Jason Jonkman

Coupled Dynamic Modeling of Floating Wind Turbine Systems

This article presents a collaborative research program that the Massachusetts Institute of Technology (MIT) and the National Renewable Energy Laboratory (NREL) have undertaken to develop innovative and cost-effective floating and mooring systems for offshore wind turbines in water depths of 10-200 m. Methods for the coupled structural, hydrodynamic, and aerodynamic analysis of floating wind turbine systems are presented in the frequency domain. This analysis was conducted by coupling the aerodynamics and structural dynamics code FAST [4] developed at NREL with the wave load and response simulation code WAMIT (Wave Analysis at MIT) [15] developed at MIT. Analysis tools were developed to consider coupled interactions between the wind turbine and the floating system. These include the gyroscopic loads of the wind turbine rotor on the tower and floater, the aerodynamic damping introduced by the wind turbine rotor, the hydrodynamic damping introduced by wave-body interactions, and the hydrodynamic forces caused by wave excitation. Analyses were conducted for two floater concepts coupled with the NREL 5-MW Offshore Baseline wind turbine in water depths of 10-200 m: the MIT/NREL Shallow Drafted Barge (SDB) and the MIT/NREL Tension Leg Platform (TLP). These concepts were chosen to represent two different methods of achieving stability to identify differences in performance and cost of the different stability methods. The static and dynamic analyses of these structures evaluate the systems responses to wave excitation at a range of frequencies, the systems natural frequencies, and the standard deviations of the systems motions in each degree of freedom in various wind and wave environments. This article in various wind and wave environments. This article explores the effects of coupling the wind turbine with the floating platform, the effects of water depth, and the effects of wind speed on the systems performance. An economic feasibility analysis of the two concepts was also performed. Key cost components included the material and construction costs of the buoy; material and installation costs of the tethers, mooring lines, and anchor technologies; costs of transporting and installing the system at the chosen site; and the cost of mounting the wind turbine to the platform. The two systems were evaluated based on their static and dynamic performance and the total system installed cost. Both systems demonstrated acceptable motions, and have estimated costs of

Influence of Control on the Pitch Damping of a Floating Wind Turbine

1.4-

Development of Fully Coupled Aeroelastic and Hydrodynamic Models for Offshore Wind Turbines

1.8 million, not including the cost of the wind turbine, the power electronics, or the electrical transmission.

Development and Verification of a Fully Coupled Simulator for Offshore Wind Turbines

This paper presents the influence of conventional wind turbine blade-pitch control actions on the pitch damping of a wind turbine supported by an offshore floating barge with catenary moorings.

Modal Dynamics of Large Wind Turbines with Different Support Structures

Aeroelastic simulation tools are routinely used to design and analyze onshore wind turbines, in order to obtain cost effective machines that achieve favorable performance while maintaining structural integrity. These tools employ sophisticated models of wind-inflow; aerodynamic, gravitational, and inertial loading of the rotor, nacelle, and tower; elastic effects within and between components; and mechanical actuation and electrical responses of the generator and of control and protection systems. For offshore wind turbines, additional models of the hydrodynamic loading in regular and irregular seas, the dynamic coupling between the support platform motions and wind turbine motions, and the dynamic characterization of mooring systems for compliant floating platforms are also important. Hydrodynamic loading includes contributions from hydrostatics, wave radiation, and wave scattering, including free surface memory effects. The integration of all of these models into comprehensive simulation tools, capable of modeling the fully coupled aeroelastic and hydrodynamic responses of floating offshore wind turbines, is presented.

The effects of second-order hydrodynamics on a semisubmersible floating offshore wind turbine

†‡ The vast deepwater wind resource represents a potential to use floating offshore wind turbines to power much of the world with renewable energy. Comprehensive simulation tools that account for the coupled excitation and response of the complete system, including the influences of wind-inflow, aerodynamics, structural dynamics, controls, and, for offshore systems, waves, currents, and hydrodynamics, are used to design and analyze wind turbines. Continuing our work presented previously, we outline the development of such an analysis tool for floating offshore wind turbines, including a recently added, quasi-static mooring system module. The fully coupled simulator was developed with enough sophistication to address the limitations of previous frequency and time domain studies and to have the features required to perform an integrated loads analysis. It is also universal enough to analyze a variety of wind turbine, support platform, and mooring system configurations. The simulation capability was tested by model-to-model comparisons to ensure its correctness. The results of all of the verification exercises are favorable and give us confidence to pursue more thorough investigations into the behavior of floating offshore wind turbines. Some of the potential challenges to their design are highlighted through sample response simulations.

New Developments for the NWTC's FAST Aeroelastic HAWT Simulator: Preprint

This paper presents modal dynamics of floating-platform-supported and monopile-supported offshore wind turbines.

BeamDyn: a high‐fidelity wind turbine blade solver in the FAST modular framework

The objective of this paper is to assess the second-order hydrodynamic effects on a semisubmersible floating offshore wind turbine. Second-order hydrodynamics induce loads and motions at the sum- and difference-frequencies of the incident waves. These effects have often been ignored in offshore wind analysis, under the assumption that they are significantly smaller than first-order effects. The sum- and difference-frequency loads can, however, excite eigenfrequencies of a floating system, leading to large oscillations that strain the mooring system or vibrations that cause fatigue damage to the structure. Observations of supposed second-order responses in wave-tank tests performed by the DeepCwind consortium at the Maritime Research Institute Netherlands (MARIN) offshore basin suggest that these effects might be more important than originally expected. These observations inspired interest in investigating how second-order excitation affects floating offshore wind turbines and whether second-order hydrodynamics should be included in offshore wind simulation tools like FAST. In this work, the effects of second-order hydrodynamics on a floating semisubmersible offshore wind turbine are investigated. Because FAST is currently unable to account for second-order effects, a method to assess these effects was applied in which linearized properties of the floating wind system derived from FAST (including the 6x6 mass and stiffness matrices) are used by WAMIT to solve the first- and second-order hydrodynamics problems in the frequency domain. The method was applied to the Offshore Code Comparison Collaboration Continuation OC4-DeepCwind semisubmersible platform, supporting the National Renewable Energy Laboratorys 5-MW baseline wind turbine. In this paper, the loads and response of the system caused by the second-order hydrodynamics are analysed and compared to the first-order hydrodynamic loads and induced motions in the frequency domain. Further, the second-order loads and induced response data are compared to the loads and motions induced by aerodynamic loading as solved by FAST.

Model Development and Loads Analysis of a Wind Turbine on a Floating Offshore Tension Leg Platform

Discrepancies in response predictions among FAST, ADAMS, and other industry-accepted wind turbine analysis codes led the National Renewable Energy Laboratory to dedicate significant time and effort to overhauling its FAST aeroelastic horizontal-axis wind turbine simulator. Included in the overhaul were improvements to the system dynamics models and upgrades in functionality. Improvements were made to the drive train dynamics models, output processing algorithms, tower and blade deflection characterizations, and other models. New features include an enhanced input/output environment, aeroacoustic noise prediction algorithms, periodic linearization routines for controls design, as well as a preprocessing utility that enables FAST to generate ADAMS datasets of wind turbine models. In order to verify that the new features and improved models included in the upgraded FAST were correct, verification tests were run against ADAMS. Comparisons of response predictions between the codes, in general, show excellent agreement. Regions where the different response predictions do not exactly coalesce are attributable to differences in the modeling techniques. This work has culminated in an upgraded version of FAST, equipped with more functionality, that predicts more accurate wind turbine responses than previous versions.

Calibration and Validation of a Spar-Type Floating Offshore Wind Turbine Model using the FAST Dynamic Simulation Tool

This paper presents a numerical implementation of the geometrically exact beam theory based on the Legendre-spectral-finite-element (LSFE) method. The displacement-based geometrically exact beam theory is presented, and the special treatment of three-dimensional rotation parameters is reviewed. An LSFE is a high-order finite element with nodes located at the Gauss–Legendre–Lobatto points. These elements can be an order of magnitude more computationally efficient than low-order finite elements for a given accuracy level. The new module, BeamDyn, is implemented in the FAST modularization framework for dynamic simulation of highly flexible composite-material wind turbine blades within the FAST aeroelastic engineering model. The framework allows for fully interactive simulations of turbine blades in operating conditions. Numerical examples are provided to validate BeamDyn and examine the LSFE performance as well as the coupling algorithm in the FAST modularization framework. BeamDyn can also be used as a stand-alone high-fidelity beam tool. Copyright