Category Archives: Operation and Maintenance

Coalesced effect of cavitation and silt erosion in hydro turbines—A review


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Pannkaj P. Gohil and R.P. Saini – Renewable and Sustainable Energy Reviews, May 2014

Abstract

Cavitation is a phenomenon which manifests itself in the pitting of the metallic surfaces of turbine parts because of the formation of cavities. However, silt erosion is caused by the dynamic action of silt flowing along with water, impacting against a solid surface. The erosion and abrasive wear not only reduce the efficiency and the life of the turbine but also cause problems in operation and maintenance, which ultimately lead to economic losses. Researchers have studied that the cavitation in silt flow is more serious than in pure water. However, the coalesced effect of silt erosion and cavitation is found to be more pronounced than their individual effects.

In the present paper the studies in this field carried out by various investigators are discussed and presented. Parameters related to the combined effect of cavitation and silt erosion which are responsible for efficiency loss due to erosion as investigated by researchers have also been discussed.

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Filed under Materials and coatings, Operation and Maintenance, Review

A new method for failure modes and effects analysis and its application in a hydrokinetic turbine system


Liang Xie – Missouri University of Science and Technology, Masters Thesis, 2013

Abstract

The traditional failure modes and effects analysis (FMEA) is a conceptual design methodology for dealing with potential failures. FMEA uses the risk priority number (RPN), which is the product of three ranked factors to prioritize risks of different failure modes. The three factors are occurrence, severity, and detection. However, the RPN may not be able to provide consistent evaluation of risks for the following reasons: the RPN has a high degree of subjectivity, it is difficult to compare different RPNs, and possible failures may be overlooked in the traditional FMEA method. Continue reading

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Filed under Economics, Operation and Maintenance

Methods for predicting seabed scour around marine current turbine


Long Chen and Wei-Haur Lam – Renewable and Sustainable Energy Reviews, January 2014

Abstract

Marine energy sources are able to make significant contributions to future energy demands. Marine current has huge potential to supply renewable energy as compared to the other energy sources. Marine environment is harsh for the installation and operation of marine current turbine (MCT). Seabed scour around marine current turbine is induced when the flow suppression occurs at the seabed. Seabed scour is widely recognised as a difficult engineering problem which is likely to cause structural instability. The study found that the previous works mainly focus on the bridge piers, wind turbines and ship propeller jets induced scour. Little information to date was found to predict the MCT induced scour. The current paper proposes the potential equations to predict the MCT induced scour. The study also recommends the consideration of the rotor into the existing equations for future research.

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Analysis of grouted connections for offshore wind turbines


Thomas Löhning, Marc Voßbeck, and Martin Kelm – Proceedings of the ICE – Energy, November 2013

Abstract

In offshore wind turbines grouted connections are generally used to install a transition piece between the steel tower and the monopile foundation. The transition piece is plugged on to the monopile, aligned vertically and the annulus in between is filled with high-strength grout. During service operations unexpected settlement of the transition piece has been observed at several wind turbines. The serious findings have called for additional, extensive numerical analyses for the detailed design of the London Array offshore wind farm. The advanced non-linear finite-element analyses provide a more detailed insight into the structural behaviour of grouted connections. Important effects and a possible mechanism for the settlement at existing wind turbines are detected. The previous practice of designing separately for bending moment and transverse force on the one hand and axial force and torsion on the other hand leads, among other things, to the overestimation of capacity. The interaction has to be taken into account.

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Filed under Modeling, Operation and Maintenance

Capacitive sensors for offshore scour monitoring


Panagiotis Michalis, Mohamed Saafi, and Martin Judd – Proceedings of the ICE – Energy, November 2013

Abstract

One of the main challenges in the design and operation of offshore wind turbines arises from the uncertainty about maximum scour depth around their foundations. Scour action can lead to excessive excavation of the surrounding seabed and is being considered as a major risk for offshore wind farm developments. An ability to gather information concerning the evolution of scouring will enable the validation of models derived from laboratory-based studies, the assessment of different engineering designs and the development of improved scour countermeasure techniques. However, real-time scour data are not being collected due to a lack of available instrumentation techniques. This paper proposes a new scour monitoring technology for offshore wind turbine installations. The monitoring system consists of arrays of small capacitive scour probes installed around the foundation structure and linked to a wireless network to enable remote data acquisition. Based on this research, it is concluded that the sensor is capable of exhibiting high sensitivity to scour and sediment deposition processes for common sea floor mediums under different temperature conditions in saline water. The proposed monitoring system has considerable potential for field applications that will contribute to improving the resilience and sustainability of offshore structures.

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Filed under Instrumentation, Operation and Maintenance

Numerical Modeling to Aid in the Structural Health Monitoring of Wave Energy Converters


William Finnegan and Jamie Goggins – Key Engineering Materials, July 2013

Abstract

A vital aspect of ensuring the cost effectiveness of wave energy converters (WECs) is being able to monitor their performance remotely through structural health monitoring, as these devices are deployed in very harsh environments in terms of both accessibility and potential damage to the devices. The WECs are monitored through the use of measuring equipment, which is strategically placed on the device. This measured data is then compared to the output from a numerical model of the WEC under the same ocean wave conditions. Any deviations would suggest that there are problems or issues with the WEC. The development of accurate and effective numerical models is necessary to minimise the number of times the visual, or physical, inspection of a deployed WEC is required. In this paper, a numerical wave tank model is, first, validated by comparing the waves generated to those generated experimentally using the wave flume located at the National University of Ireland, Galway. This model is then extended so it is suitable for generating real ocean waves. A wave record observed at the Atlantic marine energy test site has been replicated in the model to a high level of accuracy. A rectangular floating prism is then introduced into the model in order to explore wave-structure interaction. The dynamic response of the structure is compared to a simple analytical solution and found to be in good agreement.

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Filed under Experiments, Instrumentation, Modeling, Operation and Maintenance

A New Way for Access and Maintenance of Offshore Wind Farms: The Use of Cableway to Reduce Cost and Improve Accessibility


Massimo Grecchi, Luigi Meroni, and Piergiorgio Betteto – Wind Engineering, June 2013

Abstract

This work proposes a new method in order to deploy an affordable and reliable way for maintenance when it is necessary to access to offshore wind farms. The new system, based on cableway infrastructure is aimed to allow a lower cost of maintenance compared to other system for the same kind of operation but also to improve the reactivity and accessibility compared to them. Maintenance activities are taken into consideration in term of cost, period, nature, accessibility of wind farm, kind of maintenance we want/need to use in order to ameliorate the availability/reliability of the wind farm. Five different configurations with related cableway system are analyzed in order to demonstrate that facing a reasonable increasing of Capital Cost, sizable saving and extra revenue can be obtained if projected on the expected life of wind farms.

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Filed under Component Development, Operation and Maintenance

Calculating weather windows: Application to transit, installation and the implications on deployment success


R.T. Walker, J. van Nieuwkoop-McCall, L. Johanning, and R.J. Parkinsonb – Ocean Engineering, May 2013

Abstract

In order to fully utilise test sites, marine energy device developers must be able to deploy, maintain and decommission their equipment in a timely and cost effective manner. In addition, the marine energy industry is moving towards array deployments and whilst these deployments present an excellent opportunity to maximise resource usage whilst minimising the associated costs, for example of deployment, it is essential that said deployment is performed in a cost effective manner. Critical to this is the knowledge of the metocean conditions at the site and the weather window availability, particularly when this is coupled with vessel availability and downtime costs.

In this paper a method is presented based on a Weibull model which uses cumulative distributions of the mean duration of persistence of exceedance. The method discussed has been applied in a case study for the South West of England using site specific environmental parameters and empirical expressions to calculate the accessible periods. The outcomes from the case study are applied to identify the accessible periods and the waiting time for marine operations, and a discussion is made regarding the installation of wave energy devices at the south west Wave Hub.

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