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MULTI-DISCIPLINARY CONSTRAINED OPTIMIZATION OF WIND TURBINES C.L. Bottasso , F. Campagnolo , A. Croce Politecnico di Milano, Italy EWEC 2010 Warsaw, Poland, April 20-23, 2010. Outline. Introduction and motivation Approach: Constrained multi-disciplinary optimization Simulation models

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  1. MULTI-DISCIPLINARY CONSTRAINED OPTIMIZATION OF WIND TURBINESC.L. Bottasso, F. Campagnolo, A. CrocePolitecnicodi Milano, ItalyEWEC 2010 Warsaw, Poland, April 20-23, 2010

  2. Outline • Introduction and motivation • Approach: • Constrained multi-disciplinary optimization • Simulation models • Aerodynamic optimization • Structural optimization • Combined aero-structural optimization • Applications and results • Conclusions and outlook

  3. Introduction and Motivation • Focus of present work: integrated multi-disciplinary (holistic) constraineddesign of wind turbines, i.e. optimal coupled sizing of: • Aerodynamic shape • Structural members (loads, aero-servo-elasticity and controls) • Constraints: ensure a viable design by enforcing all necessary design requirements • Applications: • Sizing of a new machine • Improvement of a tentative configuration • Trade-off studies (e.g. performance-cost) • Modifications to exiting models • Previous work: • Duineveld, Wind Turbine Blade Workshop 2008; Fuglsang & Madsen, JWEIA 1999; Fuglsang, EWEC 2008; etc.

  4. Outline • Introduction and motivation • Approach: • Constrained multi-disciplinary optimization • Simulation models • Aerodynamic optimization • Structural optimization • Combined aero-structural optimization • Applications and results • Conclusions and outlook

  5. Approach • Optimizer • Local/global solvers (SQP, GA) • Functional approximators • Aerodynamic parameters: • chord, twist, airfoils Cp-Lambda aero-servo-elastic multibodysimulator ANBA cross sectional analyzer Parameters • Macro parameters: • rotor radius, max chord, tapering, … Cost function & constraints • Structural parameters: • thickness of shell and spar caps, width and location of shear webs Partition of optimization parameters:aerodynamic, structural, macro (i.e. combined aero-structural)

  6. Blade parameterization: • Chord and twist shape functions deform a baseline configuration • Richer shape with fewer dofs • Constraints: • Noise constraint (V tip): regulation in region II1/2 • Torque-TSR stability • Max chord • …

  7. Cp-Lambda (Code for Performance, Loads, Aero-elasticity by Multi-Body Dynamic Analysis): • Global aero-servo-elastic FEM model • ANBA (Anisotropic Beam Analysis) cross sectional model: • Evaluation of cross sectional stiffness (6 by 6 fully populated) • Recovery of sectional stresses and strains Compute sectional stiffness of equivalent beam model Compute cross sectional stresses and strains • Rigid body • Geometrically exact beam • Revolute joint • Flexible joint • Actuator

  8. Modeling: • Extract reduced model from multibody one • Linearize reduced model • Synthesize controller: • Compute LQR gains • Analyses: • DLCs (IEC61400: load envelope, fatigue DELs) • Eigenfrequencies (Campbell diagram) • Stability • Compute constraints: • Max tip deflection • Frequency placement • Update process: • Analyses: • Transfer loads from multibody to cross sectional models • Recover sectional stresses and strains • Compute cost function: • Weight • Compute constraints: • Stress/strains safety margins

  9. Structural Blade Modeling Cross section types Sectional structural dofs Spanwise shape functions Location of structural dofs and load computation section Load computation section Twisted shear webs Maximum chord line Straight webs Caps extend to embrace full root circle

  10. Parameter: radius, max chord, etc. • Example: tapering • Example: AEP over weight • Example: spar cap thickness

  11. Outline • Introduction and motivation • Approach: • Constrained multi-disciplinary optimization • Simulation models • Aerodynamic optimization • Structural optimization • Combined aero-structural optimization • Applications and results • Conclusions and outlook

  12. Optimization of a 3 MW Wind Turbine • Parameter: blade tapering, constrained max chord • Long blade span (D=106.4m) and small maximum chord (3.9m) is penalized by excessive outboard chords • (lower flap frequency/increased tip deflections) • Optimal solution: intermediate taper

  13. WT2, the Wind Turbine in a Wind Tunnel Aero-elasticallyscaled wind turbine model for: • Testing and comparison of advanced control lawsand supporting technologies • Testing of extreme operating conditions Civil-Aeronautical Wind Tunnel - Politecnicodi Milano • Individual blade pitch • Torque control

  14. Design of an Aero-elastically Scaled Composite Blade • Objective: size spars (width, chordwise position & thickness) for desired sectional stiffness within mass budget • Cost function: sectional stiffness error wrt target (scaled stiffness) • Constraints: lowest 3 frequencies • Carbon fiber spars for desired stiffness Sectional optimization variables (position, width, thickness) Span-wise shape function interpolation • Rohacell core with grooves for the housing of carbon fiber spars Width Chordwise Position • ANBA(ANisotropicBeam Analysis) FEM cross sectional model: • Evaluation of cross sectional stiffness (6 by 6 fully populated matrix) Thickness • Thermo-retractable film

  15. Design of an Aero-elastically Scaled Composite Blade • Solid line: scaled reference values • Mass gap can be corrected with weights • Dash-dotted line: optimal sizing Filippo Campagnolo

  16. Conclusions • Presented holistic optimization procedures for wind turbines: • Refined models: aero-servo-elastic multibody + FEM cross sectional analysis can account for complex effects and couplings from the very inception of the design process (no a-posteriori fixes) • Fully automated: no manual intervention, including self-tuning model-based controller that adjusts to changes in the design • Fast design loop: can perform a full design in 1-2 days on standard desktop computing hardware • General and expandable: can readily add constraints to include further design requirements • Ready-to-use multibody aero-servo-elastic model of final design: available for further analyses/verifications, evaluation of loads for design of sub-components, etc.

  17. Outlook • Real-life applications: • Completed design of 45m blade (to be manufactured end 2010) • Design of 16.5m blade under development • Software enhancements: • Improved speed: parallelization of analyses (DLCs, Campbell, FEM cross sectional analyses, etc.) • Improved coupling between aerodynamic and structural optimizations • Automated generation of CAD model (mould manufacture, FEM analysis) • Automated generation of 3D FEM model for detailed verification (stress & strains, buckling, max tip deflection, fatigue, etc.)

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