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

Numerical analysis of point absorber for wave energy conversion in Malaysian seas

Wave energy conversion by using point absorber has recently gained intensive research in renewable energy. However, a majority of research works only focused on the regions with high wave heights, which may not be readily achievable in Malaysian seas condition. As the technology of point absorber facing the concern on less-applicability in low wave height conditions in Malaysia, a numerical modeling to understand the maximum potential power output to be generated by point absorber is now in demand to predict the power capture ability of point absorber in Malaysian waters. In order to complete this research gap, this paper is aiming to determine the sensitivity of different configurations of power take-off system in point absorber and to numerically analyze the potential maximum power output to be generated by the point absorber in Malaysian water, under regular wave motion. The significance of this study leads to a better understanding of the envelope of power output generated by point absorber in Malaysian seas. The methodology is conducted with theoretical modeling of point absorber, developing a numerical model of power take-off system to identify the maximum magnetic flux density of different stator-translator configuration, and simulating the power output of point absorber in time-domain under regular wave condition based on Malaysia seas data. The results show that power output of point absorber can be increased by a double-sided stator. The envelope of maximum power output to be generated has been identified. This research provides a further understanding of the development of point absorber technologies in Malaysian seas condition

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

Suppression of hydrodynamic sloshing in liquefied natural gas tank with floating baffle: Experimental and numerical studies

A fixed anti-sloshing mechanism such as baffles which modifies the tank structure may lead to increment of the maintenance cost. This paper proposes a floating baffle, and reviews its investigation on the sloshing behaviour in a membrane-type tank model under unidirectional excitation with 30% and 50% of filling ratio. An LNG tank was numerically simulated in OpenFOAM under regular sinusoidal motion with an amplitude of 3 cm and excitation frequency set to the natural frequency at 1.1 seconds. Impulsive pressure on the tank wall was obtained, and then benchmarked with the experimental results from the pressure sensors. The simulation and experiment results showed an acceptable agreement with a root mean squared error of less than 10%. The findings are expected to become a significant reference for safer sea transportations such as conventional LNG vessels