• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.252-252
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• 2003

• Environmental Engineering Research
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• v.10 no.1
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• pp.15-21
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• 2005

A computer program is developed for the prediction of the flow pattern and the removal efficiency of suspended solid (SS) in a circular secondary clarifier. In this study the increased density effect by SS on hydrodynamics has been systematically investigated in terms of Froude Number (Fr), baffle existence, and a couple of important empirical models associated with the particle settling and Reynolds stresses. A control-volume based-finite difference method by Patankar is employed together with the SIMPLEC algorithm for the resolution of pressure-velocity coupling. The k-ε turbulence and its modified version are incorporated for the evaluation of Reynolds stresses. The calculation results predicts well the overall flow pattern such as the waterfall phenomenon at the front end of the clarifier and the bottom density current with the formation of strong recirculation especially for the case of decrease of Fr. Even if there are some noticeable differences in the prediction of two turbulence models, the calculated results of the radial velocity profiles are generally in good agreement against experimental data appeared in open literature. Parametric investigation has been systematically made with the Fr and baffle condition with detailed analysis.

• Journal of the Korea Computer Graphics Society
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• v.23 no.1
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• pp.17-24
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• 2017

We propose an efficient method to express water spray effects by adaptively modeling air particles in particle-based water simulation. In real world, water and air continuously interacts with each other around free surfaces and this phenomenon is commonly observed in waterfall or sea with rough waves. Due to thin spray water, the interfaces between water and air become vague and the interactions between them lead to heavy vortex phenomenon. To express this phenomenon, we propose methods of 1) generating adaptive air cell in particle-based water simulation, 2) expressing water spray effects by creating and evolving air particles in the adaptive air cells, and 3) guaranteeing robustness of simulation by solving drifting problem occurred when adjacent air particles are insufficient. Experiments convincingly demonstrate that the proposed approach is efficient and easy to use while delivering high-quality results.

• Journal of Digital Contents Society
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• v.11 no.4
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• pp.579-588
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• 2010

Generalization of the web, development of one-person media such as the blog and mini homepage, and integration of video digital devices have generalized multimedia video services on the web. However, flash videos, the previously used bit map-based multimedia videos, exhibit problems like the waterfall phenomenon, lag phenomenon, or non-synchronization of audios or videos. Thereupon, This study is conducted to suggest a converting technique to provide efficient web video service on the web by solving problems of bitmap-based flash video through file format-converting software and movie editing programs. And this paper also conducts experiments on five videos for 13 CODECs and analyzes converted results comparatively. The recommendable method considering the characteristics of each videos is to utilize MainConcept H.264 Video CODEC using SWF2Video pro. The result of this research can be used to produce web videos on the web more effectively.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.179-190
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• 2011

The swirling flow developing in Francis turbine draft tube under part load operation leads to pressure fluctuations usually in the range of 0.2 to 0.4 times the runner rotational frequency resulting from the so-called vortex breakdown. For low cavitation number, the flow features a cavitation vortex rope animated with precession motion. Under given conditions, these pressure fluctuations may lead to undesirable pressure fluctuations in the entire hydraulic system and also produce active power oscillations. For the upper part load range, between 0.7 and 0.85 times the best efficiency discharge, pressure fluctuations may appear in a higher frequency range of 2 to 4 times the runner rotational speed and feature modulations with vortex rope precession. It has been pointed out that for this particular operating point, the vortex rope features elliptical cross section and is animated of a self-rotation. This paper presents an experimental investigation focusing on this peculiar phenomenon, defined as the upper part load vortex rope. The experimental investigation is carried out on a high specific speed Francis turbine scale model installed on a test rig of the EPFL Laboratory for Hydraulic Machines. The selected operating point corresponds to a discharge of 0.83 times the best efficiency discharge. Observations of the cavitation vortex carried out with high speed camera have been recorded and synchronized with pressure fluctuations measurements at the draft tube cone. First, the vortex rope self rotation frequency is evidenced and the related frequency is deduced. Then, the influence of the sigma cavitation number on vortex rope shape and pressure fluctuations is presented. The waterfall diagram of the pressure fluctuations evidences resonance effects with the hydraulic circuit. The influence of outlet bubble cavitation and air injection is also investigated for low cavitation number. The time evolution of the vortex rope volume is compared with pressure fluctuations time evolution using image processing. Finally, the influence of the Froude number on the vortex rope shape and the associated pressure fluctuations is analyzed by varying the rotational speed.