Time-domain Simulation Of Land-based Oscillating Water Column Wave Energy Convertor

With the development of economy and deterioration of ecological environment, all countries in the world have an urgent demand for clean and renewable energy. Wave energy is a kind of clean and renewable energy. One of the most successful and most extensively used wave energy convertor is the Oscillating Water Column (OWC), it has many advantages including simple structure, good reliability, easy to be installed and maintained.Based on a higher-order boundary element method (HOBEM), a two-dimensional (2D) fully nonlinear numerical model is developed in time-domain. The incident wave is generated by the inner-domain sources. A pneumatic model is implemented to simulate gas-liquid coupling and a viscous model is used to simulate viscous dissipation. In the solving process, the mixed Eulerian-Lagrangian method is adopted to track the transient water surface and the4th Runga-Kutta technique is used to refresh the velocity potential and free surface at the next time step. Meanwhile, the grid division is also needed at every time step.The numerical model is validated against other published analytical solution, experimental data and numerical results for the cases relating to an OWC with an air chamber in the flat-bottom and slope-bottom flumes, respectively. Numerical experiments are performed to study the hydrodynamic performance of the land-based OWC wave energy convertor in regular and irregular waves.The following conclusions can be obtained by numerical tests. For regular wave, different turbine optimal damping coefficient corresponds to different incident wave period. The hydrodynamic efficiency is insensitive to turbine damping coefficient for long waves. The changes of structure size influence the resonant frequency and hydrodynamic efficiency of the OWC. The front wall shape has little effect on hydrodynamic efficiency in the low-frequency region. However, the chamber width influences the hydrodynamic efficiency in the whole working frequency region. The hydrodynamic efficiency increases with the decrease of slope angle in the low-frequency region, and vice versa in the high-frequency region. The form of horizontal wave-load depends on the incident wave period, in which the first-order component occupies the dominant near the resonant region. The contributions from higher-order components become more apparent in low and high-frequency region. For irregular wave, the peak spectral frequencies of the free-surface elevation at the center of the chamber and air pressure in the chamber are higher than those of incident waves. The time history of power output becomes completely unstable.