• Title/Summary/Keyword: 유동화

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Flow-Induced Noise Prediction for Submarines (잠수함 형상의 유동소음 해석기법 연구)

  • Yeo, Sang-Jae;Hong, Suk-Yoon;Song, Jee-Hun;Kwon, Hyun-Wung;Seol, Hanshin
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.24 no.7
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    • pp.930-938
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    • 2018

  • Underwater noise radiated from submarines is directly related to the probability of being detected by the sonar of an enemy vessel. Therefore, minimizing the noise of a submarine is essential for improving survival outcomes. For modern submarines, as the speed and size of a submarine increase and noise reduction technology is developed, interest in flow noise around the hull has been increasing. In this study, a noise analysis technique was developed to predict flow noise generated around a submarine shape considering the free surface effect. When a submarine is operated near a free surface, turbulence-induced noise due to the turbulence of the flow and bubble noise from breaking waves arise. First, to analyze the flow around a submarine, VOF-based incompressible two-phase flow analysis was performed to derive flow field data and the shape of the free surface around the submarine. Turbulence-induced noise was analyzed by applying permeable FW-H, which is an acoustic analogy technique. Bubble noise was derived through a noise model for breaking waves based on the turbulent kinetic energy distribution results obtained from the CFD results. The analysis method developed was verified by comparison with experimental results for a submarine model measured in a Large Cavitation Tunnel (LCT).

  • https://doi.org/10.7837/kosomes.2018.24.7.930 인용 PDF KSCI

Characteristics of Fluidized Bed Type Gasification of Kideco Coal (키데코탄의 유동층 가스화 반응 특성)

  • Bae, Dal-Hee;Jo, Sung-Ho;Shun, Do-Won;Moon, Young-Sub
    • Journal of Energy Engineering
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    • v.16 no.1 s.49
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    • pp.32-39
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    • 2007

  • Coal pyrolysis processes vary with the origin and rank of coal. It is difficult to generalize the characteristics of coal pyrolysis reaction because the process consists of numerous reactions including pyrolysis, gasification, and combustion. To find out the optimum process condition it is necessary to determine the condition fur each coal from the smatter scale experiment. In this study pressurized ($2kg_{f}/cm^{2}$) fluidized bed, low temperature ($735{\sim}831^{\circ}C$) gasification using Kideco coal was performed. The reaction condition and product gas composition were determined from the variables including steam flow rate, coal feed rate and air flow rate. Optimum reaction condition was determined from the concentrations of $H_{2}$, and CO in the product gas. The ratio of air/coal was 4.45 and that of steam/coal was 0.21 respectively. The concentrations of CO and $H_{2}$ decreased with the increase of $CO_{2}$. It is important to control the feed rates of coal and steam because the reaction temperature rapidly increased when the combustion reaction dominates over the gasification reaction. The concentrations of CO and $H_{2}$ were 18%, 17% respectively from the continuous operating condition.

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Effect of Grid, Turbulence Modeling and Discretization on the Solution of CFD (격자, 난류모형 및 이산화 방법이 유동해석 결과에 미치는 영향)

  • Park, Dong-Woo;Yoon, Hyun-Sik
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.20 no.4
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    • pp.419-425
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    • 2014

  • The current work investigated the variation of numerical solutions according to the grid number, the distance of the first grid point off the ship surface, turbulence modeling and discretization. The subject vessel is KVLCC. A commercial code, Gridgen V15 and FLUENT were used the generation of the ship hull surface and spatial system and flow computation. The first part of examination, the effect of solutions were accessed depending on the grid number, turbulence modeling and discretization. The second part was focus on the suitable selection of the distance of the first grid point off the ship surface: $Y_P+$. When grid number and discretization were fixed the same value, the friction resistance showed differences within 1 % but the pressure resistance showed big differences 9 % depending on the turbulence modeling. When $Y_P+$ were set 30 and 50 for the same discretization, friction resistance showed almost same results within 1 % according to the turbulence modeling. However, when $Y_P+$ were fixed 100, friction resistance showed more differences of 3 % compared to $Y_P+$ of 30 and 50. Whereas pressure resistance showed big differences of 10 % regardless of turbulence modeling. When turbulence modeling and discretization were set the same value, friction, pressure and total resistance showed almost same result within 0.3 % depending on the grid number. Lastly, When turbulence modeling and discretization were fixed the same value, the friction resistance showed differences within 5~8 % but the pressure resistance showed small differences depending on the $Y_P+$.

  • https://doi.org/10.7837/kosomes.2014.20.4.419 인용 PDF KSCI