• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6A
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• pp.389-398
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• 2012

In this study, structural strain responses of the jacket-type Uldolmok tidal current power plant structure under severe tidal environments were measured and analyzed using long-term measurement system during construction and also operation. It was observed that there were significant changes in strain responses at the steps of jacket lifting, block loading, pile ejection and insertion. Strains due to dead loads and tidal loads were analyzed before and after removal of a jacket leg, and it was also found that the strains due to dead load were much significantly changed after jacket leg removal. From the measurement data during operation, it was found that strain responses were fluctuated with M2 and M4 tidal periods and also relatively short period of about 10 min due to the peculiar tidal characteristics in the Uldolmok strait. Finally, the neural network-based non-parametric estimation models were investigated to build up the signal-based structural damage monitoring system.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.40 no.6
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• pp.106-113
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• 2003

The modified discrete cosine transform (MDCT) and inverse MDCT (IMDCT) are employed in subband/transform coding schemes as the analysis/synthesis filter bank based on time domain aliasing cancellation (TDAC). And the MDCT and IMDCT are the most computational intensive operations in layer III of the MPEG audio coding standard. In this paper, we propose a new efficient algorithm for the MDCT/IMDCT computation in various audio coding systems. It is based on the MDCT/IMDCT computation algorithm using the discrete cosine transforms (DCTs), and It employs two discrete cosine transform of type II (DCT-II) to compute the MDCT/IMDCT In addition, it takes advantage of ability in calculating the MDCT/IMDCT computation, where the length of a data block Is divisible by 4. The Proposed algorithm in this paper requires less calculation complexity than the existing method does. Also, it can be implemented by the parallel structure, therefore its structure is particularly suitable for VLSI realization

• Journal of the Korean Ceramic Society
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• v.35 no.2
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• pp.172-179
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• 1998

Valve lifter namely tappet is supported by lifter hole which is located upper side of camshaft in cylinder block transforms rotatic mvement of camshaft into linear movement and helps to open and shut the en-gine valve as an engine parts. The face of valve lifter which is continuously contacting with camshaft brings about abnormal wears such as unfair wear and early wear because it is severely loaded in the valve train system. These wears act as a defect like over-clearance and cause imperfect combustion of fuel during the valve lifting in the combustion chamber. Consequently this imperfect combustion makes the engine out-put decrease and has cause on air pollution. To prevent these wears therefore The valve lifter cast in me-tal developed into SiC ceramics valve lifter which has an excellence in wear and impact resistance As a results the optimum process conditions like injection condition mixture ratio and debonding process could be established. After sintering fine-sinered dual microstructure in which prior ${\alpha}$-SiC matches well with new SiC(${\beta}$-SiC) produced by reaction among the ${\alpha}$-SiC carbon and silicon was obtained. Based on the study it is verified that mechanical properties of SiC valve lifter are excellent in Vickers hardness 1100-1200 bending strength (300-350 Pa) fracture toughness(1.5-1.7 Mpa$.$m1/2) Through engine dynamo test-ing SiC valve lifter and metal valve lifter are examined and compared into abnormal phenomena such as early fracture unfair and early wear. It is hoped that this research will serve as an important springboard for the future study of heavy duty diesel engine parts developed by ceramics which has a good wear resis-tance relaibility and lightability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.12
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• pp.924-930
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• 2008

Immersed boundary method (IBM) is the most effective method to overcome the disadvantage of LBM (Lattice Boltzmann Method) related to the limitation of the grid shape. IBM also make LBM possible to simulate flow over complex shape of obstacle without any treatment on the curved boundary. In the research, IBLBM was used to perform LBM simulation of a flow over a moving circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of IBLBM on the moving obstacle near the wall, it was first simulated for the case of the flow over a fixed circular cylinder in a channel and the results were compared against the solution of moving cylinder in the channel using IBLBM. The simulations were performed in a moderate range of Reynolds number at each moving cylinder to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag and lift coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical Reynolds number for vortex shedding is Re=50 and the result is the same as the case of fixed cylinder. As the cylinder approaching to a wall (${\gamma}<2.5$), the 2nd vortex is developed by interacting with the wall boundary-layer vorticity. When the cylinder is very closed to the wall, ${\gamma}<0.6$, the cylinder acts like blockage to block the flow between the cylinder and wall so that the vortex developed on the upper cylinder elongated and time averaged lifting and drag coefficients abruptly increase.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• autumn
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• pp.232-239
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• 2001

Young Jong Grand Bridge is approach traffic road of New Inchon International Airport which covers hub airport function in northeast asia. The total span length of this bridge is $4,420{\cal}m$ and this main bridge type is, the first in the world, Double Deck Self Anchored Suspension Bridge, designed as double deck systems to be arranged by road and railroad. Approach bridges to be connected with main span also are composed double deck steel truss and steel box girder to consider a continuity with this span. Our company erected $1,375{\cal}m$(about 60,000tons) of double deck steel truss bridge type which is composed by 6 traffic lane on upper deck and 4 traffic lane and Double track railroad on lower deck. The original installation method of this bridge was planed to install about 75 meters bridge blocks to use floating crane, after temporary bent was constructed between permanent piers. But this method which had to construct many temporary bents in the sea had the matter that construction periods can become lengthen and construction cost can be risen. To overcome the uncertainty to ensure high qualify of bridge and economic project execution, our company developed new bridge erection method to assure both quality control and economic construction work. The new erection method which was developed by us was one that could transport and install long bridge block, $120{\cal}m$ unit at a time and that temporary bent was not required. We hope that this paper is used as technical data which will erect bridge in the western sea and others marine region.