This research project will develop the high quality science required to make major advances in marine renewable energy, and more generally offshore and coastal engineering. Waves still provide much of the impetus for research in offshore and coastal engineering, so we will 1. link slow changes in the wave climate, both for operating and survivability conditions, to large-scale geophysics such as the North Atlantic Oscillation. 2. model extreme waves on a sheared current, both via a novel fully Lagrangian model and experimentally in the wavecurrent facilities at UCL. Both of these topics are important, the first is incremental research based on previous work. In contrast the second is highly innovative applied mathematics applied to a very challenging problem. The Lagrangian approach shows great promise in resolving much of the uncertainty in nonlinear wave dynamics but requires great mathematical insight to make progress, and the output will be of major benefit to all those interested in violent wave-structure interactions.These waves will be incident on marine renewable devices (both wave and tidal current). Thus a major thrust in the project is to measure and then to make widely available forces on components of the devices, and also internal blade stresses for tidal turbines. This will yield a unique large dataset of great value for device developers, engineering consultants, energy utilities and regulatory and certifying authorities to benchmark their in-house analysis capabilities against. The final block of technical work is to use leading edge CFD to simulate computationally the loads measured on model devices at UCL. A combination of hierarchical models from actuator disk theory upwards will be used to explore what level of sophistication and complexity yields the most appropriate results. We will also use the open source suite OpenFOAM to explore the case of survivability loads. The ultimate aim of this part of the programme is to provide examples of 'best practice' analysis in the open domain - CFD is very powerful but the code user needs to have significant understanding of what the codes can and can't do and how to get the best out of them