The TripleSpar Campaign: Validation of a Reduced-Order Simulation Model for Floating Wind Turbines

Different research groups have recently tested scaled floating offshore wind turbines including blade pitch control. A test conducted by the University of Stuttgart (Germany), DTU (Denmark) and CENER (Spain) at the Danish Hydraulic Institute (DHI) in 2016 successfully demonstrated a real-time blade pitch controller on the public 10MW TripleSpar semi-submersible concept at a scale of 1/60. In the presented work a reduced-order simulation model including control is compared against the model tests. The model has only five degrees of freedom and is formulated either in the time-domain or in the frequency-domain. In a first step the Morison drag coefficients are identified from decay tests as well as irregular wave cases. The identified drag coefficients depend clearly on the sea state, with the highest ones for the decay tests and small sea states. This is an important finding, for example for the design of a robust controller, which depends on the system damping. It is shown that the simplified model can well represent the dominant physical effects of the coupled system with a substantially reduced simulation time, compared to state-of-the-art models.

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Iterative Frequency-Domain Response of Floating Offshore Wind Turbines with Parametric Drag

Journal of Marine Science and Engineering ◽

10.3390/jmse6040118 ◽

2018 ◽

Vol 6 (4) ◽

pp. 118 ◽

Cited By ~ 5

Author(s):

Frank Lemmer ◽

Wei Yu ◽

Po Cheng

Keyword(s):

System Dynamics ◽

Frequency Domain ◽

Wind Turbines ◽

Domain Model ◽

Offshore Wind ◽

Viscous Drag ◽

Drag Coefficients ◽

Reduced Order ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

Methods for coupled aero-hydro-servo-elastic time-domain simulations of Floating Offshore Wind Turbines (FOWTs) have been successfully developed. One of the present challenges is a realistic approximation of the viscous drag of the wetted members of the floating platform. This paper presents a method for an iterative response calculation with a reduced-order frequency-domain model. It has heave plate drag coefficients, which are parameterized functions of literature data. The reduced-order model does not represent more than the most relevant effects on the FOWT system dynamics. It includes first-order and second-order wave forces, coupled with the wind turbine structural dynamics, aerodynamics and control system dynamics. So far, the viscous drag coefficients are usually defined as constants, independent of the load cases. With the computationally efficient frequency-domain model, it is possible to iterate the drag, such that it fits to the obtained amplitudes of oscillation of the different members. The results show that the drag coefficients vary significantly across operational load conditions. The viscous drag coefficients converge quickly and the method is applicable for concept-level design studies of FOWTs with load case-dependent drag.

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Numerical Study of a Proposed Semi-Submersible Floating Platform with Different Numbers of Offset Columns Based on the DeepCwind Prototype for Improving the Wave-Resistance Ability

Applied Sciences ◽

10.3390/app9061255 ◽

2019 ◽

Vol 9 (6) ◽

pp. 1255

Author(s):

Zhenqing Liu ◽

Yicheng Fan ◽

Wei Wang ◽

Guowei Qian

Keyword(s):

Wind Turbines ◽

Numerical Study ◽

Wind Farms ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Floating Platform ◽

Offshore Wind Turbines ◽

Irregular Wave ◽

Decay Test ◽

Floating Offshore Wind Turbines

DeepCwind semi-submersible floating offshore wind turbines have been widely examined, and in some countries this type of floating offshore wind turbine has been adopted in the construction of floating wind farms. However, the DeepCwind semi-submersible floating offshore wind turbines still experience large surge motion that limits their operational time. Therefore, in this study, a semi-submersible floating platform with different numbers of offset columns, but with the same total weight, based on the DeepCwind prototype is proposed. From the free-decay test, it was found that the number of the floating columns will affect the natural frequency of the platform. Furthermore, the regular wave test in the time domain and the irregular wave test in the frequency domain show that increasing the number of the floating columns will reduce the surge motion greatly, while the effects in the heave and pitch motions are not obvious.

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An efficient frequency-domain model for quick load analysis of floating offshore wind turbines

Wind Energy Science ◽

10.5194/wes-3-693-2018 ◽

2018 ◽

Vol 3 (2) ◽

pp. 693-712 ◽

Cited By ~ 9

Author(s):

Antonio Pegalajar-Jurado ◽

Michael Borg ◽

Henrik Bredmose

Keyword(s):

Wind Speed ◽

Frequency Domain ◽

Wind Turbines ◽

Degrees Of Freedom ◽

Bending Moment ◽

Domain Model ◽

Offshore Wind ◽

Hydrodynamic Damping ◽

Floating Offshore Wind Turbines ◽

Load Analysis

Abstract. A model for Quick Load Analysis of Floating wind turbines (QuLAF) is presented and validated here. The model is a linear, frequency-domain, efficient tool with four planar degrees of freedom: floater surge, heave, pitch and first tower modal deflection. The model relies on state-of-the-art tools from which hydrodynamic, aerodynamic and mooring loads are extracted and cascaded into QuLAF. Hydrodynamic and aerodynamic loads are pre-computed in WAMIT and FAST, respectively, while the mooring system is linearized around the equilibrium position for each wind speed using MoorDyn. An approximate approach to viscous hydrodynamic damping is developed, and the aerodynamic damping is extracted from decay tests specific for each degree of freedom. Without any calibration, the model predicts the motions of the system in stochastic wind and waves with good accuracy when compared to FAST. The damage-equivalent bending moment at the tower base is estimated with errors between 0.2 % and 11.3 % for all the load cases considered. The largest errors are associated with the most severe wave climates for wave-only conditions and with turbine operation around rated wind speed for combined wind and waves. The computational speed of the model is between 1300 and 2700 times faster than real time.

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Advances on Reduced-Order Modeling of Floating Offshore Wind Turbines

10.1115/omae2021-63701 ◽

2021 ◽

Author(s):

Frank Lemmer ◽

Wei Yu ◽

Heiner Steinacker ◽

Danai Skandali ◽

Steffen Raach

Keyword(s):

Wind Turbines ◽

State Feedback ◽

The State ◽

Offshore Wind ◽

Weight Functions ◽

Elastic Model ◽

Reduced Order ◽

Offshore Wind Turbines ◽

Modeling Uncertainties ◽

Floating Offshore Wind Turbines

Abstract Aero-hydro-servo-elastic modeling of Floating Offshore Wind Turbines (FOWTs) is a key component in the design process of various components of the system. Different approaches to order reduction have been investigated with the aim of improving structural design, manufacturing, transport and installation, but also the dynamic behavior, which is largely affected by the blade pitch controller. The present work builds on previous works on the SLOW (Simplified Low-Order Wind Turbine) code, which has already been used for the above purposes, including controller design. While the previous rigid rotor model gives good controllers in most cases, we investigate in the present work the question if aero-elastic effects in the design model can improve advanced controllers. The SLOW model is extended for the flap-wise bending and coupled to NREL’s AeroDyn, linearized and verified with the OlavOlsen OO-Star Wind Floater Semi 10MW public FOWT model. The results show that the nonlinear and linear reduced-order SLOW models agree well against OpenFAST. The state-feedback Linear Quadratic Regulator (LQR) applied with the same weight functions to both models, the old actuator disk, and the new aero-elastic model shows that the LQR becomes more sensitive to nonlinear excitation and that the state feedback matrix is significantly different, which has an effect on the performance and potentially also on the robustness. Thus modeling uncertainties might even be more critical for the LQR of the higher-fidelity model.

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Scale Effects on Heave Plates for Floating Offshore Wind Turbines

Volume 11A: Honoring Symposium for Professor Carlos Guedes Soares on Marine Technology and Ocean Engineering ◽

10.1115/omae2018-78062 ◽

2018 ◽

Author(s):

Ana Bezunartea-Barrio ◽

Sergio Fernandez-Ruano ◽

Adolfo Maron-Loureiro ◽

Enrique Molinelli-Fernandez ◽

Francisco Moreno-Buron ◽

...

Keyword(s):

Wind Turbines ◽

Scale Effects ◽

Added Mass ◽

Offshore Wind ◽

Forced Oscillations ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Heave Plate ◽

Decay Tests ◽

Heave Motion

An essential aspect of experimental campaigns in ocean basins is the extrapolation of results to prototype scale. In the case of “spar” or semi-submersible platforms for floating wind turbines, it is customary to use heave plates that reduce the heave motion and/or tune its period. As part of the Hiprwind project, it was decided to study the scale effects on the hydrodynamics of these elements. To this aim, models of one column of the platform, equipped with a plain heave plate, were built. This model is a simplified representation of the actual one, which incorporates an edge vertical flap. The scales were 1:20, 1:27.6, and 1:45.45, with the former leading to added mass values of the order of 300kg, becoming one of the largest model for which experiments with heave oscillations have been carried out. Decay tests starting from various amplitudes and forced oscillations tests were performed at a range of frequencies and operational and extreme KCs (range of motion). Results related to these tests will be discussed in the paper.

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Control of Floating Offshore Wind Turbines: Reduced-Order Modeling and Real-Time Implementation for Wind Tunnel Tests

Volume 10: Ocean Renewable Energy ◽

10.1115/omae2018-77840 ◽

2018 ◽

Cited By ~ 1

Author(s):

Alessandro Fontanella ◽

Ilmas Bayati ◽

Marco Belloli

Keyword(s):

Wind Tunnel ◽

Wind Turbine ◽

Wind Turbines ◽

Offshore Wind ◽

Scale Model ◽

System Response ◽

Wind Tunnel Tests ◽

Reduced Order ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

The present work deals with the implementation of a variable-speed variable-pitch control strategy on a wind turbine scale model for hybrid/HIL wind tunnel tests on floating offshore wind turbines. The effects that scaling issues, due to low-Reynolds aerodynamics and rotor structural properties, have in combination with the HIL technique developed by the authors are studied through a dedicated reduced-order linear coupled model. The model is used to tune the original pitch controller gains so to be able to reproduce the system response of the full-scale floating wind turbine during HIL tests.

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Linear coupled model for floating wind turbine control

Wind Engineering ◽

10.1177/0309524x18756970 ◽

2018 ◽

Vol 42 (2) ◽

pp. 115-127 ◽

Cited By ~ 10

Author(s):

Alessandro Fontanella ◽

Ilmas Bayati ◽

Marco Belloli

Keyword(s):

Degrees Of Freedom ◽

Coupled Model ◽

Control Design ◽

Offshore Wind ◽

Order Model ◽

Reduced Order ◽

Offshore Wind Turbines ◽

Wind Turbine Control ◽

Floating Offshore Wind Turbines ◽

Three Degrees Of Freedom

This work deals with an analytical linear coupled model describing the integrated aero-hydrodynamics of floating offshore wind turbines. Three degrees of freedom (platform surge, platform pitch and rotor azimuth) were considered with the goal of building a reduced-order model suitable for being integrated in control design algorithms as well as to be used for a straightforward evaluation and comprehension of the global system dynamics.

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An efficient frequency-domain model for quick load analysis of floating offshore wind turbines

10.5194/wes-2018-25 ◽

2018 ◽

Cited By ~ 1

Author(s):

Antonio Pegalajar-Jurado ◽

Michael Borg ◽

Henrik Bredmose

Keyword(s):

Wind Speed ◽

Frequency Domain ◽

Wind Turbines ◽

Degrees Of Freedom ◽

Bending Moment ◽

Domain Model ◽

Offshore Wind ◽

Hydrodynamic Damping ◽

Floating Offshore Wind Turbines ◽

Load Analysis

Abstract. A model for Quick Load Analysis of Floating wind turbines, QuLAF, is presented and validated here. The model is a linear, frequency-domain, efficient tool with four planar degrees of freedom: platform surge, heave, pitch and tower modal deflection. The model relies on state-of-the-art tools from which hydrodynamic, aerodynamic and mooring loads are extracted and cascaded into QuLAF. Hydrodynamic and aerodynamic loads are precomputed in WAMIT and FAST respectively, while the mooring system is linearized around the equilibrium position for each wind speed using MoorDyn. An approximate approach to viscous hydrodynamic damping is developed, and the aerodynamic damping is extracted from decay tests specific for each degree of freedom. Without any calibration, the model predicts the motions of the system in stochastic wind and waves with good accuracy when compared to FAST. The damage-equivalent bending moment at the tower bottom is estimated with errors between 0.2 % and 11.3 % for all the load cases considered. The largest errors are associated with the most severe wave climates for wave-only conditions and with turbine operation around rated wind speed for combined wind and waves. The computational speed of the model is between 1300 and 2700 times faster than real-time.

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Numerical and Physical Modeling of a Tension-Leg Platform for Offshore Wind Turbines

Energies ◽

10.3390/en14123554 ◽

2021 ◽

Vol 14 (12) ◽

pp. 3554

Author(s):

Daniel Walia ◽

Paul Schünemann ◽

Hauke Hartmann ◽

Frank Adam ◽

Jochen Großmann

Keyword(s):

Numerical Model ◽

Wind Turbines ◽

Model Testing ◽

Offshore Wind ◽

Scaled Model ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Cost Efficient ◽

Decay Tests ◽

Floating Platforms

In order to tap the world wide offshore wind resources above deep waters, cost efficient floating platforms are inevitable. Tension-Leg Platforms (TLPs) could enable that crucial cost reduction in floating wind due to their smaller size and lighter weight compared to spars and semi-submersibles. The continuous development of the GICON®-TLP is driven by computer-aided engineering. So-called aero-hydro-servo-elastic coupled simulations are state-of-the-art for predicting loads and simulating the global system behavior for floating offshore wind turbines. Considering the complexity of such simulations, it is good scientific praxis to validate these numerical calculations by use of scaled model testing. This paper addresses the setup of the scaled model testing as carried out at the offshore basin of the École Centrale de Nantes, as well as the numerical model for the GICON®-TLP. The results of dedicated decay tests of the scaled model are used to validate the computational model at the first stage and to determine the natural frequencies of the system. Besides different challenges to the scaled model during the survey, it was possible to take these difficulties into account when updating the numerical model. The results show good agreements for the tank tests and the numerical model.

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