• Journal of Navigation and Port Research
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• v.44 no.3
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• pp.145-150
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• 2020

The ship motion of large LNG ships affects ships' safety. The purpose of this study was to estimate the transfer function of roll motion among the hull motion of 153,000 m3 class LNG vessels. The ship motion transfer function was modeled using a Linear Time-Invarient system with single input, single output, and transfer function. The transfer function of the ship motion was estimated by the system identification method using single ocean wave as input of the model, and using the roll motion of the LNG ship obtained through ANSYS as the output of the model. The usefulness of the experimental results was evaluated using the precision and estimation rate of the model for cases wherein the different transfer function dimensions. Results of the experiment showed a precision at 99% and 98%, with estimation rate at 78% and 50%. From these results, we found the proposed method of estimating the transfer function of ship motion in this study reasonable. In the future, data of ship motion in actual sea conditions will be acquired and it will be applied to make the construction of models with multiple inputs and multiple outputs for practical use.

• Journal of Advanced Navigation Technology
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• v.17 no.5
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• pp.516-523
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• 2013

In this paper, The path loss model of Air Traffic Control(ATC) telecommunication radio channel has been studied at the Incheon International Airport(IIA) with the terminal with two antlers. We measured two frequencies among VHF/UHF channel bands. The transmitting site radiated the Continuous Wave(CW). The propagation measurement was taken using the moving vehicle equipped with receiver and antenna. The transmitting power, frequency and antenna height are the same as the current operating condition. The path loss exponent and intercept parameters were extracted by the basic path loss model and hata model. The path loss exponents at passager terminal areas were 3.32 and 3.10 respectively in 128.2 MHz and 269.1 MHz. The deviation of prediction error is 9.69 and 9.65. The new path loss equation at the terminal area was also developed using the derived path loss parameters. The new path loss was compared with other models. This result will be helpful for the ATC site selection and service quality evaluation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.5
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• pp.287-296
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• 2019

In this study, the effect of ground boundary conditions on the evaluation of blast resistance performance of precast arch structures was evaluated by a numerical analysis method. Two types of boundary conditions, namely, fixed boundary conditions and a perfectly matched layer (PML) were applied to numerical models. Blast loads that were much higher than the design load of the target structure were applied to compare the effects of the boundary conditions. The distribution and path of the ground explosion pressure, structural displacement, fracture of concrete, stress of concrete, and reinforcing bars were compared according to the ground boundary condition settings. As a result, the reflecting pressure shock wave at the ground boundaries could be effectively eliminated using PML elements; furthermore, the displacement of the foundation was reduced. However, no distinct difference could be observed in the overall structural behavior including the fracture and stress of the concrete and rebar. Therefore, when blast simulations are performed in the design of protective structures, it is rational to apply the fixed boundary condition on the ground boundaries as conservative design results can be achieved with relatively short computation times.

• Korean Journal of Labor Studies
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• v.24 no.3
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• pp.35-71
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• 2018

The purpose of this study is to examine which job-related factors are associated with presenteeism, which is defined as attending work while ill. Although presenteeism is a relatively new concept in academic research, it should be regarded as an important social issue in that presenteeism threatens employees' job prospects and quality of life as well as it causes loss of work productivity. I analyzed a cross-sectional survey of 24,571 wage workers over 15 from the fourth wave of the Korean Working Conditions Survey in 2014. Five logistic regression models were analyzed on experience of presenteeism, and work hours and private life, occupational environment, job insecurity, rewards and welfare were assessed as key predictors of presenteeism. I found that 1) work hours with bad fit with private life, 2) high level of work time-pressure, and low job satisfaction 3) job insecurity, and 4) low benefits are associated with experience of presenteeism. The findings are fairly consistent with the theory of job-person mismatch, which explains that workers tend to preserve their personal resources by going to work while ill (presenteeism) when job demands or work conditions do not match with their level of personal expectation and, thus, workers are afraid of loss of personal resources. Presenteeism influences worker's long-term health and quality of life negatively as well as causes serious social costs. Therefore, we need organizational efforts to prevent the negative effects of presenteeism on society as well as workers.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.371-381
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• 2019

This study explored how retirement satisfaction or dissatisfaction influences on retirees' life satisfaction, comparing to workers and the gender differences were examined. The study sample was 2,609 persons (1,886 workers, 723 retirees) aged 45 or older who participated in the 1-2 waves of the Korean Longitudinal Study of Ageing (KLoSA), and the retirees were classified into continuously dissatisfied retirees and satisfied retirees during wave 1 and 2. Using SPSS 21.0, the multiple regression models were examined, and in order to clarify the gender difference, the multi-group analysis and the wald-test were conducted to test the difference of the regression coefficients according to gender using Mplus 7.3. According to the results, the life satisfaction of dissatisfied retirees was lower than that of the employed, but when satisfied with retirement, the life satisfaction was higher than that of the employed. In addition, the dissatisfied retirees in both gender were less satisfied with life than the employed, and this effect was greater in female group. However, the life satisfaction of female satisfied with retirement was higher than that of the employed, whereas the evidence of the male influence was not found to be significant. Based on the results of this study, discussion about heterogeneity of retirees and gender differences in life span were presented.

• Explosives and Blasting
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• v.39 no.2
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• pp.1-14
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• 2021

Recently, with the development of high-performance processing devices such as GPGPU, a three-dimensional dynamic analysis technique that can replace expensive rock material impact tests has been actively developed in the defense and aerospace fields. Experimentally observing or measuring fracture processes occurring in rocks subjected to high impact loads, such as blasting and earth penetration of small-diameter missiles, are difficult due to the inhomogeneity and opacity of rock materials. In this study, a three-dimensional dynamic fracture process analysis technique (3D-DFPA) was developed to simulate the fracture behavior of rocks due to impact. In order to improve the operation speed, an algorithm capable of GPGPU operation was developed for explicit analysis and contact element search. To verify the proposed dynamic fracture process analysis technique, the dynamic fracture toughness tests of the Straight Notched Disk Bending (SNDB) limestone samples were simulated and the propagation of the reflection and transmission of the stress waves at the rock-impact bar interfaces and the fracture process of the rock samples were compared. The dynamic load tests for the SNDB sample applied a Pulse Shape controlled Split Hopkinson presure bar (PS-SHPB) that can control the waveform of the incident stress wave, the stress state, and the fracture process of the rock models were analyzed with experimental results.

• Journal of Family Relations
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• v.21 no.2
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• pp.129-147
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• 2016

Objective: This study examined the role of siblings with respect to living arrangements between married children and their parents. Previous studies have rarely considered the possibility that family context such as siblings may be associated with intergenerational residential proximity. Method: Using data from first wave of the Korean Longitudinal Study of Ageing (2006), I investigated if, among married children, their sibling characteristics may be associated with the probability of their coresiding with the parent(s), living nearby (within a 30-minute distance from parent(s) by public transportation), or living further away. Specifically, the total numbers of sisters and brothers, the numbers of siblings coresiding with the parent(s) and living nearby, their relative position in the sibling network (first-born son, later-born son, first-born daughter, later-born daughter), and sibship existence and gender configurations (only child, son with brother(s) only, son with sister(s) only, son with both brother(s) and sister(s), daughter with brother(s) only, daughter with sister(s) only, daughter with both brother(s) and sister(s)) were evaluated in the study. For data analysis, multinomial logit models with robust standard errors were estimated using the Stata mlogit procedure. Results: Results suggest that the probability of a married child living together with the parent(s), relative to living close by, was significantly higher the more sisters he or she has. Being a son, especially first-born son, was associated with a higher probability of intergenerational coresidence compared to near residence, respectively. Also, the numbers of siblings coresiding with the parent(s) and living in close proximity were linked to a higher risk of intergenerational coresidence and near residence. Supplementary analyses revealed that the last finding was held over and above the total number of siblings, their relative position in the sibling network, as well as sibling existence and gender configurations. Conclusion: Overall, the study findings indicate that sibling characteristics have significant impacts on intergenerational living arrangement. The influence of traditional patrilineal norm of intergenerational coresidence and a trend towards modified extended family have emerged when siblings characteristics are taken into consideration as determinants of intergenerational living arrangement.

• Journal of Korea Water Resources Association
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• v.55 no.1
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• pp.71-84
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• 2022

The objective of this study is to develop a two-dimensional (2D) flood model that can perform accurate flood analysis with simple input data. The 2D flood inundation models currently used to create flood forecast maps require complex input data and grid generation tools. This sometimes requires a lot of time and effort for flood modeling, and there may be difficulties in constructing input data depending on the situation. In order to compensate for these shortcomings, in this study, a grid-based model that can derive accurate and rapid flood analysis by reflecting correct topography as simple input data was developed. The calculation efficiency was improved by extending the existing 2×2 sub-grid model to a 5×5. In order to examine the accuracy and applicability of the model, it was applied to the Gamcheon Basin where both urban and river flooding occurred due to Typhoon Rusa. For efficient flood analysis according to user's selection, flood wave propagation patterns, accuracy and execution time according to grid size and number of sub-grids were investigated. The developed model is expected to be highly useful for flood disaster mapping as it can present the results of flooding analysis for various situations, from the flood inundation map showing accurate flooding to the flood risk map showing only approximate flooding.

• 한국노년학
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• v.40 no.4
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• pp.691-706
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• 2020

This study aims to explore health behavior profiles and the association between the derived profiles and living arrangement among middle-aged and older adults. Using data from wave 6 (2016) of the Korean Longitudinal Study of Aging, latent profile analyses were applied to identify patterns of health behaviors and multinomial logistic regression models were conducted to predict profile membership using living arrangement (i.e., living alone, living with spouse only, living with family members) and sociodemographic characteristics. A sample of 7,048 respondents aged 55 and older were included in the study. Results revealed that Korean middle-aged and older adults can be grouped into four health behavior profiles: "High health-compromising" (4%), "Moderate health-compromising" (28%), "Low health-compromising" (65%), and "High physical activity" (3%). Also, living arrangement showed significant profile differences. Compared to the respondents living alone, those living with spouse only were more likely to belong to low and moderate levels of health-compromising behavior profiles than the "High physicial activity profile". Respondents living with family members were more likely to belong to the "High health-compromising profile" than the "High physical activity profile" compared to those living with spouse only. These findings indicate that living arrangement needs to be taken into consideration when developing health promoting programs and supports. Moreover, policy interventions suiting the needs of various sociodemographic subgroups are recommended.

• 한국노년학
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• v.40 no.1
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• pp.91-109
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• 2020

This study aims to investigate the interdependence of Korean middle and old-aged couples in the association between exercise and life satisfaction through grip strength trajectory. Data were drawn from the nationally representative Korea Longitudinal Study of Aging (KLoSA) collected from 2006 to 2016. The sample included couples over 45 years of age in the first wave and participated in all six waves of the survey (Ncouple=1,997). There were three steps for analyses: correlation, parallel latent growth curve model, tests of indirect effects of the mediation paths. Covariates included in the models were husbands and wives' characteristics (age, education, work status, chronic diseases, marital satisfaction, contact frequency with friends or neighbors) and couple's household income. Results showed husbands' and wives' life satisfaction and grip strength were interdependent upon each other. Also, exercise participation of both husbands and wives was associated with both husbands' and wives' life satisfaction via the initial level of grip strength of husbands. Moreover, exercise participation of only husbands was associated with wives' life satisfaction through the initial grip strength of husbands. These results suggest the aging processes of middle and old-aged couples need to be understood in the context of gender dynamics and couple interdependence.