Marine Energy

IES is world-leading in marine energy research and development ranging from resource assessment and prediction, to converter design, optimisation and control. Renewable resources covered include wave, tidal and offshore wind. In addition to the descriptions given here please visit the website of Supergen Marine Energy Consortium to see details of our work. A further, closely-related research area is coastal defence.

Much of IES's research aims to support the development of marine energy resources. These include developing solutions to the technical difficulties posed by connecting marine renewables to networks and improving its competitiveness (Power Systems Operation and Control) and development of alternative energy vectors to assist the power system harness variable renewables (Energy and Climate Change).

Current Research Areas:

• Marine Energy Converters
• Marine Energy Control and Power Take-Off
• Marine Energy Resources
• Coastal Defence

There is a variety of ongoing research projects into Wave Energy Convertors (WECs) including the reknowned 'Salter's Duck' and the Sloped IPS Buoy. A critical component of IES research is the validation of device performance and we are able to carry out this work using a state-of-the-art curved wave tank.

The development of means to harness the power of tidal streams is also receiving the attention of IES staff. Further details can be found here.

Real Time Wave Field Mapping for the Offshore Renewable Energy Industry

EPSRC has awarded IES £238,000 to investigate the feasibility of using a novel distributed array of floating sensors to provide water surface elevation in real time. The 18-month project will involve a range of project partners including Heriot-Watt University, Hydraulics and Maritime Research Centre, Cork, Maritime Institute of Ireland, Measurand Inc, Queen's University of Belfast and Wavebob Ltd.

• The Real Time Waves project website

Recent reports highlight the need for continued tank testing of Marine Energy Converters (MECs). From conception and throughout development, tank tests provide essential insight into the interaction of a MEC with its environment. Consideration of the location and resulting operating conditions of a device is required to ensure technological and economic viability. Experiments, both physical and numerical, need to be built around this concept. With this in mind modelling will focus on both the sensitivity to and ability to compensate for changes in wave field. Compensation is usually achieved either inherently in the design or by active control strategies. Regardless of method these strategies will require information – a spatial and temporal description of the surrounding wave field. In the lab this description can be obtained at varying resolution, with high precision possible, whilst at sea a discrepancy between measured and experienced wave field will exist. Control strategy sensitivity to the source of the wave field description and any associated error will be investigated. Commercial software can predict device behaviour with increasing levels of detail and will be used in comparisons with experimental work. Ensuring best practice whilst conducting these tests should lead to improved confidence in the testing methodologies and their outcomes.

Evaluation of vertical axis tidal current turbines

A vertical-axis turbine is one device for extracting energy from tidal currents. This form of turbine was initially conceived for wind energy extraction, and for many years it was unclear whether this or the horizontal-axis form would dominate. Whilst there appear to be similarities between wind and tidal currents - in both cases we are apparently extracting energy from the kinetic energy in a flow - there are factors (e.g. free surface above the tidal flow, density, mean and extreme velocities and cavitation) which enforce an upper limit on the speed of a tidal current turbine blade. The aim of this work is primarily to re-evaluate the vertical-axis concept for tidal currents in light of the aforementioned differences between wind and tide. Computer-based modelling is being used to this end. First, a simple semi-analytical (Blade Element Momentum) model is used to explore the effect of key turbine design variables on performance. Secondly, detailed Computational Fluid Dynamics modelling is being carried out using a commercial, general purpose code (CFX), to investigate in greater detail the interaction between the turbine and the flow.

Establishment and Assessment of Laboratory Testing Procedures of Tidal Current Energy Devices

The establishment of comprehensive and practical testing procedures for tidal current energy conversion devices is crucial for improving the performance of single tidal turbines large-scale tidal farms. Unlike the testing of wave energy devices, which has been performed at laboratory scale since the late 1970s, the laboratory testing of scale model tidal current energy conversion devices is still an embryonic activity. As such, the objectives of this work are to: identify clear guidelines to the performance of scale laboratory tests on tidal current energy converters in towing tanks and moving flow channels; test these guidelines for robustness with respect to scale and system geometry; and establish the operational limits to effective scale model testing.

Application of a Potential Flow Model to the Hydrodynamic Interaction between a Tidal Turbine, its Wake and the Free-Surface

Use of high pressure oil transmission systems coupled with hydraulic accumulators as well as variable speed, doubly fed induction generators will be considered as a means of power contitioning. Intelligent control of the reactive power exchanged between the generator and the network, has been developed by the University of Edinburgh in a previous project. These algorithms are being extended and applied to MECs in order to mitigate voltage fluctuation due to the variability of the marine energy resource. This work comprises Work Package 7 of the Supergen Marine consortium Phase 2.

Nonlinear modeling of the Power Take Off of Wave Energy Converters

This research looks at modeling (analytically, numerically and physically) the response of the Power Take Off (PTO) of a Wave Energy Converter (WEC). A generic WEC is considered which is a off-shore, slack moored, point absorber. The model considers large scale nonlinear effects of the PTO coupled to the hydrodynamic motion due to the sea. The WEC is initially limited to move in heave, with a regular monochromatic sea. As this research progresses, movement in pitch and surge will be considered. [More...]

Novel control systems for marine energy converters

Machines for Marine Energy

A significant part of IES's effort in marine energy relates to the ability to extract power from the sea. In particular this includes novel direct drive linear and rotary electrical generators and further information on these projects can be found in the Machines and Power Electronics section.

One of IES's key areas of expertise is in assessment of renewable energy resources including wave and tidal alongside others like wind and hydropower. Such analysis is vitally important for project feasibility studies, planning policy, wider energy network analysis as well as specification of marine energy devices. A wide range of projects are described on the Energy and Climate Change group page.

A key part of our work is in understanding resource variability in the long term particularly with a changing climate. Work in IES is pioneering assessment of climate impacts and adaptation in wave and tidal energy systems. [More...]

Coastal and shallow wave responses, such as wave overtopping at seawalls, pose a significant hazard to both property and personnel. The established random wave modelling methods tend to be inefficient when used to study the extreme response at a structure. This research examines statistical techniques which allow extreme responses such as maximum overtopping discharge to be predicted using shorter test runs. These techniques increase the occurrence frequency of the extreme events while still maintaining the realism of using random wave trains. Testing of these new tools is currently being carried out in the wave tank but they are equally applicable to numerical modelling methods.

Violent Overtopping by Waves at Seawalls (VOWS)

Wave overtopping is a major factor in the design and serviceability of seawalls and breakwaters as overtopping of seawalls may lead to flooding and seawalls and breakwaters are frequently areas used by people and vehicles: overtopping waves may present a significant safety hazard. Many coastal seawalls are designed for a (tolerable) mean discharge to overtop the structure over a storm event. Prediction of mean overtopping discharge rates are based on empirical formulae fitted to laboratory measurements. These formulae mainly cover pulsating wave conditions, but studies have indicated configurations of vertical and composite walls for which impulsive breaking may occur, and have demonstrated that present methods may under-estimate overtopping under impact conditions. Importantly, impulsive breaking leads to sudden overtopping where water is thrown landward at considerable velocity. Such events have overturned railway wagons on a breakwater (Dover 1942), cars/vans have been swept into the sea (Port Talbot 1985), small buildings destroyed (Seaford 1996), and people drowned (Alderney 1992). These processes show great potential to cause damage to developments close to the defence, but little generic guidance is available to predict the magnitude and effects of such events. [More...]

Blockwork Coastal Structures

Around the UK and the Mediterranean, there are many coastal defence and harbour structures constructed of natural stone or concrete blocks. At some sites, the structures are in relatively good repair, but in many other these structures have suffered deterioration or significant damage. In the UK and in Italy, these historic structures often support important infrastructure, but often with little any explicit understanding of the importance of the structure. Worse, repair or rehabilitation of these structures is severely hampered by an almost complete lack of information on the mechanisms of failure. An understanding of the failures can be gained only from a combination of careful analysis of historical failure records, field data, new hydraulic models tests, and physical and numerical modelling of the detail of failure initiation mechanisms such as pressure propagation in cracks. This is being carried out through the BloCSnet network which intends to synthesise the knowledge and skills of its members in order to develop a focussed research strategy in this field. The longer term aim of the team is to analyse the failure mechanisms, and facilitate the development and then dissemination of guidance on how these old structures work, how they should be analysed, and what methods should be used in their repair and rehabilitation. [More...]

Group Leader

Professor Ian Bryden