• Journal of Advanced Research in Ocean Engineering
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• v.2 no.3
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• pp.99-111
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• 2016

Seabed affected by scouring, sedimentation, and siltation occurrences often cause exposure, which induces risks to existing structures or crude oil or gas pipeline buried subsea. In order to prevent possible risks, more economical structure installation methodology is proposed in this study by predicting and managing the risk. Also, the seabed does not only consist of sandy material, but clayey soil is also widespread, and the effect of undrained shear strength should be considered, and by cyclic environmental load, pore water pressure will occur in the seabed, which reduces shear strength and allows particles to move easily. Based on previous research regarding sedimentation or erosion, the average value of external environmental loads should be applied; for scouring, a 100-year period of environmental conditions should be applied. Also, sedimentation and erosion are mainly categorized by the bed load and suspended load; also, they are calculated as the sum of bed load and suspended load, which can be obtained from the movement of particles caused by sedimentation or erosion.

• Journal of Powder Materials
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• v.13 no.4 s.57
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• pp.263-268
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• 2006

In this study, the colloidal stability and sedimentation behavior of crystalline $TiO_2$ particles (300nm) in various organic solvents have been investigated by means of a backscattered light flux profile (Turbiscan). The backscattered light flux profiles revealed that the $TiO_2$ nanoparticles were readily sedimented in water, methyl alcohol, and ethyl alcohol due to a flocculation-induced particle growth, while a particle coalescence and a sedimentation of the $TiO_2$ nanoparticles were hardly observed in isopropyl alcohol. The migration velocities of the $TiO_2$ particle were measured as around 6.15/min, 12.53 m/min, 6.51m/min, and 0.18m/min for water, methyl alcohol, ethyl alcohol, and isopropyl alcohol, respectively, showing a remarkably slow migration of the $TiO_2$ particles in isopropyl alcohol.

• Journal of Magnetics
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• v.20 no.3
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• pp.317-321
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• 2015

In this paper, magnetorheological fluids (MRFs) based on micro-sized iron particles dispersed in silicone oil are presented. The iron particles are modified by adding different ratios of oleic acid and lauric acid as surfactants to the suspensions. Lauric acid was found to reduce the stability of the MRFs, and more lauric acid results in a higher rate of sedimentation. Further study showed that the formation and structure of lauric acid may result in the sedimentation of micrometer-sized particles. Meanwhile, the electro-resistance of MRF in this paper shows a decrease from beyond $6000M{\Omega}$ to $190{\Omega}$ with an increase in the external field from 0 mT to 400 mT.

• Nuclear Engineering and Technology
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• v.48 no.2
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• pp.457-469
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• 2016

During the late phase of severe accidents of light water reactors, a porous debris bed is expected to develop on the bottom of the flooded reactor cavity after breakup of the melt in water. The geometrical configuration, i.e., internal and external characteristics, of the debris bed is significant for the adequate assessment of the coolability of the relocated corium. The internal structure of a debris bed was investigated experimentally using the DAVINCI (Debris bed research Apparatus for Validation of the bubble-Induced Natural Convection effect Issue) test facility. Particle sedimentation under the influence of a two-phase natural convection flow due to the decay heat in the debris bed was simulated by dropping various sizes of particles into a water vessel with air bubble injection from the bottom. Settled particles were collected and sieved to obtain the particle mass, size distribution in the radial and axial positions, and the bed porosity and permeability. The experimental results showed that the center part of the particle bed tended to have larger particles than the peripheral area. For the axial distribution, the lower layer had a higher fraction of larger particles. As the sedimentation progressed, the size distribution in the upper layers can shift to larger sizes because of the higher vapor generation rate and stronger flow intensity.

• Analytical Science and Technology
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• v.25 no.6
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• pp.476-482
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• 2012

Asian dust particles are known to have sizes ranging from a few nanometers up to about a few micrometers. The environmental and health effects depend on the size of the dust particles. The smaller, the farther they are transported, and the deeper they penetrate into the human respiratory system. Sedimentation field-flow fractionation (SdFFF) provides separation of nano to microparticles using a combination of centrifugal force and parabolic laminar flow in a channel. In this study, the steric mode of SdFFF (Sd/StFFF) was tested for size-based separation and characterization of Asian dust particles. Various SdFFF experimental parameters including flow rate, stop-flow time and field strength of the centrifugal field were optimized for the size analysis of Asian dust. The Sd/StFFF calibration curve showed a good linearity with $R^2$ value of 0.9983, and results showed an excellent capability of Sd/StFFF for a size-based separation of micron-sized particles.The optical microscopy (OM) was also used to study the size and the shape of the dust particles. The size distributions of the samples collected during a thick dust period were shifted towards larger sizes than those of the samples collected during thin dust periods. It was also observed that size distribution of the sample collected during dry period shifts further towards larger sizes than that of the samples collected during raining period, suggesting the sizes of the dust particle decrease during raining periods as the components adsorbed on the surface of the dust particles were removed by the rain water. Results show Sd/StFFFis a useful tool for size characterization of environmental particles such as the Asian dust.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.2
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• pp.191-200
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• 2004

DAF process has been designed considering raw water quality characteristics in Korea. Although direct filtration is usually operated, DAF is operated when the freshwater blooms occut or raw water turbidity become high. Pre-sedimentation iS prepared in case when raw water turbidity is very high by rainstorms. A main feature of this plant is that the operation mode can be changed (controlled) based on the characteristics of raw water to optimize the effluent quality and the operation costs. Treatment capacity (surface loading rate) and efficiency of DAF was found to be better than conventional sedimentation process. Moreover, low-density particles (algae and alum flocs) are easily separated while it is difficult to remove in sedimentation. One of the main concerns in adoption of DAF (Dissolved Air-Flotation) process is a high raw water turbidity problem. That is, DAF is not adequate for raw water, which is more turbid than 100NTU. In order to avoid this problem, pre-sedimentation basins are prepared in DAF plant to decrease the turbidity of DAF influent. For simulation of the actual operation, bench and full-scale tests were performed for highly turbid water conditions. Consequently, DAF process coupled with sedimentation is suggested that pre-sedimentation with optimum coagulation prior to DAF would be appropriate.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.3
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• pp.1247-1252
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• 2014

In the present study, sedimentation and shear stress of MR fluid are investigated to physical characteristics of MR fluid along temperature conditions. MR fluid is a suspension of micrometer-sized magnetic particles in a base liquid. Therefore, dispersion of MR fluid is important in the case of the design and optimization of the system using MR fluid. Due to sedimentation characteristics of MR fluid by magnetic particles, the sedimentation and shear stress of commercial MR fluid are investigated at $25^{\circ}C$ and $80^{\circ}C$ temperatures by using a forced convection oven and a viscometer. From experimental results, the sedimentation and shear stress are more affected by the temperatures of $80^{\circ}C$ than $25^{\circ}C$ and the mixing time of 5min than 10min. Shear stress by the applied current increases the shape of a quadratic equation and are lower 6-18% at $80^{\circ}C$ than $25^{\circ}C$.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.5
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• pp.33-40
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• 2002

The purpose of this study is to find the variation of sedimentation patterns after Saemangeum reclamation. Residual flow after Saemangeum reclamation was calculated prognostically from the observed water temperature and salinity data in May 1992 by the Marine Development Institute of Gunsan National University and wind data which were obtained from spring 1969 through winter 1977 by the Kunsan Meteorological Observatory. Three dimensional movements of injected particles due to currents, turbulence and sinking velocity are tracked by the Euler-Lagrange method. When suspended sediments with the size of soil grain of 30 ㎛ are injected in the Sinsi drainage sluice, their dispersion range of sediment is around Gogunsan islands. When suspended sediments with the size of soil grain of 200 ㎛ are injected in the Garyeok drainage sluice, their dispersion range of sediment was around the Garyeok drainage sluice and Byeonsan coastal area.

• Journal of the Korean Ceramic Society
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• v.45 no.2
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• pp.99-104
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• 2008

Zeta potential, sedimentation bulk density and rheology in the dispersion system have been studied in terms of solid loading (40-55 vol%), and types of additives. Ammonium polymethacrylate, glycerol, ethoxylated acetylenic diol, and polyvinyl alcohol have been used as the dispersant, cryo-protectant, surfactant, and binder, respectively. Sedimentation density greatly increased upon adding dispersant; the effect was more pronounced with ionic alumina suspension compared with covalent silicon carbide. With further addition of cryo-protectant and surfactant to dispersant, the sedimentation density increased somewhat. The suspension viscosity generally behaviored in an opposite manner to the sedimentation density, i.e., high sedimentation gave low high-shear viscosity, indicative of low order structure formation in the suspended particles. Shear rate rheology in shear rate of $2-300\;sec^{-1}$ showed a shear thinning and its onset began at similar shear rate (${\sim}100\;sce^{-1}$), regardless of solid loading.

• Journal of the korean society of oceanography
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• v.31 no.2
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• pp.43-54
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• 1996

Jinhae Bay, one of the largest tidal bays on the southern coast of Korea, is an area with thick accumulations of recent, fine-grained sediments, mainly supplied from the Nakdong River. The preponderance of silt and clay particles reflects the large quantity of sediments transported in suspension. Although the clay mineral assemblage is similar to that derived from the nearby Nakdong River, relatively high concentration (3-9%) of smectite suggests some local input of fine particles from several streams around the bay or some contribution from the offshore water that may be influenced by the Tsushima Current. The content of organic matters in sediments is as high as 12%, and their C/N ratios imply that they are comprised of mixtures derived from marine plankton and terrestrial plants. $^{210}Pb$ excess activity profiles of sediment cores yield an average sedimentation rate (a 100-year time scale) of about 2-5 mm/yr, which coincides well with the long-term sedimentation rate (a 1000-year time scale) estimated from the sediment isopach map. On the basis of sediment bulk density and sedimentation rate, an annual sink of mud in the bay is estimated approximately 1.0 ${\times}$ $10^{6}$ tons per year.