• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.185-194
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• 2004

In order to analyze the motion errors of the aerostatic stage, it is necessary to consider the influence of the moment variation occurred inside the pads. In this paper, a motion error analysis method utilizing the transfer functions on the reaction force and moment is proposed, and general characteristics of the transfer functions are discussed. Calculated motion errors by the proposed method show good agreement with the ones calculated by Multi fad Method, which is considered the entire table as an analysis object. Also, by the introduction of the transfer function of motion errors, which represent the relationship between the spatial frequency components of the rail form error and motion errors, motional characteristics of the porous aerostatic stage can be generalized. In detail, the influence of the spatial frequencies is analyzed qualitatively, and the patterns of the insensitive frequencies which almost do not affect the linear motion error or angular motion error according to the rail length ratio and the number of the pad are verified. The relationship between the moment variation occurred inside the pads and the motion errors is also verified together.

• Korean Journal of Optics and Photonics
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• v.2 no.4
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• pp.203-208
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• 1991

We investigated the nonradiative energy transfer process from Rhodamine 6G to Malachite Green in ethylen glycol solvent using time correlated single photon counting system equipped with a modelocked Ar ' laser. The reduced concentration and critical transfer distance for various acceptor concentration were obtained by using a full-fitting analysis of the fluorescence decay curves. We found that Huber model is more suitable than Forster model and the influence of energy migration through the dipole-dipole interaction becomes more significant for the low acceptor concentrations relative to the donor concentration($5\times 10^4$mol/l).

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.3
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• pp.173-182
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• 2013

The building design projects which are being proceeded nowadays pursue a complex and various shape of structures, escaping from the traditional and regular shape of buildings. In this new trend of the architecture, there rises a demand of the research in the structural engineering for the effective realization of such complex-shaped buildings which disassembles the orthogonality of frames. As a distinguished characteristics of the buildings in a complex-shape, there frequently are inclined columns included in the structural frame. The inclined column causes extra axial force and bending moment at the beam-column connection so it is necessary to assess those effects on the structural behavior of the frame and the connection by experiment or analysis. However, with comparing to the studies on the normal beam-column connections, the inclined column connections have not been studied sufficiently. Therefore, this study evaluated the beam-column connections having an inclined column using nonlinear and finite element analysis method. In this paper, steel moment frames having inclined columns were analyzed by the nonlinear pushover analysis to check the global behavior and beam-column connection models were analyzed by the finite element analysis to check the buckling behavior and the fracture potentials.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.3
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• pp.69-77
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• 2003

This paper presents test results on eight reduced beam section(RBS) steel moment connections. The testing program addressed bolted versus welded web connection and panel zone(PZ) strength as key variables, Specimens with medium PZ strength were designed to promote energy dissipation from both PZ and RBS regions such that the requirement for expensive doublet plates could be reduced. Both strong and medium PZ specimens with a welded web connection were able to provide satisfactory connection rotation capacity for special moment-resisting frames. On the other hand, specimens with a bolted web connection performed poorly due to premature brittle fracture of the beam flange of the weld access hole. If fracture within the beam flange groove weld was avoided using quality welding, the fracture tended to move into the beam flange base metal of the weld access hole. Plausible explanation of a higher incidence of base metal fracture in bolted web specimens was presented. The measured strain data confirmed that the classical beam theory dose not provide reliable shear transfer prediction in the connection. The practice of providing web bolts uniformly along the beam depth was brought into question. Criteria for a balanced PZ strength improves the plastic rotation capacity while reduces the amount of beam distortion ore also proposed.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.8
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• pp.1-6
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• 2011

In this paper, another analytical approach for dual-hop amplify-and-forward(AF) relay systems is proposed over Rayleigh fading channels. Previous approaches derived the moment generating function(MGF) by using the cumulative distribution function(CDF) or probability density function(PDF) of the received signal-to-noise ratio(SNR) for source-relay-destination(S-R-D) link. Then, the average symbol error rate is expressed based on derived MGFs. In this paper, another new approach is proposed. It means that the MGF is directly derived by utilizing PDFs of both source-relay(S-R) and relay-destination(R-D) links. Additionary, the newly derived MGF is compared and analyzed with previous ones. Furthermore, simulation results are presented to validate the accuracy of proposed analytical expression. Based on this, it is confirmed that the proposed analytical approach can be a another solution for dual-hop AF relay systems.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.263-263
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• 2012

핵융합 플라즈마에서의 고속이온은 NBI 및 ICRF에 의한 이온 가열과 핵융합 반응에 의하여 발생하며, 핵융합 반응률을 크게 하고 일차적으로 그 에너지를 전자에게 전달하는 특성을 갖는다. 따라서 핵융합을 지향하는 플라즈마에서는 그 성능을 나타내는 지표이기도 하면서, 맥스웰 분포를 갖는 열화 플라즈마의 수송특성을 크게 변화 시킨다. 또한 알펜파 등의 파동 또는 불안정성을 유발시키며 이로 인한 플라즈마 손실은 국지적인 일차벽의 가열을 유발할 수 있는 것으로 여겨진다. 본 연구에서는 일반적인 기하학적 구조를 갖는 토카막에서의 NBI 가열에 의한 고속이온 발생과 위상공간에서의 수송 및 손실을 시간 의존적인 Fokker-Planck 방정식을 수치적으로 풀어서, 위치에 따른 고속이온 분포의 변화를 계산한다. NBI 입사의 기하학적 모델에서는 각 계산 위치에서의 피치각 변화와 stagnation point의 변화에 의한 영향을 고려하며, 일반적인 고속이온의 각종 모멘트 뿐 아니라 즉발 이온 손실률을 계산에 포함한다. 해석된 고속이온 분포는 중성입자 검출기에서 측정한 KSTAR 플라즈마의 고속이온 에너지 분포와 비교한다. 차후에는 본 연구에서 사용한 Fokker-Planck 출동연산자에 고주파 가열에 의한 고속이온발생 항을 추가하여 ICRF 가열에 의한 효과를 예측할 수 있도록 할 것이다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.93-96
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• 2009

바퀴동력계는 차량에 지면으로부터 전달되는 힘과 모멘트를 측정하는 로드셀이다. 본 연구에서 개발한 바퀴동력계는 스트레인 게이지식 로드셀로써 이러한 로드셀을 설계하는데 있어서 몇가지 고려해야 하는 사항이 있다. 우선 스트레인 게이지를 부착하기 쉬운 구조가 되어야 하고 조립시의 오차를 줄이기 위하여 한 몸체로 제작되어야 한다. 이와 동시에 가장 중요하게 고려되어야 하는 인자로 감도를 위해 재료가 허용하는 응력내에서 되도록 큰 변형률이 발생해야 하고 상호 간섭 오차가 발생하지 말아야 한다. 본 연구에서는 수식을 이용하여 이론적으로 상호 간섭 오차를 0으로 만들 수 있었다. 또한 설계 변수 및 재료 물성치의 산포를 고려한 신뢰성 기반 최적설계 기법을 사용하였으며, 이를 통해 허용 응력하에서 최대의 변형률이 발생하는 바퀴동력계를 설계하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.9
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• pp.741-753
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• 2007

The elliptic conceptual second moment model for turbulent heat fluxes, which was proposed on the basis of elliptic-relaxation equation, was applied to calculate the turbulent heat transfer in an axially rotating pipe flow. The model was closely linked to the elliptic blending model which was used for the prediction of Reynolds stress. The effects of rotation on the turbulent characteristics including the mean velocity, the Reynolds stress tensor, the mean temperature and the turbulent heat flux vector were examined by the model. The numerical results by the present model were directly compared to the DNS as well as the experimental results to assess the performance of the model predictions and showed that the behaviors of the turbulent heat transfer in the axially rotating pipe flow were satisfactorily captured by the present models.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.2
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• pp.138-144
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• 2006

Kinematic and dynamic characteristics of a Stewart platform based parallel manipulators are fixed once they are constructed. Thus parallel manipulators with various configurations are required to meet a variety of applications. In this research a parallel manipulator with variable platform (PMVP) has been developed, in which the length of the arm linking the platform center to the platform-leg contact point can be varied by an actuator. The workspace of the PMVP is larger than that of a traditional Stewart platform and especially the range in which the maximum orientation angles can be maintained is significantly expanded. Furthermore, the characteristics of force and moment transmission between the legs and platform can be adjusted to meet the requirements of various tasks. Kinematic and dynamics analysis was performed to verify the usefulness of the PMVP and the actual hardware was built to demonstrate the feasibility.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.416-425
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• 1993

To investigate the characteristics of the merged jet arising from the interaction of two opposing curved wall jets over a circular cylinder in still air, mean velocity, Reynolds stresses, triple moments and integral length scale were measured using hot-wire anenometry. The turbulent kinetic energy and shear stress budget were evaluated using the measured data. The variations of the Reynolds stresses, the triple moment and integral length scale are severe in the interaction region. The pressure diffusion terms are found to be very large when compared the other terms in the interaction region. The distributions of the Reynolds stress and the triple moment in the similar region are found to be similar to those of conventional plane jets.