Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND No. SAND2015-9794 PE

Challenges and Opportunities for Large-scale Floating Offshore

Vertical Axis Wind Turbines

D. Todd Griffith, PhD

Sandia National Laboratories 2016 Wind Turbine Blade Workshop

Albuquerque, NM August 31, 2016

Document Number: SAND2015-9794 PE

Characteristics of Offshore Wind

Opportunities Proximity to population centers Better winds Vast resource Scale-up opportunity

Challenges High LCOE High BOS costs Accessibility Inexperience, Immaturity

2

Large reduction in Deepwater Offshore COE may require non-incremental system

solutions

Floating VAWTs

Available at www.sandia.gov/wind

Partners

Sandia Team: Roles and Responsibilities

4

T. Griffith Project Coordinator System Design, Dynamics & Loads, Cost Analysis

B. Owens VAWT Codes & VAWT Design

D. Bull K. Ruehl Carlos Michelen B. Gunawan S. Bredin V. Neary

Floating Systems (platform and mooring) Met ocean conditions Wave characterization & analysis Hydrodynamics codes

B. Ennis K. Moore

VAWT aero-hydro-elastic simulations Modal Analysis Drivetrain Modeling

G. Bacelli Controls; Design Optimization; Dynamic Stability M. Barone VAWT Aerodynamics J. Paquette VAWT Structural Analysis

Sandia Wind Program: From 1970s to 1990s

5

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND No. SAND2015-9794 PE

Standards Applicable to Large-

scale Floating VAWTs

Standards and Load Cases

IEC 61400-3 addresses offshore wind design conditions Gust with Direction Change

VAWTS are less sensitive as tower clearance would not be an issue and they aren’t as affected by direction changes

Vertical Shear VAWTs are less sensitive to vertical wind shear as they

assimilate those changes along the height of the rotor. Extreme Gusts

VAWTs may be more impacted as the total blades solidity will likely be higher.

Cut-Out VAWTs will likely be much more sensitive to cut-out load cases

because of stall control

7

Project Objectives

8

Improve knowledge of the technical and economic feasibility of a floating offshore VAWT system.

The most critical barrier to offshore wind, high Cost of Energy (COE), is specifically targeted through a series of studies:

1. Technical Barriers & Standards 2. Rotor Design Studies 3. Platform and Mooring Design Studies 4. VAWT Design Codes 5. Innovations & Opportunities 6. LCOE Analysis

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND No. SAND2015-9794 PE

Rotor Design Studies

VAWT Structural Design Study

Reduction of parameter space was essential at the early stages of the design process: Architecture of the rotor Number of blades Chord length Material Blade tapering scheme

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Structural Design Study: Configurations

Parameter Values Considered

Architecture Darrieus, V

Number of Blades 2, 3

Tip Chord Length 2m, 3m

Composite Material: Glass/Epoxy, Carbon/Epoxy

Tapering Scheme (Darrieus only, V-VAWTS used Single Taper)

No Taper, Single Taper, Double Taper

Curvature or Power Law Exponent (V-VAWT)

n=1, n=3, n=5 0

20

40

60

80

100

120

140

160

180

0 20 40 60

Heig

ht (m

)

Radius (m)

DarrieusV, n=1V, n=2V, n=3V, n=4V, n=5

ANSYS Beam Models of D and V

VAWTS

D and V VAWT Shapes

Rotor Aero Design Population

24 Candidate Rotor Design External Shapes 12 Darrieus :

large/small chord single/double/no blade taper two/three blades

12 “V”-Rotors : large/small chord power law shape exponent = 1/3/5 two/three blades

Constraints Max radius = 54 m Same capture area NACA 0021 airfoil section

12

VAWT Aerodynamic Design Analysis

13

AEP

Platform

Fatigue

Power curves

Parked Loads

Operating Loads

1 2

3 4

XY

Z

X Y

Z

X

Y

Z

X

YZ

JUL 13 201214:35:33

JUL 13 201214:35:33

JUL 13 201214:35:33

JUL 13 201214:35:33

DISPLACEMENT DISPLACEMENT

DISPLACEMENT DISPLACEMENT

STEP=1SUB =5FREQ=2.0265DMX =.021155

STEP=1SUB =5FREQ=2.0265DMX =.021155

STEP=1SUB =5FREQ=2.0265DMX =.021155

STEP=1SUB =5FREQ=2.0265DMX =.021155

CACTUS to OWENS Code Coupling Results

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Configuration Max Tower Top Disp.

(m)

Max Blade Total Disp.

(m)

% Tower Top Disp.

% Blade Disp. at

Mid-Span DC2LCDT 2.14 2.05 1.6 3.1 DC3LCDT 2.68 2.35 2.0 3.6 DG2LCDT 7.53 4.41 5.7 6.7 DG3LCDT 1.26 0.95 1.0 1.4 VC2N5LC 0.23 1.92 0.4 1.9 VC3N5LC 0.23 1.66 0.4 1.6

Ultimate strain allowable: 6000 micro-strain

Fatigue strain allowable: 3500 micro-strain

Displacements:

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND No. SAND2015-9794 PE

Platform & Mooring Design Studies

Platform Options Tailored solution to a floating VAWT

16

Spar

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Semi-Submersible

Platform Sizing Study for Range of Topside Masses

Dynamic Loading on Platform is Important for VAWTs

RPM 2P (seconds) 4P (seconds)4 7.500 3.750

7.2 4.167 2.083

RPM 3P (seconds) 6P (seconds)4 5.000 2.500

6.3 3.175 1.587

Two sources: Wave and VAWT Dynamics VAWT periods: Due to oscillating VAWT loads (torque, pitch, and roll)

VAWT Periods for 2 and 3 bladed Darrieus machines:

The lower per rev is dominant.

3 bladed VAWT has lower period of primary loading (close to 3 seconds).

Comparison: Spar vs. Semisubmersible

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HAWT

VAWT (with equal mass of

600 mt)

VAWT (with mass of 973

mt) Spar-buoy

Semi-Sub

Spar-buoy

Semi-Sub

Spar-buoy

Semi-Sub

Topside Mass (mt) 600 600 600 600 973 973

Platform Steel Mass (mt) 2,000 2,900 1045 1708 1,500 2,370

Percent mass reduction versus HAWT

-- -- 48% 41% 25% 18%

Comparison of platform steel mass for two platform/floater types and two topside types of equal power rating (5MW)

1. Fowler, M., Bull, D., and Goupee, A.: A Comparison of Platform Options for Deep-water Floating Offshore Vertical Axis Wind Turbines: An Initial Study, Sandia National Laboratories Technical Report, SAND2014-16800, August 2014. 2. Griffith, D. T., Paquette, J., Barone, M., Goupee, A., Fowler, M., Bull, D., and Owens, B.: A study of rotor and platform design trade-offs for large-scale floating vertical axis wind turbines, Science of making torque from wind conference, Munich, Germany, 2016.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND No. SAND2015-9794 PE

VAWT Design Codes @ Sandia

Sandia VAWT Codes List

Geometry/Modeling & Post-processing VAWTGen Code

Aerodynamics CACTUS code

Structural Dynamics OWENS code Features: Modal, Transient, Static

Hydrodynamics WaveEC2Wire code Notes: Coupled with OWENS

21

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of

Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND No. 2012-5130P

Innovations and Analysis to Mitigate Barriers and Design Challenges

Summary of Investigated Topics

1. Novel VAWT Airfoils (TU-Delft) 2. Aero-elastic Stability Analysis 3. Rotor-Platform Coupled Dynamic Stability 4. Manufacturing (ISU/Sandia) 5. Balance of Station Cost Reduction 6. Storm Survival and Load Alleviation

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Is Aeroelastic Stability an issue for large-scale VAWTs?

0 5 10 15 20 25 30-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

Rotor Speed (RPM)

Dam

ping

Rat

io

DG2LCDTDG3LCDTDC2LCDTDC3LCDTVC2N5LCVC3N5LC

Owens B.C. and Griffith, D.T. “Aeroelastic Stability Investigations for Large-scale Vertical Axis Wind Turbines,” Science of Making Torque from Wind Conference, Copenhagen, Denmark, June 2014

5 MW Design Studies

Trend with Increasing Blade Length: Approaching Flutter Speed for Horizontal Axis Wind Turbines (HAWTs

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND No. SAND2015-9794 PE

Deep-water Offshore VAWT LCOE Analysis

System LCOE Trends: AEP, RPM, Rotor vs Platform

26

Website and References (selected)

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http://www.sandia.gov/wind http://energy.sandia.gov/energy/renewable-energy/wind-power/offshore-wind/innovative-offshore-vertical-axis-wind-turbine-rotors/ Publications 1. Sutherland, H.J., Berg, D.E., and Ashwill, T.D., “A Retrospective of VAWT Technology,” Sandia National Laboratories

Technical Report, SAND2012-0304, January 2012. 2. Owens, B., Hurtado, J., Barone, M., and Paquette, J., “An Energy Preserving Time Integration Method for Gyric Systems:

Development of the Offshore Wind Energy Simulation Toolkit” Proceedings of the European Wind Energy Association Conference & Exhibition. Vienna, Austria, 2013.

3. Owens, B.C., Hurtado, J.E., Paquette, J., Griffith, D.T., and Barone, M., “Aeroelastic Modeling of Large Offshore Vertical-axis Wind Turbines: Development of the Offshore Wind Energy Simulation Toolkit,” 54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, April 8–11, 2013, Boston, MA, USA, AIAA-2013-1552.

4. Owens, B.C., Griffith, D.T., and Hurtado, J.E., “Modal Dynamics and Stability of Large Multi-megawatt Deepwater Offshore Vertical-axis Wind Turbines: Initial Support Structure and Rotor Design Impact Studies,” 32nd ASME Wind Energy Symposium, National Harbor, MD, USA, January 2014.

5. Ragni, D., Simao-Ferreira, C., and Barone, M., “Experimental and Numerical Investigation of an Optimized Airfoil for Vertical Axis Wind Turbines,” 32nd ASME Wind Energy Symposium, National Harbor, MD, USA, January 2014.

6. Fowler, M.J., Owens, B.C., Goupee, A.J., Hurtado, J.E., Griffith, D.T., and Alves, M., “Hydrodynamic Module Coupling in the Offshore Wind Energy Simulation (OWENS) Toolkit,” Proceedings of the 33rd ASME International Conference on Ocean, Offshore and Arctic Engineering (OMAE2014), June 8–13, 2014, San Francisco, California, USA, Paper OMAE2014-24175.

7. Owens, B.C., and Griffith, D.T., “Aeroelastic Stability Investigations of Large-scale Vertical Axis Wind Turbines,” Journal of Physics Conference Series, Science of Making Torque from Wind Conference, June 18–20, 2014, Lyngby, Denmark.

8. Fowler, M., Bull, D., and Goupee, A, “A Comparison of Platform Options for Deep-water Floating Offshore Vertical Axis Wind Turbines: An Initial Study,” Sandia National Laboratories Technical Report, SAND2014-16800, August 2014.

9. Griffith, D. T., Paquette, J., Barone, M., Goupee, A., Fowler, M., Bull, D., and Owens, B.: A study of rotor and platform design trade-offs for large-scale floating vertical axis wind turbines, Science of making torque from wind conference, Munich, Germany, 2016.

High-resolution Offshore Wind Farm Modeling

Offshore Wind @ Sandia

Deepwater Offshore

VAWT

Offshore Siting Analysis

Large Offshore Rotors

Sensing, Structural Health, and Prognostics

• Vision: Promote & accelerate the commercial OW industry and reduce costs through technical innovation:

• Siting/Permitting: Sediment Transport & Radar • Large offshore HAWT rotors • Deepwater VAWT system • Structural health and prognostics management • Offshore wind farm modeling