Research at HR Wallingford, the UK’s hydraulics research institute, in collaboration with the Coastal & Hydraulics Laboratory (CHL) in the USA has resulted in an accurate simulation of the response of floating structures under realistic sea states. It is expected to be particularly useful for designing renewable energy devices, such as floating wind turbines.
Being able to understand and predict the behaviour of offshore floating structures, under typical or extreme environmental loads, is central to being able to assess their viability. This is particularly important in the case of offshore renewable energy where devices are intentionally placed in rough seas.
A variety of concepts for floating offshore renewable energy devices is under development around the world, and each one presents its own challenges, HR Wallingford says. This is not only due to the marine environments in which the devices may be placed, where they will frequently be exposed to significant wave forces, known as hydrodynamic loads, but also due to their respective operating methods. While floating wind turbines aim to limit the response to wave loads, wave energy converters, for example, are tuned to have a high response to the most energetic waves.
HR Wallingford visiting researcher Tristan de Lataillade explained: “What our new research shows is that by combining open-source numerical tools, we have the potential to simulate with accuracy the response of complex offshore floating structures to environmental loads in the marine environment.”
The toolkit consists of two main components: computational fluid dynamics (CFD) using Proteus open-source software, and multi-body dynamics (MBD) using the Chrono open-source solver. Both models have been validated separately and together.
HR Wallingford senior engineer Aggelos Dimakopoulos added: “We have put a special focus on the fully dynamic simulation of mooring cables, as they can significantly affect station‑keeping and the overall response of the device, which in turn affects its energy extraction efficiency.”
Renewable energy lead Michael Case added: “Using a CFD model at an early stage can reduce costs in design optimisation, by performing full-scale simulations under realistic sea states, before performing laboratory tests which may be subject to practical limitations. This is important as it provides a further opportunity to drive down the levelised cost of energy (LCoE).”