Date of Award

Summer 8-21-2020

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Advisor

Kimberly D. Huguenard

Second Committee Member

David W. Fredriksson

Third Committee Member

William G. Davids

Additional Committee Members

Lauren Ross

Xudong Zheng

Abstract

Large aquaculture systems may have the potential to damp wave energy for coastal protection. The performance of these systems are influenced by the dynamics of components such as flexible kelp blades and mussel droppers. In this thesis, the dynamics of kelp blades and mussel droppers were investigated with a consistent-mass cable model with focus on understanding the asymmetric motion of kelp blades. The results showed the asymmetric blade motion in symmetric waves is caused by the spatial asymmetry of the encountered wave orbital velocities due to blade displacements and the asymmetric action on the blade by vertical wave orbital velocities. For the kelp grown from the bottom, the asymmetry of blade motion provides ‘shelter’ that could inhibit sediment suspension and coastal erosion. For suspended kelp attached to a longline, the asymmetric motion would induce the kelp to roll over the attachment in large wave conditions. With understanding the blade dynamics, physical model experiments using the morphological and mechanical properties of the cultivated Saccharina latissima at Saco Bay, Maine in the USA were conducted to investigate the wave attenuation characteristics of suspended kelp farms. The results indicated that 20 longlines with 100 plants/m could reduce up to 23% energy of 6.3 s waves. To predict wave attenuation under wider conditions, numerical and analytical wave attenuation models coupled with blade motion were developed for regular and irregular waves. With the analytical model, a case study at a site in Northeastern US showed the potential of suspended aquaculture farms to dissipate wave energy in a storm event. Compared to naturally occurring submerged aquatic vegetation (SAV), suspended aquaculture farms were found to perform better at attenuating shorter waves and less impacted by water level changes due to tides, surge and sea level rise. Implementing offshore aquaculture structures in conjunction with SAV-based living shorelines that can enhance the coastal defense of SAV-based living shorelines. This research is useful for the design of suspended aquaculture structures for nature-based coastal protection. The analytical wave attenuation models are also convenient to implement in large-scale models to analyze the influences of wave attenuation on coastal morphology.

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