In the conversion of wind power, the rotor is the first point of energy transformation, transforming the kinetic energy of the wind into torque and rotation. Rotor technology sets a limit of the energy converted and the loading required to convert this energy. The load cycles are design drivers, influencing the mass and operation of the rotor, and therefore the entire turbine. In addition to extracting kinetic energy from the flow, the rotor creates a pressure field that generates the wake and leads to noise generation. Rotor design optimisation must therefore account for power and load optimisation, constrained by the full lifecycle, fatigue life and noise, among other boundary conditions. This session focus on innovations in both rotor design methodologies and components.
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Learning objectives
- Understand the effect of geometric non-linearities in the fatigue life of the blade;
- Evaluate the possible impact of flexible certification guidelines in rotor design optimisation;
- Analyse the application of trailing edge serrations as a noise reduction device;
- Evaluate the potential of active flap control for both alleviation and power optimisation;
- Evaluate the impact of integrating the turbine lifecycle in the design optimisation of rotors.
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Presenter
Co-authors:
Johannes Georg Leib (1) F Christoph Brokopf (1) Simon Pansart (1)
(1) DNV GL, Hamburg, Germany
Presenter's biography
Biographies are supplied directly by presenters at WindEurope Summit 2016 and are published here uneditedJohannes Georg Leib has more than 10 years of experience in FRP composites and has been working in the wind industry since 2008. He studied Mechanical Engineering and Plastics Processing at RWTH Aachen University. Currently Mr. Leib works as a Senior Engineer for wind turbine rotor blades in DNV GL. During his 8 years being with DNV GL, he gained broad experience in the structural aspects of wind turbine rotor blades, from the design, manufacturing and in-field operation point of view.
Abstract
Cost of energy saving potentials by innovative technical guidelines for wind turbine rotor blades
Introduction
Technical guidelines for certification of wind turbine components have partly been considered as hostile to innovation and risk-averse in the past. Restrictive partial safety factor concepts often made it difficult for designers and manufacturers to utilize the full potential out of their design and the materials used. Innovative design approaches as well as excellent control of manufacturing tolerances and quality were often not rewarded as the guidelines were not flexible enough. By the example of wind turbine rotor blades, this presentation demonstrates how novel flexible partial safety factor concepts can lead to significantly lower product cost and thereby reduce the overall cost of energy.
Approach
Novel concepts for deriving partial safety factors open the option to consider more product reliability related aspects such as manufacturing tolerances, sophisticated verification methods or the level of quality control. For wind turbine rotor blades reducing the partial safety factors in most cases leads directly to a reduction of the amount of material needed to build a blade while still fulfilling the requirements from an appropriate technical guideline. The product cost reduction for wind turbine rotor blades by applying innovative partial safety factor concepts can be proven by a case study analysing the cost for a typical large wind blade for different safety factor scenarios.
Main body of abstract
DNV GL has published a new technical standard for wind turbine rotor blades (DNVGL-ST-0376) in December 2015. This new standard opens the option to decrease the partial safety factors such as for material strengths, stability verification or tip-to-tower clearance. In order to utilize these options, the effort for verification, manufacturing or quality control of the blade has to be increased on the other hand, e.g.:
* In order to reduce the partial safety factor for stability analysis, sophisticated calculation methods such as non-linear FE-analysis, validation tests and/or proper consideration of material property variations shall be applied.
* In order to reduce the required safety margin on tip-to-tower clearance, the blade stiffness shall not only be calculated and exemplarily tested, but regularly tested in blade serial production.
* In order to reduce the partial safety factors on material strengths, adverse manufacturing effects shall be quantified and/or validated by testing.
By a comprehensive case study on an exemplarily chosen 60 m rotor blade it is proven that utilizing the above-mentioned options for reducing safety factors can lead to a significant reduction in overall product cost. Different scenarios such as designs dominated/restricted by minimum tip-to-tower clearance, inter-fibre failure effort or stability etc. are taken into account.
Conclusion
A novel more flexible partial safety factor concept for wind turbine rotor blades is introduced to the industry by DNV GL. The case study carried out on a typical wind blade clearly proves the cost reduction, if measures in design, verification and manufacturing that allow the reduction of partial safety factors are taken. The cost reduction is mainly caused by the fact that increased utilization of material allowables leads to a reduced amount of material needed to produce a wind blade which however has an identical safety margin level.
Learning objectives
Delegates will learn that the new rotor blade standard introduced to the industry by DNV GL opens the option to reduce product cost and thereby the overall cost of energy. Some of the measures to gain that benefit are already established in some companies, but in order to fully yield those potentials, blade designers and producers need to invest more effort into manufacturing accuracy, sophisticated verification methods, material and (sub-)component testing and quality control during blade serial production.
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