Existing commercial software is not suitable for designing net cages. The main reason is that they are in general focusing on verification of forces in the entire farm, including mooring and cages. This leads to long simulation times, limited number of design options and often very coarse and simplified net models. Egersund Net desired a numerical tool for easy and quick design of new net cages. The numerical tool should also give results that can be used when certifying the net cages.
The main method used for the project has been a scrum inspired agile method. The project group has had regular meetings every two weeks where we have looked at a list of requirements for the software and prioritized what is feasible to implement during the next two week period. To ensure feedback from the customer we have had several meetings with Egersund Net where we presented the software so far and gathered feedback on wanted functionality and future priorities. In 2013 the first beta version was released and presented to Egersund Net and within 2013 the first release version will be available.
Results and Discussion
The demonstrator consists of a graphical user interface where users can specify the physical dimensions of a net cage, the physical properties of the net and ropes, and environmental loads like current and waves. The software takes this input and translates it to an input xml file for the fhSim Core 1.0, which then takes over and runs a simulation on the specified net structure. Both circular and rectangular nets can be modeled; with different geometries. Supportropes can be added vertically and horizontally. For circular cages the floating collar can be either rigid or flexible. The weight system can be either individual weights connected to the crossropes or a sinkertube, the weights can be calculated automatically or given manually. The demonstrator supports environmental conditions through current simulations on the net structure as well as regular and irregular waves.
Finn Olav Bjørnson, Martin Føre, Brad Schofield, Per Runtop, Per Christian Endresen (SINTEF Fisheries and Aquaculture)