Experimental Observation of the Effects of Liquid Temperature and Bubbles on Impact Pressure Inside Gas Pocket
- Yonghwan Kim (Seoul National University) | Jeoungkyu Lee (Seoul National University) | Jieung Kim (Seoul National University)
- Document ID
- International Society of Offshore and Polar Engineers
- International Journal of Offshore and Polar Engineering
- Publication Date
- March 2017
- Document Type
- Journal Paper
- 1 - 10
- 2017. The International Society of Offshore and Polar Engineers
- bubble effects, LNG CCS design, sloshing impact, Sloshing, phase transition
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- 86 since 2007
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In this study, a series of drop tests were carried out to observe the effects of the impact pressure inside a gas pocket of water with different temperatures and/or a lot of bubbles. Cylindrical gas pockets were generated by dropping the body into the water with different temperatures and/or different bubble sizes. Dynamic pressures in gas pockets were measured by various types of pressure sensors installed on the disc that was part of the body. The results of this study are expected to be very useful in understanding the physical phenomena of sloshing inside real liquefied natural gas (LNG) cargo.
A liquefied natural gas (LNG) carrier involves sloshing issues due to partially filled LNG inside a cargo containment system (CCS). As the size of ships becomes larger with the LNG tank, the importance of a sloshing analysis inside the tank is increased. In order to investigate the sloshing phenomenon, plenty of studies have performed model tests rather than numerical analyses. In the traditional model test, Froude and geometric scaling have been generally applied, so the impact pressure measured in the model test used to be scaled up to full scale with those scaling laws. However, Froude scaling does not consider some physical phenomena, such as the phase transition and fluid-structure interaction, which occur during the impact. Although Froude scaling shows good agreement in global flow, there is limited accuracy in local impact. As the sloshing impact occurs due to local flow, it is necessary to find the appropriate scale parameter considering the fluid properties.
The local sloshing impact can be categorized into three modes: impact without a gas pocket, impact with a gas pocket between the liquid and the wall, and impact by a broken wave with mixed gas bubbles (Lugni et al., 2010). In the first mode, the incipient breaking wave leads to the formation of jet flow such as a flip-through event on a tank wall, and the impact pressure shows nonoscillating behavior due to the absence of a gas pocket. In other modes, the air-liquid interaction is considered during the impact. Especially in the second mode, entrapped pure gas generates the oscillation of the impact pressure. In the real sloshing problem, a phase transition occurs between the entrapped gas and surging liquid. In addition, a lot of bubbles are generated inside liquid during the violent sloshing flows, so a study of the gas pocket and bubbles should be conducted, which considers the characteristics of gas such as the density ratio between liquid and gas, ullage pressure, compressibility of gas, and phase transition.
|File Size||3 MB||Number of Pages||10|