Reliability assessment of wave energy devices

Ambühl, Simon; Kramer, Morten; Kofoed, Jens Peter; Sørensen, John Dalsgaard; Ferreira, Claudio Bittencourt

doi:10.1201/b16387-755

Cited by 6 publications

(7 citation statements)

References 1 publication

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“…Over the previous decade, a range of scale experiments and real sea tests have been performed in order to investigate different aspects of the device design [10,11,12]. In a recent set of experiments, performed in the COAST Lab- oratory Ocean basin at Plymouth University and supported by MARINET, the survivability of the device under extreme conditions was assessed in a controlled environment [13].…”

Section: The Wavestar Machinementioning

confidence: 99%

RANS-VOF modelling of the Wavestar point absorber

et al. 2017

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Numerical modelling has become commonplace in the development of offshore structures, however for dynamic systems such as Wave Energy Convertors (WECs) conventional numerical tools may not be able to capture the full range of behaviours required for engineering analysis. This is particularly problematic in extreme seas where the nonlinearities and coupled nature of these systems become important. In this work a fully nonlinear, coupled tool for simulation of WECs is produced and compare with physical measurements. Regular wave interactions with both a fixed and freely-pitching, 1:10 scale model of the Wavestar are reproduced numerically. The numerical model is shown to be capable of predicting the pressure on the float's surface and the fully coupled motion of the device. However, the results indicate that the higher-order free surface behaviour in the vicinity of the device is not being captured correctly. Finally, the numerical model is shown to cope with an extreme regular wave including large amplitude motion, full submersion and high levels of free surface distortion. The results presented suggest that the quality of the numerical reproduction does not decrease with wave steepness; however the execution time of simulations increases significantly with increased float oscillation.

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Section: The Wavestar Machinementioning

confidence: 99%

RANS-VOF modelling of the Wavestar point absorber

et al. 2017

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“…Sources which may affect the downtime of a fixed offshore WEC when a component has to be replaced. 13 …”

Section: Maintenance Strategiesmentioning

confidence: 99%

“…Sources which may affect the downtime of a fixed offshore WEC when a component has to be replaced. 13 stored on the device offshore. In this case, the delivery time of the component can be reduced.…”

Section: Maintenance Strategiesmentioning

confidence: 99%

“…15 Thies et al 16 show an example of important failure modes and their failure rates for a generic hydraulic WEC. An FMEA for the Wavestar WEC prototype is performed in Ambu¨hl et al 13 Furthermore, it should be accounted for that partial failure of the device may also occur, for example, one floater of the Wavestar prototype, which consists of two floaters, can fail, and the other floater still produces electricity.…”

Section: Maintenance Strategiesmentioning

confidence: 99%

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Operation and maintenance strategies for wave energy converters

Ambühl

Marquis

Kofoed

et al. 2015

Proceedings of the Institution of Mechanical Engineers, Part O:

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Inspection and maintenance costs are a significant contributor to the cost of energy for wave energy converters. There are different operation and maintenance strategies for wave energy converters. Maintenance can be performed after failure (corrective) or before a breakdown (preventive) occurs. Furthermore, a helicopter and boats can be used to transport equipment and personnel to the device, or the whole device can be towed to a harbour for operation and maintenance actions. This article describes, among others, a risk-based inspection and maintenance planning approach where the overall repair costs including costs due to lost electricity production are minimized. The risk-based approach is compared with an approach where only boats are used and another approach where the target is to minimize the downtime of the device. This article presents a dynamic approach for total operation and maintenance costs estimations for wave energy converter applications including real weather data and damage accumulation. Furthermore, uncertainties related with costs, structural damage accumulation, inspection accuracy and different maintenance strategies can be included. This article contains a case study where different maintenance strategies are applied for the Wavestar device, and the influences of the different parameters, for example, failure rate, inspection quality and inspection interval, are evaluated for the overall costs and the number of repairs needed during its lifetime.

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“…There have been structural reliability studies on bolted and welded details previously with a focus on WEC applications (see, e.g., [6,7]). Bearings are also of importance for WEC applications, but so far, there has not been any reliability studies on bearings for WEC applications based on a probabilistic reliability approach.…”

Section: Introductionmentioning

confidence: 99%

Structural Reliability of Plain Bearings for Wave Energy Converter Applications

2016

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Abstract:The levelized cost of energy (LCOE) from wave energy converters (WECs) needs to be decreased in order to be able to become competitive with other renewable electricity sources. Probabilistic reliability methods can be used to optimize the structure of WECs. Optimization is often performed for critical structural components, like welded details, bolts or bearings. This paper considers reliability studies with a focus on plain bearings available from stock for the Wavestar device, which exists at the prototype level. The Wavestar device is a point absorber WEC. The plan is to mount a new power take-off (PTO) system consisting of a discrete displacement cylinder (DDC), which will allow different hydraulic cycles to operate at constant pressure levels. This setup increases the conversion efficiency, as well as decouples the electricity production from the pressure variations within the hydraulic cycle when waves are passing. The new PTO system leads to different load characteristics at the floater itself compared to the actual setup where the turbine/generator is directly coupled to the fluctuating hydraulic pressure within the PTO system. This paper calculates the structural reliability of the different available plain bearings planned to be mounted at the new PTO system based on a probabilistic approach, and the paper gives suggestions for fulfilling the minimal target reliability levels. The considered failure mode in this paper is the brittle fatigue failure of plain bearings. The performed sensitivity analysis shows that parameters defining the initial crack size have a big impact on the resulting reliability of the plain bearing.

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Reliability assessment of wave energy devices

Cited by 6 publications

References 1 publication

RANS-VOF modelling of the Wavestar point absorber

RANS-VOF modelling of the Wavestar point absorber

Operation and maintenance strategies for wave energy converters

Structural Reliability of Plain Bearings for Wave Energy Converter Applications

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