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Jang S.-K.,Mokpo Maritime University | Park J.-C.,Korean Register of Shipping | Jeong J.-Y.,Mokpo Maritime University | Han M.-S.,Mokpo Maritime University | Kim S.-J.,Mokpo Maritime University
Science of Advanced Materials | Year: 2014

The reliability for offshore structures is very important since they operate under harsh operating conditions for a long time. Material damage in seawater involves not only physical damage due to cavitation but also corrosion damage by Cl- ions; thus, seawater deteriorates the mechanical performance and lifetime of a ship's components. This study investigated the protection potential of ALBC3 alloy to minimize the cavitation-induced damage by employing the hydrogen overvoltage phenomenon. To achieve this, a hybrid potentiostatic apparatus was devised for the characterization of electrochemical properties of the alloy with cavitation. A cavitation experiment was conducted at 30 μm of amplitude by using an ultrasonic vibratory generator in accordance with modified ASTM G32 regulation. Consequently, the optimum potential range to enhance the cavitation resistance is considered to lie between -2.8 V and -2.2 V, which corresponds to the activation polarization range. © 2014 by American Scientific Publishers.

Oh H.,Korean Register of Shipping | Kim B.,Jeju National University
Energy | Year: 2015

After a wind farm construction is completed, the power performance guaranteed by the wind turbine manufacturer is usually verified based on the international standard IEC61400-12-1. Because of an insufficient project budget and the constraint on the minimum separation distance of the meteorological mast from the installed wind turbines, it is a common practice to verify the power performance of one representative wind turbine and apply the result as the reference power performance guarantee for all the wind turbines. In this study, the power performances of five wind turbines operating at a commercial wind farm located on complex terrain were measured and analyzed. The results showed large power performance differences between the turbines. Because the power performance of one representative wind turbine cannot guarantee the power performances of all the wind turbines in a wind farm located on complex terrain, we submit that it is necessary to carry out power performance verifications on many or all of the wind turbines. © 2015 Elsevier Ltd.

Lee S.,Korean Register of Shipping | Chu B.,Korea Advanced Institute of Science and Technology | Chang D.,Korea Advanced Institute of Science and Technology
International Journal of Precision Engineering and Manufacturing | Year: 2014

To achieve drilling safety, a risk-based design of the dolly assembly control system is proposed. The risk and cost-benefit assessments are conducted to obtain information needed to make decisions about the safe design of the system. A failure modes and effects analysis (FMEA) is performed to identify and analyze the plausible hazardous scenarios by determining the failure modes of the subcomponents and their effects on the system operation. The priorities of risks are ranked by assigning a risk priority number for further investigation. Appropriate recommendations are made as risk reduction measures to achieve a more intrinsically safe design. A subsequent fault-tree analysis (FTA) is performed to provide a more quantitative risk evaluation. Monte Carlo simulations (MCSs) are conducted to determine the change of the availability between the original design and a system with recommendations adopted. For the sake of decision making, a cost-benefit assessment is performed, which demonstrated that the suggestions provided in this study are highly justifiable and strongly recommendable. © 2014, Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.

Yun S.,Inha University | Kim J.,Inha University | Lee K.-S.,Korean Register of Shipping
International Journal of Precision Engineering and Manufacturing | Year: 2010

Cellulose has been discovered as a smart material that can be used as sensor and actuator material. In this paper, cellulose smart material termed as electro-active paper (EAPap) is prepared by an automated process that includes tape casting and zone stretching. To evaluate characteristics of the EAPap, its Young's modulus and piezoelectric charge constant are measured depending on the orientation angle, in comparison with the manually fabricated EAPap results. The zone stretching method can effectively align the cellulose fibers in the EAPap so as to improve its Young's modulus as well as piezoelectric charge constant. The 0 degree oriented sample shows its maximum Young's modulus and the 45 degree oriented sample exhibits the maximum piezoelectric charge constant. This 45 degree is associated with its shear piezoelectricity. The actuator performance of EAPap is evaluated by measuring its bending displacement depending on the orientation angle and the excitation voltage. The 45 degree oriented sample exhibits the maximum bending displacement. Details of the material preparation, the automation process, characterization and the actuator performance are addressed. This automated process that includes tape casting and zone stretching is suitable for mass production of the EAPap. © KSPE and Springer 2010.

Kim S.-J.,Mokpo Maritime University | Park J.-C.,Korean Register of Shipping | Jang S.-K.,Mokpo Maritime University
Advanced Materials Research | Year: 2013

The Al alloy is environmental friendly, easy to recycle, and provides a high added value to fishing boats. Aluminum alloy do not corrode due to the formation of an anticorrosive passive film, such as, Al2O3 or Al2O3·3H2O which resists corrosion in neutral solution. In seawater, however, Cl- ions destroy this passive film. We investigated on several electrochemical tests undertaken to determine the optimum conditions in seawater for corrosion protection of casted AC7AV aluminum alloy. The components of casted AC7AV aluminum alloy are similar with Al-Mg alloys(5xxx series) which are used for ship. Result of electochemical experiment, the optimum protection potential range with regards to hydrogen embrittlement and stress corrosion cracking was determined to lie between -1.3 and -0.7 V(vs Ag/AgCl). © (2013) Trans Tech Publications, Switzerland.

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