Reliability Analysis and Risk-Based Methods for Planning of Operation and Maintenance of Offshore Wind Turbines

2017 ◽  
Author(s):  
John Dalsgaard Sørensen
Keyword(s):  
Wind Turbine ◽  
Reliability Analysis ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Offshore Wind ◽  
Special Focus ◽  
Life Cycle Approach ◽  
Structural Components ◽  
Safety Factors ◽  
Partial Safety Factors

Reliability analysis and probabilistic models for wind turbines are considered with special focus on structural components and application for reliability-based calibration of partial safety factors. The main design load cases to be considered in design of wind turbine components are presented including the effects of the control system and possible faults due to failure of electrical / mechanical components. Considerations are presented on the target reliability level for wind turbine structural components. Application is shown for reliability-based calibrations of partial safety factors for extreme and fatigue limit states are presented. Operation & Maintenance planning often follows corrective and preventive strategies based on information from condition monitoring and structural health monitoring systems. A reliability- and risk-based approach is presented where a life-cycle approach is used. An example with wind turbine blades is considered using the NORCOWE reference wind farm.

scholarly journals A Review of Recent Advancements in Offshore Wind Turbine Technology

Energies ◽  
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.

scholarly journals Response-Based Assessment of Operational Limits for Mating Blades on Monopile-Type Offshore Wind Turbines

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1867 ◽  
Author(s):  
Amrit Shankar Verma ◽  
Zhiyu Jiang ◽  
Zhengru Ren ◽  
Zhen Gao ◽  
Nils Petter Vedvik
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Wind Wave ◽  
Turbine Blades ◽  
Offshore Wind ◽  
Extreme Value Analysis ◽  
Wind Turbine Blades ◽  
Value Analysis ◽  
Offshore Wind Turbines ◽  
Blade Root

Installation of wind-turbine blades on monopile-type offshore wind turbines is a demanding task. Typically, a jack-up crane vessel is used, and blades are individually lifted from the vessel deck and docked with the preinstalled hub. During the process of mating, large relative motions are developed between the hub and root due to combined effects of wind-generated blade-root responses and wave-generated monopile vibrations. This can cause impact loads at the blade root and induce severe damages at the blade-root connection. Such events are highly likely to cause the failure of the mating task, while affecting the subsequent activities, and thus require competent planning. The purpose of this paper is to present a probabilistic response-based methodology for estimating the allowable sea states for planning a wind-turbine blade-mating task, considering impact risks with the hub as the hazardous event. A case study is presented where the installation system consisting of blade-lift and monopile system are modelled using multibody formulations. Time-domain analyses are carried out for various sea states, and impact velocities between root and hub are analyzed. Finally, an extreme value analysis using the Gumbel fitting of response parameters is performed and limiting sea state curves are obtained by comparing characteristic extreme responses with allowable values. It is found that the limiting sea states for blade-root mating tasks are low for aligned wind–wave conditions, and further increase with increased wind–wave misalignment. The results of the study also show that the parameter T p is essential for estimating limiting sea states given that this parameter significantly influences monopile vibrations during the blade-root mating task. Overall, the findings of the study can be used for a safer and more cost-effective mating of wind-turbine blades.

scholarly journals A Coupled CFD/Multibody Dynamics Analysis Tool for Offshore Wind Turbines With Aeroelastic Blades

2017 ◽  
Author(s):  
Yuanchuan Liu ◽  
Qing Xiao ◽  
Atilla Incecik
Keyword(s):  
Wind Turbine ◽  
Multibody Dynamics ◽  
Wind Turbines ◽  
Large Scale ◽  
Turbine Blades ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Analysis Tool ◽  
Dynamics Analysis ◽  
Offshore Wind Turbines

Aero-elasticity is an important issue for modern large scale offshore wind turbines with long slender blades. The behaviour of deformable turbine blades influences the structure stress and thus the sustainability of blades under large unsteady wind loads. In this paper, we present a fully coupled CFD/MultiBody Dynamics analysis tool to examine this problem. The fluid flow around the turbine is solved using a high-fidelity CFD method while the structural dynamics of flexible blades is predicted using an open source code MBDyn, in which the flexible blades are modelled via a series of beam elements. Firstly, a flexible cantilever beam is simulated to verify the developed tool. The NREL 5 MW offshore wind turbine is then studied with both rigid and flexible blades to analyse the aero-elastic influence on the wind turbine structural response and aerodynamic performance. Comparison is also made against the publicly available data.

scholarly journals Comparing the Effect of Rotor Tilt Angle on Performance of Floating Offshore and Fixed Tower Wind Turbines

2019 ◽  
Vol 12 (5) ◽  
pp. 84
Author(s):  
Wongsakorn Wisatesajja ◽  
Wirachai Roynarin ◽  
Decha Intholo
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Tilt Angle ◽  
Turbine Blades ◽  
Angle Of Attack ◽  
Offshore Wind ◽  
Floating Platform ◽  
Optimal Position ◽  
Wind Speeds ◽  
Floating Offshore Wind Turbines

The development of Floating Offshore Wind Turbines (FOWTs) aims to improve the potential performance of the wind turbine. However, a problem arises due to the angle of tilt from the wind flow and the floating platform, which leads to a vertical misalignment of the turbine axis, thereby reducing the available blade area and lowering the capacity to capture energy. To address this problem, this paper seeks to compare the influence of the rotor tilt angle on wind turbine performance between fixed tower wind turbines and FOWTs. The models used in the experiments have R1235 airfoil blades of diameter 84 cm. The experiment was analyzed using a wind tunnel and mathematical modelling techniques. Measurements were obtained using an angle meter, anemometer and tachometer. Testing involved wind speeds ranging from 2 m/s to 5.5 m/s, and the rotational speeds of the two turbine designs were compared. The study found that the rotational speeds of the FOWTs were lower than those of the fixed tower turbines. Moreover, at tilt angles from 3.5° – 6.1° there was a loss in performance which varied between 22% and 32% at different wind speeds. The tilt angle had a significant effect upon FOWTs due to the angle of attack was continuously changing, thus altering the optimal position of the turbine blades. This changing angle of attack caused the effective area of the rotor blade to change, leading to a reduction in power output at suboptimal angles. The study finally makes recommendations for future studies.

Structural damping sensitivity affecting the flutter performance of a 10-MW offshore wind turbine

2020 ◽  
Vol 23 (14) ◽  
pp. 3037-3047
Author(s):  
Xugang Hua ◽  
Qingshen Meng ◽  
Bei Chen ◽  
Zili Zhang
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Delay Model ◽  
Structural Damping ◽  
Torsional Mode ◽  
Offshore Wind Turbines

Classical flutter of wind turbine blades is one of the most destructive instability phenomena of wind turbines especially for several-MW-scale turbines. In the present work, flutter performance of the DTU 10-MW offshore wind turbine is investigated using a 907-degree-of-freedom aero-hydro-servo-elastic wind turbine model. This model involves the couplings between tower, blades and drivetrain vibrations. Furthermore, the three-dimensional aerodynamic effects on wind turbine blade tip have also been considered through the blade element momentum theory with Bak’s stall delay model and Shen’s tip loss correction model. Numerical simulations have been carried out using data calibrated to the referential DTU 10-MW offshore wind turbine. Comparison of the aeroelastic responses between the onshore and offshore wind turbines is made. Effect of structural damping on the flutter speed of this 10-MW offshore wind turbine is investigated. Results show that the damping in the torsional mode has predominant impact on the flutter limits in comparison with that in the bending mode. Furthermore, for shallow water offshore wind turbines, hydrodynamic loads have small effects on its aeroelastic response.

scholarly journals Probabilistic and Risk-Informed Life Extension Assessment of Wind Turbine Structural Components

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 821
Author(s):  
Jannie Sønderkær Nielsen ◽  
Lindsay Miller-Branovacki ◽  
Rupp Carriveau
Keyword(s):  
Fatigue Life ◽  
Wind Turbine ◽  
Wind Farm ◽  
Assessment Method ◽  
Economic Feasibility ◽  
Life Extension ◽  
Structural Components ◽  
Safety Factors ◽  
Original Design ◽  
Partial Safety Factors

Reassessment of the fatigue life for wind turbine structural components is typically performed using deterministic methods with the same partial safety factors as used for the original design. However, in relation to life extension, the conditions are generally different from the assumptions used for calibration of partial safety factors; and using a deterministic assessment method with these partial safety factors might not lead to optimal decisions. In this paper, the deterministic assessment method is compared to probabilistic and risk-based approaches, and the economic feasibility is assessed for a case wind farm. Using the models also used for calibration of partial safety factors in IEC61400-1 ed. 4, it is found that the probabilistic assessment generally leads to longer additional fatigue life than the deterministic assessment method. The longer duration of the extended life can make life extension feasible in more situations. The risk-based model is applied to include the risk of failure directly in the economic feasibility assessment and it is found that the reliability can be much lower than the target for new turbines, without compromising the economic feasibility.

Small-Scale Wind Turbines Optimized for Class 2 Wind: A Wind Siting Survey and Annual Energy Production Analysis

2014 ◽  
Author(s):  
Timothy A. Burdett ◽  
Kenneth W. Van Treuren
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Energy Production ◽  
Turbine Blades ◽  
Cost Effective ◽  
Department Of Energy ◽  
Offshore Wind ◽  
Wind Data ◽  
Small Scale ◽  
Site Survey

A crucial step in evaluating a potential location for a wind turbine, especially small-scale wind turbines, is a proper wind site survey. Eventually the wind site survey is used to calculate the annual energy production (AEP) of the wind turbine and determine if this location will be profitable. Generally, a wind classification of 3 or above is recommended for any wind turbine site, according to the U.S. Department of Energy. Wind Classes of 1–2 are not considered suitable; however, data suggests that a wind site with Class of 2 wind has the potential to be more cost effective than even the least expensive offshore wind and deserves consideration. Wind data usually exists at locations such as local airports; however, the height at which this data are taken is not representative of the heights at which wind turbines will be installed and thus, airport wind data should not be used. Also, with the variability in wind from location to location, the airport data are generally not near the potential site for the wind turbine and thus, are not useful. A local wind site survey generally entails a two year study of the site using a meteorological (MET) tower. Waco, TX is being studied for the application of small-scale wind turbines. Waco is in a Class 2 wind area; however, no proper wind survey had ever been accomplished. Such a study was undertaken using a MET tower of 100 ft with two anemometers at 100 ft, one anemometer at 75 ft and one anemometer at 50 ft. This paper will describe the potential of Class 2 wind as an energy source, the erection of the MET tower, collection of the data and analysis of the data for the potential of locating a small-scale wind turbine at the site. Techniques for analyzing data when two anemometers are present will be discussed. Focus will be on identifying invalid data with an emphasis on correcting this invalid data. The data from two anemometers was then used in a novel way to identify and correct the invalid data found at both the 75 ft and 50 ft elevations. A filtering technique has also been developed to help identify invalid data. Based on the results of the wind survey, it will be shown that it is feasible to purposely design wind turbine blades for Class 2 wind which will perform better than commercially available small-scale wind turbines.

Support Structure Reliability of Offshore Wind Turbines Utilizing an Adaptive Response Surface Method

2010 ◽  
Author(s):  
Sebastian Tho¨ns ◽  
Michael H. Faber ◽  
Werner Ru¨cker
Keyword(s):  
Wind Turbine ◽  
Reliability Analysis ◽  
Response Surface ◽  
Wind Turbines ◽  
Adaptive Response ◽  
Offshore Wind ◽  
Limit States ◽  
Support Structure ◽  
Prediction Variance ◽  
The Individual

This paper focuses on a reliability analysis of an offshore wind turbine support structure which is part of an assessment and monitoring framework for wind turbines in operation. The reliability analysis builds upon structural, loading, limit state and uncertainty models comprising design, production and erection data. This model basis facilitates the reliability analysis of the ultimate, the fatigue and the serviceability limit states utilizing stochastic finite elements. The complexity of the individual models dictates an efficient solution scheme for the reliability analysis. Such an algorithm is developed in the present paper consisting of an adaptive response surface algorithm and an importance sampling Monte-Carlo algorithm. The response surface algorithm is based on predetermined experimental designs and facilitates the adjustment of design parameters for an optimized prediction variance in the design point region. Approaches for the consideration of multiple design points and the augmentation of the design for reduction of the prediction variance are introduced. In this paper, a reliability analysis for a tripod support structure of a Multibrid M5000 wind turbine is performed. A comparison with the target reliabilities specified in DIN EN 1990 (2002) shows that the requirements are fully met. However, the consideration of system reliability leads to the conclusion that at the end of the service life there is a significant probability of fatigue damages. The quantification of the reliability for the individual structural components for all limit states facilitates an identification of sensitive components. The results of this study can support the targeted application of monitoring systems, the optimization of the support structures and additionally highlight the need for criteria to the systems reliability.

Long-Term Reliability Analysis of a Spar Buoy-Supported Floating Offshore Wind Turbine

2011 ◽  
Author(s):  
A. Sultania ◽  
L. Manuel
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Reliability Analysis ◽  
Wave Height ◽  
Wind Turbines ◽  
Return Period ◽  
Random Variables ◽  
Offshore Wind ◽  
Floating Platform

Most offshore wind turbines constructed to date have support structures for the turbine towers that extend to the seabed. Such bottom-supported turbines are confined to shallow waters closer to the shore. Sites farther offshore provide a better wind resource (i.e., stronger wind and less turbulence) while also reducing concerns related to visual impact and noise. However, in deeper waters, bottom-supported turbines are less economical. Wind turbines mounted atop floating platforms are, thus, being considered for deepwater sites. Several floating platform concepts are being considered; they differ mainly in how they provide stability to counter the large mass of the rotor-nacelle assembly located high above the water. One of these alternative concepts is a spar buoy floating platform with a deep draft structure and a low center of gravity, below the center of buoyancy. The reliability analysis of a spar-supported 5MW wind turbine based on stochastic simulation is the subject of this study. Environmental data from a selected deepwater reference site are employed in the numerical studies. Using time-domain simulations, the dynamic behavior of the coupled platform-turbine system is studied; statistics of tower and rotor loads as well as platform motions are estimated and critical combinations of wind speed and wave height identified. Long-term loads associated with a 50-year return period are estimated using statistical extrapolation based on loads derived from the simulations. Inverse reliability procedures that seek appropriate load fractiles for the underlying random variables consistent with the target return period are employed; these include use of: (i) the 2D Inverse First-Order Reliability Method (FORM) where an extreme load is selected at its median level (conditional on a derived critical wind speed and wave height combination); and (ii) the 3D Inverse FORM where variability in the environmental and load random variables is fully represented to derive the 50-year load.

scholarly journals A Summary of the Recent Work at NTNU on Marine Operations Related to Installation of Offshore Wind Turbines

2018 ◽  
Author(s):  
Zhen Gao ◽  
Amrit Verma ◽  
Yuna Zhao ◽  
Zhiyu Jiang ◽  
Zhengru Ren
Keyword(s):  
Wind Turbine ◽  
Recent Work ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Structural Safety ◽  
Offshore Wind Turbines ◽  
Global Dynamic ◽  
Contact Impact

In this paper, a summary of the recent work at NTNU on the installation of offshore wind turbines using jack-up and floating vessels will be reported. The wind turbine components considered here are the monopile foundations and the blades. The detailed discussions are given to the crane operations for installing wind turbine blades as well as novel installation methods for pre-assembled rotor-nacelle-tower. It includes numerical modelling and analysis for global dynamic responses of the installation system (installation vessels plus wind turbines) and for local structural responses of the blades in case of contact/impact. In particular, the stochastic nature of the environmental conditions (mainly wind and waves) and their influence on the global dynamic responses of the installation system will be assessed based on time-domain simulations. In addition, tugger line tension control is introduced for the final connection to the hub in order to reduce the motions of the blade and therefore the potential damages to the blades. It is then followed by a discussion about nonlinear structural analysis of the blade in contact with tower or surrounding structures using ABAQUS. Damages in the composite plies and sandwich core materials of the blade due to contact/impact for a given initial velocity are then estimated. The obtained damage distribution formulates the basis for a probabilistic assessment of structural safety during installation. Novel installation methods in which the rotor-nacelle-tower structure is pre-assembled onshore and installed on top of the foundation offshore, and the corresponding installation vessels are discussed at the end of the paper. Finally, the main conclusions and the recommendations for future work are drawn.

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