• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.1-8
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• 2000

A modified low-Reynolds-number Reynolds stress model is developed for the calculation of drag-reducing turbulent flows induced by polymer injection. The results without polymer injection are compared with the results of direct numerical simulation to ensure the validity of the basic model. In case of drag reduction, profiles of mean velocity and Reynolds stress components, in two-dimensional channel flow, obtained with a proper value of viscosity ratio are presented and discussed. Computed mean velocity profile is in very good agreement with experimental data. And, the qualitative behavior of Reynolds stress components with the viscosity ratio is also reasonable.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1145-1150
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• 2005

The aim of this paper is to investigate the effect of surface texturing on metal surface and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 is recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.431-437
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• 1998

This study was performed to ascertain the three-dimensional effect of the crack reduction and the restrained effect of crack growth, and to yield a suitable mixing ratio of the synthetic fiber reinforced soil. The results of the study are as follows ; 1) The synthetic fiber has the resisting force for crack because of the adhesion due to the attraction of soil particles. 2) As the synthetic fiber length and the mixing ratio are increased, mono filament synthetic fiber reinforced soil is increased the effects of crack reduction and the restraint of crack growth. 3) The fibrillated synthetic fiber is more effective than mono filament synthetic fiber for crack. 4) A suitable mixing ratio of synthetic fiber reinforced soil is 0.5% of the fibrillated synthetic fiber.

• Journal of the Korean Society of Safety
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• v.21 no.3 s.75
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• pp.59-66
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• 2006

Injury Ratio Survey Regulations(IRS) was introduced to the construction industry in the Republic of Korea since 1992 and brought positive effect on occupational accidents reduction. There were tremendous decrease of injury ratios and enforcing of contractors' safety organizations from the beginning of IRS. In spite of these positive results, there were some negative effects such as contractors' shrinking injury reports to keep good injury ratios since these figures had a great impact on pre-qualification stage of bidding when general contractors were competing for new construction projects. Thus, this study aims to devote on lessening construction injury and elimination of above negative impacts through the quantitative statistic analysis of the effectiveness on the occupational accidents prevention of IRS. According to this assessment, there were decrease of from 6.37% to 44.34% in the accident ratios compared to those of non-IRS groups and decrease of from 3.32% to 83.51 % in the accident ratios compared to those of general industry including the unreported accidents.

• Smart Structures and Systems
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• v.17 no.5
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• pp.725-742
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• 2016

This paper is focused on stiffness ratio effect and a new method to specify the best pattern of piezoelectric patches placement around a hole in a plate under tension to reduce the stress concentration factor. To investigate the stiffness ratio effect, some different values greater and less than unity are considered. Then a python code is developed by using particle swarm optimization algorithm to specify the best locations of piezoelectric actuators around the hole for each stiffness ratio. The results show that, there is a line called "reference line" for each plate with a hole under tension, which can guide the location of actuator patches in plate to have the maximum stress concentration reduction. The reference line also specifies that actuators should be located horizontally or vertically. This reference line is located at an angle of about 65 degrees from the stress line in plate. Finally two experimental tests for two different locations of the patches with various voltages are carried out for validation of the results.

• Proceedings of the Korean Environmental Health Society Conference
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• 2003.06a
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• pp.208-212
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• 2003

This study was performed to examine the effects of chaff as bulking materials on temperature, pH, weight and volume reduction and salinity in aerobic composting of food wastes. Volume ratios of food wastes to chaff in reactor Control, Ch-1, Ch-2, Ch-3 and Ch-4 were 4:0, 4:1, 4:2, 4:3 and 4:4, respectively. Reactors were operated for 24 days with 1 hour stirring by 1 rpm and 2 hours aeration per day. The lowering of the volume ratio of food wastes to chaff resulted in the ascending of the highest reaction temperature and the elongation of the high temperature reaction period. The lowering of the volume ratio of food wastes to chaff resulted in the more fast time of pH ascending. The lowering of the volume ratio of food wastes to chaff resulted in the more fast consistency in the weight and volume reduction rates. Salinities were condensed by reaction days. The final salinity of Control was 2.79%, and the final range of salinities of chaff mixtures was 2.18 - 2.37%.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.555-558
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• 2005

The purpose of this study is to evaluate the chemical resistance of polymer powder-modified mortars with special accelerator component. Polymer powder-modified mortars with the accelerator are prepared with various polymer-binder ratios, and tested for flexural and compressive strengths and mass change. Chemicals resistance was tested by dealing with $10\%$ HCl and $5\%\;H_2SO_4$ aqueous solution. As a result, the weight reduction ratio of the mortars decreased with increasing polymer-binder ratio. However, in the viewpoint of strength reduction by chemical attacks, the maximum chemical resistance of the mortars was shown at a polymer-binder ratio of $5\%$.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.86-89
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• 2003

It is recognized that reinforcement corrosion is the main distress behind the present concern regarding concrete durability. In this study, to confirm corrosion of reinforced concrete affected by thickness of cover, kinds of surface coating, measured electric potential, ratio of corrosion area, weight reduction, corrosion velocity of steel bar under environment of complex deterioration. The results showed that an increase in age also increases corrosion of steel bar. Ratio of corrosion area is largely related to ratio of weight reduction. as well, corrosion of steel bar by thickness of cover is superior to l0mm thick than 20mm thick. It showed that an increase in thickness of cover prevent steel bar from deteriorating. The results of this study showed that corrosion velocity was affected by thickness of cover, kinds of surface coating. data on the development of corrosion velocity made with none, organic B, organic A, inorganic B, and inorganic A is shown.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1183-1186
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• 2005

A new reset method for high contrast ratio and reduction of the reset time is presented. In this new reset method, except the first subfield, a new reset pulse with only ramp-up period is adopted. In this reset method, from the third subfield, the background luminance generated during the reset period is theoretically zero until the first subfield of the following frame. Employing the new reset method, the dark room contrast ratio improved to 3084.7:1 from 189.1:1 of the conventional reset method. The new reset method reduced the required time for reset per subfield to 160us except the first subfield.

• Journal of Environmental Health Sciences
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• v.29 no.2
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• pp.56-61
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• 2003

This study was performed to examine the effects of chaff as a bulking material on temperature, pH, weight and volume reduction and salinity in aerobic composting of food wastes. Volume ratios of food wastes to chaff in reactor of Control, Ch-1. Ch-2, Ch-3 and Ch-4 were 4:0, 4:1, 4:2, 4:3 and 4:4. respectively. Reactors were operated for 24 days with 1 hour stirring by 1 rpm and 2 hours aeration per day. The lowering of the volume ratio of food wasted to chaff resulted in the reaction at higher reaction temperature and the elongation of the high temperature reaction period. The lowering of the volume ratio of food wastes to chaff resulted in the more faster pH increase. The lowering of the volume ratio of food wastes to chaff resulted in the more faster reduction in the weight and the volume of wastes. Salinities were condensed by reaction days. The final salinity of Control and the final range of salinities of chaff mixtures were 2.79%, and 2.18~2.37%. respectively.