Applied Ocean Research 67 (2017) 21–30 Contents lists available at ScienceDirect Applied Ocean Research journal homepage: www.elsevier.com/locate/apor An experimental investigation into the wave power extraction of a floating box-type breakwater with dual pneumatic chambers Fang He, Jie Leng, Xizeng Zhao ∗ Ocean College, Zhejiang University, Hangzhou, Zhejiang, 310058, China a r t i c l e i n f o Article history: Received 23 May 2017 Received in revised form 23 June 2017 Accepted 30 June 2017 Keywords: Experimental investigation Wave power extraction Oscillating water column Floating breakwater a b s t r a c t The oscillating water column (OWC) device is in a leading position for wave power extraction but has not achieved fully commercial at the current stage. In addition to enhancing the OWC performance, installing OWCs on floating breakwaters, which owns the merits of both cost-sharing and offshore power supply, is a practicality with high economic viability. In this study, a series of wave-flume experiments were con- ducted in regular waves to examine the wave power extraction of a floating box-type breakwater with dual pneumatic chambers. The flow characteristics of the orifices used to simulate the PTOs was pre- calibrated through another series of experiments, so the power extraction in this study can be obtained with only the pressure measurement. The effects of wave period, chamber draft, water depth and arrange- ment of chambers on the power extraction were examined. Our experimental results showed that the power extraction was mainly due to the water column oscillation inside the chamber, and differentiation in the designed natural periods of dual chambers could widen the efficiency bandwidth of power extrac- tion. The front chamber always played the main role in power extraction and its natural period should be designed against the dominating period of the wave spectrum; in contrast, the power extraction of the rear chamber was only a supplement and its natural period should be designed against longer waves which were more easily transmitted, thus a PTO of small power capacity maybe more realistic. It was also worth noting that the water column oscillation was more dependent on the wave period rather than controlled by the wave scattering under different water depths. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction As worldwide energy demand continuously expands and global environmental problem increasingly aggravates, new growth of energy generation in renewable and sustainable ways is actively explored by lots of researchers. The ocean is vast and power- ful, enabling marine renewable energy potentially be a significant energy supply in the future [1]. Marine renewable energy includes the forms of tides, currents, waves, heat, salinity gradients, etc., amongst wave energy has long been considered as one of the most promising resources thanks to its high power density and long time availability [2]. Currently, wave energy converters (WECs) are diversified [3–5], and oscillating water column (OWC) type device is in a leading position [6]. A typical OWC device mainly consists of two components: a hollow pneumatic chamber with a largely open underwater bot- tom and a power take-off (PTO) system usually on the roof of the ∗ Corresponding author. E-mail address: xizengzhao@zju.edu.cn (X. Zhao). chamber. The incident wave excites the water column inside the chamber to oscillate and transfer energy to the air above the water column within the chamber, and then the pneumatic power can be converted into electricity while the air is flowing through the PTO system coupled with an electric generator. The PTO system is mostly a self-rectifying turbine whose rotation is unidirectional regardless of the airflow direction. Compared with most of other WECs, the configuration of OWC device is especially simple, whose only moving mechanical part is a turbine, located above the water. Due to the nature of simplicity, the OWC devices can be flexibly adapted to the shoreline, nearshore and offshore through different forms. OWC devices have been extensively examined by a large amount of theoretical, numerical and experimental studies. Theoretical studies mainly based on potential theory help us understand the hydrodynamic fundamentals of OWCs. Evans [7] early developed a theory for OWC devices assuming the free surface inside the cham- ber acted as a rigid piston, which was actually valid only if the chamber size was small enough compared with the wave length. Later Evans [8] derived a reciprocal relation taking surface pres- sure distribution and spatial variation of internal water surface http://dx.doi.org/10.1016/j.apor.2017.06.009 0141-1187/© 2017 Elsevier Ltd. All rights reserved.