Centre for Marine and Renewable Energy (MaREI) - Journal Articles

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Operational expenditure costs for wave energy projects and impacts on financial returns
(Elsevier, 2012-10-04) O'Connor, Michael; Lewis, Anthony; Dalton, Gordon; Science Foundation Ireland
This paper examines 'availability' and the input metrics of operational expenditure (OPEX) for wave energy projects and reports on a case study which assesses the impact of these inputs on project profit returns. Case study simulations modelled a 75 MW wave energy project at two locations; the west coast of Ireland and the north coast of Portugal. Access and availability with respect to weather windows at both locations are discussed and their impact on energy output and wave farm operations is quantified. The input metrics used to calculate OPEX of wave energy projects are defined as well as the impact of OPEX on project net present value (NPV) and internal rate of return (IRR). Results indicate that access and resultant availability factors have a significant impact on case study results by reducing energy output and correspondingly financial returns. Furthermore, the technology maturity level designated for a project also impacts on availability factors and consequently energy output and NPV. Case study profits proved to be very sensitive to annual OPEX, especially if overhaul and replacement costs were accounted for. As a result of the impact of 'availability' on project profit returns. Feed-in tariffs will need to be tailored to the location in question as well as the device technology maturity level, with case study simulations indicating that high FIT will be required to support early stage WEC projects. (C) 2012 Elsevier Ltd. All rights reserved.
On thermodynamics in the primary power conversion of oscillating water column wave energy converters
(American Institute of Physics, 2013-03-06) Sheng, Wanan; Alcorn, Raymond; Lewis, Anthony; Science Foundation Ireland
The paper presents an investigation to the thermodynamics of the air flow in the air chamber for the oscillating water column wave energy converters, in which the oscillating water surface in the water column pressurizes or de-pressurises the air in the chamber. To study the thermodynamics and the compressibility of the air in the chamber, a method is developed in this research: the power take-off is replaced with an accepted semi-empirical relationship between the air flow rate and the oscillating water column chamber pressure, and the thermodynamic process is simplified as an isentropic process. This facilitates the use of a direct expression for the work done on the power take-off by the flowing air and the generation of a single differential equation that defines the thermodynamic process occurring inside the air chamber. Solving the differential equation, the chamber pressure can be obtained if the interior water surface motion is known or the chamber volume (thus the interior water surface motion) if the chamber pressure is known. As a result, the effects of the air compressibility can be studied. Examples given in the paper have shown the compressibility, and its effects on the power losses for large oscillating water column devices.
Stable ships for smooth servicing of offshore wind farms
(University College Cork, 2014) Shanley, Matthew; University College Cork
There is a rapid increase in the number of offshore wind farms in European waters to help meet renewable energy targets. Wind turbines are being installed in progressively more exposed areas of the North Sea and the Irish Sea, with the eventual aim of placing them in the Atlantic Ocean. As offshore wind farms require regular maintenance, being able to access the wind turbines during rough sea conditions is a key issue for profitable operation. The operation involves transferring personnel from the service ship to the wind turbine. The current wave height limit for this is 1.5 m, slightly less than 5 feet, increasing this results in significant savings over the lifetime of the wind farm. Each wind farm service ship has 12 maintenance crew. Imagine you are one waiting on port for the sea and weather conditions to be right so that you can head out to the wind turbine. You’ve been waiting for two weeks, you can see the wind turbine from land but the sea is so rough that stepping from the ship to the turbine is impossible. The only way to transfer the maintenance crew to the turbines is from the front (bow) of the ship, out at the wind farm this is the best way for the ship to maintain position. Standing at the bow of a ship is much like standing on the end of a seesaw; which means that accessing the wind turbine can only occur during reasonably calm conditions. Quantitatively, this results in the average of the highest one-third waves being 1.5 m, which is described as a sea state code of slight to moderate. This research aims to develop designs that can operate in the sea state code of rough, with an average height of the highest one-third of the waves being 3 metres or more.
Evaluating conditions for transboundary Marine Spatial Planning: challenges and opportunities on the island of Ireland
(Elsevier, 2014-08-23) Flannery, Wesley; O'Hagan, Anne Marie; O'Mahony, Cathal; Ritchie, Heather; Twomey, Sarah; Science Foundation Ireland
Transboundary cooperation is viewed as an essential element of Marine Spatial Planning (MSP). While much of the MSP literature focuses on the need for, and benefits of, transboundary MSP, this paper explores the political and institutional factors that may facilitate the effective transition to such an approach. Drawing on transboundary planning theory and practice, key contextual factors that are likely to expedite the transition to transboundary MSP are reviewed. These include: policy convergence in neighbouring jurisdictions; prior experience of transboundary planning; and good working relations amongst key actors. Based on this review, an assessment of the conditions for transboundary MSP in the adjoining waters of Northern Ireland and the Republic of Ireland is undertaken. A number of recommendations are then advanced for transboundary MSP on the island of Ireland, including, the need to address the role of formal transboundary institutions and the lack of an agreed legal maritime boundary. The paper concludes with some commentary on the political realities of implementing transboundary MSP.
Assessment of primary energy conversions of oscillating water columns. II. Power take-off and validations
(American Institute of Physics, 2014-09-29) Sheng, Wanan; Alcorn, Raymond; Lewis, Anthony
This is the second part of the assessment of primary energy conversions of oscillating water columns (OWCs) wave energy converters. In the first part of the research work, the hydrodynamic performance of OWC wave energy converter has been extensively examined, targeting on a reliable numerical assessment method. In this part of the research work, the application of the air turbine power take-off (PTO) to the OWC device leads to a coupled model of the hydrodynamics and thermodynamics of the OWC wave energy converters, in a manner that under the wave excitation, the varying air volume due to the internal water surface motion creates a reciprocating chamber pressure (alternative positive and negative chamber pressure), whilst the chamber pressure, in turn, modifies the motions of the device and the internal water surface. To do this, the thermodynamics of the air chamber is first examined and applied by including the air compressibility in the oscillating water columns for different types of the air turbine PTOs. The developed thermodynamics is then coupled with the hydrodynamics of the OWC wave energy converters. This proposed assessment method is then applied to two generic OWC wave energy converters (one bottom fixed and another floating), and the numerical results are compared to the experimental results. From the comparison to the model test data, it can be seen that this numerical method is capable of assessing the primary energy conversion for the oscillating water column wave energy converters.
Assessment of primary energy conversions of oscillating water columns. I. Hydrodynamic analysis
(American Institute of Physics, 2014-09-29) Sheng, Wanan; Alcorn, Raymond; Lewis, Anthony; Science Foundation Ireland
This is an investigation on the development of a numerical assessment method for the hydrodynamic performance of an oscillating water column (OWC) wave energy converter. In the research work, a systematic study has been carried out on how the hydrodynamic problem can be solved and represented reliably, focusing on the phenomena of the interactions of the wave-structure and the wave-internal water surface. These phenomena are extensively examined numerically to show how the hydrodynamic parameters can be reliably obtained and used for the OWC performance assessment. In studying the dynamic system, a two-body system is used for the OWC wave energy converter. The first body is the device itself, and the second body is an imaginary “piston,” which replaces part of the water at the internal water surface in the water column. One advantage of the two-body system for an OWC wave energy converter is its physical representations, and therefore, the relevant mathematical expressions and the numerical simulation can be straightforward. That is, the main hydrodynamic parameters can be assessed using the boundary element method of the potential flow in frequency domain, and the relevant parameters are transformed directly from frequency domain to time domain for the two-body system. However, as it is shown in the research, an appropriate representation of the “imaginary” piston is very important, especially when the relevant parameters have to be transformed from frequency-domain to time domain for a further analysis. The examples given in the research have shown that the correct parameters transformed from frequency domain to time domain can be a vital factor for a successful numerical simulation.
A Delay Vector Variance based marker for an output-only assessment of structural changes in tension leg platforms
(IOP Publishing Ltd, 2015-07) Jaksic, Vesna; Wright, Christopher S.; Mandic, D. P.; Murphy, Jimmy; Pakrashi, Vikram; Science Foundation Ireland; Marine Renewable Energy Ireland
Although aspects of power generation of many offshore renewable devices are well understood, their dynamic responses under high wind and wave conditions are still to be investigated to a great detail. Output only statistical markers are important for these offshore devices, since access to the device is limited and information about the exposure conditions and the true behaviour of the devices are generally partial, limited, and vague or even absent. The markers can summarise and characterise the behaviour of these devices from their dynamic response available as time series data. The behaviour may be linear or nonlinear and consequently a marker that can track the changes in structural situations can be quite important. These markers can then be helpful in assessing the current condition of the structure and can indicate possible intervention, monitoring or assessment. This paper considers a Delay Vector Variance based marker for changes in a tension leg platform tested in an ocean wave basin for structural changes brought about by single column dampers. The approach is based on dynamic outputs of the device alone and is based on the estimation of the nonlinearity of the output signal. The advantages of the selected marker and its response with changing structural properties are discussed. The marker is observed to be important for monitoring the as- deployed structural condition and is sensitive to changes in such conditions. Influence of exposure conditions of wave loading is also discussed in this study based only on experimental data.
Performance of a single liquid column damper for the control of dynamic responses of a tension leg platform
(IOP Publishing Ltd, 2015-07) Jaksic, Vesna; Wright, Christopher S.; Chanayil, Afeef; Ali, Shaikh Faruque; Murphy, Jimmy; Pakrashi, Vikram; Science Foundation Ireland; Marine Renewable Energy Ireland
Tuned liquid column dampers have been proved to be successful in mitigating the dynamic responses of civil infrastructure. There have been some recent applications of this concept on wind turbines and this passive control system can help to mitigate responses of offshore floating platforms and wave devices. The control of dynamic responses of these devices is important for reducing loads on structural elements and facilitating operations and maintenance (O&M) activities. This paper outlines the use of a tuned single liquid column damper for the control of a tension leg platform supported wind turbine. Theoretical studies were carried out and a scaled model was tested in a wave basin to assess the performance of the damper. The tests on the model presented in this paper correspond to a platform with a very low natural frequency for surge, sway and yaw motions. For practical purposes, it was not possible to tune the liquid damper exactly to this frequency. The consequent approach taken and the efficiency of such approach are presented in this paper. Responses to waves of a single frequency are investigated along with responses obtained from wave spectra characterising typical sea states. The extent of control is quantified using peak and root mean squared dynamic responses respectively. The tests present some guidelines and challenges for testing scaled devices in relation to including response control mechanisms. Additionally, the results provide a basis for dictating future research on tuned liquid column damper based control on floating platforms.
Numerical hydrodynamic modelling of a pitching wave energy converter
(Taylor & Francis, 2015-11-13) Bhinder, Majid A.; Rahmati, M. T.; Mingham, C. G.; Aggidis, G. A.; Joule Centre, United Kingdom; Science Foundation Ireland
Two computational methodologies – computational fluid dynamics (CFD) and the numerical modelling using linear potential theory based boundary element method (BEM) are compared against experimental measurements of the motion response of a pitching wave energy converter. CFD is considered as relatively rigorous approach offering non-linear incorporation of viscous and vortex phenomenon and capturing of the flow turbulence to some extent, whereas numerical approach of the BEM relies upon the linear frequency domain hydrodynamic calculations that can be further used for the time-domain analysis offering robust preliminary design analysis. This paper reports results from both approaches and concludes upon the comparison of numerical and experimental findings.
Dynamic effects of anchor positional tolerance on tension moored floating wind turbine
(IOP Publishing, 2016) Wright, Christopher S.; Pakrashi, Vikram; Murphy, Jimmy; Science Foundation Ireland
For water depths greater than 60m floating wind turbines will become the most economical option for generating offshore wind energy. Tension mooring stabilised units are one type of platform being considered by the offshore wind energy industry. The complex mooring arrangement used by this type of platform means that the dynamics are greatly effected by offsets in the positioning of the anchors. This paper examines the issue of tendon anchor position tolerances. The dynamic effects of three positional tolerances are analysed in survival state using the time domain FASTLink. The severe impact of worst case anchor positional offsets on platform and turbine survivability is shown. The worst anchor misposition combinations are highlighted and should be strongly avoided. Novel methods to mitigate this issue are presented.
The validation of a new GSTA case in a dynamic coastal environment using morphodynamic modelling and bathymetric monitoring
(MDPI AG, 2016-03-17) O'Shea, Michael; Murphy, Jimmy
Several methods of monitoring sediment transport exist and have varying degrees of success depending on the study sites characteristics. Grain Size Trend Analysis (GSTA) is an experimental method based on identifying transport trends from the variation of sediment grain characteristics within a defined study area. The parameters examined when performing GSTA are mean grain size, sorting coefficient and skewness, the most common cases found in field studies being; finer, better sorted and negatively skewed (FB´) or coarser, better sorted and positively skewed (CB+), as most transport trends follow one or the other trend. However, on Rossbeigh beach, Co. Kerry, Ireland, a coarser poorer and more negatively skewed (CP´) trend case gave the most realistic plot of sediment transport trend when compared with sediment transport calculation, bathymetry surveys, hydrodynamic monitoring and morphological modelling.
Land-ocean interactions in the coastal zone: Past, present and future
(Elsevier Ltd., 2016-04-06) Ramesh, R.; Chen, Z.; Cummins, Valerie; Day, J.; D'Elia, C.; Dennison, B.; Forbes, D. L.; Glaeser, B.; Glaser, M.; Glavovic, B.; Kremer, H.; Lange, Marcus; Larsen, J. N.; Le Tissier, Martin; Newton, A.; Pelling, M.; Purvaja, R.; Wolanski, E.
The Land-ocean Interactions in the Coastal Zone (LOICZ) project was established in 1993 as a core project of the International Geosphere-Biosphere Programme (IGBP) to provide the science knowledge to answer "How will changes in land use, sea level and climate alter coastal systems, and what are the wider consequences?" In its first phase of operation (1993-2003) LOICZ began a fundamental investigation focused on biophysical dimensions, including seminal assessments of coastal seas as net sources or sinks of atmospheric CO2, river discharge to the oceans, and biogeochemical modelling. In the second generation of LOICZ (2004-2014), increased attention was paid to the human dimensions of the coast, involving the inclusion of cross-cutting themes such as coastal governance, social-ecological systems, ecological economics and activities around capacity building and the promotion of early career scientists. This paper provides a synthesis of this work and looks forward to the future challenges for the project. With the transition to Future Earth, there is a paradigm shift emerging. The new vision is to support transformation to a sustainable and resilient future for society and nature on the coast, by facilitating innovative, integrated and solutions-oriented science. Realising this vision takes LOICZ into a third generation: to be at the forefront of co-designing, co-producing and co-implementing knowledge for coastal resilience and sustainability. LOICZ as Future Earth Coasts will continue to address 'hotspots' of coastal vulnerability, focusing on themes of dynamic coasts, human development and the coast, and pathways to global coastal sustainability and constraints thereof.
First observations of the freshwater jellyfish Craspedacusta sowerbii Lankester, 1880 in Ireland coincides with unusually high water temperatures
(Regional Euro-Asian Biological Invasions Centre, Helsinki, Finland, 2016-04-10) Minchin, Dan; Caffrey, Joe M.; Haberlin, Damien; Germaine, David; Walsh, Colm; Boelens, Rick; Doyle, Thomas K.
The freshwater hydrozoan Craspedacusta sowerbii was observed for the first time in Ireland at five localities in two separate river catchments (Shannon and Erne) during the summer of 2013. All collected medusae from Lough Derg on the Shannon catchment were female. Analysis of water temperature data for the period 2001–2015 found that water temperatures greater than 21°C were only recorded in 2013. The occurrence of medusae in three distinct areas during this unusually warm summer suggests that it may have been present in its polyp form for some years, or even decades. While it is not known when the species arrived in Ireland, the spread of this species may have involved different pathways. With climate warming, further appearances of the medusa-stage may be expected.
Optimising power transmission options for marine energy converter farms
(Elsevier, 2016-04-23) Nambiar, Anup J.; Collin, Adam J.; Karatzounis, Sotirios; Rea, Judy; Whitby, Ben; Jeffrey, Henry; Kiprakis, Aristides E.; European Commission; Engineering and Physical Sciences Research Council
This paper introduces a techno-economic analysis framework to assess different transmission options for marine energy converter (MEC) farms. On the technical front, the feasibility of the transmission options considering supply quality constraints and the optimal sizing of reactive power compensation to allow maximum real power transfer capability in the subsea transmission cable have been considered. The economic viability of different transmission options are measured based on component costs and the costs associated with the transmission losses. A case study has been presented in the paper, which demonstrates the application of this techno-economic analysis framework on a range of MEC farm sizes and distances from the shore. The results characterise the performance of different transmission system options with respect to three key design parameters – distance to shore, array power and transmission voltage – and provide guidance for system design.
Survey on demand side sensitivity to power quality in Ireland
(Elsevier, 2016-04-30) Rea, Judith A.; Herring, Jack; Sopoćko, Michał; Dempsey, Paul; Armstrong, Sara; Enterprise Ireland; Science Foundation Ireland
Power systems require a reliable supply and good power quality. The impact of power supply interruptions is well acknowledged and well quantified. However, a system may perform reliably without any interruptions but may have poor power quality. Although poor power quality has cost implications for all actors in the electrical power systems, only some users are aware of its impact. Power system operators are much attuned to the impact of low power quality on their equipment and have the appropriate monitoring systems in place. However, over recent years certain industries have come increasingly vulnerable to negative cost implications of poor power quality arising from changes in their load characteristics and load sensitivities, and therefore increasingly implement power quality monitoring and mitigation solutions. This paper reviews several historical studies which investigate the cost implications of poor power quality on industry. These surveys are largely focused on outages, whilst the impact of poor power quality such as harmonics, short interruptions, voltage dips and swells, and transients is less well studied and understood. This paper examines the difficulties in quantifying the costs of poor power quality, and uses the chi-squared method to determine the consequences for industry of power quality phenomenon using a case study of over 40 manufacturing and data centres in Ireland.
Wave energy conversion of oscillating water column devices including air compressibility
(AIP Publishing, 2016-09-23) Sheng, Wanan; Lewis, Anthony; Science Foundation Ireland; Environment Research Institute, University College Cork
This paper presents an investigation on air compressibility in the air chamber and its effects on the power conversion of oscillating water column (OWC) devices. As it is well known that for practical OWC plants, their air chambers may be large enough for accommodating significant air compressibility, the “spring effect,” an effect that is frequently and simply regarded to store and release energy during the reciprocating process of a wave cycle. Its insight effects on the device’s performance and power conversion, however, have not been studied in detail. This research will investigate the phenomena with a special focus on the effects of air compressibility on wave energy conversion. Air compressibility itself is a complicated nonlinear process in nature, but it can be linearised for numerical simulations under certain assumptions for frequency domain analysis. In this research work, air compressibility in the OWC devices is first linearised and further coupled with the hydrodynamics of the OWC. It is able to show mathematically that in frequency-domain, air compressibility can increase the spring coefficients of both the water body motion and the device motion (if it is a floating device), and enhance the coupling effects between the water body and the structure. Corresponding to these changes, the OWC performance, the capture power, and the optimised Power Take-off (PTO) damping coefficient in the wave energy conversion can be all modified due to air compressibility. To validate the frequency-domain results and understand the problems better, the more accurate time-domain simulations with fewer assumptions have been used for comparison. It is shown that air compressibility may significantly change the dynamic responses and the capacity of converting wave energy of the OWC devices if the air chamber is very large.
Investigating key decision problems to optimize the operation and maintenance strategy of offshore wind farms
(Elsevier, 2016-10-13) Sperstad, Iver Bakken; Devoy McAuliffe, Fiona; Kolstad, Magne; Sjømark, Severin
This paper investigates three decision problems with potential to optimize operation and maintenance and logistics strategies for offshore wind farms: the timing of pre-determined jack-up vessel campaigns; selection of crew transfer vessel fleet; and timing of annual services. These problems are compared both in terms of potential cost reduction and the stochastic variability and associated uncertainty of the outcome. Pre-determined jack-up vessel campaigns appear to have a high cost reduction potential but also a higher stochastic variability than the other decision problems. The paper also demonstrates the benefits and difficulties of considering problems together rather than solving them in isolation.
Energy conversion: a comparison of fix- and self-referenced wave energy converters
(MDPI, 2016-12-15) Sheng, Wanan; Lewis, Tony; Science Foundation Ireland
The paper presents an investigation of fix-referenced and self-referenced wave energy converters and a comparison of their corresponding wave energy conversion capacities from real seas. For conducting the comparisons, two popular wave energy converters, point absorber and oscillating water column, and their power conversion capacities in the fixed-referenced and self-referenced forms have been numerically studied and compared. In the numerical models, the deviceâ s power extractions from seas are maximized using the correspondingly optimized power take-offs in different sea states, thus their power conversion capacities can be calculated and compared. From the comparisons and analyses, it is shown that the energy conversion capacities of the self-referenced devices can be significantly increased if the motions of the device itself can be utilized for wave energy conversion; and the self-referenced devices can be possibly designed to be compliant in long waves, which could be a very beneficial factor for device survivability in the extreme wave conditions (normally long waves). In this regards, the self-referenced WECs (wave energy converters) may be better options in terms of wave energy conversion from the targeted waves in seas (frequently the most occurred), and in terms of the device survivability, especially in the extreme waves when compared to the fix-referenced counterparts.
Automatically identifying and predicting unplanned wind turbine stoppages using SCADA and alarms system data: case study and results
(IOP Publishing, 2017) Leahy, Kevin; Gallagher, Colm V.; Bruton, Ken; O'Donovan, Peter; O'Sullivan, Dominic T. J.; Science Foundation Ireland
Using 10-minute wind turbine SCADA data for fault prediction offers an attractive way of gaining additional prognostic capabilities without needing to invest in extra hardware. To use these data-driven methods effectively, the historical SCADA data must be labelled with the periods when the turbine was in faulty operation as well the sub-system the fault was attributed to. Manually identifying faults using maintenance logs can be effective, but is also highly time consuming and tedious due to the disparate nature of these logs across manufacturers, operators and even individual maintenance events. Turbine alarm systems can help to identify these periods, but the sheer volume of alarms and false positives generated makes analysing them on an individual basis ineffective. In this work, we present a new method for automatically identifying historical stoppages on the turbine using SCADA and alarms data. Each stoppage is associated with either a fault in one of the turbine's sub-systems, a routine maintenance activity, a grid-related event or a number of other categories. This is then checked against maintenance logs for accuracy and the labelled data fed into a classifier for predicting when these stoppages will occur. Results show that the automated labelling process correctly identifies each type of stoppage, and can be effectively used for SCADA-based prediction of turbine faults
Governance barriers to sustainable energy transitions – Assessing Ireland's capacity towards marine energy futures
(Elsevier Ltd, 2017) Lange, Marcus; O'Hagan, Anne Marie; Devoy, Robert R. N.; Le Tissier, Martin; Cummins, Valerie; Science Foundation Ireland
Marine energies (ME), including offshore hydcrocarbons along with marine renewable energies (MRE), such as offshore wind, wave and tidal energy, are increasingly important in the future energy mix of many nations. We observe that ME governance is complex, as development offshore involves engagement and may often result in conflict. This paper examines the Irish case, where offshore gas and oil remain relatively undeveloped, and yet have provoked extensive controversy. Moreover, Ireland exhibits very ambitious plans for MRE developments. Against a background, where ME development seems to have stalled, the objective of the paper is to analyse the Irish governance setup and its capacity to deliver ME and whether the current system is equipped to enable transition to MREs. Current governance systems lack efficacy in terms of policy integration and enforcement, government oversight, and public trust due to past failures. Although, management approaches have been developed to address some of the barriers, domains such as policy/regulation, industry development and public engagement are disconnected. Results: presented may not simply be generalised, as each country context is different. An analysis of examples with similar issues must focus on studying the context of the governance setup and balances of power across domains.

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