PNNL

Abstract

Macroalgae in the open ocean can potentially be a reliable and promising source of food, animal feed, fertilizer, and will become an important source of biofuel in coming years. Therefore, analysis and design of innovative offshore macroalgae cultivation systems to optimize farming operation, increase biomass production, and lower system and operational costs are needed. In this study, an offshore binary species free-floating longline macroalgae farming system (MFS) is designed and modeled numerically to understand the hydrodynamic effects on the MFS under extreme ocean environmental conditions. The validated sugar kelp cluster model and bull kelp plant model are applied to simulate the binary species MFS in four different growth periods and associated locations under extreme environmental conditions. The models show that the maximum tensions on the longline for all stages are far less than the longline breakage limit and that all of the maximum tensions at the holdfasts of bull kelp plants and sugar kelp clusters are below the breakage limit obtained from the laboratory tests. A potential damage mode of the young kelp may occur if the longline stretches out of the water, exposing the kelp to the air (hence to gravity force) without buoyance support. Buoy-longline contact interaction may damage the buoy, resulting in total loss of the system by sinking. Finally, the model results show that kelp-longline, kelp- supporting line, and kelp-kelp entanglements may potentially occur, causing kelp damage and biomass loss.