Scotland has substantial wave and tidal energy resources and is at the forefront of the development of marine renewable technologies and ocean energy exploitation. The next phase will see these wave and tidal devices deployed in arrays, with many sites being developed. Although developers have entered into agreements with The Crown Estate for seabed leases, all projects remain subject to licensing requirements under the Marine Scotland Act (2010). As part of the licensing arrangements, environmental effects in the immediate vicinity of devices and arrays will be addressed in the EIA (Environmental Impact Assessment) process that each developer must undertake. It is essential, however, that the regulatory authorities understand how a number of multi-site developments collectively impact on the physical and biological processes over a wider region, both in relation to cumulative effects of the developments and marine planning responsibilities. At a regional scale, careful selection of sites may enable the optimum exploitation of the resource while minimising any environmental impacts to an acceptable level. The TeraWatt Consortium has been established through the auspices of The Marine Alliance for Science & Technology for Scotland (MASTS) with Heriot-Watt University, and the Universities of Edinburgh, Glasgow, Strathclyde, the Highlands and Islands and Marine Scotland Science (MSS). The consortium has the support and anticipates the full engagement of the marine renewable developers in many aspects of the work. The research programme has been designed to specifically respond to questions posed by Marine Scotland Science, the organisation responsible for providing scientific advice to the licensing authority. In particular to the following questions: (1) What is the best way to assess the wave and tidal resource and the effects of energy extraction on it? (2) What are the physical consequences of wave and tidal energy extraction? (3) What are the ecological consequences of wave and tidal energy extraction? The overarching objective of the research is to generate a suite of methodologies that can provide better understandings of, and be used to assess, the alteration of the resource from energy extraction, and of the physical and ecological consequence. Illustration of the use of these in key development area, such as the Pentland Firth and Orkney Waters, and their availability as tools will enable the acceleration of array deployments. The TeraWatt research programme is structured in 4 workstreams. The first, led by MSS, will collate all necessary data to be used, develop the hypothetical multi-site array configurations in conjunction with developers and evaluate acceptance criteria for impacts. The second led by Edinburgh University will use separate and coupled models of wave and tide at a resolution necessary to consider multi-site array effects on the resource, providing important inputs to workstreams 3 and 4 which will address in turn, the spatial changes in physical processes affecting sediments, the shoreline and seabed (led by Glasgow and Strathclyde), and the spatial changes affecting organisms living in the seabed, their distribution and the significance of these for other ecological processes (led by Heriot-Watt University). Each workstream will provide reviews of the methodologies used which will be synthesised into a single methods toolbox. Where possible all regional scale modelling, used to illustrate these methodologies, will be validated by field data and the consortium has assembled both existing and data not previously available, for this purpose with the support of MSS and marine renewable developers. The TeraWatt project, which will be managed by MASTS, envisages direct participation from industry in various aspects of its work, and has a number of wider knowledge exchange and stakeholder engagement activities planned.

The Scottish Government is committed to promoting substantial sustainable growth in its marine renewable industries. Agreements for sea bed leases are already in place for 2GW of wave and tidal developments, and projects are progressing through the licensing process. Strategic marine planning for future phases of wave, tidal and offshore wind development is now in progress. For marine renewables to significantly contribute to the low-carbon energy mix towards 2050, significant offshore development in the form of very large scale arrays will be needed. In planning for such a future, the Government must consider the mix of technologies, the locations and configurations of very large scale arrays and their performance, and the implications of anticipated changes to the marine environment from climate change. In establishing its strategic policy positions, the Government must also ensure that legal obligations are met, particularly those under the European Marine Strategy Framework Directive (MSFD) to achieve Good Environmental Status (GES) by 2020. The EcoWatt2050 consortium has been established through the auspices of the Marine Alliance for Science and Technology for Scotland (MASTS) with Heriot-Watt University and the Universities of Edinburgh, Aberdeen, Strathclyde, Swansea and the Highlands and Islands, the National Oceanography Centre (Liverpool) and with Marine Scotland Science (MSS), the organization responsible for providing scientific advice to the Scottish Government on all aspects of marine renewable energy development, policy and planning. The research programme has been specifically designed to respond to questions posed by MSS: (1) How can marine planning be used to lay the foundation for the sustainable development of very large scale arrays of marine renewable energy devices? (2) What criteria should be used to determine the ecological limits to marine renewable energy extraction, and what are the implications for very large scale array characteristics? (3) How can we differentiate the effects of climate change from energy extraction on the marine ecosystem? (4) Are there ways in which marine renewables development may ameliorate or exacerbate the predicted effects of climate change on marine ecosystems? The overarching objective is thus to determine ways in which marine spatial planning and policy development, can enable the maximum level of marine energy extraction, while minimizing environmental impacts and ensuring that these meet the legal criteria established by European law. The research is structured in 5 workstreams. The first led by MSS will monitor progress and set out scenarios for the mix of technologies, very large scale array configurations, and environmental acceptance criteria. The second led by Edinburgh University will develop the hydrodynamic models necessary to examine the physical changes brought about by very large scale energy extraction, including under conditions anticipated from climate change. These outputs feed directly into workstreams 3 and 4 led by HWU and Aberdeen University respectively. These extend this work to examine changes in availability and location of critical habitats for benthic and mobile marine species, and to determine the consequences of changes in critical habitat for the ecosystem as a whole. Finally, workstream 5 led by MSS provides a synthesis of this research, quantifying the balance between energy extraction and environmental change and acceptance criteria to be used in marine spatial planning and policy development. EcoWat2050 builds in direct participation from industry in various aspects of its work, and has a number of wider knowledge exchange and stakeholder engagement activities planned.

Floating offshore wind turbine (FOWT) deployments are predicted to increase in the future and the outlook is that globally, 6.2 GW of FOWTs will be built in the next 10 years (https://tinyurl.com/camyybxk). Highly dynamic, free hanging power cables transport power generated by these FOWTs to substations and the onshore grid. Safety critical design of such power cables in order for them to operate in the ocean without failure is of utmost importance, given that these cables are highly expensive to install and replace and any down-time of turbine electrical output results in huge revenue loss. In FOWTs, a large length of the power cable, from the base of the floating foundation to the seabed, is directly exposed to dynamic loading caused by ocean waves, currents, and turbulence. Waves move the floating foundation, and currents produce cable oscillations generated by vortex shedding. In the water column a cable experiences enhanced dynamic loads and undergoes complicated motions. When a dynamic cable is installed in deep water, the upper portion of the cable is exposed to high mechanical load and fatigue, and the lower part to substantial hydrostatic pressure. Motion of the floating foundation in surge, sway, and heave causes the power cable to undergo oscillatory motions that in turn promote vortex-induced vibration (VIV) - which is analogous to the vibration experienced by long marine risers used in offshore oil and gas platforms. As a result, large and complex deflections of the cable occur at various locations along its length, altering its mechanical properties and strength, and eventually leading to fatigue-induced failure. The dynamic forces produce cyclical motions of the cable, and a sharp transition in cable stiffness is expected in cases where these motions and loads concentrate toward a rigid connection point. Repetition of the foregoing process and over-bending can also lead to fatigue damage to the cable. To date, hardly any research has been undertaken to investigate the 3-dimensional nature of VIV, dynamic loads, and motion of power cables subject to combined waves, currents, and turbulence. Moreover, no detailed guidance is given in design standards for the offshore wind industry on how to predict, assess, and suppress fatigue failure of dynamic cables under wave-current-turbulence conditions. Power cable failure is much more likely to occur if the design of such cables is based on poor understanding of the hydrodynamic interactions between cables and the ocean environment. This fundamental scientific research aims to investigate the dynamic loading, motion response, impact of vortex induced vibration and its suppression mechanism, and fatigue failure of subsea power cables subjected to combined 3-dimensional waves, currents, and turbulence. This research will be approached by both numerical and physical modelling of power cable's response. Controlled experimental tests on scale models of power cables will be undertaken in Edinburgh University's FloWave wave-current facility where multi-directional waves and currents of various combinations of amplitudes, frequencies, and directions can be generated. Advanced novel phenomenological wake oscillator models, calibrated and validated with FloWave experimental results, will be used to simulate the hydrodynamic behaviour of power cables. The resulting software tools, experimental data, analysis techniques for characterising cable dynamics and VIV, methodologies established for fatigue analysis, and other outcomes of this research will enhance the design of cost-effective power cables. By reducing uncertainty, our research will lead to increased reliability of offshore power cables, of benefit to the power cable manufacturing industry.

Tidal currents are known to have complex turbulent structures. Whilst the magnitude and directional variation of a tidal flow is deterministic, the characteristics of turbulent flow within a wave-current environment are stochastic in nature, and not well understood. Ambient upstream turbulent intensity affects the performance of a tidal turbine, while influencing downstream wake formation; the latter of which is crucial when arrays of tidal turbines are planned. When waves are added to the turbulent tidal current, the resulting wave-current induced turbulence and its impact on a tidal turbine make the design problem truly challenging. Although some very interesting and useful field measurements of tidal turbulence have been obtained at several sites around the world, only limited measurements have been made where waves and tidal currents co-exist, such as in the PFOW. Also, as these measurements are made at those sites licensed to particular marine energy device developers, the data are not accessible to academic researchers or other device developers. Given the ongoing development of tidal stream power in the Pentland Firth, there is a pressing need for advanced in situ field measurements at locations in the vicinity of planned device deployments. Equally, controlled generation of waves, currents and turbulence in the laboratory, and measurement of the performance characteristics of a model-scale tidal turbine will aid in further understanding of wave-current interactions. Such measurements would provide a proper understanding of the combined effects of waves and misaligned tidal stream flows on tidal turbine performance, and the resulting cyclic loadings on individual devices and complete arrays. The availability of such measurements will reduce uncertainty in analysis (and hence risk) leading to increased reliability (and hence cost reductions) through the informed design of more optimised tidal turbine blades and rotor structures. An understanding of wave-current-structure interaction and how this affects the dynamic loading on the rotor, support structure, foundation, and other structural components is essential not only for the evaluation of power or performance, but also for the estimation of normal operational and extreme wave and current scenarios used to assess the survivability and economic viability of the technology, and to predict associated risks. The proposal aims to address these issues through laboratory and field measurements. This research will investigate the combined effect of tidal currents, gravity waves, and ambient flow turbulence on the dynamic response of tidal energy converters. A high quality database will be established comprising field-scale measurements from the Pentland Firth, Orkney waters, and Shetland region, supplemented by laboratory-scale measurements from Edinburgh University's FloWave wave-current facility. Controlled experiments will be carried out at Edinburgh University's FloWave facility to determine hydrodynamic loads on a tidal current device and hence parameterise wave-current-turbulence-induced fatigue loading on the turbine's rotor and foundation.