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Definition of the Floating System for Phase IV of OC3

Description: 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.
Date: May 1, 2010
Creator: Jonkman, J.
Partner: UNT Libraries Government Documents Department

New Modularization Framework for the FAST Wind Turbine CAE Tool: Preprint

Description: NREL has recently put considerable effort into improving the overall modularity of its FAST wind turbine aero-hydro-servo-elastic tool to (1) improve the ability to read, implement, and maintain source code; (2) increase module sharing and shared code development across the wind community; (3) improve numerical performance and robustness; and (4) greatly enhance flexibility and expandability to enable further developments of functionality without the need to recode established modules. The new FAST modularization framework supports module-independent inputs, outputs, states, and parameters; states in continuous-time, discrete-time, and in constraint form; loose and tight coupling; independent time and spatial discretizations; time marching, operating-point determination, and linearization; data encapsulation; dynamic allocation; and save/retrieve capability. This paper explains the features of the new FAST modularization framework, as well as the concepts and mathematical background needed to understand and apply it correctly. It is envisioned that the new modularization framework will transform FAST into a powerful, robust, and flexible wind turbine modeling tool with a large number of developers and a range of modeling fidelities across the aerodynamic, hydrodynamic, servo-dynamic, and structural-dynamic components.
Date: January 1, 2013
Creator: Jonkman, J.
Partner: UNT Libraries Government Documents Department

Hydrodynamic Optimization Method and Design Code for Stall-Regulated Hydrokinetic Turbine Rotors

Description: This report describes the adaptation of a wind turbine performance code for use in the development of a general use design code and optimization method for stall-regulated horizontal-axis hydrokinetic turbine rotors. This rotor optimization code couples a modern genetic algorithm and blade-element momentum performance code in a user-friendly graphical user interface (GUI) that allows for rapid and intuitive design of optimal stall-regulated rotors. This optimization method calculates the optimal chord, twist, and hydrofoil distributions which maximize the hydrodynamic efficiency and ensure that the rotor produces an ideal power curve and avoids cavitation. Optimizing a rotor for maximum efficiency does not necessarily create a turbine with the lowest cost of energy, but maximizing the efficiency is an excellent criterion to use as a first pass in the design process. To test the capabilities of this optimization method, two conceptual rotors were designed which successfully met the design objectives.
Date: August 1, 2009
Creator: Sale, D.; Jonkman, J. & Musial, W.
Partner: UNT Libraries Government Documents Department

Offshore Code Comparison Collaboration (OC3) for IEA Wind Task 23 Offshore Wind Technology and Deployment

Description: This final report for IEA Wind Task 23, Offshore Wind Energy Technology and Deployment, is made up of two separate reports, Subtask 1: Experience with Critical Deployment Issues and Subtask 2: Offshore Code Comparison Collaborative (OC3). Subtask 1 discusses ecological issues and regulation, electrical system integration, external conditions, and key conclusions for Subtask 1. Subtask 2 included here, is the larger of the two volumes and contains five chapters that cover background information and objectives of Subtask 2 and results from each of the four phases of the project.
Date: December 1, 2010
Creator: Jonkman, J. & Musial, W.
Partner: UNT Libraries Government Documents Department

Definition of a 5-MW Reference Wind Turbine for Offshore System Development

Description: 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.
Date: February 1, 2009
Creator: Jonkman, J.; Butterfield, S.; Musial, W. & Scott, G.
Partner: UNT Libraries Government Documents Department

Challenges in Simulation of Aerodynamics, Hydrodynamics, and Mooring-Line Dynamics of Floating Offshore Wind Turbines

Description: This paper presents the current major modeling challenges for floating offshore wind turbine design tools and describes aerodynamic and hydrodynamic effects due to rotor and platform motions and usage of non-slender support structures.
Date: October 1, 2011
Creator: Matha, D.; Schlipf, M.; Cordle, A.; Pereira, R. & Jonkman, J.
Partner: UNT Libraries Government Documents Department

Hybrid Electro-Mechanical Simulation Tool for Wind Turbine Generators: Preprint

Description: This paper describes the use of MATLAB/Simulink to simulate the electrical and grid-related aspects of a WTG and the FAST aero-elastic wind turbine code to simulate the aerodynamic and mechanical aspects of the WTG. The combination of the two enables studies involving both electrical and mechanical aspects of the WTG.
Date: May 1, 2013
Creator: Singh, M.; Muljadi, E. & Jonkman, J.
Partner: UNT Libraries Government Documents Department

Loads Analysis of a Floating Offshore Wind Turbine Using Fully Coupled Simulation: Preprint

Description: This paper presents the use of fully coupled aero-hydro-servo-elastic simulation tools to perform a loads analysis of a 5-MW offshore wind turbine supported by a barge with moorings, one of many promising floating platform concepts.
Date: June 1, 2007
Creator: Jonkman, J. M. & Buhl, M. L., Jr.
Partner: UNT Libraries Government Documents Department

Nonlinear Legendre Spectral Finite Elements for Wind Turbine Blade Dynamics: Preprint

Description: This paper presents a numerical implementation and examination of new wind turbine blade finite element model based on Geometrically Exact Beam Theory (GEBT) and a high-order spectral finite element method. The displacement-based GEBT is presented, which includes the coupling effects that exist in composite structures and geometric nonlinearity. Legendre spectral finite elements (LSFEs) are high-order finite elements with nodes located at the Gauss-Legendre-Lobatto points. LSFEs can be an order of magnitude more efficient that low-order finite elements for a given accuracy level. Interpolation of the three-dimensional rotation, a major technical barrier in large-deformation simulation, is discussed in the context of LSFEs. It is shown, by numerical example, that the high-order LSFEs, where weak forms are evaluated with nodal quadrature, do not suffer from a drawback that exists in low-order finite elements where the tangent-stiffness matrix is calculated at the Gauss points. Finally, the new LSFE code is implemented in the new FAST Modularization Framework for dynamic simulation of highly flexible composite-material wind turbine blades. The framework allows for fully interactive simulations of turbine blades in operating conditions. Numerical examples showing validation and LSFE performance will be provided in the final paper.
Date: January 1, 2014
Creator: Wang, Q.; Sprague, M. A.; Jonkman, J. & Johnson, N.
Partner: UNT Libraries Government Documents Department

Inverse Load Calculation of Wind Turbine Support Structures - A Numerical Verification Using the Comprehensive Simulation Code FAST: Preprint (Revised)

Description: Physically measuring the dynamic responses of wind turbine support structures enables the calculation of the applied loads using an inverse procedure. In this process, inverse means deriving the inputs/forces from the outputs/responses. This paper presents results of a numerical verification of such an inverse load calculation. For this verification, the comprehensive simulation code FAST is used. FAST accounts for the coupled dynamics of wind inflow, aerodynamics, elasticity and turbine controls. Simulations are run using a 5-MW onshore wind turbine model with a tubular tower. Both the applied loads due to the instantaneous wind field and the resulting system responses are known from the simulations. Using the system responses as inputs to the inverse calculation, the applied loads are calculated, which in this case are the rotor thrust forces. These forces are compared to the rotor thrust forces known from the FAST simulations. The results of these comparisons are presented to assess the accuracy of the inverse calculation. To study the influences of turbine controls, load cases in normal operation between cut-in and rated wind speed, near rated wind speed and between rated and cut-out wind speed are chosen. The presented study shows that the inverse load calculation is capable of computing very good estimates of the rotor thrust. The accuracy of the inverse calculation does not depend on the control activity of the wind turbine.
Date: November 1, 2012
Creator: Pahn, T.; Jonkman, J.; Rolges, R. & Robertson, A.
Partner: UNT Libraries Government Documents Department

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

Description: This report presents results of the analysis of a 5-MW wind turbine located on a floating offshore tension leg platform (TLP) that was conducted using the fully coupled time-domain aero-hydro-servo-elastic design code FAST with AeroDyn and HydroDyn. Models in this code are of greater fidelity than most of the models that have been used to analyze floating turbines in the past--which have neglected important hydrodynamic and mooring system effects. The report provides a description of the development process of a TLP model, which is a modified version of a Massachusetts Institute of Technology design derived from a parametric linear frequency-domain optimization process. An extensive loads and stability analysis for ultimate and fatigue loads according to the procedure of the International Electrotechnical Commission offshore wind turbine design standard was performed with the verified TLP model. Response statistics, extreme event tables, fatigue lifetimes, and selected time histories of design-driving extreme events are analyzed and presented. Loads for the wind turbine on the TLP are compared to those of an equivalent land-based turbine in terms of load ratios. Major instabilities for the TLP are identified and described.
Date: February 1, 2010
Creator: Matha, D.; Fischer, T.; Kuhn, M. & Jonkman, J.
Partner: UNT Libraries Government Documents Department

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

Description: This report outlines the development of an analysis tool capable of analyzing 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.
Date: January 1, 2007
Creator: Jonkman, J. M. & Buhl, M. L. Jr.
Partner: UNT Libraries Government Documents Department

Atmospheric and Wake Turbulence Impacts on Wind Turbine Fatigue Loading: Preprint

Description: Large-eddy simulations of atmospheric boundary layers under various stability and surface roughness conditions are performed to investigate the turbulence impact on wind turbines. In particular, the aeroelastic responses of the turbines are studied to characterize the fatigue loading of the turbulence present in the boundary layer and in the wake of the turbines. Two utility-scale 5 MW turbines that are separated by seven rotor diameters are placed in a 3 km by 3 km by 1 km domain. They are subjected to atmospheric turbulent boundary layer flow and data is collected on the structural response of the turbine components. The surface roughness was found to increase the fatigue loads while the atmospheric instability had a small influence. Furthermore, the downstream turbines yielded higher fatigue loads indicating that the turbulent wakes generated from the upstream turbines have significant impact.
Date: December 1, 2011
Creator: Lee, S.; Churchfield, M.; Moriarty, P.; Jonkman, J. & Michalakes, J.
Partner: UNT Libraries Government Documents Department

New Structural-Dynamics Module for Offshore Multimember Substructures within the Wind Turbine Computer-Aided Engineering Tool FAST: Preprint

Description: FAST, developed by the National Renewable Energy Laboratory (NREL), is a computer-aided engineering (CAE) tool for aero-hydro-servo-elastic analysis of land-based and offshore wind turbines. This paper discusses recent upgrades made to FAST to enable loads simulations of offshore wind turbines with fixed-bottom, multimember support structures (e.g., jackets and tripods, which are commonly used in transitional-depth waters). The main theory and strategies for the implementation of the multimember substructure dynamics module (SubDyn) within the new FAST modularization framework are introduced. SubDyn relies on two main engineering schematizations: 1) a linear frame finite-element beam (LFEB) model and 2) a dynamics system reduction via Craig-Bampton's method. A jacket support structure and an offshore system consisting of a turbine atop a jacket substructure were simulated to test the SubDyn module and to preliminarily assess results against results from a commercial finite-element code.
Date: August 1, 2013
Creator: Song, H.; Damiani, R.; Robertson, A. & Jonkman, J.
Partner: UNT Libraries Government Documents Department

Investigation of a FAST-OrcaFlex Coupling Module for Integrating Turbine and Mooring Dynamics of Offshore Floating Wind Turbines: Preprint

Description: To enable offshore floating wind turbine design, the following are required: accurate modeling of the wind turbine structural dynamics, aerodynamics, platform hydrodynamics, a mooring system, and control algorithms. Mooring and anchor design can appreciably affect the dynamic response of offshore wind platforms that are subject to environmental loads. From an engineering perspective, system behavior and line loads must be studied well to ensure the overall design is fit for the intended purpose. FAST (Fatigue, Aerodynamics, Structures and Turbulence) is a comprehensive simulation tool used for modeling land-based and offshore wind turbines. In the case of a floating turbine, continuous cable theory is used to emulate mooring line dynamics. Higher modeling fidelity can be gained through the use of finite element mooring theory. This can be achieved through the FASTlink coupling module, which couples FAST with OrcaFlex, a commercial simulation tool used for modeling mooring line dynamics. In this application, FAST is responsible for capturing the aerodynamic loads and flexure of the wind turbine and its tower, and OrcaFlex models the mooring line and hydrodynamic effects below the water surface. This paper investigates the accuracy and stability of the FAST/OrcaFlex coupling operation.
Date: October 1, 2011
Creator: Masciola, M.; Robertson, A.; Jonkman, J. & Driscoll, F.
Partner: UNT Libraries Government Documents Department

State-Space Realization of the Wave-Radiation Force within FAST: Preprint

Description: Several methods have been proposed in the literature to find a state-space model for the wave-radiation forces. In this paper, four methods were compared, two in the frequency domain and two in the time domain. The frequency-response function and the impulse response of the resulting state-space models were compared against the ones derived by the numerical code WAMIT. The implementation of the state-space module within the FAST offshore wind turbine computer-aided engineering (CAE) tool was verified, comparing the results against the previously implemented numerical convolution method. The results agreed between the two methods, with a significant reduction in required computational time when using the state-space module.
Date: June 1, 2013
Creator: Duarte, T.; Sarmento, A.; Alves, M. & Jonkman, J.
Partner: UNT Libraries Government Documents Department

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

Description: In 2007, the FAST wind turbine simulation tool, developed and maintained by the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL), was expanded to include capabilities that are suitable for modeling floating offshore wind turbines. In an effort to validate FAST and other offshore wind energy modeling tools, DOE funded the DeepCwind project that tested three prototype floating wind turbines at 1/50th scale in a wave basin, including a semisubmersible, a tension-leg platform, and a spar buoy. This paper describes the use of the results of the spar wave basin tests to calibrate and validate the FAST offshore floating simulation tool, and presents some initial results of simulated dynamic responses of the spar to several combinations of wind and sea states.
Date: November 1, 2012
Creator: Browning, J. R.; Jonkman, J.; Robertson, A. & Goupee, A. J.
Partner: UNT Libraries Government Documents Department

Incorporation of Multi-Member Substructure Capabilities in FAST for Analysis of Offshore Wind Turbines: Preprint

Description: FAST, developed by the National Renewable Energy Laboratory (NREL), is an aero-hydro-servo-elastic tool widely used for analyzing onshore and offshore wind turbines. This paper discusses recent modifications made to FAST to enable the examination of offshore wind turbines with fixed-bottom, multi-member support structures (which are commonly used in transitional-depth waters).; This paper addresses the methods used for incorporating the hydrostatic and hydrodynamic loading on multi-member structures in FAST through its hydronamic loading module, HydroDyn. Modeling of the hydrodynamic loads was accomplished through the incorporation of Morison and buoyancy loads on the support structures. Issues addressed include how to model loads at the joints of intersecting members and on tapered and tilted members of the support structure. Three example structures are modeled to test and verify the solutions generated by the modifications to HydroDyn, including a monopile, tripod, and jacket structure. Verification is achieved through comparison of the results to a computational fluid dynamics (CFD)-derived solution using the commercial software tool STAR-CCM+.
Date: May 1, 2012
Creator: Song, H.; Robertson, A.; Jonkman, J. & Sewell, D.
Partner: UNT Libraries Government Documents Department