Ice-structure impact contact load test setup and impact contact load calculation

Shipping in arctic and other ice conditions is increasing. Modern propulsion systems often utilize azimuthing thrusters in their various forms. When operating azimuthing thruster equipped ships in ice conditions, the thruster will interact with ice. One such interaction type is an impact type contact of ice block and thruster. The contact causes certain loading to thruster. The contact load problem can be considered as ice impact to steel structure. In a research project related to developing Finnish-Swedish ice class rules, the impact forces due to ice contact to steel structure are dealt with a simple theoretical model and experimental approach is used for model validation. In this paper, the experiment setup and result examples are presented. The experimental setup presented was used for studying the contact force during an impact type contact. Impacts were hit to solid ice and floating ice block, contact point was submerged. The test device is representing a ship and thruster structure, and is laboratory scale equipment. The test device is a pendulum mass with changeable impact contact head. The device provides impact contact load measurement, pendulum motion measurement and the ice movement measurement. In addition, synchronized video recording was made. Tests were performed on sea ice during March 2013. The speed range capability for the test device is representative for ship speed in ice channel operation. In the tests, impact energy was varied by varying the pendulum start level. Two sizes of hemispherical contact geometries were used. Test results indicate distribution of energy in the impact event, i.e. ice kinetic energy, impacting mass kinetic energy and the rest is assumed to be drag and ice crushing energy. The test setup can very simply be tuned to different dynamic state to represent different stiffness of thruster installation to ship, and it can accommodate different contact geometries.