• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.5
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• pp.639-650
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• 2022

In areas where large-scale sediment transport occurs, it is important to apply appropriate countermeasure method because the phenomenon tends to accelerate by time duration. Among the various countermeasure methods applied so far, beach nourishment needs to be reviewed as an erosion prevention measure because the erosion pattern is mitigated and environmentally friendly depending on the particle size. In the case of beach nourishment. a detailed review is required to determine the size, range, etc., of an appropriate particle diameter. In this study, we investigated the characteristics of the related topographic change using the change in the particle size of nourishment materials, the application of partial area, and the condition under the coexistence of waves and wind as variables because those factors are hard to be analyzed and interpreted within results and limitation of that the existing numerical models are not able to calculate and result out so that it is required that phenomenon or efforts are reviewed at the same time through physical model experiments, field monitoring and etc. So we attempt to reproduce the tendency of beach erosion and deposition and predict possible phenomena in the future using machine learning techniques for phenomena that it is not able to be interpreted by numerical models. we used the hydraulic experiment results for the training data, and the accuracy of the prediction results according to the change in the training method was simultaneously analyzed. As a result of the study it was found that topographic changes using machine learning tended to be similar to those of previous studies in short-term predictions, but we also found differences in the formation of scour and sandbars.

• Journal of the Korean Society of Radiology
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• v.15 no.5
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• pp.697-704
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• 2021

It is hard to get Filaments which are materials of the 3D printing Fused Deposition Modeling(FDM) method as radiation shielding in Korea. and also related research is insufficient. This study aims to provide basic data for the development of radiation shields using 3D printing by evaluating the physical properties and radiation shielding capabilities of filaments containing metal particles. after selecting five metal filaments containing metal particle reinforcement materials, the radiation shielding rate was calculated according to the Korean Industrial Standard's protective equipment test method to evaluate physical properties such as tensile strength, density, X-ray Diffraction(XRD), and weight measurement using ASTM's evaluation method. In the tensile strength evaluation, PLA + SS was the highest, ABS + W was the lowest, and ABS + W is 3.13 g/cm³ which value was the highest among the composite filaments in the density evaluation. As a result of the XRD, it may be confirmed that the XRD peak pattern of the particles on the surface of the specimen coincides with the pattern of each particle reinforcing material powder metal, and thus it was confirmed that the printed specimen contained powder metal. The shielding effect for each 3D printed composite filament was found to have a high shielding rate in proportion to the effective atomic number and density in the order of ABS + W, ABS + Bi, PLA+SS, PLA + Cu, and PLA + Al. In this study, it was confirmed that the metal particle composite filament containing metal powder as a reinforcing material has radiation shielding ability, and the possibility of using a radiation shielding filament in the future.

• Journal of Korea Water Resources Association
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• v.46 no.8
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• pp.821-831
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• 2013

Recently image velocimetries, including particle image velocimetry (PIV) and surface image velocimetry (SIV), are often used to measure flow velocities in laboratories and rivers. The most difficult point in using image velocimetries may be how to determine the sizes of the interrogation areas and the measurement uncertainties. Especially, it is a little hard for unskilled users to use these instruments, since any standardized measuring techniques or measurement uncertainties are not well evaluated. Sometimes the user's skill and understanding on the instruments may make a wide gap between velocity measurement results. The present study aims to evaluate image velocimetry's uncertainties due to the changes in the sizes of interrogation areas and searching areas with the error analyses. For the purpose, we generated 12 series of artificial images with known velocity fields and various numbers and sizes of particles. The analysis results showed that the accuracy of velocity measurements of the image velocimetry was significantly affected by the change of the size of interrogation area. Generally speaking, the error was reduced as the size of interrogation areas became small. For the same sizes of interrogation areas, the larger particle sizes and the larger number of particles resulted smaller errors. Especially, the errors of the image velocimetries were more affected by the number of particles rather than the sizes of them. As the sizes of interrogation areas were increased, the differences between the maximum and the minimum errors seemed to be reduced. For the size of the interrogation area whose average errors were less than 5%, the differences between the maximum and the minimum errors seemed a little large. For the case, in other words, the uncertainty of the velocity measurements of the image velocimetry was large. In the viewpoint of the particle density, the size of the interrogation area was small for large particle density cases. For the cases of large number of particle and small particle density, however, the minimum size of interrogation area became smaller.

• Korean Journal of Breeding Science
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• v.42 no.1
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• pp.61-74
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• 2010

Flour characteristics of 26 Korean wheat cultivars (KWC) were evaluated to assess consumer satisfaction with 6 imported wheat and 5 commercial wheat flours. In physical characteristics of flours, Particle size of SW (soft white) was similar to Dahong, Geuru, Milsung, Olgeuru, Seodun, Tapdong, and Uri. DNS (dark northern spring) was similar to Jeokjoong, Joeun, Sukang, and Younbaek. Ash and damaged starch content of KWC was similar to that of imported wheat and commercial flour (Com), but lightness value ($L^*$) were lower than those of Com. Particle size of flour positively correlated with ash, damaged starch, and lightness value ($L^*$) of flour. L ($^*$) value of flour negatively correlated with ash, damaged starch, and particle size of flour. In protein characteristics, Protein content of SW and commercial flour for baking cookie (Com5) was similar to Baekjoong, Jinpoom, Milsung, Olgeuru, Saeol, and Uri. HRW (hard red winter) and commercial flour for baking bread (Com3) was similar to Hanbaek, Joeun, Jopoom, Keumkang, and Sukang. SDS sedimentation volume based on a constant flour weight (SDSS) of KWC was lower than those of DNS and Com3. Mixograph water absorption of KWC similar to imported wheat and Com. Mixing time and maximum dough height (Hm) of KWC were higher than those of imported wheat and Com. Protein content positively correlated with SDS sedimentation volume and water absorption of mixograph. SDS-sedimentation volume positively correlated with water absorption of mixograph, mixing time of mixograph, and height of dough development. In starch characteristics of flour, ASW (Australian standard white) flours showed lower amylose content, higher peak viscosity, breakdown, and setback in pasting properties than other flours. KWV flours showed higher amylose content and lower peak viscosity than those of AH (Australian hard), ASW, commercial flour for making white salted noodles (Com1), commercial flour for making yellow alkaline noodles (Com2), and Com3.

• Food Science and Preservation
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• v.22 no.2
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• pp.174-181
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• 2015

This study investigated the physicochemical properties of three different types of rice flour prepared via dry and wet milling. The powder, soft, and hard-types of rice flour were Suwon No. 542, Suwon No. 541, and Unbong No. 30, respectively. The analysis of the proximate compositions of the different types of rice flour showed that their moisture content was 7.03~7.99%, their crude protein was 7.94~8.35%, their crude lipid was 0.71~1.49% and their crude ash was 0.25~0.82%. For the Hunter's color values, the L value was highest in the wet-milled rice flour, the a value was highest in the dry-milled rice flour, and the b value was highest in the dry-milled rice flour. All the samples showed distinctive rice starch particles in the particle analysis using scanning electron microscope. The dry-milled rice flour showed the greatest amount of irregular particles and the coarsest texture. The water absorption and water solubility indices were higher in the wet-milled soft- and hard-type rice flour. The crystallinities of the samples by X-ray diffractography were all A-type, but the crystallinity of the dry-milled hard-type rice flour was higher in diffraction degree. For the amylogram properties, the wet-milled soft-type rice flour showed the highest maximum viscosity, breakdown and setback. In the meanwhile, the dry-milled soft-type rice flour showed the highest initial pasting temperature, onset, peak, and end temperatures despite of the reverse enthalpy.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.4
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• pp.589-609
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• 2017

This study carried out the density and energy dispersive X-ray spectroscopy and particle size analysis which are the physical characteristics of coal dust by collecting samples of coal dust in the five domestic mines to control the coal dust through ventilation in the workplace for coal mining in the country. This will contribute to a more comfortable working environment by understanding the physical characteristics of the coal dust which is derived from any hard coal produced domestically. In particular, the result of PSA analysis showed that the size of coal dust sample for this study ranged from $0.007{\sim}88.614{\mu}m$ were the particles less than $3.5{\mu}m$, the size range responsible for pneumoconiosis. To observe the flow of coal dust collected on the wind speed, the fallout of coal dust produced by the wind tunnel for the wind was measured and the particle size analysis of coal dust fallout was carried out. In addition, airborne dust is measured according to the mine velocity by using a multi-stage Anderson sampler in the mine where fine dust is generated in a large amount and the wind speed is found out to control the coal dust below $3.5{\mu}m$. In addition, natural ventilation pressure of A mine was calculated to prevent over design of the main fan.

• Geomechanics and Engineering
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• v.9 no.5
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• pp.619-629
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• 2015

Influenced by various mining activities, fractures in rock masses have different densities, set numbers and lengths, which induce different mechanical properties and failure modes of rock masses. Therefore, precisely expressing the failure criterion of the fractured rock influenced by coal mining is significant for the support design, safety assessment and disaster prevention of underground mining engineering subjected to multiple mining activities. By adopting PFC2D particle flow simulation software, this study investigated the propagation and fractal evolution laws of the micro cracks occurring in two typical kinds of rocks under uniaxial compressive condition. Furthermore, it calculated compressive strengths of the rocks with different confining pressures and box-counting dimensions. Moreover, the quantitative relation between the box-counting dimension of the rocks and the empirical parameters m and s in Hoek-Brown strength criterion was established. Results showed that with the increase of the strain, the box-counting dimension of the rocks first increased slowly at the beginning and then exhibited an exponential increase approximately. In the case of small strains of same value, the box-counting dimensions of hard rocks were smaller than those of weak rocks, while the former increased rapidly and were larger than the latter under large strain. The results also presented that there was a negative correlation between the parameters m and s in Hoek-Brown strength criterion and the box-counting dimension of the rocks suffering from variable mining activities. In other words, as the box-counting dimensions increased, the parameters m and s decreased linearly, and their relationship could be described using first order polynomial function.

• Journal of the Korean Society for Marine Environment & Energy
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• v.17 no.2
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• pp.104-115
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• 2014

Abundance and composition of marine debris on 13 beaches of Tongyeong City, South Korea were surveyed in 2013 Autumn. The average quantity of macro debris (>25 mm) was about 30 particle/$m^2$ and that of micro debris (1 mm-25 mm) was about 26,971 particle/$m^2$. This is a very high level compared with other areas of South Korea and the other countries. Among the 7 material types of debris (styrofoam, hard plastic, fiber, metal, glass, wood and others), styrofoam composed a large portion: 75% of macro debris and 98% of micro debris. And among the 'whole' styrofoam debris items whose original volume is remained more than 50%, styrofoam buoy debris composed 93%. This result suggests that the beaches surveyed are seriously contaminated by marine debris, and most of its sources are aquaculture styrofoam buoys. Management of styrofoam buoy debris used for oyster aquaculture in Tongyeong City is important not only for Tongyeong city, but also for other areas, because Tongyeong city hosts the biggest number of oyster aquaculture areas in South Korea.

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.449-454
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• 2016

In this study, highly monodispersed porous carbon microcapsules with a hollow core were synthesized using polystyrene (PS) beads as a hard template. The surface of PS was first modified with polyvinylpyrollidone (PVP) for the easy attachment of inorganic silica sol. After coating the surface of PVP modified PS microspheres with SBA-16 sol, the carbon microcapsules with a hollow macroporous core were fabricated through reverse replication method by filling carbon sources in the mesopores of silica mold. The hollow carbons having a mesoporous shell structure and narrow particle size distribution could be obtained after the carbonization of carbon source and the dissolution of silica mold by HF solution. The mesoporous characteristics and electrochemical properties of hollow carbon microcapsules were characterized by XRD, SEM, TEM, $N_2$ adsorption/desorption analysis and cyclic voltammetry. They showed the high electric conductivity and capability for use as efficient electro-materials such as a supercapacitor.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.3
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• pp.353-360
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• 2006

This study identified a particle size distribution (PSD) of fine particulate matter and emission characteristics of V and Ni by the comparison between anthropogenic sources of oil combustion (industrial boiler, oil power plant, etc.) and lab-scale combustion using a drop-tube furnace. In oil combustion source, the mass fraction of fine particles (less than 2.5 micrometers in diameter) was higher than that of coarse particles (larger than 2.5 micrometers in diameter) in $PM_{10}$ (less than 10 micrometers in diameter) as like in lab-scale oil combustion. In addition to this, it was identified that ultra-fine particles (less than 0.1 micrometers in diameter) had a large distribution in fine particles. Toxic metals like V and Ni had large mass fractions in fine particles, and most of all was distributed in ultra-fine particles. Most of ultra-fine particles containing toxic metals have been emitted into ambient by combustion source because it is hard to control by the existing air pollution control device. Hence, we must be careful on these pollutants because it is obvious that these are associated with adverse health and environmental effect.