Fatigue Damage to the Spar-Type Offshore Floating Wind Turbine Under Blade Pitch Controller Faults

The safety and reliability margin of offshore floating wind turbines need to be higher than that of onshore wind turbines due to larger environmental loads and higher operational and maintenance costs for offshore wind turbines compared to onshore wind turbines. However rotor cyclic loads coupled with 6 DOFs motions of the substructure, amplifies the fatigue damage in offshore floating wind turbines. In general a lower fatigue design factor is used for offshore wind turbines compared to that of the stationary oil and gas platforms. This is because the consequence of a failure in offshore wind turbines in general is lower than that of the offshore oil and gas platforms. In offshore floating wind turbines a sub-system fault in the electrical system and blade pitch angle controller also induces additional fatigue loading on the wind turbine structure. In this paper effect of selected controller system faults on the fatigue damage of an offshore floating wind turbine is investigated, in a case which fault is not detected by a fault detection system due to a failure in the fault detection system or operator decided to continue operation under fault condition. Two fault cases in the blade pitch angle controller of the NREL 5MW offshore floating wind turbine are modeled and simulated. These faults include: bias error in the blade pitch angle rotary encoder and valve blockage or line disconnection in the blade pitch angle actuator. The short-term fatigue damage due to these faults on the composite blade root, steel low-speed shaft, tower bottom and hub are calculated and compared with the fatigue damage under normal operational conditions considering same environmental conditions for both cases. This comparison shows that how risky is to work under the fault conditions which could be useful for wind turbine operators. The servo-hydro-aeroelastic code HAWC2 is used to simulate the time domain responses of the spar-type offshore floating wind turbine under normal and faulty operational conditions. The rain-flow cycle counting method is used to calculate the load cycles under normal operational and fault conditions. The short term fatigue damage to the composite blade root and steel structures are calculated for 6-hour reference period. The bi-linear Goodman diagram and a linear SN curve are used to estimate the fatigue damage to the composite blade root and the steel structures respectively. Moreover the fatigue damage for different mean wind speeds, sea states and fault amplitudes are calculated to figure out the region of wind speeds operation with the highest risk of damage.

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

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4031312 ◽

2015 ◽

Vol 137 (6) ◽

Cited By ~ 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.

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Blade Pitch Angle Control for Floating Offshore Wind Turbines by Model Predictive Control

IEEJ Transactions on Electronics Information and Systems ◽

10.1541/ieejeiss.135.882 ◽

2015 ◽

Vol 135 (7) ◽

pp. 882-892 ◽

Cited By ~ 4

Author(s):

Segolene Dessort ◽

Sho Tsujimoto ◽

Naoyuki Hara ◽

Keiji Konishi

Keyword(s):

Model Predictive Control ◽

Predictive Control ◽

Wind Turbines ◽

Pitch Angle ◽

Offshore Wind ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Blade Pitch Angle

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Investigations of Unsteady Aerodynamics of an Offshore Floating Wind Turbine With Platform Motions Using Dual-Sliding Method

Volume 12: Wind Energy ◽

10.1115/gt2020-14350 ◽

2020 ◽

Author(s):

Xiaodong Wang ◽

Zhaoliang Ye ◽

Ziwen Chen ◽

Yize Guo ◽

Yujun Qiao

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Aerodynamic Performance ◽

Offshore Wind ◽

Sliding Mesh ◽

Unsteady Aerodynamic ◽

Floating Wind Turbine ◽

Mesh Method ◽

Offshore Floating Wind Turbine ◽

Platform Motions

Abstract Offshore wind energy developed rapidly in recent years. Due to the platform motions causing by ocean waves, the aerodynamics of floating offshore wind turbines (FOWT) show strong unsteady characters than onshore wind turbines. The widely used methods to investigate the unsteady aerodynamic performance of wind turbine are Blade Element Momentum (BEM) and Free-Vortex Wake (FVW) methods. The accuracy of these two methods strongly depend on empirical formula or correction models. However, for dynamics motions of wind turbine, there is still a lack of accurate models. CFD simulations using overset or dynamic mesh methods also have been used for FOWT aerodynamic investigations. However, the mesh deforming or reconstruction methods are usually suitable for small movement of wind turbine blade. In this paper, a dual-sliding mesh method is employed to simulate the unsteady aerodynamic characters of an offshore floating wind turbine with supporting platform motions using Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations. Both rotor rotation and platform motions are treated as rigid angular motions. The relative motion and data exchange were simulated using sliding mesh method. The NREL 5MW reference wind turbine with platform pitching and rolling motions are considered. The pitching and rolling motions of floating platform are simplified in the form of a prescribed sinusoidal function. Different conditions with two amplitudes and two frequencies of pitching and rolling motions were investigated. URANS were performed with full structured mesh for wind turbine rotor using commercial software FLUENT. The platform motions were set using User Defined Function (UDF). Transitional Shear Stress Turbulence (T-SST) model was employed. The simulation results were compared with BEM method and FVW method results. Both steady status and dynamic pitching processes are investigated. The variations of wind turbine aerodynamic load, as well as the aerodynamic character of airfoils at different spanwise positions, were obtained and analyzed in detail. The simulations results show that the platform pitching introduce remarkable influence on the wind turbine aerodynamic performance. The platform pitching has much larger influence on the wind turbine power and thrust than the platform rolling. The dual-sliding mesh method shows potentials to investigation the dynamic process with multiple rigid motions.

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Guideline for Offshore Floating Wind Turbine Structures

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 3 ◽

10.1115/omae2010-20344 ◽

2010 ◽

Cited By ~ 1

Author(s):

Knut O. Ronold ◽

Vigleik L. Hansen ◽

Marte Godvik ◽

Einar Landet ◽

Erik R. Jo̸rgensen ◽

...

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Wind Farms ◽

Oil And Gas Industry ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Technical Requirements ◽

Floating Wind Turbine ◽

Floating Offshore Wind Turbines ◽

Offshore Floating Wind Turbine

Floating offshore wind turbines is a field undergoing major development. Several companies and research institutes worldwide are engaged in research programs, pilot projects and even planning of commercial floating wind farms. Developing standards for design of floating wind turbine structures and a framework for prevailing rules are crucial and necessary for the industry to continue to grow. Det Norske Veritas (DNV) is an international provider of offshore standards for both the oil and gas industry and the wind energy industry. The standard DNV-OS-J101 “Design of Offshore Wind Turbine Structures” provides principles, technical requirements and guidance for design, construction and in-service inspection of offshore wind turbine structures. As a first step towards updating this standard to fully cover floating wind turbine structures, a DNV Guideline for Offshore Floating Wind Turbines has been established. This development is based on identification of current floating wind turbine concepts and the guideline includes an evaluation of what is required to make DNV-OS-J101 suitable for floating wind turbine structures. This paper presents the highlights of the new DNV Guideline for Offshore Floating Wind Turbine Structures.

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Vibration and Load Suppression of Offshore Floating Wind Turbine

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1025-1026.891 ◽

2014 ◽

Vol 1025-1026 ◽

pp. 891-896 ◽

Cited By ~ 2

Author(s):

Er Ming He ◽

Ya Qi Hu ◽

Yang Zhang ◽

Ge Liang Yin

Keyword(s):

Wind Turbine ◽

Structural Dynamics ◽

Wind Turbines ◽

Structural Control ◽

Offshore Wind ◽

Dynamics Simulation ◽

Type Model ◽

Simulation Code ◽

Offshore Wind Turbines ◽

Floating Wind Turbine

The application of tuned mass dampers (TMDs) to offshore wind turbines has a huge potential to suppress the large vibration responses of these systems. Control module of TMDs is added into the wind turbine structural dynamics simulation code FAST and fully coupled aero-hydro-TMD-structural dynamics model of the 5MW Barge-type floating wind turbine by National Renewable Energy Laboratory (NREL) is established. A multi-parameter optimization study is performed to determine the optimal parameters of a fore-aft TMD system in the Barge-type model. The wind turbine model equipped with the optimal TMD is then simulated under five typical load conditions and the performance of the new system is evaluated. The results show that longitudinal loads at tower base and deflections at tower top reductions of up to 50% and longitudinal loads at blade root and deflections at blade tip reductions of up to 40% are achieved, which indicates that the optimal TMD can be used to suppress the vibration response of offshore wind turbines and also demonstrates the potential for TMD structural control approaches.

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Fatigue Assessment of Monopile Supported Offshore Wind Turbine under Non-Gaussian Wind Field

Shock and Vibration ◽

10.1155/2021/6467617 ◽

2021 ◽

Vol 2021 ◽

pp. 1-12

Author(s):

Bing Li ◽

Kang Rong ◽

Haifeng Cheng ◽

Yongxin Wu

Keyword(s):

Fatigue Life ◽

Wind Turbine ◽

Fatigue Damage ◽

Wind Turbines ◽

Wind Field ◽

Pile Foundation ◽

Offshore Wind ◽

Wind Fields ◽

Offshore Wind Turbines ◽

Non Gaussian

The vibration of offshore wind turbines caused by external loads is significant, which will cause fatigue damage to offshore wind turbines. Wind load is the main load during the operation period of the wind turbine, and available studies have shown that the external wind field often exhibits certain non-Gaussian characteristics. This article aims to obtain the fatigue assessment of the monopile foundation of the wind turbine under the non-Gaussian wind fields. A 5 MW wind turbine is selected in this article, and OpenFAST is applied to simulate the wind load. By comparing the Mises stress time histories of the pile foundation at a different depth, the fatigue analysis of the critical spots of the pile foundation is obtained. In the analysis of fatigue damage, the rain flow counting method is adopted, and the two-segment S-N curve is selected to analyze the fatigue life of the critical spots. The results show that, by taking the non-Gaussian characteristic of the wind field into account, the fatigue life of the monopile foundation decreases. Therefore, attention should be paid to the influence of non-Gaussian characteristics of wind fields on the fatigue life of monopile-supported wind turbines.

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Experimental results of floating platform vibration control with mode change function using full-scale spar-type floating offshore wind turbine

Wind Engineering ◽

10.1177/0309524x17737336 ◽

2017 ◽

Vol 42 (3) ◽

pp. 230-242 ◽

Cited By ~ 3

Author(s):

Hiromu Kakuya ◽

Takashi Shiraishi ◽

Shigeo Yoshida ◽

Tomoaki Utsunomiya ◽

Iku Sato

Keyword(s):

Vibration Control ◽

Wind Turbine ◽

Pitch Angle ◽

Full Scale ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Floating Platform ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Blade Pitch Angle

Floating offshore wind turbines have great potential for harvesting renewable energy sources since offshore wind is stronger and more stable than onshore wind. The foundations of floating offshore wind turbines are not rigidly fixed and it leads to vibration of the floating platform pitch angle. This vibration is caused by fast blade pitch angle motions of variable speed control for controlling rotor speed at rated values. This study proposes a control method to address this vibration, floating platform vibration control. This method extracts a natural frequency component of the vibration from the floating platform pitch angle signal by a band pass filter and controls the blade pitch angle on the basis of proportional–derivative control. Its key characteristic is changing control modes in accordance with electrical power. Experiments using a full-scale spar-type floating offshore wind turbine were performed, and results show that the proposed floating platform vibration control can suppress the vibration of floating platform pitch angle.

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

Volume 5: Ocean Space Utilization; Ocean Renewable Energy ◽

10.1115/omae2011-49793 ◽

2011 ◽

Cited By ~ 2

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.

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Importance of Control Strategies on Fatigue Life of Floating Wind Turbines

Volume 5: Ocean Space Utilization; Polar and Arctic Sciences and Technology; The Robert Dean Symposium on Coastal and Ocean Engineering; Special Symposium on Offshore Renewable Energy ◽

10.1115/omae2007-29277 ◽

2007 ◽

Cited By ~ 23

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.

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