• 전기학회논문지P
• /
• 제57권2호
• /
• pp.91-95
• /
• 2008

The large AC generator fault may lead to large impacts or perturbations in power system. The generator protection control systems in Korea have been imported and operated through a turn-key from overseas entirely. Therefore a study of the generator protection field has in urgent need for a stable operation of the imported goods. In present, the algorithm using the current ratio differential relaying based DFT for stator winding protection or a fault detection had been applied that of internal fault protection of a generator. the DFT used for the analysis of transient state signal conventionally had defects losing a time information in the course of transforming a target signal to frequency domain. In this paper, the discrete wavelet transform (DWT) was applied a fault detection of the generator being superior to a transient state signal analysis and being easy to real time realization. The fault signals after executing a terminal fault modeling collect using a MATLAB package, and calculate the wavelet coefficients through the process of a muiti-level decomposition (MLD). The proposed algorithm for a fault detection using the Daubechies WT (wavelet transform) was executed with a C language and the commend line function for the real time realization after analyzing MATLAB's graphical interface. The advanced technique had improved faster a speed of fault discrimination than a conventional DFR based on DFT.

• Bulletin of the Korean Chemical Society
• /
• 제31권4호
• /
• pp.910-914
• /
• 2010

A novel synthetic route has been developed to prepare $\alpha$-cobalt hydroxide with intercalated nitrate anions. It was successfully synthesized by $\gamma$-ray irradiation under simple conditions, i.e., air atmosphere, without base. Under $\gamma$-ray irradiation, it leads to the formation of layered cobalt hydroxynitrate compounds which have small crystalline size and have the role of a generator of hydroxyl anion. Structural and morphological characterizations were performed by using power X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and high resolution transmission electron microscopy (HR-TEM). The component and thermal stability of the sample were respectively measured by Fourier transform infrared (FT-IR) spectroscopy, elemental analysis, and thermal analyses, including thermogravimetry (TG) and differential thermal analysis (DTA).

• Journal of Electrical Engineering and Technology
• /
• 제13권5호
• /
• pp.1935-1944
• /
• 2018

With the increase of the production of energy from renewable, it becomes important to look at techniques to store this energy. Therefore, a single winding bearingless flywheel motor (SWBFM) specially for flywheel energy storage system is introduced. For the control system of SWBFM, coupling between the torque and the suspension subsystems exists inevitably. It is necessary to build a reasonable radial force mathematical model to precisely control SWBFM. However, SWBFM has twelve independently controlled windings which leads to high-order matrix transformation and complex differential calculation in the process of mathematical modeling based on virtual displacement method. In this frame, a Maxwell tensor modeling method which is no need the detailed derivation and complex theoretical computation is present. Moreover, it possesses advantages of universality, accuracy, and directness. The fringing magnetic path is improved from straight and circular lines to elliptical line and the rationality of elliptical line is verified by virtual displacement theory according to electromagnetic torque characteristics. A correction function is taken to increase the model accuracy based on finite element analysis. Simulation and experimental results show that the control system of SWBFM with radial force mathematical model based on Maxwell tensor method is feasible and has high precision.

• Steel and Composite Structures
• /
• 제33권2호
• /
• pp.307-318
• /
• 2019

This is the first attempt to consider the nonlinear bending analysis of porous functionally graded (FG) thick annular and circular nanoplates resting on Kerr foundation. The size effects are captured based on modified couple stress theory (MCST). The material properties of the porous FG nanostructure are assumed to vary smoothly through the thickness according to a power law distribution of the volume fraction of the constituent materials. The elastic medium is modeled by Kerr elastic foundation which consists of two spring layers and one shear layer. The governing equations are extracted based on Hamilton's principle and two variables refined plate theory. Utilizing generalized differential quadrature method (GDQM), the nonlinear static behavior of the nanostructure is obtained under different boundary conditions. The effects of various parameters such as material length scale parameter, boundary conditions, and geometrical parameters of the nanoplate, elastic medium constants, porosity and FG index are shown on the nonlinear deflection of the annular and circular nanoplates. The results indicate that with increasing the material length scale parameter, the nonlinear deflection is decreased. In addition, the dimensionless nonlinear deflection of the porous annular nanoplate is diminished with the increase of porosity parameter. It is hoped that the present work may provide a benchmark in the study of nonlinear static behavior of porous nanoplates.

• Steel and Composite Structures
• /
• 제17권5호
• /
• pp.753-776
• /
• 2014

In this paper, nonlinear vibration and post-buckling analysis of beams made of functionally graded materials (FGMs) resting on nonlinear elastic foundation subjected to thermo-mechanical loading are studied. The thermo-mechanical material properties of the beams are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and to be temperature-dependent. The assumption of a small strain, moderate deformation is used. Based on Euler-Bernoulli beam theory and von-Karman geometric nonlinearity, the integral partial differential equation of motion is derived. Then this PDE problem which has quadratic and cubic nonlinearities is simplified into an ODE problem by using the Galerkin method. Finally, the governing equation is solved analytically using the variational iteration method (VIM). Some new results for the nonlinear natural frequencies and buckling load of the FG beams such as the influences of thermal effect, the effect of vibration amplitude, elastic coefficients of foundation, axial force, end supports and material inhomogenity are presented for future references. Results show that the thermal loading has a significant effect on the vibration and post-buckling response of FG beams.

• Advances in nano research
• /
• 제10권3호
• /
• pp.281-293
• /
• 2021

This paper presents a new nonlocal Hyperbolic Shear Deformation Beam Theory (HSDBT) for the free vibration of porous Functionally Graded (FG) nanobeams. A new displacement field containing integrals is proposed which involves only three variables. The present model incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect and its account for shear deformation by a hyperbolic variation of all displacements through the thickness without using the shear correction factor. It has been observed that during the manufacture of Functionally Graded Materials (FGMs), micro-voids and porosities can occur inside the material. Thus, in this work, the investigation of the free vibration analysis of FG beams taking into account the influence of these imperfections is established. Four different porosity types are considered for FG nanobeam. Material characteristics of the FG beam are supposed to vary continuously within thickness direction according to a power-law scheme which is modified to approximate material characteristics for considering the influence of porosities. Based on the nonlocal differential constitutive relations of Eringen, the equations of motion of the nanobeam are derived using Hamilton's principle. The effects of nonlocal parameter, aspect ratio, and the porosity types on the dynamic responses of the nanobeam are discussed.

• 대한전자공학회논문지TC
• /
• 제43권10호
• /
• pp.46-54
• /
• 2006

본 논문에서는 기존의 아날로그 트랜시버가 가지고 있는 단점을 극복하기 위한 디지털 트랜시버를 제안한다. 제안된 트랜시버는 불연속적인 협대역 채널들로 구성된 환경에서 사용된다고 가정하였다. 그리고 어느 정도의 보안성을 가지며 개인 대(對) 개인뿐만 아니라, 개인 대(對) 그룹, 그룹 대(對) 그룹의 음성 및 데이터 통신이 가능하여야 하며, 음성과 데이터를 동시에 전송할 경우 1 Mbps의 데이터 율을 가져야 한다고 가정하였다. 주파수 대역의 제한 때문에 FH-SS(Frequency Hopping-Spread Spectrum) 방식을, 구현의 복잡성 때문에 D8PSK(Differential 8 Phase Shift Keying) 방식을 채택하였다. 반송파와 심볼 타이밍 복원을 위해 IEEE 802.11 FHSS 프레임 구조를 바탕으로 새로운 프리앰블 구조를 제안하여 검출 확률을 높였다. 전산 모의 실험과 전력 계산을 통하여 제안된 시스템은 아날로그 워키토키와 같은 간단한 무선 통신에 사용될 수 있음을 보였다.

• 전자공학회논문지C
• /
• 제36C권7호
• /
• pp.10-16
• /
• 1999

본 논문은 FCSR(Freedback Control Swing voltage Reduction) 방식을 이용하여 bus 구동전압을 수백 mV이내로 줄일 수 있는 구동기에 대한 내용을 다루고 있다. 이는 MDL 구조와 같이 대용량, 대단위 bus에서의 전력소모를 줄이기 위한 연구로 FCSR은 dual-line bus와 bus precharging을 기본구조로 채택하고 있다. Bus 환경이 변화함에 따라 일정한 구동전압을 유지하기 위하여 구동기의 크기를 자동적으로 조절할 수 있도록 구동기와 bus를 모델링 하였고 또한 odd mode로 동작하는 이웃하는 선간의 커플링 영향을 평행 전류원으로 모델링하여 선간간섭(crosstalk) 영향을 분석하였다. 현대 0.8um 공정으로 제작된 chip은 bus를 600mV로 구동하도록 설계되었으며 테스트결과 3.3V에서 70Mhz로 동작 가능하다. Hspice 시뮬레이션으로 FCSR은 3.3V에서 250Mhz의 동작이 가능하다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제20권5호
• /
• pp.102-108
• /
• 2016

이 연구의 목적은 개착식 전력구 콘크리트에 발생하는 부등건조수축에 의한 균열특성을 파악하고, 수축저감제 혼입에 따른 건조수축균열특성을 분석하는데 있다. 따라서 이 연구에서는 전력구 박스형 콘크리트 구조물의 부등건조수축에 의한 균열특성을 파악하기 위하여 세 가지 주요영향인자를 고려한 수치해석과 수치해석을 한 결과와 실제 전력구 타설을 하여 측정한 차이를 확인해 보았다. 본 연구로부터 건조 수축 시험체에 대한 건조수축량을 산정에 대한 해석 기법을 개발하였으며, 실제 전력구 타설 실험을 통해 종방향 및 횡방향 균열발생 가능성을 입증 하였다. 전력구 실증시험체 건조수축량 수치해석 결과, 균열저감 콘크리트 배합의 경우 종방향 및 횡방향 응력에 있어 일반배합에 비해 40~50%정도의 현저한 감소를 보이며, 이에 따라 균열저감 콘크리트를 전력구에 적용하였을 경우 현저한 균열감소 효과를 보일 것으로 예측된다.

• Nuclear Engineering and Technology
• /
• 제53권5호
• /
• pp.1540-1555
• /
• 2021

The plate-type fuel assembly adopted in nuclear research reactor suffers from complicated effect induced by non-uniform irradiation, which might affect its stress conditions, mechanical behavior and thermal-hydraulic performance. A reliable numerical method is of great importance to reveal the complex evolution of mechanical deformation, flow redistribution and temperature field for the plate-type fuel assembly under non-uniform irradiation. This paper is the first part of a two-part study developing the numerical methodology for the thermal-fluid-structure coupling behaviors of plate-type fuel assembly under irradiation. In this paper, the thermal-fluid-structure coupling methodology has been developed for plate-type fuel assembly under non-uniform irradiation condition by exchanging thermal-hydraulic and mechanical deformation parameters between Finite Element Model (FEM) software and Computational Fluid Dynamic (CFD) software with Mesh-based parallel Code Coupling Interface (MpCCI), which has been validated with experimental results. Based on the established methodology, the effects of non-uniform irradiation and fluid were discussed, which demonstrated that the maximum mechanical deformation with irradiation was dozens of times larger than that without irradiation and the hydraulic load on fuel plates due to differential pressure played a dominant role in the mechanical deformation.