Possibilities to determine design loads for thrusters

Drive trains of icebreakers in arctic conditions are subjected to high stress levels. Due to collisions between ice and propeller, overloads and torsional vibrations occur. The main objective of the “Arctic Thruster Ecosystem” (ArTEco) project is to increase the reliability of vessels in arctic conditions. In order to achieve this goal different load scenarios are analyzed with multibody-system (MBS) simulation tools complemented by a test rig facility located in Tuusula (Finland). It is operated by the technical research center of Finland (VTT) and Wärtsilä. On the test rig, various loads can be applied to different azimuth thrusters, which are equipped with diagnostic instruments. For further analysis a simulation model is assembled and verified by several time-based data sets and modal analysis of the test rig. Thereby, overloads and high dynamic loads that are unobtainable at the test rig become accessible in simulations. To reduce torsional vibrations, different damping systems, designed at the department of intelligent hydraulics and automation (IHA) Tampere and the VTT, can be analyzed with the MBS-model. Besides torsional vibrations, one objective is the displacement analysis of the bevel gears. Using simulation-based displacement data and the software BECAL [1], a precise contact pattern can be determined, which allows conclusions regarding the required safety factors