Design and Analysis of a Floating-Wind Shallow-Water Mooring System Featuring Polymer Springs: Paper No. IOWTC2022-98149

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

Research output: Contribution to conferencePaper

3 Scopus Citations


This paper presents a mooring system design featuring polymer springs 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 modeling 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%, whereas 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 pages10
StatePublished - 2023
EventASME 2022 4th International Offshore Wind Technical Conference - Boston, Massachusetts
Duration: 7 Dec 20228 Dec 2022


ConferenceASME 2022 4th International Offshore Wind Technical Conference
CityBoston, Massachusetts

Bibliographical note

See NREL/CP-5000-83342 for preprint

NREL Publication Number

  • NREL/CP-5000-85492


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


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