Centre for Marine and Renewable Energy (MaREI) - Conference Items

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Artificial neural network application in short-term prediction in an oscillating water column
(The International Society of Offshore and Polar Engineers (ISOPE), 2010-01) Sheng, Wanan; Lewis, Anthony; Science Foundation Ireland; Department of Communications, Energy and Natural Resources, Ireland
Oscillating Water Column (OWC) is one type of promising wave energy devices due to its obvious advantage over many other wave energy converters: no moving component in sea water. Two types of OWCs (bottom-fixed and floating) have been widely investigated, and the bottom-fixed OWCs have been very successful in several practical applications. Recently, the proposal of massive wave energy production and the availability of wave energy have pushed OWC applications from near-shore to deeper water regions where floating OWCs are a better choice. For an OWC under sea waves, the air flow driving air turbine to generate electricity is a random process. In such a working condition, single design/operation point is nonexistent. To improve energy extraction, and to optimise the performance of the device, a system capable of controlling the air turbine rotation speed is desirable. To achieve that, this paper presents a short-term prediction of the random, process by an artificial neural network (ANN), which can provide near-future information for the control system. In this research, ANN is explored and tuned for a better prediction of the airflow (as well as the device motions for a wide application). It is found that, by carefully constructing ANN platform and optimizing the relevant parameters, ANN is capable of predicting the random process a few steps ahead of the real, time with a good accuracy. More importantly, the tuned ANN works for a large range of different types of random, process.
Development and operation of a power take off rig for ocean energy research and testing
(2011-01) Rea, Judith A.; Kelly, James F.; Alcorn, Raymond; O'Sullivan, Dara
Partnerships involving stakeholders in the Celtic Sea ecosystem (PISCES): Translating EU maritime policy into practical outputs for multiple sectors spanning Ireland, the UK, France and Spain
(Environmental Sciences Association of Ireland, 2011-04) Twomey, Sarah; O'Mahony, Cathal; Sutton, Gerry; European Commission
The Celtic Sea marine ecosystem is an area of diverse wildlife and important ecological activity. It is also one of the most heavily used bodies of water in the world of with multiple sectors including industry, shipping, commercial fishing and coastal recreation competing for space and resources. Like oceans and seas globally, this region is experiencing pressures due to increasing human activity. In response to this growing problem, the European Commission LIFE+ programme funded a project called Partnerships Involving Stakeholders in the Celtic Sea Eco-System (PISCES). The primary aims of PISCES are to: find new and innovative ways to engage stakeholders in working together on environmentally sound solutions for the region; develop stakeholder understanding of the ecosystem-based approach to marine management; and, produce a set of stakeholder-led guidelines for an ecosystem-based approach to management of activities in the area. Current EU-wide marine management policies rely on effective application of an ecosystem-based approach (e.g., the EU Marine Strategy Framework Directive; the Common Fisheries Policy). PISCES is a pioneering project in that it is translating EU maritime policy into practical outputs for multiple sectors and across a multinational area encompassing four countries: the UK, Ireland, France and Spain. This three-year project, which began at the end of 2009, identifies the key players in the Celtic Sea representing all major human uses and impacts, and builds successful stakeholder partnerships through a series of workshops whilst also facilitating additional interactions in order to maximise the out-reach and impact of the practical guidelines. Stakeholders include the fishing and aquaculture industries, marine renewable energy companies, shipping, oil, gas and aggregate extraction industries, ports, environmental agencies, coastal tourism and recreation industries, as well as key policy makers from the four countries.
Offshore wind farm service vessel, hull design optimisation
(International Conference on Ocean Energy (ICOE), 2012-10) Shanley, Matthew; Murphy, Jimmy; Molloy, Padraig; University College Cork
Access to a wind turbine is a major issue, currently there is a 1.5m significant wave height (Hs) limit for the standard “step over” method for transferring personnel to an offshore wind turbine. According to the Carbon Trust being able to access, wind turbines at a wave height of 3m would be worth ₤3 billion to the offshore wind industry. The current research addresses this issue by examining a novel multihull design concept for an Offshore Wind Farm Service Vessel. The objective of this work is to carry out a feasibility study of the proposed design as previous research indicated that the design reduces the heave and pitch motions by dampening its response to the wave motion. The proposed design is analysed with both hydrostatic and hydrodynamic analysis using the computational fluid dynamic (CFD) package ANSYS CFX. Also to be undertaken is physical model testing of the analysed design in the National Ocean Test Facility’s wave basin to determine the accuracy of the computational analysis.
Guiding stakeholders to participate in Marine Strategy Framework implementation
(MARMONI project, 2012-11) Twomey, Sarah; Baltic Environmental Forum and the MARMONI project.
Large marine areas and regional seas present a challenge in terms of management. They are often bordered by numerous maritime jurisdictions; with multi-use and multi-sector environments; involving varying governance arrangements; and generation of sufficient levels of data to best inform decision-makers. Marine management at the regional scale involves a range of mechanisms and approaches to ensure all relevant stakeholders have an opportunity to engage in the process; and these approaches can differ in their legal and regulatory conditions. At present, no such comparable structures exist at the transnational level for the ecosystem-based management of the Celtic Sea. Against this backdrop, a participative process, involving representatives from differing sectors of activity in the Celtic Sea spanning four Member States, was established for the purpose of identifying realistic and meaningful management principles in line with the goals of the Marine Strategy Framework Directive.
Primary wave energy conversions of oscillating water columns
(European Wave and Tidal Energy Conference, 2013-09) Sheng, Wanan; Alcorn, Raymond; Lewis, Anthony; Science Foundation Ireland
This paper presents a study on the numerical simulation of the primary wave energy conversion in the oscillating water column (OWC) wave energy converters (WECs). The new proposed numerical approach consists of three major components: potential flow analysis for the conventional hydrodynamic parameters, such as added mass, damping coefficients, restoring force coefficients and wave excitations; the thermodynamic analysis of the air in the air chamber, which is under the assumptions of the given power take-off characteristics and an isentropic process of air flow. In the formulation, the air compressibility and its effects have been included; and a time-domain analysis by combining the linear potential flow and the thermodynamics of the air flow in the chamber, in which the hydrodynamics and thermodynamics/aerodynamics have been coupled together by the force generated by the pressurised and de-pressurised air in the air chamber, which in turn has effects on the motions of the structure and the internal water surface. As an example, the new developed approach has been applied to a fixed OWC device. The comparisons of the measured data and the simulation results show the new method is very capable of predicting the performance of the OWC devices.
Physical and numerical analysis of a concept offshore wind farm service vessel hull design
(The Royal Institution of Naval Architects, 2014) Shanley, Matthew; Murphy, Jimmy; The Royal Institution of Naval Architects; University College Cork
Wind turbine maintenance and access during high sea states is a key issue for the successful operation of an offshore wind farm. Currently there is a 1.5m significant wave height (Hs) limit for the standard ‘step over’ method of transferring personnel to an offshore wind turbine. Increasing the Hs that offshore wind turbines can be accessed at would reduce the lifetime, levelised cost of energy and address a health and safety issue. The paper addresses this issue by examining a concept hull design for an offshore wind farm service vessel. The proposed design reduces the vessel’s heave and motion by dampening its response to the wave motion. The design underwent both numerical and physical methods of testing. The numerical modelling was carried out in a 3-D wave basin built in ANSYS CFX and is based on symmetry across the hull which allows for three degrees of freedom. Physical modelling at 1:25 scale took place in the wave basin at Beaufort Research in University College Cork. A number of variations of the concept were tested and the results showed the aspects of the concept that could be beneficial to personnel transfer, through reduced response amplitude operators at zero forward speed.
Latching control theory for wave energy conversion
(2014-03) Sheng, Wanan; Alcorn, Raymond; Lewis, Anthony; Science Foundation Ireland
Performance study of the Galway Bay wave energy test site floating power system
(International Conference on Ocean Energy, 2014-11) Bosma, Bret; Sheng, Wanan; Thiebaut, Florent; Marine Institute; Science Foundation Ireland; University College Cork; Department of Energy, United States
The Galway Bay wave energy test site promises to be a vital resource for wave energy researchers and developers. As part of the development of this site, a floating power system is being developed to provide power and data acquisition capabilities, including its function as a local grid connection, allowing for the connection of up to three wave energy converter devices. This work shows results from scaled physical model testing and numerical modelling of the floating power system and an oscillating water column connected with an umbilical. Results from this study will be used to influence further scaled testing as well as the full scale design and build of the floating power system in Galway Bay.
Experimental study on the wave measurements of wave buoys
(International Conference on Ocean Energy, 2014-11) Liu, Qiulin; Lewis, Anthony; Zhang, Yongliang; Sheng, Wanan; National Natural Science Foundation of China; National High Technology Research and Development Program, China; State Key Laboratory of Hydroscience and Engineering, China
Wave measurement is of vital importance for assessing the wave power resources and for developing wave energy devices, especially for the wave energy production and the survivability of the wave energy device. Wave buoys are one of the most popular measuring technologies developed and used for long-term wave measurements. In order to figure out whether the wave characteristics can be recorded by using the wave buoys accurately, an experimental study was carried out on the performance of three wave buoy models, viz two WaveScan buoys and one ODAS buoy, in a wave tank using the European FP7 MARINET facilities. This paper presents the test results in both time and frequency domains and the comparison between the wave buoys and wave gauge measurements. The analysis results reveal that for both regular and irregular waves, the WaveScan buoys have better performances than the ODAS buoy in terms of accuracy and the WaveScan buoys measurements have a very good correlation with those from the wave gauges.
A new latching control technology for improving wave energy conversion
(2014-11) Sheng, Wanan; Alcorn, Raymond; Lewis, Anthony; Science Foundation Ireland
Extracting wave energy from seas has been proven to be very difficult although various technologies have been developed since 1970s. Among the proposed technologies, only few of them have been actually progressed to the advanced stages such as sea trials or pre-commercial sea trial and engineering. One critical question may be how we can design an efficient wave energy converter or how the efficiency of a wave energy converter can be improved using optimal and control technologies, because higher energy conversion efficiency for a wave energy converter is always pursued and it mainly decides the cost of the wave energy production. In this first part of the investigation, some conventional optimal and control technologies for improving wave energy conversion are examined in a form of more physical meanings, rather than the purely complex mathematical expressions, in which it is hoped to clarify some confusions in the development and the terminologies of the technologies and to help to understand the physics behind the optimal and control technologies. As a result of the understanding of the physics and the principles of the optima, a new latching technology is proposed, in which the latching duration is simply calculated from the wave period, rather than based on the future information/prediction, hence the technology could remove one of the technical barriers in implementing this control technology. From the examples given in the context, this new latching control technology can achieve a phase optimum in regular waves, and hence significantly improve wave energy conversion. Further development on this latching control technologies can be found in the second part of the investigation.
Performance improvements of mooring systems for wave energy converters
(2014-11) Casaubieilh, Pierre; Thiebaut, Florent; Bosma, Bret; Retzler, C.; Shaw, M.; Letertre, Y.; Sheng, Wanan; European Commission
In the development of wave energy converters, the mooring system is a key component for a safe station-keeping and an important factor in the cost of the wave energy production. Generally, when designing a mooring system for a wave energy converter, two important conditions must be considered: (i) that the mooring system must be strong enough to limit the drifting motions, even in extreme waves, tidal and wind conditions and (ii) it must be compliant enough so that the impact on wave energy production can be minimised. It is frequently found that these two conditions are contradictory. The existing solutions mainly include the use of heavy chains, which create a catenary shaped mooring configuration, allowing limited flexibility within the mooring system, and hence very large forces may still be present on mooring lines and thus on anchors. This solution is normally quite expensive if the costs of the materials and installation are included. This paper presents a new solution to the mooring system for wave energy converters within the FP7 project, ‘GeoWAVE’, which is a project aiming to develop a new generation of the moorings system for minimising the loads on mooring lines and anchors, the impact on the device motions for power conversion, and the footprint if it is applicable, and meanwhile the new types of anchors are also addressed within the project. However this paper will focus on the new mooring system by presenting the wave tank test results of the Pelamis wave energy converter model and the new developed mooring system. It can be seen that the new generation of mooring system can significantly reduce the loads on mooring lines and anchors, and reduce the device excursions as a result of the new mooring system when compare to the conventional catenary mooring.
Hydrodynamics of oscillating water column wave energy converters
(2014-11) Sheng, Wanan; Alcorn, Raymond; Lewis, Anthony; Science Foundation Ireland
This work deals with the numerical studies on hydrodynamics of oscillating water column (OWC) wave energy converters and its damping optimization on maximizing wave energy conversion by the OWC device. As a fundamental step, the hydrodynamic problems have been systematically studied by considering the interactions of the wave-structure and of the wave-internal water surface. Our first attention is on how the hydrodynamic performance can be reliably assessed, especially when it comes to the time-domain analysis, and what the physics behind the considerations is. Further on, a damping optimization for the OWC wave energy converter is also present based on the dynamics of the linear system, and a study on how we can optimize the damping for the given sea states so that the power conversion from irregular waves from irregular waves can be maximized.
Effects of tidal range on mooring systems of wave energy converters
(EWTEC, 2015-09) Murphy, Stephen; Bhinder, Majid A.; Casaubieilh, Pierre; Sheng, Wanan
Wave energy converters are currently proposed to be deployed near coastal area for the closeness to the infrastructure and for ease of maintenance in order to reduce operational costs. The motivation behind this work is the fact that the deployment depths during the highest and lowest tides will have a significant effect on the mooring system of WECs. In this paper, the issue will be investigated by numerical modelling (using ANSYS AQWA) for both catenary and taut moorings to examine the performance of the mooring system in varying tides. The case study being considered is the ¼- scale wave energy test site in Galway Bay off the west coast of Ireland where some marine renewable energy devices can be tested. In this test site, the tidal range is macro-tidal with a range of approximately 6 m which is a large value relative to the water depth. In the numerical analysis, ANSYS AQWA suite has been used to simulate moored devices under wave excitation at varying tidal ranges. Results show that the highest tide will give rise to larger forces. While at lower depths, slackening of the mooring occurs. Therefore, the mooring lines must be designed to accommodate both situations.
An innovative hull design for an offshore wind farm support vessel
(The Royal Institution of Naval Architects, 2016-03) Shanley, Matthew; Balke, Sebastian; Murphy, Jimmy; The Royal Institution of Naval Architects; University College Cork
Utilising the Cross Industry Standard Process for Data Mining to reduce uncertainty in the Measurement and Verification of energy savings
(Springer International Publishing AG, 2016-06-14) Gallagher, Colm V.; Bruton, Ken; O'Sullivan, Dominic T. J.; Science Foundation Ireland; NTR Foundation, Ireland
This paper investigates the application of Data Mining (DM) to predict baseline energy consumption for the improvement of energy savings estimation accuracy in Measurement and Verification (M&V). M&V is a requirement of a certified energy management system (EnMS). A critical stage of the M&V process is the normalisation of data post Energy Conservation Measure (ECM) to pre-ECM conditions. Traditional M&V approaches utilise simplistic modelling techniques, which dilute the power of the available data. DM enables the true power of the available energy data to be harnessed with complex modelling techniques. The methodology proposed incorporates DM into the M&V process to improve prediction accuracy. The application of multi-variate regression and artificial neural networks to predict compressed air energy consumption in a manufacturing facility is presented. Predictions made using DM were consistently more accurate than those found using traditional approaches when the training period was greater than two months.
Tupperwave-preliminary numerical modelling of a floating OWC equipped with a unidirectional turbine
(European Wave and Tidal Energy Conference (EWTEC), 2017) Vicente, Miguel; Benreguig, Pierre; Crowley, Sarah; Murphy, Jimmy; Horizon 2020
The TUPPERWAVE project is supported by the European Commission's OceanEraNet program. It aims to design and validate an innovative Oscillating Water Column (OWC) Power Take-Off (PTO) concept at laboratory scale. A conventional OWC typically generates a highly fluctuating bidirectional air flow through a self-rectifying turbine. To reduce the pneumatic power fluctuations through the turbine and the acoustic impact and ultimately increase the device efficiency, the TUPPERWAVE concept generates unidirectional air flow in a closed circuit, which can be converted into electricity via a conventional, high efficiency, unidirectional turbine. The principle is based on the use of a pair of non-return valves, two additional chambers above the water column and a unidirectional turbine harnessing energy from the resulting air flow between the two chambers. The concept was adapted to a floating axisymmetric structure. Numerical time-domain models have been developed by UCC and WavEC to determine the deviceâ s primary conversion from hydrodynamic to pneumatic power. Comparison of the output from the two models showed good agreement and allowed an initial optimization of the PTO main design parameters. A set of design parameters were chosen which maximize the pneumatic average power output flowing through the turbine whilst minimizing the power fluctuations, in regular and irregular sea states. When compared to a conventional OWC with the same structure geometry, the optimised Tupperwave device was shown to produce similar pneumatic average power with much lower fluctuations.
Access to a floating wind turbine
(The Royal Institution of Naval Architects, 2017-03) Shanley, Matthew; Wright, Christopher S.; Otter, Aldert; Desmond, Cian J.; Murphy, Jimmy; The Royal Institution of Naval Architects; Lir National Ocean Test Facility, Ireland; Science Foundation Ireland
The offshore wind turbine service industry is now well established with a large number of turbines being successfully operated and maintained. A number of methods and technologies are available to allow the safe transfer of service crews to these primarily fixed monopile installations. The most common of these is the bow transfer method which uses a combination of a high friction fender and a large vessel thrust to minimise relative motion between the bow and the turbine foundation. An upcoming challenge for the offshore wind turbine service industry will be the increasing use of floating foundations in far offshore and deep water sites. A number of structures are currently being developed and the first commercial floating wind farm is expected to be commissioned in late 2017. The use of floating structures will make it more difficult to ensure crew safety and comfort during transfer operations as the interaction between two floating bodies needs to be considered. Thus, the bow transfer method used to access fixed foundations may not be suitable for accessing floating turbine platforms. This paper will use a combination of physical and numerical modelling to assess the ability of a wind farm service vessel to maintain contact with a floating offshore wind turbine structure by use of the bow transfer method.
Distributed hierarchical droop control of boost converters in DC microgrids
(Institute of Electrical and Electronics Engineers (IEEE), 2017-07-20) O'Keefe, Daniel; Riverso, Stefano; Albiol-Tendillo, Laura; Lightbody, Gordon; Irish Research Council; University College Cork
Voltage stability and accurate current-sharing are primary features of an efficiently operating power distribution network, such as a dc islanded-microgrid. This paper presents the development of a distributed hierarchical droop control architecture for dc-dc boost converters within a dc islanded-microgrid. Decentralised controllers are conventionally designed for local voltage and current control without accounting for coupling to other converters. However, due to the non-minimum phase action of boost converters, global knowledge of coupling is required to inform stable local controller tuning over a range of load disturbances. Consensus-based distributed secondary controllers, utilising low-bandwidth communications, are designed to coordinate voltage levels and improve current-sharing accuracy. The control architecture is tested in response to communication faults, non-linear loads, and plug-and-play operations.
Tidal flyer; innovation, design & evolution (TIDE)
(EWTEC, 2017-09) Devaney, Theo; Holmes, Brian; Bhinder, Majid A.; Sustainable Energy Authority of Ireland
Open Ocean Energy (OOE) Ltd. is a tidal energy company developing a vertical hydrofoil based device, the Tidal Flyer. Following the initial years proving the concept and progressing the design of the system for the past 3 years OOE have been working intensively with Black & Veatch (B& V) on the techno-economic optimisation of the Tidal Flyer configuration. This paper will outline recently conducted Phase 1 physical testing of various aspects of the technical design evolving from the study. CFD work investigating critical features of the system dynamics was also undertaken but is not reported here. The Phase 1 testing was constructed to inform the design of a full, dynamic model due for testing at the combined wave and current tank, Flowave in Edinburgh, Scotland. The latter trials will be undertaken as a Phase 2 test programme. At the end of the physical test schedule, OOE will have completed up to TRL 4 and satisfied a series of predefined stage gates criteria. The programme of empirical testing involved two visits (8 testing days) to the IFREMER flow flume in Boulogne-sur-Mer, France. The CFD analysis is being undertaken at UCC as part of the SFI funded Marine Renewable Energy Ireland [MaREI] scheme. Initially the empirical setups were simulated to verify the test plan.

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