• Journal of the Society of Naval Architects of Korea
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• v.54 no.2
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• pp.151-160
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• 2017

Growing demand and rapid development of the synthetic fiber rope in mooring system have taken place since it has been used in deep water platform lately. Unlike a chain mooring, synthetic fiber rope composed of lightweight materials such as Polyester(polyethylene terephthalate), HMPE(high modulus polyethylene) and Aramid(aromatic polyamide). Non-linear stiffness and another failure mode are distinct characteristics of synthetic fiber rope when compared to mooring chain. When these ropes are exposed to environmental load for a long time, the length of rope will be increased permanently. This is called 'the creep phenomenon'. Due to the phenomenon, The initial characteristics of mooring systems would be changed because the length and stiffness of the rope have been changed as time goes on. The changed characteristics of fiber rope cause different mooring tension and vessel offset compared to the initial design condition. Commercial mooring analysis software that widely used in industries is unable to take into account this phenomenon automatically. Even though the American Petroleum Institute (API) or other classification rules present some standard or criteria with respect to length and stiffness of a mooring line, simulation guide considers the mechanical properties that is not mentioned in such rules. In this paper, the effect of creep phenomenon in the fiber rope mooring system under specific environment condition is investigated. Desiged mooring system for a Mobile Offshore Drilling Unit(MODU) with HMPE rope which has the highest creep is analyzed in a time domain in order to investigate the effects creep phenomenon to vessel offset and mooring tension. We have developed a new procedure to an analysis of mooring system reflecting the creep phenomenon and it is validated through a time domain simulation using non-linear mooring analysis software, OrcaFlex. The result shows that the creep phenomenon should be considered in analysis procedure because it affects the length and stiffness of synthetic fiber rope in case of high water temperature and permanent mooring system.

• Journal of the Korean Geotechnical Society
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• v.35 no.6
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• pp.39-48
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• 2019

This study investigated the lateral behavior of monopile embedded in the dry sand through cyclic lateral loading test using a centrifuge test. The sand sample for the experiment was the dry Jumunjin standard sand at 80% relative density and the friction angle of $38^{\circ}$. In the experimental procedure, firstly, it was determined the static lateral bearing capacity by performing the static lateral loading test to decide the cyclic load. This derived static lateral bearing capacity values of 30%, 50%, 80%, 120% were determined as the cyclic lateral load, and the number of cycle was performed 100 times. Through the results, the experiment cyclic p-y curve was calculated, and the cyclic p-y backbone curve by depth was derived using the derived maximum soil resistance point by the load. The initial slope at the same depth was underestimated than API (1987) p-y curves, and the ultimate soil resistance was overestimated than API (1987) p-y curves. In addition, the result of the comparison with the suggested dynamic p-y curve was that the suggested dynamic p-y curve was overestimated than the cyclic p-y backbone curve on the initial slope and soil resistance at the same depth. It is considered that the p-y curve should be applied differently depending on the loading conditions of the pile.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.719-727
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• 2021

In the field of architecture, retractable devices capable of responding flexibly to the environment have been applied widely to large structures. Among these devices, the aesthetically pleasing retractable membrane is lightweight so that the membrane can be opened easily using only a traction device. On the other hand, because the towed membrane moves as it is connected to the main cable by a trolley, the number of trolleys needed increases in proportion to the roof's area. This study proposes an optimal model for an open-type trolley (OTT), which is used widely in these devices, using topology optimization. The analysis used the ANSYS program. A new model was proposed based on the results and reviewed through the feedback. Through this process, it was possible to develop a prototype with increased durability and reduced weight. For OTT, optimization was performed based on static analysis and the boundary conditions, so three prototypes were designed. A comparison of the proposed trolley with the conventional one under the same conditions revealed an up to 71.04% decrease in volume while the yield-strength reached 8.67 to 11.43%. In conclusion, the optimal trolley proposed was found to be reliable in terms of economy and stability.

• Journal of Digital Convergence
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• v.19 no.3
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• pp.437-444
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• 2021

The purpose of this study is to investigate the relationship between consciousness of marine safety, re-participation behavior of marine safety virtual reality experience education. For the study, participants in marine safety virtual reality experience education were surveyed from July to August 2020. Specifically, all participants were NakDanbo Water leisure center and Song-do Marine leisure center. A total of 300 participants were sampled using convenience sampling method, but 253 were finally used in the data analysis excepting incomplete or faithless questionnaires. the data analysis was conducted through frequency analysis, Cronbach's alpha, Exploratory Factor Analysis (EFA), correlation analysis, simple and Multiple regression analysis using SPSS 20.0. The results are as follows. Firstly, participants in marine safety virtual reality experience education positive impact on had a significant effect on consciousness of marine safety. Secondly, participants in marine safety virtual reality experience education positive impact on had a significant effect on re-participation behavior intention. Lastly, consciousness of marine safety had positive effects on re-participation behavior intention.

• The Journal of the Convergence on Culture Technology
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• v.8 no.1
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• pp.349-359
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• 2022

The purpose of this study is to add and revalidate items of learning cognition and learning emotion factors for online use of the K-LSS for junior college. It is important for self-reflection and improvement of academic achievement to specifically explore and analyze the sub-factors of learning cognition, learning behavior, and learning emotion for each item that can affect the learning strategy of junior college students. The added items are two items for diagnosing the concentration of attention in the learning information processing process of the learning cognitive factor and two questions about the interpersonal anxiety factor for diagnosing the level of anxiety about others in the learning emotional factor. The study area was conducted in 5 areas nationwide, and the subjects of the study were 923 junior college students excluding 327 respondents who answered insincerity. The K-LSS_r scale is a learning strategy diagnosis scale of 52 questions composed of three sub-elements of learning cognition (18 questions), learning emotion (15 questions), and learning behavior (19 questions), and reliability for generalization in this study. As a result of the verification, Cronbach's α coefficient of the entire scale was .896, and Cronbach's α coefficient of the three factors ranged from .876 to .910. The half-segment reliability coefficient of the scale was .858 in total, and the half-segment reliability coefficients of the three factors ranged from .792 to .843. The test-retest reliability verification result for 3 weeks for 350 Junior college Students in 5 regions was .884, and the validity test for generalization also confirmed that the recruitment validity is significant.

• Journal of Industrial Convergence
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• v.20 no.3
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• pp.11-21
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• 2022

The purpose of this study is to provide fundamental background to improve the quality of teaching and learning performance in online classes by analyzing the students' learning experience aspects on online environment. This study explores the relationship between learning experience and teaching and learning performance according to the online classes types(synchronous/asynchronous class), and identifies the mediation effect of students' perception and attitude toward online classes using Structural Equations Model(SEM). The findings are shown as follows: First, learning experience has positive effect on teaching and learning performance statistically. Second, learning experience has different effect on teaching and learning performance depending on the type of online classes. Specifically, learning experience in synchronous environment has higher influence on teaching and learning performance than in asynchronous environment. On the other hand, perception and attitude toward online classes have greater influence on teaching and learning performance in asynchronous class than in synchronous class. Lastly, the students' perception and attitude toward online classes do not have mediation effects significantly in the relationship between learning experience and teaching and learning performance. The result of this study can be a guide for researcher to approach to teaching and learning performance in online environment of university.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1222-1230
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• 2022

The rotor blade is an important component of a tidal stream turbine and is affected by a large thrust force and load due to the high density of seawater. Therefore, the performance must be secured through the geometrical and structural design of the blade and the blade structural safety to which the composite material is applied. In this study, a 1 MW class large turbine blade was designed using the blade element momentum (BEM) theory. GFRP is a fiber-reinforced plastic used for turbine blade materials. A sandwich structure was applied with CFRP to lay-up the blade cross-section. In addition, to evaluate structural safety according to flow variations, static load analysis within the linear elasticity range was performed using the fluid-structure interactive (FSI) method. Structural safety was evaluated by analyzing tip deflection, strain, and failure index of the blade due to bending moment. As a result, Model-B was able to reduce blade tip deflection and weight. In addition, safety could be secured by indicating that the failure index, inverse reserve factor (IRF), was 1 or less in all load ranges excluding 3.0*Vr of Model-A. In the future, structural safety will be evaluated by applying various failure theories and redesigning the laminated pattern as well as the change of blade material.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.293-303
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• 2012

Recently, as construction technology improved, concrete structures not only became larger, taller and longer but were able to perform various functions. However, if extreme loads such as impact, blast, and fire are applied to those structures, it would cause severe property damages and human casualties. Especially, the structural responses from extreme loading are totally different than that from quasi-static loading, because large pressure is applied to structures from mass acceleration effect of impact and blast loads. Therefore, the strain rate effect and damage levels should be considered when concrete structure is designed. In this study, the low velocity impact loading test of steel fiber reinforced concrete (SFRC) slabs including 0%~1.5% (by volume) of steel fibers, and strengthened with two types of FRP sheets was performed to develop an impact resistant structural member. From the test results, the maximum impact load, dissipated energy and the number of drop to failure increased, whereas the maximum displacement and support rotation were reduced by strengthening SFRC slab with FRP sheets in tensile zone. The test results showed that the impact resistance of concrete slab can be substantially improved by externally strengthening using FRP sheets. This result can be used in designing of primary facilities exposed to such extreme loads. The dynamic responses of SFRC slab strengthened with FRP sheets under low velocity impact load were also analyzed using LS-DYNA, a finite element analysis program with an explicit time integration scheme. The comparison of test and analytical results showed that they were within 5% of error with respect to maximum displacements.

• The Journal of the Petrological Society of Korea
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• v.18 no.3
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• pp.223-236
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• 2009

Ultramafic xenoliths from southeastern part of Jeju Island can be grouped into two types: Type I and Type II. Type I xenoliths are magnesian and olivine-rich peridotite (mg#=89-91), which are commonly found at the outcrop. Most previous works have been focused on Type I xenoliths. Type II xenoliths, consisting of olivine, orthopyroxene and clinopyroxene with higher Fe and Ti components (mg#=77-83) and lower Mg, Ni, Cr, are reported in this study. They are less common with a more extensive compositional range. The studied Type II xenoliths are wehrlite, olivine-clinopyroxenite, olivine websterite, and websterite. They sometimes show ophitic textures in outcrops indicating cumulate natures. The textural characteristics, such as kink banding and more straight grain boundaries with triple junctions, are interpreted as the result of recrystallization and annealing. Large pyroxene grains have exsolution textures and show almost the same major compositions as small exsolution-free pyroxenes. Although the exsolution texture indicates a previous high-temperature history, all mineral phases are completely reequilibrated to some lower temperature. Orthopyroxenes replacing clinopyroxene margin or olivine indicate an orthopyroxene enrichment event. Mineral phases of Type II are compared with Type I xenoliths, gabbroic xenoliths, and the host basalts. Those from Type II xenoliths show a distinct discontinuity with those from Type I mantle xenoliths, whereas they show a continuous or overlapping relation with those from gabbroic xenoliths and the host basalts. Our petrographic and geochemical results suggest that the studied type II xenoliths appear to be cumulates derived from the host magma-related system, being formed by early fractional crystallization, although these xenoliths may not be directly linked to the host basalt.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.456-467
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• 2019

The rapid aging of South Korea is causing difficulties in meeting the man-power demands for the increasing number of elderly nursing hospitals. To cope with this gap in supply and demand, more foreign workers are now being hired to provide elderly care services. The purpose of this study is to examine the influence of the quality of the care services provided by foreign caregivers in nursing hospitals for the elderly. For this purpose, the researcher surveyed 249 senior citizens who are receiving care services from Chinese-Korean caregivers in six elderly nursing hospitals in Seoul and Gyeonggi region. The data collected from the survey were analyzed through SPSS and AMOS. The result of the analyses showed that, first, the quality factors of the care services of the caregivers at elderly nursing hospitals, such as reliability, responsibility, empathy, formality, and expertise, all turned out to have a positive correlation with the trust in, satisfaction with, and intent to revisit the institute. Second, thefluencing factors for the qualities of the care services by Chinese-Korean care givers in elderly nursing hospitals included responsiveness, materiality, and expertise, while the factors that influenced satisfaction with significance included trust, materiality, and expertise. Also, the trust in and satisfaction with the institution both influenced the intent of revisit in a positive manner. Third, the indirect effect of trust in the relationship between the quality of the care services by the Chinese-Korean care givers and satisfaction, appeared in all independent variable except for responsiveness, which was a factor of the quality of the care services. And, it was also shown that the satisfaction level had an indirect effect in the relationship between trust and revisiting intent. The result of this study implicates that, in order to cause the quality of the care service by the Chinese-Korean care givers in elderly nursing hospitals to increase the revisit rate, it would be necessary to provide a strategy to increase the levels of trust and satisfaction through a higher quality level of care services.