 하였으며, 수치해석과 실험결과를 비교하였다.

• 대한화학회지
• /
• 제35권6호
• /
• pp.699-706
• /
• 1991

헬륨 기체를 사용하여 중급 출력(500W) 마이크로파 유도 플라즈마(Microwave Induced Plasma:MIP)를 헬륨 기체를 사용하여 만든 뒤 직접 수용액 시료 분석에 사용하였다. Beenakker의 cavity를 변형시켜 얻은 안정된 헬륨 플라즈마는 실린더 형태의 모양을 하고 있고 기체의 흐름량을 조절하여 "toroidal"형태의 플라즈마도 얻을 수 있으나 분석학적 능력은 오히려 감소되었다. Glass Frit Nebuliser를 이용하여 분석하였을 때 금속 원소는 10~100 ppb 근처의 검출한계를 보였고 비금속원소인 염소의 경우는 50ppm근처의 검출한계를 보였다.