Dynamics of offshore floating wind turbines—analysis of three concepts
TL;DR: In this paper, a dynamic response analysis of three offshore floating wind turbine concepts is presented, and the results of this analysis will help resolve the fundamental design trade-offs between the floating-system concepts.
Abstract: This work presents a comprehensive dynamic–response analysis of three offshore floating wind turbine concepts. Models were composed of one 5 MW turbine supported on land and three 5 MW turbines located offshore on a tension leg platform, a spar buoy and a barge. A loads and stability analysis adhering to the procedures of international design standards was performed for each model using the fully coupled time domain aero-hydro-servo-elastic simulation tool FAST with AeroDyn and HydroDyn. The concepts are compared based on the calculated ultimate loads, fatigue loads and instabilities. The loads in the barge-supported turbine are the highest found for the three floating concepts. The differences in the loads between the tension leg platform–supported turbine and spar buoy–supported turbine are not significant, except for the loads in the tower, which are greater in the spar system. Instabilities in all systems also must be resolved. The results of this analysis will help resolve the fundamental design trade-offs between the floating-system concepts. Copyright © 2011 John Wiley & Sons, Ltd.
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18 May 2015
TL;DR: The most successful generator-converter configurations are addressed along with few promising topologies available in the literature from the market based survey, and the past, present and future trends in megawatt WECS are reviewed in terms of mechanical and electrical technologies, integration to power systems, and control theory.
Abstract: This paper presents a comprehensive study on the state-of-the-art and emerging wind energy technologies from the electrical engineering perspective. In an attempt to decrease cost of energy, increase the wind energy conversion efficiency, reliability, power density, and comply with the stringent grid codes, the electric generators and power electronic converters have emerged in a rigorous manner. From the market based survey, the most successful generator-converter configurations are addressed along with few promising topologies available in the literature. The back-to-back connected converters, passive generator-side converters, converters for multiphase generators, and converters without intermediate dc-link are investigated for high-power wind energy conversion systems (WECS), and presented in low and medium voltage category. The onshore and offshore wind farm configurations are analyzed with respect to the series/parallel connection of wind turbine ac/dc output terminals, and high voltage ac/dc transmission. The fault-ride through compliance methods used in the induction and synchronous generator based WECS are also discussed. The past, present and future trends in megawatt WECS are reviewed in terms of mechanical and electrical technologies, integration to power systems, and control theory. The important survey results, and technical merits and demerits of various WECS electrical systems are summarized by tables. The list of current and future wind turbines are also provided along with technical details.
694 citations
Cites background from "Dynamics of offshore floating wind ..."
...foundations which have already been used in offshore oil and gas industry are promising for future deep water (> 40 m) projects [7], [248]....
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TL;DR: In this article, the aerodynamics and fluid-structure interaction (FSI) simulation of wind turbines at full scale, and in the presence of the nacelle and tower, is presented.
Abstract: In this paper we present our aerodynamics and fluid---structure interaction (FSI) computational techniques that enable dynamic, fully coupled, 3D FSI simulation of wind turbines at full scale, and in the presence of the nacelle and tower (i.e., simulation of the "full machine"). For the interaction of wind and flexible blades we employ a nonmatching interface discretization approach, where the aerodynamics is computed using a low-order finite-element-based ALE-VMS technique, while the rotor blades are modeled as thin composite shells discretized using NURBS-based isogeometric analysis (IGA). We find that coupling FEM and IGA in this manner gives a good combination of efficiency, accuracy, and flexibility of the computational procedures for wind turbine FSI. The interaction between the rotor and tower is handled using a non-overlapping sliding-interface approach, where both moving- and stationary-domain formulations of aerodynamics are employed. At the fluid---structure and sliding interfaces, the kinematic and traction continuity is enforced weakly, which is a key ingredient of the proposed numerical methodology. We present several simulations of a three-blade 5~MW wind turbine, with and without the tower. We find that, in the case of no tower, the presence of the sliding interface has no effect on the prediction of aerodynamic loads on the rotor. From this we conclude that weak enforcement of the kinematics gives just as accurate results as the strong enforcement, and thus enables the simulation of rotor---tower interaction (as well as other applications involving mechanical components in relative motion). We also find that the blade passing the tower produces a 10---12 % drop (per blade) in the aerodynamic torque. We feel this finding may be important when it comes to the fatigue-life analysis and prediction for wind turbine blades.
279 citations
TL;DR: In this paper, the authors presented the validation of a model constructed in the National Renewable Energy Laboratory (NREL) floating wind turbine simulator FAST with 1/50th-scale model test data for a semi-submersible floating turbine system.
Abstract: There are global efforts in the offshore wind community to develop reliable floating wind turbine technologies that are capable of exploiting the abundant deepwater wind resource. These efforts require validated numerical simulation tools to predict the coupled aero-hydro-servo-elastic behavior of such systems. To date, little has been done in the public domain to validate floating wind turbine simulation tools. This work begins to address this problem by presenting the validation of a model constructed in the National Renewable Energy Laboratory (NREL) floating wind turbine simulator FAST with 1/50th-scale model test data for a semi-submersible floating wind turbine system. The test was conducted by the University of Maine DeepCwind program at Maritime Research Institute Netherlands' offshore wind/wave basin, located in the Netherlands. The floating wind turbine used in the tests was a 1/50th-scale model of the NREL 5-MW horizontal-axis reference wind turbine with a 126 m rotor diameter. This turbine was mounted to the DeepCwind semi-submersible floating platform. This paper first outlines the details of the floating system studied, including the wind turbine, tower, platform, and mooring components. Subsequently, the calibration procedures used for tuning the FAST floating wind turbine model are discussed. Following this calibration, comparisons of FAST predictions and test data are presented that focus on system global and structural response resulting from aerodynamic and hydrodynamic loads. The results indicate that FAST captures many of the pertinent physics in the coupled floating wind turbine dynamics problem. In addition, the results highlight potential areas of improvement for both FAST and experimentation procedures to ensure accurate numerical modeling of floating wind turbine systems.
216 citations
TL;DR: In this article, the aerodynamic modeling of VAWTs is discussed, and a comparison between conventional horizontal axis wind turbines and VAWT is presented, outlining the advantages and disadvantages of these technologies for the floating wind industry.
Abstract: The need to further exploit offshore wind resources has pushed offshore wind farms into deeper waters, requiring the use of floating support structures to be economically sustainable. The use of conventional wind turbines may not continue to be the optimal design for floating applications. Therefore it is important to assess other alternative concepts in this context. Vertical axis wind turbines (VAWTs) are one promising concept, and it is important to first understand the coupled and relatively complex dynamics of floating VAWTs to assess their technical feasibility. A comprehensive review detailing the areas of engineering expertise utilised in developing an understanding of the coupled dynamics of floating VAWTs has been developed through a series of articles. This first article details the aerodynamic modelling of VAWTs, providing a review of available models, discussing their applicability to floating VAWTs and current implementations by researchers in this field. A concise comparison between conventional horizontal axis wind turbines and VAWTs is also presented, outlining the advantages and disadvantages of these technologies for the floating wind industry. This article has been written both for researchers new to this research area, outlining underlying theory whilst providing a comprehensive review of the latest work, and for experts in this area, providing a comprehensive list of the relevant references where the details of modelling approaches may be found.
163 citations
Cites background from "Dynamics of offshore floating wind ..."
...fixed) support structures for offshore wind turbines do not remain the most economically viable option [1]....
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TL;DR: In this article, a combined concept involving a combination of Spar-type wind turbines and an axi-symmetric two-body wave energy converters is considered, which would imply reduced capital costs of the total project because it will reduce the number of power cables, mooring line and the structural mass of the WECs.
142 citations
References
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01 Feb 2009
TL;DR: In this article, a three-bladed, upwind, variable speed, variable blade-pitch-to-feather-controlled multimegawatt wind turbine model developed by NREL to support concept studies aimed at assessing offshore wind technology is described.
Abstract: This report describes a three-bladed, upwind, variable-speed, variable blade-pitch-to-feather-controlled multimegawatt wind turbine model developed by NREL to support concept studies aimed at assessing offshore wind technology.
4,194 citations
01 May 2010
TL;DR: In this article, the authors present the specifications of an offshore floating wind turbine, which are needed by the participants for building aero-hydro-servo-elastic models during the IEA Annex XXIII Offshore Code Comparison Collaboration (OC3).
Abstract: Phase IV of the IEA Annex XXIII Offshore Code Comparison Collaboration (OC3) involves the modeling of an offshore floating wind turbine. This report documents the specifications of the floating system, which are needed by the OC3 participants for building aero-hydro-servo-elastic models.
515 citations
TL;DR: In this article, the authors present a simulation tool for modeling the coupled dynamic response of offshore floating wind turbines and the verification of the simulation tool through model-to-model comparisons.
Abstract: The vast deepwater wind resource represents a potential to use offshore floating wind turbines to power much of the world with renewable energy. Many floating wind turbine concepts have been proposed, but dynamics models, which account for the wind inflow, aerodynamics, elasticity and controls of the wind turbine, along with the incident waves, sea current, hydrodynamics, and platform and mooring dynamics of the floater, were needed to determine their technical and economic feasibility. This work presents the development of a comprehensive simulation tool for modelling the coupled dynamic response of offshore floating wind turbines and the verification of the simulation tool through model-to-model comparisons. The fully coupled time-domain aero-hydro-servo-elastic simulation tool was developed with enough sophistication to address limitations of previous studies and has features required to perform loads analyses for a variety of rotor-nacelle assembly, tower, support platform and mooring system configurations. The developed hydrodynamics module accounts for linear hydrostatic restoring; non-linear viscous drag; the added-mass and damping contributions from linear wave radiation, including free-surface memory effects; and the incident-wave excitation from linear diffraction in regular or irregular seas. The developed mooring line module is quasi-static and accounts for the elastic stretching of an array of homogenous taut or slack catenary lines with seabed interaction. The hydrodynamics module, the moorings module, and the overall simulation tool were tested by comparing to results of other models, including frequency-domain models. The favourable results of all the verification exercises provided confidence to perform more thorough analyses. Copyright © 2009 John Wiley & Sons, Ltd.
319 citations
01 Jul 2007
TL;DR: In this paper, a control algorithm for wind turbines mounted on floating platforms is presented, including the tuning method (pole-placement) to ensure the desired control frequency which provides stable tower vibration modes.
Abstract: Wind turbines mounted on floating platforms is subjected to completely different and soft foundation properties, than seen for onshore wind turbines. This leads to much lower natural frequencies, related to the rigid body motion of the structure which again leads to an unfavorable coupling between tower motion and the pitch control of the turbine. The tower motion in combination with the aerodynamics and the pitch control will be poor or even negative damped which causes large transient loads if not accounted for. The reason for this low damping is shown to be caused by a too fast pitch regulation compared to the motion of the tower or in other words the lowest control-structure natural frequency must be lower than the lowest critical tower frequency. A control algorithm is presented including the tuning method (pole-placement) to ensure the desired control frequency which provides stable tower vibration modes.
309 citations