• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.10 s.241
• /
• pp.1111-1118
• /
• 2005

In this study, a unified numerical investigation has been performed on the evolution of weld pool and key-hole geometry during low-power and high-power density laser welding. Unsteady phase-change heat transfer and fluid flow with the surface tension are examined. The one-dimensional vaporization model is introduced to model the overheated surface temperature and recoil pressure during high-power density laser welding. It is shown that Marangoni convection in the weld pool is dominant at low-power density laser welding, and the keyhole with thin liquid layer and the hump are visible at high-power density laser welding. It is also shown that the transition from conduction welding to penetration welding fur iron plate exists when the laser power density is about $10^6W/Cm^2$.

• Journal of the Korean Ceramic Society
• /
• v.50 no.3
• /
• pp.212-217
• /
• 2013

Ultra hard TiN coatings were fabricated by DC and ICP (inductively coupled plasma) magnetron sputtering techniques. The effects of ICP power, ranging from 0 to 300 W, on the coating microstructure, crystallographic, and mechanical properties were systematically investigated with FE-SEM, AFM, HR-XRD and nanoindentation. The results show that ICP power has a significant influence on the coating microstructure and mechanical properties of TiN coatings. With an increasing ICP power, the film microstructure evolves from an apparent columnar structure to a highly dense one. Grain sizes of TiN coatings decreased from 12.6 nm to 8.7 nm with an increase of the ICP power. A maximum nanohardness of 67.6 GPa was obtained for the coatings deposited at an ICP power of 300 W. The crystal structure and preferred orientation in the TiN coatings also varied with the ICP power, exerting an effective influence on film nanohardness.

• Journal of Power System Engineering
• /
• v.17 no.5
• /
• pp.38-43
• /
• 2013

In order to design a wave energy generating system, a 6-DOF analysis technique is applied to CFD analysis on of a floating body and the behavior is interpreted according to the nature of the incoming waves. A spring constant is adopted to control the motion of multi floating bodies and to calculate the total average power absorption. Three cases of different wavelengths namely 20D, 30D and 40D have been modeled to analyze the total average power absorption. The average power absorption not only varies with the position of the floating body but also varies with wavelength. From the results obtained, it is concluded that the maximum total average power absorption is 9W approximately in wavelength 30D and the minimum total average power absorption is 4.3W approximately in wavelength 40D.

• Journal of Power System Engineering
• /
• v.21 no.5
• /
• pp.29-34
• /
• 2017

Many household appliances, including vacuum cleaners, are being subjected to various of impact damages, and made of plastic. However, researches on the damage of appliances materials by repetitive impacts have been rarely conducted. the mechanical stress exerted upon impact-modified polycarbonate (PC) has a great influence not only on the quality of the product but also on the life span. The purpose of this research was to quantify the effects of repetitive impact on the polycarbonate. Second, it was to design the repetitive impact tester for controlling the impact energy. The mechanical properties of tensile strength, yielding stress and strain on the specimens subjected to cyclic impacts were discussed. Tensile strength was sharply declined at the beginning of the impact cycles, while the strain gradually decreased during impact cycles.

• Journal of Power Electronics
• /
• v.11 no.2
• /
• pp.211-217
• /
• 2011

The dynamic response of a multi-MW wind turbine to a sudden change in wind speed is usually slow, because of the slow pitch control system. This could cause a large excursion of the rotor speed and an output power over the rated. A feedforward pitch control can be applied to minimize the fluctuations of these parameters. This paper introduces the complete design steps for a feedforward pitch controller, which consist of three stages, i.e. the aerodynamic torque estimation, the 3-dimensional lookup table for the wind seed estimation, and the calculation of the feedforward pitch amount. The effectiveness of the feedforward control is verified through numerical simulations of a multi-MW wind turbine.

• Industrial Engineering and Management Systems
• /
• v.6 no.1
• /
• pp.22-27
• /
• 2007

This paper describes the optimization of maintenance workforce scheduling at Afam power station in Nigeria. The objective is to determine the optimum schedule to satisfy growing maintenance labour requirements with minimum cost and highest efficiency. Three alternative maintenance workforce schedules are compared. The first alternative is to continue with the traditional five-day workweek schedule currently being practiced by Afam power station maintenance line. The second alternative is to switch to a seven-day workweek schedule for the morning shift only. The third alternative is to use a seven-day workweek schedule for all three work shifts. The third alternative is chosen, as it is expected to save 11% of the maintenance labour cost.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.8
• /
• pp.687-694
• /
• 2002

In order to replace the jacket material for URD power cables, the 6 kinds of polyethylene compounds were manufactured and evaluated. The characteristics of the compounds were investigated by water vapor transmission (WVT) test, thermal and mechanical test. In WVT test, all the polyethylene compounds showed the superior water resistance to conventional PVC. The molecular structure and density of polyethylene play an important role in WVT. Also, the polyethylene compounds showed the suitable characteristics in thermal and mechanical test. Especially, the linear polyethylene compounds showed the superior characteristics to LDPE ones. Due to the fillers in compounds, the abrasion resistance was decreased and the cut-through resistance was increased. From this study, it can be considered that the polyethylene compounds may be suitable to jacket material for URD power cables.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.7
• /
• pp.1052-1059
• /
• 2009

The effects of varying the inlet flow angle on the output power of a Francis hydraulic turbine were studied numerically and the result was compared to the experimental results conducted at Korea Institute of Energy Research to determine the brake power of the turbine for each set of operating conditions. The loss of mechanical power of the model turbine was determined by comparing the numerical and experimental results, and thus the turbine efficiency or energy conversion efficiency of the model turbine could be estimated. From the result, it was found that the maximum brake efficiency of the turbine is approximately 46% at an induced angle of 35 degrees. The maximum indicated mechanical efficiency of the turbine is approximately 93% at an induced angle of 25~30 degrees.

• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.2
• /
• pp.211-218
• /
• 2011

We reported the design, prototype, test drive, and mechanical & electrical engineering analyses of a power-lifting wheelchair using mecanum wheels. Mecanum wheels enable translational and rotational movement of the device in any direction on the ground. The power-lifting capability enables the seated individual to reach the standing height of a non-disabled individual. This mecanum wheelchair is fully controlled by the joystick attached to the armrest. The motion of the wheelchair and lifting action of the seat were studied using statics and dynamics. We believe this mecanum wheelchair is a prime candidate for commercial production.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.05c
• /
• pp.7-10
• /
• 2002

In this study, polyolefin compounds were developed and evaluated for replacing a jacket material of URD power cables. The characteristics of compounds were investigated by water vapor transmission (WVT) test and mechanical test. In WVT test, all polyolefin compounds showed the superior water resistance to conventional PVC. The molecular structure and density of polyolefin play an important role in WVT. Also, polyolefin compounds showed the suitable characteristics in mechanical test. Especially, polyolefin compounds having linear molecules showed the superior characteristics to LDPE ones. From this study, it can be considered that polyolefin compounds may be suitable to jacket material for URD power cables.