Structural design of exposed aquaculture structures

PhD-student: Pål Takle Bore

Supervisors: Professor Jørgen Amdahl, David Kristiansen

Duration: Q4 2015 – Q1 2019


Proper design of aquaculture structures against extreme environmental conditions is essential as the industry moves towards more exposed areas. This topic is addressed in this thesis, with particular focus on waves and currents.

For traditional aquaculture fish-cages, loads on the net is typically dominating the global load equation. Two different types of hydrodynamic models are usually applied for calculation of viscous forces on nets or screens: (1) Morison type and (2) screen models. Experimentally obtained force coefficients for net panels are generally presented as ‘screen model force coefficients’, while commercial analysis software are often restricted to a Morison model. In [1], a modified Morison model is presented which is based on converting screen model coefficients to directional dependent Morison coefficients. The model shows good agreement with screen models and yields improved results compared to the classical Morison model.

Relatively simple statistical methods for determination of extreme environmental conditions on exposed aquaculture locations are presented in [2]. Particular focus is on waves, and directionality is found to be important to account for when estimating extreme sea states (HS and Tp).

Knowledge about ocean currents and their vertical structure is important when designing offshore structures. In [3], a method for statistical modelling of extreme vertical current velocity profiles is proposed. The method is tested using measured current profiles at two coastal location in Norway, demonstration good performance.

The effect (in terms of structural response) due to extreme environmental loads on aquaculture structures will be examined.

Publications:

[1] Bore, P. T., Amdahl, J., Kristiansen, D., 2017. Modelling of hydrodynamic loads on aquaculture net cages by a modified Morison model. In: 7th International Conference on Computational Methods in Marine Engineering, MARINE 2017, pp. 647-662.

[2] Bore, P.T., Amdahl, J., 2017. Determination of environmental conditions relevant for the ultimate limit state at an exposed aquaculture location. In: Proceeding of the 36th International Conference on Ocean, Offshore and Artic Engineering, OMAE 2017.

[3] Bore, P. T., Amdahl, J., Kristiansen, D., 2019. Statistical modelling of extreme ocean current velocity profiles. Submitted to Ocean Engineering.