• Proceedings of the KSME Conference
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• 2004.04a
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• pp.450-455
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• 2004

There is few research about contact problem for a rigid surface with an arbitrary shape in SPH. The variational equation based on the virtual work principle is derived and its solution is obtained by the penalty method. It is proposed a new method that can determine the parameters for a penetration and a penetration rate used in the penalty method. The reproducing condition is adopted to correct the deficiency of kernel on the boundary. In order to calculate a penetration of particles, after checking boundary particles for deformable body boundary normal vectors were determined on the rigid surface. Numerical simulations for models which have rigid surface with an arbitrary shape were conducted to validate the proposed method in 2D. The results of those analysis represent that the contact algorithm proposed in this study works properly.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.831-838
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• 2004

A fluid-solid conjugate solver has been newly developed and applied to an actual engine disk system. Most of the currently available conjugate solvers lack the special thermal modeling for turbomachinery disk system applications. In the present new code, these special models are implemented to expand the applicability of the conjugate method and to reduce the required computational resources. Most of the conjugate analysis work so far are limited to the axisymmetric framework. However, the actual disk system includes several non-axisymmetric components which inevitably affect the local heat transfer phenomena. Also the previous work devoted to this area usually concentrate their efforts on the steady-state thermal field, although the one in the transient condition is more critical to the engine components. This paper presents full 3D conjugate analysis of a single stage high pressure turbine rotor-stator disk system to assess the three-dimensional effects (Fig. 1). The analysis is carried out not only in the steady-state but also in the engine accelerating transient condition. The predicted temperatures shows good agreement with measured data.

• Journal of the Korean Society of Safety
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• v.23 no.6
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• pp.7-13
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• 2008

It is important to prevent roll failure in hot rolling process for reducing maintenance cost and production loss. The relationship between rolling pass schedule and the work roll wear profile will be presented. The roll wear pattern is related with roll catastrophic failure. The irregular and deep roll wear pattern should be removed by On-line Roll Grinder(ORG) for roll failure prevention. In this study, a computer roll wear prediction model under real process working condition is developed and evaluated with hot rolling pass schedule. The method of building wear calculation functions for center portion abrasion and marginal abrasion respectively was used to develop a work roll wear prediction mathematical model. The three type rolling schedule are evaluated by wear prediction model. The optimum roll grinding methods is suggested for schedule tree rolling technique.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.4
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• pp.49-55
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• 2011

Recently, various efforts to make more speedy and precision machine tool to improve productivity and also various efforts to solve environmental problem are going on, so that dry cutting in manufacturing industry, which needs environmental conscious design and development of manufacturing technique, is becoming a very important assignment to solve. Because dry cutting does not use cutting fluid, we need other methods that can be used instead of cutting fluid, which does cooling, lubricating, chip washing, and anti-corrosion. Especially, because turning is a continuous work, the consideration of tool life and surface roughness due to continuous heat and poor lubrication is important. The purposes of this paper are the consideration of how well the compressed air can work instead of cutting fluid, and also the development of the method to select the optimum machining condition by the minimum numbers of experiments through the Taguchi method.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.69-80
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• 1993

It is important to prevent roll failure in hot rolling process for reducing maintenance coat and production loss. Roll material and rolling conditions such as the roll force and torque have been intensively investigated to overcome the roll failures. In this study, a computer roll life prediction system under working condition is developed and evaluated on IBM-PC level. The system is composed and fatigue estimation models which are stress analysis, crack propagation, wear and fatigue estimation. Roll damage can be predicted by calculating the stress anplification, crack depth propagation and fatigue level in the roll using this computer model. The developed system is applied to a work roll in actual hot rolling process for reliability evaluation. Roll failures can be diagnosed and the propriety of current working condition can be determined through roll life prediction simulation.

• Safety and Health at Work
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• v.10 no.4
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• pp.512-517
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• 2019

Background: Rest breaks at work are reported to reduce fatigue and job stress. Apartment janitors in Korea who perform night shift work and work long hours can be exposed to various health problems (HPs). However, few studies have evaluated relationships between their rest breaks and HPs. This study was conducted to examine the relationships between long working hours, shift work, and insufficient rest breaks and HPs among Korean apartment janitors. Methods: Data on 1,212 selected male apartment janitors were obtained from the 3rd and 4th Korean Working Conditions Surveys. Demographic and occupational characteristics were collected using self-reported questionnaires. Rest breaks at work were classified as "sufficient" or "insufficient." Long working hours were considered as working more than 60 hours per week. Zero-inflated negative binomial (ZINB) regression was performed to investigate the effects of shift work and long working hours on HPs and the effects of rest breaks on relationships between HPs and long working hours and shift work. Results: Among those with insufficient rest breaks at work, significant associations were found between long working hours and the risk of HPs [odds ratio (OR) = 1.489; 95% confidence interval (CI) = 1.038-2.136] and work-related HPs (WRHPs) [OR 1.621; 95% CI = 1.156-2.272], and between shift work and HPs [OR = 1.603; 95% CI = 1.084-2.372]. These relationships became nonsignificant when sufficient rest breaks were provided. Conclusion: It is important to provide breaks at work to reduce HPs because of long working hours and shift work among aged workers such as apartment janitors.

• Journal of Nutrition and Health
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• v.36 no.7
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• pp.769-776
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• 2003

This study has analyzed the association of physical activity and television watching time with obesity in 30-50 aged women from middle income town in Busan city area. Data were obtained using a questionnaire, including information about physical activity, TV watching time and health habit; social data regarding educational level and monthly income; family history of chronic condition. Height and weight were measured. Outcome variable was obesity, defined as a body mass index 25 kg/m$^2$ or greater. Odds ratios (OR) for obesity were estimated by multivariate logistic regression, and interpreted as a relative risk of obesity. The prevalence of obesity was 11.8%. The mean BMI of obese women was 26.9 kg/m$^2$. The OR of obesity was higher in subject of 40s than 30s. Subjects who had higher educational level presented lower OR than those of elementary or middle school education. Family income was not associated with obesity. Women having a family history of chronic condition had higher risk of obesity than those who did not have it. The OR was lower in active people at work (OR = 0.51; 95% CI = 0.26 - 0.98) than in inactive ones, and the ORs associated with regular exercise or activity at leisure time were not statistically different. However, subjects watching TV $\geq$ 3.5 hr/day showed higher OR (OR = 2.34; 95% CI = 1.16 - 4.74), compared with those watching TV $\geq$ 1.5 hr/day. Association of the joint classification of physical activity variables with obesity was estimated. The highest relative risk of 5.99 was in women in physically inactive at work and high category of TV watching ($\geq$ 3.5 hr/day). Even in women in active at work, the watching TV $\geq$ 3.5 hr/day made them have the high OR (OR = 2.44; 95% CI = 1.03 - 5.77). And at each time level of TV watching, the increasing activity level at work was associated with lower OR for obesity. These findings suggest that both TV watching time and physical activity at work were related to obesity in adult female, each with independent effects on obesity. TV watching time seems to be a significant factor that could partly evaluate the energy expenditure.

• Journal of the Ergonomics Society of Korea
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• v.35 no.5
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• pp.465-472
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• 2016

Objective:This study is on the characteristics of motorcycle accidents occurring in the mail delivery process by skill level. Background: The tendency of delivery postmen's driving in a hurry may become the cause of accidents since there is a constraint that delivery should be completed within a limited time. Method: This study analyzed the traffic accident data of 259 delivery postmen, who had been approved as occupation-related industrial accident victims from 2009 to 2012, by their work experience in view of season, day of the week of an accident occurrence, accident occurrence time, accident cause, collision type, and driving situation. Results: Accident characteristics of delivery postmen show that the ratio of accidents occurring to those who had less than 10 years of work experience was high. There were many motorcycle collisions in winter and summer by season and an unexpected object, along with road condition, took up 70.7% of the accident sources. There were no differences in accident occurrence time, the day of the week, season, accident source, and collision type between the group of delivery postmen with less than 10 years of work experience and those with 10 years or more of work experience. However, there was a difference in distribution of driving condition. Conclusion and Applications: The results of this study can be used to present the policies or guidelines for the accident prevention of delivery postmen since the results show the characteristics of the injured and accident occurrence characteristics in relation with the delivery postmen's motorcycle collisions.

• Journal of the Korean GEO-environmental Society
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• v.21 no.6
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• pp.19-25
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• 2020

In the recent downtown works, there are frequent cases where the work on existing piles is impossible due to the influence from lack of space and surrounding environment. In such cases, there has been growing cases of using the micropile method that is available to work with the small equipment and asserts the bearing capacity of the existing piles. The micropile method is a type of drilled shaft with the diameter of a pile to be around 75 mm~300 mm that, even for a case where it has certain surrounding structure, foundation and spatial obstacle, there is almost no work difficulty and the work is feasible under all types of soil conditions. In addition, the work can be done in places where the ceiling of the building is low with less vibration and noise in the work process that such method is significantly used for foundation reinforcement of existing buildings. With respect to the motion characteristics that are changed depending on the foundational characteristics or when the micropile is applied with compression or tensile force, there is very few studies conducted. Therefore, under this study, through the data analysis of the field loading test regarding the micropile worked in the fields, it clarifies the settlement and characteristics of bearing capacity following the embedded condition of the ingredients and piles that consist the foundation if the compression and tensile force are applied to the micropile, and by facilitating the statistical analysis program, SAS, to carry out the analysis on the main elements influencing on settlement of the micropile and bearing capacity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.200-210
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• 2020

The maintenance of educational facilities was assembled in 12 project classifications of the Educational Improvement Program. The priorities were decided by the evaluation scores derived from the condition investigation, and maintenance works were budgeted in the order of priorities. These priorities were a schedule for conducting maintenance and an important criterion for obtaining a construction order. Several restrictions in the condition investigation exist, which derives budgets and conducts maintenance separately based on the priorities. An educational facility manager has a restriction in quantity take-off, which results in an incorrect budget. Discomfort would occur in an educational environment, and a period of infringing safety would increase. This study proposes applying a BIM in the condition investigation and the planning framework for work-type packaging. A BIM supports a budget calculation and derives evaluation scores by linking a repair and an inspection result. The work-type packaging algorithm divides a budget allocation range and derives the result of a grouped work-types applied in an equivalent space and element. As a result of applying cases, it could shorten the duration by approximately 37.4%. Its usability in selecting a grouped work-type was evaluated through an assessment with workers.