AbstractThis PhD thesis focuses on using advanced numerical simulation to develop an integrated wave energy converter (WEC)-breakwater system. The integrated WEC-breakwater system is a hybrid system that combines the WEC and the breakwater into one system to share the construction cost and space. In addition, both the functions of coastal protection and wave energy conversion can be achieved in this WEC-breakwater system. The heave-oscillating type of WEC is investigated in this PhD thesis to combine with breakwaters.
The numerical tools are firstly discussed in this PhD research. The open-source CFD package based on Navier-Stokes equations, OpenFOAM, is a mature toolbox to simulate wave-structure interactions in coastal and offshore structures like the WEC-breakwater systems. An in-house CFD model, Particle-In-Cell (PIC) solver, at the University of Bath is also an efficient method for coastal and offshore engineering simulations. This PhD thesis compares the PIC solver with OpenFOAM in terms of accuracy and efficiency. Moreover, it is the first time to directly discuss the efficiency of these two CFD tools by comparing the execution time of the same case simulated by the two CFD tools using the same number of CPU cores on the same computing facility.
Both 2D and 3D models are investigated. In the 2D research, OpenFOAM is employed to conduct parametric research on an existing WEC-breakwater system. The functional performance of wave energy conversion and wave attenuation of the current WEC-breakwater system is improved in this parametric research by changing different parameters of structures in the WEC-breakwater system. Different dimensions of structures and the gap width between multiple structures are discussed in this research. The hydrodynamics changed with different parameters are also discussed and investigated in this research. Because there are two structures in one WEC-breakwater system, gap resonance might occur inside the narrow gap between the two structures. Gap resonance will bring extreme loads on structures. By considering the stability of the WEC-breakwater system, the gap resonance is investigated in a similar setup as the 2D WEC-breakwater system. Further, the influences of the heave motions of floating buoys on gap resonance are investigated numerically.
A cylindrical WEC is investigated in the 3D model. Viscous model such as OpenFOAM will generally be costly in modelling 3D test cases. To save computational, an open-source software, HAMS, is used. HAMS is a potential flow theory solver to obtain more accurate results. This research initially utilises OpenFOAM to modify HAMS with viscosity corrections to obtain accurate and efficient results. The modified HAMS is validated in this research by compared with experimental results. Furthermore, the parametric research is conducted by using the modified HAMS. An original concept of the WEC-breakwater system is proposed and evaluated in this research. As a significant outcome of this PhD research, this new concept increases the potential efficiency of wave energy extraction of the WEC-breakwater system to about 80%. In addition, the poor performance of wave energy extraction (wave energy extraction efficiency < 20%) of previous concepts of heave oscillating WEC in high wave frequency region (dimensionless wave number kh > 4) is obviously improved with the new concept setup.
|Date of Award||25 May 2022|
|Supervisor||Jun Zang (Supervisor) & Chris Blenkinsopp (Supervisor)|