I would like to point out that while it might be true that Budal, who discovered the principle that "a good wave absorber has to be a good wavemaker" in the 1970s, worked mostly with point absorbers and often neglected the diffracted wave in his early analyses, that principle is applicable to any wave energy device(s) of any shape(s) and size(s), be it a single device or an array of devices. Three papers in the Royal Society meeting presented derivations of this principle, and no assumption was made about the size(s) and shape(s) of the device(s) in all of them, nor was the diffracted wave neglected in any of them.

http://rsta.royalsocietypublishing.org/content/370/1959.toc

Dear Adi, thank you for your comment and for having read our paper.

Our point is that Oyster's design criteria are pretty different from those of resonating devices. Since Oyster is not designed to resonate, applying the results obtained earlier for resonating devices - including point absorbers - to Oyster can be misleading. The main factor in generating wave power with Oyster is the exciting torque. In fact the optimal design of Oyster aims at maximising the exciting torque, which is a diffractive property. This is a change in perspective. We are seeing the wave-structure interaction from a different viewpoint, since our focus in on Oyster's behaviour as a breakwater, rather than as a wavemaker. Then of course the two viewpoints are related via the hydrodynamic relations, that we examine in some detail in our Applied Ocean Research paper. This does not imply that other devices designed according to Budal's criterion are less efficient, as we did not make comparisons with other WECs. For that, certainly a beautiful example of comparing different technology types is in your paper with Aurelien in Renewable Energy.

I hope this clarifies the issue.

Article Relations for a periodic array of flap-type wave energy converters

Yes, I was just trying to clarify that "a good wave energy absorber must be a good wave radiator" is not a "point-absorber criterion", as you mentioned in your paper. And the principle does apply to an OWSC like Oyster as well.

A source of confusion might be the phrase "a good wave energy absorber". A good wave energy absorber is not necessarily a good device, because there are other objectives that the device must be designed to satisfy apart from maximizing the absorbed power. In general, these objectives are competing, so a compromise must be found. Depending on the relative importance one places on each of these objectives, some degree of subjectivity will be involved.

In fact, if they operate singly, point-absorbers are poor wave radiators, especially when compared to flaps, which have a much more superior wave-making ability. So, a single point-absorber is a poorer wave energy absorber than a single flap. But perhaps the fact that they could offer an economic potential when operated in an array and that they are less dependent on wave direction and water depth are strong enough reasons why we still have interest in them.