The marine environment and the response characteristics of any engineering system exposed to it are inherently non-linear in form and behaviour. In addition, the traditional analysis of the wave climate uses spectral methods, which implies assumptions of linearity and short-term stationarity. To be able to optimise control for maximum energy capture, cost-efficient design and survival, there is a need to determine the minimum necessary complexity of non-linear modelling of ocean waves to adequately represent the wave climate.
Tidal current energy systems are inherently non-linear. The kinetic component of the energy flux is proportional to the cube of the flow speed. The total energy flux contains components of different degrees of non-linearity, such as turbulence, bed friction, pressure head and wave-current interactions.