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Author ORCID Identifier

https://orcid.org/0000-0002-6713-6645

Document Type

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Mechanical Engineering

Year Degree Awarded

2020

Month Degree Awarded

February

First Advisor

Krish T. Sharman

Second Advisor

David Schmidt

Third Advisor

Sanjay Arwade

Subject Categories

Ocean Engineering | Polymer and Organic Materials

Abstract

Aquaculture products currently account for approximately 46% of the total seafood supply around the world with a continuous increase of 6.6% a year. The technology and practices employed in the industry, however, are still based on experience and conventional wisdom due to the lack of standards and guidelines. Recently, growth in the industry has resulted in the expansion of fish farming into open waters, rendering some cages exposed to the hostile elements of nature. As a result, mooring ropes – one of the most important elements of an aquaculture farm - often break, leaving behind stranded cages, or cage structures that are washed ashore as debris along the shoreline. The need for a standardized mooring system guideline for industrial aquaculture has thus become ever imminent.

The dissertation first aims to develop a theoretical model, which could potentially expand to an industrial guideline in the future, with simplified loading calculations that could be utilized easily by local small-scale growers for initial farm planning. Two field campaigns were carried out at two types of aquaculture farms – cage and longline systems - in the Damariscotta River (Maine). While the first study focuses on the behaviors of the mooring system at an oyster farm (cage type), the second study was conducted on a kelp farm (longline system). Mooring tensions along with environmental conditions over hundreds of hours at these sites were recorded and analyzed. From the results, formulations for various environmental loadings on the farms’ structures, including tidal, current, and wind forces, were developed. Empirical coefficients to model the drag effects of ambient water as recommended by offshore oil industry guidelines were incorporated. The results from the formulations correlate well with the measured data for normal operating conditions.

The second part of the dissertation seeks to improve the current state of the art of numerical simulation with synthetic mooring rope systems. A numerical mooring tool that offers the capability to predict the performance of both inextensible (chain) and extensible (synthetic rope) mooring ropes have been developed. The program employed an implicit finite-difference approach to model the dynamic behaviors of the mooring line subjected to user-defined motions of the fairlead. As opposed to a linear stress-strain relationship typically incorporated in other mooring software, nonlinear thermodynamic-based constitutive models are employed in the model to account for the visco-elastic and visco-plastic characteristics of synthetic lines. Comparison with published data show that the model can capture accurately both nonlinear reversible and irreversible changes in lengths of the fibrous ropes. Creep and stress relaxation tests are both qualitatively predicted by the model.

Creative Commons License

Creative Commons Attribution-Share Alike 4.0 License
This work is licensed under a Creative Commons Attribution-Share Alike 4.0 License.

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