With the aim of broadening the wave-frequency bandwidth of high-efficiency, a small-scaled dual oscillating-water-column (OWC) system consisting of two heave-only and onshore units was numerically investigated by a well-validated computational fluid dynamics (CFD) model. Based on the popular open source package OpenFOAM, the volume of fluid (VOF) method was employed to track the transformation of the air–water interface under the excitation of regular waves. The six degree of freedom (6DOF) solver was applied to duplicate the heaving motion of the floating device. The effects of the two chamber widths b 1 and b 2 , the vertical restraint force (represented by the dimensionless stiffness coefficient K), the back-lip draught d 2 of the floating device, and the gap Δ L between the two OWCs on the hydrodynamic characteristics and the wave energy conversion efficiencies were examined. The numerical results show that a larger width ratio b 2 / b 1 with a relatively shallow back-lip draught is more conducive to the high-performance over a broader frequency range. The floating device with a stronger vertical restraint force is more satisfactory for the high-performance of the system. Moreover, a relatively small gap is more recommended in the stage of design and construction.

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To share the construction and maintenance cost, an asymmetric oscillating water column (OWC) device integrated with a pile-fixed box-typed offshore breakwater is considered experimentally and numerically. A fully nonlinear numerical wave tank is established and validated with the open source solver OpenFOAM. The effects of the width and draft of rear box, and the incident wave height on the wave energy conversion efficiency, reflection and transmission coefficients, and energy dissipation coefficient are examined. In addition, the superiority of the present coupling system, compared to the traditional box-type breakwater, is discussed. With well comparisons, the results show that the existence of the rear breakwater is beneficial for the formation of partial standing waves and further wave energy conversion. In the range of wave heights tested, the higher the incident wave height, the larger the energy absorption efficiency except for the short-wave regimes. Moreover, the OWC-breakwater coupling system can obtain a similar wave blocking ability to the traditional one, and simultaneously extract wave energy and decrease wave reflection.