On the wave-current interaction effects on linear motion for floating bridges

Abstract

In recent years, a methodology for doing global engineering analysis of floating bridges has been established. Commercial engineering tools based on slender marine elements with single point hydrodynamics for each floater have been adapted for the purpose. The wave kinematics for the wave field is typically established using Airy wave theory, together with a wave spectrum (i.e., JONSWAP). Both the single point hydrodynamics and the wave field assumptions are questionable when currents influence the wave field. In reality, the wavelength increases when current aligns with the wave’s propagation direction. For waves opposing the current, the wavelengths are reduced. In both cases, the wave frequencies in an Earth-fixed reference frame are kept. These changes are reflected by the current modification of the linear dispersion relationship. This has significant influence on the response of the floating bridge, as the pattern of the wave loads is different and might coincide with the modal form of the bridge, causing higher response at resonance. In this work, we discuss how to account for the wave-current interaction in an efficient manner in standard engineering tools.