Wave Energy Converters : An experimental approach to onshore testing, deployments and offshore monitoring

Sammanfattning: The wave energy converter (WEC) concept developed at Uppsala University consists of a point absorbing buoy, directly connected to a permanent magnet linear generator. Since 2006, over a dozen full scale WECs have been deployed at the Lysekil Research Site, on the west coast of Sweden. Beyond the development of the WEC concept itself, the full scale approach enables, and requires, experimental and multidisciplinary research within several peripheral areas, such as instrumentation, offshore operations, and wave power infrastructure.This thesis addresses technical challenges of testing, deploying and monitoring full scale WECs. It is divided accordingly into three topics: offshore measurement systems, onshore WEC testing and deployments. Each topic presents new or improved technical solutions to enable offshore wave power research.For the offshore measurement systems, a new portable data acquisition unit was developed, together with a new sensor system to be installed inside the WEC. The developed system offers a cheap and flexible option for short term offshore measurement ventures, when or where site infrastructure is not available. The system has been developed and tested during both onshore and offshore experiments, with promising results.On the topic of onshore WEC testing, the thesis presents an experimental approach for assessing the power take-off (PTO) damping of the WEC. In previous experimental studies, it has been measured via the generated electrical power, which neglects both mechanical losses and iron losses. Consequently, the full PTO force acting on the WEC has been underestimated. The thesis presents experimentally attained trends for the speed dependence of the PTO damping at different resistive loads, as measured from both generated electric power and from measurements of the buoy line force. A study was also performed on how the generator damping is affected by partial stator overlap, which varies with the translator position. In order to assess how the characterized damping behavior will affect the WEC operation at sea, two simulation case studies were performed.Finally, the thesis presents a new WEC deployment method, which has been developed through several deployment trials. By using only a tugboat, a WEC unit is transported and deployed, together with its buoy, in less than half a day. The procedure has proven to be faster, cheaper and safer than the previously used methods.