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Peak forces on a point absorbing wave energy converter impacted by tsunami waves
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Center for Natural Disaster Science (CNDS), Uppsala, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0001-9213-6447
2019 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 133, p. 1024-1033Article in journal (Refereed) Published
Abstract [en]

Although a tsunami wave in deep sea can be simulated using linear shallow water theory, the wave dynamics of a tsunami running up a continental shelf is very complex, and different phenomena may occur, depending on the width and profile of the shelf, the topography of the coast, incident angle of the tsunami and other factors. How to simulate tsunami waves at an intermediate depth is studied in this paper by using three different simulation approaches for tsunamis, a soliton, a simulated high incident current and a dam-break approach. The surface wave profiles as well as the velocity- and pressure profiles for the undisturbed waves are compared. A regular Stokes 5th wave of the same amplitude is simulated for comparison. A wave energy converter model, previously validated with wave tank experiment, is then used to study the survivability of the Uppsala University wave energy device for the different waves. The force in the mooring line is studied together with the resulting force on a bottom mounted column, corresponding to the linear generator on the seabed.

Place, publisher, year, edition, pages
2019. Vol. 133, p. 1024-1033
Keywords [en]
Wave energy, Extreme forces, Tsunami, OpenFOAM
National Category
Marine Engineering Energy Systems
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-328486DOI: 10.1016/j.renene.2018.10.092ISI: 000456761300091OAI: oai:DiVA.org:uu-328486DiVA, id: diva2:1135735
Funder
Natural-Disaster ScienceSwedish Research Council, 2015-04657Swedish National Infrastructure for Computing (SNIC)Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2019-03-15Bibliographically approved
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

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