Slosh Suppression Blocks - A concept for mitigating fluid motions in floating closed containment fish pen in high energy environments

Abstract

This paper introduces a new concept to mitigate sloshing, tailored to floating closed containment aquaculture systems, termed slosh suppression blocks. Slosh suppression blocks reduce the natural sloshing periods by contracting the free surface area without any significant reduction of the operational volume in the tank, and can be retrofitted to existing systems. Sloshing energy is dissipated on top of the suppression blocks, out of the fluid domain to reduce the spread of turbulent eddies in the main body of the fluid in the tank. The fundamental idea and working principles of the slosh suppression blocks are illustrated with an experimental setup representing a 2D section of a closed-containment system under forced horizontal excitations. Maximum sloshing amplitudes are compared for 25 different test configurations for a range of excitation frequencies, using cubic slosh suppression blocks of different sizes. For selected configurations, the fluid's internal state is assessed by visualising the fluid motions both experimentally and by numerical simulations. The results show that slosh suppression blocks reduce the total sloshing volume and turbulent motions within the main body of the tank, providing a much calmer, controlled low energy living environment which is regarded essential for fish wellbeing. It is found that positioning the top of the slosh suppression blocks flush with the still water level mitigates and damps internal sloshing most effectively. To quantify and characterise the degree of slosh suppression, three slosh indices are introduced; the slosh reduction index, the slosh overtopping index and the slosh free surface index. The novel concept of slosh suppression blocks provides an important step forward in the design of floating closed containment aquaculture tanks that minimises sloshing and internal fluid motions in energetic environments.