Efficient critical design load case identification for floating offshore wind turbines with a reduced nonlinear model

Matha, Denis; Sandner, Frank; Schlipf, David

doi:10.1088/1742-6596/555/1/012069

Cited by 20 publications

(16 citation statements)

References 4 publications

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“…A first development of the model was presented in [73] with a verification across different load cases in [62]. Earlier versions of the model were used in the European projects INNWIND.EU [87], LIFES50+ [43], and TELWIND [92] for controller design and preliminary load case analysis.…”

Section: Reduced-order Modelingmentioning

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: Reduced-order Modelingmentioning

confidence: 99%

Multibody modeling for concept-level floating offshore wind turbine design

Lemmer

Luhmann³

et al. 2020

Multibody Syst Dyn

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“…For the analyses of offshore wind turbine systems, various design load cases are recommended by standards [41][42][43][44][45]. Based on these guidelines, only a reduced number of design relevant LCs and environmental conditions are selected for the application in research studies [46][47][48]. Within phase IV of OC3, a separate set of LCs is specified, which is grouped into three categories: (1) LC 1.…”

Section: Simulated Load Casesmentioning

confidence: 99%

Development and Verification of an Aero-Hydro-Servo-Elastic Coupled Model of Dynamics for FOWT, Based on the MoWiT Library

2020

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The complexity of floating offshore wind turbine (FOWT) systems, with their coupled motions, aero-hydro-servo-elastic dynamics, as well as non-linear system behavior and components, makes modeling and simulation indispensable. To ensure the correct implementation of the multi-physics, the engineering models and codes have to be verified and, subsequently, validated for proving the realistic representation of the real system behavior. Within the IEA (International Energy Agency) Wind Task 23 Subtask 2 offshore code-to-code comparisons have been performed. Based on these studies, using the OC3 phase IV spar-buoy FOWT system, the Modelica for Wind Turbines (MoWiT) library, developed at Fraunhofer IWES, is verified. MoWiT is capable of fully-coupled aero-hydro-servo-elastic simulations of wind turbine systems, onshore, offshore bottom-fixed, or even offshore floating. The hierarchical programing and multibody approach in the object-oriented and equation-based modeling language Modelica have the advantage (over some other simulation tools) of component-based modeling and, hence, easily modifying the implemented system model. The code-to-code comparisons with the results from the OC3 studies show, apart from expected differences due to required assumptions in consequence of missing data and incomplete information, good agreement and, consequently, substantiate the capability of MoWiT for fully-coupled aero-hydro-servo-elastic simulations of FOWT systems.

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“…Here, a simplified multibody model, initially presented in [21] and verified in [22] has been adapted for the new system.…”

Section: Modelingmentioning

confidence: 99%

Prospects of Linear Model Predictive Control on a 10 MW Floating Wind Turbine

Lemmer

Raach

Schlipf

et al. 2015

Volume 9: Ocean Renewable Energy

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The presented research has the objective of supporting the integrated conceptual design of floating offshore wind turbines (FOWT). The dynamics of the multidisciplinary coupled system with the aerodynamics, hydrodynamics, structural dynamics, the catenary mooring lines and the controller shall be represented in simulation models adapted to the current design stage. Here, a linear model-predictive controller (MPC) as an optimal multiple input-multiple output (MIMO) controller is designed for a novel concept of the floating foundation for a 10MW wind turbine. The performance of this controller is easily adjustable by a cost function with multiple objectives. Therefore, the MPC can be seen as a benchmark controller in the concept phase, based on a simplified coupled simulation model with only approximate model information. The linear model is verified against its nonlinear counterpart and the performance of the MPC compared to a SISO PI-controller, which is also designed in this work. The developed models show to be well suited and the linear MPC shows a reduction of the rotor speed overshoot and tower bending from a deterministic gust.

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Efficient critical design load case identification for floating offshore wind turbines with a reduced nonlinear model

Cited by 20 publications

References 4 publications

Multibody modeling for concept-level floating offshore wind turbine design

Multibody modeling for concept-level floating offshore wind turbine design

Development and Verification of an Aero-Hydro-Servo-Elastic Coupled Model of Dynamics for FOWT, Based on the MoWiT Library

Prospects of Linear Model Predictive Control on a 10 MW Floating Wind Turbine

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