Session: 12-01-01 Blue Economy I

Submission Number: 157750

Experimental Testing and Calibrated Mechanical-Hydrodynamic Modelling of Net for a Modular Fish Pen 

This study aims to provide calibrated models for accurate analysis of a lightweight modular fish pen. The modular fish pen uses a commercial lightweight net with high strength, and antibiofouling resistance. The net is made from PET monofilament with mass density of 1380 kg/m³. It is a knotless hexagonal mesh net with nominal diameter of 2.5mm, mesh size of 35mm and solidity ratio of 0.15. The net is not only to keep the fish in the pen and withstand the wave and current actions but also to protect the fish from predators such as seals and sharks.

Mechanical properties of the net are studied using physical testing in the Structures Laboratory of Griffith University. Owing to its orthotropic behaviour, the in-plane tensile tests were carried out on a net mesh with a size of 1m × 1m in two orthogonal directions. The out-of-plane properties were measured by applying a central patch load and measuring deformations in different points on the mesh. To predict the reduced capacity of the net due to wear and tear, out-of-plane tests were carried out on a net with a local damage zone.

The results of the in-plane tests show a breaking force of 48.8kN and displacement of 670mm in the longitudinal direction. In the lateral direction, a breaking force of 12.9kN and displacement of 1047.5mm were obtained. The net exhibited a significantly higher breaking force in the longitudinal direction, but its displacement at break was about 64% of the lateral displacement. The out-of-plane test results show breaking forces of 14.1kN and 3.96kN, with displacements of 344mm and 202mm on the new and damaged nets respectively. The damage induced on the net significantly reduced its stiffness. These out-of-plane results are important to ascertain the capacity of the net to withstand sharks and seals attacks.

The data from the experimental tests are then used to model the modular fish pen including the effect of stiffness of the net in the commercial package, AquaSim. The Aquasim model has been initially calibrated to the experimental test results of a conventional fish pen. The simulation results provide deeper understanding of the overall contribution of the net on the hydrodynamic performance of the modular fish pen.

Presenting Author: Lazarus Gyang Griffith University

Presenting Author Biography: Lazarus Gyang is a structural engineer with more than 6 years of experience in the planning, design, and construction of various civil engineering projects. He holds a BSc (hons) in Civil Engineering from University of East London and MSc in Structural Engineering from University of Putra Malaysia (UPM). He is passionate about the development of marine and offshore structures; hence he focused his MSc research on development of a concrete barge for floating offshore wind turbine. He is currently pursuing a PhD in Structural Engineering at Griffith University, Australia, focused on the development of aquaculture fish pen from lightweight materials. It is his goal to be an active contributor to the development of offshore engineering structures worldwide.