Philosophy
Wave energy conversion by point absorbers or hinged beam rafts has theoretical limits. Systems with multiple floats responding in multiple modes increase the power capture to be similar to wind turbines. M4 is a modular hinged raft-type system enabling this philosophy.
Strategy
Target LCOE 10p/kWh or less through device with high energy capture
Multi-bodies for high wave energy capture across range of real wave conditions through streamlined floats with multi-mode hydrodynamic interactions
Moored floating device for easy deployment and long-term maintenance in port
Survivability in extreme waves
Scalable to several power take offs for high capacity as offshore wind
Power take off at each hinge accessible above deck for maintenance
Environmentally non-intrusive
On-Going Activity
Time domain linear wave modelling by University of Manchester has been successful coupling with PTOs and mooring. This is being generalised further.
Economic assessment for sites around the world so far indicating LCOE in 10-20 p/kWh range with simple damper. There is immediate scope for optimising prime mover structure (reducing mass of steel).
Ocean trials planning at Western Australia (1/5th-1/3rd scale).
Methods for PTO control for optimising energy capture is ongoing with Queen Mary University London. Optimal control shows power improvement by 40-100%, reducing LCOE correspondingly.
Contact
Peter Stansby FREng, Osborne Reynolds Professor of Fluid Mechanics, University of Manchester,
3 FLOAT M4 TESTING IN THE PLYMOUTH OCEAN BASIN (1:50 SCALE)
Note PTO on protoype would be hinged on to the deck.
3 FLOAT M4 in extreme focussed waves
Wave height is approximately 10m full scale.
6 FLOAT M4 TESTING AT Lir OCEAN BASIN, UNIVERSITY COLLEGE CORK
WITH TWO PTOs
VIDEO BELOW
6 FLOAT M4 TESTING AT Lir OCEAN BASIN , EXTREME WAVES WITHOUT PTO , VIDEO BELOW
Technical Criteria
Hydrodynamic design with floats at approximately half wavelength spacing responding predominantly in anti-phase. The small bow float and mid float(s) are rigidly connected. A hinge with the PTO above a mid float is connected by a beam to a large stern float and power is generated from the relative angular rotation.
A large stern float and mid floats have different heave resonance periods within wave period range of a particular wave climate. The anti-phase heave motion of the bow and mid floats generates pitching motion in anti-phase with stern float(s).
The anti-phase surge forcing between mid and stern floats increases power generation due to the anti-phase moments about the hinge above mid float (shown by mathematical modelling).
Broad band power generation in irregular waves results.
Reducing spectral peakedness and increasing directional spread in irregular waves slightly reduces power capture
There are negligible drag losses with rounded base floats shown by experimental and mathematical modelling.
Acceptable motion in extreme waves with negligible power generation. An upper limit on relative pitch motion is inferred from model tests at about ± 40 deg but may be reduced further.
Story So Far
Tests in lab in Manchester at 1:50 scale.
EPSRC funding from Supergen Marine Challenge : project Step WEC.
Tests in wave basin in Plymouth at 1:10 scale as well as 1:50 demonstrate Froude scaling so results may be extrapolated to full scale.
Mathematical modelling to optimise float sizes and shape.
Experimental results with rounded base floats improve power capture.
Optimising power take off control will increase capture width further.
Mathematical modelling allows any float number, up to 8 tested.
6 float configuration (132) tested in laboratory shows model underestimates power slightly (EU Marinet2 project)
Effective sea keeping in extreme waves observed in basin testing (see figure above).
LCOE is comparable with offshore wind depending on site.
Figure with different multi-float configurations showing capture width ratio CWR in JONSWAP waves with γ=3.3 against model scale peak period Tp. The CWR is the average power generated divided by the average wave power per metre crest divided by the energy period wavelength. A typical target offshore period of 7s gives a scale of 1:50. The CWR is a non-dimensional parameter applying at all scales. This definition of CWR should not be confused with definition based on device width used in some references.
The Team
Professor Peter Stansby
Lead, design, computational modelling, ocean basin testing
University of Manchester
and M4 WavePower Ltd
Experimental team
Bob Brown, Professor Peter Stansby, Dr Efrain Carpintero Moreno
University of Manchester
Dr Guang Li
PTO control theory and design
Queen Mary University of London
and Zhijiang Liao (PhD student)
Dr Sam Draycott
Extreme wave specification
University of Manchester
Professor Paul Taylor
Ocean wave data and extreme analysis
University of Western Australia
Bob Brown
Electronics technician
University of Manchester
Publications
Stansby,P., Carpintero Moreno,E., Stallard,T.,Maggi,A. 2015 Three-float broad-band resonant line absorber with surge for wave energy conversion, Renewable Energy, 78, 132-140
​
Stansby,P., Carpintero Moreno,E., Stallard,T . 2015 Capture width of the three-float multi-mode multi-resonance broad-band wave energy line absorber M4 from laboratory studies with irregular waves of different spectral shape and directional spread, J. Ocean Engineering and Marine Energy, 1(3), 287-298,
​
Santo,H., Taylor,P.H., Eatock Taylor,R., Stansby, P. 2016 Decadal variability of wave power production in the North-East Atlantic and North Sea for the M4 machine, Renewable Energy 91, 442-450
​
Eatock Taylor,R., Taylor,P.H. and Stansby, P.K. 2016 A coupled hydrodynamic-structural model of the M4 wave energy converter, J. Fluids and Struct. 63, 77–96.
Sun,L., Stansby,P., Zang,J., Carpintero Moreno, E., Taylor,P. 2016 Linear diffraction analysis and optimisation of the three-float multi-mode wave energy converter M4 in regular waves including small arrays, J. Ocean Engineering and Marine Energy, 2(4), 429-438.
Stansby, P.K., Carpintero Moreno, E. & Stallard, T. 2016. Modelling of the 3-float WEC M4 with nonlinear PTO options and longer bow beam, Proc. 2nd Int. Conf. on Renewable Energies Offshore, Lisbon (RENEW 2016).
​
Sun,L., Zang,J., Stansby,P., Carpintero Moreno, E., Taylor,P., Eatock Taylor,R. 2017 Linear diffraction analysis of the three-float multi-mode wave energy converter M4 for power capture and structural analysis in irregular waves with experimental validation, J. Ocean Eng. Mar. Energy, 3(1), 51-68.
​
Santo, H., Taylor, P.H., Carpintero Moreno, E., Stansby, P., Eatock Taylor, R., Sun, L., Zang, J. 2017 Extreme motion and response statistics for survival of the M4 wave energy converter, J. Fluid Mechanics, 813, 175-204.
​
Stansby,P., Carpintero Moreno,E., Stallard,T., 2017 Large capacity multi-float configurations for the wave energy converter M4 using a time-domain linear diffraction model, Applied Ocean Research, 68 , 53–64.
​
Carpintero Moreno, E., Stansby, P.K. 2019 The 6-float wave energy converter M4: ocean basin tests giving capture width ratios, response and energy yield for several sites, Renewable and Sustainable Energy Reviews, 104, 307–318.
​
Liao,Z., Gai,N., Stansby,P., Li,G. 2019 Linear Non-Causal Optimal Control of an Attenuator Type Wave Energy Converter M4, IEEE Trans on Sustainable Energy, DOI 10.1109/TSTE.2019.2922782.
​
Santo,H., Taylor,P.H., Stansby, P. 2020 The performance of the three-float M4 wave energy converter off Albany, on the south coast of Western Australia, compared to Orkney (EMEC) in the UK, Renewable Energy, 146, 444-459
​
Liao,Z., Stansby,P.K., Li, G., 2020 A generic linear non-causal optimal control framework integrated with wave excitation force prediction for multi-mode wave energy converters with application to M4, Applied Ocean Research , 97, 102056, doi.org/10.1016/j.apor.2020.102056
​
Stansby,P.K., Carpintero Moreno, E. 2020 Hydrodynamics of the multi-float wave energy converter M4 with slack moorings: time domain linear diffraction-radiation modelling with mean force and experimental comparison, Applied Ocean Research, 97, 102070, doi.org/10.1016/j.apor.2020.102070
​
Stansby, P. and Carpintero Moreno, E. 2020 Study of snap loads for idealized mooring configurations with a buoy, inextensible and elastic cable combinations for the multi-float M4 wave energy converter, Water, 12, 2818, Special issue on Numerical and Experimental Modelling of Wave Field Variations around Arrays of Wave Energy Converters.
​
Zhang,Y., Stansby,P., Li.G. 2020 Non-causal Linear Optimal Control with Adaptive Sliding Mode Observer for Multi-Body Wave Energy Converters, IEEE Trans on Sustainable Energy, 12(1), 568-577.
​
Gaspar, J.F., Stansby,P.K., Calvario,M., Guedes Soares, C. 2021 Hydraulic Power Take-Off concept for the M4 Wave Energy Converter, Applied Ocean Research, 106, 102462
​
Liao,Z., Stansby,P., Li,G., Carpintero Moreno, E. 2021 High-capacity wave energy conversion by multi-floats, multi-PTO, control and prediction: generalised state-space modelling with linear optimal control and arbitrary headings, IEEE Transactions on Sustainable Energy, 12(4), 2123–2131
​
Stansby,P.K., Carpintero Moreno, E., Draycott,S. and Stallard, T. 2021 Total wave power absorption by a multi-float wave energy converter and a semi-submersible wind platform with a fast far field model for arrays, Journal of Ocean Engineering and Marine Energy, 8(1), 43-63
​
Patent : Stansby,P. 2013 Surge based wave energy converter PCT/GB2013/050787