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Influence of foundation damping on offshore wind turbine monopile design loads
Abstract The dynamic behavior of offshore wind turbines (OWTs) must be designed considering stochastic load amplitudes and frequencies from waves and mechanical loads associated with the spinning rotor during power production. The proximity of the OWT natural frequency to excitation frequencies combined with low damping necessitates a thorough analysis of sources of damping; of these sources of damping, least is known about the contributions of damping from soil-structure interaction (foundation damping). This paper studies the influence of foundation damping on cyclic load demand for monopile-supported OWTs considering the design situations of power production, emergency shutdown, and parked conditions. The NREL 5 MW Reference Turbine was modeled using the aero-hydro-elastic software FAST and included equivalent linear foundation stiffness and damping matrices. These matrices were determined using an iterative approach with FAST mudline loads as input to a soil-pile finite element software which calculates hysteretic material damping. Accounting for foundation damping in time history analysis can reduce cyclic foundation moment demand by as much as 30% during parked conditions, 25–33% during emergency shutdown, but only 2–3% reduction during power production without wave and wind misalignment. The calculated foundation damping from the emergency shutdown cases agreed with experimental testing performed in similar site conditions.
Highlights Offshore wind turbines are lightly damped, dynamically sensitive structures. Foundation damping is hysteretic material damping from soil-pile interaction. Soil-pile interaction was modeled with equivalent linear mudline stiffness and damping matrices. The reduction in foundation design loads as a function of foundation damping is investigated. Power production, parked, and emergency shutdown design situations are considered.
Influence of foundation damping on offshore wind turbine monopile design loads
Abstract The dynamic behavior of offshore wind turbines (OWTs) must be designed considering stochastic load amplitudes and frequencies from waves and mechanical loads associated with the spinning rotor during power production. The proximity of the OWT natural frequency to excitation frequencies combined with low damping necessitates a thorough analysis of sources of damping; of these sources of damping, least is known about the contributions of damping from soil-structure interaction (foundation damping). This paper studies the influence of foundation damping on cyclic load demand for monopile-supported OWTs considering the design situations of power production, emergency shutdown, and parked conditions. The NREL 5 MW Reference Turbine was modeled using the aero-hydro-elastic software FAST and included equivalent linear foundation stiffness and damping matrices. These matrices were determined using an iterative approach with FAST mudline loads as input to a soil-pile finite element software which calculates hysteretic material damping. Accounting for foundation damping in time history analysis can reduce cyclic foundation moment demand by as much as 30% during parked conditions, 25–33% during emergency shutdown, but only 2–3% reduction during power production without wave and wind misalignment. The calculated foundation damping from the emergency shutdown cases agreed with experimental testing performed in similar site conditions.
Highlights Offshore wind turbines are lightly damped, dynamically sensitive structures. Foundation damping is hysteretic material damping from soil-pile interaction. Soil-pile interaction was modeled with equivalent linear mudline stiffness and damping matrices. The reduction in foundation design loads as a function of foundation damping is investigated. Power production, parked, and emergency shutdown design situations are considered.
Influence of foundation damping on offshore wind turbine monopile design loads
Carswell, Wystan (author) / Arwade, Sanjay R. (author) / Johansson, Jörgen (author) / DeGroot, Don J. (author)
Marine Structures ; 83
2021-12-16
Article (Journal)
Electronic Resource
English
| European Patent Office | 2020
Configurational Influence Factor Analysis of Offshore Wind Turbine Monopile Foundation
| DOAJ | 2019