• Journal of Ocean Engineering and Technology
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• v.31 no.3
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• pp.189-195
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• 2017

A three-dimensional higher order boundary element method based on the B-spline is presented. The method accurately models piecewise continuous bodies and induced velocity potentials using B-spline tensor product representations, and it is capable of obtaining accurate pointwise values for the potential and its derivatives, especially in the trailing edge and tip region of the lift generating body, which may be difficult or impossible to evaluate with constant panel methods. In addition, we implement a wake roll-up and examine the tip vortex formation in the near wake region. The results are compared with existing numerical results and the results of experiments performed out at the cavitation tunnel of Chungnam National University.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09b
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• pp.951-951
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• 2005

The characteristics of Boussinesq starting forced plumes were investigated in this study. Two distinct periods in the transient plume penetration were identified, namely the Period of Flow Development (PFD) and Period of Developed Flow (PDF). PFD refers to the time period whereby the penetration rate is governed by the complex vortex dynamics initiated by the exit conditions that can include vortex coalescence, vortex leapfrogging, pinching off of the head vortex from the trailing stem and the eventual reconnection. The pinch-off and reconnection leads to an overshoot of the plume front which is a common observation reported in previous studies. The penetration rate in PDF is more predictable and depends on the continuous feeding of buoyancy and momentum into the head vortex by the trailing buoyant-jet stem. Similarity solutions are developed for PDF to describe the temporal variation of the penetration rate, by incorporating the behavior of an isolated buoyant vortex ring and recent laboratory results on the trailing buoyant jet. In particular, the variations of velocity ratios between the head vortex and trailing buoyant jet are analytically computed. To verify the similarity solutions, experiments were conducted on vertical starting forced plumes using planar laser induced fluorescence (PLIF).

• Steel and Composite Structures
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• v.47 no.3
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• pp.355-363
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• 2023

The main purpose of this study is to characterize the size-dependent strain rate sensitivity in structural steel using the continue stiffness measurement (CSM) indentation. A series of experiments, such as CSM indentation and optical microscope examination, has been performed at the room temperature at different rate conditions. The results indicated that indentation hardness, strain rate, and flow stress showed size-dependent behavior. The dependency of indentation hardness, strain rate, and flow stress on the indentation size was attributed to the transition of the dislocation nucleation rate and the dislocation behaviors during the indentation process. Since both hardness and strain rate showed the size-dependent behavior, SRS tended to depend on the indentation depth. The results indicated that the SRS was quite high over 2.0 at the indentation depth of 240 nm and quickly dropping to 0.08, finally around 0.046 at large indents. The SRS values at large indentations strongly agree with the general range reported for several types of low-carbon steel in the literature (Chatfield and Rote 1974, Nguyen et al. 2018b, Luecke et al. 2005). The results from the present study can be used in both static and dynamic analyses of structures as well as to assess and understand the deformation mechanism and the stress-state of material underneath the indenter tip during the process of the indentation testing.

• Membrane Journal
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• v.4 no.1
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• pp.1-8
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• 1994

There are growing needs to produce relatively high purity(99.0% or higher) oxygen at low cost. For small scale production, both pressure swing adsorption(PSA) and membrane process are competitive and less expensive or more convenient than well known cryogenic fractionation technology. A continuous membrane column(CMC) combined with a PSA oxygen generator can be employed to produce high purity oxygen continuously. The oxygen enriched gas generated by a PSA unit, with a concentration of 93~94%, is fed to the CMC that consism of three modules of poly(imide) hollow fibers. Several experiments were conducted by varying parameters, such as feed flow rate, transmembrane pressure drop, stage cut, and feed location in order to obtain a high oxygen concentration above 99.0%. A two-series unit mode was also employed with CMC operation to optimize the given membrane area.

• Carbon letters
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• v.4 no.2
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• pp.64-68
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• 2003

A study on the electrosorption of uranium ions onto a porous activated carbon fiber (ACF) was performed to treat uraniumcontaining lagoon sludge. The result of the continuous flow-through cell electrosorption experiments showed that the applied negative potential increased the adsorption kinetics and capacity in comparison to the open-circuit potential (OCP) adsorption for uranium ions. Effective U(VI) removal is accomplished when a negative potential is applied to the activated carbon fiber (ACF) electrode. For a feed concentration of 100 mg/L, the concentration of U(VI) in the cell effluent is reduced to less than 1 mg/L. The selective removal of uranium ions from electrolyte was possible by the electrosorption process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2670-2677
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• 2002

The ring rolling process involves three-dimensional non-steady material flow and continuous change of radius and thickness of the ring workpiece. In this study, the deformation analysis and geometric updating algorithm of the ring rolling process were verified by using the three-dimensional rigid-plastic finite element method. Manufacturing processes for plain ring and T-shaped ring were investigated by comparing experiments with simulation results, especially in side spread, load-stroke and pressure distribution, showing a good agreement. It was concluded that the simulation method would be a useful tool for the design of a ring rolling process.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.11 s.176
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• pp.151-158
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• 2005

Micro-machine tool is essential in the micro/meso cutting for the sake of saving of space, resources, and energy. In this research, a micro-turning lathe was fabricated with piezoelectric feed drive mechanism, and motion of each axis was generated by stepwise mechanism with two piezo actuators. The resolution to drive the axis was $0.05{\mu}m$ and position accuracy less than $2{\mu}m$ was assured. From the positioning experiment, piezo feed mechanism is good enough for the micro machine tools. Many fuming experiments were carried out with diamond-cutting tools to evaluate cutting capability of a machine tool. Continuous flow type chip could be obtained even if the cutting speed was very low due to small diameter of workpiece. However, thorough investigation about machineability in micro/meso cutting is inevitable to assure high quality surface roughness in micro machine tool.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.2
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• pp.183-190
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• 2005

In the process of ice-slurry making, ice adhesion on cooling wall or in narrow flow Path disturbs continuous ice formation. In this study, the effect on the ice adhesion to cooling surface by some freezing experiments was investigated, quantitatively. Three types of solutions were frozen in various coating vessels with stirring. In the experiment, the ice adhesion between cooling wall and Ice-slurry was evaluated by measuring stirring power. From the result, the stirring power of slurry mixture in PTFE-coating vessel was smaller than those in PE-coating, PFA-coating and bare SUS vessel. Especially, in EG H PG 1.S/ HD 1.5 mass$\%$ solution, the stirring power in the PE-coating vessel was smaller than that in the PFA-coating or SUS vessel.

• Proceedings of the Membrane Society of Korea Conference
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• 1994.03a
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• pp.1-21
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• 1994

There are growing needs to produce relatively high purity (99.0% or higher) oxygen at low cost. For small scale production, both pressure swing adsorption (PSA) and membrane process are competitve and less expensive or more convient than well known crygenic fractionation technology. A continuous membrane colume (CMC) combined with a PSA oxygen generator can be employed to produce high purity oxygen continuosly. The oxygen-enriched gas generated by a PSA unit, with a concentration of 93-94%, is fed to the CMC that consists of three modules of poly(imide) hollow fibers. Several experiments were conducted by varying parameters, such feed flow rate, transmenbrane pressure drop, stage cut, and feed location in order to obtain a high oxygen concentration above 99.0%. A two-series unit mode was also employed with CMC operation to optimize the given membrane area.

• Journal of the Korean institute of surface engineering
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• v.29 no.2
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• pp.132-139
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• 1996

Experiments on the automatic control of NaOH concentration and on the spraying condition of NaOH solution in the alkaline degreasing process of a continuous hot-dip galvanizing line have been carried out in order to improve degreasing performance of a galvanizing sheet steel using laboratory degreasing and galvanizing simulators. The concentration of NaOH for the good degreasing has been determined to be 6.0% and more and this concentration has been able to be automatically well controlled within $\pm$0.1% by employing a solution electrical conductivity meter under a flow injection analysis condition rather than by employing a sodium ion selective electrode in the degreasing simulator. Frequent blocking of the spraying nozzles of the solution has been reduced considerably by the set-up and periodical operation of an automatic valve system in the nozzle system. By applying this automatic valve system and by automatic controlling the NaOH concentration and other ordinary variables in the degreasing process, the degreasing performance has been increased from the conventional 76% to the new 85%.