PI: Richard Sause

Co-PI: Jeongjoo Kim

University: Lehigh University

Industry partner: Whitehill Manufacturing  

According to the National Renewable Energy Laboratory (2019), most of the potential U.S. offshore wind energy resources are in deep water (over 60 meters in depth), requiring the use of floating offshore wind turbines (FOWTs). Cost-effective FOWT substructures (platform, moorings, and foundations) are critical to future use of these deepwater wind resources. This project will focus on understanding and quantifying the forces in mooring lines for FOWTs from numerical simulations of a prototype 15-megawatt FOWT under operational and extreme loading conditions. 

These mooring lines are designed to extend from seafloor anchors to the floating platform of the FOWT to keep it in place under complex wind and wave loading conditions. FOWT mooring lines are expected to be semi-taut. Synthetic fiber ropes are the most likely technology for the large length of mooring line (hundreds of meters) between the fairlead and seafloor anchor. Very little data is available on the expected force demands on FOWT mooring lines for offshore U.S. locations, which limits the potential for creating efficient and reliable engineering designs. In addition, the forces in mooring lines of floating structures depend on the material characteristics (e.g., compliance) of the mooring lines. Mooring lines that are more flexible will generally experience smaller amplitude forces. The required force information includes data under normal operating conditions for establishing the fatigue demands on mooring lines, and data under extreme conditions for establishing the strength demands on mooring lines. 

Polyester synthetic fiber ropes have been studied in the past, and recommended engineering practices are available. This project will focus on forces on non-polyester synthetic fiber ropes for mooring lines of floating offshore wind and marine energy systems. The proposed project will leverage an ongoing multidisciplinary research project on FOWTs, which focuses on numerical simulations of a prototype FOWT. The results from this project will help to develop and promote new types of synthetic fiber ropes for future FOWT applications.