Date of Award

Summer 8-19-2017

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Habib J. Dagher

Second Committee Member

Andrew J. Goupee

Third Committee Member

Eric N. Landis

Additional Committee Members

Anthony M. Viselli

Abstract

The abundance of consistent high strength winds off the world’s coastlines and the close proximity to dense population centers has led to development of innovative marine structures to support wind turbines to capture this energy resource. Off the US coast, 60% of the offshore wind resource within 50 miles (80 km) lies in deep water, greater than 200 ft (60 m), where the development of Floating Offshore Wind Turbine (FOWT) hull technology will likely be required. The hostile marine environment requires the use of materials that are cost-effective, corrosion resistant, require little maintenance and are highly durable. This has led the University of Maine to develop a concrete hull technology called VolturnUS, and a design for a 6MW FOWT. The construction method will include adhesive joints in the structure below the waterline.

In this work, experimental testing was conducted to verify the performance of the concrete as well as the submerged joints under fatigue, serviceability, and ultimate loading conditions as required by the American Bureau of Shipping (ABS) Guide for Building and Classing Floating Offshore Wind Turbines. The testing included structural testing sub-components of the hull and served as experimental verification of ABS concrete design methodology. Concrete fatigue testing of an offshore high durability lightweight aggregate concrete mix design was conducted. A test method to confirm water-tightness of segmental adhesive joints both with and without load applied was developed and partially validated. A novel testing program to verify that a lightweight concrete mix and adhesive joint system can meet ABS performance requirements was developed. A near-full-scale durability testing method for segmental hull components was developed. Through this testing, it was found that the concrete and joint system considered maintains water-tightness beyond the ABS serviceability-loading limit, up to ultimate bending strength of the concrete section when loaded in one direction subjected to flexural loads. No loss in water-tightness due to fatigue regimes tested was observed. The two fatigue loading regimes appear to be conservative fatigue limits when designing concrete for resistance to fatigue due to bending.

This work is being used by the University of Maine to design the first commercial scale FOWTs in the United States. Two 6MW wind turbines supported on VolturnUS concrete hulls will be used for the New England Aqua Ventus I project. The project is planned to be deployed and connected to the grid by 2019 off Monhegan Island, Maine with partial funding by the U.S. Department of Energy.

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