• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.1162-1167
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• 2006

Because the mixing efficiency is influenced remarkably by varying the geometrical configurations, the study of flow characteristics inside the agitator is very important. The draught tube in the agitator makes intermixing between the screw and tube by interrupting radial flow, and the helical screw agitator with a draught tube (HSA) is proved more efficient to mix than the others. Consequently, the shapes of helical screw and number of pitches are the main parameters for improving the performance of HSA. In this study, numerical analyses were carried out, using a commercial CFD code, Fluent, to obtain the velocity and pressure distributions under steady, laminar flow and no-slip condition. Results are graphically depicted with various parameters.

• The KSFM Journal of Fluid Machinery
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• v.10 no.1 s.40
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• pp.56-63
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• 2007

Because the mixing efficiency is influenced remarkably by varying the geometrical configurations, the study of flow characteristics inside the mechanical agitator is very important to improve the performances. The draught tube in the agitator makes intermixing between the screw and tube by interrupting radial flow, and it makes circulation region in a mixing chamber. In general, the helical screw agitator with a draught tube (HSA) is proved more efficient to mix than the others. Consequently, such as the shapes of helical screw, number of pitches and the variation of angular velocity are the main parameters for improving the capacity of HSA. And also the suspension of the solid particles in the agitator can be determined these parameters. The rate of solids suspension in the mixing chamber was quantified with a statistical average value, of. Numerical analyses were carried out, using a commercial CFD code, Fluent, to obtain the velocity, pressure and particle distributions under steady, laminar flow and no-slip conditions. Results are graphically depicted with various parameters.

• Journal of the Korean Society of Safety
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• v.9 no.3
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• pp.67-73
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• 1994

The gas holdup and volumeteric liquid phase mass transfer coefficient with the variation of the concentration of CMC aqueous solution, gas velocity, diameter and area of the draught tube were investigated. As the results of the experiments, the gas holdup and volumetric liquid phase mass transfer coefficient decreased with decreasing the concentration of CMC aqueous solution, increased with increasing the gas velocity and increased with increasing the circulated area ratio of the draught tube.

• KSBB Journal
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• v.11 no.3
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• pp.353-359
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• 1996

The experiments were conducted in the leaching of aqueous uranium from low-grade uranium ore by Thiobacillus ferrooxidans. The optimal concentration of ferrous iron in 9K medium was 16.2g/L when the uranium ore concentration in slurry was 40g/L. The leaching rates were increased by decreasing the particle size of uranium ore and by increasing uranium ore concentration. In the leaching experiments in an agitated vessel reactor, only 39.3% of uranium was leached out within 12 days, which was comparable as that in the shaking incubator, without any notable improvement. Hence, it was observed that an agitated vessel reactor was not effective in the leaching of uranium from uranium ore by T. ferrooxidans. In the leaching experiments in a draught-tube reactor, the maximum concentration of uranium leached and cell number were a 12.8mg/L and $2.47{\times}1010cells/mL$ respectively. The uranium yield reached up to 91.4% within 11 days culture due to enhanced aeration and mixing characteristics of draught-tube reactor as compared to agitated vessel reactor.

• Smart Structures and Systems
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• v.9 no.1
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• pp.71-104
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• 2012

In this research, a typical tension-leg type of floating platform incorporated with an innovative concept of underwater tuned liquid column damper system (UWTLCD) is studied. The purpose of this study is to improve the structural safety by means of mitigating the wave induced vibrations and stresses on the offshore floating Tension Leg Platform (TLP) system. Based on some encouraging results from a previous study, where a Tuned Liquid Column Damper (TLCD) system was employed in a floating platform system to reduce the vibration of the main structure, in this study, the traditional TLCD system was modified and tested. Firstly, the orifice-tube was replaced with a smaller horizontal tube and secondly, the TLCD system was combined into the pontoon system under the platform. The modification creates a multipurpose pontoon system associated with vibration mitigation function. On the other hand, the UWTLCD that is installed underwater instead would not occupy any additional space on the platform and yet provide buoyancy to the system. Experimental tests were performed for the mitigation effect and parameters besides the wave conditions, such as pontoon draught and liquid-length in the TLCD were taken into account in the test. It is found that the accurately tuned UWTLCD system could effectively reduce the dynamic response of the offshore platform system in terms of both the vibration amplitude and tensile forces measured in the mooring tethers.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.4
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• pp.412-418
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• 2020

Generally, the propeller shaft that constitutes the ship shaft system has different patterns of behavior due to the ef ects of engine power, propeller load and eccentric thrust, which increases the risk of bearing failure by causing local load variations. To prevent this, different studies of the propulsion shaft system have been conducted focused the relative inclination angle and oil film retention between the shaft and the support bearing, mainly with respect to the Rules for the Classification of Steel Ships. However, in order to secure the stability of the propulsion shaft via a more detailed evaluation, it is necessary to consider dynamic conditions, including the transient state due to sudden change in the stern wakefield. In this context, a 50,000 DWT vessel was analyzed using the strain gauge method, and the effects of propeller shaft movement were analyzed on the starboard rudder turn which is a typical transient state during normal continuous rate(NCR) operation in ballast draught condition. Analysis results confirm that the changed propeller eccentric thrust acts as a force that temporarily pushes down the shaft to increase the local load of the stern tube bearing and negatively affects the stability of the shaft system.