This paper examines the experimental data on ice floes collisions from the HYDRALAB+ Transnational Access project: Loads on Structure and Waves in Ice (LS-WICE). The paper quantifies the contribution from ice-floes collisions to wave energy attenuation. Time-domain and different frequency-domain analysis techniques are applied to analyse the data. Two different methods are proposed to identify collision contacts. Results of the different methods are generally similar and they show that the wave energy dissipated by collisions is approximately 10% of the total energy loss. In addition, collisions between ice floes induced by waves are nearly perfectly inelastic.
A consequence of global climate change is the dramatic decrease in sea ice volume and area of extent in the Arctic Ocean (Stopa, 2016, Thomson et al., 2016). This results in larger open water areas (i.e. longer fetches) available for the generation and growth of ocean surface waves. Due to the presence of sea ice, these waves will be scattered, refracted, attenuated (Wadhams et al., 1988, Sutherland and Rabault, 2016, Li et al., 2017), and they will experience shoaling and a change of their lengths. Concomitantly, the waves will move the sea ice, break it up (Kohout et al., 2014), accelerate its melting and contribute to the formation of pancake ice (Shen and Squire, 1998).
Waves and ice interact with each other in a coupled and nonlinear manner. Many of the interaction processes and phenomena are not yet fully understood. One of these processes is collisions between ice floes forced by the waves. It is known that collision of ice floes contributes to wave energy attenuation especially when there is a high concentration of ice floes (McKenna and Crocker, 1992, Bennetts and Williams, 2015, Shen and Squire, 1998). However, dissipation mechanism and its percentage are less known.
Research pertinent to collisions of ice floes has a long history and dates back to 1980s. Martin and Becker (1987, 1988) concluded that collisions between ice floes reappeared with swell period using field measurements performed at Greenland Sea and Bering Sea. The association between wave forcing and collisions implied that the collision is caused by wave action (McKenna and Crocker, 1990). Historically, collisions are considered to be induced by differential drift velocities between adjacent floes (Shen and Ackley, 1991, Frankenstein and Shen, 1993, Shen and Squire, 1998). Contrastingly, McKenna and Crocker (1992) considered that out-of-phase surge motions bring adjacent floes into contact. Besides, collision can also occur due to out-of-phase pitch motion if the separations between ice floes are small (Bennetts and Williams, 2015). Therefore, drift, surge and pitch motion amplitude and phase of floes, together with separation between floes determine the occurring of collisions (see Bennetts et al., 2014, Meylan et al., 2015).
