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Nguyen K.T.,Sejong University | Lee J.,Sejong University | Lee K.,Green and Industrial Technology Center | Ahn N.,Sejong University
Journal of Asian Architecture and Building Engineering | Year: 2012

Construction materials have been greatly improved in recent years and reinforced concrete is no exception. However, corrosion inside reinforced concrete continues to be a primary problem in the construction field. This paper considers the corrosion rate of special kinds of steel inside reinforced concrete pavement. Corrosion is caused by chloride ions present in the deicing salts used to melt snow on pavement. These chloride ions cause endosmosis in the structure of steel and eventually destroy it. In order to prevent such corrosion, layers have been created to protect the steel. The authors use the polarization resistance method to check the ability of such barriers. The variables of this experimental study were four kinds of steel: black rebar, stainless steel 304 clad rebar, galvanized coated rebar A and galvanized coated rebar B. According to the test result, black steel corroded much more than the others with the presence of salt. Although the galvanized A rebar corroded more slowly than the galvanized B rebar in Ca(OH)2 plus the threshold amount NaCl, the corroding resistance of the galvanized B rebar was better in the presence of 3.5% NaCl. However, of the four kinds of steel, the pure stainless steel 304 clad rebar proved to be the best in terms of corrosion resistance.

Kim S.-J.,Mokpo Maritime University | Kim S.-K.,Seoul National University of Science and Technology | Park J.-C.,Green and Industrial Technology Center
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2012

To improve the durability of underwater rotating products, the corrosion characteristics in harsh marine environment were evaluated through various electrochemical experiments on the Al2O3-3TiO2 and CoNiCrAlY coating layers by atmospheric pressure plasma spray coating process. By evaluating the corrosion resistance of these materials, their applicability to environmentally friendly power generation equipment such as blades of tidal current turbines was examined. According to the Tafel analysis for micro-areas including the coating layer, the coating/metal interlayer and the base metal, the Al2O3-3TiO2 coating layer and the CoNiCrAlY coating layer show markedly lower corrosion current density than the base metal. The corrosion current density of the CoNiCrAlY coating layer (9.75316×10-8 A/cm2) is about 1.6 times more than that of the Al2O3-3TiO2 coating layer (6.13139×10-8 A/cm2). © 2012 The Nonferrous Metals Society of China.

Lee K.-S.,Green and Industrial Technology Center | Park R.-S.,University of Ulsan
International Journal of Offshore and Polar Engineering | Year: 2012

The main object of this research is to minimize the shock effects which frequently result in fatal damage to the windmeasuring met mast after impact with a service boat. The collision between wind-measuring met mast and service boat is generally a complex problem, and it is often impractical to perform rigorous finite element analyses to include all effects and sequences during the collision. This paper focuses on the structural behaviors of the wind-measuring met mast. A significant part of the collision energy is dissipated in terms of strain energy, and the contribution from the elastic strain can normally be neglected. On applying the impact force of a service boat to the wind-measuring met mast, the maximum acceleration, internal energy and plastic strain are calculated for each load case using the finite element method. LS-dyna, a commercial explicit finite element code from ANSYS software, is used to produce a finite element model and analyze the nonlinear responses of the met mast due to the service boat collision. A parametric study is carried out by changing design variables of the service boat's velocity and the thickness of the wind-measuring met mast. Three types of materials for rubber fenders are taken into account where Mooney-Rivlin coefficients are determined based on the experimental data. It is assumed that the effect of the wave-induced vertical motion of a service boat is negligible. It is concluded that this paper provides a designing process used for rubber fenders considering a service boat impact. © The International Society of Offshore and Polar Engineers.

Bang H.-J.,Korea Institute of Energy Research | Kim H.-I.,Korea Advanced Institute of Science and Technology | Lee K.-S.,Green and Industrial Technology Center
International Journal of Precision Engineering and Manufacturing | Year: 2012

This paper introduces a fiber Bragg grating (FBG) based arrayed sensor system for use in the measurement of strain and bending deflection of an 1. 5 MW wind turbine tower, and describes the results of field tests of structural monitoring of turbine start and feathering load conditions. A wavelength division multiplexing (WDM) FBG interrogator was developed with a spectrometer-type demodulator based on a linear photo detector for high-speed strain sensing. Real-time shape estimation of the wind turbine tower was accomplished using strain data gathered by surface mounted fiber Bragg grating sensors. The finite element model of the wind turbine tower was created and the displacement-strain transformation (DST) matrix on the basis of the modal approach was obtained. To monitor the dynamic structural behavior of the wind turbine, 10 FBG sensors were arrayed and installed on the inner surface of the tower located at the primary wind direction. The time histories of the strain were gathered using the FBG sensors and the deflections of the tower top position were simultaneously transformed using the DST matrix. Finally, the full deflection shapes of the tower were successfully estimated using arrayed FBG sensors. © 2012 Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.

Kim B.-H.,Korea Maritime and Ocean University | Wata J.,Korea Maritime and Ocean University | Zullah M.A.,Green and Industrial Technology Center | Ahmed M.R.,University of The South Pacific | Lee Y.-H.,KMOU
Renewable Energy | Year: 2014

Experiments and several numerical studies were done on a power-take off system of a novel floating wave energy convertor. The wave energy convertor utilizes the changes in surface elevation of the waves to cause a column of water to rise and fall periodically in the caisson which creates a bi-directional flow. A cross flow turbine within the device uses this bi-directional flow to rotate in one direction. A 6 DOF ocean simulator was used to conduct experiments on the PTO system at a model to prototype scale of 1:3, for no-load conditions and loaded conditions. In the experiment, the parameters like pitching angles of the device, moment of inertia on the shaft, wave periods and rotational speeds of the turbine were varied. It was found that for all pitching angles, the device had optimum response at a wave period of 3s. A moment of inertia of 0.053kgm2 was found to be appropriate for all test cases. Peak hydraulic efficiencies between 35% and 45% were obtained for the range of 40-50RPM for most test cases. Particle image velocimetry (PIV) tests then done to document and investigate the flow around the turbine and the inlet and exit nozzles. A commercial CFD software was used to carry out the numerical calculations and to observe the internal flow. Finally, a floating body simulation was conducted on to calculate the motion of the device at sea and thus calculate the overall performance of the device. © 2014.

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