• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.416-421
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• 2002

This paper dealt with an experimental study on the hydro-elastic vibration of clamped perforated rectangular plates submerged in water. The penetration of holes in the plates had a triangular pattern with P/D (pitch to diameter) 1.750, 2.125, 2.500, 3.000 and 3.750. The natural frequencies of the perforated plates in air were obtained by the analytical method based n the relation between the reference kinetic and maximum potential energy and compared with the experimental results. Good agreement between the results was found for the natural frequencies of the perforated plates in air. It was empirically found that the natural frequencies of the perforated plate in air increase with an increase of P/D, on the other hand, the natural frequencies of the perforated plate in contact with water decrease with an increase of P/D. Additionally, the effect of the submerged depth on the natural frequency was investigated.

• Corrosion Science and Technology
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• v.11 no.4
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• pp.141-150
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• 2012

Stress corrosion cracks in Alloy 600 compact tension specimens tested at $325^{\circ}C$ in a simulated primary water environment of pressurized water reactor were analyzed by analytical transmission electron microscopy and secondary ion mass spectroscopy (SIMS). From a fine-probe chemical analysis, oxygen was found on the grain boundary just ahead of the crack tip, and chromium oxides were precipitated on the crack tip and the grain boundary attacked by the oxygen diffusion, leaving a Cr/Fe depletion (or Ni enrichment) zone. The oxide layer inside the crack was revealed to consist of a double (inner and outer) layer. Chromium oxides existed in the inner layer, with NiO and (Ni,Cr) spinels in the outer layer. From the nano-SIMS analysis, oxygen was detected at the locations of intergranular chromium carbides ahead of the crack tip, which means that oxygen diffused into the grain boundary and oxidized the surfaces of the chromium carbides. The intergranular chromium carbide blunted the crack tip, thereby suppressing the crack propagation.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.13 no.5
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• pp.180-188
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• 2010

This study was carried out to evaluate the analysis of environmental change (forest resources and soil water conservation by land types) after planting for prevention of between 2003 and 2006 from the stone hazarding areas in Guizhou province, China. Mean diameter growth of the trees was highest for Melia azedarach, followed by Robinia pseudoacacia, Lonicera fulvotomentosa, Choerospondias axillaris, Cupressus duclouxiana, and Eucommia uimoides Oliv. Mean height growth of the trees was greatest for R. pseudoacacia, followed by Ilex kudincha, M. azedarach, C. duclouxiana, C. axillaris, E. uimoides Oliv, Zanthoxylum bungeanum, and L. fulvotomentosa. Tree biomass was greater at the afforestation sites by 1.22-1.71 ton/ha compared to that of severely eroded mountain areas. The capacities of soil water conservation by land types were 2,790 ton/ha at latent rock desertification farmland, 2,655 ton/ha at rock desertification farmland, 1,680 ton/ha at dolomite sandstone hilly country, 1,650 ton/ha at halfstony hilly country, and 1,590 ton/ha at karst physiognomy site. Soil erosion was estimated to be 1,285 ton/$km^2$ which had been 2,178 ton/$km^2$ before afforestation. Also, we should be continuative manage after planting for prevention of the stone hazarding areas in Guizhou province, China.

• Journal of the Korean Wood Science and Technology
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• v.47 no.4
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• pp.486-497
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• 2019

The non-isothermal and isothermal pyrolysis properties of H lignin and P lignin extracted from different biorefinery processes (such as supercritical water hydrolysis and fast pyrolysis) were studied using thermogravimetry analysis (TGA) and pyrolyzer-gas chromatography/mass spectrometry (Py-GC/MS). The lignins were characterized by ultimate/proximate analysis, FT-IR and GPC. Based on the thermogravimetry (TG) and derivative thermogravimetry (DTG) curves, the thermal decomposition stages were obtained and the pyrolysis products were analyzed at each thermal decomposition stage of non-isothermal pyrolysis. The isothermal pyrolysis of lignins was also carried out at 400, 500, and $600^{\circ}C$ to investigate the pyrolysis product distribution at each temperature. In non-isothermal pyrolysis, P lignin recovered from a fast pyrolysis process started to decompose and produced pyrolysis products at a lower temperature than H lignin recovered from a supercritical water hydrolysis process. In isothermal pyrolysis, guaiacyl and syringyl type were the major pyrolysis products at every temperature, while the amounts of p-hydroxyphenyl type and aromatic hydrocarbons increased with the pyrolysis temperature.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.5
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• pp.501-511
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• 2008

The Objective of this study is to examine the characteristic of fine aerosol $(PM_{2.5})$ obtained at Ieodo Ocean Research Station, which lies between the eastern part of China and the south western part of Korea. The average mass concentration of $PM_{2.5}$ was $21.5{\pm}17.0{\mu}g/m^3$ during June $2004{\sim}June 2006$. The concentration was the highest in winter $(34.8{\mu}g/m^3)$ and lowest in summer $(16.5{\mu}g/m^3)$. Water soluble ions were measured for samples collected from December 2004 to September 2005. Among them, $SO_4^{2-}\;and\;NH_4^+$ were the most abundant species and accounted for 32.2% and 14.2% of the $PM_{2.5}$ mass, respectively. The mass fraction of $SO_4^{2-}$ was higher in winter (42%) than in spring (26%). Nitrate concentrations were much lower than those of sulfate due mainly to evaporation during sampling period. The cluster analysis of backward airmass trajectories showed that the high mass loadings $(26.9{\mu}g/m^3\;on\;average)$ were associated with air originating inland China. Also, the seasonal variation of $PM_{2.5}$ mass was well correlated with the frequency of westerly winds passing through the western part of China. During the ABC-EAREX2005 (March 2005), $PM_{2.5}$ mass and major ionic concentrations were higher at Ieodo, compared with $PM_{2.5}$ measurements at Gosan while they were similar in variation pattern. These results suggested that $PM_{2.5}$ mass and its ionic composition of Ieodo Ocean Research Station were greatly influenced by continental outflows from China.

• Journal of Ocean Engineering and Technology
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• v.25 no.4
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• pp.7-11
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• 2011

The installation phase for a topside module suggested can be divided into 9 stages, which include start, pre-lifting, lifting, lifted, rotating, positioning, lowering, mating, and end of installation. The transfer of the topside module from a transport barge to a crane vessel takes place in the first three stages, from start to lifting, while the transfer of the module onto a floating spar hull occurs in the last three stages, from lowering to the end. The coupled multi-body motions are calculated in both calm water and in irregular waves with significant wave height (1.52m), with suggested force equilibrium diagrams. The effects of the hydrodynamic interactions between the crane vessel and barge during the lifting stage have been considered. The internal forces caused by the load transfer and ballasting are derived for the lifting phases. The results of these internal forces for the calm water condition are compared with those in the irregular sea condition. Although the effect of pitch motion on the relative vertical motion between the deck of the floating structure and the topside module is significant in the lifting phases, the internal force induced pitch motion is too small to show its influence. However, the effect of the internal force on the wave-induced heave responses in the lifting phases is noticeable in the irregular sea condition because the transfer mass-induced draught changes in the floating structure are observed to have higher amplitudes than the external force induced responses.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.1 s.12
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• pp.1-14
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• 2004

The objective of this study is firstly to frame up the seismic safety of concrete gravity dams. It is necessary to analyze seismic response and evaluate seismic performance of concrete gravity dams during earthquake. In this study, seismic damage and dynamic analysis of concrete gravity dams using structural analysis package such as SAP2000 and MIDAS were performed. Additional dynamic water pressure due to earthquake considered as additional mass for numerical seismic analysis. According detailed analysis, the vibration through the dam structure (transverse to water flow) seems to be very critical depending on the shape of the dam. For more precise evaluation of seismic fragility of concrete gravity dams, further research is still needed.

• Journal of the Korean Society of Visualization
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• v.18 no.2
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• pp.18-27
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• 2020

Air lift pump operated by buoyancy is mainly used for the continuous circulation and the purification of fluids. In this study, the computational flow analysis has been performed with the geometric and operating conditions of the air lift pump. The numerical data from the analysis have been verified by comparing with the previous experimental data. The following results are obtained which advance the efficiency of the air lift pump. As the submergence length of pipe increases and the pipe length over the water surface decreases, the non-dimensional mass flow ratio increases in both cases. When the position of the air injection hole is within the pipe, the circulation range of the surrounding fluid becomes widened with the distance between the air injection hole and the pipe inlet relatively becoming narrower. It is more efficient both when the air injection velocity is at 10 m/s and at 15 m/s, and when the diameter of the pipe with holes is doubled near the water surface. It is expected that these results can be provided as fundamental data for operating the air lift pump.

• Analytical Science and Technology
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• v.18 no.2
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• pp.154-162
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• 2005

Recently, 1,4-Dioxane is known as the contaminant in water plants in Korea. Owing to its toxicity and potential health effect, 1,4-Dioxane must be determined at very low levels in drinking water. Studies on the removal of 1,4-Dioxane in drinking water were performed by using multi filtration system with activated carbons and membrane filter. For extraction of 1,4-Dioxane, methyl-t-butyl ether (MTBE) was used and then analyzed using gas chromatography-mass selective detection (GC/MSD). Removal experiment was proceeded for 300 L with a sample volume of 30 L. At first. The removal was 70%, 95% and 100% after using activated carbon, membrane and second activated carbon respectively. At larger accumulated water fluxes, the removal rate decreased at each filter. After the flow volume was 300 L, the removal rate was 30%, 88% and 99% through the first activated carbon, membrane and second activated carbon respectively.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.1
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• pp.22-28
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• 2013

The heat transfer characteristics of LNG(Liquefied Natural Gas) vaporizer on the ship was performed by numerical simulation to get the optimum NG(Natural Gas) generating condition. The glycol-water was used for heating in LNG vaporizer, and the cooling water of main engine was used as heating souse for glycol-water. This cooling water temperature increases again after recirculating from the main engine, and then it can be used to heat the glycol-water. The numerical analysis results has good agreement with the experimental results by liquid nitrogen for validation. So CFD technique was used to simulate the heat transfer characteristics of LNG vaporizer on the ship. The numerical results show that the operation condition of LNG vaporizer shows NG temperature of $6^{\circ}C$ in the outlet of LNG vaporizer, and the mass flow rates of LNG and glycol-water were showed 0.111 kg/s and 1.805 kg/s, respectively.