• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.4
• /
• pp.27-36
• /
• 2005

Some studies have shown that unstable factors are inherent in WEDM process, causing the instability of the discharging pulse to reach about 40∼60％ in normal machining. Transient stability is an important subject in WEDM process since there is a close relationship between stability and machining performance, such as the characteristics of a machined surface, machining speed and problem of instability like wire rupture phenomenon. Among the many machining parameters affecting WEDM machining state, three specific parameters (Vr, Ip, off time ) are major controllable variables that can be applied in transient stability control. And, this research investigates the implementation and analysis of real-time micro control of the discharging stability of WEDM (Wire Electric Discharge Machining) process.

• Journal of the Korean Society of Safety
• /
• v.29 no.3
• /
• pp.34-38
• /
• 2014

In Display such as LCD, LED, and AMOLED or semiconductor related industries are required to have static ionizer in order to produce reliable goods since the ionizer can create balanced ion that is delivered to producing goods to minimize electrical damages when manufacturing. However, the most general type of ionization is called, "Corona Discharge" that has a slight chances to generate unequal and unstable amount of each +/- ion to the target object. Then, the ionization performance will drastically decrease and end up with quality deterioration problem. In this research, our objective to resolve the current issue via applying "Coupling Condenser" on each counter electrodes of Corona discharging type ionizer. The result is that the ion balance was maintained the satisfied range that is within +/-100V when we changed the duty ratio of the High Voltage of Pulse AC about 40 ~ 70%. In addition, when levelling the High Voltage of Pulse AC, the ion balance holds the range within +20 ~ 0V. Even though we have tested the same experiment for a year, we have seen the range changes roughly ${\pm}50V$.

• Journal of Korea Port Economic Association
• /
• v.37 no.4
• /
• pp.161-173
• /
• 2021

The shipping industry plummeted and was depressed due to the global economic crisis caused by the bankruptcy of Lehman Brothers in the US in 2008. In 2020, the shipping market also suffered from a collapse in the unstable global economic situation due to the COVID-19 pandemic, but unexpectedly, it changed to an upward trend from the end of 2020, and in 2021, it exceeded the market of the boom period of 2008. According to the Clarksons report published in May 2021, the decrease in cargo volume due to the COVID-19 pandemic in 2020 has returned to the pre-corona level by the end of 2020, and the tramper bulk carrier capacity of 103~104% of the Panamax has been in the ports due to congestion. Earnings across the bulker segments have risen to ten-year highs in recent months. In this study, as factors affecting BDI, the capacity and congestion ratio of Cape and Panamax ships on the supply side, iron ore and coal seaborne tonnge on the demand side and Granger causality test, IRF(Impulse Response Function) and FEVD(Forecast Error Variance Decomposition) were performed using VAR model to analyze the impact on BDI by congestion caused by strengthen quarantine at the port due to the COVID-19 pandemic and the loading and discharging operation delay due to the infection of the stevedore, etc and to predict the shipping market after the pandemic. As a result of the Granger causality test of variables and BDI using time series data from January 2016 to July 2021, causality was found in the Fleet and Congestion variables, and as a result of the Impulse Response Function, Congestion variable was found to have significant at both upper and lower limit of the confidence interval. As a result of the Forecast Error Variance Decomposition, Congestion variable showed an explanatory power upto 25% for the change in BDI. If the congestion in ports decreases after With Corona, it is expected that there is down-risk in the shipping market. The COVID-19 pandemic occurred not from economic factors but from an ecological factor by the pandemic is different from the past economic crisis. It is necessary to analyze from a different point of view than the past economic crisis. This study has meaningful to analyze the causality and explanatory power of Congestion factor by pandemic.