Dynamic ice contact load model for azimuthing thrusters

For ships operating in winter conditions, ice loads are important load scenarios for designing azimuthing main propulsion units. One such contact scenario is ice impacting into an azimuthing thruster. In this paper, the formulation of this type of load scenario is presented and existing calculation methods are investigated. A calculation method for dynamic contact load is proposed for ice impact against the main propulsion unit. The basic principle of the proposed load calculation method is an impact of moving bodies combined with dynamic reaction of the structure. The contact load determination is based on the contact pressure–area relationship between an ice block and a steel structure. The dynamic contact problem is solved with a forward difference method. The method is validated with a controlled laboratory-scale test and the test principle is introduced. The dynamic load model is applied to study the effect of dynamics on the response load level.