Investigation of a self-submersible SPM cage system in random waves

•Physical model tests of self-submersible SPM cage concept verify the numerical simulation results.•Submergence of the cage system in irregular waves is less pronounced compared to in regular waves.•The cage system's response to increasing wave heights is additional submergence for a given current speed.•The cage system is tuned to a range of current speeds and wave heights for more effective submergence.•Submergence of the cage system in random waves is more effective for wind wave spectrums.

Farming in offshore waters to address the increasing demand for food fish is as much a technological challenge as a social challenge. At present, there are only few successful cage design concepts for offshore conditions. In a series of recent works by the authors, the single-point mooring (SPM) cage concept has been identified as being potentially suitable for mariculture in offshore waters. In contrast to cages with manual or automatic control of the submergence, the feasibility of the self-submersible SPM cage depends on its “empirical” operational performance in offshore environments. This paper examines the submergence characteristics of the cage concept in random waves with following current using numerical simulations and experimental model tests. The scaled model tests confirmed the submergence characteristics of the cage system that were observed in the numerical simulations. In random waves, the cage system responded to increasing wave regimes with additional submergence. However, the level of submergence was found to be less pronounced than the cage submergence response in regular waves, which was investigated as part of earlier studies. While the cage system with less reserve buoyancy submerged deeper, the peak factor of the wave spectrum did not substantially change the submergence characteristics. It was also found that the cage system is dynamically stable during and after submergence, regardless of the magnitude of the wave heights observed in random seas.