Experimental and computational damping estimation of an offshore wind turbine on a monopile foundation

Shirzadeh, Rasoul; Devriendt, Christof; Bidakhvidi, Mohammad Ahmadi; Guillaume, Patrick

doi:10.1016/j.jweia.2013.07.004

Cited by 140 publications

(93 citation statements)

References 9 publications

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“…The over all damping η tot of an offshore wind turbine consists of aerodynamic damping η areo , hydrodynamic damping η hydro , soil damping η soil , and structural damping (includes material damping and control damping) η struc [61][62][63].…”

Section: (3) Dampingmentioning

confidence: 99%

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Seismic Fragility Analysis of Monopile Offshore Wind Turbines under Different Operational Conditions

Kang

et al. 2017

Energies

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Offshore wind turbines in seismic active areas suffer from earthquake impacts. In this study, seismic fragility analysis of a monopile offshore wind turbine considering different operational conditions was performed. A finite element model for a 5 MW monopile offshore wind turbine was developed using the OpenSees platform. The interaction between the monopile and the seabed soil was modeled as a beam-on-nonlinear-winkler-foundation (BNWF). A nonlinear time history truncated incremental dynamic analysis (TIDA) was conducted to obtain seismic responses and engineering demand parameters. Potential damage states (DSs) were defined as excessive displacement at the nacelle, rotation at the tower top, and the allowable and yield stresses at the transition piece. Fragility curves were plotted to assess the probability of exceeding different damage states. It was found that seismic responses of the wind turbine are considerably influenced by environmental wind and wave loads. Subject to earthquake motions, wind turbines in normal operation at the rated wind speed experience higher levels of probability of exceeding damage states than those in other operational conditions, i.e., in idling or operating at higher or lower wind speed conditions.

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Section: (3) Dampingmentioning

confidence: 99%

“…In standstill conditions when the blades are pitched to the maximum pitch angle the aerodynamic damping is very small and can be neglected [62]. On the other hand, in the power generation condition the aerodynamic damping can be rather high [63].…”

Section: (3) Dampingmentioning

confidence: 99%

Seismic Fragility Analysis of Monopile Offshore Wind Turbines under Different Operational Conditions

Kang

et al. 2017

Energies

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“…Damgaard et al (2012) and (2013) [8,11] used a hysteretic p-y method, wherein a hysteretic loop was defined using a traditional p-y spring-supported pile per [10], whereas Versteijlen et al (2011) [3] used modified p-y curves adjusted for rigid-behavior monopiles with damping proportional to spring stiffness. Minimal description of the soil modeling was given in Shirzadeh et al (2013) [7], only that a form of Rayleigh damping was used to apply damping as part of the input for the aeroelastic code HAWC2. Most similarly to the process used in this paper, Tarp-Johansen et al…”

Section: Free Vibration Analysismentioning

confidence: 99%

“…This type of soil damping should be more specifically labeled OWT monopile foundation damping (or generally referred to in this paper as "OWT foundation damping") due to the specific formulation and mechanism of hysteretic material soil damping within the OWT soil-structure foundation system. Some researchers [3,6,11,14] have examined the signals from instrumented OWTs during emergency shutdown (sometimes referred to as a "rotor-stop test"), ambient excitation, and overspeed stops [7] to estimate OWT natural frequency and damping. Subsequently, OWT foundation damping values from 0.25 to 1.5% have been estimated from the residual damping after aerodynamic, hydrodynamic, structural, and nacelle tuned mass damping have been accounted for in numerical modeling.…”

Section: Introductionmentioning

confidence: 99%

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Foundation damping and the dynamics of offshore wind turbine monopiles

et al. 2015

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a b s t r a c tThe contribution of foundation damping to offshore wind turbines (OWTs) is not well known, though researchers have back-calculated foundation damping from "rotor-stop" tests after estimating aerodynamic, hydrodynamic, and structural damping with numerical models. Because design guidelines do not currently recommend methods for determining foundation damping, it is typically neglected. This paper investigates the significance of foundation damping on monopile-supported OWTs subjected to extreme storm loading using a linear elastic two-dimensional finite element model. The effect of foundation damping primarily on the first natural frequency of the OWT was considered as OWT behavior is dominated by the first mode under storm loading. A simplified foundation model based on the soil-pile mudline stiffness matrix was used to represent the monopile, hydrodynamic effects were modeled via added hydrodynamic mass, and 1.00% Rayleigh structural damping was assumed. Hysteretic energy loss in the foundation was converted into a viscous, rotational dashpot at the mudline to represent foundation damping. Using the logarithmic decrement method on a finite element free vibration time history, 0.17%-0.28% of critical damping was attributed to foundation damping. Stochastic time history analysis of extreme storm conditions indicated that mudline OWT foundation damping decreases the maximum and standard deviation of mudline moment by 7e9%.

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