Abstract

Thrusters are vital for the functionalities of remotely operated vehicles (ROVs). The development of thruster design is a trade-off between cost, thrust force, physical weight and size. A six degree of freedom model is created in OpenModelica to investigate the vibrations and bearing responses in thruster systems. The model consists of a marine propeller, a shaft, and two bearings. The propeller used is based on the Wageningen B-screw propeller series. The hydrodynamic added mass and damping forces are calculated from empirical equations based on open water tests and are functions of the propeller geometry, rotational speed and fluid density. Meanwhile, the mean thrust and torque are obtained from open water test data of the relevant propeller and are used to calculate the dynamic forces and moments from the marine propeller. Displacements in the axial, horizontal, and vertical directions are calculated and used to investigate vibration amplitudes and bearing life.

Initial steady-state simulations show that the bearing life of the bearings in the thruster is found to be highly dependent on the axial load acting on the bearing, i.e., the thrust force. Moreover, if the propeller is not balanced then high centrifugal forces can occur and result in severe forces in the radial direction which can be of concern regarding the bearing life.

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