Influence of wave modelling on the prediction of fatigue for offshore wind turbines

Veldkamp, Herman F.; Tempel, Jan van der

doi:10.1002/we.138

Cited by 32 publications

(14 citation statements)

References 10 publications

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“…The study by DNV estimates a fatigue damage increase of 7.5% on the foundation with second‐order wave models using a Wöhler exponent of 5. In another paper, Veldkamp and van der Tempel found that the fatigue damage increase using more sophisticated models of wave kinematics is about 5–10%, and they concluded it is ‘on the threshold of significance’. The force exerted by the waves on the support structure is estimated by Morison's equation:

d F_{T} ((),, z, t) = d F_{D} ((),, z, t) + d F_{I} ((),, z, t) = \frac{1}{2} ρ_{w} D_{P} C_{D} u ((),, z, t) (||, u ((),, z, t)) + C_{m} ρ_{w} A_{P} \overset{u}{true} ((),, z, t)

where dF T , dF D and dF I are the total wave force, the drag force and the inertia force per length, respectively; C D is the drag coefficient of the support structure with suggested values between 0.7 and 1.2; C m = 1 + C a is the inertia coefficient with suggested values between 1.5 and 2; C a is the added mass coefficient, ρ w is the density of water, D P is the diameter of the monopile/substructure and

A_{P} = D_{P}^{2} π true/ 4

is the cross‐sectional area of the pile (more precisely, the area of the outer circle).…”

Section: Complexity Of Loading and Bending Moment Spectramentioning

confidence: 99%

Simplified critical mudline bending moment spectra of offshore wind turbine support structures

et al. 2014

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Offshore wind turbines are subjected to multiple dynamic loads arising from the wind, waves, rotational frequency (1P) and blade passing frequency (3P) loads. In the literature, these loads are often represented using a frequency plot where the power spectral densities (PSDs) of wave height and wind turbulence are plotted against the corresponding frequency range. The PSD magnitudes are usually normalized to unity, probably because they have different units, and thus, the magnitudes are not directly comparable. In this paper, a generalized attempt has been made to evaluate the relative magnitudes of these four loadings by transforming them into bending moment spectra using site-specific and turbine-specific data. A formulation is proposed to construct bending moment spectra at the mudline, i.e. at the location where the highest fatigue damage is expected. Equally, this formulation can also be tailored to find the bending moment at any other critical cross section, e.g. the transition piece level. Finally, an example case study is considered to demonstrate the application of the proposed methodology. The constructed spectra serve as a basis for frequency-domain fatigue estimation methods available in the literatur

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d F_{T} ((),, z, t) = d F_{D} ((),, z, t) + d F_{I} ((),, z, t) = \frac{1}{2} ρ_{w} D_{P} C_{D} u ((),, z, t) (||, u ((),, z, t)) + C_{m} ρ_{w} A_{P} \overset{u}{true} ((),, z, t)

A_{P} = D_{P}^{2} π true/ 4

is the cross‐sectional area of the pile (more precisely, the area of the outer circle).…”

Section: Complexity Of Loading and Bending Moment Spectramentioning

confidence: 99%

Simplified critical mudline bending moment spectra of offshore wind turbine support structures

et al. 2014

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“…Morrison's equation is the sum of two force components: an inertia force in phase with the local flow acceleration and a drag force proportional to the square of the instantaneous flow velocity. According to Veldkamp and Van Der Tempel, 16 the inertia component is dominant for offshore wind turbine support structures with the currently characteristic diameter of 3-5 m in intermediate water depths of 5-25 m. Several empirical calculation methods exist to find the appropriate inertia (C m ) and drag (C d ) coefficients. For random wave fields used in fatigue calculations, the design rules advise, for a vertical cylinder following coefficients, C m D 2.0 and C d D 0.65.…”

Section: Hydrodynamic Modelmentioning

confidence: 99%

The dynamics of an offshore wind turbine in parked conditions: a comparison between simulations and measurements

et al. 2014

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Offshore wind turbines are complex structures, and their dynamics can vary significantly because of changes in operating conditions, e.g., rotor-speed, pitch angle or changes in the ambient conditions, e.g., wind speed, wave height or wave period. Especially in parked conditions, with reduced aerodynamic damping forces, the response due to wave actions with wave frequencies close to the first structural resonance frequencies can be high. Therefore, this paper will present numerical simulations using the HAWC2 code to study an offshore wind turbine in parked conditions. The model has been created according to best practice and current standards based on the design of an existing Vestas V90 offshore wind turbine on a monopile foundation in the Belgian North Sea. The damping value of the model's first fore-aft mode has been tuned on the basis of measurements obtained from a long-term ambient monitoring campaign on the same wind turbine. Using the updated model of the offshore wind turbine, the paper will present some of the effects of the different design parameters and the different ambient conditions on the dynamics of an offshore wind turbine. The results from the simulations will be compared with the processed data obtained from the real measurements. The accuracy of the model will be discussed in terms of resonance frequencies, mode shapes, damping value and acceleration levels, and the limitations of the simulations in modeling of an offshore wind turbine will be addressed.

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“…Veldkamp and van der Tempel [17] investigated the sensitivity of fatigue loads for a monopile-supported offshore wind turbine to three factors: (i) the shape of the wave spectrum; (ii) assumed wave kinematics models arising from first-order, second-order and nonlinear theories; and (iii) inertia and drag coefficients used with Morison's equation. The main conclusions from that study were that, for the selected site-specific data set, the JONSWAP spectrum provided an acceptable representation of the actual wave conditions at least for loads associated with the dominant (first-order) wave frequency.…”

Section: Introductionmentioning

confidence: 99%

“…With regard to the calibration of the inertial term in Morison's equation, the authors concluded that a value of 2 appeared to be the best choice for the Keulegan-Carpenter (KC) number considered. While on (i) and (ii), Veldkamp and van der Tempel [17] provided qualitative and quantitative results, on (ii) actual fatigue loads associated with the different wave models were not computed. In Ref.…”

Section: Introductionmentioning

confidence: 99%

Offshore wind turbine fatigue loads: The influence of alternative wave modeling for different turbulent and mean winds

2017

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a b s t r a c tThe coupled hydro-aero-elastic response and fatigue loads of a bottom-supported offshore wind turbine under different wind conditions and for different wave modeling assumptions is the subject of this study. Nonlinear modeling of hydrodynamic forcing can bring about resonant vibrations of the tower leading to significant stress amplitude cycles. A comparison between linear and fully nonlinear wave models is presented, with consideration for different accompanying mean wind speeds and turbulence intensities. Hydrodynamic and aerodynamic loads acting on the support structure and on the rotor of a 5-MW wind turbine are modeled in a fully coupled hydro-aero-elastic solver. A key finding is that when the turbine is in a parked state, the widely used linear wave modeling approach significantly underestimates fatigue loads. On the other hand, when the wind turbine is in power production, aerodynamic loads are dominant and the effects due to consideration of nonlinear wave kinematics become less important.

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Influence of wave modelling on the prediction of fatigue for offshore wind turbines

Cited by 32 publications

References 10 publications

Simplified critical mudline bending moment spectra of offshore wind turbine support structures

Simplified critical mudline bending moment spectra of offshore wind turbine support structures

The dynamics of an offshore wind turbine in parked conditions: a comparison between simulations and measurements

Offshore wind turbine fatigue loads: The influence of alternative wave modeling for different turbulent and mean winds

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