RENEWABLES
HORIZONTAL-AXIS
WIND TURBINE
A multi-objective structural optimization
of a composite blade
CLIENT
Start-up company in the wind turbine sector
CHALLENGE
Improve the structural characteristics of the blade
SUCCESS
A more resistant material allowed a reduction of the total mass while increasing the structural properties of the blade
01
CHALLENGE
The horizontal-axis wind turbine (HAWT) is one of the most diffused architectures among traditional wind energy conversion systems (WECS), due to its high aerodynamic efficiency. Several works about HAWTs concern the various fluid dynamic aspects of the rotor blade, in order to improve its efficiency and therefore the overall energy production.
Different airfoil shapes and design solutions have been characterized and studied, but a limited number of works dwell on the structural analysis of the blade, pointing mainly at its modal characterization.
Nevertheless, the internal structure of a rotor blade is an essential aspect of its design, intended to ensure the resistance of this huge mechanical component during the entire life cycle of the machine.
02
SOLUTION
The numerical investigations are based on the analysis of a Composite Blade for the AOC 15/50 wind turbine made by the Sandia National Laboratories. The same finite element model is applied on a similar rotor blade, obtained from the geometrical data.
To develop an optimization strategy for the structural design of a rotor blade — named S.O.C.R.A.TE., for Structural Optimization for Composite Rotor Air TurbinE — the study combines a structural analysis and a modified genetic algorithm. The purpose is to improve the structural characteristics of the blade, reducing both the maximum displacements and the mass of the original AOC 15/50 blade, by changing the original layup of the composite materials.
The optimization concerns the choice of the materials and their positioning. The disposal of the materials in the composite layout is the main design variable of the problem: the skin of the blade includes several layers, each characterized by its material, the orientation of the fibers and the thickness. A function computing the main deformations of the blade and a mass function are the two objective functions.
The layout of the composite skin has been encoded parametrically and optimized with a genetic algorithm. The evolutionary process required decomposing the original problem into four successive optimizations for the different layout zones, each result becoming the initial model for the next. The four stages follow the structural components of the blade: the external composite skin, the internal reinforcement, the spar flange and the spar web.
03
RESULTS
An evolution of the optimal Pareto front can be seen at every stage of optimization. The movement of the solutions towards the minimum values of the objective functions represents an increase in the structural performance of the blade — observable both through the generations within a single step and across the sequence of four.
The complete process delivered a good improvement of the blade's structural characteristics: weight down 8% and flapwise deformation down 12%, against a slight 3% increase in edgewise deformation.
The improvements are mainly due to the presence of the more resistant material D155 in every component of the blade. Using D155 allows a reduction of the total mass while increasing the structural properties of the blade.
RECOGNITION
POSTER AWARD
Andrea Dal Monte won the Poster Award at the CAE Conference 2018 for this research activity, carried out at the University of Padova.
“With this tool the wind turbine designer can estimate both the annual energy production and the structural response of the blades.”
Andrea Dal Monte, Ph.D.
