Risk‐based derivation of target reliability levels for life extension of wind turbine structural components

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.

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Remaining Useful Life Estimation of Wind Turbine Blades under Variable Wind Speed Conditions Using Particle Filters

Annual Conference of the PHM Society ◽

10.36001/phmconf.2018.v10i1.481 ◽

2018 ◽

Vol 10 (1) ◽

Author(s):

Bhavana Valeti ◽

Shamim N. Pakzad

Keyword(s):

Wind Speed ◽

Wind Turbine ◽

Turbine Blades ◽

Remaining Useful Life ◽

Structural Components ◽

Wind Turbine Blades ◽

Average Wind Speed ◽

Average Wind ◽

Useful Life ◽

Variable Wind

Rotor blades are the most complex structural components in a wind turbine and are subjected to continuous cyclic loads of wind and self-weight variation. The structural maintenance operations in wind farms are moving towards condition based maintenance (CBM) to avoid premature failures. For this, damage prognosis with remaining useful life (RUL) estimation in wind turbine blades is necessary. Wind speed variation plays an important role influencing the loading and consequently the RUL of the structural components. This study investigates the effect of variable wind speed between the cutin and cut-out speeds of a typical wind farm on the RUL of a damage detected wind turbine blade as opposed to average wind speed assumption. RUL of wind turbine blades are estimated for different initial crack sizes using particle filtering method which forecasts the evolution of fatigue crack addressing the non-linearity and uncertainty in crack propagation. The stresses on a numerically simulated life size onshore wind turbine blade subjected to the above wind speed loading cases are used in computing the crack propagation observation data for particle filters. The effects of variable wind speed on the damage propagation rates and RUL in comparison to those at an average wind speed condition are studied and discussed.

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Use of ultrasonic models in the design and validation of new NDE techniques

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1986.0122 ◽

1986 ◽

Vol 320 (1554) ◽

pp. 329-340 ◽

Cited By ~ 16

Keyword(s):

Fracture Mechanics ◽

Elastic Wave ◽

Structural Integrity ◽

Life Extension ◽

Experimental Demonstration ◽

Structural Components ◽

Model Calculations ◽

Model Predictions ◽

The Cost ◽

Theoretical Scattering

In implementing fracture mechanics based techniques for the design and life extension of structural components, it is necessary to establish the reliability with which various flaw sizes and types can be detected and characterized. Traditionally, this has been accomplished through extensive experimental demonstration programmes. This paper discusses present efforts to use model predictions to reduce the required amount of experimentation, and hence the cost, of such programmes. Formalisms whereby the extensive elastic-wave theoretical scattering effort of the last decade can be applied to practical problems are first reviewed. This is followed by several specific examples which have occurred in the nuclear and aerospace industries. The paper concludes with the identification of some important remaining theoretical problems and a discussion of possible strategies for future implementation of model calculations as tools in structural integrity programmes.

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Extending the life of wind turbine blade leading edges by reducing the tip speed during extreme precipitation events

Wind Energy Science ◽

10.5194/wes-3-729-2018 ◽

2018 ◽

Vol 3 (2) ◽

pp. 729-748 ◽

Cited By ~ 24

Author(s):

Jakob Ilsted Bech ◽

Charlotte Bay Hasager ◽

Christian Bak

Keyword(s):

Wind Turbine ◽

Extreme Precipitation ◽

Turbine Blades ◽

Leading Edge ◽

Life Extension ◽

Wind Turbine Blades ◽

Worst Case ◽

Severe Problem ◽

Extreme Precipitation Events ◽

Leading Edges

Abstract. Impact fatigue caused by collision with rain droplets, hail stones and other airborne particles, also known as leading-edge erosion, is a severe problem for wind turbine blades. Each impact on the leading edge adds an increment to the accumulated damage in the material. After a number of impacts the leading-edge material will crack. This paper presents and supports the hypothesis that the vast majority of the damage accumulated in the leading edge is imposed at extreme precipitation condition events, which occur during a very small fraction of the turbine's operation life. By reducing the tip speed of the blades during these events, the service life of the leading edges significantly increases from a few years to the full expected lifetime of the wind turbine. This life extension may cost a negligible reduction in annual energy production (AEP) in the worst case, and in the best case a significant increase in AEP will be achieved.

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

Volume 9: Offshore Geotechnics; Torgeir Moan Honoring Symposium ◽

10.1115/omae2017-62713 ◽

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.

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WT Load Measurement Uncertainty: Load-Based Versus Analytical Strain-Gauge Calibration Method

Journal of Solar Energy Engineering ◽

10.1115/1.3027508 ◽

2009 ◽

Vol 131 (1) ◽

Cited By ~ 3

Author(s):

D. J. Lekou ◽

F. Mouzakis

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Technical Specification ◽

Calibration Method ◽

Structural Components ◽

Large Magnitude ◽

Uncertainty Sources ◽

Accredited Laboratory ◽

Measurement Uncertainties ◽

Analytical Calibration

For load measurements conducted on current wind turbines according to technical specification IEC 61400-13 load-based as well as analytically determined calibrations are possible. The uncertainties involved in load measurements due to the employment of these two methods may vary from application to application, which should be documented by the accredited laboratory and taken into account by the wind turbine designer∕manufacturer. To this end, a comparative study is conducted to define the measurement uncertainties when applying load-based or analytical calibration. Examples are presented for the resulting uncertainties and both techniques are assessed with respect not only to the uncertainties introduced but also to the specific requirements of each application. Although the analysis of the uncertainties involved especially in the analytical calibration regarded the primary uncertainty sources, from the results it is shown that the mechanical calibration should be preferred to the analytical one wherever possible. However, since the wind turbines and their structural components are becoming larger the mechanical calibration might not always be possible. Moreover, given that the problem of imposing loads of large magnitude, that is, of magnitude comparable to the ultimate loads expected to be applied on the structure will become more difficult in the future due to the continuous enlargement of the wind turbine and its components, probably more reliable results can be attained by use of a combination of both methods.

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