• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.438-440
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• 2006

포항가속기 연구소의 선형가속기와 빔 전송선에는 22개의 솔레노이드 전자석, 38개의 사극전자석 그리고 전자빔의 궤도 조절을 위한 29개의 2극 전자석이 있다. 전자빔의 정밀 제어를 위한 전자적 전원장치는 고정도, 고안정도 출력 특성을 가져야 한다. 이를 위하여 풀-브릿지 4-상한 DC-DC 컨버터 토플로지의 4단 병렬운전을 채택하였다. 전원장치의 입력전압은 직류 40V이고, 최대 출력전류는 직류 50A이며 그리고 스윗칭 주파수는 50 kHz이다. 고정밀, 고안정도 출력전류를 얻기 위하여 입력단의 전원 노이즈 및 전력변환부의 스윗칭 노이즈를 제거하여야 한다. 이를 위하여 채택된 low-pass 필터의 cut-off 주파수는 입력과 출력단 각각 26 Hz와 4.5 kHz 이다. 출력전류에서 전원장치로부처 발생하는 주파수 성분을 완벽하게 제거하였다. 출력전류의 분해능은 1mA 이하이며, 안정도는 10시간 이상 장시간의 경우 +/-15 ppm 이하이고 1시간 이하 단시간의 경우 +/-10ppm 이하이다. 본 논문에서는 풀-브릿지 4-상한 DC-DC 컨버터 토플로지의 4단 병렬운전을 채택한 전자석 전원장치의 구성, 특성 그리고 실험결과에 대하여 기술하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.50-57
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• 2003

In the paper, the design and evaluation of a helicopter trajectory tracking controller are presented. The control algorithm is implemented using the feedback linearization technique and the two time-scale separation architecture. In addition, and on-line adaptive architecture that employs a neural network compensating the model inversion error caused by the deficiency of full knowledge of helicopter dynamic is applied to augment the attitude control system. Trajectory tracking performance of the control system in evaluated using modified TMAN simulation program representing as Apache helicopter. It is show that the on-line neural network in an adaptive control architecture is very effective in dealing with the performance depreciation problem of the trajectory tracking control caused by insufficient information of dynamics.

• Journal of the Korean Society for Railway
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• v.13 no.6
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• pp.577-582
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• 2010

The importance of maintenance of rail surface defects is increasing according to the KTX operation. That is because during high speed operation of rolling stocks, rail surface defects shorten fatigue life of rail, accelerate track degradation and deteriorate ride comfort. Rail grinding has been applied for effective rail maintenance in Kyeong-Bu HS line. This paper evaluates the effectiveness of rail grinding in term of rail fatigue life. To this end, the stresses of the rail are measured under KTX running and the equivalent stress range is calculated by RMC after the frequency analysis done with rainflow counting method. Also, The Modified Miner's rule is applied to predict the fatigue life of ground rail. The result of the analysis shows that the fatigue life of ground rail is increased by 15%.

• Journal of Korean Society of Water and Wastewater
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• v.35 no.1
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• pp.15-25
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• 2021

In this study, a method of leakage detection was proposed to locate leak position for a reservoir pipeline valve system using wavelet coherence analysis for an injected pressure wave. An unsteady flow analyzer handled nonlinear valve maneuver and corresponding experimental result were compared. Time series of pressure head were analyzed through wavelet coherence analysis both for no leak and leak conditions. The leak information can be obtained through either time domain reflectometry or the difference in wavelet coherence level, which provide predictions in terms of leak location. The reconstructed pressure signal facilitates the identification of leak presence comparing with existing wavelet coherence analysis.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.579-584
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• 2017

The damper oil seal of a high-speed railway vehicle is made from nitrile butadiene rubber (NBR) in order to prevent lubricant from leaking into the damper and to stop harmful contaminants from entering the external environment while in service. Oil leakage through the seal primarily occurs from fatigue failure of the damper. Cumulative damage of the seal occurs due to the contact force between the rod and the rubber during movement due to track irregularities and cants, among other factors. Thus, the design of the oil seal should minimize the maximum principal strain at weak points. In this study, the optimal cross section of the damper oil seal was found using the multi-island genetic algorithm method to improve the durability of the damper. The optimal shape of the oil seal was derived using process automation and design optimization software. Nonlinear material properties for finite element analysis (FEA) of the rubber were determined by Marlow's model. The nonlinear FEA confirmed that the maximum principal strain at the oil leakage point was decreased 24% between the initial design and the optimum design.

• Journal of the Korean Society for Railway
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• v.20 no.2
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• pp.165-172
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• 2017

High frequency squeal noise can be generated when a railroad vehicle runs a sharp curved section; this noise causes environmental complaints and excessive wear on the wheel and the railroad track. In this paper, curved squeal noise experiments on a commercial railway were carried out to investigate this phenomenon. The relationship of the squeal noise pressure level, the frequency characteristics, the railway running speed, and the modal behavior of the wheel were investigated. At the same time, the lateral motion of the wheel relative to the rail was captured using a video camera; wheel movement was calculated when the noise was generated. queal noise occurred at the highest level at the inner front wheel; this phenomena is considered to be related to the lateral vibration response characteristics of the wheel. It can be seen that the magnitude of this squeal noise is not directly related to the increase in vehicle speed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2C
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• pp.71-79
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• 2009

This study is to develope the resilient modulus prediction model, which is the function of mean effective principal stress and axial strain, for three types of railroad trackbed materials such as crushed stone, weathered granite soil, and crushed-rock soil mixture. The model consists of the maximum Young's modulus and nonlinear values for higher strain, analogous to dynamic shear modulus. The maximum value is modeled by model parameters, $A_E$ and the power of mean effective principal stress, $n_E$. The nonlinear portion is represented by modified hyperbolic model, with the model parameters of reference strain, ${\varepsilon}_r$ and curvature coefficient, a. To assess the performance of the prediction models proposed herein, the elastic response of a test trackbed near PyeongTaek, Korea, was evaluated using a 3-D elastic multilayer computer program (GEOTRACK). The results were compared with measured elastic vertical displacement during the passages of freight and passenger trains at two locations, whose sub-ballasts were crushed stone and weathered granite soil, respectively. The calculated vertical displacements of the sub-ballasts are within the order of 0.6mm, and agree well with measured values. The prediction models are thus concluded to work properly in the preliminary investigation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.669-677
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• 2009

In general, the pitch momentum biased system that induces inherently nutational motion in roll/yaw plane, has been adapted for geosynchronous communications satellites. This paper discusses the method of roll attitude control using yaw axis momentum management method for a low earth orbit(LEO) satellite which is a pitch momentum biased system equipped with only two reaction wheels. The robustness of wheel momentum management method with PI-controller is investigated comparing with wheel torque control method. The transfer function of roll/yaw axis momentum management system that is useful for attitude controller design is derived. The disturbance effect of roll/yaw axis momentum management system for attitude control is investigated to identify design parameters such as magnitude of momentum bias and to get the insight for controller design. As an example, the PID controller design result of momentum management system for roll/yaw axis control is provided and the simulation results are presented to provide further physical insight into the momentum management system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.1
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• pp.151-158
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• 1992

Topographic mapping from economic SPOT stereo imagery than aerial photographs has become possible. Many of authors have studied the possibility of base map revisions and the accuracy of results. They have concluded that the SPOT image is suitable for 1/50,000 to 1/100,000 topographic map. For topographic map, orthophoto and DTM generation from SPOT imagery, accurate exterior orientation parameters are needed. But since the geometric characteristic of SPOT image is dynamic linear array imagery, the conventional bundle adjustment for photogrammetry can not be directly applied. Reliability is the ability to detect gross error, which is called the internal reliability, and the effect of non-detectable gross error on the results of exterior orientation, which is called the external reliability. This paper shows how the reliability of SPOT imagery depends on the different coordinate systems, presentations of coordinate for flight direction, orders of exterior orientation parameters and distribution of control points, and thus analyses the theoretical reliability of the exterior orientation, which can provide a basis for the planning of SPOT projects.

• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.177-183
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• 2013

As the development of available binder in the harsh conditions is needed, we propose the proper binder for high-voltage lithium-ion secondary batteries based on the quantum chemistry modeling. The optimized structures, HOMO (Highest Occupied Molecular Orbital) energies and ionization potentials of 4 binders, which were considered from monomer to tetramer, were investigated by the semi-empirical and DFT (Density Functional Theory) calculations. The results show that the ionization potential values by calculation tend to be close to the oxidation potentials from the measurement of linear sweep voltametry (LSV). The order of oxidative resistance from high value to low value is following: poly(hexafluropropylene), poly(vinylidene fluoride), poly(methyl acrylate) and poly(acryl amide). Also these results correspond with the experimental values. Thus, we find the reason why HOMO (Highest Occupied Molecular Orbital) energy of PHFP has the highest value than other binders by analysis of HOMO orbital structures.