• Smart Structures and Systems
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• v.17 no.2
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• pp.209-230
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• 2016

The Canton Tower is a high-rise slender structure with a height of 610 m. A structural health monitoring system has been instrumented on the structure, by which data is continuously monitored. This paper presents an investigation on the identified modal properties of the Canton Tower using ambient vibration data collected during a whole day (24 hours). A recently developed Fast Bayesian FFT method is utilized for operational modal analysis on the basis of the measured acceleration data. The approach views modal identification as an inference problem where probability is used as a measure for the relative plausibility of outcomes given a model of the structure and measured data. Focusing on the first several modes, the modal properties of this supertall slender structure are identified on non-overlapping time windows during the whole day under normal wind speed. With the identified modal parameters and the associated posterior uncertainty, the distribution of the modal parameters in the future is predicted and assessed. By defining the modal root-mean-square value in terms of the power spectral density of modal force identified, the identified natural frequencies and damping ratios versus the vibration amplitude are investigated with the associated posterior uncertainty considered. Meanwhile, the correlations between modal parameters and temperature, modal parameters and wind speed are studied. For comparison purpose, the frequency domain decomposition (FDD) method is also utilized to identify the modal parameters. The identified results obtained by the Bayesian method, the FDD method and a finite element model are compared and discussed.

• Progress in Superconductivity and Cryogenics
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• v.16 no.2
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• pp.42-46
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• 2014

In this study we investigated ac transport current losses in the face to face stack for the anti-parallel current flow, and compared the electromagnetic properties with those of the single SC tape as well as those of the same stack for the parallel current path. The gap between the SC tapes in the stack varied in order to verify the electromagnetic influence of the neighbors when current flows in opposite direction, and the model was implemented in the finite element method program by the commercial software, COMSOL Multiphysics 4.2a. Conclusively speaking, the loss was remarkably decreased for the anti-parallel current case, which is attributed the magnetic flux compensation between the SC layers due to the opposite direction of the current flows. As the gap between SC tapes was increased, the loss mitigation became less effective. Besides, the current density distribution is very flat cross the sample width for the narrower gap case, which is believed to be benefit for the power electric system. These results are all in good agreement with those predicted theoretically for an infinite bifilar stack.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.723-725
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• 2003

The result of design and Partial fabrication of a 1 MVA single phase high temperature superconducting(HTS) transformer for power distributions are presented in this paper. The HTS windings are wound as double pancake windings which have advantages of uniform distribution of high voltage over the windings. the rated primary and secondary voltages are 22.9 kV and 6.6 kV respectively. Four HTS tapes are wound in parallel for secondary windings considering the rated currents of the transformer. The HTS windings will be cooled down to 65 K by natural convection of sub-cooled liquid nitrogen using a single-staged GM-cryocooler in order to make the stability of the HTS windings better. The iron core is designed as shell type and isolated from the liquid nitrogen by an FRP cryostat which have a room temperature bore. After the complete fabrication of the total HTS transformer system, performance test of the transformer will be carried out.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.2
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• pp.278-283
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• 2013

With the increasing power demands, size of the fault current in electrical grids is steadily increasing, and it exceeds the breaking capacity of circuit breakers. To effectively cope with these problems, a high-speed interrupter was suggested. The high-speed interrupter provides fault current with a bypass to a fault current limiter in case of accidents and consequently, fault current can be restricted. In this study, behavioral characteristics of high-speed interrupter were analyzed by accident types occurred in a distribution system. When accidents occurred, a and b contact of the high-speed interrupter were turned-off and then, turned-on. Accordingly, fault current flowed to the circuit connected to a current limiting element, and the fault current limiter restricted fault current to within a half-cycle. Nevertheless, the behavior of the high-speed interrupter was slowed down by a switching surge. As a result, fault current was confirmed to be restricted not to within the anticipated half-cycle, but to after a half-cycle. Moreover, the behavioral characteristics of the high-speed interrupter changed not only by accident types, but by behaviors of R, S, and T phases. This was due to the errors in stroke lengths of the high-speed interrupters, which resulted in a slight time discrepancy among three interrupters. In addition, the switching behaviors of the b and a contact were confirmed not to have coincided due to the switching surge; b contact behaved first and a contact followed. because of this, accuracy of stroke length and switching surges through the solenoid suction increases may be necessary to resolve.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.8
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• pp.49-54
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• 2015

Molded Circucit Breaker(MCCB) is a most widely used device to protect loads from the over-current in low power level distribution system. When the MCCB interrupts the over-current, the arc discharge occurred between fixed contact and moving contact to create hot gas. By the Lorentz force due to arc current, the occurred arc is bent to the grids. The grids extend and cool and divide it for arc extinguish. In the majority cases, the MCCB protects loads by interrupting the over-current successfully but in some cases the re-ignition is occurred by hot-gas created during process of interruption. The re-ignition arises when the recovery voltage(RV) is more higher than the recovery strength between contacts and it leads to interruption fault. Therefore to find out the dielectric recovery characteristics of protecting device has a great importance for preventing interruption fault. In this paper, we studies measurement method of the dielectric recovery characteristics considering inherent attribute of the MCCB. To measure the dielectric recovery characteristic of MCCB, we makes an experiment circuit for applying the over-current and the randomly recovery voltage. The measurement methode to find out the dielectric recovery voltage of the MCCB was established and the result was based on experiment results.

• Korean Journal of Applied Biomechanics
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• v.20 no.4
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• pp.387-393
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• 2010

The purpose of this study was to compare pregnant women's gait parameters and mechanical energies caused by changes in hormone levels and anatomical features such as body mass, body-mass distribution, joint laxity, and musculo-tendinous strength from pregnancy to postpartum. Ten subjects (height: $161{\pm}6.5cm$, mass: $62.7{\pm}10.4\;kg$, $66.4{\pm}9.3\;kg$, $68.4{\pm}7.7\;kg$, $57.2{\pm}7.7\;kg$) participated in the four times experiments (the first, middle, last term and after birth) and walked ten trials at a self-selected pace without shoes. The gait motions were captured with Qualisys system and gait parameters were calculated with Visual-3D. Pregnant women's gait velocities were decreased during the pregnancy periods, but increased after birth. Stride width and cycle time were increased during pregnancy, but decreased after birth. Thigh energy (77.4%) was greater than shank energy (19.06%) or feet (3.54%) about total energy of the lower limbs. Their feet (Left R2=0.881, Right R2=0.852) and shank (Left R2=0.318, Right R2=0.226) energies were significantly increased (positive correlation), but double limb stance time (DLST, R2=0.679) and body total energy (R2=0.138) were decreased (negative correlation) for their velocities. These differences suggest that thigh segment may be a dominant segment among lower limbs, and have something to do with gait velocities. Further studies should investigate joint power and joint work to find energy dissipation or absorption from pregnancy period to postpartum.

• Applied Chemistry for Engineering
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• v.27 no.2
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• pp.123-127
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• 2016

Methanol fuel cells having advantages of relatively favorable reaction kinetics and higher energy density have attracted increasing interests as best alternative to hydrogen fuel cell because of H2 production, storage and distribution issues. While there have been extensive research works on developing key components such as electrocatalysts as well as their physicochemical properties in practical formic acid fuel cells, there have also been urgent requests for investigating which fuel sources will be more suitable for direct liquid fuel cells in future. In this mini-review, we highlight the overall interest and outlook of formic acid fuel cells in terms of electrocatalysts, fuel supply and crossover, water management, fuel cell efficiency and system integration in comparison with methanol fuel cells.

• Korean Journal of Remote Sensing
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• v.37 no.5_1
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• pp.1187-1198
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• 2021

Sea wind isrecently drawing attraction as one of the sources of renewable energy. Thisstudy describes a new method to produce a 10 m resolution sea wind field using Sentinel-1 images and low-resolution NWP (Numerical Weather Prediction) data with artificial intelligence technique. The experiment for the South East coast in Korea, 2015-2020,showed a 40% decreased MAE (Mean Absolute Error) than the generic CMOD (C-band Model) function, and the CC (correlation coefficient) of our method was 0.901 and 0.826, respectively, for the U and V wind components. We created 10m resolution sea wind maps for the study area, which showed a typical trend of wind distribution and a spatially detailed wind pattern as well. The proposed method can be applied to surveying for wind power and information service for coastal disaster prevention and leisure activities.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1417-1427
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• 2019

In this study, we evaluated the performance of a commercial pixelated cadmium zinc telluride (CZT) detector for spectroscopy and identified its feasibility as a Compton camera for radiation monitoring in a nuclear power plant. The detection system consisted of a $20mm{\times}20mm{\times}5mm$ CZT crystal with $8{\times}8$ pixelated anodes and a common cathode, in addition to an application specific integrated circuit. The performance of the various radioisotopes $^{57}Co$, $^{133}Ba$, $^{22}Na$, and $^{137}Cs$ was evaluated. In general, the amplitude of the induced signal in a CZT crystal depends on the interaction position and material non-uniformity. To minimize this dependency, a drift time correction was applied. The depth of each interaction was calculated by the drift time and the positional dependency of the signal amplitude was corrected based on the depth information. After the correction, the Compton regions of each spectrum were reduced, and energy resolutions of 122 keV, 356 keV, 511 keV, and 662 keV peaks were improved from 13.59%, 9.56%, 6.08%, and 5%-4.61%, 2.94%, 2.08%, and 2.2%, respectively. For the Compton imaging, simulations and experiments using one $^{137}Cs$ source with various angular positions and two $^{137}Cs$ sources were performed. Individual and multiple sources of $^{133}Ba$, $^{22}Na$, and $^{137}Cs$ were also measured. The images were successfully reconstructed by weighted list-mode maximum likelihood expectation maximization method. The angular resolutions and intrinsic efficiency of the $^{137}Cs$ experiments were approximately $7^{\circ}-9^{\circ}$ and $5{\times}10^{-4}-7{\times}10^{-4}$, respectively. The distortions of the source distribution were proportional to the offset angle.

• The Journal of the Korea Contents Association
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• v.21 no.6
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• pp.552-560
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• 2021

With the recent development of the art distribution system, interest in art investment is increasing rather than seeing art as an object of aesthetic utility. Unlike stocks and bonds, the price of artworks has a heterogeneous characteristic that is determined by reflecting both objective and subjective factors, so the uncertainty in price prediction is high. In this study, we used LSTM Recurrent Neural Network deep learning model to predict the auction winning price by inputting the artist, physical and sales charateristics of the Korean artist. According to the result, the RMSE value, which explains the difference between the predicted and actual price by model, was 0.064. Painter Lee Dae Won had the highest predictive power, and Lee Joong Seop had the lowest. The results suggest the art market becomes more active as investment goods and demand for auction winning price increases.