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A User’s Guide

This report describes the development, verification, and application of a comprehensive simulation tool for modeling coupled dynamic responses of offshore floating wind turbines.

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Dynamics Modeling and Loads Analysis of an Offshore Floating Wind Turbine

Wind energy, commonly recognized to be a clean and environmentally friendly renewable energy resource that can reduce our dependency on fossil fuels, has developed rapidly in recent years. Its mature technology and comparatively low cost make it promising as an important primary energy source in the future. However, there are potential environmental impacts due to the installation and operation of the wind turbines that cannot be ignored. This paper aims to provide an overview of world wind energy scenarios, the current status of wind turbine development, development trends of offshore wind farms, and the environmental and climatic impact of wind farms. The wake effect of wind turbines and modeling studies regarding this effect are also reviewed.

Wind energy development and its environmental impact: A review

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.

/pdf/definition-of-the-floating-system-for-phase-iv-of-oc3-2h9xihawzt.pdf

Definition of the Floating System for Phase IV of OC3

This paper reviews the trends in wind turbine generator systems. After discussing some important requirements and basic relations, it describes the currently used systems: the constant speed system with squirrel-cage induction generator, and the three variable speed systems with doubly fed induction generator (DFIG), with gearbox and fully rated converter, and direct drive (DD). Then, possible future generator systems are reviewed. Hydraulic transmissions are significantly lighter than gearboxes and enable continuously variable transmission, but their efficiency is lower. A brushless DFIG is a medium speed generator without brushes and with improved low-voltage ride-through characteristics compared with the DFIG. Magnetic pseudo DDs are smaller and lighter than DD generators, but need a sufficiently low and stable magnet price to be successful. In addition, superconducting generators can be smaller and lighter than normal DD generators, but both cost and reliability need experimental demonstration. In power electronics, there is a trend toward reliable modular multilevel topologies.

Trends in Wind Turbine Generator Systems

Two different simulation models for integrated dynamic analysis of floating offshore wind turbines are described and compared with model scale experiments for the Hywind concept for floating offshore wind turbines. A variety of both environmental conditions and wind turbine control schemes are tested. A maximum power control strategy is applied for wind velocities below the rated wind speed for the wind turbine, while a constant power control strategy is achieved by controlling the rotor blade pitch for wind velocities above rated wind speed. Conventional rotor blade pitch control for wind velocities above rated wind speed introduces negative damping of the tower motion. This results in excitation of the natural frequency in pitch for the tower and may lead to unacceptable tower motions. Active damping of the undesirable tower motions is obtained by an additional pitch control algorithm based on measurement of the tower velocity.Copyright © 2006 by ASME

Integrated dynamic analysis of floating offshore wind turbines

Integrated Dynamic Analysis of Floating Offshore Wind Turbines

A comparative dynamic analysis between full-scale measurements from the floating wind turbine Hywind Demo and corresponding numerical simulations is presented. A description of the main characteristics of the Hywind Demo structure, control system and important measurements are given.

A method for estimation of the incident wave elevation on Hywind Demo is outlined. Comparative dynamic simulations are carried out with the estimated wave elevation time series as input, together measured and further refined statistical parameters of the wind field.

Roll, pitch and yaw motions, tower bending moments, mooring line tensions, power production, rotor speed and blade pitch angle are compared for one case below and one case above the rated wind speed. Overall, good agreement is seen between the measured and simulated responses, and it is believed that the considered analysis tool is well suited for confirming the design of a future optimized floating wind turbine based on the Hywind concept. Copyright © 2014 John Wiley & Sons, Ltd.

Analysis of measurements and simulations from the Hywind Demo floating wind turbine

Exploitation of wind energy at deep-waters locations requires floating wind turbine foundations. Several floating wind turbine foundation concepts are reported in the literature, and a common challenge is to make a low cost foundation with acceptable motion characteristics. In order to analyze the fatigue life of floating offshore wind turbines, the coupled action of wind, waves, current and blade pitch control strategy must be considered. State-of-the-art computer programs for motion analysis of moored offshore bodies, Simo-Riflex from Sintef Marintek, are coupled to a state-of-the-art aero-elastic computer program for wind turbines, Hawc2 from Riso National Laboratory. The wave loads on the body may include wave diffraction and radiation loads as well as viscous forces. The mooring lines are modelled using cable finite elements with inertia and drag forces. The wind load on the rotor is based on common rotor aerodynamics including corrections for skew inflow and relative motion caused by large displacement and large tilt and yaw rotations of the rotor. Conventional wind turbine control strategies lead to wind-induced loads that may amplify or damp the motions of the floating wind turbine. The first case is a result of the blade pitch control strategy above rated wind speed for the wind turbine, and can result in large resonant motions that will reduce the fatigue life of the floating wind turbine significantly. The latter case implies energy extraction from the waves. This paper addresses the importance of control strategies on fatigue life for a given floating offshore wind turbine. A fatigue life time comparison between a conventional blade pitch control strategy and an estimator based blade pitch control strategy show that the fatigue life of floating offshore wind turbines can be significantly increased by use of alternative blade pitch control strategies.Copyright © 2007 by ASME

Importance of Control Strategies on Fatigue Life of Floating Wind Turbines

https://cyberleninka.org/article/n/1444844.pdf

Bjørn Skaare

Papers

Integrated dynamic analysis of floating offshore wind turbines

Integrated Dynamic Analysis of Floating Offshore Wind Turbines

Analysis of measurements and simulations from the Hywind Demo floating wind turbine

Importance of Control Strategies on Fatigue Life of Floating Wind Turbines

Validation of a FAST Model of the Statoil-hywind Demo Floating Wind Turbine☆