Date of Award

Spring 5-10-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

First Committee Advisor

Amrit Verma

Second Committee Member

Andrew Goupee

Third Committee Member

Richard Kimball

Abstract

The floating offshore wind industry is poised for growth with advancing technologies and expanding commercial projects. Towing is a key marine operation in offshore wind, where safety and efficiency depend on selecting a suitable tug, tow speed, and predicting towline tensions in a variety of sea states.

This work focuses on the development of tools and techniques for the modeling of marine towing operations for floating offshore wind turbines (FOWTs). The research was motivated by the construction of a 1:4-scale of the University of Maine's VolturnUS+ barge-type FOWT platform. This platform is a novel design using unique geometry and hydrodynamic characteristics that have not been previously studied. Marine transportation was required for the deployment of VolturnUS 1:4, consisting of three phases of towing operations: (1) a short launch tow, (2) a transit to the turbine installation site, and (3) a final tow to the operational site.

To support the planning and evaluation of these operations, a towing toolbox was developed utilizing a methodology for predicting bollard pull and towline tensions of a FOWT towing system. The toolbox was first validated against data collected during the VolturnUS 1:8 tow-out operation that occurred in 2013 and a higher-fidelity numerical tool. Scale model basin towing experiments were conducted to inform toolbox inputs for the VolturnUS+ 1:4 design in two different towing configurations, as well as study the platform motions and the behavior in waves. Interesting platform motion was observed during experimental testing, prompting computational fluid dynamics (CFD) analysis to further explain potential flow-induced motions (FIM). Additionally, a weather window analysis technique based on the exact and average statistical characteristics of calm and storm periods was developed within the towing toolbox. To showcase a potential use case for the weather window analysis toolbox integration, it was applied to a theoretical full-scale towing operation in the Gulf of Maine. The towing toolbox was then used to make predictions for the VolturnUS+ 1:4 towing operations, informing key decisions of the towing system design and defining operational limits. Conservative planning practices were used to ensure safe towing procedures for the unique platform design. Finally, details from the first two phases of the VolturnUS+ 1:4 towing operations are presented and compared to the prediction calculations. Discussion of the two towing operations is supplemented with images and diagrams that provide insight into unique and notable towing behavior.

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