Session: 13-01-02 Blue Economy II

Paper Number: 102097

102097 - Novel Solution for Mitigating Sloshing in Floating Closed-Containment Aquaculture Tanks 

Marine aquaculture in floating closed containment tanks is a promising proposition for the seafood farming industry as it addresses many challenges of farming in open net pens, such as satisfying the contained water environment for healthy growth of fish, meets biosecurity requirements, solves the problem of sea lice, pathogen infections and predators and does not pollute the environment as wastes are collected and disposed in a responsible manner. Current floating closed containment structures typically have a relatively large free surface area and the contained fluid makes up most of the total mass. One major outstanding challenge is sloshing of water in the tanks when they are sited at more exposed farming sites. Significant sloshing affects the structural integrity of the containment tank, the day-to-day operation and fish well-being. As fish benefit from a calm, controlled environment with a free surface for air and sunlight, it is necessary to find an engineering solution to mitigate sloshing while live fish are in the tanks. A novel solution developed by University of Queensland (UQ) researchers is to install slosh suppression blocks placed at the top end of the tanks. These suppression blocks may be fabricated from HDPE material and they form an annular slab with its top surface in line with the internal water surface. These suppression blocks contract the free water surface and interfere with resonance by letting sloshing fluid overtop onto them. Experiments were carried out on a containment tank model fitted with slosh suppression blocks in the UQ wave flume. The experimental results demonstrated that appropriately designed slosh suppression blocks can mitigate resonant sloshing and sloshing amplitude while reducing the spread of turbulent eddies throughout the entire water volume in the containment tank. For rigid concrete containment tanks, sloshing amplitudes are governed by sloshing mode shapes with the circumferential wave number being equal to one. In this instance, based on the linear potential theory, wave diffraction software DIFFRAC may be used to determine the water motions in the containment tank and the expected sloshing amplitudes. The damping lid method may be used to quantify the internal sloshing amplitudes so that one can assess the effect of slosh suppression blocks. For effectiveness, the damping values are tuned to experimental sloshing amplitudes for different slosh suppression block widths. The findings of this study enable the formulation of design guidelines for determining the required slosh suppression block width for various wave amplitude to tank diameter ratios for maximum sloshing amplitude reduction.

Presenting Author: Johannes Wiegerink The University of Queensland

Presenting Author Biography: J.J. Wiegerink obtained his bachelor's degree in Aerospace engineering in 2012 at the Delft University of Technology. At the same university, in 2015, he received his MSc in Offshore Engineering. He specialized in floating structures and studied how motion compensation systems on ships affect the ship's dynamic behaviour. After working in the industry for four years, he started a PhD at the University of Queensland in Australia. His PhD aims to find solutions to make Floating Closed Containment Aquaculture systems suitable for working in higher energy environments by addressing the issues with sloshing.

Authors:

Johannes Wiegerink The University of Queensland
Tom Baldock The University of Queensland
David Callaghan The University of Queensland
Chien Ming Wang The University of Queensland