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Experimental study of generator damping at partial stator overlap in a linear generator for wave power
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
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2017 (English)In: 12th European Wave and Tidal Energy Conference Series, Cork, Ireland, 27 August - 1 September, 2017, 2017Conference paper, Oral presentation only (Refereed)
Place, publisher, year, edition, pages
2017.
National Category
Marine Engineering
Identifiers
URN: urn:nbn:se:uu:diva-328496OAI: oai:DiVA.org:uu-328496DiVA, id: diva2:1135768
Conference
EWTEC2017
Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2017-09-21
In thesis
1. Wave Loads and Peak Forces on Moored Wave Energy Devices in Tsunamis and Extreme Waves
Open this publication in new window or tab >>Wave Loads and Peak Forces on Moored Wave Energy Devices in Tsunamis and Extreme Waves
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface gravity waves carry enormous amounts of energy over our oceans, and if their energy could be harvested to generate electricity, it could make a significant contribution to the worlds power demand. But the survivability of wave energy devices in harsh operating conditions has proven challenging, and for wave energy to be a possibility, peak forces during storms and extreme waves must be studied and the devices behaviour understood. Although the wave power industry has benefited from research and development in traditional offshore industries, there are important differences. Traditional offshore structures are designed to minimize power absorption and to have small motion response, while wave power devices are designed to maximize power absorption and to have a high motion response. This increase the difficulty of the already challenging survivability issue. Further, nonlinear effects such as turbulence and overtopping can not be neglected in harsh operating conditions. In contrast to traditional offshore structures, it is also important to correctly account for the power take off system in a wave energy converter (WEC), as it is strongly coupled to the devices behaviour.

The focus in this thesis is the wave loads and the peak forces that occur when a WEC with a limited stroke length is operated in waves higher than the maximum stroke length. The studied WEC is developed at Uppsala University, Sweden, and consists of a linear generator at the seabed that is directly driven by a surface buoy. A fully nonlinear CFD model is developed in the finite volume software OpenFOAM, and validated with physical wave tank experiments. It is then used to study the motion and the forces on the WEC in extreme waves; high regular waves and during tsunami events, and how the WECs behaviour is influenced by different generator parameters, such as generator damping, friction and the length of the connection line. Further, physical experiments are performed on full scale linear generators, measuring the total speed dependent damping force that can be expected for different loads. The OpenFOAM model is used to study how the measured generator behaviour affects the force in the connection line.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 86
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1551
Keywords
OpenFOAM, CFD, Wave power, Tsunami waves, Extreme waves, Offshore
National Category
Marine Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-328499 (URN)978-91-513-0054-2 (ISBN)
Public defence
2017-10-20, Polhemsalen, 10134, Ångström, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-09-28 Created: 2017-08-24 Last updated: 2017-10-17
2. Wave Energy Converters: An experimental approach to onshore testing, deployments and offshore monitoring
Open this publication in new window or tab >>Wave Energy Converters: An experimental approach to onshore testing, deployments and offshore monitoring
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 100
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1563
Keywords
wave power, ocean energy, linear generator, measurements, sensors, point absorber, offshore, PTO, force
National Category
Energy Engineering Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-329856 (URN)978-91-513-0077-1 (ISBN)
Public defence
2017-11-10, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-10-18 Created: 2017-09-21 Last updated: 2018-03-08

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