• Proceedings of the Korean Fiber Society Conference
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• 1988.06a
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• pp.30-31
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• 1988

• Environmental Engineering Research
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• v.21 no.3
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• pp.233-240
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• 2016

The research aims to study the different flexible rubber tube diffusers used in urban wastewater treatment processes and aquaculture systems. The experiment was conducted in small-scale aeration tank with different physical properties of the tubes that were used as aerators. The volumetric mass transfer coefficient ($k_La$), oxygen transfer efficiency (OTE) and aeration efficiency (AE) were measured and determined to compare the diffusers. Moreover, the bubble hydrodynamic parameters were analyzed in terms of bubble diameter ($d_B$) and rising velocity ($U_B$) by a high speed camera (2,000 frames/s). Then the interfacial area (a) and liquid-side mass transfer coefficient ($k_L$) can be calculated. The physical properties (tube wall thickness, tensile strength, orifice size, hardness and elongation) have been proven to be the key factor that controls the performance (kLa and OTE). The effects of hardness and elongation on bubble formation, orifice size and a-area were clearly proved. It is not necessary to generate too much fine bubbles to increase the a-area: this relates to high power consumption and the decrease of the kL. Finally, the wall thickness, elongation and hardness associated of the flexible tube diffuser (tube No. 12) were concluded, to be the suitable properties for practically producing, in this research.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.491-500
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• 2020

The present study proposes a time domain model for the Vortex-induced Vibration (VIV) simulation of a catenary riser under the combination of the current and oscillatory flow induced by vessel motion. In this model, the hydrodynamic force of VIV comprises excitation force, hydrodynamic damping and added mass, which are taken as functions of the non-dimensional frequency and amplitude ratio. The non-dimensional frequency is related with the response frequency, natural frequency, lock-in range and the fluid velocity. The relatively oscillatory flow induced by vessel motion is taken into account in the fluid velocity. Considering that the added mass coefficient and the non-dimensional frequency can affect each other, an iterative analysis is conducted at each time step to update the added mass coefficient and the natural frequency. This model is in detail validated against the published test models. The results show that the model can reasonably reflect the effect of the added mass coefficient on the VIV, and can well predict the riser's VIV under stationary and oscillatory flow induced by vessel motion. Based on the model, this study carries out the VIV simulation of a catenary riser with harmonic vessel motion. By analyzing the bending moment near the touchdown point, it is found that under the combination of the ocean current and oscillatory flow the vessel motion may decrease the VIV response, while increase the excited frequencies. In addition, the decreasing rate of the VIV under vessel surge is larger than that under vessel heave at small vessel motion velocity, while the situation becomes opposite at large vessel motion velocity.

• Journal of Environmental Science International
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• v.15 no.10
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• pp.951-960
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• 2006

The eco-hydrodynamic model was used to estimate the environmental capacity in Gamak Bay. It is composed of the three-dimensional hydrodynamic model for the simulation of water flow and ecosystem model for the simulation of phytoplankton. As the results of three-dimensional hydrodynamic simulation, the computed tidal currents are toward the inner part of bay through Yeosu Harbor and the southern mouth of the bay during the flood tide, and being in the opposite direction during the ebb tide. The computed residual currents were dominated southward flow at Yeosu Harbor and sea flow at mouth of bay, The comparison between the simulated and observed tidal ellipses at three station showed fairly good agreement. The distributions of COD in the Gamak bay were simulated and reproduced by an ecosystem model. The simulated results of COD were fairly good coincided with the observed values within relative error of 1.93%, correlation coefficient(r) of 0.88. In order to estimate the environmental capacity in Gamak bay, the simulations were performed by controlling quantitatively the pollution loads with an ecosystem model. In case the pollution loads including streams become 10 times as high as the present loads, the results showed the concentration of COD to be $1.33{\sim}4.74mg/{\ell}(mean\;2.28mg/{\ell})$, which is the third class criterion of Korean standards for marine water quality In case the pollution loads including streams become 30 times as high as the present loads, the results showed the concentration of COD to be $1.38{\sim}7.87mg/{\ell}(mean\;2.97mg/{\ell})$, which is the third class criterion of Korean standards for marine water quality. In case the pollution loads including streams become 50 times as high as the present loads, the results showed the concentration of COD to be $1.44{\sim}9.80mg/{\ell}(mean\;3.56mg/{\ell})$, which is the third class criterion of Korean standards for marine water quality.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.4
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• pp.174-186
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• 2004

Striations are growth-induced inhomogeneities which hamper the applications of solid-solution crystals and of doped crystals in numerous technologies. Thus the optimized performance of solid solutions often can not be exploited. The inhomogeneity problem can be solved in specific cases by achieving a distribution coefficient one in growth from melts and from solutions. Macrostep-induced striations can be suppressed by controlling the growth mode, by achieving growth on facets thereby preventing step bunching. Thermal striations are commonly assumed to be caused by convective instabilities so that reduced convection by microgravity or by damping magnetic fields was and is widely attempted to reduce such inhomogeneities. Here it will be shown that temperature fluctuations at the growth interface cause striations, and that hydrodynamic fluctuations in a quasi-isothermal growth system do not cause striations. The theoretically derived conditions were experimentally established and allowed the growth of striation-free crystals of $KTa_{1-x}Nb_xO_3$"KTN" solid solutions. Hydrodynamic variations from the accelerated crucible rotation technique ACRT did not cause striations as long as the temperature was controlled within $0.03^{\circ}$ at $1200^{\circ}C$ growth temperature. Alternative approaches to solve or reduce the segregation and striation problems in growth from melts and from solutions are discussed as well.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.682-691
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• 2005

This paper describes the design, fabrication, and testing of a microturbine developed at Seoul National University. Here, the term 'microturbine' refers to a radial turbine with a diameter on the order of a centimeter. Such devices can be used to transmit power for various systems. The turbine is designed using a commercial CFD code, and it has a design flow coefficient of 0.238 and work coefficient of 0.542. It has 31 stator blades and 24 rotor blades. A hydrodynamic journal bearing and hydrostatic thrust bearings counteract radial and axial forces on the rotor. The test turbine consists of a stack of five wafers and is fabricated by MEMS technology, using photolithography, DRIE, and bonding processes. The first, second, fourth, and fifth layers contain plumbing, and hydrostatic axial thrust bearings for the turbine. The third wafer contains the turbine's stator, rotor, and hydrodynamic journal bearings. Furthermore, a turbine test facility containing a flow control system and instrumentation has been designed and constructed. In performance tests, a maximum rotation speed of 11,400 rpm and flow rate of 16,000 sccm have been achieved.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.6
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• pp.623-630
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• 2013

This study was to evaluate hydrodynamic performance evaluation between an abroad product, a developed inflatable kayak and new developed kayaks. In order to test, inclining and turning trial test were carried out in the Ocean engineering Basin. Also, resistance test was carried out using a reduced scale model in the circulating water channel. In conclusion, stability of KONA was evaluated was the most greatest, the coefficient of resistance and center of gravity from RD-FK-12 were considerable, and turning performance of RD-FK-11 was greater than this of KONA and RD-FK-12.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.4 s.148
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• pp.460-466
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• 2006

The three-dimensional RANS equations were applied to analyze the flow field of a submarine. To validate the code, the DARPA SUBOFF bare hull and an eliipsoid at angles of attack of $10^{\circ}\;and\;30^{\circ}$ were simulated and good agreement with experiments was obtained. After the code validation, the flows over the full configuration of DARPA SUBOFF model having a fairwater and four stern appendages were simulated at four angles of attack $(0^{\circ},\;10^{\circ},\;20^{\circ},\;30^{\circ})$ and three yaw angles $(10^{\circ},\;20^{\circ},\;30^{\circ})$ Specifically, the pressure contours and streamlines of fairwater and stern appendage were compared as the angle of attack and yaw angle changed. The variations of hydrodynamic forces were also calculated.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.5
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• pp.465-472
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• 2011

Recently, ultra large scale of ship is being ordered continuously and because of that, the accurate prediction of ship maneuverability in design stage becomes important matter. The model test like PMM test or CFD analysis are representative methods for predicting the maneuverability of ship. In this study, the captive model tests were carried out for predicting maneuverability of MOERI container ship(KCS) which is opened to the public using X-Y Carriage of Ocean Engineering Wide Tank of University of Ulsan. Considering the dimensions of tank, 2m class model ship was used for captive model test. CMT(Circular Motion Test) was performed for obtaining purer hydrodynamic coefficients related to yawing velocity. For getting hydrodynamic coefficients which cannot be obtained using CMT, PMM test(Planar Motion Mechanism test) were also performed. The maneuverability prediction results by simulation are compared with those of other research institutes.

• Biotechnology and Bioprocess Engineering:BBE
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• v.11 no.3
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• pp.268-272
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• 2006

A dense, pellicular UpFront adsorbent ($p=1.5 g/cm^3$, UpFront Chromatography, Cophenhagen, Denmark) was characterized in terms of hydrodynamic properties and protein adsorption performance in expanded bed chromatography. Cibacron Blue 3GA was immobilised into the adsorbent and protein adsorption of bovine serum albumin (BSA) was selected to test the setup. The Bodenstein number and axial dispersion coefficient estimated for this dense pellicular adsorbent was 54 and $1.63{\times}10^{-5}m^2/s$, respectively, indicating a stable expanded bed. It could be shown that the BSA protein was captured by the adsorbent in the presence of 30% (w/v) of whole-yeast cells with an estimated dynamic binding capacity $(C/C_o = 0.01)$ of approximately 6.5 mg/mL adsorbent.