Suppression of sloshing in liquefied natural gas during ocean-going transportation by using spherical floaters and blanket

Malaysia National Key Economic Area (NKEA) is endeavouring to promote the liquefied natural gas (LNG) as one of the dominant greener energy resources which significantly benefits Malaysia as the world's third-largest exporter of LNG. However, safer sea transportation of LNG is in high demands because sloshing of liquid bulks can cause structural damage and disastrous safety issue towards the LNG carrier. Conventional methods, such as baffle inside the liquid tank still has major problems as it could be damaged by very violent liquid sloshing and require regular inspection. On the other hand, floaters and blanket have been proven as a more effective solution. However, a better understanding of the behaviours of floaters and blanket is needed to design more effective anti-sloshing devices, which have huge potential benefits to Malaysian LNG transporters. In this paper, sloshing experiment under random unidirectional excitations was conducted to investigate the effectiveness of liquid surface suppression by using floaters and blanket. The results of the liquid free surface without suppressors, liquid surface covered by scattered floaters and liquid surface covered by blanket were analysed and discussed. The findings are expected to contribute to the design of anti-sloshing devices towards safer sea transportation of LNG which could largely benefit our nation

Sloshing in a closed domain under unidirectional excitation

1145-1153Sloshing is a phenomenon where a partially filled tank is exerted into various environmental sea conditions, such as wave and wind. Sloshing in a tank of liquefied natural gas carrier can lead to structural damage of tank structures and motion instability of the carrier. Thus, sloshing analysis needs to be conducted beforehand to minimize the risk of damages. This paper presents experimental and numerical study on sloshing phenomenon in a prismatic membrane tank model under unidirectional excitation with 30% water filling condition. A regular wave motion stimulated by the linear actuator was applied to the model tank and recorded by a video camera. Meanwhile, OpenFoam software was used to simulate the sloshing numerically in a volume of fluid method based on Navier-Stokes theorem. The sloshing patterns and free surface elevation in the prismatic membrane model tank, with the same input amplitude and frequency, were investigated for both cases. Both experimental and simulation results showed reasonable agreement on the sloshing profile, while the internal free surface elevation in the closed domain indicated a deviation with maximum absolute error of 4.9 cm

Sloshing suppression by floating baffle

Sloshing is a phenomenon which may lead to dynamic stability and damages on the local structure of the tank. Hence, several anti-sloshing devices are introduced in order to reduce the impact pressure and free surface elevation of liquid. A fixed baffle is the most prevailing anti-sloshing mechanism compared to the other methods. However, the additional of the baffle as the internal structure of the LNG tank can lead to frequent damages in long-term usage as this structure absorbs the sloshing loads and thus increases the maintenance cost and downtime. In this paper, a novel type of floating baffle is proposed to suppress the sloshing effect in LNG tank without the need for reconstructing the tank. The sloshing phenomenon in a membrane type LNG tank model was excited under sway motion with 30% and 50% filling condition in the model test. A regular motion by a linear actuator was applied to the tank model at different amplitudes and constant period at 1.1 seconds. Three pressure sensors were installed on the tank wall to measure the impact pressure, and a high-speed camera was utilized to record the sloshing motion. The floater baffle was modeled on the basis of uniform-discretization of domain and tested based on parametric variations. Data of pressure sensors were collected for cases without- and with-floating baffle. The results indicated successful reduction of surface run-up and impulsive pressure by using a floating baffle. The findings are expected to bring significant impacts towards safer sea transportation of LNG