As part of a global drive to produce renewable electricity, devices are being designed to harness energy from the waves and tidal currents. Physical scale model testing is an important part of the development process for this and other technologies. The FloWave Ocean Energy Research Facility at The University of Edinburgh is designed to conduct these tests. Here it is possible to produce multi-directional waves combined with currents in the circular tank, re-creating the complexity of the ocean. The research was driven by commercial requirements of the facility, aiming to highlight what can be learnt from testing at scale with complex conditions in a controlled environment. To enable this, it was first necessary to extend the characterisation of this new facility. Wave generation and reflections were assessed in a previous project. In this work, flow measurements taken throughout the test volume of the tank, allowed spatial and temporal variations in the currents to be determined. Waves and currents interact in a complex manner, compounded by the method of reproducing them in a tank. The influence of currents on waves in the basin was assessed. This included cases with an oblique angle between them, on which little has been published. The other part of the project addressed issues to be considered when testing in a combined wave-current basin such as FloWave. • At many sites of interest for offshore renewable energy, waves are influenced by water depth. Implications of not scaling depth consistently were considered, and design diagrams produced to facilitate understanding and quantification of potential errors. • At FloWave, waves are generated in still water around the outside of the tank. A process was therefore developed and verified to produce the desired combined conditions in the central test area following their interaction with the current. • There is a wealth of published guidance on tank testing, for ships, offshore structures, and more recently renewable energy. This has been reviewed and suggestions offered to augment this by including testing in the more advanced conditions possible in a facility like FloWave. • Tools and guidance have been developed to highlight many of the issues to be considered by clients prior to testing at FloWave. This aims to facilitate planning of a test programme by highlighting potential knowledge gaps and recording decisions made. Flowcharts have been produced to represent this graphically, with a corresponding checklist of questions for clients, which have been trialled in a pilot study. Outputs from this research are being used to help deliver both academic and commercial client tests at FloWave. The test area in currents was shown to be > 50m2 with < 10% variation in flow, and the combined wave-current conditions possible have been explored. Results that are important when designing client test plans.

Wave tank tests facilitate the understanding of how complex sea conditions influence the dynamics of man-made structures. If a potential deployment location is known, site data can be used to improve the relevance and realism of the test conditions, thus helping de-risk device development. Generally this data is difficult to obtain and even if available is used simplistically due to established practices and limitations of test facilities. In this work four years of buoy data from the European Marine Energy Centre is characterised and simulated at the FloWave Ocean Energy Research Facility; a circular combined wave-current test tank. Particular emphasis is placed on the characterisation and validation processes, aiming to preserve spectral and directional complexity of the site, whilst proving that the defined representative conditions can be effectively created. When creating representative site-specific sea states, particular focus is given to the application of clustering algorithms, which enable the entire spectral (frequency or directional) form to be considered in the characterisation process. This enables the true complex nature of the site to be considered in the data reduction process. Prior to generating and measuring the resulting sea states, issues with scaling are explored, the facility itself is characterised, and emphasis is placed on developing measurement strategies for the validation of directional spectra. Wave gauge arrays are designed and used to characterise various elements of the FloWave tank, including reflections, spatio-temporal variability and wave shape. A new method for directional spectrum reconstruction (SPAIR) is also developed, enabling more effective measurement and validation of the resulting directional sea states. Through comparison with other characterisation methods, inherent method-induced trade-offs are understood, and it is found that there is no absolute favourable approach, necessitating an application specific procedure. Despite this, a useful set of 'generic' sea states are created for the simulation of both production and extreme conditions. For sea state measurement, the SPAIR method is proven to be significantly more effective than current approaches, reducing errors and introducing additional capability. This method is used in combination with a directional wave gauge array to effectively measure, correct, and validate the resulting directional wave conditions. It is also demonstrated that site-specific wave-current scenarios can be effectively re-created, thus demonstrating that truly complex ocean conditions can be simulated at FloWave. This ability, along with the considered characterisation approach used, means that representative site-specific sea states can be simulated with confidence, increasing the realism of the test environment and helping de-risk device development.