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Structural Optimization of Composite Blades for Wind and Hydrokinetic Turbines
Global Marine Renewable Energy Conference (GMREC VI)Almas Temple, Washington D.C.
April 11, 2013
Image: Marine Current Turbines
Danny Sale*, Alberto Aliseda*, and Michael Motley***Dept. of Mechanical Engineering
**Dept. of Civil & Environmental EngineeringUniversity of WashingtonSeattle, Washington, USA
Ye Li, IEEE Senior MemberNational Wind Technology Center
National Renewable Energy LaboratoryGolden, Colorado, USA
Outline● Background Info
● design of composite turbine blades
● Technical Approach● structural mechanics● validation● optimization
● Preliminary Results● optimized composite blade● effects of uncertain material properties
● Ongoing Work● exploring alternative blade designs for MHK● coupling of hydrodynamic and structural optimization
K. Dykes & R. Meadows (2012) “Applications of Systems Engineering to the Research, Design, and Development of Wind Energy Systems”
(artist: Rick Hinrichs)
Systems Optimization
Anatomy of a Composite BladeHydrokinetic blades similar to wind blades?
J. Mandell (2012). “The SNL/MSU/DOE Fatigue Program: Recent Trends”, 2012 SNL Blade Workshop.
Approach: Structural Mechanics● Classical Lamination Theory
● discretize cross sections as laminated plates
● Euler-Bernoulli Theory w/ Shear Flow Theory Applied to Composite Beams● Coupling between axial, bending, twisting
● Recovery of 2D Lamina-Level Strain/Stress
● Linear Buckling Analysis
● Coupled Mode Shapes (BModes – FEM code from NREL)
Validation● Comparison of Co-Blade results to FEM solutions
personal communication:Hongli Jia (Ms.)MS-PhD CandidateStructures and Composites Laboratory Hanyang University, Korea
Validation● Comparison of Co-Blade results to FEM solutions
personal communication:Hongli Jia (Ms.)MS-PhD CandidateStructures and Composites Laboratory Hanyang University, Korea
Turbine Design Specs
Image: Marine Current Turbines
● Based off DOE Ref. Model
● Design load case:
● A “rotor sized” eddy approaches...
● Free stream increases from 2.3 m/s (nominal) to 3 m/s (x 1.3)
● Pitch control cannot respond to shed excess load
Multi-Objective Optimization
● Structural objectives compete w/ hydrodynamic objectives
● Identify Pareto frontier: set of “equally optimal” designs
● How do we select a design? Make trade-offs within set
Bill of Materials
J. Mandell, D. Samborsky, P. Agastra, A. Sears, and T. Wilson. "Analysis of SNL/MSU/DOE Fatigue Database Trends for Wind Turbine Blade Materials." Contractor Report SAND2010-7052, Sandia National Laboratories, Albuquerque, NM, 2010.
tri-axial weave
+- 45 weave
uni-directional structural foam
Structural Optimization● Design Variables (control points)
-material thicknesses within each sub-component of the blade
-dimensions of root build-up, spar cap, LEP/TEP, shear webs
Structural Optimization
Results: Stress Analysis
critical stress area
blade-shell: E-glass
blade-root: E-glass
spar-uni: carbon
web-shell: E-glass
Predict failure of carbon fiber spar cap● blade is very thin at ~75% span● no more space inside for materials –
approaching limits of thin-wall theory!● try again, increasing chord and hydrofoil
thickness – should improve structural integrity
● highlights importance of coupling the hydrodynamic & structural design process
Visualize stresses within each layer of the composite blade
● almost all materials withstand loads within acceptable limits, but...
Uncertain Material Properties
spar-uni: carbon
Uncertain material properties can arise from● Manufacturing process● Degradation & corrosion in marine environment
Use Monte Carlo analysis to quantify effect on blade response● vary material props.
E11
, E22
, G12
, ν12
, ρ● observe blade response
Uncertain Material Properties
spar-uni: carbon
Co-Blade source code & user's guide:code.google.com/p/co-blade/
site visits: ~230 Downloads since Aug. 2012
Development of a Design Tool for Wind and MHK Turbines● Code repositories help foster collaboration● Track usage statistics, feedback on desired code features
Conclusion
spar-uni: carbon
Progress to Date:● Developed design tools for wind & MHK devices
-method is generalized to a variety of turbine configurations-consider large number of design variables & constraints-focus on optimizing energy production, blade response, & reducing loads-reduce development time & lead to improved designs
Areas for Refinement:(short-term)
● Extend Monte Carlo analysis-geometric uncertainty (blade geom., ply angles, ply thickness)-modal analysis (natural frequencies, mode shapes)
(longer-term)● Need more validation! Especially stress/strain & buckling data● Tighter coupling between hydrodynamic & structural design● Coupling w/ unsteady fluid solver to study fluid-structure
interaction (GPU accelerated vortex particle methods & SPH)
Thank you!
Questions?This work has also been made possible by
● National Science Foundation Graduate Research Fellowship under Grant No. DGE-0718124
● Department of Energy, National Renewable Energy Laboratory● University of Washington, Northwest National Marine Renewable
Energy Center