This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

As fish farming is becoming increasingly important worldwide, ongoing investigations aim to numerically calculate and experimentally analyse highly stressed wire connections, such as those found in offshore fish farming cages, to provide a basis for more accurate lifetime estimation. The challenge is to recognise possible wire breaks that can occur due to different environmental conditions during the product life cycle of a cage and to be able to derive suggestions that increase the system service life. This is done on the one hand for financial reasons and on the other to prevent the mixing of farmed and wild fish through escapes. In order to improve the possibility of understanding the behaviour of high-strength stainless steel wires from which the cages are made, structural calculation models are being set up, which will ultimately be compared with the experimental behaviour of the structures in the laboratory and in operation. Test series of quasi-static tensile tests performed on both straight wire specimens and the smallest part of a wire mesh (referred to as One-link) provide data for the design and validation of a finite element model in the context of a non-linear structural analysis. At the same time, in order to optimize the calculation efficiency, a possibility is sought to dispense with 3D modelling of the entire fish farm. Here, the approach of a spring stiffness substitute model is used, with which it is possible to represent the wire mesh periphery around one or more interconnected One-links (3x5 or more). Clamping devices specially developed for the experiments are used for the testing purpose, with which wire connections (One-Link and a Mesh segment of 3x5 connected One-Links) can be stressed in a defined way for a consistent generation of comparable data, which is then compared with the simulation results. These results and findings are used as adaption of the calculation models and form the basis for further simulations. In addition to the static strength investigations and the assessments of other effects that may occur during operation, fatigue tests (up to 2 million load cycles) provide new insights, allowing the prediction of potential fatigue damage due to operational loads such as waves or water flow. With the results of fluid-structure interaction calculations, the loads on a fish farm cage depending on the flow conditions can be determined, conclusions can ultimately be drawn about the site-specific service life. All tests and simulations are conducted without considering the corrosive effects of the water in which fish farming is carried out. Previous studies on stainless steels and their behaviour in corrosive environments are linked to this investigation to make lifetime predictions even more accurate.