WavEC Annual Seminar 2013

Powering the Future Portugal and Holland join forces in Offshore Renewables

Lisbon, 25th November 2013

SPARBUOY-OWC: floating wave energy converter with air turbine

Luís M. C. Gato

The Oscillating Water Column (OWC)

Japan, 1978-86

Australia, 2012

Ireland, 2008-11 IST Sparbuoy NAREC, 2012

IST Sparbuoy Nazaré, 2012

Spain

Portugal

UK

Mutriku, Spain

The Sparbuoy-OWC

Principle of operation similar to the fixed OWC

Characteristics •Floater oscillation in heave: radiation of waves •Relative motion between device and internal free surface: air flow •Two-body system (floater and OWC): two resonance peaks, if well tuned, the system performs well over a wide range of frequencies

The axisymmetric floating OWC

R.P.F. Gomes, J.C.C. Henriques, L.M.C. Gato, A.F.O. Falcão. “Hydrodynamic optimization of an axisymmetric floating oscillating water column for wave energy conversion”, Renewable Energy, Vol. 44, pp. 328-339, 2012

• 5 design parameters with lower and upper bonds

• 1 constraint: submerged lenght

• Fixed loater diameter

Small-scale model testing

R.P.F. Gomes, J.C.C. Henriques, L.M.C. Gato, A.F.O. Falcão. “Testing of a small-scale floating OWC model in a wave flume”, ICOE 2012, 4th International Conference on Ocean Energy, Dublin, 2012

Medium-scale model testing

.

2.1m

Tests of the 1:35th-scale model (0.57m x 2.10m) at IHRH-FEUP (Porto, PT) wave tank (28m x 12m x 1.1m with central pit).

1:16 scale model testing

4 m

NAREC, UK, 2012

BIRADIAL self-rectifying air turbine

Patent applications (2012): Europe, USA, Chile, Australia, New Zealand, Indonesia

Version 1: the guide vanes are radially offset from the rotor.

Advantage: reduce the stalling loss at the exit guide vanes

Guide vanes

Patent applications (2012): Europe, USA, Chile, Australia, New Zealand, Indonesia

Version 2: the sets of guide vanes can axially slide together.

Advantage: remove the guide vanes from flow at rotor exit.

Patent applications (2012): Europe, USA, Chile, Australia, New Zealand, Indonesia

Model testing in unidirectional flow

• Measured peak efficiency in model 80%. • Non-linear pressure flow curve. . •Wide range of flow rates. . .

Dimensionless results from model testing of turbine 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

0.00

0.05

0.10

0.15

0.20

0.25

68.41 K

55.32 K

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40.0

0.2

0.4

0.6

0.8

,

,

,

flo

w r

ate

pressure

pressure

Biradial turbine

Time average efficiency in random waves up to 71%

Air Turbine and Converter Matching

J.C.C. Henriques, A.F.O. Falcão, R.P.F. Gomes, L.M.C. Gato. “Air turbine and primary converter matching in spar-buoy OWC wave energy device”, OMAE2013, 32nd Int. Conf. On Ocean, Offshore and Arctic Engineering, June 2013.

Wave climate: 12 sea states, Pierson-Moskowitz spectrum and frequency of occurrence

Spar-Buoy: 16m diameter floater and 48m draught Biradial turbine rotor diameters: 1.0, 1.25, 1.5, 1.75 and 2.0 m

Dimensionless capture length based on turbine power output as a function of

the turbine rotor diameter

Turbine rotor diameter (m)

Latching Control in Regular Waves

J.C.C. Henriques, A.F.O. Falcão, R.P.F. Gomes, L.M.C. Gato. “Latching control of an OWC spar-buoy wave energy converter in regular waves, ASME Journal of Offshore Mechanics and Arctic Engineering, in press, 2013.

Time series, with latching control, of the mass flow rate of air, diffraction force on the buoy, buoy velocity, and dimensionless relative chamber

pressure, for regular wave period T=8s and height H=2m

Experimental testing of control strategies for the biradial turbine in the OWC spar-buoy,

Tecnalia (Bilbao), 2013

Generator 11 kW 750 rpm

Motor 15kW 1500 rpm

Flywheel 1.2 kg m2

225 230 235 2400

1

2

3

4x 10

6

time [s]

Pow

er

[W]

225 230 235 24080

100

120

140

160

180

200

time [s]

om

ega [

rad/s

]

turbine

generator

exp

num

Low Inertia

• Experimental testing of the electrical components of the power take-off unit (biradial turbine)

• Simulation in real-time of the OWC spar-buoy dynamics coupled with a ‘real’ generator

• Simulation of different control strategies and different moments of inertia (flywheel)

170 175 180 185 190 195 200 205 210 215 2200

1

2

3

4

5

6x 10

6

time [s]

Pow

er

[W]

170 175 180 185 190 195 200 205 210 215 22040

60

80

100

120

140

160

time [s]

om

ega [

rad/s

]

turbine

generator

exp

num

High Inertia

Planning for 2014-15

• 2014: 1:32 scale model tests in extreme waves, array of 3 devices, Plymouth, UK (MARINET, FP7)

• 2014-15: Sea trials with a small version for oceanographic applications (with MBARI, USA)

Conclusion

• Floating OWCs are appropriate for large-scale exploitation of wave energy.

• OWC spar-buoy may operate efficiently with large damping and small air-flow rate.

• A relatively small biradial turbine at large rotational speed can match those requirements.

• This may result in a reliable, efficient and cost-effective wave energy converter.

• Latching control may significantly improve wave energy conversion by OWC spar-buoy.