Kim H.,Korea Polytechnic University
Engineering Failure Analysis | Year: 2011
A crack of the fourth stage blade in a low-pressure turbine of a 500. MW steam turbine is studied. From non-destructive inspection, the crack was found at the leading edge vane of the fourth stage blade. Material composition analysis, hardness measurement and microstructure analysis were performed to study the cause and process of the cracked blade. On further examination using the replication of the cracked surface for the blade vane, the crack was induced by corrosion pits. It is assumed that the causes of the corrosion pits are the induction of seawater from the condenser tube that has small leakage, and improper water treatment. It is shown that the corrosion pits acted as stress concentration site and facilitated crack initiation under cyclic loading experienced during normal operation of the blade. From the fracture surface of the blade, it is concluded that the crack is initiated from the corrosion pits at the leading edge of the blade vane, and propagated inside by fatigue due to the vibration of the blade. © 2010 Elsevier Ltd. Source
Kim P.-S.,Korea Polytechnic University
Digital Signal Processing: A Review Journal | Year: 2010
To overcome the resulting problems of existing finite impulse response (FIR) structure filters, this paper proposes an alternative FIR filter for state estimation in discrete-time systems, which is derived from the well-known Kalman filter with recursive infinite impulse response (IIR) structure. The proposed FIR filter obtains a posteriori knowledge about the window initial condition from the most recent finite observations, while existing FIR filters handle this task arbitrarily or heuristically. The gain matrix for the proposed FIR filter incorporates a posteriori knowledge about the window initial condition during its design and is shown to be time-invariant. The proposed FIR filter is shown to have good inherent properties such as unbiasedness and deadbeat. Through extensive computer simulations, the proposed FIR filter can be shown to be comparable with the Kalman filter for the nominal system and better than that for the temporarily uncertain system. © 2009 Elsevier Inc. All rights reserved. Source
Choi K.-H.,Korea Polytechnic University |
Ang B.W.,National University of Singapore
Energy Economics | Year: 2012
In this paper we extend the methodology of index decomposition analysis (IDA) in energy studies by quantifying the contribution of individual attributes to the percent change of factors such as the real energy intensity index and structural change index. We apply the proposed method to the real energy intensity index in the multiplicative Logarithmic Mean Divisia Index (M-LMDI) approach, a major IDA technique. Since the M-LMDI is based on geometric mean type indices and chain computation, we need some appropriate method to cope with the difficulties that arise. We present a numerical illustration of the proposed method using the energy consumption and real value added data of the US manufacturing industry, and compare the results obtained by the Fisher real energy intensity index. © 2011 Elsevier B.V. Source
Korea Polytechnic University and Seoul Opto Device Co. | Date: 2010-08-27
Provided are a high-quality non-polar/semi-polar semiconductor device having reduced defect density of a nitride semiconductor layer and improved internal quantum efficiency and light extraction efficiency, and a manufacturing method thereof. The method for manufacturing a semiconductor device is to form a template layer and a semiconductor device structure on a sapphire, SiC or Si substrate having a crystal plane for a growth of a non-polar or semi-polar nitride semiconductor layer. The manufacturing method includes: forming a nitride semiconductor layer on the substrate; performing a porous surface modification such that the nitride semiconductor layer has pores; forming the template layer by re-growing a nitride semiconductor layer on the surface-modified nitride semiconductor layer; and forming the semiconductor device structure on the template layer.
Korea Polytechnic University and Samsung | Date: 2011-12-20
A method of processing an image signal includes: converting a source image signal into an image signal corresponding to a color space for a color gamut mapping; reducing a color gamut of the image signal; and mapping the image signal corresponding to colors within the reduced color gamut into an image signal corresponding to colors within a display color gamut, wherein the colors of the display color gamut are displayed by a display panel.