A 3D consistent mass-based model, cable model, is proposed to simulate the large deflection of the culture line structure. The 3D model couples the components of the entire aquaculture system. The simulations are performed with results compared with published data for suspended blades in both steady and oscillatory flow. Dynamics of a kelp longline system are studied for tidal currents scenarios. Results show that the longline tension follows water level to the peak at high tide and sensitive to water level in high tide. The non-parallel currents could enhance the tension as well as the deflection of the longline system.
Longline aquaculture systems are often used for the grow out of both shellfish and macroalgae products in protected waters. As this sector of the industry grows, more exposed sites will be considered. Longline gear components, however, will need to be optimized to survive extreme wave and current conditions while minimizing costs at exposed sites. These aquaculture structures may also have potential for shore protection as a kind of a living breakwater (Zhu and Zou, 2017). In each of these applications, numerical modeling tools are necessary that represent the dominating fluid and aquaculture system interaction processes. To analyze the dynamics of a mussel longline system, Raman-Nair et al (2008) developed a 3D numerical model coupling the longline and mussel dropper components. The longline was modeled as a lumped mass and tension-only springs system with the attached mussel culture components modeled as rigid cylinders. Cheng et al. (2017) developed a 2D numerical model for a kelp culture line modeled as a series of segments connected by hinges and springs to represent large deflections. A 2D consistent mass, cable model was proposed by Zhu et al. (2018) to simulate the dynamics of flexible kelp blades in waves. The results showed that the blade-induced vortices are asymmetric at both upstream and downstream positions of the flexible kelp model. The 2D models, however, are not able to simulate the dynamics of the longline system with non-parallel incident waves and currents because the motion of the culture line is 3D. Therefore, to build upon this work, the objectives of this paper are, (1) to propose a 3D form of the cable model to simulate the dynamics of the culture line, (2) incorporate hydrodynamic input for kelp blades, and (3) to couple the components of the entire aquaculture system based on the cable model. The coupled 3D model was then used to investigate the performance of a kelp longline system in tidal currents.
