• Magazine of the Korean Society of Agricultural Engineers
• /
• v.35 no.4
• /
• pp.38-46
• /
• 1993

This study is to analyze effect of exposure environment and mode of ASR on the engineering properties of synthetic lightweight aggregate concrete, such as dynamic modulus of elasticity and ultrasonic pulse velocity. The results of this study are summarized as foflows ; 1. The expansion rate of each exposure environment in 380$^{\circ}$C and NaCI 4% solution was shown higher than in 20$^{\circ}$C and normal water. The expansion rate of each exposure mode was largely shown in order of fjill immersion, wetting/drying, half immersion. 2. The dynamic modulus of elasticty and ultrasonic pulse velocity of each exposure environment in 38$^{\circ}$C and NaCl 4% solution was shown less than in 20$^{\circ}$C and normal water. The dynamic modulus of elasticity and ultrasonic pulse velocity of each exposure mode was shown smaller in order of full immersion, wetting/drying, half imersion.3. The relation between dynamic modulus of elasticity and ultrasonic pulse velocity was highly significant. The dynamic modulus of elasticity was increased with increase of ultrasonic pulse velocity. The decreasing rate of the dynamic modulus of elasticity was shown 2.1~3.4 times higher than the ultrasonic pulse velocity at each age, exposure environment and mode, respectively. 4. The expansion of each exposure environment and mode was increased with increase of curing age. The dynamic modulus of elasticity and ultrasonic pulse velocity of those concrete was increased with increase of curing age. At the curing age 28 days, the highest properties was showed at each type concrete, it was gradually decreased with increase of curing age. Specially, at the curing age 98 days of full immersion, the rate of expansion of type D was shown 3.95 times higher than the type A. But the dynamic modulus of elasticity and ultrasonic pulse velocity was decreased 17% and 8.3%.

• Journal of Technologic Dentistry
• /
• v.42 no.3
• /
• pp.208-212
• /
• 2020

Purpose: This study aimed to analyze the shrinkage and expansion strain of ultraviolet (UV)-cured resin according to the wavelength of the light source and compare the shrinkage and expansion. Methods: We prepared the mold with according to the ISO 4049 specimen. The size of the circle in the mold was prepared with a height of 6.02 mm and a diameter of 4 mm. UV-curable resin for three-dimensional (3D) printing was injected into the circular mold. The control group was irradiated with a wavelength of 400~405 nm using UV-curing equipment (400 group), and the experimental group was irradiated with a wavelength of 460~465 nm (460 group). Both groups were produced ten specimens. The produced specimen was first measured with a digital micrometer. After the first measurement, the specimen was immersed in a constant temperature water bath for 15 days, after which the second measurement was performed, and the third measurement was taken after 30 days. The measured values were analyzed using the independent sample t-test (α=0.05). Results: In the non-immersion water tank, the contraction was 0.9% in the 400 group and 1.3% in the 460 group. In the constant temperature bath, the expansion was high at -0.4% in the 400 group for 15 days, and the smallest expansion was -0.03% for the 400 group for 30 days. There were significant differences between the two groups (p<0.05). Conclusion: The 400 group had a lower UV resin specimen strain than the 460 group. Therefore, it is recommended to use the wavelength required by the UV-curing resin.

• Journal of Korean Society on Water Environment
• /
• v.22 no.3
• /
• pp.397-405
• /
• 2006

Since the first sewage treatment plant had been in operation in 1976, the Korean water industry was in the logarithmic growing stage corresponded with the country's rapid economic expansion up to late 1990's. Unfortunately, however, the current industry status seems to require not only new paradigm for water environment but the development of new growth engine, since there are various warning signals for stalling growth from the field engineers to policy makers. Because of sharing of the awareness, the Korean government recently launched an ambitious development policy for water industry. This paper describes the new paradigm-shift in water environment in view point of the water as renewable resources. Based on the new paradigm, it has been suggested the prerequisite conditions to meet for the development of a new Korean water industry.

• Journal of Korea Water Resources Association
• /
• v.33 no.S1
• /
• pp.415-421
• /
• 2000

• Proceedings of the Korea Water Resources Association Conference
• /
• 2010.05a
• /
• pp.122-126
• /
• 2010

This paper elaborates on difficulties when ones tried to apply domestically developed technology to other countries from both technical and sociological aspects. Next, the author proposes possible solutions to expand the applicability of domestic technology. The main one is breaking down a technology to smaller components so that anybody can clarify the applicability of each component. The author presents an example of this methodology to flood hazard mapping.

• Tunnel and Underground Space
• /
• v.7 no.1
• /
• pp.13-19
• /
• 1997

It is necessary to study on thermo-hydro-mechanical effect at rock mass performing project such as radiowaste disposal in deep rock mass. In this study, thermo-hydro-mechanical coupling analysis which is considered interaction and the variation of rock properties induced by temperature increase was performed for the circular shaft when appling temperature of 20$0^{\circ}C$ at the shaft wall. The shaft is diameter of 2 m and under hydrostatic stress of 5 MPa. In the cases, thermal expansion by temperature increase progress from the wall to outward and thermal expansion could induce tensile stress over the tensile strength of rock mass at the wall. When rock properties were given as a function of temperature, thermal expansion increased, tensile stress zone expanded. Lately, water flow is activated by increase of permeability and decrease of viscosity.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2000.03b
• /
• pp.231-238
• /
• 2000

Sand piling method is one of the most widely used methods to improve soft soils. There are several methods to install sand piles, but driven pile method is considered as one of the easiest method. This method simply pushes down the sand piles into soft soils, so that the excess pore pressure would be generated if the soil is saturated. This pore pressure acts as consolidation load. If the amount of sand pile induced pore pressure can be predicted in reasonable ways, the effects of sand piling to improve soft soils would be predicted, and the height of preload can be reduced. In this article, sand pile induced excess pressure was predicted by cavity expansion theory, and the predicted values were compared with the field measured values. The results showed fair agreements between the measured and the predicted excess pore pressure.

• Journal of the korean Society of Automotive Engineers
• /
• v.15 no.1
• /
• pp.45-54
• /
• 1993

The reattachment lengths of the Non-Newtonian fluid are investigated in the sudden expansion pipes whose ratios are 2.316 and 3.368, and the range of the Reynolds numbers is 100-30000. The reattachment lengths for the viscoelastic fluid in the laminar flow region are found to be much shorter than those of the Newtonian fluid, and decrease significantly with the increase of the concentration of viscoelastic fluid is two or three times longer than those of water, and gradually increases with the increase of the concentration of viscoelastic fluid.

• Journal of the Korean Society of Safety
• /
• v.25 no.4
• /
• pp.25-29
• /
• 2010

Foam concentrate is used for fire-extinguishing purposes, occurring foam, mixed with air. In huge oil-fire or the efficiency of fire-extinguishing with small quantity of water, Foam concentrate is used widely. However, perfluorooc tanoicsulfonate and nonylpenol that are included in Foam concentrate could be exposure in danger while they were discharged. The purpose of the research is the development of environment-friendly high expansion foam that exclude the dangerous substances and improvement of danger of the existing foam concentrate. The developed foam is analyzed as the environment-friendly foam in indexes of the environment-toxicity, the biodegradation appraisal, and the dangerous substances-detecting. In addition, the performances of expansion rate, discharge rate, and fire-extinguishing are suitable in the domestic regulation, so it is useful for fire-extinguishing in real fire situation.

• The KSFM Journal of Fluid Machinery
• /
• v.12 no.5
• /
• pp.33-38
• /
• 2009

In this study, the effect of flow disturbance such as contraction, expansion pipe and velocity deviation from low velocity of $0.1\;^m/s$ to $2.5\;^m/s$ on the error characteristics of the flowmeter was studied. Flow experiments using flowmeter calibration facility of K-water were undertaken for the cases of ultrasonic flowmeter based on transit-time method and electromagnetic flowmeter. Experimental results are presented that measurement error of expansion pipe are larger than contraction pipe. It is shown that the minimum straight length were required to remain of ${\pm}0.5%$ error for electromagnetic flowmeter and ${\pm}2.0%$ error for ultrasonic flowmeter.