The Hydrostatic Buckling of SPM Systems of Fish Cages and a Design Method to Prevent It

Abstract

This study presents an inherent buckling issue of SPM (Single Point Mooring) systems for open sea aquaculture and a design method to analyze and solve this issue. The SPM arrangement of a row of cages is very efficient, as it minimizes the anchoring load by masking of the current applied to the downstream cages, hence saves anchors and mooring lines. However, a sudden reversal of the current direction presents a risk of buckling of the row of cages, if it applies a compression load along the array of cages before rotation of the entire cage system takes place. This study presents the concept of Hydrostatic Buckling of a row of cages and a method of design and analysis to control the stability of the system at the situation of sudden current reversal. First, a simple method for preliminarily assessment by applying the principle of virtual work is formulated. Then, an analysis of the structure by a parametric finite elements code is presented. The reversal current limits for the stability of the structure, are parametrically studied, by the analyses of two hypothetical practical scenarios. This study presents practical design tools and results, such as the method of the analysis, simplified loading states for representing the critical events, the scantlings of the structure, as well as guidelines for designing a SPM system of cages that withstand critical situations of reversal current.

Keywords

• flexible submerged structures
• open sea aquaculture
• offshore cages
• single point mooring
• design method