• Proceedings of the KIPE Conference
• /
• 2017.11a
• /
• pp.93-94
• /
• 2017

본 논문은 quasi P+MR 전압 제어를 활용한 삼상 인버터의 계통 동기화 방식을 제안한다. 계통동기화 과정 시 시스템이 고정자 좌표계하에서 제어 또는 모델링된다면 독립운전에서의 정전압 및 정주파수를 갖는 교류 지령 전압은 교류 계통 전압으로 즉각 대체되며 이때 인버터의 실제 전압과 계통 전압 간의 위상차에 기인하여 상당한 제어 오차가 발생할 수 있고 이는 심각한 전압 동특성 저하를 야기하기도 한다. 게다가 인버터 출력단에 비선형 부하가 연결될 경우 부하로부터 발생하는 고조파로 인해 이러한 전압 품질에 대한 문제가 더욱 증대된다. 본 논문에서는 독립 운전 모드에서의 전압제어를 위하여 이러한 비선형 부하의 고조파 영향을 고려한 고정자 좌표계 기반의 PR 제어를 사용한 매끄러운 계통 동기화 방식이 제안되었다. 제안된 매끄러운 계통 동기화 방식의 타당성은 기존의 고정자 좌표계 기반의 계통 동기화 방식과의 비교 사례연구를 기반으로 한 실험을 통해 입증된다.

• Journal of the Korean Operations Research and Management Science Society
• /
• v.41 no.2
• /
• pp.35-51
• /
• 2016

This paper proposes a new approximate approach to calculate the order fill rate and the probability of filling an entire customer order immediately from the shelf in a business environment under purchase dependence characterized by customer purchase patterns observed in such areas as marketing, manufacturing systems, and distribution systems. The new approximate approach divides customer orders into item orders and calculates fill rates of all order types to approximate the order fill rate. We develop a greed iterative search algorithm (GISA) based on the Gauss-Seidel method to avoid dimensionality and prevent the solution divergence for larger instances. Through the computational analysis that compares the GISA with the simulation, we demonstrate that the GISA is a dependable algorithm for deriving the stationary joint distribution of on-hand inventories in the type-K pure system. We also present some managerial insights.

• Wind and Structures
• /
• v.8 no.1
• /
• pp.1-12
• /
• 2005

A simplified analysis able to point out the most relevant geometrical and aerodynamic parameters that can influence the flutter of long span modern bridges is the aim of the paper. With this goal, by using a continuous model of the suspension bridge and by a quasi stationary approach, a simple formula of the combined vertical/torsional flutter wind speed is given. A good agreement is obtained comparing the predictions from the proposed formula with the flutter speeds of three modern suspension or cable stayed bridges: the Great Belt East Bridge, the Akashi and Normandie bridges. The paper ends with some comments and comparisons with the well known Selberg formula.

• International Journal of Control, Automation, and Systems
• /
• v.5 no.1
• /
• pp.51-60
• /
• 2007

This paper describes a visual tracking control law of an Unmanned Aerial Vehicle(UAV) for monitoring of structures and maintenance of bridges. It presents a control law based on computer vision for quasi-stationary flights above a planar target. The first part of the UAV's mission is the navigation from an initial position to a final position to define a desired trajectory in an unknown 3D environment. The proposed method uses the homography matrix computed from the visual information and derives, using backstepping techniques, an adaptive nonlinear tracking control law allowing the effective tracking and depth estimation. The depth represents the desired distance separating the camera from the target.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.10
• /
• pp.1623-1629
• /
• 2003

In this paper, the arc beam is considered as a moving disc heat source with a pseudo-Gaussian distribution of heat intensity. The solution for temperature distribution on welds is derived by using the image heat source method and the superposition method. It is general solution in that it can determine the temperature-rise distribution in and around the arc beam heat source, as well as the width and depth of the melt pool (MP) and the heat-affected zone (HAZ) in welding short lengths, where quasi-stationary conditions may not have been established. As a comparative study, the results of this analytical approach has been compared with that of the finite-element modeling. As a result, The theoretical analysis presented here has shown good consistency and is more time/cost-effective method compared with FEM.

• Journal of the Korean Institute of Telematics and Electronics S
• /
• v.34S no.4
• /
• pp.33-41
• /
• 1997

Korean unvoiced phonemes consist of nonstationary parts comparing that the vowels and nasal consonants consist of quasi-stationary part. And some phonemes, which have smae point of articulation but differnt manner of articulation, has similar characteristics, so it makes to be hard to distinguish each other. A new method usin gchanges and characteristics of acoustic properties of these phonemes to improve recognition rate are proposed. And because these changes and cahracteristics evidently occur in continuous speech except some unvoiced consonants are articulated as voiced phoneme in case to be used as an midial between voiced phonemes, this method can be applied easily. The features of the frames extracted to represent each phonemes are used asinputs to the hierarchical neural network. And with these results final decision for phoneme recognition is made thorugh post processing which the new method is applied to. Through the experimental recognition results for 9 unvoiced consonants which belong to bilabial, alveolar, and velar phoneme series, 89.4% recognition rate to distinguish in same phoneme series is obtained, and 85.6% recognition rate is obtained in case of including cistinguishing phoneme series.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2007.05a
• /
• pp.1437-1440
• /
• 2007

Many hydroclimatic time series are marked by interannual and longer quasi-period features that are associated with narrow band oscillatory climate modes. A time series modeling approach that directly considers such structures is developed and presented. The essence of the approach is to first develop a wavelet decomposition of the time series that retains only the statistically significant wavelet components, and to then model each such component and the residual time series as univariate autoregressive processes. The efficacy of this approach is demonstrated through the simulation of observed and paleo reconstructions of climate indices related to ENSO and AMO, tree ring and rainfall time series. Long ensemble simulations that preserve the spectral attributes of the time series in each ensemble member can be generated. The usual low order statistics are preserved by the proposed model, and its long memory performance is superior to the direction application of an autoregressive model.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.13 no.1
• /
• pp.61-68
• /
• 1995

This paper is to provide a reference surface geoid for geodetic applications of satellite altimeter data. The paticular satellite alone or the combination with other altimeter data could be used for the recovery of geoid un-dulations and gravity anomalies in the ocean areas. This paper also describes the geoidal undulation in the ocean area of Korean Peninusla using Geosat, ERS-1 and Topex/Poseidon data. The results show that the quasi-stationary sea surface topography (557) is estimated to be less than 10 cm RMS value in the ocean area of Korean Peninsula. This can be considered as an altimeter geoid.

• Journal of Ship and Ocean Technology
• /
• v.8 no.4
• /
• pp.10-16
• /
• 2004

A response of a swept wing boundary layer to a single free-stream stationary axial vortex of a limited spanwise extent is considered as an example of typical problems that one can find in laminar-turbulent transition research and control. The response is dominated by streamwise velocity perturbations that grow quasi-exponentially downstream. It is shown that the formation of the boundary layer disturbance occurs for the most part close to the leading edge. The disturbance represents itself a wave packet consisted of the waves with characteristics specific for cross-flow instability. However, an admixture of growing disturbances whose origin can be attributed to transient effects and to a distributed receptivity mechanism is also identified.

• Special Issue of the Society of Naval Architects of Korea
• /
• 2007.09a
• /
• pp.128-134
• /
• 2007

Induction heating process includes magnetic and thermal situations. In order to analyze the induction heating, material properties depending on temperature are considered. In this paper, three dimensional analysis of induction heating process for moving inductor is analyzed using moving coordinate. The skin effect is confirmed inside the steel plate in the electro-magnetic analysis. The heat generation at the initial state is different from that at the quasi-stationary state. Therefore, material properties depending on temperature must be considered. The results of finite element analysis agree well with the experimental temperature results.