• 천문학회보
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• 제37권1호
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• pp.90.1-90.1
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• 2012

Understanding the dynamics of relativistic electron acceleration, loss, and transport in the Earth's radiation belt during magnetic storms is a challenging task. The U.S. National Science Foundation's Geospace Environment Modeling (GEM) has identified five magnetic storms for in-depth study that occurred during the second half of the Combined Release and Radiation Effects Satellite (CRRES) mission in the year 1991. In this study, we show the responses of relativistic radiation belt electrons to the magnetic storms by comparing the time-dependent 3-D Versatile Electron Radiation Belt (VERB) simulations with the CRRES MEA 1 MeV electron observations in order to investigate the relative roles of the competing effects of previously proposed scattering mechanisms at different storm phases, as well as to examine the extent to which the simulations can reproduce observations. The major scattering processes in our model are radial transport due to Ultra Low Frequency (ULF) electromagnetic fluctuations, pitch-angle and energy diffusion including mixed diffusion by whistler mode chorus waves outside the plasmasphere, and pitch-angle scattering by plasmaspheric hiss inside the plasmasphere. We provide a detailed description of simulations for each of the GEM storm events.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.445-450
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• 2003

This study was performed 10 develop the accelerated life test method using Weibull-IPL(Inverse Power Law) model for mechanical components. Weibull-IPL model is concerned with determining the assurance life with confidence level and the accelerated life test time From the relation of weibull distribution factors and confidence limit, the testing times on the no number of failure acceptance criteria arc determined. The mechanical components generally represent wear and fatigue characteristics as a failure mode. IPL based on the cumulative damage theory is applied effectively the mechanical components to reduce the testing time and to achieve the accelerating test conditions. As the actual application example, accelerated life test method of agricultural tractor transmission was described. Life distribution of agricultural tractor transmission was supposed to follow Weibull distribution and life test time was calculated under the conditions of average life (MTBF) 3,000 hours and 90% confidence level for one test sample. According to IPL, because test time call be shorten in case increase test load test time could be reduced by 482 hours when we put the load 1.1 times of rated load than 0.73 times of rated load that is equivalent load calculated by load spectrum of the agricultural tractor. This time, acceleration coefficient was 11.7.

• 전기전자학회논문지
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• 제11권4호
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• pp.137-144
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• 2007

함포의 사격통제장치 성능은 크게 하드웨어(H/W)적인 오차와 소프트웨어(S/W)적인 오차로 구분할 수 있으며, 이중 S/W 오차에 해당하는 표적의 위치, 속도, 가속도 등을 추정하는 추적필터 오차는 탄도계산장치의 성능에 중요한 영향을 미친다. 함포의 정확한 예상탄착점 형성과 사격시 명중률 향상을 위하여 정확한 미래위치의 표적 상태정보가 필요하다. 표적 추적필터 알고리즘은 Single Singer Model, Fixed Gain 필터 알고리즘, IMM, PBIMM등이 있다. 본 논문에서는 최근 국내 함정에 적용예정인 IMM 추적필터를 설계하였다. IMM 추적필터를 위해 CV모델, Song 모델, CTR모델을 사용하여 동역학 모델을 만들었으며, 추적성능을 Monte-Carlo 시뮬레이션을 통해 해석해 보았다.

• Tribology and Lubricants
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• 제31권3호
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• pp.102-108
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• 2015

In this research, we experimentally investigated the sealing performance of elastomeric rotary lip seals for washing machines. In general, NBR is used as a material for elastomeric rotary lip seals in washing machines, but the mixing formula of the rubber material can affect the sealing performance. In this study, we manufactured rotary lip seals using three kinds of NBRs with a different mixing formula, and examined the sealing performance using an acceleration test mode. The results of an SEM investigation into the surfaces of three kinds of specimens showed a much smaller wear volume and better sealing performance for the specimens with smaller particle sizes of mixing composition than for the specimen with the larger. Repeated deformation and recovery by the shaft-to-seal eccentricity on rotation were shown to cause a phase difference in the rubber material, and we measured the recovery ratio to find the influence of this phase difference on the sealing performance. As another method for checking the phase difference, we also measured tan ä, and a lower tan ä was revealed as the recovery ratio increased for each specimen. Specimens with a higher recovery ratio (lower tan ä) were shown to have a better sealing performance. Consequently, specimens with a smaller particle size in the mixing composition had a better sealing performance because they show a higher recovery ratio.

• Structural Engineering and Mechanics
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• 제51권3호
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• pp.377-402
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• 2014

In this study, optimal distribution of springs which supports a cantilever beam is investigated to minimize two objective functions defined. The optimal size and location of the springs are ascertained to minimize the tip deflection of the cantilever beam. Afterwards, the optimization problem of springs is set up to minimize the tip absolute acceleration of the beam. The Fourier Transform is applied on the equation of motion and the response of the structure is defined in terms of transfer functions. By using any structural mode, the proposed method is applied to find optimal stiffness and location of springs which supports a cantilever beam. The stiffness coefficients of springs are chosen as the design variables. There is an active constraint on the sum of the stiffness coefficients and there are passive constraints on the upper and lower bounds of the stiffness coefficients. Optimality criteria are derived by using the Lagrange Multipliers. Gradient information required for solution of the optimization problem is analytically derived. Optimal designs obtained are compared with the uniform design in terms of frequency responses and time response. Numerical results show that the proposed method is considerably effective to determine optimal stiffness coefficients and locations of the springs.

• Wind and Structures
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• 제17권6호
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• pp.609-627
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• 2013

The Yingxian wooden tower in China is currently the tallest wooden tower in the world. It was built in 1056 AD and is 65.86 m high. Field measurements of wind speed and wind-induced response of this tower are conducted. The wind characteristics, including the average wind speed, wind direction, turbulence intensity, gust factor, turbulence integral length scale and velocity spectrum are investigated. The power spectral density and the root-mean-square wind-induced acceleration are analyzed. The structural modal parameters of this tower are identified with two different methods, including the Empirical Mode Decomposition (EMD) combined with the Random Decrement Technique (RDT) and Hilbert transform technique, and the stochastic subspace identification (SSI) method. Results show that strong wind is coming predominantly from the West-South of the tower which is in the same direction as the inclination of the structure. The Von Karman spectrum can describe the spectrum of wind speed well. Wind-induced torsional vibration obviously occurs in this tower. The natural frequencies identified by EMD, RDT and Hilbert Transform are close to those identified by SSI method, but there is obvious difference between the identified damping ratios for the first two modes.

• 대한기계학회논문집A
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• 제28권8호
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• pp.1203-1211
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• 2004

A traction control systems (TCSs) composed of either a wheel slip controller or a throttle valve controller or an integrated controller of both systems are proposed in this study. To validatethe dynamic characteristics of a vehicle and TCS, a full car model that can simulate the responses of both front wheel drive (2WD) and four wheel drive (4WD) vehicle is also developed. The wheel slip controller uses a sliding mode control scheme and the throttle valve is controlled by a PID controller. The results shows that tHe brake TCS and the engine TCS achieve rapid acceleration, and reduce slip angle on slippery road. When a vehicle is cornering and accelerating maneuver with the brake or engine TCS, understeer or oversteer occur, depending on the driving conditions. The integrated TCS prevents most of these problems and improves the stability and controllability of the vehicle.

• Smart Structures and Systems
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• 제26권5호
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• pp.667-680
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• 2020

This study aims at reporting a systematic procedure for evaluating the static and dynamic structural performance of steel bridges based on a short-period structural health monitoring measurement. Sungsu bridge located in Korea is considered as a case study presenting the most recent tests carried out to examine the bridge condition. Short-period measurements of Structural Health Monitoring (SHM) system were used during the bridge testing phase. A novel symmetry index is introduced using statistical analyses of deflection and strain measurements. Frequency Domain Decomposition (FDD) is implemented to the strain measurements to estimate the bridge mode shapes and damping ratios. Furthermore, Markov Chain Monte Carlo (MCMC) is also implemented to examine the reliability of bridge performance while ambient design trucks are in static or moving at different speeds. Strain, displacement and acceleration were measured at selected locations on the bridge. The results show that the symmetry index can be an efficient and useful measure in assessing the steel bridge performance. The results from the used method reveal that the performance of the Sungsu bridge is safe under operational conditions.

• International Journal of Automotive Technology
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• 제8권1호
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• pp.49-57
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• 2007

This paper proposes a traction control system (TCS) that uses a sliding mode wheel slip controller and a PID throttle valve controller. In addition, a yaw motion controller (YMC) is also developed to improve lateral stability using a PID rear wheel steering angle controller. The dynamics of a vehicle and characteristics of the controllers are validated using a proposed full-car model. A driver model is also designed to steer the vehicle during maneuvers on a split ${\mu}$ road and double lane change maneuver. The simulation results show that the proposed full-car model is sufficient to predict vehicle responses accurately. The developed TCS provides improved acceleration performances on uniform slippery roads and split ${\mu}$ roads. When the vehicle is cornering and accelerating with the brake or engine TCS, understeer occurs. An integrated TCS eliminates these problems. The YMC with the integrated TCS improved the lateral stability and controllability of the vehicle.

• 동력기계공학회지
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• 제19권6호
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• pp.39-46
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• 2015

With rising fuel costs and the depletion of fossil fuels, electric vehicles of high efficiency has been increasing interest. although high-performance battery continually is developing, Electric vehicles is not satisfied with the characteristics of the environment. In this study, By using the current fuel economy testing methods(5-cycle test), until the fully discharged battery electric vehicles is evaluated for a variety of environmental and operating conditions. As a result, Electric vehicles showed a low energy consumption efficiency in low temperature and rapid acceleration, deceleration in the operating environment compared with normal temperature.