• Journal of the Korean Society for Marine Environment & Energy
• /
• v.9 no.2
• /
• pp.79-84
• /
• 2006

The present study deals with the flow over a flat plate with repeated roughness elements of 2-dimensional rectangular shape, which can be applied into the study on the natural geographical roughness and the turbulent flow on roughened solid surface. Experiment was performed using PIV technique in the circulating water channel. Results showed that the flow over roughness elements was characterized by the high shear flow emanating from top of roughness element and the recirculating region formed at the trough of two roughness elements. In general, the ratio between the spacing and the height of roughness elements plays a crucial role in developing the flow pattern near wall surface.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.9 no.2
• /
• pp.85-91
• /
• 2006

This study deals with the flow over a flat plate with repeated roughness elements of 2-dimensional rectangular shape, which can be applied into the study on the natural geographical roughness and the turbulent flow on roughened solid surface. Part 1 of the study showed that the ratio between the spacing and the height of roughness elements plays a crucial role in developing the flow pattern near wall surface. The present study complements the turbulence characteristics, the utilization of friction velocity as well as integral parameters. Results confirmed that k-type roughness(s/H=7 or 14) is certainly a more effective means than d-type roughness (s/H=3.5) in thickening the viscous region.

• Korean Chemical Engineering Research
• /
• v.58 no.4
• /
• pp.624-634
• /
• 2020

The ability of natural and modified clay to adsorb phenol was studied. The clay samples were analyzed by different technical instruments, such as X-ray fluorescence (XRF), X-ray diffraction (XRD) and FT-IR spectroscopy. Surface area, pore volume and average pore diameter were also determined using B.E.T method. Up to 73 and 99% of phenol was successfully adsorbed by natural and activated clay, respectively, from the aqueous solution. The experiments carried out show that the time required to reach the equilibrium of phenol adsorption on all the samples is very close to 60 min. The amount of phenol adsorbed shows a declining trend with higher pH as well as with lower pH, with most extreme elimination of phenol at pH 4. The adsorption of phenol increases proportionally with the initial phenol concentration. The maximum adsorption capacity at 25 ℃ and pH 4 was 29.661 mg/g for modified clay (NaMt). However, the effect of temperature on phenol adsorption was not significant. The simple modification causes the formation of smaller pores in the solid particles, resulting in a higher surface area of NaMt. The equilibrium results in aqueous systems were well fitted by the Freundlich isotherm equation (R² > 0.98). Kinetic studies showed that the adsorption process is best described by the pseudo-second-order kinetics (R² > 0.99). The adsorption of phenol on natural and modified clay was spontaneous and exothermal.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• v.38 no.6
• /
• pp.332-336
• /
• 2012

Objectives: This study sought to evaluate fixation methods and determine the best method for the postoperative stabilization of maxillary osteotomy. For our analysis we performed a three-dimensional finite element analysis of stress distribution on the plate, screw, and surrounding bone, as well as displacement onto the plate. Materials and Methods: We generated a model using synthetic skull scan data; an initital surface model was changed to a solid model using software. Modified anterior segmental osteotomy (using Park's method) was made using the program, and four different types of fixation methods were used. An anterior load of 100 N was applied on the palatal surface of two central incisors. Results: The Type 1 (L-shaped) fixation method gave stresses of 187.8 MPa at the plate, 45.8 MPa at the screw, and 15.4 MPa at the bone around the plate. The Type 2 (I-shaped) fixation method gave stresses of 186.6 MPa at the plate, 75.7 MPa at the screw, and 13.8 MPa at the bone around the plate. The Type 3 (inverted L-shaped) fixation method gave stresses of 28.6 MPa at the plate, 29.9 MPa at the screw, and 15.3 MPa at the bone around the plate. The Type 4 (I-shaped) fixation method gave stresses of 34.8 MPa at the plate, 36.9 MPa at the screw, and 14.9 MPa at the bone around the plate. The deflection of the plates for the four fixation methods was 0.014 mm, 0.022 mm, 0.017 mm, and 0.018 mm, respectively. Conclusion: The Type 3 (inverted L-shaped) fixation method offers more stability than the other fixation methods. We therefore recommend this method for the postoperative stabilization of maxillary osteotomy.

• Journal of the Korean Ceramic Society
• /
• v.52 no.6
• /
• pp.497-501
• /
• 2015

Inkjet printing is a widespread technology, offering advantages such as high-quality decoration, a continuous process, and the accurate direct reproduction of patterns or pictures. In inkjet printing technology, the dispersion stability of ceramic ink is one of the most important factors. In this study, the dispersion stability of blue $CoAl_2O_4$ ink for ceramic inkjet printing is systematically investigated. Blue $CoAl_2O_4$ pigment was synthesized by a solid-state reaction and then milled to less than 300nm in size. In order to investigate the influence of the viscosity on the dispersion stability, two types of $CoAl_2O_4$ ceramic inks (termed here Blue L and Blue H) were prepared using different volume ratios of ethylene glycol and ethanol. The Blue L and Blue H ink solutions contained cetyltrimethylammonium bromide(CTAB) as a dispersive agent. The viscosity, surface tension and jetting stability of the $CoAl_2O_4$ ceramic inks were analyzed using a rheometer, a surface tension meter and a dropwatcher. The dispersion stability of the $CoAl_2O_4$ ceramic ink was investigated by a multiple light-scattering method. Blue H, a ceramic ink with higher viscosity, showed much better dispersion stability than the Blue L ceramic ink.

• Journal of the Korean Ceramic Society
• /
• v.54 no.1
• /
• pp.23-27
• /
• 2017

A series of $CeO_2-TiO_2$ composite samples with different Ce/Ti molar ratios were prepared by the paper template. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to confirm a face-centered cubic lattice of $CeO_2$ with Ce/Ti =8:2 or 9:1 and a two phase mixture of anatase titania and face-centered cubic ceria with Ce/Ti = 7 : 3. The field emission scanning electron microscopy (FESEM) results suggest that the products are micron braid structures consisting of fibers with diameters in a range of $1-6{\mu}m$ and lengths of several hundred micrometers. $N_2$ absorption-desorption testing shows that the composite at Ce/Ti molar fraction of 8 : 2 has the largest BET surface area (about $81m^2{\cdot}g^{-1}$). Compared to the pure $CeO_2$ sample, the composites show superior catalytic activity for $H_2$ reduction and CO oxidation. For the micron braid structure $CeO_2-TiO_2$ composite (Ce/Ti = 8 : 2), due to the high surface area and the solid solution with appropriate $Ti^{4+}$ incorporation, the CO conversion at about $280^{\circ}C$ was above 50% and at $400^{\circ}C$ was 100%.

• Korean Chemical Engineering Research
• /
• v.49 no.2
• /
• pp.155-160
• /
• 2011

Dimethyl ether draws an attention as a green fuel in recent years. In this study, we investigated dehydration of methanol to produce DME using solid-acid catalysts, a series of zeolite. We found that ceria took a role of promoting the reaction conversion as well as selectivity of DME formation as a cocatalyst to the zeolite catalyst. We varied Si/Al ratio and ceria percentage on the surface of the catalyst to get high performance catalyst. ZSM5-30 with 5 wt% ceria on the surface was found to have excellent DME selectivity and to be little influenced by water content in methanol feed. We proposed a reaction model and obtained kinetic parameters for the DME formation using the catalyst based on experimental results using a microreactor.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• v.38 no.5
• /
• pp.271-275
• /
• 2012

Objectives: This study evaluated a range of fixation methods to determine which is best for the postoperative stabilization of a mandibular osteotomy using three-dimensional finite element analysis of the stress distribution on the plate, screw and surrounding bone and displacement of the lower incisors. Materials and Methods: The model was generated using the synthetic skull scan data, and the surface model was changed to a solid model using software. Bilateral sagittal split ramus osteotomy was performed using the program, and 8 different types of fixation methods were evaluated. A vertical load of 10 N was applied to the occlusal surface of the first molar. Results: In the case of bicortical screws, von-Mises stress on the screws and screw hole and deflection of the lower central incisor were minimal in type 2 (inverted L pattern with 3 bicortical repositioning screws). In the case of plates, von-Mises stress was minimal in type 8 (fixation 5 mm above the inferior border of the mandible with 1 metal plate and 4 monocortical screws), and deflection of the lower central incisor was minimal in types 6 (fixation 5 mm below the superior border of the mandible with 1 metal plate and 4 monocortical screws) and 7 (fixation 12 mm below the superior border of the mandible with 1 metal plate and 4 monocortical screws). Conclusion: Types 2 and 6 fixation methods provide better stability than the others.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.2
• /
• pp.125-130
• /
• 2012

The nematode Caenorhabditis elegans is a widely used model organism in biological research. Thanks to the availability of well-established knowledge about its neural connectivity, a wide range of studies have been attempted to uncover the relationship between behaviors and the responsible neurons. In our research, the adaptive behavior of C. elegans in solid environments with different surface rigidities is investigated, where the worm adapts to different mechanical stiffnesses by modulating its crawling waveform. The amplitude and wavelength of the crawling waveform decrease as the environment becomes more rigid. Interestingly, the mechanosensation-defective mutant shows different responses to the surface rigidity compared to those of the wild-type worm. To explain the adaptation process in mechanically different environments, we suggest a plausible neural circuit model.

• Structural Engineering and Mechanics
• /
• v.61 no.3
• /
• pp.407-417
• /
• 2017

RC shear walls are considered one of the main lateral resisting members in buildings. In recent years, FRP has been widely utilized in order to strengthen and retrofit concrete structures. A number of experimental studies used CFRP sheets as an external bracing system for retrofitting of RC shear walls. It has been found that the common mode of failure is the debonding of the CFRP-concrete adhesive material. In this study, behavior of RC shear wall was investigated with three different micro models. The analysis included 2D model using plane stress element, 3D model using shell element and 3D model using solid element. To allow for the debonding mode of failure, the adhesive layer was modeled using cohesive surface-to-surface interaction model at 3D analysis model and node-to-node interaction method using Cartesian elastic-plastic connector element at 2D analysis model. The FE model results are validated comparing the experimental results in the literature. It is shown that the proposed FE model can predict the modes of failure due to debonding of CFRP and behavior of CFRP strengthened RC shear wall reasonably well. Additionally, using 2D plane stress model, many parameters on the behavior of the cohesive surfaces are investigated such as fracture energy, interfacial shear stress, partial bonding, proposed CFRP anchor location and using different bracing of CFRP strips. Using two anchors near end of each diagonal CFRP strips delay the end debonding and increase the ductility for RC shear walls.