• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.4
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• pp.199-208
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• 2019

Regular waves were generated in a wave flume under perfect reflection condition to evaluate performance of three CFD models of CADMAS-SURF, olaFlow, and KIOSTFOAM. The experiments and numerical simulations were carried out for three different conditions of non-breaking, breaking of standing waves, and breaking of incident waves. Among the three CFD models, KIOSTFOAM showed best performance in reproducing the experimental results. Although the run time was reduced by using CADMAS-SURF, its computational accuracy was worse than KIOSTFOAM. olaFlow was the fastest model, but active wave absorption at the wave generation boundary was not satisfactory. In addition, the model excessively dissipated wave energy when wave breaking occurred.

• Land and Housing Review
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• v.13 no.4
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• pp.115-123
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• 2022

This study aims to introduce a temperature discoloration roof system and its cooling effect in the summer. Temperature discoloration paints can reverse their colors based on temperature changes. If these paints on the roof surface could color-shift between white in the summer and black in the winter, the indoor cooling and heating loads can be affected by the changes in reflection and absorption of solar radiation. Focusing on the summer period, the study analyzed the cooling effect of applying temperature discoloration paint that color-shifts from white to black on the roof surface of a small experimental building module and compared it to commonly used gray and green roof colors. Results of the experiment showed that the surface temperature of the roof with temperature discoloration paint was lower than the gray and green color roofs by a maximum of 10℃. Furthermore, the indoor temperature of the experimental module with the temperature discoloration roof was lower than the gray and green roofs by approximately 3℃. Findings of the study indicate that the application of temperature discoloration paint to the roof can reduce indoor cooling loads.

• Journal of Advanced Navigation Technology
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• v.22 no.2
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• pp.123-132
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• 2018

In this paper, we design and fabricate a dual liner polarization sinuous antenna with improved cross polarization isolation (XPI). The proposed antenna is composed of four arm radiators for generating dual linear polarization and excited by wideband microstrip balun with Klopfenstein taper structure. Also, two-step cylindrical cavity structure is applied to reduce back radiation. Honeycomb-typed absorbing material is inserted into the cavity to reduce performance degradation by reflected wave. To enhance cross polarization isolation in low frequency band, resistors are adapted between outer arm and the rim of cavity. We confirmed that the fabricated antenna can be applied for polarization measurement due to improved XPI in the low band.

• Plant Journal
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• v.17 no.2
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• pp.48-53
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• 2021

In the case of a 900 MW combined cycle power plant, most of the load on the site is a rotating device and is operated at a low power factor, and the power factor decrease increases the reactive power, which causes the efficiency of the device to be consumed and unnecessary unnecessary power consumption. This study intends to present the results by installing and operating a reactive power compensation device that absorbs and removes reactive power, which is a solution to this problem, on a 6.9 kV on-board bus. As a result of application of this system, first, it was confirmed that the power factor of the rotating machine was improved to 0.22 and the load power in the house was reduced by 1.4%, and the thermal efficiency of the generator was increased by 0.1% and the power generation power by 810 kW. Next, it was confirmed that the cost of construction and operation can be reduced in the future due to economic feasibility, with a decrease of 200 million won/year in electricity loss compared to 1.5 billion won in investment, an increase of 1 billion won/year in sales, and a one-year capital recovery period.

• Composites Research
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• v.35 no.3
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• pp.175-181
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• 2022

Due to the increasing number of wireless communication devices in mmWave frequency bands, there is a high demand for electromagnetic interference (EMI) shielding and heat dissipating materials to avoid device malfunctions. This paper proposes an EMI shielding composite film with a high heat dissipation characteristic. To achieve this, a conductive grid is integrated with a polymer-based composite layer including magnetic and heat dissipating filler materials. A high shielding effectiveness (>40 dB), low reflection shielding effectiveness (<3 dB), high thermal conductivity (>10 W/m·K), thin thickness (<500 ㎛) are simultaneously achieved with a tailored design of composite layer compositions and grid geometries in 5G communication band of 26.5 GHz.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.24-34
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• 2022

This paper investigates the capture of a 12U-sized CubeSat space object using a spider-web structure-based space net. The structural dynamics analysis program ABAQUS is used to simulate the shock-absorbing capability of the space net with a diagonal length of 2.828 m. The space object is modelled as a rigid body, and the space net is modelled using non-linear elastic beam elements. The simulations reveal that the spider-web structure-based space net outperforms the squared space net of the same structural weight in capturing the space object. The numerical simulations are conducted to examine the successful or unsuccessful captures of the space object in various cooperative and non-cooperative motions.

• Journal of the Korean Geotechnical Society
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• v.38 no.8
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• pp.39-52
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• 2022

Multilayer perceptron neural network was trained to determine the factor of safety and slip surface of the slope. Slope geometry is a simple slope based on Korean design standards, and the case of dry and existing groundwater levels are both considered, and the properties of the soil composing the slope are considered to be sandy soil including fine particles. When curating the data required for model training, slope stability analysis was performed in 42,000 cases using the limit equilibrium method. Steady-state seepage analysis of groundwater was also performed, and the results generated were applied to slope stability analysis. Results show that the multilayer perceptron model can predict the factor of safety and failure arc with high performance when the slope's physical properties data are input. A method for quantitative validation of the model performance is presented.

• Composites Research
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• v.36 no.1
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• pp.25-31
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• 2023

Composite structures have been designed by stacking the laminae with different stacking angles to meet the required mechanical performance. Although the induced stresses on the composite structures under the external loads usually differ depending on the location, we determined the stacking sequence based on the maximum stress, which leads to low efficiency and generally is not the optimum design. Recently, piecewise integrated composites (PICs) were suggested for solving this inefficiency. PICs assume the perfect bonding between adjacent pieces, but this is ideal and hard to accomplish. Therefore, the overlap at the boundary is essential to prevent separation from each other. In this study, we investigated the effect of the overlap design on the impact failure mode of PIC plates. We fabricated the sample composite plates with different overlap designs using the fast curing carbon prepreg and conducted the impact tests according to ASTM D 7136. We found that PICs had different failure modes according to the overlap design, which lead the changes of absorbed impact energies as well as impact load curves.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.6
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• pp.381-386
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• 2022

This paper details the analytical and experimental studies performed to propose a steel damper based on the flexural yielding mechanism. The damper is composed of a set of damping plates that are designed to yield in flexure. The comparison of experimental and finite element analysis results indicate that the analytical approach adopted in this study should be appropriate to perform sensitivity studies on the geometries of the damping plates. Although the damper is originally proposed to work based on the flexural mechanism, it is observed that the contribution of the tensile behavior of the damping plate could be considerable. As the thickness of the damping plate increases, the plastic energy due to the flexural yield increases. As the thickness of the damping plate decreases, the contribution of the tensile behavior increases, and the shape of the hysteresis loop distorts.

• Clean Technology
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• v.15 no.3
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• pp.202-209
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• 2009

N-incorporated $WO_3$ ($WO_3$:N) films were synthesized using a reactive RF magnetron sputtering on unheated substrate and then post-annealed at different temperatures from 300 to $500^{\circ}C$ in air. The N anion narrowed optical band gap, due to its mixing effect with the O 2p valence states. Furthermore, it was found that the crystallinity of the $WO_3$:N films was significantly improved by the post-annealing at $350^{\circ}C$ and higher. As a result, the $WO_3$:N films exhibited much better photoelectrochemical performance, compared with pure $WO_3$ films post-annealed at the same temperature.