• Transactions of the Korean hydrogen and new energy society
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• v.31 no.4
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• pp.387-394
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• 2020

A parametric study of a 2.5 kW class propeller type micro hydraulic turbine was performed. In order to analyze the internal flow characteristics in the hydraulic turbine, three dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model were used and the hexahedral grid system was used to construct computational domain. To secure the reliability of the numerical analysis, the grid dependency test was performed using the grid convergence index method based on the Richardson extrapolation, and the grid dependency was removed when about 1.7 million nodes were used. For the parametric study, the axial distance at shroud span (L) between the inlet guide vane and the runner, and the inlet and outlet blade angles (β₁, β₂) of the runner were selected as the geometric parameters. The inlet and outlet angles of the runner were defined in the 3 spans from the hub to tip, and a total of 7 geometric parameters were investigated. It was confirmed that the outlet angles of the runner had the most sensitive effect on the power and efficiency of the micro hydraulic turbine.

• Child Health Nursing Research
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• v.10 no.1
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• pp.37-47
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• 2004

Purpose: This study aimed to identify the alcohol drinking pattern of parents and to analyze drinking related factors in problem drinking among adolescent's parents. Method: This study was conducted through a structured questioning from November 5th to 22th in 2002. Those are 2,522 parents of the students of the 1st and 2nd grade who were selected randomly among 26 middle and high schools located in Socho-gu, Seoul. Data was analyzed using SAS program that included descriptive statistics, Chi-square test, and multiple logistic regression analysis. Result: 1. For frequency of drinking, 33.1％ of the subjects responded to drink two-four times a month, 26.0％ drink more than two times a week. 2. For the amount of drinking, 29.6％ drink one or two glasses while 9.4％ drink over ten glasses at a time. 3. The mean AUDIT score was 8.27 7.02(score of range: 0- 40). 4. Based on AUDIT score, drinkers with less than eight point from AUDIT(normal group) were 55.1％, from more than eight point to less than twelve point from AUDIT(problematic drinker) were 16.3％, and more than twelve point from AUDIT(alcohol abuse and dependency) were 28.6％. 5. Based on more than twelve point from AUDIT, female(mother), high school and, have religion, housekeeper were the significantly higher score than counter parts. Conclusion: Alcohol drinking pattern and level of drinking of their parents links to their children's drinking and results in family, social, and national loss. Active prevention is needed. Specially, pertinent education about drinking and public education for mothers who are housekeepers should be carried out with concentrated intervention programs for the problematic drinker so alcohol abuse and dependency can be reduced.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.397-401
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• 2000

The corrosion-fatigue characteristics of the 12Cr steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the Rayleigh surface wave. In this study, the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the aged specimens, and then compared to the corrosion-fatigue characteristics. The width of the backward radiation profile decreases as the increase of the aging temperature, which seems to result from the increase of the effective degrading layer thickness. This parameter also shows an inversely proportionality to the exponent, m, in the Paris law which predicts the crack size increasement due to fatigue. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion-fatigue characteristics of the aged materials.

• 한국노년학
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• v.38 no.1
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• pp.203-223
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• 2018

This study examined the validity and the reliability of the perceived elderly stigma scale. Moreover, we investigated the relationships between the perceived elderly stigma and demographic factors (age, gender, education, and income). The initial scale consisted of 5 factors (ability, personality, appearance, authoritarian dependency, and child-obsession) and 28 items. In order to test the validity and the reliability of the scale, this study conducted a survey with 693 adults aged 18 to 65. Based on the confirmatory factor analysis (CFA), the scale was modified to 5 factors (ability, personality, appearance, authoritarian dependency, and child-obsession) and 15 items and its convergent validity and discriminant validity were confirmed. In terms of the relationships between the perceived elderly stigma and demographic factors, age had a negative relationship with the "ability" stigma, and education was a negatively associated with the "appearance" stigma.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.529-536
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• 2008

The failure behavior of structures is changed under different loading rates, which might arise from the rate dependency of materials. This phenomenon has been focused in the engineering fields. However, the failure mechanism is not fully understood yet, so that it is hard to be implemented in numerical simulations. In this study, the numerical experiments to a brittle material are simulated by the Molecular Dynamics (MD) for understanding the rate dependent failure behavior. The material specimen with a notch is modeled for the compact tension test simulation. Lennard-Jones potential is used to describe the properties of a brittle material. Several dynamic failure features under 6 different loading rates are achieved from the numerical experiments, where remarkable characteristics such as crack roughness, crack recession/arrest, and crack branching are observed during the crack propagation. These observations are interpreted by the energy inflow-consumption rates. This study will provides insight about the dynamic failure mechanism under different loading rates. In addition, the applicability of the MD to the macroscopic mechanics is estimated by simulating the previous experimental research.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1603-1611
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• 2004

The validity of 'modified overlay model' to describe the cyclic behavior of annealed 316L stainless steel at room temperature was investigated. Material parameters(~f$_{i}$, m$_{i}$b, η, E) fur the model were obtained through constant strain amplitude test. The strain amplitude dependency of elastic limit and cyclic hardening, which were the characteristics of this model, were considered. Eight subelements were used to describe the nonlinearity of the hysteresis loops. The calculated hysteresis curve in each condition (0.5％, 0.7％, 0.9％ train amplitude test) was very close to the experimental one. Two tests, incremental step test and 5-step test, ere performed to check the validity of 'modified overlay model'. The elastic limit was saturated to the one of the highest strain amplitudes of the block in the incremental step test, so it seemed to be Masing material at the stabilized block. Cyclic hardening was successfully described in the increasing sequence of the strain amplitude in 5-step test. But, the slight cyclic softening followed by higher strain amplitude would not be able to simulate by'modified overlay model'. However, the discrepancy induced was very small between the calculated hystereses and the experimental ones. In conclusion,'Modified overlay model'was proved to be appropriate in strain range of 0.35％~ 1.0％..0％.

• Journal of the Ergonomics Society of Korea
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• v.34 no.4
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• pp.335-351
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• 2015

Objective: The aim of this study was to perform a usability test for CPAD (Cognitive Perceptual Assessment for Driving) and improve it based on the test results. Background: The cognitive perceptual assessment for driving is a computer-based assessment tool to assess the driving capacity of people with brain-damages. It may be a good tool for evaluating the brain-damaged drivers' safe driving capabilities and screening cognitive and perceptual deficits related to driving. We performed a usability test to improve the CPAD based on the result. Method: Both the software consisting of 8 sub-tests (depth perception, sustained attention, divided attention, stroop test, field dependency, digit span, trail making A, trail making B) and the hardware including the input and output devices ( joystick, mouse, keyboard, touch screen) were evaluated through user interviews. Also we identified the problems and issues in using them by observing the participants performing the CPAD tasks. Results: Based on the results, the task instructions were visually and auditorily improved and more practice examples were added to help the users understand the instructions better and increase the input accuracy, a response time window was added and the joystick and touch screen were simplified, which made it easier for the user to perform the CAPD tasks. Conclusion: User discomforts were minimized by improving the task environment, unless it had affected the evaluation criteria. Application: We plan to distribute the improved version of the CPAD to the regional rehabilitation hospitals, and the driving support centers for people with disabilities throughout the country, so it could be used as an evaluation tool for disabled drivers' cognitive and perceptual functions.

• Transactions of the KSME C: Technology and Education
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• v.3 no.1
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• pp.37-44
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• 2015

In this paper dynamic deformation of lower hinge of refrigerator is simulated using dynamic finite element analysis while refrigerator is being dropped. The flow stress curves considering velocity dependency of hinge and lower packing material are determined through bending test and compression test at several dropping speeds. The determined material properties and flow stress from reverse engineering were used as input data for refrigerator's drop test using a dynamic finite element analysis software LS-DYNA. Additionally the result between CAE and 3D deformation measurement from real refrigerator drop test are compared and the result shows that the proposed analysis model is very useful to design lower hinge and lower packing endurable to the impulsive drop impact.

• Culinary science and hospitality research
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• v.21 no.2
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• pp.171-186
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• 2015

This study is designed to test the effects of innovativeness, information dependency, informative sufficiency, and review reliability on perceived usefulness, perceived ease of use, and eventually continuous use in mobile bakery applications and to provide useful information for the bakery industry. A total of 500 questionnaires were distributed for data collection from September $1^{st}$ to $30^{th}$ in 2014. Out of 455 returned questionnaires, 441 were useable. Statistical techniques utilized in the study were a factor analysis, reliability tests, and a covariance structure analysis using SPSS 18.0 and AMOS 18.0. The results were as follows: first, innovativeness had significant effects on perceived usefulness and perceived ease of use. Second, information dependency had significant effects on perceived usefulness and perceived ease of use. Third, informative sufficiency had significant effects on perceived usefulness and perceived ease of use. Fourth, review reliability had significant effects on perceived usefulness and perceived ease of use. Fifth, perceived ease of use had a significant effect on perceived usefulness. Finally, perceived usefulness and perceived ease of use had significant effects on the continuous use of a mobile bakery application.

• Tunnel and Underground Space
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• v.23 no.5
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• pp.383-391
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• 2013

A number of true triaxial tests on rock samples have been conducted since the late 1960 and their results strongly suggest that the intermediate principal stress has a considerable effect on rock strength. Based on these experimental evidence, various 3-D rock failure criteria accounting for the effect of the intermediate principal stress have been proposed. Most of the 3-D failure criteria, however, are focused on the phenomenological description of the rock strength from the true triaxial tests, so that the associated strength parameters have little physical meaning. In order to confirm the likelihood that the intermediate principal stress dependency of rock strength is related to the presence of weak planes and their distribution to the preferred orientation, true triaxial tests are simulated with the transversely isotropic rock model. The conventional Mohr-Coulomb criterion is extended to its anisotropic version by incorporating the concept of microstructure tensor. With the anisotropic Mohr-Coulomb criterion, the critical plane approach is applied to calculate the strength of the transversely isotropic rock model and the orientation of the fracture plane. This investigation hints that the spatial distribution of microstructural planes with respect to the principal stress triad is closely related to the intermediate principal stress dependency of rock strength.