• Journal of the Korean Society of Visualization
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• v.15 no.2
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• pp.33-40
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• 2017

Abstract In the present study, the characteristics of kinematics and dynamics in the fluttering motion of free-falling plates are investigated at Reynolds number of $10^5$. We record quasi-two-dimensional trajectories of free-falling plates with and without superhydrophobic coating using high-speed camera, and compute the drag and lift forces by trajectory analysis. Translational and angular velocities are modeled as harmonic functions with specific phase differences. In particular, periodic mass elevations near turning points are explained using the suggested models. At each turning point, a sudden drop in lift and a rapid increase in drag occur simultaneously due to fast increase in angle of attack. However, the lift is increased over the buoyancy-corrected weight of plate during gliding flight, resulting in periodic mass elevations near turning points. Superhydrophobicity is shown to increase lift but to reduce drag on a fluttering plate, resulting in the decrease of mean descent speed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.12
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• pp.996-1003
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• 2002

Heat transfer characteristics were investigated for the falling film flowing down the outside of an electrically heated vertical tube. Water was used for the falling film, and its Reynolds number was varied in the range of 70～500. Because water is heated and evaporated as it flows down, both sensible and latent heat transfer should be considered. The effect of the surrounding air movement was investigated by changing the direction of the air injection; without air injection, parallel-flow, and counter-flow. For all cases, sensible teat transfer rate was almost linearly increased with the increasing film flow rate. It was found that the film heat transfer coefficient was hardly influenced by the parallel air flow. However, the counter-flow of air reduced the heat transfer coefficient, which might be caused by the uneven distribution or flooding of the film. At high heat flux, a sudden change of the film heat transfer coefficient was detected as the film flow rate reached the transition value. It is supposed that this phenomenon was caused by the change in the film flow pattern.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.90-96
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• 2003

Numerical analyses have been performed to obtain the absorption heat and mass transfer coefficients and the absorption mass flux from a falling film of LiBr solution. In the present study, the behavior of laminar-wavy falling film in the vertical absorber was studied analytically and experimentally. The change of absorption performance on mean film thickness, wave amplitude, wave celerity was analysed. The heat and mass transfer equations are solved simultaneously to give the temperature and concentration variations at the LiBr solution/refrigeration vapor interface and at the wall. Effects of uniform film, wavy film and film Reynolds number on the heat and mass transfer coefficients have been estimated. The analytical results of the uniform and wavy falling film in the bare tube was higher than experimental result for $Rd_{t}<100$. The absorption performance showed the maximum at the wavy film by the insert device(spring).

• Research in Community and Public Health Nursing
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• v.30 no.2
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• pp.141-149
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• 2019

Purpose: The purpose of this study is to identify risk factors of accidental falls by age in the Korean elderly. Methods: The study subjects included 10,242 community-dwelling elders aged 65 or over. The data were analyzed by logistic regression analysis. Results: The risk factors of accidental falls in the younger old group (aged 65~74) include fear of falling (OR=16.28, 95% CI: 12.03~22.03), depression (OR=1.24, 95% CI: 1.06~1.44), and hearing impairment (OR=1.20, 95% CI: 1.01~1.43). The risk factors of accidental falls in the older old group (aged 75~84) include fear of falling (OR=11.54, 95% CI: 7.04~18.93), muscle strength (OR=1.36, 95% CI: 1.15~1.60), number of chronic disease (OR=1.65, 95% CI: 1.09~2.50), and presence of spouse (OR=1.27, 95% CI: 1.06~1.51). The risk factors of accidental falls in the oldest old group (aged 85 years old or older) include fear of falling (OR=8.05, 95% CI: 1.85~34.98) and exercise (OR=2.91, 95% CI: 1.36~6.24). Fear of falling is defined as a common factor in the all age groups. Conclusion: Different strategies should be developed for age groups to prevent elderly falls with understanding of contributing factors of falls in each group.

• The Journal of the Acoustical Society of Korea
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• v.24 no.2
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• pp.117-126
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• 2005

This study investigates the prosodic characteristics of Korean through the analysis of a large database. One female and one male speakers each read 650 sentences and they were segmentally and prosodically labeled. Statistical analyses were done on these utterances regarding the tonal pattern and the size of prosodic units, correlation between the size of higher level prosodic units and the number of lower level prosodic units. and the slope and F0 of the falling and rising contours of an accentual phrase. The results showed that the duration and the number of words and syllables of a prosodic unit were significantly different not only between speakers but also between its positions within a higher level prosodic nit. The munber of a prosodic unit showed a high correlation with the duration and the number of syllables of its higher level units. The slope of the falling contour within an accentual phrase was inversely Proportional to the number of its syllables. The slope was different depending on the first tone type of an accentual phrase, which could be explained with the F0 rising and the different amount of rising between tones when an accentual phrase starts with an H tone. The slope of the falling contour across an accentual phrase boundary showed a constant and larger value compared to one within an accentual phrase. The rising contours in the beginning and end of an accentual Phrase were similar in their slopes but they differ in the amount of F0 change : the former showed a larger amount of change. The slope of the rising contour which forms an accentual Phrase on its own was inversely Proportional to the number of its syllables.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.85-88
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• 2002

We have implemented a system of falling weight impact tester. Absorbed energy of orthotropic composites with using T300 fiber, which are composed of the same fiber and stacking number is higher than that of quasi-isotropic specimen over impact energy 7J, but in case of using T700 fiber, much difference does not show. Also, absorbed energy of orthotropic composites with using T300 fiber, which are composed of stacking number and orientation became more than that of T700 fiber specimen; however great change doesn't show in case of quasi-isotropic specimens. Delamination area of impacted specimens was measured with ultrasonic C-scanner to find correlation between impact energy and delamination area. Delamination area and frequency responses was evaluated between impacted and unimpacted specimens. There is a strong correlation between frequency responses and impact-induced delamination. The presence and scale of damages have been investigated based on the variations of frequency responses.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.431-439
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• 1998

Falling film absorption process is an important problem in application such as absorption chillers. The presence of waves on the film affects the absorption process significantly. In the present study the characteristics of heat and mass transfer in laminar-wavy falling film were studied numerically. The wavy flow behavior was incorporated in the energy and diffusion equation. The numerical solution indicated that the interfacial wave increased the transfer rates remarkably. Interfacial shear stress and wave frequency seemed to be the dominant factors on the film Nusselt number and Sherwood number in the wavy film. A comparison of the transfer rates of the wavy film to that of the smooth film showed that the mass transfer rate could be increased by more than 50%.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.106-109
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• 2000

Impact tester was build up to evaluate the characterization of CFRP laminate plates under the low velocity impact. The tests were conducted on several laminates of different ply orientation A system was budded for the impact strength of CFRP laminates in consideration of stress wave propagation theory using drop-weight impact tester as one of impact test. Results indicate that absorbed energy of quasi-isotropic specimen having four interfaces is higher than that of orthotropic laminates with two interfaces. Also the damage area was measured with ultrasonic C-scanner on some samples. In the specimens the relationship was linear between damaged area and absorbed energy to some degree. Absorbed energy in the specimen that ply number, interface number and fiber stacking sequences is same but having hybrid is higher than that of orthotropic laminates without hybrid.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.146-152
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• 1997

The number of accidents due to slipping, falling and awkward postures are estimated to account for over forty percent of annual industrial accidents in Korea. To prevent such accidents, stability-maintaining capabilities of workers should be understood before any other approach. This research was aimed to analyze capabilities of the workers with the help of yours male students maintaining standing postures on a tiltable stability platform. The experimental result showed that tilting direction, height of pivoting point, and permissible degree of swaying made significant effects on stability-maintaining duration. Besides, humans are more capable of maintaining their standing body postures on a platform tiltable fore and aft rather than or one tiltable sideways. The number of falling or tripping supported this phenomenon. A mechanical and physical discussion on the stability was added.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.278-287
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• 2019

This study was conducted to identify the predictors influencing fear of falling in community-dewelling elderly. A secondary data analysis was performed using data of 65 years or older elderly who participating in the 2014 Korean Elderly Survey(Jun. 11th ~ Sep. 4th 2014). Multivariated logistic regression analysis was used to identify the risk factors of fear of falling. 81.5% of the elderly had fear of falling. There were significant factors, sex(OR=2.87, p<.001), education(OR=1.73, p<.001), presence of cohabiting spouse(OR=1.19, p<.001), experience of falling(OR=6.35, p<.001), arthritis(OR=1.83, p<.001), depression(OR=2.25, p<.001), cognitive deficit (OR=1.24, p<.001), instrumental activities of daily living (OR=1.98, p<.001), exercise(OR=1.29, p<.001) and the number of chronic diseases(over 3: OR=2.53, p<.001, 1~2: OR=1.73, p<.001), predicting fear of falling in community-dwelling elderly. Fear of falling was associated with multifactorial condition, and arthritis was an important factor in chronic disease. This study will provide fundamental information on programming and a policy proposal related to fear of falling.