Computational Fluid Dynamics applied to wave energy extraction in a coastal environment

Unlike ships and offshore structures, which are designed to have minimal response in bad weather, wave power devices must respond to the waves. The design of a floating unit, which is both an efficient wave power absorber and survives in a storm environment, is therefore a formidable challenge. With large vessel motions, traditional analysis tools based on linear or weakly nonlinear theory may not be sufficiently accurate to verify the survival of a floating wave power device. Furthermore, to plan and design a commercial wave power plant, a reliable estimate of the available wave power and the harshness of the environment at the location is essential. For offshore locations, global or regional hindcast models give a good estimate of the wave environment. For nearshore locations, however, local phase averaged models may not be reliable and do not provide data on individual waves and kinematics, needed for seakeeping analysis of the floating unit. The objective of the present PhD project is to apply state-of-the-art methods within Computational Fluid Dynamics (CFD) to these problems to compute motion response of highly nonlinear floating structures and the calculation of phase-resolved irregular wave conditions in shallow waters. The outcome of the project is expected to reduce the uncertainty in the calculation of wave loading on floating units and give a more accurate description of the wave conditions at nearshore locations. The development in this project is also expected to benefit the design of other coastal structures, such as floating solar, bottom fixed and floating wind turbines and fish farming infrastructure.

Unlike for ships and offshore structures which are designed to have minimal response in bad weather, wave power devices must respond to the waves. The design of a floating unit which is both an efficient wave power absorber and survives in a storm environment is therefore a formidable challenge. With large motion response, linear or weakly nonlinear methods for wave loading and motion response may not be sufficiently accurate to verify the survival of a floating wave power device. In order to plan and design a commercial wave power plant, a reliable estimate of the available wave power is essential. For offshore locations, global or regional hindcast models give a good estimate of the wave environment. For a nearshore location, weakly nonlinear local models may not be reliable. The objective of the present PhD project is to apply Computational Fluid Dynamics (CFD) methods to these problems and reduce the uncertainty in wave loading on a floating unit and wave conditions at a nearshore location. - Using as a starting point the OpenFoam software with the mesh overlay method, a method will be developed for calculating motion and wave loading on a floating wave power device in operational and survival conditions. A statistical method for providing the governing wave loads using this method will be proposed. - Using as a starting point the Basilisk software with the multilayer method, a method for propagating offshore waves into the nearshore environment will be developed. A statistical method for providing the governing seastates for design purposes will be proposed. The CFD results will be compared with established weakly nonlinear analysis, model tests and full scale measurements. Although this project addresses the challenges associated with a floating wave power device, the outcomes are also of interest for others with activities in the coastal areas such as aquaculture, floating solar, fixed and floating wind, harbour facilities and the oil and gas industry.