• Tribology and Lubricants
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• v.38 no.6
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• pp.287-290
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• 2022

Compressed-water-type launching devices convert the force from compressed water into force-launching underwater structures, such as torpedos and autonomous underwater vehicles. In particular, the overpressure wave in the launching tube is a critical design factor for the launching device. This paper presents a simplified formula for simulating overpressure waves in the launching tube of a compressed-water-type launching device. Scaled model experiments were performed to obtain actual measurement data of overpressure waves in a launching tube with varying piston speeds to examine the practical applicability of the simplified formula. The main factor of the simplified formula was estimated using an optimization technique. The time history of the overpressure waves was satisfactorily simulated using the estimated factor values and showed consistency with the measurement data. In addition, the trend of change by the piston speed of the estimated factors was reviewed, and the practical applicability was demonstrated. A systematic study of the factors influencing the overpressure waves in launching tubes will be possible using experimental data for more various conditions and the proposed simplified formula.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.3
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• pp.110-122
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• 1996

Finite element analysis tool was developed to analyze the casting process. Generally, casting process consists of mold filling and solidification. Both filling and solidication process were simulated simultaneously to investigate the effects of process variables and to predict the defect. At filling process, thermal coupling was especially considered to investigate thermal history of material during the filling stage. And thermal condition at the final stage of filling is used as the initial conditions in a solidification process for the exact simullation of the actual casting processes. At mold filling process, Lagragian-type finite element method with automatic remeshing scheme was used to find the material flow. A perturbation method with artificial viscosity is adopted to avoid numerical instability in low viscous fluid. At solidification process, enthalpy-based finite element method was used to solove the heat transfer problem with phase change. And elastic stress analysis has been performed to predict the thermal residual stress. Through the FE analysis, solidification time, position of solidus line, liquidus line and thermal residual stress are found. Through the study, the importance of combined analysis has been emphasized. Finite element tools developed in this study will be used process design of casting process and may be basic structure for total CAE system of castings which will be constructed afterward.

• Steel and Composite Structures
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• v.47 no.5
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• pp.615-631
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• 2023

Steel corrosion induces structural deterioration of concrete-filled steel tubes (CFSTs), and any potential extreme action on a corroded CFST would pose a severe threat. This paper presents a comprehensive investigation on the lateral impact behaviour of CFSTs suffering from localised pitting corrosion damage. A refined finite element analysis model is developed for the simulation of locally corroded CFSTs subjected to lateral impact loads, which takes into account the strain rate effects on concrete and steel materials as well as the random nature of corrosion pits, i.e., the distribution patterns and the geometric characteristics. Full-range nonlinear analysis on the lateral impact behaviour in terms of loading and deforming time-history relations, nonlinear material stresses, composite actions, and energy dissipations are presented for CFSTs with no corrosion, uniform corrosion and pitting corrosion, respectively. Localised pitting corrosion is found to pose a more severe deterioration on the lateral impact behaviour of CFSTs due to the plastic deformation concentration, the weakened confinement and the reduction in energy absorption capacity of the steel tube. An extended parametric study is then carried out to identify the influence of the key parameters on the lateral impact behaviour of CFSTs with localised pitting corrosion. Finally, simplified design methods considering the features of pitting corrosion are proposed to predict the dynamic flexural capacity of locally pitted CFSTs subjected to lateral impact loads, and reasonable accuracy is obtained.

• Structural Engineering and Mechanics
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• v.87 no.3
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• pp.273-282
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• 2023

Concrete construction, one of the oldest building practices, is commonly used in all parts of the world. Concrete is the primary building material for both residential and commercial constructions. The challenge of protecting the buildings, hence nation, against the attack of terrorism has raised the importance to explore the understanding of building materials against the explosion. In this research, a security check-post (reinforced concrete frame filled with plain cement concrete) has been chosen to study the behavior of structural elements under blast loading. Eight nitroglycerines-based dynamite blasts with varying amounts of explosive charge, up to 17 kg weight has been carried out at various scale distances. Pressure and acceleration time history records are measured using blast measuring instruments. Security check post after being exposed by explosive loading are photographed to view cracking/failure patterns on the structural elements. It is noted that with the increase of quantity of explosive, the dimensions of spalling and crack patterns increase on the front panels. Simple empirical analyses are conducted using ConWep and other design manuals such as UFC 3-340-02 (2008) and AASTP-1 (2010) for the purpose of comparison of blast parameters with the experimental records. The results of experimental workings are also compared with earlier researchers to check the compatibility of developed equations. It is believed that the current study presents the simple and preliminary procedure for calculating the air blast and ground shock parameters on the structures exposed to blast explosion.

• Journal of Information Technology Services
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• v.22 no.6
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• pp.71-86
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• 2023

The rapid change in industry and the technological gap give rise to social demand for upskilling and reskilling and spread of alternative education. Against this backdrop, digital certification and career management tools can be used to manage various types of learning activities comprehensively. Digital badges provide various kinds of history information related to individual learning, and the reliability and transparency of the issued information can be strengthened by applying blockchain technology. There have been various discussions about digital badges for a long time, but due to the lack of standards to support the issuance and distribution of digital badges, they have been partially used in some areas. However, interest in digital badges is increasing due to the development of related technologies, establishment of standards, paradigm changes in higher education, and government policies related to nurturing digital talent. This paper deals with the use of digital badges for efficient and transparent learning management and career management in an online learning environment. The researcher analyzes the technical characteristics and use cases of digital badges, and proposes a plan for use in online higher education based on them.

• Earthquakes and Structures
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• v.27 no.1
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• pp.69-82
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• 2024

In the conventional seismic design approach for a bridge pier, the function of the stopper, and shear key are to serve as mechanisms for unseating prevention devices that retain and transmit the lateral load to the pier under strong earthquakes. This frequently inflicts immense shear forces and bending moments concentrated at the plastic hinge zone. In this study, a shear panel damper plus gap (SPDG) is proposed as a low-cost alternative with high energy dissipation capacity to improve the seismic performance of the pier. Therefore, this study aimed to investigate the seismic performance of the pre-stressed concrete I girder (PCI-girder) bridge equipped with SPDG. The bridge structure was analyzed using nonlinear time history analysis with seven-scaled ground motion records using the guidelines of ASCE 7-10 standard. Consequently, the implementation of SPDG technology on the bridge system yielded a notable decrease in maximum displacement by 41.49% and a reduction in earthquake input energy by 51.05% in comparison to the traditional system. This indicates that the presence of SPDG was able to enhance the seismic performance of the existing conventional bridge structure, enabling an improvement from a collapse prevention (CP) level to an immediate occupancy (IO).

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.4
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• pp.175-184
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• 2006

Two methods of the nonlinear static pushover analysis have been presented for the performance-based seismic design and evaluation of MDOF continuous bridges. Guidelines for buildings presented in FEMA-273 applying the Displacement Coefficient Method (DCM) and in ATC applying the Capacity Spectrum Method(CSM) have been modified for MDOF bridges. Two methods are compared with the time- history analysis. The lateral load distribution pattern for seismic loads has been examined in the static pushover analysis. The force-based fiber frame finite element has been implemented in the modeling of reinforced concrete piers.

• Journal of Korean Association for Spatial Structures
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• v.24 no.3
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• pp.61-68
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• 2024

High-rise buildings are equipped with TMD (Tuned Mass Damper), a vibration control device that ensure the stability and usability of the building. In this study, the seismic response control performance was evaluated by selecting the design variables of the TMD based on the installation location of the twisted irregular building. To this end, we selected analysis models of 60, 80, and 100 floors with a twist angle of 1 degree per floor, and performed time history analysis by applying historical seismic loads and resonant harmonic loads. The total mass ratio of TMDs was set to 1.0%, and the distributed installation locations of TMDs were selected through mode analysis. The analysis results showed that the top-floor displacement responses of all analysis models increased, but the maximum story drift ratio decreased. In order to secure the seismic response control performance by distributed installation of TMDs in twisted irregular buildings, it is judged that the mass ratio distribution of TMDs will act as a key variable.

• Journal of the Korean Institute of Landscape Architecture
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• v.43 no.4
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• pp.27-36
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• 2015

This study analyzed the characteristics of the entries at the design competition for the Hoehyeon section of Namsan from a perspective of the Historic Urban Landscape and made suggestions from them. Hoehyeon, located at the foot of Namsan, is the most changing site in the park and Seoul City Wall. Recent excavation of the old city walls of the Joseon Era has uncovered evidence of the Japanese occupation period, making it a site where park facilities in modern and contemporary history coexist. The frame analysis has been made by the concept of the Historic Urban Landscape, the methods of approach, specialists' discussion and the guidelines of the competition. The entries were analyzed by classification of the understanding of the spatiality and cultural diversity, the recognition of the periodic layers of time, and the design implementation, the preservation, the park plan, and the future management plan. From a perspective of an Historic Urban Landscape, this study has found that each entry placed priority on the objects for preservation and suggested creative involvement and comprehensive designs for the preservation and the park plan through the understanding of the spatiality and cultural diversity and the reflection of the periodic layers of time in the designs. This study provided two implications. Firstly, there was a possibility for new recognition and the methods of approach for preservation and development. Secondly, the basic plan for the Historic Landscape should be established through research and mapping for the preservation and management of objects in Seoul having valuable historic variability. Further study for resident participation and the process by network from public to private should be taken. This study looks forward to the consideration of the direction for the design plans of places with historic and cultural value.

• The Journal of the Korea Contents Association
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• v.14 no.3
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• pp.151-165
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• 2014

Korean traditional alcohol's growth gets declined after Makgeolli's boom and it's time to enter the takeoff stage using cup based on the characteristics of each alcohols in order to their globalization and quality improvement. For now, there are 3 features of Korean traditional alcohol's cup design development; subdivision, quality improvement, systematization. However, there's no product design case that reflect the characteristics of the alcohol from the planning phase. Therefore, it needs to establish process technology for storytelling and emotion based cup design. This research aims to extract the specification for cup design and to find out the visualization element of cup's shape and material by studying 5 senses and traditional alcohol's objective informations. Through the study, the elements that can maximize the specific traditional alcohol's marketability: cup's label, pattern, decorative element based on the storytelling like history and tale were found. As a result, those result can give a new export strategy by developing competitive design that has emotional element and storytelling from the traditional alcohol's characteristics in a situation of stagnant export of the small sized home-brewed liquor business.