Structural Optimization of Composite Blades for Wind and Hydrokinetic 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
Image: Marine Current Turbines
Global Marine Renewable Energy Conference (GMREC VI) Almas Temple, Washington D.C. April 11, 2013
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
Systems Optimization
K. Dykes & R. Meadows (2012) “Applications of Systems Engineering to the Research, Design, and Development of Wind Energy Systems” (artist: Rick Hinrichs)
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.
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 Candidate Structures and Composites Laboratory Hanyang University, Korea
Validation ●
Comparison of Co-Blade results to FEM solutions personal communication: Hongli Jia (Ms.) MS-PhD Candidate Structures and Composites Laboratory Hanyang University, Korea
Turbine Design Specs ●
Based off DOE Ref. Model
●
Design load case: ●
●
●
Image: Marine Current Turbines
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 tri-axial weave
+- 45 weave
uni-directional
structural foam
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.
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 blade-shell: E-glass
blade-root: E-glass
Visualize stresses within each layer of the composite blade ●
almost all materials withstand loads within acceptable limits, but...
Predict failure of carbon fiber spar cap ●
critical stress area
spar-uni: carbon
●
●
●
web-shell: E-glass
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
Uncertain Material Properties 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. spar-uni: carbon 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/ Development of a Design Tool for Wind and MHK Turbines ● Code repositories help foster collaboration ● Track usage statistics, feedback on desired code features
site visits:
~230 Downloads since Aug. 2012
Conclusion 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 spar-uni: designs carbon -reduce development time & lead to improved 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
