• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.174-179
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• 2004

The growth of the critical size bubble by diffusion process in viscoelastic medium was treated by an integral method for the concentration boundary layer adjacent to the bubble wall. In this study, we obtained a set of the first order time dependent equations to obtain bubble radius and gas pressure inside the bubble simultaneously. The calculated final cell sizes depending on the initial saturation pressure are in close agreement with the observed ones. The governing equations developed in this study may be used in polymer processing of microcellular foams.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2004년도 춘계종합학술대회
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• pp.472-474
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• 2004

본 연구에서는 변형된 Folded 다이폴 안테나의 특성을 모멘트법을 이용하여 조사하였다. 안테나의 중심주파수는 200MHz, 도선의 반지름은 0.5mm이고 두 개의 선형 다이폴 사이의 간격은 2cm이다. 시뮬레이션 결과 18cm 정도의 내부 sub 변화와 4.5cm 정도의 외부 stub 변화는 SWR 기준으로 3 미만을 유지한다. 이는 변형된 Folded 다이폴 안테나가 추가적인 정합회로 없이 광대역 특성을 보이는 것을 의미한다.

• Bulletin of the Korean Chemical Society
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• 제19권10호
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• pp.1054-1059
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• 1998

Fluorescence and dynamic light scattering measurements were applied to the study of formation and structure of aggregated colloidal particles in modified poly(ethylene-co-methylacrylate) ionomers in aqueous solution. Both 8-anillino-l-naphthalene-sulfonic acid (ANS) and pyrene were used as fluorescence probe to obtain the information on the structure of particle surface and inside, respectively. Three different ionomers used in this study started to aggregate at very dilute concentration, 3-8 x 10-6 g/mL. In this study, we demonstrate that the polyethylene ionomers can form stable nanoparticles. The hydrophobic core made of the polyethylene backbone chains is stabilized by the ionic groups on the particle surface. Such a formed stable nanoparticles have a relatively narrow size distribution with an average radius in the range of 27-48 nm, depending on the kind of ionic groups. Once the stable particles are formed, the particle size distributions were nearly constant. This study shows another way to prepare surfactant-free polyethylene nanoparticles.

• Nuclear Engineering and Technology
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• 제54권1호
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• pp.401-413
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• 2022

This paper provides a simple method by which to estimate the cross-section stress profiles for nozzles designed according to ASME Code Section III. Further, this method validates the effectiveness of earlier work performed by the authors on standard nozzles. The method requires only the geometric information of the pressure vessel and the attached nozzle. A PWR direct vessel injection nozzle, a PWR outlet nozzle, a PWR inlet nozzle and a BWR recirculation outlet nozzle are selected based on their corresponding specific designs, e.g., a varying nozzle radius, a varying nozzle thickness and an outlet nozzle boss. A cross-section stress profile comparison shows that the estimates are in good agreement with the finite element analysis results. Differences in stress intensity factors calculated in accordance with ASME BPVC Section XI Appendix G are discussed. In addition, a change in the dimensions of an alternate nozzle design relative to the standard values is discussed, focusing on the stress concentration factors of the nozzle inside corner.

• 반도체디스플레이기술학회지
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• 제21권4호
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• pp.163-167
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• 2022

In this paper, an optimization design method of a diffuser using Bernoulli's theorem was reviewed. The aspect ratio of the cylindrical diffuser chamber and the diameter ratio of the air inlet and outlet were used as design parameters. For the optimal design of the cylindrical diffuser chamber, the air flow inside the chamber was simulated using ANSYS while changing the aspect ratio of the chamber. In order to confirm the simulation results, the diffuser manufactured using the laser processing machine was measured. Through ANSYS simulation and measurement, it was found that the optimal design condition was when the aspect ratio (chamber height/radius) of the diffuser chamber was 1/2 and the diameter ratio of the air inlet and outlet was also 1/2.

• Advances in nano research
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• 제13권5호
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• pp.427-435
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• 2022

Static stability behaviors of annular sandwich plates constructed from two layers of particle-reinforced nanocomposites have been investigated in the present article. The type of nanoscale particles has been considered to be graphene oxide powders (GOPs). The particles are assumed to have uniform and graded dispersions inside the matrix and the material properties have been defined according to Halpin-Tsai micromechanical model. The core layer is assumed to have honeycomb configuration. Annular plate has been formulated according to thin shell assumptions considering geometrical nonlinearities. After solving the governing equations via Galerkin's technique, it is showed that the post-buckling curves of annular sandwich plates rely on the core wall thickness, amount of GOP particles, sector radius, and thickness of layers.

• 대한기계학회논문집B
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• 제39권3호
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• pp.231-236
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• 2015

공동유동은 종래 많은 연구가 수행되었으나 대부분의 연구는 공동 상류의 압력구배가 없는 수평면 상에 위치한 공동 유동에 대한 연구가 수행되어 왔으며, 실제 공학적 응용에서 나타나는 곡면 벽상에 위치한 공동 유동에 대한 연구는 거의 수행되지 않고 있다. 일반적으로 곡면 벽상에 위치한 공동유동에는 원심력이 작용하여 종래의 공동 유동 연구결과와 상이한 유동특성을 가질 것으로 판단되나, 이러한 데이터는 지금까지 보고되지 않았다. 본 연구에서는 곡면 벽상에 설치한 공동 유동을 수치해석법으로 조사하여 곡면의 곡률반경 및 유동의 마하수가 천음속 및 초음속 공동유동의 특성에 미치는 영향을 조사하였다. 그 결과 곡면의 곡률반경이 작아질수록, 유동의 마하수가 증가할수록, 공동내부에서 발생하는 피크압력의 크기는 증가하였으며 공동으로 인한 전압력손실 증가한다는 것을 확인할 수 있다.

• 한국정보처리학회논문지
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• 제3권1호
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• pp.95-106
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• 1996

가상현실 기법이 일반적인 3차원 컴퓨터 그래픽스 기법과 구별되는 가장 큰 차이 는 상대적인 현실감의 극대화에 달려 있으며. 따라서 가상현실 기법에서는 입체 음향 이나 데이타장갑 등 인간의 지각및 인식 기능을 향상미키는 수단이 중요시되기도 한다. 그러나 이러한 하드웨어적 요소보다 중요한 것은 가상현실 기법으로 표현되는 내부 객체들 의 행동에서 유래되는 현실감이다. 본 연구에서는 가상현실의 각 장면을 구성하는 본질 적 요소인 객체들을 연결하는 상호작용을 능동적으로 모델링함 으로써 다양한 현실 감을 부여한다. 이를 위해 본 연구에서는 개개의 객체의 특성에 따른 지각 반경 및 자극반경을 기초로, 가상현실 공간을 하나의 물리적인 장의 형태로 설정한 필드 모델 을 제시하고 구현한다. 현실감을 극대화하기 위한 가장 본질적인 요소로서의 객체간의 인과작용 및 일반적인 상호작용을 이 필드 모델 안에서 상호간의 에너지교환의 형태로 나타내어지며, 결과적으로 지각반경, 자극반경 및 이들간에 적용되는 행동논리만으로 가상현실 내부의 모든 객체가 능동적으로 반응할 있는 능동객체 시스템을 이룰 수 있게 된다.

• 한국운동역학회지
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• 제30권1호
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• pp.17-25
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• 2020

Objective: The purpose of this study is to provide a better understanding of long turn mechanism by describing long turns after kinematic analysis and provide skiers and winter sports instructors with data through which they are able to analyze right postures for turns in skiing in a systematic, rational and scientific manner. Method: For this, a mean difference of kinematic variables (the center of gravity (CG) displacement of distance, trajectory, velocity, angle) was verified against a total of 12 skiers (skilled and unskilled, 6 persons each), regarding motions from the up-start to down-end points for long turns. Results: First, concerning the horizontal displacement of CG during a turn in skiing, skilled skiers were positioned on the right side at the upstart and edge-change points at a long turn. There was no difference in anteroposterior and vertical displacements. Second, in terms of CG-trajectory differences, skilled skiers revealed a significant difference during a long turn. Third, regarding skiing velocity, skilled skiers were fast at the edge-change and maximum inclination points in long turns. Fourth, there was no difference in a hip joint in terms of a lower limb joint angle. In a knee joint, a large angle was found at the up-start point among skilled skiers when they made a long turn. Conclusion: In overall, when skilled and unskilled skiers were compared, to make a good turn, it is required to turn according to the radius of turn by reducing weight, concerning the CG displacement. Regarding the CG-trajectory differences, the edge angle should be adjusted via proper inclination angulation. In addition, a skier should be more leaned toward the inside of a turn when they make a long turn. In terms of skiing velocity, it is needed to reduce friction on snow through the edging and pivoting of the radius or turn according to curvature and controlling ski pressure. Regarding a lower limb joint angle, it is important to make an up move by increasing ankle and knee angles instead of keeping the upper body straight during an up motion.

• Steel and Composite Structures
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• 제30권2호
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• pp.81-96
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• 2019

The behavior of a new Three-Tube Buckling-Restrained Brace (TTBRB) with circumference pre-stress (${\sigma}_{{\theta},pre}$) in core tube are investigated through a verified finite element model. The TTBRB is composed of one core tube and two restraining tubes. The core tube is in the middle to provide the axial stiffness, to carry the axial load and to dissipate the earthquake energy. The two restraining tubes are at inside and outside of the core tube, respectively, to restrain the global and local buckling of the core tube. Based on the yield criteria of fringe fiber, a design method for restraining tubes is proposed. The applicability of the proposed design equations are verified by TTBRBs with different radius-thickness ratios, with different gap widths between core tube and restraining tubs, and with different levels of ${\sigma}_{{\theta},pre}$. The outer and inner tubes will restrain the deformation of the core tube in radius direction, which causes circumference stress (${\sigma}_{\theta}$) in the core tube. Together with the ${\sigma}_{{\theta},pre}$ in the core tube that is applied through interference fit of the three tubes, the yield strength of the core tube in the axial direction is improved from 160 MPa to 235 MPa. Effects of gap width between the core tube and restraining tubes, and ${\sigma}_{{\theta},pre}$ on hysteretic behavior of TTBRBs are presented. Analysis results showed that the gap width and the ${\sigma}_{{\theta},pre}$ can significantly affect the hysteretic behavior of a TTBRB.