Automaton waves

Waves in time and space: Reubin Margolin's favourite subject material. The sculpture above, 'Yellow wiggle' (2008), demonstrates the superposition of two sine waves with different frequencies. Most of his works are 3D waves, and they really give the impression of a weightless fluid surface, in spite of their true nature.

Black Friday SuperGen

The newspapers described Fri 28 November as 'black'. Not quite sure why; something to do with the embedded carbon in all the impulse purchases? Anyhow, it seemed an apt description to me, given the black week suffered by marine energy. The world leading wave developer, Pelamis, was in administration, and the world leading tidal developer, MCT, had been put up for sale by their owners, Siemens. Rumours of others following in their wake were confirmed this week (Aquamarine 'downsizing'). This was the run-up to the SuperGen Marine annual assembly, so it was bound to be interesting.

The cost-revenue conundrum

Here's a wave power conundrum: what must be done to reduce the cost of energy? The resource is free, so 'efficiency' is measured by how well the structure earns its keep. Back in 1980 the physicist Sir Hermann Bondi wrote (In 'Power from Sea Waves', edited by Brian Count) that you pay for the peaks and get paid for the averages. He had also noted that you pay for loads and get paid for power. Thus the intermittent, reciprocal, high force, slow moving, nature of sea waves is an intrinsic challenge. Consideration of the ratio of expenditure to revenue in terms of the loads is a view now acknowledged by many leading engineers.

EU funding for cross-border collaboration

Ocean Energy ERA-NET is inviting joint calls for collaborative research and innovation projects on wave, and tidal, as well as salinity and thermal gradient technologies. The funding is available to both industry and academia: http://www.oceaneranet.eu/pages/joint-calls-8.html. The deadline for the first call is 18 December 2014: http://www.oceaneranet.eu/News/first-oceanera-net-joint-call-2014-now-open-62.html. Topics include design and development of devices and components, sea trials, development of design tools and standards, and work aimed at improving reliability, survivability, cost of energy and environmental impacts.

In a nutshell: Peaks and troughs (Garrad)

Another of my favourite talks at the Royal Society’s ‘Peaks and Troughs’ workshop is ‘Lessons from the wind energy industry’. Andrew Garrad (as in Garrad-Hassan), describes what worked for onshore wind, as well as what didn’t, and suggested what marine renewables could learn from this experience. His seminar is essential reading (or listening: the sound recording is available) for anyone who is interested in what is driving the current investment climate, and what can be done to weather it.

Tank check-list for wave energy

What type of tank is needed to test a wave energy absorber? Standard tanks for testing ships are a good start, but wave energy has 'special needs'. Here is a check-list of specifications, including a wish-list of features that are nice to have. They are grouped under 7 headings: repeatability, depth, working area, get the waves you want, know the waves you get, get the data you need, don't let scale muck things up.

Cheap, reliable, now

Cheap, reliable, now. You want all 3 things from a new technology. Choose 2.

-ANCIENT ENGINEERING LORE 

What would today's 'Temeraire' be fighting?

"The fighting 'Temeraire' tugged to her last berth to be broken up" by William Turner (1839) has some great imagery that sums up timeless social acceptance issues. It shows the sailing ship 'Temeraire' at the end of her service. It is no co-incidence that she is being brought in by a 'modern' vessel: a coal-fired paddle tug. We are witnessing not just the end of one sailing ship, but the era of wind-powered ships, which is being drawn to a close by the advent of steam-powered vessels. The dramatic sunset (a sunrise would be most inappropriate; it is clearly the end of the day for the 'Temeraire') serves to emphasize the poignancy of this moment.

Comparative tank test challenges: Part II - Reducing systemic errors & bias

Part I discussed some of the inherent difficulties with comparing different concepts of wave energy converter using tank tests. Some of these problems we are stuck with; others can be avoided if we know about them in advance.

Open Source Simulation Tool

Now available from: http://en.openei.org/wiki/WEC-Sim.

All Energy 2014 – Pelamis cost of energy study

Background

In the last session of All Energy 2014, Jacob Ahlqvist presented key findings from Pelamis's recently completed cost reduction project commissioned by the ETI. The project goals were to:

1. maximise returns from the two P2 machines presently being tested at Orkney
2. drive down cost of energy
3. deliver the next design iteration, the P2e, as quickly as possible

Jacob noted that the P2e would 'address the short-comings of the P2', i.e. apply lessons learnt from testing at Orkney to design changes targeted at improving the cost of energy. The final project report was reviewed by independent consultants Black and Veatch, and approved by the ETI review panel. The report itself is not publicly available, but I've heard there are plans to disseminate the results. In the meanwhile, here is what I jotted down during the talk.

In a nutshell: Cummins

W.E. Cummins (1962), The Impulse Response Function and Ship Motions, Schiffstechnik

This paper derives the equation of motion that is most commonly used to model the dynamics of a body in water, including ships and wave energy converters (WECs). The part of the mathematical argument essential to WECs will be summarised here.

The paper starts off with an interesting bit of history. Up until the 1950s, `classical' sea-keeping research only modelled sinusoidal waves and response. The models had the form of second order differential equations. In the 1950s there was growing interest in investigating response to spectra. Initially, they kept the form of the second order differential equations, and expressed the hydrodynamic added mass and damping as frequency dependent parameters. To run such a time domain model, it would be necessary to choose `the frequency' at which added mass and damping were to be considered. There was growing disquiet about the rigor of this approach, not to mention the fact that the models did not describe experiments very well. As Cummins muses in this paper "The shoe is squeezed on, with no regard for the shape of the foot". He goes on to derive a better fitting model.

OES modelling workshop

The OES Annex V workshop on Computational Modeling and Analysis of Marine Energy Converters (25-26 Nov 2013) was organised by Roger Bagbey (Cardinal, USA) and Bob Thresher (NREL, USA), and hosted by Henry Jeffrey (The University of Edinburgh, Scotland UK).

Launching the boat

Skagen is a small town at the northern tip of Denmark, at the meeting of the North and Baltic Seas. There was a group of artists living here around the turn of the nineteenth century. A favourite subject was the local folk who worked the sea. One of the Skagen painters, Michael Ancher, painted the fisherman and lifeboat man, Lars Kruse. Kruse had earned a medal for saving many lives, but this was revoked upon discovery that in his youth he had done some illegal beach-combing. Ancher championed his cause, and did several paintings depicting the harsh and heroic lives of the lifeboat men [Chief lifeboatman Lars Kruse, The drowned fisherman, Fishermen launching a rowing boat]. Kruse's medal was eventually reinstated.

Apache to the rescue

The announcement of an American competition for an open source hydrodynamic solver posed a conundrum for a French research laboratory with their own in-house hydrodynamic code. The LHEEA lab at École Centrale de Nantes (ECN) had been thinking of open-sourcing their code Nemoh for some time. Submitting Nemoh to NREL's OpenWARP competition would make it available to a wide audience, but this would come at a cost: ECN would effectively loose authorship of the code. It was decided to make Nemoh open source first, and then to submit it to OpenWARP.

This idea posed a couple of problems for NREL. Firstly, with Nemoh open source, any old cowboy could submit Nemoh as an entry to OpenWARP. Secondly, the type of open source licence that ECN had planned to attach to Nemoh was problematic.

Battle of the BEMs

2014 looks set to being a good year for open access code for marine renewables. Three projects are due to go online this year: WEC-Sim, OPEN-WARP, and Nemoh. The last two are Boundary Element Method (BEM) codes: if one of these turns out to the long-awaited open source equivalent to the excellent but prohibitively expensive WAMIT, this could be a real boost to marine renewables. The availability of free code for modelling WECs will considerably reduce the cost, complexity and effort associated with development at early technology readiness levels. So please spread the word:

Do you have any dusty unloved code that has slipped down the back of the couch? Time to stop sitting on it! Check out the OPEN-WARP competition.

What makes a WEC concept 'good'?

The topic of innovation in the design of WECs has been a bit of a recurring theme for me lately. It has cropped up in the form of an innovation competition for WECs, new concepts aired at this year's All Energy Opportunities conference, and in Weber's paper on the Performance/Readiness Matrix. All this leads to a conundrum that has been puzzling me for some time now:

“How can you tell if a particular WEC concept is any good?”