Design and Analysis of a Floating-Wind Shallow-Water Mooring System Featuring Polymer Springs: Preprint

Ericka Lozon, Matthew Hall, Paul McEvoy, Seojin Kim, Bradley Ling

Research output: Contribution to conferencePaper


In this paper, a mooring system featuring polymer springs is designed for the VolturnUS-S 15 MW reference floating wind turbine in site conditions for the New York Bight at a 50-m water depth. Polymer springs have a nonlinear stress-strain curve that allows a stiffer response at low loads and a more flexible response at higher loads, potentially reducing peak mooring line tensions. The mooring dynamics model MoorDyn has been extended to model springs with nonlinear tension-strain curves from a user-inputted look-up table. This MoorDyn modelling advancement is verified against OrcaFlex simulation results. Using MoorDyn's updated capabilities, a spring-equipped catenary mooring system is designed for the 15 MW floating system, along with a baseline catenary mooring system that does not use polymer springs. The floating wind turbine simulator OpenFAST is used to simulate the mooring systems in design-driving load cases to show the effect of polymer springs on key dynamic behaviours. The results show that the spring-equipped design reduces peak tensions by up to 60%, while the turbine offsets stay within a maximum of 7.2 m, which is still a reasonable offset limit for cable considerations. The reduction in peak tensions results in a significant decrease in damage equivalent loads, on the order of 50% for upwind lines in fully loaded conditions. These results show that polymer springs can effectively reduce peak tensions and fatigue loads in mooring systems at shallow water depths.
Original languageAmerican English
Number of pages13
StatePublished - 2022
EventInternational Offshore Wind Technical Conference (IOWTC2022) - Boston, Massachusetts
Duration: 7 Dec 20228 Dec 2022


ConferenceInternational Offshore Wind Technical Conference (IOWTC2022)
CityBoston, Massachusetts

Bibliographical note

See NREL/CP-5000-85492 for paper as published in proceedings

NREL Publication Number

  • NREL/CP-5000-83342


  • floating offshore wind
  • mooring system
  • polymer springs
  • shallow water


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