Assessment of Aquaculture Structure Resilience to Environmental Change

Project Description

Two significant challenges to offshore aquaculture are loading from storms and the costs of anchoring equipment at depth. Much of the anchoring expense is from installation, where barge/vessel size, a limited supply of advanced anchor installation equipment and expertise, and risk associated with over water operations drive costs. A critical objective for marine aquaculture is the reduction of costs associated with designing resilient floating systems and installation and maintenance of such systems, including anchors. Typically, gravity anchors (weights and concrete blocks) that allow for multi-directional loading are used; however, as developments become larger in scale or are required to withstand greater environmental loading from climate change, anchors with higher efficiency (e.g., holding power to weight) are required. The offshore oil and gas (O&G) industry has historically pioneered anchor systems research; however offshore O&G development is moving into deeper waters further offshore. Marine aquaculture, wind, and marine hydrokinetic energy must innovate in shallower, more energetic waters, where multi-platform systems interact with the environment.

The focus of the project is to (1) develop guidance documents to better understand seafloor sediments and the impact they have on the anchor system options, design, and construction, and (2) investigate the use of higher efficiency helical anchors for multi-directional loading and their comparison with traditional anchors used in Maine aquaculture.

Development of educational and guidance materials on how to identify and understand seafloor sediment conditions, and how this information can be used to design and deploy efficient anchors for a wide range of species, will be critical to ensuring resilience of infrastructure regardless of farm size, water depth, and ocean dynamics.

This research involves investigating complex soil-structure interaction and geotechnical capacities that can be obtained with helical anchor systems for marine aquaculture applications. Specifically, parametric finite element analyses (FEA) will be performed using PLAXIS to evaluate the influence of geometry and plate size, depth, soil properties, and plate spacing on design efficiency and holding capacity. Differences between predicted (numerical analyses) and observed performance for an installed aquaculture farm will be reconciled by evaluating the validity of assumed and measure soil constitutive parameters, loading, and inherent limitations with numerical models. Physical testing and numerical simulations will be used to develop design charts that consider required geotechnical capacity, anchor depths, helical plate size, and anchor spacing/efficiency based on helical anchor geometry and soil properties.

Results from the simulations will be used to develop a document of best practices for site investigation and anchoring. Researchers will determine scientifically ideal site and sediment investigation techniques and anchoring options and designs for farming considerations. This document will be customized depending on the species of interest, bioregion, and needs of the farm. Researchers will communicate the value of this document with Theme 4 to optimize outreach to the community. Researchers hope to address the technological needs of Maine aquaculture and determine how to best prepare for future environmental changes.

Results and Accomplishments

Recruited new project lead, Landon, and new graduate students, Cortes-Garcia and Barnett. Numerical simulations have been initiated to investigate more efficient anchoring systems (e.g., helical anchors) for general floating aquaculture loading using PLAXIS soil-structure interaction software. Plans are in place to collect sediment cores and instrument mooring lines of a kelp farm with helical anchors to gather sediment and load data for use in validating numerical simulations.

Summary of Data Being Collected

Data	Type	Quantity	Location
Current velocity profiles	Field	12 days continuously. Data was sampled every hour	Mook Sea Farms in the Damariscotta River
Loan on mooring lines	Field	12 days continuously. Data was sampled every second	Mook Sea Farms in the Damariscotta River
Wind speed and direction	Field	12 days continuously. Data was sampled every 5 minutes	Newcastle station
Wave height, frequency and direction	Field	12 days continuously. Data was sampled every 10 minutes	Mook Sea Farms in the Damariscotta River
6DOF motion of 3m discus scaled oceanographic buoy	Lab experiment	12 days continuously. Data was collected for 40s in each run	Moor Laboratory (Crosby Hall), UMaine