Offshore turbines with bottom-fixed or floating substructures

Matha, Denis; Lemmer, Frank; Muskulus, Michael

doi:10.1049/pbpo125g_ch5

Cited by 2 publications

(2 citation statements)

References 66 publications

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“…In offshore engineering, it is common to model floating rigid bodies with the six DoFs of unconstrained motion ξ and the mass matrix M in the frequency-domain [60]: (1) wave (ω). For a time-domain simulation of the hydrodynamics in the present model, Eq.…”

Section: Hydrodynamic Modelmentioning

confidence: 99%

Multibody modeling for concept-level floating offshore wind turbine design

Lemmer

Luhmann³

et al. 2020

Multibody Syst Dyn

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Existing Floating Offshore Wind Turbine (FOWT) platforms are usually designed using static or rigid-body models for the concept stage and, subsequently, sophisticated integrated aero-hydro-servo-elastic models, applicable for design certification. For the new technology of FOWTs, a comprehensive understanding of the system dynamics at the concept phase is crucial to save costs in later design phases. This requires low-and medium-fidelity models. The proposed modeling approach aims at representing no more than the relevant physical effects for the system dynamics. It consists, in its core, of a flexible multibody system. The applied Newton-Euler algorithm is independent of the multibody layout and avoids constraint equations. From the nonlinear model a linearized counterpart is derived. First, to be used for controller design and second, for an efficient calculation of the response to stochastic load spectra in the frequency-domain. From these spectra the fatigue damage is calculated with Dirlik's method and short-term extremes by assuming a normal distribution of the response. The set of degrees of freedom is reduced, with a response calculated only in the two-dimensional plane, in which the aligned wind and wave forces act. The aerodynamic model is a quasistatic actuator disk model. The hydrodynamic model includes a simplified radiation model, based on potential flow-derived added mass coefficients and nodal viscous drag coefficients with an approximate representation of the second-order slow-drift forces. The verification through a comparison of the nonlinear and the linearized model against a higher-fidelity model and experiments shows that even with the simplifications, the system response magnitude at the system eigenfrequencies and the forced response magnitude to wind and wave forces can be well predicted. One-hour simulations complete in about 25 seconds and even less in the case of the frequency-domain model. Hence, large sensitivity studies and even multidisciplinary optimizations for systems engineering approaches are possible.

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Section: Hydrodynamic Modelmentioning

confidence: 99%

Multibody modeling for concept-level floating offshore wind turbine design

Lemmer

Luhmann³

et al. 2020

Multibody Syst Dyn

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“…[6,7,8]. Hydrodynamic forces, important for the system dynamics of semi-submersibles, are the Froude-Krylov wave loads including diffraction, viscous drag excitation, viscous drag damping (both from Morison's drag term) [9,10,11] and second-order slow-drift forces at the difference-frequency of bichromatic waves from potential flow theory, i.e. [12,13].…”

Section: System Dynamics Of Floating Wind Turbinesmentioning

confidence: 99%

Semi-submersible wind turbine hull shape design for a favorable system response behavior

Lemmer

Müller

et al. 2020

Marine Structures

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Floating offshore wind turbines are a novel technology, which has reached, with the first wind farm in operation, an advanced state of development. The question of how floating wind systems can be optimized to operate smoothly in harsh wind and wave conditions is the subject of the present work. An integrated optimization was conducted, where the hull shape of a semi-submersible, as well as the wind turbine controller were varied with the goal of finding a cost-efficient design, which does not respond to wind and wave excitations, resulting in small structural fatigue and extreme loads.The optimum design was found to have a remarkably low tower-base fatigue load response and small rotor fore-aft amplitudes. Further investigations showed that the reason for the good dynamic behavior is a particularly favorable response to first-order wave loads: The floating wind turbine rotates in pitchdirection about a point close to the rotor hub and the rotor fore-aft motion is almost unaffected by the wave excitation. As a result, the power production and the blade loads are not influenced by the waves. A comparable effect was so far known for Tension Leg Platforms but not for semi-submersible wind turbines. The methodology builds on a low-order simulation model, coupled to a parametric panel code model, a detailed viscous drag model and an individually tuned blade pitch controller. The results are confirmed by the higher-fidelity model FAST. A new indicator to express the optimal behavior through a single design criterion has been developed.

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Offshore turbines with bottom-fixed or floating substructures

Cited by 2 publications

References 66 publications

Multibody modeling for concept-level floating offshore wind turbine design

Multibody modeling for concept-level floating offshore wind turbine design

Semi-submersible wind turbine hull shape design for a favorable system response behavior

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