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Development of fuzzy controller for inverter DC resistance spot welding using system identification
이희준,유지영 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.8
Adaptive Resistance spot welding (RSW) technologies have been developed and applied within the automotive industry to improve the weldability of automotive steels, including conventional and high strength steels. Almost all adaptive RSW systems require an inverter DC RSW system as a platform because such a system can generate various types of current waveforms effectively with higher control frequency than an AC RSW system. In this work, a fuzzy controller for an inverter DC RSW system that can control constant current and more complex current waveforms was developed as a platform for adaptive control of RSW. This study used System identification (SI) to model the inverter DC welding system effectively. To optimize the fuzzy controller for the SI model, fuzzy scaling factors were optimized using a genetic algorithm. To apply the scaling factor of the fuzzy controller with the SI model to a real system, the scaling factors were adjusted using response surface methodology.
이희준,도종대,김선신,박원경,전기천 한국해양과학기술원 2016 Ocean science journal Vol.51 No.4
Haeundae Beach represents Korean pocket beaches that are currently erosional and dominated by summertime typhoons. The decadal wave characteristics 9 km offshore of Haeundae Beach were analyzed using the WAM model that was validated through the 2007 wave observations. The wave statistics modelled for 1979–2007 indicates that the seasonal mean significant wave height (Hs) is highest (0.6–0.7 m) in summer due to typhoons, in contrast to the lowest (around 0.5 m) autumn analog. The wave direction is also pronouncedly seasonal with the principal bearings of SSW and NE in the summer and winter seasons, respectively. The WAM results additionally show that the Hs has gradually increased over the region of Haeundae Beach since 1993. Beach profiling during June–November 2014 shows the opposite processes of the typhoon and fair-weather on beach sands. During a typhoon, foreshore sands were eroded and then accumulated as sand bars on the surf zone. In the subsequent fair-weather, the sand bars moved back to the beach resulting in the surf-zone erosion and foreshore accretion. A total of 5 cycles of these beach-wide sand movements yielded a net retreat (up to 20 m) of the shoreline associated with large foreshore erosion. However, the surf zone only slightly accumulated as a result of the sand cycles. This was attributed to the sand escape offshore from the westernmost tip of the beach. The present study may provide an important clue to understanding the erosional processes in Haeundae Beach.
Experimental Assessment on the Internal Instability of Broadly Graded Silty Sand
이희준,김인현,정충기 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.4
Suffusion can occur when fine particles are under low effective stress and free to travel through constrictions between coarse particles, and sufficient seepage forces move the fine particles through the voids. Generally, gap-graded soils, which are a binary mixture of two distinct particle sizes, are susceptible to suffusion. Such soils show clear manifestations of suffusion, such as a significant quantity of fine particles discharged and an increase in permeability and void ratio. Therefore, in previous studies on seepage erosion problems, gap-graded soils were mostly utilized as the target soil. However, it is not clear whether the broadly graded soils, the fill dam materials in South Korea, are susceptible to suffusion according to the existing criteria and previous research. Additionally, experimental studies on broadly graded soils have rarely been conducted, especially in terms of hydraulic conditions. Therefore, a deeper understanding of the suffusion progress on broadly graded soils under various hydraulic conditions (hydraulic gradients) is required. In the present study, suffusion tests were performed on gap-graded andbroadly graded soils with different relative densities by using the newly developed suffusion test apparatus. During the test, the hydraulic gradient was increased stepwise, and the occurrence and progress of internal erosion were analyzed based on the amount of discharged soil and the coefficient of permeability. In contrast to gap-graded soils, the test results for broadly graded soils showed a continuous reduction in k before the initiation of erosion. At the onset of internal instability, sudden increases in k and soil discharge occurred under a relatively high hydraulic gradient. Additionally, a series of seepage tests on broadly graded soils showed that the higher the relative density, the higher the hydraulic gradient required to reach an unstable state.