This document summarizes research on optimizing the structural design of composite blades for wind and marine hydrokinetic turbines. The researchers developed computational tools to model the structural mechanics of composite blades and optimize blade designs for energy production while reducing loads. Preliminary results show the tools can identify optimal blade designs and analyze effects of uncertain material properties. Ongoing work includes further validation and tighter coupling of hydrodynamic and structural models to better capture fluid-structure interaction.

1. 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 Engineering
University of Washington
Seattle, Washington, USA
Ye Li, IEEE Senior Member
National Wind Technology Center
National Renewable Energy Laboratory
Golden, Colorado, USA

2. 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

3. K. Dykes & R. Meadows (2012) “Applications of Systems Engineering to the Research, Design, and Development of Wind
Energy Systems”
(artist: Rick Hinrichs)
Systems Optimization

4. Anatomy of a Composite Blade
Hydrokinetic blades similar to wind blades?
J. Mandell (2012).
“The SNL/MSU/DOE Fatigue
Program: Recent Trends”, 2012
SNL Blade Workshop.

5. 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)

6. Validation
● Comparison of Co-Blade results to FEM solutions
personal communication:
Hongli Jia (Ms.)
MS-PhD Candidate
Structures and Composites Laboratory
Hanyang University, Korea

7. Validation
● Comparison of Co-Blade results to FEM solutions
personal communication:
Hongli Jia (Ms.)
MS-PhD Candidate
Structures and Composites Laboratory
Hanyang University, Korea

8. 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

9. 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

10. 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

11. 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

12. Structural Optimization

13. 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...

14. 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

15. Uncertain Material Properties
spar-uni: carbon

16. 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

17. 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)

18. 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