Monday, 25 February 2013

In a nutshell: technology readiness and performance matrix

Weber (2012), 'WEC Technology Readiness and Performance Matrix - finding the best research technology development strategy', 4th International Conference on Ocean Energy, 17 October, Dublin.

Fig 1: Readiness-performance matrix (reproduced with permission from Weber)

The technology readiness level (TRL) is the de-facto metric for describing the development stages of wave energy technologies. The TRL indicates a technology's maturity, and is strongly related to the amount of investment. Weber's paper proposes a second metric, the technology performance level (TPL). Arranged like TRL on a scale of 1 to 9, it measures a technology's economy, and is inversely related to the cost of energy.

In a two-dimensional graphic these two metrics give us the readiness-performance matrix. The development trajectory of a wave energy technology can be plotted against it. Fig 1 shows three hypothetical trajectories:
  • Orange: Readiness before performance
  • Green: Performance before readiness
  • Black: Performance and readiness developed together

Monday, 18 February 2013

Liberazione di Andomeda (Piero di Cosimo 1461) - they don't make art like this anymore!

They don't make art like this anymore. Partly because no one would take a sea monster that looked like the grandfather of the Luckdragon from the Never Ending Story seriously. And partly because our expectations have been raised by the ubiquity of fairly decent physics to represent fluids in computer games and animated film.

Monday, 11 February 2013

Complex conjugate control without the equations

Many people would like to know about complex conjugate control of wave energy converters, and the problems with its implementation, without wading through masses of equations. Ok, lets not kid ourselves, only a few people want to know this, but I cater to all tastes, including highly refined ones.

While I won't use equations directly, I will need to make reference to a well-known mathematical model, if you're an engineer, that is. Different mathematical models suit different purposes. For explaining how complex conjugate control works, a simple linear mass-spring-damper model, with excitation at one frequency only, is a good place to start. If you need to brush up on this model, there are some reminders here.

The natural frequency of the system (fn) is where the response amplitude is highest, which happens to be the only frequency where the response phase is zero (with respect to the excitation phase). A system that is being excited at its natural frequency is described as resonant.

The basic idea behind complex conjugate control is to have a small (= low cost) absorber that has a natural frequency higher than the power-rich frequency components of a typical wave spectrum, and to then force the system into resonance by doing clever things with the power take off (PTO) force.

Wednesday, 6 February 2013

Doctor doctor! I had to tie it down to stop it thrashing about!

Q: We had to tightly moor our device, otherwise its movement would have resulted in waves being radiated away. What could be causing this problem?

First we need to define what we're looking at. We'll dismiss the trivial case of a single body absorber: clearly preventing its motion will give us zero power capture! Hence we must be talking about a floating system with more than one wave activated body. Furthermore, as we talk about tightly mooring the device, it makes sense that one body is a large structure and the other smaller body/ies (e.g. oscillating water columns or flaps) move/s with respect to this main structure.