• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.4
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• pp.517-526
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• 2019

In the present study, unsteady flows around a projectile ejected from an aircraft platform have been numerically investigated by using a three dimensional compressible RANS flow solver based on unstructured meshes. The relative motion between the platform and projectile was described by six degrees of freedom(6DOF) equations of motion with Euler angles and a chimera technique. Initial behavior of the projectile for varying conditions, such as roll and pitch-yaw command on the control surface of the projectile, flight Mach number, and platform pitch angle, was investigated. The ejection stability of the projectile was degraded as Mach number increases. In the transonic condition, the initial behavior of the projectile was found to be unstable as increase of platform pitch angle. By applying the command to control surfaces of the projectile, initial stability was highly enhanced. It was concluded that the proposed simulation data are useful for estimating the ejection behavior of a projectile in design phase.

• Journal of Aerospace System Engineering
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• v.16 no.4
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• pp.53-59
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• 2022

Static seals are used to seal high temperature gas and cryogenic fluid under high pressure, at interfaces between liquid rocket engine components such as combustion chamber, turbopump, gas generator, valves, etc. As thermal expansion and contraction at assembly interfaces cause undesirable leakage under cryogenic and high temperature environments, static seals applied for sealing of joint interfaces without relative motion should be designed properly. The additional function of rotation at the sealing face is also required for static seals, when the spherical flange is used for improvement of assembly at misalignment interfaces. In this study, structural analysis and leak tightness test of simulating test rig for several important interfaces are performed, to verify structural integrity of static seals.

• Journal of the Korea Society of Computer and Information
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• v.29 no.10
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• pp.121-128
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• 2024

Demand forecasting is a critical element of revenue management in the tourism industry. Since the 2010s, with the globalization of the tourism industry and the increase of different forms of marketing and information sharing, such as SNS, forecasting has become difficult due to non-linear activities and unstructured information. Various forecasting models for resolving the problems have been studied, and ML models have been used effectively. In this study, we applied the feature selection technique (NSGA3) to time series models and compared their performance. In hotel demand forecasting, it was found that the TCN model has a high forecasting performance of MAPE 9.73% with a performance improvement of 7.05% compared to no feature selection. The results of this study are expected to be useful for decision support through improved forecasting performance.

• The Journal of Society for e-Business Studies
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• v.21 no.2
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• pp.1-22
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• 2016

News contents has been collected, selected, edited and sometimes distorted by the news recommendation mechanisms of online portals in nowadays. Prior studies had not confirmed the consensus of newsworthiness, and they had not tried to empirically validate the impacts of newsworthiness on audience reactions. This study challenged to summarize the concepts of newsworthiness and validate the impact of representativeness of both editor's and audience's perspective on audience reactions as perceived news quality, trust on news portal, perceived usefulness, service satisfaction, loyalty, continuous usage intention, and word-of-mouth intention by adopting the representativeness heuristics method and information adoption model. 357 valid data had been collected using a scenario survey method. Subjects in each groups are exposed by 3 news recommendation mechanisms: 1) the time-priority news exposure mechanism (control group), 2) the reference-score-based news recommendation mechanism (a single treatment group), and 3) the major-news-priority exposure mechanism sorting by the reference scores made by peer audiences (the mixed treatment group). Data had been analyzed by the MANOVA and PLS method. MANOVA results indicate that only mixed method of both editor and audience recommendation mechanisms impacts on perceived news quality and trust. PLS results indicate that perceived news quality and trust could significantly affect on the perceived usefulness, service satisfaction, loyalty, continuance usage, and word-of-mouth intention. This study would contributions to empathize the role of information technology in media industry, to conceptualize the news value in the balanced views of both editors and audiences, and to empirically validate the benefits of news recommendation mechanisms in academy. For practice, the results of this study suggest that online news portals would be better to make mixed news recommendation mechanisms to attract audiences.

• Membrane Journal
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• v.27 no.4
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• pp.328-335
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• 2017

Fabricating photocatalytic composite membrane with a mesoporous and tailored morphological structure would have significant implication for environmental remediation. In this study, we reported hybrid $TiO_2$ immobilized photocatalytic membrane and its application for the treatment of dye solution. Photocatalytic film with high porosity and homogeneity was fabricated by graft copolymer as polymer template. Hybridization of membrane filtration with photocatalysis was successfully achieved by photocatalytic membrane reactor developed. Result showed that membrane permeability was significantly reduced after immobilizing the $TiO_2$ film on bare $Al_2O_3$ support. The membrane characterization indicated that well organized $TiO_2$ film was successfully formed on $Al_2O_3$ support. Benefiting from the controlled morphology of $TiO_2$ film, the composite membrane exhibited almost complete degradation of organic dye within 5 h of filtration under UV illumination. Langmuir-Hinshelwood model explained degradation of organic dye. First-order rate constant was approximately six times with $TiO_2$ immobilized composite ceramic membrane, higher than the one with the bare $Al_2O_3$ support (0.0081 vs. $0.0013min^{-1}$).

• Geophysics and Geophysical Exploration
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• v.22 no.4
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• pp.177-185
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• 2019

Ground roll is a surface wave which is usually observed in the land seismic data. It is one of the typical coherent noise. During the reflection data processing, ground roll is removed because it is considered as noise. This removal process often causes the loss of reflection signals if the ground roll overlaps reflection signals. In this study, we look over Karhunen-Loeve Transform (KLT) and analyze its effects to suppress the ground roll appropriately while reducing the reflection loss. Numerical tests in homogeneous elastic media show that the ground roll has been properly rejected. However, the field data application reveals that there is no significant suppression of ground roll when compared to band-pass filtering. This can be considered that it is hard to calculate horizontally aligned gathers in the field data because the ground roll contains a wide range of frequency bands. On the contrary, the result of singular value decomposition (SVD) filtering shows that the ground roll has been significantly reduced. It is thought that the SVD filtering performs better in the ground roll suppression than KLT because it is easy to calculate the horizontally aligned gathers in the SVD filtering.

• Journal of Biomedical Engineering Research
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• v.19 no.4
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• pp.403-416
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• 1998

Socket pressure distributions with gait analysis of a trnsfemoral and a transtibial prostheses were measured in order to assess an optimal socket fitting and function. Ankle joint was aligned by the neutral and the dorsi/plantar flexed positions. Compared to dorsi and plantar flexed positions of ankle joint, cadence and walking speed increased with the neutral ankle joint alignment. Other gait parameters were close to the normative data with the neutral ankle joint alignment. For the transfemoral amputee, dorsiflexed alignment of the ankle joint created high pressure on the lateral aspect of the socket, on the other hand, plantarflexed alignment resulted in increased pressure on the medial aspect of the socket. For the transtibial amputee, dorsiflexed alignment of the ankle resulted in high pressure on the antero-lateral aspect of the socket during mid-stance, but apltarflexion of the ankle joint showed slight increases in pressure at the same location in the socket. The present study clearly demonstarted that malalignment of a prosthesis results in localized increasesing pressure within the socket. Proper slignment of the prosthesis is required in order to acquire an appropriate socket-limb interface as well as the proper gait.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.12
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• pp.122-129
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• 2008

This paper gives the experimental results for the effective precipitation of particulated matter(PM) below 1[${\mu}m$] of diameter using the electrostatic precipitator, which is designed by ourselves. In order to improve the precipitation efficiency, the vertical and parallel magnetic field to the electric field is applied simultaneously by arranging ferrite magnets. When the parallel magnetic field is applied, the precipitation efficiency does not improve in comparison with non-magnets. However, when the vertical magnetic field is applied, it is improved about 5[%] more than the case of non-magnetized ferrite plate used. In addition, when the magnets are installed at the center of ground plate electrodes, the precipitation efficiency is ranged from 17 to 32[%] under the applied voltage of 5[kV]. It is similar to the case of the magnet arrangement at the front part of ground electrode. Also, the precipitation efficiency is more improved by arranging magnets as the inside part and zigzag on the electrodes. Especially, large particles of 0.7 and 1[${\mu}m$] is more easily captured by electrostatic precipitator. Consequently, it is convinced that the vertical magnetic field is more desirable than parallel magnetic field on the electric field for the effective treatment of particulated matter.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.3
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• pp.275-282
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• 2009

Generally, the sinusoidal cavity dither is adopted to ring laser gyroscope for eliminating the lock-in which is non-linear effect at the small rotation input. Despite this method, there are some remained errors which are generated at the dither turnaround, and those errors produce random walk which is a general character of a ring laser gyroscope. As one of the numerous research results for compensating these errors, there is a special lock-in compensation method which is the method of error estimation and compensation by comparing the beat signal periods of before and after the dither turnarounds. In this paper, by ring laser gyroscope modeling and numerical analysis, we verified the theoretical validity and confirmed the effectiveness of this method in expectation of the possible beat signal measurement time resolution. As a result, we confirmed the random walk decreases from a-half to a-third by this lock-in compensation method. So, it is expected to be a remarkable method for reducing the INS alignment time.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.2
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• pp.62-72
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• 2019

Due to the difficulties in forecasting the intensity and the source location of tsunami the countermeasures prepared based on the deterministic approach fail to work properly. Thus, there is an increasing demand of the tsunami hazard analyses that consider the uncertainties of tsunami behavior in probabilistic approach. In this paper a fundamental study is conducted to perform the probabilistic tsunami hazard analysis (PTHA) for the tsunamis that caused the disaster to the east coast of Korea. A logic tree approach is employed to consider the uncertainties of the initial free surface displacement and the tsunami height distribution along the coast. The branches of the logic tree are constructed by reflecting characteristics of tsunamis that have attacked the east coast of Korea. The computational time is nonlinearly increasing if the number of branches increases in the process of extracting the fractile curves. Thus, an improved method valid even for the case of a huge number of branches is proposed to save the computational time. The performance of the discrete weight distribution method proposed first in this study is compared with those of the conventional sorting method and the Monte Carlo method. The present method is comparable to the conventional methods in its accuracy, and is efficient in the sense of computational time when compared with the conventional sorting method. The Monte Carlo method, however, is more efficient than the other two methods if the number of branches and the number of fault segments increase significantly.