BILLUND AQUACULTURE

At Kirkholm Maskiningeniører, we have a collaboration with the company Billund Aquaculture, which supplies turnkey RAS systems to most of the world. Recirculating Aquaculture Systems (RAS) is an environmentally friendly and efficient method for modern fish farming in places, where there is limited access to fresh water. Up to 99% of the water is recycled in RAS fish farming, and the purification of ammonium in particular, is done by biofiltration.

The circulation of the water in the tanks is therefore incredibly important to ensure water quality. The correct flow ensures that the water is cleaned optimally, and that unwanted sediment does not build up in tanks due to pockets of stagnant water.

As two RAS plants are rarely the same, and the requirements for plant capacity continue to increase, there is a need to be able to design new plants quickly and efficiently with a high level of safety. The large construction costs require that the facility functions are planned from day one. Not only from an efficiency point of view, but also to ensure that the fish thrive optimally, that the quality of the fish is as high as desired and not least to limit the environmental impact of fish farming as much as possible.

Advantages of simulation software

The big advantage of CFD simulations is that you reduce risk and optimize the result relatively quick. It is often an advantage to simulate in the virtual world before starting a large and expensive project, which many have already learned the expensive way. There is positive economy in discovering design errors before the actual construction begins, as the costs of correcting errors increase dramatically as the project progresses.

Therefore, we recommend that you consider time and resources to make CFD simulations early in the design phase, because you will achieve an accelerated level of knowledge early in the project. This means that mistakes are avoided and a certain amount of money is saved by not having to correct mistakes later in the construction phase or when the project is finished.

To achieve these benefits, the calculations that underlie the early design decisions must be of high quality and require top-shelf specialist knowledge in both software and simulation processes. Kirkholm has made it one of our specialties to deliver large and complex calculations, as companies themselves often do not have employees with the required expertise.

What is CFD?

The abbreviation CFD covers Computational Fluid Dynamics, i.e. numerical simulations of the movement of liquids or gases under different conditions. CTO Jacob Mac Rygaard has worked with CFD analyzes since his student years and through his thesis project at Koenigsegg in Sweden. At Kirkholm, he is one of our CFD specialists, and an expert in utilizing CFD software to achieve safe and reliable simulations.

"We always listen to the customer, and we make sure that the simulation accuracy meets their needs and wishes. This means that we can help them further from the idea phase to standing with very precise knowledge about the facility they want to construct. The software is a very powerful tool that requires knowledge and experience to master. The results in software are never better than the inputs you feed it with. So in order to get the right results, it is crucial to set the right parameters, understand the context and that you can both analyze and understand the results. Most of the time, the software would probably help you get simulation results - but can you trust them to be correct? It takes experience to know this", says Jacob Mac Rygaard.

Specifically, one can – based on the Navier–Stokes equations – determine velocities, pressures and temperatures in a defined flow domain, e.g. a water tank for fish farming. Before the actual simulation work begins, it is extremely important that the problem(s) and the goal(s) are clearly defined.

For Billund Aquaculture, the requirements for water quality, knowledge of flow and water exchange are essential. The bottom conditions in particular are important, which means that the simulation model focuses on bottom conditions. Since CFD simulations require a lot of computer power and often a long simulation time, it is important to simplify as much as possible without compromising on either the result or accuracy.

When the target is in place, the domain (the tank) is divided into small cells (a mesh). In CFD, the mesh quality is of great importance to the accuracy of the results, and it therefore requires great care to build a usable mesh. In addition to the mesh, as mentioned, there are a number of other parameters that must be assessed when the simulation model is made. You have to assess whether the flow is laminar or turbulent, which turbulence model will be relevant, whether it should be static or transient simulation, as well as consider fluid properties, boundary conditions on inlets, outlets and walls - just to name a few.

Security, safe production and economic benefits

Based on the customer's critical points, we do a sensitivity study on our simulation models, where we change selected parameters to know the significance of the results. In this way, we achieve an extra high degree of accuracy, which ensures that we get sufficiently close to the actual conditions in the finished tank. In this way, we can predict that the facility will function as desired and expected. It contributes to security and ensures the best possible productivity, as well as economy for the customer.

Is your company facing a large construction project and/or are you unsure how CFD can help you in your projects? Then contact us for a non-binding chat about the possibilities with simulation software. You are also welcome to read more about CFD here or read more cases about CFD simulation here.