OPERATION OF THRUSTERS IN ARCTIC WATERS ARCTIC THRUSTER ECOSYSTEM

Due to collisions between ice and propeller the drive train of ice breakers in artic conditions is a highly stressed system. Aim of the ArTEco 'Arctic Thruster Ecosystem' project is to increase the reliability of vessels when overloads and torsional vibrations occurs. To achieve this aim different load scenarios will be analysed on a test rig located in Tuusula (Finland). Here the WST14 azimuth thruster, which is equipped with measuring instruments, is operated by the VTT and Wartsila. To investigate the behaviour of the test rig and the thruster different simulation models are created. These multibody system simulation (MBS) and finite element models (FE) are required to understand the behaviour of the thruster and investigate improvement strategies. Targets of these investigations are the dynamic behaviour during ice contact and the optimization of bevel gears in prospect of safety and efficiency. Therefor estimated propeller loads that occur during ice contact of the gear box housing or loads occur by hitting the propeller blades are used. The simulation models of the thruster regards the flexible structure of the housing and shafts. Using this information the comparison considers natural eigenfrequency correlates to the test rig in Tuusula and the misalignment of the bevel gear can be investigated, validated and an optimisation achieved. For further analysis a simulation model is assembled by TU Dresden and verified by several time based data sets and modal analysis of the test rig. That way overloads and high dynamic loads which can't be applied on the test rig are evaluable. Besides the dynamic analysis a progress in design phase for bevel gear stages is done. This is achieved by using complex FE models including the elastic bevel gear contact, bearing stiffness, clearances and the support of the flexible housing. The complex load and temperature condition lead to different displacements of the gears. Using simulation based displacement data and the software BECAL [1] a precise contact pattern can be investigated to determine safety factors, damage sum and efficiency. To investigate the possible efficiency improvements of a bevel gear a design process is described. Therefor a variation of macro- and micro geometry were made. Point of interest is to shift the theoretical pitch cone relative to the contact pattern, to reduce the local sliding speed. The combination of profile shifting x(hm1), pressure angle alpha(dD) and profile crowning c(pz) modification leads to a significant efficiency improvement.