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Friday, 20 November 2015
09:30 - 11:00 Innovative design and validation tools
Turbine technology  
Onshore      Offshore    


Room: Montmartre

Guidelines to optimize design processes in terms of cost and time-to-market while ensuring necessary standards when variants are introduced, during early stages of new concepts and as the industry moves to larger turbines.

  • Progress on smart rotor control using sensing strategies for optimal design
  • Probabilistic design framework to quantify uncertainties and reduce risk in design
  • New approach to validation of simulation models for grid studies to deliver variants earlier and economically
  • Time benefits through novel dual axis fatigue testing of blades

Learning objectives

  • Delegates will take away guidelines for the optimal design of smart rotor systems
  • Delegates will be able to implement a probabilistic design method enabling assessment of which uncertainties have most influence on overall COE
  • Delegates will be able to propose a feasible alternative to traditional validation with field measurement data
  • Delegates will be able  to advocate optimized dual axis fatigue testing of blades
Lead Session Chair:
Michaela O'Donohoe, Adwen, Spain
Peter Jamieson, University of Strathclyde, United Kingdom
Peter Greaves Offshore Renewable Energy Catapult, United Kingdom
Co-authors:
Peter Greaves (1) F Paul McKeever (1) Rob Dominy (2) Raul Prieto (1)
(1) Offshore Renewable Energy Catapult, Blyth, United Kingdom (2) Northumbria University, Newcastle upon Tyne, United Kingdom

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2015 and are published here unedited

Peter Greaves is a Blade Testing Engineer working at the Offshore Renewable Energy Catapult’s test facilities in Blyth, Northumberland. He graduated in 2006 from Newcastle University with a degree in Mechanical Engineering. After a year of working on the design of pipe laying equipment for the offshore oil and gas industry he left to obtain an MSc in Renewable Energy, which led to a job developing Narec’s 3MW and 15MW nacelle test rigs. Narec funded Peter’s doctoral studies on bi-axial blade fatigue testing, which is the basis for his current work on blade testing.

Abstract

Bi-Axial Fatigue Testing of Wind Turbine Blades

Introduction

Wind turbine design standards require blades to be tested statically for extreme loads, and fatigue tested to prove that they can survive the design lifetime. The movement towards longer blades for increased power output (5MW and greater), higher capacity factor and/or sites with lower wind speeds presents unique challenges when performing fatigue tests. These tests are usually performed by vibrating the blade at its first resonant frequency, and for large blades this can be very low, resulting in long tests. This work will describe a novel test method that allows the test to be performed in an acceptable timeframe.

Approach

In service, flapwise loading is mainly due to aerodynamic loads and edgewise loading is mainly due to gravity loads. These two sources of loading occur at the same time during the service life, but for blade fatigue tests the flapwise direction is tested separately to the edgewise direction. This approach is less representative of what occurs in service and is also more time consuming than testing both axes simultaneously. The dual axis tests were optimised to match the damage caused by the service life, and comparisons were then made between dual axis testing and single axis testing.

Main body of abstract

There are several factors which can be controlled both before and during a resonant fatigue test. These include:
- The pitch angle of the blade on the test stand (which alters the distribution of mean strain level around the blade)
- The position and mass of the test equipment (which alters the mode shape and therefore the strain amplitude distribution along the blade length, and also the mean strain distribution along the blade length)
- The amplitude of the excitation in the flapwise and edgewise directions (which alters the strain amplitude)
The fact that composite materials accrue damage at different rates depending on the amplitude and mean value of the strain cycle can then be exploited.
The target bending moment distribution in the flapwise and edgewise directions along the length of the blade is calculated from the service life damage, the number of test cycles and the material fatigue properties. This bending moment distribution is then used as a target in an optimisation routine to choose the best position and mass for the test equipment.
Many different tests with varying pitch angles and flapwise and edgewise excitation levels are then simulated to obtain the damage distribution around the blade that they would cause. The best combination of these tests (in terms of number of repeats of each test) is then found by solving a least squares problem with the target being to minimise the difference in the damage distribution due to the test and that due to the service life.


Conclusion

The results show that we can conclude that an optimised dual axis test offers very significant time benefits when compared to single axis testing as well as improving how representative the test is of the loading seen in service. The over-testing which is associated with non-optimised dual axis tests is reduced very significantly.


Learning objectives
Delegates will learn about the drivers for larger blades, blade loading, blade fatigue analysis, how fatigue tests are performed and how the test loads are calculated. They will also learn about novel methods of performing fatigue testing and how the results obtained with this method compare to the standard test described by the design standards.