Reduce Aquaculture Biological Footprint With Fluid-Structure Interaction Simulations

Aquaculture, which has existed since 1000 BCE, is gaining widespread recognition for its potential to provide sustainable fish products. This form of farming, also known as captive breeding, is the go-to method for fish farmers to satisfy the growing demand for seafood and freshwater fish. In aquaculture farming, choosing the right location is substantial for healthy breeding, such as having continuous flow and away from high sound pressure, i.e., underwater radiated noises (URNS) which can be four times higher than in air. Unfortunately, inadequate planning and execution have slowed down aquaculture production growth, but we have a solution: fluid-structure interaction studies can help design robust and sustainable fish cage nets that minimize stagnation and ensure successful fish production. Together let’s reduce the aquaculture biological footprint and make it a sustainable and exciting future toward the blue revolution!

Aquaculture started off at a small scale in ponds, and as the market grew, it was necessary to identify other means of cultivating them on a large scale, such as in an open sea. That’s when fish cages came into the picture. These cages are often equipped with mooring systems to keep them in fixed positions or to avoid excessive movement due to winds, water currents, and other environmental factors. Managing the nets adds a significant workload on a sea cage farm, which demands the use of specialized equipment. The netting material’s solidity determines the extent to which the net can withstand the different hydrodynamic forces, and the solidity ratio is used to describe how ‘tight’ the net is. As per Norwegian standards NS 9415, the breaking strength of the net inside water should not fall below 65% of its initial strength.

Although often located in isolated regions, fish farms are not immune to the negative effects of pollution, parasitic infections, and insufficient oxygen levels. These factors can contribute to a stressful environment for the fish, resulting in poor health and heightened vulnerability to infections. Therefore, it is imperative to create fish farms designed to dissolve waste and avoid water stagnation. Control units, such as flow meters, pH meters, etc., can effectively maintain an environment that supports healthy breeding. Moreover, cultivating clams, mussels, and oysters can also filter out the dissolved waste from the water.

Reduce stagnation in fish cages with fluid-structure interaction studies

When designing a fish cage, it is essential to consider the flow and heat transfer aspects, as they can significantly impact the product’s durability and structure. By using computer analysis and simulation, potential risks can be identified early in the design process, which is more cost-effective than constructing physical models. For modeling, simulating, and analyzing fluid-structure interactions in fish cage nets, computational fluid dynamics (CFD)/finite element analysis (FEA) is the most effective tool. For example, these tools can help decide on the best fish cage material to withstand extreme weather conditions and optimize the nets’ arrangement, i.e., the distance between the cages and the number of cages in a row, to avoid stagnation and enhance fish production.

A crucial relationship exists between fish behavior and net solidity at high currents. Knowing the net’s solidity is essential to simulate the flow through and around the fish farm. The findings from a CFD simulation and full-scale study on flow through fish cages of different net solidities suggest that having two rows of cages is more advantageous for water exchange. The flow velocity increased when there were two rows compared to the study with one row. Interestingly, altering the distance between cage centers did not significantly impact the flow rate. However, researchers did notice a slight increase in velocity in the last cage when the distance between centers was increased. These results suggest that multiple rows of cages may be the best option for optimizing water exchange and flow velocity.

Cadence CFD solutions offer dedicated, virtual naval architecture and marine design tools for free surface modeling and scalable, highly automated optimization processes. Our tools can be used for fluid-structure interaction studies in fish cages like the one mentioned above and for optimizing the design of aquaculture cages with multiple objectives and constraints.

Reference

Winthereig-Rasmussen, H., et al., Flow through fish farming sea cages: Comparing computational fluid dynamics simulations with scaled and full-scale experimental data. Ocean Eng. (2016), https://doi.org/10.1016/j.oceaneng.2016.07.027