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