Wave Energy Conversion Performance of an OWC System with Coupled Pneumatic Damping

Improving the conversion of incident wave energy into useful pneumatic power requires a clear understanding of the coupling among floating body motions, internal water column oscillation, air compression, and pneumatic damping in oscillating water column (OWC) systems. In this study, a coupled multi degree of freedom (MDOF) analytical framework is developed by incorporating the surge, heave, and pitch motions of the floating body together with internal water column oscillation and compressible chamber air dynamics. A distinctive feature of the framework is the direct comparison between a simplified single degree of freedom (SDOF) configuration and the coupled MDOF configuration, which enables the contribution of body motion coupling to pneumatic energy conversion to be explicitly identified. Based on potential flow theory, frequency-domain hydrodynamic characteristics are coupled with the pneumatic response to evaluate added mass, radiation damping, hydrodynamic impedance, chamber pressure, pneumatic power, and capture width ratio (CWR). The MDOF results exhibit two distinct pneumatic power peaks. The dominant peak reaches a non-dimensional pneumatic power coefficient P* of approximately 0.88 at ω ≈ 0.4 (kh ≈ 0.13), whereas a secondary peak of approximately 0.06 appears in the higher frequency regime (kh ≈ 2.2), reflecting the primary water column resonance and the contribution of coupled structural responses, respectively. Comparison with wave-basin measurements reproduces the principal CWR trend and resonance peak location, although the peak magnitude is overpredicted near resonance. The results clarify how body motion coupling and pneumatic damping jointly govern the transfer of incident wave energy into pneumatic power and provide a practical framework for resonance tuning and preliminary performance optimization of OWC systems.