• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.71-84
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• 2020

In order to improve the performance of marine centrifugal pump, a centrifugal pump whose specific speed is 66.7 was selected for the research. Outlet diameter D2, outlet width b2, blade outlet angle β2, blade wrap φ and blade number z of the impeller were chosen as the variables. The maximum weighted average efficiency and the minimum vibration intensity at the base were calculated as objectives. Based on the Latin Hypercube method, the impeller was numerically optimized. The numerical results show that after optimization, the amplitudes of pressure fluctuation on the main frequency at different monitoring points decrease in varying degrees. The radial force on impeller decreases obviously under off-design flow rates and is more symmetrical during the operation of the pump. The variation of the axial force is relatively small, which has no obvious relationship with the rotating angle of the impeller. The energy performance and vibration experiment was performed for verifying. The test results show that the weighted average efficiency under 0.8Qd, 1.0Qd and 1.2Qd increases by 4.3% after optimization. The maximal vibration intensity at M1-M4 on the pump base reduced from 0.36 mm/s to 0.25 mm/s, decreasing by 30.5%. In addition, the vibration velocities of bracket in pump side and outlet flange also have significant reductions.

• The Research Journal of the Costume Culture
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• v.29 no.2
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• pp.272-288
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• 2021

The purpose of this study is to classify the types of decoration techniques used in women's Chima and Jeogori in traditional Hanbok catalogs from 2010 to 2020, and to analyze the frequency of each type. The method of this study is as follows. This study first investigated the transition of modern Hanbok and decorative techniques by analyzing and classifying such work in previous studies. Based on this, the technique of decorating the Jeogori and Chima that appeared in the traditional Hanbok catalog of the study period was analyzed. The results of the study are as follows. In the case of Jeogori, in the first half of 2010, the decorative technique of a relatively large size was used, and the decorativeness tended to be strong. However, in the late 2010s, the number of decorative techniques used in Jeogori has decreased, and the size of the decorative technique has become smaller and more concise, leading to a tendency to understated decoration. In the case of Chima, techniques to express natural texture by processing threads or fabrics themselves were mainly used rather than techniques to add decoration to the surface, and techniques to express various surface texture tended to develop toward the late 2010s. The change in the decoration technique of Jeogori and Chima appears to be a combination of social, cultural, and economic factors such as a change in consumption culture and a reduction in the wedding market.

• The Journal of the Korea Contents Association
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• v.21 no.8
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• pp.271-284
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• 2021

The purpose of this study is to explore the current status and effects of online discussion classes in universities. To this end, a survey was conducted on university students attending a total of four universities in Seoul and Gyeonggi Province to diagnose their perceptions of the operation of online discussion classes and their effects. The collected data were analyzed using frequency analysis, descriptive statistical analysis, cross-analysis, F-test, T-test, and Scheffe test by applying SPSS program. As a result of the study, first, it was found that 'non-real-time recorded lessons' and 'real-time interactive video lessons' were mainly conducted at universities after the COVID19 crisis. Second, in the online class method, 'real-time interactive video class' had a positive effect on 'debate class preference' and was found to be more meaningful. Third, college students recognized participation in online discussion classes as a foundation for expanding creative thinking skills, suggesting that strengthening through smooth communication and exchanges based on learners' sufficient cognitive processes on discussion methods and procedures is more helpful.

• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.2
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• pp.59-69
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• 2021

Historical records of earthquakes are generally used as a basis to extrapolate the instrumental earthquake catalog in time and space during the probabilistic seismic hazard analysis (PSHA). However, the historical catalogs' input parameters determined through historical descriptions rather than any quantitative measurements are accompanied by considerable uncertainty in PSHA. Therefore, quantitative assessment to verify the historical earthquake parameters is essential for refining the reliability of PSHA. This study presents an approach and its application to constrain reliable ranges of the magnitude and corresponding epicenter of historical earthquakes. First, ranges rather than specific values of ground motion intensities are estimated at multiple locations with distances between each other for selected historical earthquakes by reviewing observed co-seismic natural phenomena, structural damage levels, or felt areas described in their historical records. Based on specific objective criteria, this study selects only one earthquake (July 24, 1643), which is potentially one of the largest historical earthquakes. Then, ground motion simulations are performed for sufficiently broadly distributed epicenters, with a regular grid to prevent one from relying on strong assumptions. Calculated peak ground accelerations and velocities in areas with the historical descriptions on corresponding earthquakes are converted to intensities with an empirical ground motion-intensity conversion equation to compare them with historical descriptions. For the ground motion simulation, ground motion prediction equations and a frequency-wavenumber method are used to consider the effects of possible source mechanisms and stress drop. From these quantitative calculations, reliable ranges of epicenters and magnitudes and the trade-off between them are inferred for the earthquake that can conservatively match the upper and lower boundaries of intensity values from historical descriptions.

• Journal of Industrial Convergence
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• v.19 no.6
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• pp.197-204
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• 2021

The purpose of this study was to examine the effect of sense of community on the quality of life of local residents and the mediating effect of residential satisfaction in the process to improve the quality of life. To this end, as a result of 1:1 survey through a face-to-face survey of 480 local residents in G, Gyeonggi-do, a total of 468 samples were finally analyzed excluding insincere answers. The analysis method was SPSS WIN 25.0, and the mediation model was verified using frequency analysis, descriptive analysis, correlation analysis, and regression analysis. As a result of the study, first, sense of community was found to have a positive (+) effect on quality of life and residential satisfaction. Second, residential satisfaction was found to have a positive (+) effect on the quality of life. Third, residential satisfaction was verified as a partial mediation in the relationship between sense of community and quality of life. Based on this study, the importance of the effect of residential satisfaction in the process of local residents' sense of community affecting their quality of life and practical measures to improve the quality of life were presented.

• The Journal of the Acoustical Society of Korea
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• v.41 no.4
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• pp.389-396
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• 2022

This paper aims to identify the causes and mechanisms of contraction-expansion noise in refrigerators and proposes noise reduction methods. Contraction-expansion noise generated in refrigerators is mainly due to stick-slip phenomenon occurring on the contact surface between inner parts. Friction experiments were conducted to identify the factors causing the stick-slip phenomenon. Furthermore, the vibration level of the internal components was measured to determine the characteristics and location of the contraction-expansion noise. Based on the experimental results, experiments have been conducted to verify the noise characteristics for each factor. From this, it was confirmed that the friction experiment and the refrigerator contraction-expansion noise generation location and frequency were the same. The vibration level also increased as the vertical force was increased due to load loading. Also, it was confirmed that the contraction-expansion noise was reduced when the surface roughness was increased. Therefore, it was concluded that increasing the surface roughness of the contact surface in the same way as the results of the friction experiment was the method of reducing contraction-expansion noise.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.151-160
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• 2022

Owing to the recent increase in the frequency of explosion accidents, blast resistive design has garnered attention to reduce the damage of important structural elements. However, domestic research on the blast resistive structures is still insufficient, and domestic design guideline against blast loads are not documented yet. In this study, a numerical study on the RC blast resistive walls, where the test variable was the presence of FRP sheet, was performed using LS-DYNA program. Based on the numerical results, displacement-time hysteretic curve, pressure-impulse diagram, and fragility curve of the test specimens were derived. It was shown that the FRP sheet strengthening method is efficient to improve the blast resistive performance of the RC wall. Also, the strengthening effect of FRP sheet on the RC wall was stronger when the magnitude of the blast load was greater.

• Journal of Advanced Navigation Technology
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• v.26 no.5
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• pp.358-364
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• 2022

The Inter Communication System for avionics is in charge of processing all voice signals that internal calls between Pilot and Co-pilot, internal calls between Pilots and Crews, external calls through communication equipment such as Ultra/Very High Frequency Receiver/Transmitter(U/VHF RT), audio signal monitoring for navigation and mission equipment such as VHF Omnidirectional Range/Instrument Landing System(VOR/ILS), Tactical Air Navigation(TACAN), audio signal output for voice recording to Flight Data Recorder(FDR) and Data Transfer System(DTS), and warning/caution audio signal generate about the status and threat of aircraft. Because Inter Communication System for avionics is sensitive to noise in the case of analog audio signals, a redundant design that can protect audio signal from electromagnetic noise inside/outside of aircraft is required for the mission of pilots and crews. In this paper, Normal/Back-up operation mode and redundancy design plan based on digital method for the redundancy of the digital Inter Communication System for avionics and manufacturing, verification results are described.

• Journal of the Society of Disaster Information
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• v.17 no.1
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• pp.81-96
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• 2021

Purpose: Based on the preceding studies in supply chain management, factors were analyzed to verify the effect of risk assessment and risk management factors of the business continuity management system (BCMS) on management performance. The purpose of this study is to establish a systematic risk management plan by deriving the risk factors of BCMS and evaluating unpredictable risks, and at the same time, contributing to a company's competitive advantage without interruption of work. Method: The structural relationship between risk assessment, risk management and management performance of BCMS was derived. To this end, a questionnaire survey was conducted of 124 managers and managers in Korean companies. Frequency analysis, validity analysis, reliability analysis, correlation analysis, and simple regression analysis were performed. Result: First, risk assessment had a positive (+) effect on risk management. Second, risk management had a positive (+) effect on management performance. Finally, risk assessment had a positive (+) effect on management performance. Conclusion: BCMS's risk assessment and risk management capabilities should be managed through financial performance, and risk management activities should be managed through non-financial performance.

• Steel and Composite Structures
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• v.41 no.6
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• pp.899-910
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• 2021

A 4-unknown shear deformation theory is applied to investigate the vibration of functionally graded plates under thermal environment. The plate is fabricated from a functionally graded material mixed of ceramic and metal with continuously varying material properties through the plate thickness. Three types of thermal loadings, uniform, linear and nonlinear temperature rises along the plate thickness are taken into account. The present theory contains four unknown functions as against five or more in other higher order shear deformation theories. The through-the-thickness distributions of transverse shear stresses of the plate are considered to vary parabolically and vanish at upper and lower surfaces. The present model does not require any problem dependent shear correction factor. Analytical solutions for the free vibration analysis are derived based on Fourier series that satisfy the boundary conditions (Navier's method). Benchmark solutions are firstly considered to evaluate the accuracy of the proposed model. Comparisons with the solutions available in literature revealed the good capabilities of the present model for the simulations of vibration responses of FG plates. Some parametric studies are carried out for the frequency analysis by varying the volume fraction profile and the temperature distribution across the plate thickness.