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

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

Volume 9A: Ocean Renewable Energy ◽

10.1115/omae2014-23235 ◽

2014 ◽

Cited By ~ 1

Author(s):

Mahmoud Etemaddar ◽

Elaheh Vahidian ◽

Otto Skjåstad

Keyword(s):

Wind Turbine ◽

Fatigue Damage ◽

Wind Turbines ◽

Pitch Angle ◽

Offshore Wind ◽

Offshore Wind Turbines ◽

Composite Blade ◽

Floating Wind Turbine ◽

Offshore Floating Wind Turbine ◽

Blade Pitch Angle

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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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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Improving the Strategy of Maintaining Offshore Wind Turbines through Petri Net Modelling

Applied Sciences ◽

10.3390/app11020574 ◽

2021 ◽

Vol 11 (2) ◽

pp. 574

Author(s):

Rundong Yan ◽

Sarah Dunnett

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Petri Net ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Maintenance Costs ◽

Offshore Wind Turbines ◽

Major Repair ◽

Wind Turbine System ◽

Periodic Maintenance

In order to improve the operation and maintenance (O&M) of offshore wind turbines, a new Petri net (PN)-based offshore wind turbine maintenance model is developed in this paper to simulate the O&M activities in an offshore wind farm. With the aid of the PN model developed, three new potential wind turbine maintenance strategies are studied. They are (1) carrying out periodic maintenance of the wind turbine components at different frequencies according to their specific reliability features; (2) conducting a full inspection of the entire wind turbine system following a major repair; and (3) equipping the wind turbine with a condition monitoring system (CMS) that has powerful fault detection capability. From the research results, it is found that periodic maintenance is essential, but in order to ensure that the turbine is operated economically, this maintenance needs to be carried out at an optimal frequency. Conducting a full inspection of the entire wind turbine system following a major repair enables efficient utilisation of the maintenance resources. If periodic maintenance is performed infrequently, this measure leads to less unexpected shutdowns, lower downtime, and lower maintenance costs. It has been shown that to install the wind turbine with a CMS is helpful to relieve the burden of periodic maintenance. Moreover, the higher the quality of the CMS, the more the downtime and maintenance costs can be reduced. However, the cost of the CMS needs to be considered, as a high cost may make the operation of the offshore wind turbine uneconomical.

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

Journal of Marine Science and Engineering ◽

10.3390/jmse9050543 ◽

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.

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Physical Modelling of Offshore Wind Turbine Foundations for TRL (Technology Readiness Level) Studies

Journal of Marine Science and Engineering ◽

10.3390/jmse9060589 ◽

2021 ◽

Vol 9 (6) ◽

pp. 589

Author(s):

Subhamoy Bhattacharya ◽

Domenico Lombardi ◽

Sadra Amani ◽

Muhammad Aleem ◽

Ganga Prakhya ◽

...

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Prior Experience ◽

Physical Modelling ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Foundation Design ◽

Offshore Wind Turbines ◽

Sea Bed ◽

Geological Conditions

Offshore wind turbines are a complex, dynamically sensitive structure due to their irregular mass and stiffness distribution, and complexity of the loading conditions they need to withstand. There are other challenges in particular locations such as typhoons, hurricanes, earthquakes, sea-bed currents, and tsunami. Because offshore wind turbines have stringent Serviceability Limit State (SLS) requirements and need to be installed in variable and often complex ground conditions, their foundation design is challenging. Foundation design must be robust due to the enormous cost of retrofitting in a challenging environment should any problem occur during the design lifetime. Traditionally, engineers use conventional types of foundation systems, such as shallow gravity-based foundations (GBF), suction caissons, or slender piles or monopiles, based on prior experience with designing such foundations for the oil and gas industry. For offshore wind turbines, however, new types of foundations are being considered for which neither prior experience nor guidelines exist. One of the major challenges is to develop a method to de-risk the life cycle of offshore wind turbines in diverse metocean and geological conditions. The paper, therefore, has the following aims: (a) provide an overview of the complexities and the common SLS performance requirements for offshore wind turbine; (b) discuss the use of physical modelling for verification and validation of innovative design concepts, taking into account all possible angles to de-risk the project; and (c) provide examples of applications in scaled model tests.

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A Surface Ice Module for Wind Turbine Dynamic Response Simulation Using FAST

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4033001 ◽

2016 ◽

Vol 138 (5) ◽

Cited By ~ 2

Author(s):

Bingbin Yu ◽

Dale G. Karr ◽

Huimin Song ◽

Senu Sirnivas

Keyword(s):

Dynamic Response ◽

Wind Turbine ◽

Wind Turbines ◽

Structural Response ◽

Simulation Software ◽

Offshore Wind ◽

Foundation Soil ◽

Offshore Wind Turbines ◽

Ice Failure ◽

Lock In

Developing offshore wind energy has become more and more serious worldwide in recent years. Many of the promising offshore wind farm locations are in cold regions that may have ice cover during wintertime. The challenge of possible ice loads on offshore wind turbines raises the demand of modeling capacity of dynamic wind turbine response under the joint action of ice, wind, wave, and current. The simulation software FAST is an open source computer-aided engineering (CAE) package maintained by the National Renewable Energy Laboratory. In this paper, a new module of FAST for assessing the dynamic response of offshore wind turbines subjected to ice forcing is presented. In the ice module, several models are presented which involve both prescribed forcing and coupled response. For conditions in which the ice forcing is essentially decoupled from the structural response, ice forces are established from existing models for brittle and ductile ice failure. For conditions in which the ice failure and the structural response are coupled, such as lock-in conditions, a rate-dependent ice model is described, which is developed in conjunction with a new modularization framework for FAST. In this paper, analytical ice mechanics models are presented that incorporate ice floe forcing, deformation, and failure. For lower speeds, forces slowly build until the ice strength is reached and ice fails resulting in a quasi-static condition. For intermediate speeds, the ice failure can be coupled with the structural response and resulting in coinciding periods of the ice failure and the structural response. A third regime occurs at high speeds of encounter in which brittle fracturing of the ice feature occurs in a random pattern, which results in a random vibration excitation of the structure. An example wind turbine response is simulated under ice loading of each of the presented models. This module adds to FAST the capabilities for analyzing the response of wind turbines subjected to forces resulting from ice impact on the turbine support structure. The conditions considered in this module are specifically addressed in the International Organization for Standardization (ISO) standard 19906:2010 for arctic offshore structures design consideration. Special consideration of lock-in vibrations is required due to the detrimental effects of such response with regard to fatigue and foundation/soil response. The use of FAST for transient, time domain simulation with the new ice module is well suited for such analyses.

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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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Fatigue life assessment of three offshore wind turbines

Life-Cycle of Engineering Systems ◽

10.1201/9781315375175-91 ◽

2016 ◽

pp. 742-747 ◽

Cited By ~ 1

Author(s):

W. Weijtjens ◽

N. Noppe ◽

T. Verbelen ◽

C. Devriendt ◽

A. Iliopoulos

Keyword(s):

Fatigue Life ◽

Wind Turbines ◽

Life Assessment ◽

Offshore Wind ◽

Offshore Wind Turbines ◽

Fatigue Life Assessment

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A Review of Recent Advancements in Offshore Wind Turbine Technology

Energies ◽

10.3390/en15020579 ◽

2022 ◽

Vol 15 (2) ◽

pp. 579

Author(s):

Taimoor Asim ◽

Sheikh Zahidul Islam ◽

Arman Hemmati ◽

Muhammad Saif Ullah Khalid

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Structural Integrity ◽

Turbine Blades ◽

Offshore Wind ◽

System Level ◽

Offshore Wind Turbine ◽

Component Level ◽

Foundation Design ◽

Offshore Wind Turbines

Offshore wind turbines are becoming increasingly popular due to their higher wind energy harnessing capabilities and lower visual pollution. Researchers around the globe have been reporting significant scientific advancements in offshore wind turbines technology, addressing key issues, such as aerodynamic characteristics of turbine blades, dynamic response of the turbine, structural integrity of the turbine foundation, design of the mooring cables, ground scouring and cost modelling for commercial viability. These investigations range from component-level design and analysis to system-level response and optimization using a multitude of analytical, empirical and numerical techniques. With such wide-ranging studies available in the public domain, there is a need to carry out an extensive yet critical literature review on the recent advancements in offshore wind turbine technology. Offshore wind turbine blades’ aerodynamics and the structural integrity of offshore wind turbines are of particular importance, which can lead towards system’s optimal design and operation, leading to reduced maintenance costs. Thus, in this study, our focus is to highlight key knowledge gaps in the scientific investigations on offshore wind turbines’ aerodynamic and structural response. It is envisaged that this study will pave the way for future concentrated efforts in better understanding the complex behavior of these machines.

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