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Resilience of wave energy farms using metocean dependent failure rates and repair operations
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS), Villavägen 16, Uppsala, 752 36, Sweden.ORCID iD: 0000-0001-9213-6447
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.ORCID iD: 0000-0002-1165-5569
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.ORCID iD: 0000-0003-3612-4817
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS), Villavägen 16, Uppsala, 752 36, Sweden.ORCID iD: 0000-0001-5096-3559
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2023 (English)In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 280, article id 114678Article in journal (Refereed) Published
Abstract [en]

Emerging offshore renewable energy technologies are expected to become an important part of the futureenergy system, and reliability for these new technologies in different metocean scenarios must be guaranteed.This poses a challenge in extreme weather scenarios like storms, in particular for less mature technologiessuch as wave energy. Not only the offshore survivability must be controlled; the restoration after disruptiveevents and failures should be addressed and optimized. Offshore operations are costly and cannot be carriedout if the weather is too harsh, and the resulting downtime after failures may be financially devastating forprojects. In this paper, the resilience of large wave energy systems is studied with respect to wave conditions,metocean dependent failure rates, and weather windows available for offshore repair operations. A metocean-and time-dependent failure rate is derived based on a Weibull distribution, which is a novelty of the paper.The performance of the farm is assessed using the varying failure rates and metocean data at different offshoresites. Critical metocean thresholds for different offshore vessels are considered, and the resilience is quantifiedusing relevant measures such as unavailability and expected energy not supplied. The resilience analysis iscoupled to an economic assessment of the wave farm and different repair strategies. Our results show thatthe commonly used assumption of constant failure rates is seen to overestimate the annual energy productionthan when a more realistic varying failure rate is used. Two offshore sites are compared, and the availabilityis found to be higher at the calmer site. Most of the evaluated repair strategies cannot be considered to beeconomically justified, when compared to the cost of the energy not supplied.

Place, publisher, year, edition, pages
Elsevier, 2023. Vol. 280, article id 114678
National Category
Energy Engineering Fluid Mechanics and Acoustics Reliability and Maintenance
Identifiers
URN: urn:nbn:se:uu:diva-501652DOI: 10.1016/j.oceaneng.2023.114678ISI: 001019734300001OAI: oai:DiVA.org:uu-501652DiVA, id: diva2:1756213
Funder
Swedish Research Council, 2020-03634Available from: 2023-05-10 Created: 2023-05-10 Last updated: 2024-04-04Bibliographically approved
In thesis
1. Time-domain modeling of a wave power farm
Open this publication in new window or tab >>Time-domain modeling of a wave power farm
2023 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this work, we model a point absorber wave energy converter (WEC) very similar to the device that originated and was developed at Uppsala University in Sweden. The device is simulated both as a one- and a two-body model. The one-body WEC model assumes a stiff connection line between the floating buoy on the sea surface and the translator inside the linear generator. The two-body model, on the other hand, allows for slack-line phenomena. This connection also acts as a mooring line for the buoy, and it is a crucial component in understanding and evaluating the survivability of WECs in the offshore environment, in particular during extreme wave conditions. The linear models are validated against experimental data, focusing on the buoy motion and the force in the mooring line. The two-body model captures the extreme dy-namics and force peaks well, whereas the one-body model predicts the WEC response with a few more inaccuracies. However, the one-body model still produces acceptable results in operational waves, and since one-body models are predominant due to their simplicity and nu-merical efficiency, we choose to extend the one-body model to simulate multiple interacting point-absorbers. Therefore, a novel, fast time-domain model is developed for an array of 6 up to 96 interacting point-absorbers. The WECs are placed in a symmetric grid, where each row contains one pair. The devices interact by scattered and radiated waves, while they are restricted to move in one degree of freedom, heave. Under the assumption of linear potential flow the-ory, the hydrodynamic coefficients for the excitation and radiation forces are obtained using an analytical multiple scattering method, as well as the boundary element software WAMIT. The equations of motion are solved following Cummins’ formulation. Modeling an array of WECs in the time domain comes down to solving a system of integro-differential equations, where convolution terms appear in the computation of the excitation and radiation forces. In the ma-jority of wave farm models, frequency-domain approaches are used to solve the equations of motion, since time-domain models are more computationally demanding and significantly more challenging to develop. This is not only because of the numerical integration involved but espe-cially due to the computation of the convolution term accounting for the radiated water waves on the free surface, implying that waves radiated by the body in the past continue to affect the dynamics in the future. Regardless of the computational effort associated with time-domain approaches, their use is required for realistic control applications and complex device dynam-ics, like non-linearities due to the power take-off configuration. It is of high interest to study whether the linear numerical model simulates accurately the performance of each interacting WEC. Therefore, the numerical results for the full array configuration are compared with ex-perimental data. The experimental results used were carried out in the COAST Lab at Plymouth University, UK, corresponding to a 1:10 scaled prototype of an array of point absorbers. De-spite the highly non-linear effects in the physical experiment, the free motion of the buoys in all directions, and the power take-off configuration, the numerical scheme is able to accurately capture the heaving motion of the buoys and their power absorption.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2023. p. 70
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-514826 (URN)
Presentation
, Uppsala (English)
Available from: 2023-11-07 Created: 2023-10-23 Last updated: 2023-11-08Bibliographically approved

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Göteman, MalinShahroozi, ZahraStavropoulou, CharitiniKatsidoniotaki, EiriniEngström, Jens

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