Ice Collision Forces Considering Structural Deformation

With increasing interest in resource exploitation and shipping in the Arctic, the focus on ice class ships and offshore structures is growing every year. In Arctic waters collision with ice is a major concern. The standard analytical ship-ice collision load model is based on the assumption that the ship structure is perfectly rigid body and the crushing energy of ice is equated to the available kinetic energy to calculate the ice load. This paper extends the standard approach by including the local plastic deformation. By considering the plastic work done to the structure in the balance of energy, a model is developed that can be used to help specify the levels of structural damage that may occur at various speeds. A simple unit side shell of ship structure is modeled to evaluate the absorbed energy and permanent deformation, with elasto-plastic response including linear strain hardening. A simple patch load is used. The purpose of this model is to provide a practical evaluation method of ice loads with the consideration of ship structure’s deformation. While there have been similar issues tackled numerically by several researchers, this work takes a more analytical approach, and will hopefully enable designers to more rapidly assess potential designs. Furthermore, this approach may provide a tool for regulation that is more related to actual risk levels and consequences. To illustrate the issues and practical application, the paper presents an assessment of the bow structure of a high ice class 150kT arctic tanker involved in an iceberg collision.