Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Experimental Investigation on Sloshing Mitigation Effect of Floating Foam Balls
Zhimin Zhou1, Jierao Dai2, Chongwei Zhang2, Peng Su2, Dezhi Ning2
1. Science and Technology on Underwater Test and Control Laboratory, the 760th Research Institute of China Shipbuilding Industry Corporation.
2. State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology.
Dalian, Liaoning Province, P. R. China

on sloshing. Nasar et al. (2019) experimentally explored the eﬀectivenessof porous baffles in a sloshing tank. Many other baffle configurations
were also considered, e. g. annual rigid baffles (Wang et al., 2013), dual
horizontal baffles (Lu et al., 2015), and T-type baffles (Wang et al., 2016).

ABSTRACTThis study considers an anti-sloshing technique based on floating foamballs. Physical experiments are conducted in a rectangular tank toinvestigate the sloshing mitigation effect (measured by the wave height
reduction factor, WHRF). Both the wave elevation and dynamic pressurein the sloshing tank are analyzed for different sizes of foam balls. It isfound that floating foam balls can help reduce the sloshing violence andthe corresponding pressure amplitude at the resonance condition. The
sloshing mitigation effect increases with the layer number of foam balls.
Meanwhile, for the sloshing tank with a fixed thickness of foam layer,
smaller foam balls have a stronger sloshing mitigation effect. The
sloshing mitigation effect tends to have positive correlation with thenumber of contacts of foam balls.

The concept of floating baffles was also considered. Floating baffles candynamically modify the natural sloshing frequencies. Koh et al. (2011)
and Koh et al. (2013) numerically and experimentally studied thedamping effect of a floating baffle. Yu et al. (2017) further used two
floating plates for sloshing suppression. Yu et al. (2019) subsequently
investigated perforated floating plates of various solidity ratios. The
perforated plate with a medium solidity ratio was found to be mosteffective among their cases.
Instead of baffles, Anai (2010) arranged membrane materials near thefree surface to restrain the sloshing. Kim et al. (2013) studied the conceptof using a deformable floating blanket. Chun et al. (2011) introduced asimilar system aiming to further help reduce the gas boil-off of LNG in
the tank. However, these solutions are expected to be expensive orcomplex to some extent. Sauret et al. (2015) carried out experiments
using liquid bubbles on the free surface in a sloshing tank. It is observedthat the liquid bubbles can help reduce liquid oscillations and dissipateenergy. Ning et al. (2019) proposed a sloshing mitigation concept byusing the floating foam layer made up of small solid foam elements. Thefoam layer may be considered as a ‘blanket’, although the tensile force
between any two neighboring elements is nonexistence. Zhang et al.
(2019) investigated the case using floating foam balls, with an analyticalsolution to help explain the experimental observations.

KEY WORDS: sloshing; anti-sloshing; floating foam; free surface;liquid tank.

INTRODUCTION
Sloshing as the liquid motion in a partly filled container is of great
concern to engineers of offshore floating liquefied natural gas (FLNG)
platforms. At a resonance condition, violent sloshing waves can cause
extreme dynamic impacts in the tank that seriously threaten the structuralsafety. Therefore, it is important to investigate proper sloshing mitigation
techniques.
At present, many researchers have paid attention to the method of
installing fixed baffles inside liquid tanks, taking advantage of baffle’s
energy dissipation effects due to flow separations. For example, Akyildiz(2012) simulated the 2D fluid motion in the tank with a vertical baffle.
Song et al. (2012) studied hydrodynamic characteristics in a liquid tankwith both horizontal and vertical baffles. Xue et al. (2017) conducted
physical experiments to investigate sloshing hydrodynamics in a squarebased liquid tank with vertical baffles of different configurations. Chu etal. (2018) investigated effects of spacing and height of multiple baffles

Following Zhang et al. (2019), this study will carry out physicalexperiments and further investigate effects of the size and statisticalproperties of foam balls on the sloshing suppression.

EXPERIMENT SET-UPS
Physical experiments are conducted on a low-frequency oscillation
platform in the State Key Laboratory of Coastal and Offshore

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