Velocity Effects on Wide Sloping Structure Ice Loads

Sloping structures are widely used in ice-infested waters because of their ability to reduce the ice loads by changing the ice sheet failure mode from crushing to bending. Model test data showed significant velocity effects on breaking component of sloping structure ice loads (Matskevitch, 2002), which are induced by both the dynamic effect of the ice sheet and the hydrodynamic effect of the sea water beneath the ice sheet. However, existing design codes and most models idealize the underlying sea water as a Winkler-type elastic foundation, without taking into account the velocity effects in the calculation of ice loading. The added mass concept has been utilized by researchers to incorporate the hydrodynamic effect (Sørensen, 1978; Sodhi, 1987), though the potential theory was reported to be more adequate in capturing the (additional) forces from the fluid foundation because the added mass varies with time and space (Zhao and Dempsey, 1996; Lubbad et al, 2008). In general, however, there is limited work done on the incorporation of velocity effects into the computation of ice breaking loads on sloping structures. In this paper, we study the velocity effects on ice breaking load through a two-dimensional problem. The ice-structure interaction problem is studied numerically by incorporating the dynamic effect of the ice sheet and the hydrodynamic effect of the sea water beneath the ice sheet. The ice-fluid interaction is captured by adopting the Euler-Bernoulli beam theory for the ice sheet and the potential theory for the fluid foundation, leading to a set of two governing equations with two loading boundary conditions. For ease of computation, we consider sub-problems with the same set of governing equations, each with modified loading boundary conditions. The numerical models are first validated against available analytical solutions for a simple problem before solving for the sub-problems. Finally, the solution to the original set of governing equations defining the ice-structure interaction is obtained from the superposition of the solutions to two sub-problems. Initial results show that the velocity effects can have a significant influence on ice breaking loads for wide sloping structures.