Hydrodynamic analysis of oscillating water column under the influence of surface tension and uniform current

Abstract

This study examines the hydrodynamic response of an offshore oscillating water column (OWC) device under the combined influence of surface tension and uniform current, factors that are often overlooked but play a vital role in its hydrodynamic performance. A linear wave-structure interaction model is developed and solved using both analytical and numerical approaches. Analytically, the eigenfunction expansion method combined with an algebraic least squares technique is employed, eliminating the need for eigenfunction orthogonality and explicit mode coupling. Numerically, the problem is addressed using the boundary element method and the finite difference method. The analysis provides new insights into the interaction of capillary-gravity waves with a uniform background current and highlights their effects on the efficiency, conductance, and susceptance characteristics of OWC. The results demonstrate that resonance behavior is highly sensitive to both environmental and structural parameters. In the absence of current and surface tension, sharp resonance peaks appear at specific chamber widths, leading to higher efficiency. However, increasing current velocity and surface tension smooth out the peaks, producing broader but less pronounced resonance bands. Following currents shift the resonance toward higher frequencies, while opposing currents cause a shift to lower frequencies. Surface tension also stabilizes the susceptance response by flattening abrupt variations, thereby enhancing operational reliability. Structural parameters, particularly chamber width and wall drafts, significantly affect the hydrodynamic performance. At higher wave frequencies, a decrease in the front wall drafts leads to an increase in efficiency. These findings provide valuable guidance for improving OWC efficiency under the influence of both surface tension and uniform current.