The dual-chamber oscillating water column (OWC) is considered in this study. The device has two sub-chambers with a shared orifice. A fully-nonlinear numerical wave flume based on the potential-flow theory is applied for the simulation. At various wave conditions, effects of the chamber geometry (i.e. the draft and breadth of two chambers) on the hydrodynamic efficiency of the OWC device are investigated numerically. The hydrodynamic efficiency of the dual-chamber OWC is compared with that of the single-chamber one. The dual-chamber device shows a higher efficiency near the resonant frequency. Then, effects of the breadth and draft of two sub-chambers are discussed. It is observed that a proper set of two sub-chambers can increase the general hydrodynamic efficiency of the OWC device.
Due to their non-polluting nature and environment friendliness, renewable energies have gained great deal of attention and deserve a substantial body of research. The wave energy as an important type of renewable energy has drawn people's attention for several decades (Dizadji and Sajadian, 2011). Thousands of prototypes of Wave Energy Converters (WECs) have been developed for many decades now for exploiting the energy of the ocean waves (Vyzikas et al., 2017). Featured by high efficiency and structural simplicity, the OWC device becomes one of the most favorable wave energy converters (Delaure and Lewis, 2003).
In recent decades, a great volume of researches has been carried out to investigate the efficiency of OWCs analytically (McCormick, 1976; Evans, 1978; Falcao and Sarmento, 1980; Evans, 1982), numerically (Zhang et al., 2012; Luo et al., 2014; Ning et al., 2015) and experimentally (Morris-Thomas et al., 2007; Falcao and Henriques, 2014; Murakami et al., 2016; Ning et al., 2016a), most of which focus on the single chamber device. For the single chamber OWC, it has been recognized that the maximum power absorption occurs only when the frequency of incident waves is close to the resonance frequency of the OWC chamber (Morris-Thomas et al., 2007; El Marjani et al., 2008; Sahinkaya et al., 2009; Iturrioz et al., 2015). To enhance the performance of the OWC devices, the multi-chamber OWC concept has been proposed. The principle of double chamber OWC device's operation has been extensively studied by Boccotti, (2007), Boccotti et al. (2007) and Wilbert et al. (2014). They observed that relative opening depth along with asymmetry value have strong effects on hydrodynamic energy conversion capacity of the device. Rezanejad et al. (2013) and Rezanejad et al. (2015) analytically and numerically analyzed the hydrodynamic efficiency of a dual-chamber OWC placed over stepped bottom. They found that by considering dual-chamber OWC device on the stepped sea bottom, the performance of the device can be improved significantly in wide range of frequencies, as compared with the single chamber case.