Assessment of wave power for sea states at different sites

Abstract

The aim of this thesis is to investigate available and captured wave power at five different locations on the Norwegian continental shelf; Haltenbanken, North Sea Center, Ekofisk, Utsira and Tromsøflaket.

A literature study on wave power and different concepts for wave power absorption has been performed. Based on the findings, one concept was chosen for further investigation; a floating point absorber.

The sea state analyses were based on a numerical approach presented by Anthony Lewis and Wanan Sheng, which was implemented in Matlab to find the captured available power at each site. The power capture response for the chosen wave energy converter was combined with the wave spectrum to find the average captured power function. From this, the total captured wave power for a certain sea state at a given location was found.

The sea state analyses showed that Haltenbanken was the site with the most available wave power, 48 kW/m, and the most captured wave power, 34 kW. However, the North Sea Center was the site with the highest capture efficiency, about 14%. The results from Ekofisk and Utsira gave relatively similar efficiencies, which was expected since these had similar distributions of the significant wave height, Hs, and the wave peak period, Tp. The chosen wave energy converter has the same dynamic characteristics regardless of the location, with a given inertia, stiffness and wave damping, and also a predefined power-take-off (PTO) and control system. For optimal efficiency, these should be adjusted after the conditions at the certain location; the phase and control system should be tuned after the incident waves.

Probability density functions for Haltenbanken, Tromsøflaket and Utsira were compared with the distribution from the scatter diagrams to investigate if the choice of distribution would result in a significant difference. For all sites the deviation was less than $3\%$, the difference was therefore seen as insignificant, and the choice of probability distribution would not contribute to large differences in the calculated captured wave power.

For further work it was recommended to design a unique system for each site. Based on the wave conditions, the geometry of the device and the PTO and control systems should be designed specifically for each site.