Wave induced motions of partially submerged bodies near a fixed structure

Abstract

Wave driven impact of small icebergs with offshore structures is a design consideration in Arctic and sub-Arctic regions. The near field hydrodynamic interaction of these wave driven ice masses has been investigated through experimental and CFD studies by Sayeed et al. (2017b, 2018a, 2018b). These studies found that motions were significantly influenced by the standing wave generated due to the superposition of the incident and reflected waves in front of the fixed structure. In regular waves the small bodies may or may not impact the structure, depending on initial starting condition whereas in irregular waves the ice masses hit the structure in all cases. Spectrum analysis carried out over the entire distance travelled by the free floating ice mass in irregular waves revealed relatively small difference in surge and heave velocity due to the presence of the structure (Sayeed et al. (2018b)). The reason is attributed to insufficient data at each separation distances to capture the motion responses for all the frequencies in the spectrum. In this paper, the surge and heave motion time series data in irregular waves are reanalyzed in a similar manner as was previously done for regular waves (Sayeed et al. (2018a). The present analysis reveals correlation of significant wavelength with the motion history at variable separation distances in front of the fixed structure. A statistical approach is then adopted to both regular and irregular wave motion data sets to identify percentiles of velocity response vs position as the small floating bodies approach head on to the fixed structure. These findings enable the identification of the motions of small bodies at specific locations in front of the structure and provide understanding of how wave-induced surge and heave velocities change as small floating bodies approach a fixed structure in a realistic wave field.