Importance of Control Strategies on Fatigue Life of Floating Wind Turbines

2007 ◽  
Author(s):  
Bjo̸rn Skaare ◽  
Tor David Hanson ◽  
Finn Gunnar Nielsen
Keyword(s):  
Fatigue Life ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Control Strategy ◽  
Control Strategies ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Pitch Control ◽  
Floating Wind Turbine ◽  
Floating Offshore Wind Turbines

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 Riso̸ 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.

Model-Inversion Feedforward Control for Wave Load Reduction in Floating Wind Turbines

2021 ◽  
Author(s):  
Alessandro Fontanella ◽  
Marco Belloli
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Control Strategy ◽  
Feedforward Control ◽  
Operating Conditions ◽  
Offshore Wind ◽  
Linear Wave ◽  
Wave Load ◽  
Floating Wind Turbine ◽  
Floating Offshore Wind Turbines

Abstract This paper develops a novel feedforward control strategy for reducing structural loads caused by waves in floating offshore wind turbines. The proposed control strategy is based on the inversion of a linear model of the floating wind turbine, and a real-time forecast of the wave obtained from an upstream measurement is utilized to compute a collective pitch control action. Two feedforward controllers are considered: one is designed to cancel the rotor speed oscillations and one to lower the towertop fore-aft shear force. The feedforward control strategies are implemented in a 10MW floating wind turbine, complementing the standard feedback controller for generator speed regulation. Numerical simulations are carried out in FAST, in four operating conditions with realistic wind and waves, proving the proposed feedforward controller effectively mitigates the structural loads caused by waves. In detail, the feedforward action reduces the loads spectra in the frequency range where linear wave is active. The best performance is realized higher winds (the FA force is reduced up to 25% in 22 m/s wind), where the wave excitation is the strongest.

Model Experiments on the Motion of a SPAR Type Floating Wind Turbine in Wind and Waves

2011 ◽  
Author(s):  
Toshiki Chujo ◽  
Shigesuke Ishida ◽  
Yoshimasa Minami ◽  
Tadashi Nimura ◽  
Shunji Inoue
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Floating Structure ◽  
Floating Structures ◽  
Water Basin ◽  
Offshore Wind Turbines ◽  
Floating Wind Turbine ◽  
Floating Offshore Wind Turbines

The study of floating offshore wind turbines has recently been attractive to many research groups in the renewable energy. Because the area of shallow water along Japanese coast is limited, the development of floating base for wind turbine is inevitable for making large scale wind farms. There are some problems to be solved for floating offshore wind turbines. Besides the mechanical problems of turbines, the influence of the motion of the floater in wind and waves to the electric generation properties, the safeties of floating structures such as the fatigue of machines and structures or criteria of electric facilities should be studied. Several types of floating structures have been proposed such as SPAR, TLP, pontoon, and semi submersibles. The authors have focused on SPAR type because its simpler shape seems to have economical advantages. In this paper, the authors performed experiments in a wind tunnel and a water basin from the viewpoint of “wind turbines on a SPAR type floating structure”. Firstly, forced pitching experiments were operated in a wind tunnel, and the difference in two types of wind turbines, upwind type and downwind type, is discussed. The former type is very popular and the latter type is thought to be suitable for floating structure. Secondly, experiments which thought to be more relevant for a floating wind turbine were carried out in a water basin. The relationship between the location of the attachment point of mooring lines and the motion of the SPAR in waves, and the influence of pitching angle of turbine blades to the motion of the SPAR in waves were inspected. In these experiments it was used a mechanism to control the pitch angle of the blades of the scale model of wind turbine.

Integrated Dynamic Analysis of Floating Offshore Wind Turbines

2006 ◽  
Author(s):  
Finn Gunnar Nielsen ◽  
Tor David Hanson ◽  
Bjo̸rn Skaare
Keyword(s):  
Wind Speed ◽  
Dynamic Analysis ◽  
Wind Turbines ◽  
Control Strategy ◽  
Rotor Blade ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Pitch Control ◽  
Floating Offshore Wind Turbines ◽  
Wind Velocities

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.

scholarly journals Impact of Typhoons on Floating Offshore Wind Turbines: A Case Study of Typhoon Mangkhut

2021 ◽  
Vol 9 (5) ◽  
pp. 543
Author(s):  
Jiawen Li ◽  
Jingyu Bian ◽  
Yuxiang Ma ◽  
Yichen Jiang
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Safety Evaluation ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Motion Response ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Coupling Motion

A typhoon is a restrictive factor in the development of floating wind power in China. However, the influences of multistage typhoon wind and waves on offshore wind turbines have not yet been studied. Based on Typhoon Mangkhut, in this study, the characteristics of the motion response and structural loads of an offshore wind turbine are investigated during the travel process. For this purpose, a framework is established and verified for investigating the typhoon-induced effects of offshore wind turbines, including a multistage typhoon wave field and a coupled dynamic model of offshore wind turbines. On this basis, the motion response and structural loads of different stages are calculated and analyzed systematically. The results show that the maximum response does not exactly correspond to the maximum wave or wind stage. Considering only the maximum wave height or wind speed may underestimate the motion response during the traveling process of the typhoon, which has problems in guiding the anti-typhoon design of offshore wind turbines. In addition, the coupling motion between the floating foundation and turbine should be considered in the safety evaluation of the floating offshore wind turbine under typhoon conditions.

Comparison of Spar and Semisubmersible Floater Concepts of Offshore Wind Turbines Using Long-Term Analysis

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Hasan Bagbanci ◽  
D. Karmakar ◽  
C. Guedes Soares
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Transfer Functions ◽  
Probability Distributions ◽  
Offshore Wind ◽  
Short Term ◽  
Offshore Wind Turbines ◽  
Floating Wind Turbine ◽  
Offshore Floating Wind Turbine

The long-term probability distributions of a spar-type and a semisubmersible-type offshore floating wind turbine response are calculated for surge, heave, and pitch motions along with the side-to-side, fore–aft, and yaw tower base bending moments. The transfer functions for surge, heave, and pitch motions for both spar-type and semisubmersible-type floaters are obtained using the fast code and the results are also compared with the results obtained in an experimental study. The long-term predictions of the most probable maximum values of motion amplitudes are used for design purposes, so as to guarantee the safety of the floating wind turbines against overturning in high waves and wind speed. The long-term distribution is carried out using North Atlantic wave data and the short-term floating wind turbine responses are represented using Rayleigh distributions. The transfer functions are used in the procedure to calculate the variances of the short-term responses. The results obtained for both spar-type and semisubmersible-type offshore floating wind turbine are compared, and the study will be helpful in the assessments of the long-term availability and economic performance of the spar-type and semisubmersible-type offshore floating wind turbine.

scholarly journals Proposal and Performance Study of a Novel Mooring System with Six Mooring Lines for Spar-Type Offshore Wind Turbines

2021 ◽  
Vol 11 (24) ◽  
pp. 11665
Author(s):  
Shi Liu ◽  
Yi Yang ◽  
Chao Wang ◽  
Yuangang Tu
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Mooring Lines ◽  
Included Angle ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Spar-type floating offshore wind turbines commonly vibrate excessively when under the coupling impact of wind and wave. The wind turbine vibration can be controlled by developing its mooring system. Thus, this study proposes a novel mooring system for the spar-type floating offshore wind turbine. The proposed mooring system has six mooring lines, which are divided into three groups, with two mooring lines in the same group being connected to the same fairlead. Subsequently, the effects of the included angle between the two mooring lines on the mooring-system’s performance are investigated. Then, these six mooring lines are connected to six independent fairleads for comparison. FAST is utilized to calculate wind turbine dynamic response. Wind turbine surge, pitch, and yaw movements are presented and analyzed in time and frequency domains to quantitatively evaluate the performances of the proposed mooring systems. Compared with the mooring system with six fairleads, the mooring system with three fairleads performed better. When the included angle was 40°, surge, pitch, and yaw movement amplitudes of the wind turbine reduced by 39.51%, 6.8%, and 12.34%, respectively, when under regular waves; they reduced by 56.08%, 25.00%, and 47.5%, respectively, when under irregular waves. Thus, the mooring system with three fairleads and 40° included angle is recommended.

scholarly journals The Effect of the Second-Order Wave Loads on Drift Motion of a Semi-Submersible Floating Offshore Wind Turbine

2020 ◽  
Vol 8 (11) ◽  
pp. 859
Author(s):  
Thanh-Dam Pham ◽  
Hyunkyoung Shin
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Second Order ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Hydrodynamic Loads ◽  
Drift Motion ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Floating offshore wind turbines (FOWTs) have been installed in Europe and Japan with relatively modern technology. The installation of floating wind farms in deep water is recommended because the wind speed is stronger and more stable. The design of the FOWT must ensure it is able to withstand complex environmental conditions including wind, wave, current, and performance of the wind turbine. It needs simulation tools with fully integrated hydrodynamic-servo-elastic modeling capabilities for the floating offshore wind turbines. Most of the numerical simulation approaches consider only first-order hydrodynamic loads; however, the second-order hydrodynamic loads have an effect on a floating platform which is moored by a catenary mooring system. At the difference-frequencies of the incident wave components, the drift motion of a FOWT system is able to have large oscillation around its natural frequency. This paper presents the effects of second-order wave loads to the drift motion of a semi-submersible type. This work also aimed to validate the hydrodynamic model of Ulsan University (UOU) in-house codes through numerical simulations and model tests. The NREL FAST code was used for the fully coupled simulation, and in-house codes of UOU generates hydrodynamic coefficients as the input for the FAST code. The model test was performed in the water tank of UOU.

Dynamic Responses of a Spar Type Floating Offshore Wind Turbine With Failed Moorings

2020 ◽  
Author(s):  
Yajun Ren ◽  
Vengatesan Venugopal
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Floating Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Platform Motions

Abstract The complex dynamic characteristics of Floating Offshore Wind Turbines (FOWTs) have raised wider consideration, as they are likely to experience harsher environments and higher instabilities than the bottom fixed offshore wind turbines. Safer design of a mooring system is critical for floating offshore wind turbine structures for station keeping. Failure of mooring lines may lead to further destruction, such as significant changes to the platform’s location and possible collisions with a neighbouring platform and eventually complete loss of the turbine structure may occur. The present study focuses on the dynamic responses of the National Renewable Energy Laboratory (NREL)’s OC3-Hywind spar type floating platform with a NREL offshore 5-MW baseline wind turbine under failed mooring conditions using the fully coupled numerical simulation tool FAST. The platform motions in surge, heave and pitch under multiple scenarios are calculated in time-domain. The results describing the FOWT motions in the form of response amplitude operators (RAOs) and spectral densities are presented and discussed in detail. The results indicate that the loss of the mooring system firstly leads to longdistance drift and changes in platform motions. The natural frequencies and the energy contents of the platform motion, the RAOs of the floating structures are affected by the mooring failure to different degrees.

scholarly journals Vibration Reduction Strategy for Offshore Wind Turbines

2020 ◽  
Vol 10 (17) ◽  
pp. 6091
Author(s):  
Haoming Liu ◽  
Suxiang Yang ◽  
Wei Tian ◽  
Min Zhao ◽  
Xiaoling Yuan ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Output Power ◽  
Wind Turbines ◽  
Reference Signal ◽  
Offshore Wind ◽  
Wave Load ◽  
Offshore Wind Turbines ◽  
Pitch Control ◽  
Simulation Results ◽  
Aerodynamic Torque

The operational environment of offshore wind turbines is much more complex than that of onshore wind turbines. Facing the persistent wind and wave forces, offshore wind turbines are prone to vibration problems, which are not conducive to their long-term operation. Under this background, first, how the wave affects the vibration characteristics of offshore wind turbines is analyzed. Based on the existing wave and wave load models, we analytically show that there exist fluctuating components related to the hydrodynamic frequency in the aerodynamic load and aerodynamic torque of offshore wind turbines. Simulation results based on a GH Bladed platform further validates the analysis. Second, in order to reduce the joint impacts of the wave, wind shear and tower shadow on the wind turbine, a variable pitch control method is proposed. The integrated tower top vibration acceleration signal is superimposed on the collective pitch reference signal, then the triple frequency (3P) fluctuating component of the wind turbine output power and the azimuth angle of each blade are converted into the pitch angle adjustment signal of each blade, which is superimposed on the collective pitch signal for individual pitch control. The simulation results show that the proposed pitch control strategy can effectively smooth the fluctuation of blade root flap-wise load caused by wind and wave, and significantly reduce the fluctuation of aerodynamic torque and output power of offshore wind turbines.

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