SMARTY - Supergen MARrine TechnologY challenge

Lead Research Organisation: University of Oxford
Department Name: Engineering Science

Abstract

Any structure exposed to breaking waves, be it a simple breakwater or a complex and expensive marine energy machine, will be exposed to high wave impact loads as overturning wave crests slam into it. The violence of the motion of the water surface as waves break are well-known to surfers who seek out such conditions. Marine renewable energy devices will be hit by the most violent storms that nature can produce, yet they are required to produce significant power when the weather is benign and the waves relatively small. This dichotomy can result in expensive failures such as that of the Osprey, a 2MW wave power prototype device located off the north coast of Scotland, which was damaged and sank in a storm. If marine renewable energy is to play a significant role in meeting the energy requirements of the the United Kingdom, all energy extraction devices must survive for many years and many large storms without damage. Hence accurate design methods are required to estimate the peak hydrodynamic loads occurring in such storms.

This project explores the science and engineering required to ensure that renewable energy devices survive extreme conditions, and seeks to identify the upper limit of device operations in less severe conditions. Key to making a significant advance in survivability is understanding how steep and violent waves behave on significant currents. Both wave power machines and marine current turbines are likely to be located in relatively shallow water with relatively fast tidal currents, obviously for tidal turbines this is a virtue! If the current is fast and the water shallow, there will be considerable resistance to the flow close to the sea-bed and less further up towards the surface. Thus, the current is likely to be highly sheared and very turbulent. Add on top of this bulk flow violently overturning steep waves and it is clear that the water will be moving around very fast in local regions. The first part of this project is to characterize the statistics of waves and how this varies over time for decades to decades. Next the waves are combined with sheared currents. Then models of marine renewable energy devices will be exposed to such violent combined wave and current events and the forces measured. Finally we aim to develop and test force computer based computational methods for assessing loads.

The overall output from this research project will make an important contribution to removing blocks limiting and slowing down the large-scale implementation of marine renewable energy.

Planned Impact

The SUPERGEN Marine challenge call on 'Accelerating the deployment of marine energy (Wave and Tidal)' stresses the need to address the issues which are holding back the deployment of marine energy, some of which were highlighted by the scoping workshop in March 2011 (attended by Dr Drake, one of the partners in this proposal).

This proposal is aimed directly at the part of the call 'Understanding extreme loading events and impact on devices and arrays'. So our work packages are constructed to tackle this problem directly via a combination of high quality laboratory experiments and numerical simulations. We expect the outputs from this work to have a major impact on marine renewable development and coastal and offshore engineering more broadly.
There remain serious scientific questions to be addressed as to the behaviour of steep and breaking waves on sheared currents, and the loads which such massively unsteady turbulent flows exert on any marine renewable systems. The SMARTY project will develop new experimental techniques using state of the art facilities, better than industry standard analysis methods in combination with strong stakeholder engagement through an advisory group meeting with the participants on a regular basis, all aimed at achieving significant improvements in device survivability and utilization.

Engagement with the advisory group will provide natural knowledge transfer. The active participation of Lloyds Register will provide guidance from a regulatory and certification viewpoint. BP will bring their expertise in physical oceanography and offshore structural analysis, as shown by the statement of support from their group chief oceanographer. The support from Peter Fraenkel from Marine Current Turbines shows that device developers will buy into our research programme. Support from EPD and E-ON shows that energy utilities believe we have something important to offer, as does that from Garrad Hassan as representative of consultants in marine renewables.

Dissemination activities will include publication of the research findings in leading international journals, and participation by SMARTY researchers in international conferences and UK meetings. Engagement with learned societies will occur through the Society of Underwater Technology via their SUTGEF group, currently chaired by the P-I Prof Taylor. The experiments at UCL will make excellent material for university open days etc. to engage the interest of visiting school groups etc. The work in this proposal will be tightly integrated into the rest of the ongoing SUPERGEN activities via the hub in Edinburgh.

Further details are given in the Pathways to Impact statement (attached).

Publications

10 25 50
 
Description Examined the variability of the power available in waves at various points around the UK coast. The first paper looks at the raw power (for an infinitely efficient wave power machine) which can operate at 100% efficiency in all waves. The variation of the annual power on a year by year basis is derived over ~ 50 years where wave information over time is available then back-estimated over the last 300 years to give information on longterm variations. In the 2nd paper the same methodology is applied to a particular design of wave power machine. Filtering the available wave field through the machine means that the annual variability of the power output is much smaller than for the raw power - this implies that wave power economics will be easier to manage.

We have also looked at the survivability of a particular wave power machine (the 3-float M4 device) as if it was installed off the Orkney Islands. Although this is an extremely challenging location, first indications are that the machine can probably be designed to survive severe storms here.
Exploitation Route We have applied the same methodology to the available wave power from a particular wave power machine, and the estimation of longterm power variation could be used by all machine developers who know the power characteristics of their individual design.

The approach that we have used to assess whether the M4 wave power machine would survive severe wind storms at a location to the west of the Orkney Islands can be applied to a whole range of other designs. The identication of an approach to specify 'designer waves' for such systems may lead to a significantly improved approach for tank testing - the machine responds to wave slope rather than to wave height, for sufficiently severe storms.
Sectors Aerospace, Defence and Marine,Communities and Social Services/Policy,Energy,Environment

URL http://ora.ox.ac.uk/objects/uuid:241a2b83-a201-4199-90fd-e0caa48a7a44
 
Description We have been working on the M4 wave power machine, designed by Prof. PK Stansby at Manchester. Our results have led to design changes. A field scale model of the updated M4 machine is presently being constructed and testing has commenced in the South China Sea.
Sector Aerospace, Defence and Marine,Energy
Impact Types Economic

 
Description Technical workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Workshop on numerical input generation for modelling of extreme waves in CFD and experiment - run by SMARTY participants from UCL and held at UCL
Year(s) Of Engagement Activity 2016